Journal of Palaeogeography（Chinese Edition）-Forthcoming Articles

Yu JiXing Yang Tian — 2023-03-28 00:00:00.0

Fluid flow types, chronological methods and applications in clastic reservoirs

2023-03-28 00:00:00.0

Fluid flows have always been an important part of clastic reservoir studies and have therefore received a great deal of attention. As the mediator of ions and heat, fluid flows have an important influence on the mineral composition and pore-throat structure of clastic rocks, making diagenetic fluid chronology studies important for reconstructing the evolutionary history of diagenetic evolution and pore evolution. The fluid flows of clastic rocks are controlled by a variety of factors, including tectonic activity, hydrothermal activities event, sedimentation, transport system and burial process, which makes it difficult to accurately determine the precise time of fluid flows. However, the rapid development of fluid inclusions, calcite mineral dating (isotopic dilution method, ESR method, LA-ICP-MS method), authigenic illite K-Ar/Ar-Ar dating, potassium feldspar overgrowth K-Ar/Ar-Ar dating, organic-rich sediment Re/Os dating and other analytical techniques provide suitable tools for the study of fluid flows. In this paper, focusing on the fluid flow in clastic rocks, the author first briefly summarized the significance of fluid flow research, followed by a systematic review of the fluid types and chronological methods. Then, the geological application potential of fluid flow chronology for determining the sedimentary age of strata, recovering the evolutionary history of diagenesis, determining the precise time of brittle tectonic activity and determining the timing of hydrocarbon charging was summarized. Finally, the existing problems and future prospects of diagenetic fluid chronology were summarized, in order to provide reference for diagenetic fluid related research work.

Control and application of sedimentary environment on gas content of coal reservoir: A case study of No.15 coal of Taiyuan Formation in Shouyang area, north Qinshui Basin

2023-03-28 00:00:00.0

The reservoir property is the dominant factor for the enrichment and high-yield of Coalbed Methane (CBM). Sedimentary environment controls on the nature and maceral composition of coal, the distribution and thickness the of coal seam, the nature and superimposed model of surrounding rocks. Therefore, sedimentary environment plays an important role in controlling the enrichment of CBM. In this study, the sedimentary environment and sequence stratigraphy of Taiyuan Formation in Shouyang area were analyzed based on drilling cores, logging and previous achievements. Then, the lithofacies and paleogeography of the roof and floor of the No.15 coal were described in detail. At last, the relationship between sedimentary environment and gas content of CBM was summarized, and the favorable zone for CBM exploration was delineate. The lower part of Taiyuan Formation in Shouyang area mainly develop shallow sea shelf, barrier island and lagoon depositional system, while the upper part mainly develop delta plain depositional system. The Taiyuan Formation record a 3rd-order transgression-regression process, which can be further divided into six 4th-order sequences (S1-S6). The S1 mainly develop tidal flat, lagoon and barrier island depositional system. The gas content for different sedimentary facies in descending order is lagoon, tidal flat and barrier island. The S2 mainly develop barrier island, lagoon, tidal flat, shallow sea shelf depositional system. The gas content for different sedimentary facies in descending order is lagoon (with thick limestone), muddy shelf, carbonate shelf, lagoon, tidal flat, barrier island. According to the relationship between sedimentary facies of S1, S2 and gas content of No.15 coal, the CBM reservoir of No.15 coal was divided into 3 types, including type Ⅰ, Ⅱ and Ⅲ. Type Ⅰ reservoir is favorable for CBM exploration, which mainly distributed in the east of the Shouyang area, including Yinlinzhi, Jingshang, Songta town. Type Ⅱ reservoir is relatively favorable for CBM exploration, which mainly distributed in the east and west of the Shouyang area. Type Ⅲ is with poor CBM exploration prospect, which mainly distributed in the northwest and the central area of the east-west direction of the Shouyang area.

A review on tidal depositional processes and characteristics

2023-03-28 00:00:00.0

Tidal deposits not only play a significant role in reconstructing paleogeographic sedimentary environments and paleoclimate, but also are important reservoirs in oil and gas exploration. Tides refer to any periodic fluctuation in the water level accompanied by horizontal flows of water, that are produced by the gravitational attraction between the earth, moon, and sun. Tidal currents are different from other currents as they show systematic changes in flow direction and current strength with intervening slack-water periods during each tidal cycle. The characteristic features of tidal currents have pronounced impact on sediment transport and deposition. Tidal processes can form a variety of sedimentary structures or features, such as tidal rhythmite, flaser-wavy-lenticular bedding, tidal bundle, reactivation surface, compound cross bedding, bidirectional cross bedding, double mud drapes, fluid mud deposit, etc. These sedimentary structures or features occur in various tidal depositional environments and are controlled by tidal depositional processes that result in complicated stratigraphic architecture of the depositional system. In oil and gas exploration, it is important to describe the rock record at more detailed scales and deduce their associated sedimentary processes in order to better predict the distribution of corresponding sedimentary facies and main sand bodies. This paper summarizes generation of tides with controlling factors, tidal depositional processes, sedimentary structures and their depositional environments, with the intention to improve the understanding of recent research progress in tidal depositional systems and to provide some scientific guidance for related oil and gas exploration and development.

Characteristics, Evolution and Genetic Mechanism of Cenozoic Island Dolostones

2023-03-28 00:00:00.0

Cenozoic island dolostones found throughout the global oceans are considered as ideal natural laboratories for deciphering the classic "dolomite problem" due to their shallow burial, eogenetic formation, and weak diagenetic modifications. This paper systematically summarized the research progress in these dolostones of their basic characteristics, time evolution, fluid properties, and genetic models, and discussed the paleoenvironmental and paleoclimatic factors that influenced their formation. The Cenozoic island dolostones (tens to hundreds of meters thick) show similar petrological (texture-retentive and texture-destructive), stoichiometric (high-calcium dolomite and low-calcium dolomite), and geochemical (e.g., carbon and oxygen isotopes, strontium content) properties, and are formed contemporarily during the ~10–0.5 Ma interval. The strontium isotopes of the dolostones indicate that the age of dolomitization generally becomes progressively younger from the bottom to the top of the dolostone sections in a continuous or semi-continuous way on individual islands (atolls, carbonate platforms) under the influences of eustatic change and tectonic subsidence. Carbonate clumped and oxygen isotopes indicate that the primary fluid for the island dolomitization is normal to slightly evaporated seawater. Furthermore, the high-calcium dolomite is formed primarily from normal seawater, while the low-calcium dolomite is formed from slightly evaporated seawater. A single fluid flowing mechanism (e.g., seepage, reflux, geothermal convection) is insufficient to explain the genesis of the Cenozoic island dolostones; and available data demonstrate that the formation of the island dolostones is promoted by multiple flow mechanisms. During the island dolomitization period (10–0.5 Ma), there is no single paleoenvironmental or paleoclimatic factor (e.g., seawater Mg/Ca ratio, temperature, SO42- concentration, redox state, pCO2, pH) that corresponds to significant dolomitization, implying that the Cenozoic island dolomitization event was probably controlled by multiple paleoenvironmental and paleoclimatic factors. To better understand the genetic mechanisms of the Cenozoic island dolostones, future researches should focus on the micro-processes of dolomitization, the application of new geochemical methods and numerical simulation.

Lithologic-carbon isotopic stratigraphic subdivision and correlation of the Sinian Dengying Formation in Sichuan Basin and its periphery and its implication

2023-03-28 00:00:00.0

Abstract: Because the stratigraphic thickness varies greatly, the subdivision of the Dengying Formation is controversial. Moreover, the formation mechanism of the Mianyang-Changning intracratonic sag is poorly understood due to the controversy in stratigraphic subdivision. In this case, based on investigation of two outcrops and three drilling wells, this paper systematically conducted a lithologic-carbon isotopic stratigraphic subdivision and correlation of the Dengying Formation, and divided it into six isochronous lithologic units with 3 three positive (DP1, DP2, DP3) and negative (DN1, DN2, DN3) carbon isotopic excursions: 1. The Deng 1 Member is marked by dolomudstone; 2. the Lower Deng 2 Submember consists of various algal dolomite with grape-like structure, showing DP1 in its lower part, DN1 in its middle part, which passes upward into DP2 gradually; 3. The Upper Deng 2 Submember is marked by dolomudstone and minor algal dolomite, locally with mixed sedimentation, showing DP2 in its lower part and DN2 in its middle-upper part; 4. The Deng 3 Member is typical of mixed sedimentation, locally with pure clastic rocks, containing characteristic tubular fossils; 5. Lower Deng 4 Submember is composed of thick dolomudstone with δ13C around 1‰ in the lower part and positively shifting into DP3 upward; 6. The Upper Deng 4 Submember consists mainly of algal dolomite, exhibiting DP3 in the base with a negative shift trend towards the Ediacaran-Cambrian boundary as DN3. Of these, the unconformity above the Upper Deng 2 Submember and Deng 4 Member can be correlated with the glaciations during 547 Ma and Ediacaran-Cambrian boundary, respectively. On the basis, the missing of the strata above the Lower Deng 2 Submember of varying degree is identified in the Pengtan 1 and Pengshen 3 wells in the Mianyang-Changning intracratonic sag. The strata missing of the Dengying Formation in the Mianyang-Changning intracratonic sag up to 600 m and the thickness of the Dengying Formation show inverse correlation with that of the Maidiping Formation, suggest that the major of Mianyang-Changning intracratonic sag of the Dengying Formation formed after the deposition of the basal Lower Deng 2 Submember and before the deposition of the Maidiping Formation, which was caused by depositional break and/or erosion related to differential uplifting.

Classification of bioith (biogenic rocks)

2023-03-28 00:00:00.0

Lithofacies characteristics, sedimentary environment and genetic model of Chang 7 black shale in Yanchang, Ordos Basin

2023-03-28 00:00:00.0

Yanchang 7 black shale in Ordos Basin has wide distribution area, large thickness and high organic matter content, and has broad shale oil exploration prospects. The shale is characterized by developed foliation and high content of organic carbon and clay, and the content of organic matter is highly correlated with the content of clay minerals and the development degree of shale laminae. There are three types of shale lithofacies bounded by TOC value of 2% and 6%. At the bottom of Chang 73, there is a very organic rich laminar shale, which transitions upward to organic rich laminar massive shale, and at Chang 71, there is an organic poor massive mudstone. Sr / Cu ratio and climate index C indicate that Chang 7 sedimentary period is characterized by warm and humid climate. The enrichment of collophanite and Ni, Cu, Mo and other nutrient elements shows that the lake basin in Chang 73 sedimentary period has high productivity and is a eutrophic lake basin to ensure the supply of organic matter. V / (V + Ni), U / TH and V / Cr ratios indicate that the highly organic rich laminar shale with TOC greater than 6% at the bottom of Chang 73 is developed in the strong reduction environment of anoxic sulfide. The vertical change of element indexes reflects the transformation of water productivity and reduction degree from strong to weak, and reflects the evolution process of rapid expansion, stable settlement and slow recovery of the lake basin. Combined with the comprehensive analysis of structure, paleogeomorphology, paleoclimate and paleohydrological conditions, the genetic mechanism of Chang 7 black shale is the stratification model of deep lake water superimposed by volcanic and hydrothermal activities under strong tectonic movement.

A review of the strait sedimentology

2022-06-08 00:00:00.0

The strait is distinguished from delta or shelf in having unique sedimentary processes and sediment distribution. The paper reviews recent progresses on origin, morphology, hydrodynamic and depositional sequences of strait. Straits show a wide variety of shapes, with a length less than several hundred kilometers and a depth ranging from several decimeters and more than one kilometer. Strait has wide mouths at either end that taper to a constriction where the cross-sectional area is the least. Due to a decrease in flow velocity, dune field developed in dune-bedded strait zone. Tidal processes are probably the most important transport agents for shallow-water strait. Other processes include uni-directional oceanic current and sediment gravity flow. Deep-water strait is dominated by oceanic currents and sediment gravity flows. High-energy zones predominantly comprise cross-bedding, whereas low-energy zone is featured by current ripples and muddy deposits. When sea level is low, the strait is exposed in which fluvial processes are dominant. During transgression, river evolves to estuary, bay and strait.

Sedimentary Characteristics and Developmental Model of Lacustrine Fine-grained Mixed Rocks in Da’anzhai Member, Northeastern Sichuan Basin

2022-06-08 00:00:00.0

Under the background of the Early Jurassic Toarcian oceanic anoxic event (~183 Ma), water body eutrophication occurred during the deposition of Jurassic Da’anzhai Member in Sichuan Basin, forming lacustrine mixed sedimentary strata of fossiliferous carbonate and mudrocks. It provides a “natural laboratory” for the study of depositional mechanism of mixed sedimentary strata. In this paper, the lithologic classification and sedimentary facies distribution of Da’anzhai Member in Yilong-Yingshan Region, northeast Sichuan Basin are studied based on core and well logging data, then the depositional process and controlling factors of the mixed sedimentary strata are discussed. The results show that: Lacustrine mixed sedimentary strata were composed of intermixing and alternation of bivalves, ostracods components and fine-grained siliceous debris (including clay minerals). The sedimentary stage of Da1 and Da3 Sub-member was dominated by shell beach and shallow lacustrine, while Da2 Sub-member was dominated by fairly deep-deep lacustrine, which forms a complete lacustrine transgressive-regressive sedimentary cycle. The lacustrine mixed depositional process was mainly facies mixing model and punctuated mixing model. The mixing sedimentary process was controlled by material source, geological agent, lake level fluctuation. The fluctuation of lake level change controls the distribution of different sedimentary microfacies. Short-term and frequent storms incident ed the sediments from different material source and microfacies (terrigenous detrital transportation, bio-chemical carbonate deposition, suspended deposition of fine particles, etc.) were mixed, and increases the internal disorder degree and expands the plane distribution range of mixed rock. Finally, the depositional mechanism model of lacustrine mixed rocks in Da’anzhai Member of Yilong-Yingshan Region was established, which can provide theoretical support for continental shale oil and gas exploration and reference for the study of mixed rocks under similar geological background.

The Mechanism and Development Model of Karst Reservoir in the Wumishan Formation in Xiong'an New Area

Rui-Jing GUO — 2022-06-08 00:00:00.0

There are abundant geothermal resources in the Wumishan Formation of Xiong'an New Area. To study the characteristics and main controlling factors of high-quality karstic geothermal reservoirs in the Wumishan Formation is the basis of the exploration of geothermal resources. Previous researches are limited within the characteristics of reservoir, but there’s little research about the diagenesis and mechanism of reservoir. We analyzed the diagenesis types and the transformation mechanism of Wumishan formation in study area, based on field crops, core data, flakes and logging data. The results show that the main lithology here is dolomite, and the main storage spaces are pores and cracks. The most constructive diagenesis is epigenetic dissolution, the most destructive diagenesis is cementation. Diagenesis in the study area are controlled by the multiple tectonic movements, lithology and paleomorphology. The reservoir has been through the process of sedimentation-quasi-contemporaneous seafloor cementation to reduce porosity—early-middle diagenetic compaction and compression—middle-late diagenetic superficial dissolution to increase porosity—late diagenetic dissolution cementation to increase porosity first and then decrease porosity, the final porosity is about 5%. Lithology, tectonic movement and paleomorphology combined diagenesis controlled the transformation of reservoir in study area.

Advance on depositional systems tracts in large lake basin and shale oil and gas exploration

2022-06-08 00:00:00.0

A large number of detritite-carbonate deposits are distributed in China, and many new oil and gas fields have been discovered in oil and gas basins, especially in tight oil / shale oil exploration in recent years. It is suitable for the study of the allo-cycle sequence with genetic connections to explain the sequence stratigraphic unit according to the evolution of the sedimentary systems tract and accommodation changes. It could build up sequence evolution models and predict the oil and gas reservoir. The advance on systems tract of deep water system shows in the fields of introduction of the concept of forced regression (sea or lake), developing from the classical three-divided systems tracts to the four systems tract and/or two systems tracts, and the distribution of internal relative comformity sequence and systems tract at different scales are closely related to naming. The falling stage systems tract (FSST) and forced regression wedge systems tract (FRW) formed under the different conditions. A_P_D parasequence stacking pattern analysis is used to analyze the Hyperpycnal and the sediment mechanism of normal fluid (Homopycnal and / or Hypopycnal), which improves the accuracy of systems tract identification and oil and gas reservoir prediction. Research examples of Qaidam Basin and Sichuan Basin confirm that the lacustrine systems tract develops with the lake level rises, shallow lake and semi-deep lake expand, the deltaic thin-layer sand and deep-water turbidite fan and multi-cycle muddy shale-marl combination is developed in sediment center. It is conducive to the development of shale oil and gas reservoir and become the "sweet spot" of exploration target area. Looking forward to the future, important progress will be made in the field of shale oil and gas exploration in the following aspects: 1) Research on the high-frequency cycle systems tract of the deep water depositional system of the salt lake basin; 2）Study on the mixing depositional system of TST related to shale type and mixed sediment shale oil types;3）The sequence-paleogeographic study in the order of systems tract; 4）Study on the source-sink system and its ancient lake distribution characteristics under the framework of systems tract; 5）Geochemical indexes analysis of lake paleo-water depth, paleo-climate and paleo-environment; 6）Study on the deposition microfacies of closed or semi-closed lake affected by sea transgression; 7) Reservoir capacity of micro-nanoscale pore-fracture system in organic matter-rich shale.

New understanding of Yanchang Formation sedimentation and isochronous stratigraphic division scheme in Ordos Basin

2022-06-08 00:00:00.0

Currently, the oil production in Yanchang Formation, Ordos Basin is more than 35 million tons per year. It is well known that chemostratigraphy correlation is significantly critical in oil production. Marker bed and equisection method are traditionally applied in define of oil formation. However, this kind of stratigraphy correlation approach has been increasingly questioned. With the constrain of drilling date, the high precision dating data in tuff from Chang 7 oil formation in various sedimentary systems and high precision seismic stratigraphic interpretation and stratigraphic isotope chronology are carried out respectively by using the high quality 3D seismic data newly collected from blocks to the north of Qingcheng. The high-precision ziron dating from sourtheast sedimentary systems in Chang 7 oil formation is belong to the Middle Trassic and we put forward the high resolution correlation of different sedimentary systems of Chang 7. It is the first time to identify 11 prograding bodies from the top of Chang 73 oil formation to the bottom of Chang 2 oil formation these blocks. 6 prograding bodies are described in Chang 7 oil formation, suggesting stratum diachronism in current stratigraphic correlation of Yanchang Formation. We proposed that high precision dating is urgently required to be a marker in Chang 7 oil formation from diverse provenance systems. Coupled with elevated frequency seismic data and thin-bed correlation by geophysical logging, a high sequence stratigraphic framework could be redefined and chemostratigraphy correlation could be established in Yanchang formation. This study could be in favor of refining reservoir distribution patterns in Yanchang Formation, and provide a valuable lesson for the study of deep-water sedimentary evolution and chemostratigraphy correlation in other lacustrine basins in the future.

Convolute laminations induced by internal-waves and internal-tides of Upper Ordovician Lashenzhong Formation in western margin of Ordos Basin

2022-06-08 00:00:00.0

Convolute lamination is an important type of soft-sediment deformation structures with multi-origin. In deep-water deposition environments, there are very important significance both in enriching the formation mechanism of convolute laminations and improving the identification of internal-wave and internal-tide deposits for discussing the relationship between them. Detail and careful field work for convolute laminations developing in ponded turbidity current deposits of Upper Ordovician Lashenzhong Formation have been carried out in Zhuozishan area, Inner Mongolia, in the north of western Ordos basin. It could be divided into two categories according to their morphology: vergent regular convolute laminations and cyclotron-like convolute laminations. The former are developed tight anticlines, flat synclines and sand nucleate underlying anticline and frequently associated with bi-directional cross-beddings. The latter are belonged to intra-stratal contortions and often contained within single laminae set with truncation surface as well as associated with sedimentary structures of combined-flow deposits and wave-ripple laminations. The comprehensive research on sedimentary characteristics, convolute lamination features, associated sedimentary structures and related research achievements perhaps suggest that: 1) vergent regular convolute lamination is mainly induced by internal-tides and the formational processes include density inversion created during liquefaction, deformation drove by Rayleigh-Taylor instability and subsequent modification due to continued horizontal shear imposed by flow; 2) cyclotron-like convolute lamination is mainly induced by internal-wives which contain random internal-waves produced by reflected turbidity currents and internal solitary waves distorted from internal-tides, and the formational processes include syn-depositional stratified liquefaction rather than density inversion, deformation drove by Kelvin–Helmholtz instability and some modification due to horizontal shear imposed by flow.

Chao Fu — 2022-06-08 00:00:00.0

Paleo-peat sedimentary environment and its controlling on trace elements enrichments in No. 11 coal seam from Donglutian mine of Pingshuo District, Ningwu Coalfield

2022-06-08 00:00:00.0

The paleopeat-forming environments has an important influence on the enrichment of trace elements in coal. Coal facies and related geochemical parameters are important indicators for the paleopeat condition. Coal facies parameters, geochemical parameters and mineralogical characteristics were used to reconstruct the paleopeat-forming environments of the Donglutian No. 11 coal seam from Pingshuo distract, Ningwu coalfield and the influence of paleopeat-forming environments on trace element enrichment was discussed. The sedimentary environment results show that: (1) The coal facies of the Donglutian No. 11 coal seam include three types, i.e., the low moors under the barrier-lagoon, lower delta plain and upper delta plain; Donglutian No. 11 coal seam is affected by Marine transgression. The pH, paleosalinity, redox degree and hydrodynamic conditions of marsh water are discussed. The contents of Li (av:133.50μg/g), Zr (av:198.12μg/g) and Pb (av:60.76μg/g) in No. 11 coal are much higher than those in hard coal in the world. In the profile of coal seam, trace elements in coal seam show two different combination characteristics, i.e., Li-Zr-Nb-Ta-Hf and Pb-Cu-Ga-Ge-Tl-REY. Li-Zr-Nb-Ta-Hf is mainly enriched in DLT-11-2, DLT-11-6 and DLT-11-10, which are characterized by similar paleopeat-forming environments, namely, seawater, anoxic to euxinic conditions, strong hydrodynamic conditions, with relatively low sulfur content, the low moors under the barrier-lagoon. Pb-Cu-Ga-Ge-Tl-REY is mainly enriched in DLT-11-0、DLT-11-4 and DLT-11-8 , which are characterized by similar paleopeat-forming environments, namely, seawater, alkaline, oxic or anoxic conditions, weak hydrodynamic conditions, with relatively high sulfur content, lower delta plain. These conclusions provide valuable theoretical basis for rational mining target selection and clean utilization of coal resources in other coal-bearing basins.

Reservoir architecture analysis of submarine fan of IIb gas group in the first member of the Late Miocene Huangliu Formation in the Dongfang X gas field, Yinggehai Basin

亚茹李 He YouBin — 2022-06-08 00:00:00.0

Submarine fan of shallow shelf are developed in the first member of the Late Miocene Huangliu Formation in the Dongfang X gas field of Yinggehai Basin .The sedimentary type in this area is special, and the sand body connectivity is complicated.The research on reservoir architecture is relatively weak, which seriously affects the oil and gas exploration and development in the Dongfang X gas field.Under the guidance of sequence stratigraphy,sedimentology, logging geology, seismic sedimentology and other theories, combined with core, drilling, logging, 3D seismic and production dynamics.The characteristics of submarine fan architecture units and the superposition and interconnection of sand bodies in this area are studied. The results show that :(1) Submarine fan is developed in the study area.And the the main sedimentary subfacies is middle fan. Channel, levee, sheet sand and fan margin sand are common in the area. (2)Channel and levee are common in the IIb gas group.Channel is mainly filled and sedimentation, which is divided into two stages of development, and it is spread in NW-SE direction.(3) There are three overlapping styles of sand body inside the reservoir, layered filling, vertical cut overlapping and lateral tangent stacking. (4) The main controlling factors include the supply of materials, the slope of the gradient and the energy of the gravitational flow. (5) Sheet sand is favorable reservoir .Channel sedimentation and levee sedimentation are potential reservoirs.

Study on the changes of the departure port of the Northern Maritime Silk Road from Sui and Tang dynasties to Ming and Qing dynasties —— the Yangtze River Delta as the example

2022-06-08 00:00:00.0

Being an important waterway for the trades between China and East Asian countries in ancient times, the northern Maritime Silk Road (MSR) promoted the great development of the MSR during Song to Yuan dynasties, and achieved the glory of the great navigation in the Ming dynasty. To well improve the systematic research on MSR and to better construct the “21st Century Maritime Silk Road”, it is important to understand the departure port changes and its causes. The concerned works are rather few so far. Based on the records in ancient Chinese books, local chronicles and historical maps, combined with the previous understanding of the environmental changes in China during the historical period, the changes of the main departure ports of the northern MSR in the Yangtze River Delta during Sui and Tang to Ming and Qing Dynasties have been focused on, and the causes are discussed. Following results could been got. 1) During Sui and Tang to Ming and Qing Dynasties, three main departure ports of the northern MSR emerged in sequence in the Yangtze River Delta. The Yangzhou port flourished during Sui and Tang dynasties, the Shanghai Port rose during Tang and Song dynasties, and the Mingzhou port (now Ningbo port) thrived during song and Yuan dynasties. 2) While the climate got cooling, the northern ethnic minorities migrated southwards, the economic and political center of China moved southwards as well following the central governments. As the result, the departure port of the northern MSR changed from the Dengzhou (now Penglai city) in northern Shandong peninsula to the Yangtze River Delta. Following the formation and extending of the series shoals and islands arranged in echelon pattern with sediment accumulation, the mouth of the Yangtze River divided into several branches, and extended eastwards and moved southwards. Consequently, the ancient trumpet shaped Yangtze River estuary was filled, and the Yangtze River delta developed step by step. That is the key reason for the departure port to move eastwards from Yangzhou port to Shanghai port and even abandoned the Yangtze River mouth to Mingzhou port in the Hangzhou Bay, that is the Qiantangjiang River estuary. 3) The development of the shoals in the Yangtze River mouth has also caused the changes of the water systems in the areas of Yangzhou port and Shanghai port, so that the specific positions of the ports are constantly adjusted following the changes of river regime while these two ports are used as the main departure ports of northern MSR. 4) The changes of foreign trade policy also played a certain role to promote or hinder the changes of the main departure port.

Recognition and prediction of fluvial sandbodies and their responses to paleoclimatic fluctuations: A case study in the Lower Member of Minghuazhen Formation, southern Shijiutuo uplift

2022-06-08 00:00:00.0

The recognition and prediction of fluvial sandbodies and associated responses to paleoclimatic fluctuations represent a hot topic of concern in fluvial sedimentology. Based on the seismic sedimentology, a three-step methodology used for the delineation of fluvial sandbody has been proposed (i.e., seismic-well tie used for the establishment of sequence stratigraphic framework, 90° phase transformation to mark lithologies, and stratal slices used to identify sandbodies). This methodology was utilized to delineate fluvial sandbodies in the Lower Member of Minghuazhen Formation, southern Shijiutuo uplift, leading to the recognition of six main types of fluvial sandbodies (e.g., straight and sinuous channel sandstones, channel-levee complexes, point bars, oxbows, river mouth bars, and crevasse splay). Paleoclimates during the deposition of the Lower Member of Minghuazhen Formation were reconstructed, based on mudstone colours and records on algae species and sporopollens. Our results suggest that early, middle, and late evolutionary stages of the Lower Member of Minghuazhen Formation underwent humid-arid transition, dominant humid, and predominant arid. The paleoclimatic evolution towards the humid led to the decrease in the sandstone widths and sinuosities, and to more occurrence of isolated channel fills characterized by ribbon-shape distribution patterns. The paleoclimatic evolution towards the arid led to the increase in the sandstone widths and sinuosities, and to more occurrence of channel-levee complexes and river mouth bars characterized by band-shape distribution patterns. The database and observations from the current study provide reference on the recognition and prediction of fluvial sandbodies in other rift basins, and have practical implications on hydrocarbon exploration of fluvial sandbodies in shrinking evolution period of lacustrine basins characterized by diluted tectonics.

Diagenetic evolution difference characteristics and its influence on shale reservoirs in the Upper Es4 Member of Shahejie Formation, Dongying Sag

2022-06-08 00:00:00.0

The pore structure characteristics and reservoir capacity of continental shale oil reservoirs are affected by the complex diagenetic transformation of mud shale during burial, and there are significant differences in vertical direction, but the relevant researches are still not thorough enough. Rock in Dongying Sag and the typical continental rich organic shale as the research object, based on the core, thin section, scanning electron microscopy (SEM), multi-scale observation methods, such as whole rock mineral combined with X ray diffraction analysis, isotope geochemistry analysis and physical property analysis and energy spectrum analysis of test data, research on the diagenetic evolution characteristics and differences of the shale. The results show that seven types of diagenesis can be identified in the study area. Among them, the constructive diagenesis is mainly calcite recrystallization, clay mineral transformation and dolomitization. As a whole, it is in the middle diagenetic stage A. Calcite recrystallization, dolomitization and clay minerals transformation in vertical showed significant difference evolution characteristics, the causes of recrystallization sparry calcite development mainly in the pure upper 3 small layer and 2 small layers, which is formed by the transformation of clay minerals in the intercrystalline-hole area mainly development as the pure upper 2 small layer. Based on the petrological characteristics, two types of dolomite are mainly developed in the study area. Among them, argillaceous dolomite is mainly developed in the pure upper 3 small layer, and microcrystalline iron dolomite is mainly developed in the pure upper 1 and 2 small layers. The cooperation of calcite recrystallization and clay mineral transformation makes a large number of micropores in the pure upper 2 small layer. At the same time, moderate iron dolomite can be used as a skeleton mineral to support the pores, which is conducive to the preservation of middle and deep pores. It is the key for the pure upper 2 small layer to become a high-quality reservoir.

Broad and narrow approaches in lithofacies paleogeography studies using the preponderant facies method

2021-02-01 00:00:00.0

Lithofacies paleogeography has a long history, during which time a set of research methods and ideas have matured. The disciplines of sedimentology, sequence stratigraphy, basin analysis and related geoscientific approaches may be combined in the study of lithofacies paleogeography. We put forward two conceptual approaches, “broad-sense” and “narrow-sense”, for the study of lithofacies paleogeography. Including cases where a study area is not large, the solution to practical scientific and exploration problems requires the analysis of both lithofacies and sedimentary facies (the “broad” approach). The “narrow” study of lithofacies paleogeography requires attention to national and international standards, quantification, international evaluation, content integrity, theoretical innovation — and so on. Sequence stratigraphic paleogeography, structural paleogeography, quantitative lithofacies paleogeography, coal-forming paleogeography, hydrocarbon reservoir paleogeography and similar questions have their distinctive characteristics and innovations, and have been an important development direction of lithofacies paleogeography. In this paper, the “preponderant facies” approach to lithofacies paleogeography is put forward, where the preponderant facies are classed into macro-groups: marine, transitional and continental groups, connected by the main line of sedimentation duration and thickness (termed “capacity space analysis”). Combining the findings of previous research with systematic studies by the authors’ research group, the isochronism of the Qaidam Basin was confirmed and the entire basin was traced (sequence stratigraphic unit). Then the lithofacies paleogeography in key periods of the formation of the Qaidam Basin were analyzed using the “preponderant facies” approach.

Sequence Stratigraphy and Coal Accumulation of Shallow Water Delta Systems under Low Accommodation Conditions: Case Study from Early Permian Shanxi Formation in the Bohai Bay Basin Region

2021-02-01 00:00:00.0

The Early Permian Shanxi Formation in the Bohai Bay Basin region was studied to unveil the sequence stratigraphy and coal accumulation of shallow water delta systems under low accommodation conditions. Five key sequence stratigraphic surfaces including land surface erosion unconformity (SU), maximum flooding surface (MFS), maximum regressive surface (MRS), intermittent expose surface (IES) and paleosol seam surface (PSS) were recognized. The Early Permian Shanxi Formation comprises three 3rd order sequences and fifteen 4th order sequences. Under the controls of the growth rate of accommodation space and peat accumulation rate, flood plain in delta plain and peat swamp in delta front are favorable coal accumulation centers. Coal seams in the flood plain is thick, and the coal accumulation center tends to move southward with the advance of the shallow water delta. The coal accumulation environment in the delta front is relatively poor, and coal seams is relatively thin, which is easy to be washed by the underwater distributary channel sand bodies.

Source analysis of Silurian and Devonian strata in Susong,Anhui Province and its tectonic significance

2021-02-01 00:00:00.0

The Silurian-Devonian strata of Susong area Anhui Province，distributed in the Qianshan-Wangjiang Basin of the east side of the southern end of the Tanlu fault zone. For the stratum division and tectonic evolution of the Qianshan-Wangjiang Basin, predecessors have achieved certain results, but the research on the sedimentary characteristics, provenance and tectonic background of the Silurian-Devonian strata in the study area is still relatively weak. In order to obtain the provenance information of the Silurian-Devonian strata in the Susong area, detrital zircon LA-ICP-MS U-Pb dating has been performed on the fine sandstone and siltstone of the Fentou, Maoshan and Wutong formations exposed in the Susong area. The results showed that the three samples all obtained major peak ages of about 970 Ma, 820 Ma, and a secondary peak age of about 450 Ma. This feature is consistent with the ages of the magmatic rocks in the Jiangnan orogenic belt and the Caledonian South China area respectively. Using the discriminant map of zircon in granite proposed by Yusuke Sawaki et al. (2017), the results show that most of the zircons belong to the I-type and S-type granite zircons,indicating that the provenance of the studied strata mainly comes from the Jiangnan orogenic belt and the South China plate. Using the model map of the difference between zircon crystallization age and sedimentary age, the tectonic setting of the Silurian-Devonian strata formation in the study area was identified as the collision background.

The character of iron heavy minerals in Quaternary sediments in Yichang area: Implication for formation of the Three Gorges

2021-02-01 00:00:00.0

The evolution of the Three Gorges of the Yangtze River has been the focus and hot spot of the debate in the field of geosciences. In recent years, many scholars have judged the provenance of the Yangtze River through the isotopic and trace element composition of heavy minerals such as zircon, garnet and amphibole, and achieved good results, but few have used single grain iron heavy minerals as provenance indicator minerals and applied them to the cutting through of Three Gorges. Therefore, in this paper, the chemical characteristics and morphologies of iron heavy minerals in Quaternary sediments in Yichang area were analyzed by electron probe, scanning electron microscope and energy dispersive spectrometer, and by comparing with the possible provenance samples, the evolution process of provenance and the cutting through time of the Three Gorges are discussed based on the occurrence of materials west of the Three Gorges in Yichang area. The results show that the source rocks of the iron heavy minerals in the Quaternary sediments in Yichang are mainly come from the Panzhihua vanadium titanomagnetite, Emeishan basalt to the west of the Three Gorges and Huangling granite to the east of the Three Gorges. After the deposition of the Shanxiyao Formation, the provenance of the Quaternary sediments in Yichang area changed obviously, and the material from the west of the three gorges appeared, which indicates that the three gorges of the Yangtze river was cutted. Combined with ESR dating data and previous research results, it can be seen that the cutting through of the Three Gorges of the Yangtze river occurred around 0.75-0.73Ma B.P..

Analysis on the evolution of special geomorphology of ancient river channel in Wayo Village, Tibet

Yu-Chuan Yang de-jun dezhao — 2021-02-01 00:00:00.0

Abstract: In recent years, the evolution of rivers has been the focus of attention of scholars. Wayo Village is located along the national Sichuan-Tibet Railway. In order to ensure the smooth progress of the railway project, the study of river geography is particularly important. The typical fluvial sediments found in Wayo Village prove that the special landform is an ancient channel of the Lancang River. The analysis of the optical luminescence age of the first and second terraces in the Wayo Village section of the Lancang River shows that the river diversion was completed at approximately 20.2±1.6 ka BP. Combined with the current geomorphic features, the reasons for the diversion of the river were analyzed, and the evolution model of the ancient river in Wayo Village was summarized.

Characteristics and Sedimentary enviroment of Binggounan formation, Neoproterozoic siliceous rock at Hongliugou section Ⅰ in Altyn Tagh fault

Xiyong qian — 2021-02-01 00:00:00.0

The fine-grained sediments and carbonate rocks of the Binggounan formation with a 300m thick, Neoproterozoic had been exposed in Hongliugou section Ⅰ, also the presentation of asphalt as oil and gas indication can be found. Based on the section measurement, petrology and geochemistry of the 160m thick siliceous rocks, the authors have shown that the chert mainly composed of quartz and clay, with a small amount of independent minerals including iron, manganese and phosphorus-bearing; it has three structural types of cryptocrystalline, microcrystalline quartz and coarse megacrystalline quartz with a "mosaic structure"; and the average values of SiO2 、Fe2O3、Ba、δEun of siliceous rocks has rather high, while that of Al2O3、MnO、MnO/TiO2、U/Th、Sr/Ba lower ;The value of ∑REE, Sr / Ba, MnO / TiO2, U/TH regularly varies along the section, he average value of δ30 Si is -0.43 ‰(-0.8 ‰ ~0.3 ‰), and δ 18 OSnow is 20.42 ‰(16~26 ‰), and the estimated average temperature is 90 °C(52 °C ~127 °C), which indicates that there are multiple cycles sedimentary of mixing of sea water and hydrothermal fluid in the continental margin basin.in which undergone the early diagenesis, shallow burial period, the multiple strike slip faulting activities with a superimposition of the thermal fluid and the fresh water alteration.

Source analysis and tectonic background judgment in Doushangtuo Formation of Sinian in Wutan1 well ， Kaijiang Area，SiChuan Basin

2021-02-01 00:00:00.0

（Purpose）In order to clarify the geologic tectonic background of the Doushantuo Formation in Wutan1 well in kaijiang area, SiChuan Basin, and to reconstruct its archetypal sedimentary basin, it will provide scientific basis for the reconstruction of palaeogeography and the further exploration and deployment of oil and gas.（Methods）Petrology, petrogeochemistry and U-Pb chronology of detrital zircons were used to analyze the provenance of Doushantuo Formation.（Result）The petrogeochemical results show that the sedimentary source rocks of Doushantuo Formation in Wudan1 well have undergone moderate chemical weathering, and the source rocks are intermediate-basic volcanic rocks.The detrital zircons U-Pb ages mainly records three stages of tectonic magmatic activity: namely 915-850Ma, 794-714.5Ma and 622-700Ma.It is mainly related to the disintegration and evolution of the Rodinia supercontinent in the northern margin of Yangtze craton and its adjacent area. The medium-base volcanic rocks in the background of this tectonic activity are the main material source of the Doushantuo Formation deposition in wutan1 well.(Conclusion)The results show that the Doushantuo Formation in Kaijiang area of Sichuan Basin is developed in the extensional tectonic setting and belongs to the craton inner rifting basin deposits, which is conducive to the development of hydrocarbon source rocks. At the same time, it provides important chronologic evidence for the decomposition evolution of the Rodinia supercontinent. This study is of great scientific significance in understanding of the geological structure in-depth, depositional and tectonic evolution and the strategic deployment of oil and gas exploration in Sichuan Basin.

Geochemical characteristics from the Yangshui Formation in the central Guizhou Province during the Ediacaran Doushantuo period and its implications for the palaeo-ocean environment

2021-02-01 00:00:00.0

To reconstruct the palaeo-ocean environment during the Ediacaran Doushantuo period, this study selected the phosphatic sequences of Xiaohe(XH) and Xifeng(XF) phosphorite deposits orefield and use the research methods of identification of rock and minerals, SEM, trace and rare earth elements analysis in phosphatic samples to reveal the interaction effect between the deposition of phosphorites and their sedimentary environment. Research results showing that the deposition of phosphorite was controlled by the palaeo-morphology of shallow shoal around the Qianzhong Oldland. The ratio of Sr/Ba in phosphatic samples in Yangshui Formation are commonly greater than 1, and their average values are 1.90(XH) and 0.95(XF) respectively. Whereas the Sr/Ba ratio of samples in Chenjiang Formation are less than 1 and average values are 0.11(XH) and 0.18(XF) respectively. The different results of Sr/Ba ratio show that the transformation from lake sedimentary environment in Chengjiang period to marine sedimentary environment. The ratios of V/Cr and Ni/Co in phosphatic deposits in Xiaohe Yansgshui Formaiton section are 1.77 and 2,17 respectively, and 1.26 and 2.93 in Xifeng section, all indicate the suboxic to oxic environment. The values of δCe in Xifeng phosphorites are limit in 0.75～0.95 and the mean value is 0.85, and the values of δCe in xiaohe phosphorites are 0.74 to 1.09 (mean value is 0.88). The increase of negative ce anomalies from bottom to top of Yangshui formation shows that the sedimentary environment transferred from suboxic to oxic. This change of paleo-ocean geochemical environment implied the increase of the ocean productivity in shallow coast, stimulating the deposition of biological action induced phosphorite，and the life evolution also changed the oxygen content and distribution in ocean. Therefore, the transformation of phosphogenesis environment is a positive response of the Neoproterozoic Oxygenation Event and life Evolution.

Radial ooids induced by photosynthetic biofilms: an example from the Miaolingian Zhangxia Formation at the Jiawang section in Xuzhou city of Jiangsu province, North-China Platform

2021-02-01 00:00:00.0

Recent continue studies on the modern marine aragonite ooids in Bahama demonstrate that microbes and extracelluar polymeric substances (EPSs) are very important in the formation of ooids, which resulted in an important scientific idea, i.e. these coated grains can be regard as “laminated organosedimentary structures” that follow some of the formative characteristics of microbialite systems. Nevertheless, following fundamental features do add some mysteries and complexities for the formation of ooids since questions of where and how they form and what biological and abiotic processes they record are still debated: 1) the 3.0 Gyr old of history; 2) diversified forming environments; 3) strongly different composition of minerals; 4) a variety of sedimentary fabrics. Radial ooids from the upper part of the Miaolingian Xuzhuang formation at the Jiawang section in Xuzhou city of Jiangsu province are made of calcite and show radial, radial-concentric, and micritic fabrics. Within both the core and the cortex of these ooids as well as the clump or clot among ooids there are excellent photosynthetic biofilm fabrics reflected as the high-density preservation of the Girvanella within dark and dense micritic fabrics, which provide a relative direct evidence of ooid formation that is genetically related to the photosynthetic biofilm, since it is relatively certain that Girvanella resembles closely recent calcified Plectonema although it had been interpreted as the analogy of the modern Scytonema. Thus, the accretion of the cortex made up of radial and fibrous calcites of radial ooids from the Zhangxia Formation are possibly nourished and promoted by photosynthetic biofilms, although radial-fibrous calcites making up the cortex can not be understood as the direct results from the microbial precipitation. Ultimately, our finding and study provide an important example for the further understanding and elucidating of the “ooid dilemma”, which still provide an important evidence for the cayanobacterial bloom in the calcite sea of the Cambrian Miaolingian that is coincided with metazoan radiation.

Comparison of correlation between magnetic susceptibility and grain size from the lacustrine sediments in the eastern Tibetan Plateau and the loess in the Chinese Loess Plateau

Shi Wei Jiang HanChao — 2021-02-01 00:00:00.0

To explore the correlation between magnetic susceptibility (SUS) and grain size of the dust deposits from the tectonically stable and active regions and its implications for environmental events, we analyzed the grain size and SUS records from the loess sediments of the Chinese Loess Plateau (CLP) and the lacustrine sediments from the eastern margin of the Tibetan Plateau (TP). Results indicate that SUS showed the strongest positive (negative) correlation with the 2-10 μm fraction for the loess (lacustrine) sediments, indicating that the 2-10 μm fraction of dust sediments was a continuous, stable and sensitive fraction of background sedimentation for the CLP and TP and even the arid to semi-arid regions in Asia. On the other hand, SUS showed the strongest negative (positive) correlation with the 32-63 μm fraction for the loess (lacustrine) sediments, indicating that the 32-63 μm fraction of dust sediments was the sensitive proxy not only for the dust storms in the CLP but also for the seismic events in the eastern margin of the TP. The correlation between SUS and grain size was higher in the beginning part than in the ending part of a seismic event in the eastern part of TP, indicating that the fresh sediments entering the study area decreased with gradual recovering of landform after a seismic event. Finally, the correlation between SUS and grain size was also influenced by the local material source.

Analysis of fluvial compound sand-body architecture hierarchy in offshore oil field

2021-02-01 00:00:00.0

Based on the existing hierarchical scheme of architectural units in clastic deposits, taking fully account of the evolution law of river sedimentation in nature, the data base and economic development scale of offshore oil fields, and following the principle and basis of the classification of geological bodies, an architecture hierarchy of fluvial compound sand-body in offshore oil field is established. In this paper, the basic characteristics of 10 grade architecture units of fluvial compound sand-body are systematically described from the aspects of geological genesis, main control factors, space-time scale, etc., and the correlation between them and related sedimentary geological body grades is analyzed. The difference between the fluvial compound sand-body architecture hierarchy and the existing classification of reservoir architecture mainly lies in the 7th "compound point bar" level, which is the combination of reservoir architecture theory, offshore oil field data resolution and offshore oil field economic development scale. It is a good practice of "seismic guidance, well seismic combination" structure research ideas in offshore oil field. It has been proved that the architecture hierarchy of fluvial compound sand-body has certain advantages for guiding offshore oil and gas development.

A pulsed oxygenation in shallow seawater recorded by Mesoproterozoic Wumishan Formation, North China

2020-07-06 00:00:00.0

Oxygen is crucial for the origin and early evolution of eukaryotes; however, the atmospheric- oceanic oxygen levels during mid-Proterozoic have been poorly constrained, with varying viewpoints of persistent low (<0.1–1% present atmosphere level, PAL), relatively high (>4–8% PAL), and highly dynamic concentrations (from <0.1–1% to >4–8% PAL). In order to further constrain the redox conditions in shallow waters where eukaryotes inhabited, Ce anomaly was investigated on the peritidal carbonates from lower Member IV of the Wumishan Formation. The results show that a ~150-m-thick interval with significant negative Ce anomalies (Ce/Ce* = 0.82 ± 0.11, n = 10) was bookended by intervals with inconspicuous positive Ce anomalies, which may have reflected a pulsed oxygenation in shallow seawater with a duration of ~5 Myr (~1480–1475 Ma). This pulsed oxygenation recorded by carbonates from Member IV of Wumishan Formation likely suggests that oceanic redox conditions during mid-Proterozoic were highly fluctuated rather than stable at low or relatively high state.

Analysis of formation of the lateral accretionary period of the composite point bar

2020-07-06 00:00:00.0

It is one of the difficulties in fluvial sedimentology to analyze the quantitative genesis of the lateral accretionary body of composite point bar. By selecting lidar data from the lower reaches of the Mississippi River, the internal characteristics of the lateral accretion of the composite point bar are analyzed, and the elevation data of the lateral accretion are counted and found to conform to the characteristics of periodic changes. The Fourier transform calculation of the elevation data is used to obtain the compound point bar lateral accumulation period, and the lateral accumulation period is fitted to the scale of the river channel. The two are in a linear relationship and have a high degree of fit. After in-depth analysis, it is believed that the lateral accumulation cycle is controlled by the seasonal flooding cycle of the river. The results provide a theoretical basis for quantitative genesis analysis of lateral accretionary body.

Classification scheme and distribution probability statistics of composite point bar architectures

2020-07-06 00:00:00.0

Abstract The analysis of heterogeneity within the composite point bar reservoirs is difficult in the study of meandering river sediments, and it is difficult to explain clearly by seismic data and well logging data alone. Regarding the characterization of the architecture of the composite point bar reservoirs, there is also a lack of quantitative guidelines. In this paper, 260 composite point bars in 13 meandering rivers are selected as data samples to carry out parameter classification and statistics to form a knowledge base of composite point bars. Composite point bars are divided into 4 categories and 25 subcategories; lateral accretion bodies are divided into 8 categories and 22 subcategories. The distribution probability relationship between different types of composite point bars and lateral accretion bodies is calculated. On this basis, the quantitative distribution probability relationship is fully used to analyze the plane heterogeneity of the composite point bar reservoirs under the condition of less data.

Deposition evolution of Late Paleozoic in Ordos Area

2020-07-06 00:00:00.0

Based on the author's research results of Late Paleozoic in Ordos Area for many years, and combined with the field measurements, stratigraphy and sequence, geochemistry and geochronology studies in recent years, the results are compared from the aspects of lithological characteristics, stratum thickness, stratum contact relationship and sedimentary facies types. It shows that the upper Paleozoic in Ordos area is a part of the North China Platform. Based on this study, the plane distribution maps of sedimentary facies of the Great Ordos Area in the all stages of Late Paleozoic was drawn, these maps extended the eastern and southern part of the origin Ordos Area, which provided a new evidence for the restoration of the original sedimentary features of the North China Platform in this period.

Architectures and Evolution of Alluvial Fans: Insights from A Flume Experiment

2020-07-06 00:00:00.0

Using time-lapse cameras and 3D laser scanners, 74 groups of sector geomorphic data of alluvial fans were obtained through flume experiments, and a detailed sedimentary analysis on these data was performed by using quantitative software. The sedimentary evolution process of the alluvial fan and its sedimentary configuration were clarified. Results suggest: that there are obvious differences in hydrodynamics, water flow patterns, and sector growth during the evolution of alluvial fans. Based on these differences, the entire simulation experiment is divided into three stages: early, middle, and late. In the early stage of the simulation experiment, the sector was relatively strong in hydrodynamics, and the sector surface expanded at the fastest rate, it has the characteristics of continuous sheet-like downward impact on the plane; multiple stages of sheet flow are superimposed on the section. According to the sedimentation distribution of flake deposition, it can be divided into overall flake deposition and local flake deposition. In the middle period of the simulation experiment, the hydrodynamic forces at the middle and distal of the fan body and the expansion rate of the fan surface are reduced, and the effects of progradation and aggradation both occur. The main controlled sedimentation is non-confined river channel and lobe body deposition, in which the non-confined river channel is mainly distributed near the source, and has the characteristics of wide, short, slow and stable development of the water channel. The lobe body is mainly distributed in the edge of the river channel. In the late stage of the simulation experiment, the hydrodynamic forces at the distal source end of the sector and the rate of expansion of the fan surface decreased compared with the early and middle stages, with mainly aggradation effects. The main controlled sedimentation is confined channel sedimentation, which is mainly distributed at the edge of unconfined channel, and has the characteristics of narrow, long, deep and large-scale shift of the channel. Through experimental research, an alluvial fan depositional configuration model with a distinct three-layer structure has been established. Among them, the bottom layer is a laminar complex, the middle layer is a watercourse plus lobe complex, and the top layer is a watercourse plus small lobe complex.

Hydrothermal activities in Middle Permian Mokou Formation in eastern Sichuan Basin

2020-07-06 00:00:00.0

The Middle Permian Maokou Formation has been found abundant hydrothermal minerals in carbonate rocks in Sichuan Basin. Two types of hydrothermal activities in Maokou Formation are identified in eastern Sichuan Basin: one is hydrothermal silica, formed as thin beds, nodules or irregular chips of chert; another is featured by hydrothermal carbonate minerals, including coarse calcite and dolomite, sometimes with few metal sulfides of pyrite and sphalerite. The carbonate minerals are usually filled into the interweaved tensional fractures or formed as “snow-flake” assemblages scattered in host rocks. The Al-Fe-Mn end-member diagram of cherts and correlation diagrams between silica and other main elements indicate a hydrothermal origin, and the silica comes from both hydrothermal and terrestrial sources. In situ sulfur isotopes of pyrite and sphalerite ranged between -3.91‰ and -6.87‰, imply mixed sulfur sources from microbial involvement and basalt. Both coarse calcite and saddle dolomite in the veins have similar geochemical features, such as higher CaO content than those in stoichiometry calcite and dolomite, rich in Strontium, Uranium, poor in REE and Titanium, obvious negative anomalies of Ce/Ce*, and positive anomalies of Eu/Eu*, and very positive Y anomalies, which provide evidences to support the assumption of hydrothermal origin as well, and suggest mixed sources of the fluids. The volcanic-related fluid and the ground water rich in calcium and magnesium irons leached from underlying marine carbonate rocks, may participate together to the formation of these carbonate minerals. High concentration of Ge and Cd, and ratios of Zn/Cd and Zn/Fe in sphalerite suggest medium mineral-forming temperatures, which are overlapped by the wide homogenization temperature zone between 54.7 and 294.3 oC measured from fluid inclusions in microcrystalline quartz, calcite and dolomite.

Gravity Flow Deposits and Associating with Ichnofossils of the middle third member of Shahejie Formation in Dongpu Sag

Changzheng ChangzhengWang — 2020-07-06 00:00:00.0

Abstract: Based on the observation and analyses of 90 exploratory well cores in Dongpu Sag, 4 types of gravity flow (including sliding, slumping, debris flow and turbidity current) deposits have been recognized in this work. Their main identification marks are outlined?below: (1) the sliding deposits are characterized by?the partial preservation of primary sedimentary structures, the development of small penecontemporaneous fracture or fault in sandstone?beds, and steep?dip of strata, that commonly occurred shore and shallow lake environments. (2) General characteristics of slumping deposits mainly are the abrupt contact between sandstone beds (top and bottom) and dark mudstone beds，and development of all kinds of penecontemporaneous soft deformation?structures such as convolution?bedding, flame structure, water-escape structure, liquefied vein and tearing debris. (3) The sandy debris flow deposits is mainly marked by the massive sandstone, abrupt contact between sandstone beds (top and bottom) and dark mudstone beds, as well as developing floating gravels near the top of sandstone beds and tearing mudstone debris in the bottom of sandstone beds, sometimes, occurring the mud-coated intraclasts. Meanwhile, slumping and sandy debris flow deposits commonly associated with the Mermoides-Parapaleodictyon ichnoassemblage produced in semi-deep?water lake environment. (4) The turbidity deposit is mainly indicated by the complete or incomplete Bouma sequences，normal grading bedding, and all kinds of sole marks as scour marks, irregular flute casts and load casts, and the Semirotundichnus-Puyangichnus ichnoassemblage frequently occurred in the middle to upper parts of the turbidite beds that formed in deep-water lake environment. After comprehensive analyses of above 2 types of gravity flow deposits and water-depth variation reflected by different ichnoassemblages, as well as the tectonic paleogeographic background?frequently occurred fault activities, it can be considered that gravity flow deposits within the middle third member of Shahejie Formation in Dongpu Sag belonging to the slump type. That is to say, the gravity flow deposits of slump genetic type were formed under the triggering?mechanism of frequent fault activities located along the delta front and occurred along a certain slope bottom of lake. Under the combined action of the gravity flow deposits and subsequent bioturbation, the physical?property of sandstone reservoir would be affected, which will play a role of enlightenment in the exploration and development of oil and gas.

Eogenetic karst characteristics and geological significance of the Mixed Siliciclastic-Carbonate Sediments within the Yuertus Formation, Early Cambrian, the Northwest Tarim Basin

2020-07-06 00:00:00.0

Through macro and micro study on the outcrop profiles in Akesu-Keping-Wushi areas in Northwestern Tarim Basin, three-phase apparent paleo-exposed surfaces within Yuertus Formation have been identified and are characterized as follows: 1) ferruginous crust, 2) near-surface karst (plastic) breccia, 3) karst trench, fissure and cystic cave, 4) breccia and terrigenous clastic fillings in Karst system, and 5) overlap sedimentation above the exposed surfaces. The comprehensive analysis shows that the Yurtus Formation in the study area is not a series of continuous deposits, but presents several internal sedimentary discontinuitiesand regional unconformable contact with the overlying Xiaoerbulake Formation. At the same time, based on a comparative analysis of eogenetic karst characteristics within limestone and dolomite, it is suggested that the mixed siliciclastic-carbonate rocks with poor percolation conditions are characterized by the development of small karst caves mostly filled and immature horizontal underflow zone. This can be used to distinguish from the typical characteristics of facies-controlled karst caves, variegated karst, and near-in-situ brecciation within limestone and dolomite-type in early diagenetic stage. The findings show that the karstification and reservoir optimization in the early diagenetic stage under open conditions are more controlled by the rock fabric, so it is inferred that under relatively closed burial conditions, the early densified rocks are difficult to undergo karst reconstruction to form phase-controlled vuggy reservoirs. This result not only has important reference significance for the formation and maintenance of reservoirs under deep burial conditions, but also provides new materials for the enrichment and development of eogenetic karst geological theory.

Sequence-palaeogeography and coal accumulation characteristics of fluvio-lacustrine Wayaopu Formation of the Upper Triassic in central Ordos Basin

2020-07-06 00:00:00.0

In order to study the sequence-palaeogeography and coal accumulation of the upper Triassic Wayaopu Formation in the central Ordos Basin, used by field outcrops, boreholes and logging datas, Wayaopu Formation was identified into five rock types and 17 rock facies types. Based on sequence stratigraphic interfaces such as regional unconformity surface, stratigraphic color mutation surface and river incised valley washed surface, the Wayaopu Formation was divided into three third-level sequences. Then we identified the sedimentary range, lithofacies combination and sedimentary system of SQ1, SQ2 and SQ3. A single factor analysis and multifactor comprehensive mapping method was applied to recover the palaeogeographic pattern within every third-level sequence as an analyzing unit．The results showed that the palaeogeographic units of SQ1, SQ2 and SQ3 in the Wayaopu period mainly included meandering river, alluvial plain, delta plain, delta front and lake. In the lithofacies palaeogeographic evolution of third-level sequences, the alluvial plain and delta gradually advanced to the lake area, while the area of lake gradually shrinked. The development of peat swamp in interdistributary bay of delta plain provided a favorable place for coal accumulation and formed a coal seam with definite industrial value. From SQ1 to SQ3, coal accumulation mainly occurred in the lacustrine transgressive systems tract and coal accumulation gradually strengthened, the rate of peat accumulation and the rate of accommodation space increase gradually reached a balance, and the total thickness of coal seam and the maximum thickness of single coal seam gradually increased too.

Holocene environmental evolution recorded by core sediments of the Judianhu Lake in the east of Lubei Plain

2020-07-06 00:00:00.0

Abstract: Judian Lake in the eastern part of Lubei Plain is located in the monsoon area of northern China, which is sensitive to global climate change and provides abundant lake sedimentary data for the study of the past climate and environment evolution in the land sea interaction area. Based on the sporopollen identification, grain size analysis and AMS14C dating of core sediments from the drilling hole of the Judian lake, the evolution process of climate and environment since 8900cal.a BP in the northern Lubei plain of was discussed. The results show that: 8900 ~ 7625cal.a BP, the temperature and precipitation increased, the climate changed from cold-dry to warm-wet; 7480 ~ 6810cal.a BP, the climate was cold- dry as a whole; 6810 ~ 4435cal.a BP, the temperature rose while the precipitation increased, showing the climate characteristics of warm and humid as a whole in the middle Holocene; 4430 ~ 3150cal.a BP, the climate was cold and humid as a whole, and there were small fluctuations of cold and warm. During the middle Holocene, there were obvious cold and dry events in 5450-5280cal.a BP and 4160-4090cal.a BP, which was consistent with the geological and climatic records in China and even in the world. It may be due to the southward movement of the equatorial convergence zone caused by the change of solar radiation, the change of ocean surface temperature and the feedback of surface vegetation.

The tidal-limit movement of the Changjiang River in historical period

2020-07-06 00:00:00.0

The tide propagated upstream for several hundred kilometers from the Changjiang River estuary. People in ancient China already knew that the tide can spread up the stream and the upper bound. In China, some information and records reflecting the Changjiang River tidal limit and its movement can be found from some ancient books, literary works and local chronicles. At the end of the 3rd and the beginning of the 4th century A.D., the tide limit of the Changjiang River had reached the upstream of Chaisang (now named Jiujiang in Jiangxi Province). The ancient poems also show that the tidal limit also moved to the lower reaches. By the early 9th century, the tide limit in the dry season has retreated to the Penpukou of Jiujiang. In the last ten years of the 13th century, the tidal limit moved down to the Xiaogushan Mountain near the border between Anhui Province and Jiangxi Province. People in Yuan Dynasty also set up a pillar to commemorate it. By the middle of the 20th century, scholars generally suggested that the tidal limit retreated to Datong in Anhui Province. During the period when the main stream of the Changjiang River was not cut off by large water conservancy projects, the tide limit should retreat continuously. From the 3rd decade of the 9th century A.D. to the last decade of the 13th century A.D., during the 470 years, the tide limit moved downstream 64 km, with an average annual rate of 0.136 km/a. During the 670 years from the end of the 13th century to the middle of the 20th century, the tide limit had moved downstream 170 km, with an average annual rate of 0.254 km/a, almost twice as much as that of the previous period. Its time scale is basically coincided with two climate events (the Medieval Warm Period, 1000–1300 CE; and the Little Ice Age, 1400–1900 CE) in the past thousand years, thus the climate change accounted for the different retreat rate of the tidal limit between the two period in the paper. In addition, a recently study found that during the extremely dry periods, when the discharge of Jiujiang station was about 8440 m3 s-1, the tidal limit is near Jiujiang. In the years when the water conservancy project on the main stream of the Changjiang River began to store water, the tide limit actually returned to the previous position of the middle Tang Dynasty more than 1100 years ago.

Optimum reservoirs prediction of Fan delta, Baikouquan formation, west slope of Mahu Sag

2020-07-06 00:00:00.0

Aiming at the problem that the physical properties of fan delta sandstone of Baikouquan Formation in Fengnan area of west slope of Mahu sag vary greatly in space and it is difficult to predict high-quality reservoir. In this study, under the guidance of sedimentary petrology, seismic sedimentary and reservoir inversion theory. High-resolution sequence stratigraphy, sedimentary microfacies description and high-quality reservoir inversion are carried out by comprehensive utilization of logging, core and 3D seismic data. The fourth-order sequence stratigraphic framework of Fengnan area was established, and the filling process of multi-stage transgression and regression in fan delta was clarified. It is pointed out that SSQ3 and SSQ5 are the development sequences of high-quality reservoirs. Sedimentary microfacies such as distributary channel, inter-channel, subaqueous distributary channel, estuary bar and sheet sand in fan delta plain were identified. It was pointed out that fan delta plain is an optimum reservoir facies belt. The reservoir facies-controlled impedance inversion of separated layers in PSTM was carried out by applying the constraints of vertical boundary of high-resolution sequence stratigraphy and lateral boundary of sedimentary facies to improve reservoir prediction accuracy. Five high-quality reservoir development areas are predicted in the sequence of SSQ3 and SSQ5, and three wells were proposed. Industrial oil flow was obtained during drilling.

Geochemical characteristics of the development and evolution of Xisha carbonate platform

2020-07-06 00:00:00.0

Located at the Shidao Island, Xisha area, well XK1 shows great variations with the depth increase on the lithological assemblages, elemental geochemistry and biomarker signatures. The information sheds significant light on the paleoenvironment of the Xisha carbonate platform since the early Miocene. By using elemental geochemistry, Tex 86 and other proxies, we aim to reconstruct the regional sea-level changes, and the formation and development of the carbonate platforms in Xisha area since the early Miocene. It is believed that the Xisha carbonate platform was initially formed during the early Miocene, gradually flourished and developed in the middle Miocene, then reached its peak at the late middle Miocene. During this time, large reefs were formed showing a wide occurrence of lagoon facies. During the late Miocene - Pliocene, the rapid sea level rise led to the gradual shrinking and submergence of the carbonate platform. Finally, the carbonate platform continued to shrink to a larger degree in the Quaternary. Element geochemistry and lithologic assemblage reveal that there were two intense dolomitization in Xisha area during the early Miocene and late Miocene-Pliocene, respectively. These events were closely related to the exposure and erosion of the carbonate platform caused by regional sea-level drop. The XK1 carbonate platform evolution indicates the prosperity and extinction of the Cenozoic carbonate platform in the South China Sea. It was under control of the interaction between the Cenozoic tectonic events and global climate changes in the South China Sea. Due to their high requirement for the optimal conditions and the sensitivity to environmental changes, the carbonate platform has become a robust archive to record the Cenozoic regional tectonic evolution and global climate change in the south China sea.

Cheng-Yifan — 2020-07-06 00:00:00.0

Characteristics of Hummocky and Hummocky-like Cross-stratification and its Genetic Mechanism for Vertical Vortex

Xiangdong Li — 2020-07-06 00:00:00.0

Hummocky and hummocky-like cross-stratification (HCS and HCS-like) as the identification criteria for sedimentary environments have recently become much confusion because of the little knowledge on their genetic mechanism based on the facts that including: ① HCS and HCS-like are often associated with storm deposits and turbidity current deposits respectively; ② the views on HCS producing in shallow water environments while HCS-like in deep-water environments have been abandon in present. According to the detail review on structural characteristics, spatial variation and vertical sequence of HCS and HCS-like from literatures, here we found that: ① the special features of HCS as follows: the sharp or erosional basal contact, the internal truncation surface, close relationship with swaley cross-stratification, and the missing some zone or amalgamation HCS in hummocky sequence; ② the special features of HCS-like often include: variation thickness of individual lamina, laterally and vertically gradation between hummocky and flat-laminated intervals, laterally gradation both with parallel bedding and small-scale wave-generated cross-bedding, and alternating sedimentary structures of upper and lower flow regime in vertical sequence. According to some hydrodynamic theory and flume experiment achievements, these results show that the genetic mechanism of HCS and HCS-like can be divided into two parts: hydrodynamic mechanism and deposition mechanism. The former could be interpreted by vertical vortex generated by baroclinic wave in nature which is same in HCS and HCS-like. And the latter is very different: HCS and HCS-like could be interpreted by erosion suspending sand mechanism and suspending sand settling mechanism respectively, and the special features in HCS and HCS-like are due to the different sediment suspension concentration and depositional flow energy. The division for hydrodynamic and deposition mechanism in genetic mechanism of HCS and HCS-like is very significant in determination sedimentary environments from depositional flow evolution.

Oncoids built by photosynthetic biofilms: An example from the Series 2 of Cambrian in the Liaotung Peninsula

2018-11-29 00:00:00.0

As a type of coated grains with the size of more than that of ooids, oncoid is marked by non-smooth circles and is commonly interpreted as a microbial origin, so different from ooid whose origin remains uncertain. Also as a variety of spherical or pseudo-spherical biosedimentary structures formed as successive laminations around both biogenic and nonbiogenic nuclei, its widespread distribution and development by oneself imply that the oncoid can be grouped into a type of microbial carbonates or a kind of spherical stromatolites. Within the Jianchang and Mantou Formations of the Series 2 of Cambrian in the Liaotung Peninsula, oncoids with the size of centimeter level as a time-specific facies concentrate in the top part of third-order sequence. In addition, several features characterize these oncoids of the Series 2 of Cambrian in the Liaotung Peninsula: 1) the symbiosis with clots or microclots; 2) the spherical and ellipsoid morphology; 3) the inhomogenous or non-layer composition of dense micrite and microspar; 4) particular calcified sheath fossils of the cyanobacteria within the cortex of oncoids and the clot among oncoids and so on. Although the greatest challenge that remains is the interpretation of ancient oncoids and their detail forming processes through the filter of the diagenesis, also the detail of the calcification of biofilms dominated by the cyanobacteria has still not get better understanding, the richness of direct evidence represented by microbial fossils especially for sheath fossils of the cyanobacteria within oncoids of both the Jianchang and the Mantou Formations of the Series 2 of Cambrian in the Liaotung Peninsula make them become a good example of oncoids built by non-layer photosynthetic biofilms.

Analysis of extreme drought events sequence in north of China over last millennium

2018-11-29 00:00:00.0

Based on historical records as proxy data, we reconstructed the extreme drought events sequence in north of China in last millennium. Next we analysed the characteristics and regularity of extreme drought events. Results are as follows: (1)The extreme drought events have inter-decadal oscillation like 50a-100a and 250a, and there exist three high-incidence periods which include mid 15th century, early 17th century and late 18th century. (2)The change of extreme drought events are consistent with humidity changes in the eastern region. When the humidity is dry, a probability of extreme droughts are high, and vice versa. (3) A probability of extreme drought events will exist ascension at warmest phase in warm period or coldest valley in Little ice age. (4) There is a stable inverse correlation at humidity changes and change of extreme drought events between North China monsoon region and non-monsoon area that influenced by westerly wind. This phenomenon is probably affected by “silk road pattern” and NAO.

SEDIMENTATION RATES BY RADIO LEAD ISOTOPE IN THE OFFSHORE AREA OF THE XINGHUA BAY AND PROPOSED CALIBRATION METHOD

2018-11-29 00:00:00.0

State Key Laboratory for Marine Geology, Tongji University, Shanghai 200092, China Abstract: CoreD37 and FJ3-12, collected from the offshore area of the Xinhua Bay, were analyzed by γ-spectrometer. Downcore variations in 210Pb, 226Ra and 137Cs activities were therefore obtained. Mean sedimentation rates of D37 and FJ3-12, calculated using CFCS and CRS models for 210Pb inventories and the 137Cs time-scale method, are 0.88 ~ 2.71 cm·yr-1 and 0.97 ~ 4.24 cm·yr-1, respectively. The difference between varied methods is obvious. It is also suggested that the incompleteness of logarithmic attenuation profile (i.e., the sampling depth less than that bearing 210Pb background value) has an adverse effect on calculating sedimentation rates by CFCS and CRS models. Therefore, a rectification method was developed for further discussion. It was suggested to calculate first the deposition age for the upper boundary of sustaining 210Pb (or none 210Pbex) layer by the CFCS model, and then mean sedimentation rates of the study core by the CRS model with this deduced data.

Sedimentary characteristics and seismic sedimentology interpretation of near-shore subaqueous fan for the Upper 4th Member of Shahejie Formation in the north steep slope, Dongying Depression

2018-11-29 00:00:00.0

Near-shore subaqueous fans is well developed in the northern steep slope and is an important sedimentary facies in the Upper 4th Member of Shahejie Formation in Dongying depression, Bohai Basin. The exploration practice revealed that this sedimentary facies is the key target of oil and gas exploration. Guided by the theory of sequence stratigraphy and seismic sedimentology, the near-shore subaqueous fan in the upper Es_4 of the north steep slope in Dongying depressiong is quantitatively studied. The sequence framework was builded, the strata slices were made, seismic attribute was extracted and the well logging was calibrated, which displayed the distribution of sedimentary facies and its evolutionary process. The channels of near-shore subaqueous fan were quantitatively characterized. Finally, the distribution and evolution of sendimentary facies was predicted to find the subtle reservoirs such as near-shore subaqueous fan in Dongying depression.

Paleoenvironment changes during the past 21 ka inferred from organic geochemical records of Lake Caohai, Guizhou

2018-10-24 00:00:00.0

Lake Caohai is located in the boundary areas between Guizhou and Yunnan provinces where the climate is dominated by Indian summer monsoon (ISM). The long lacustrine sediments provide ideal material for revealing middle and late Quaternary environmental changes. In this paper, a core of 405 cm length (NT03) was studied. The age model was established based on 7 AMS 14C ages covering the last 21 ka. Here we present the results of sediment chromatic aberration value (CIE-L*), loss on ignition at 550°C (LOI550), total organic carbon (TOC), C/N ratio and stable carbon isotope (δ13Corg). The environment proxies (L*、TOC and LOI550) varied synchronously, indicating three distinct intervals of lake level since the LGM, i.e. riverine alluvial facies, lake-wetland facies and shallow water alluvial facies respectively from 21 ~ 15 ka BP, 15 ~ 4 cal ka BP and after 4 cal ka BP. This change pattern is similar to the variation of speleothem δ18O records from the south China. The δ13Corg values, varying between -29.28‰ and -24.19‰, suggest C3 plant domination in regional vegetation, despite a possible moderate C4 plant increase during the LGM. The TOC and δ13Corg records show an important change at B/A event implying the local ecosystem and lake level are sensitive to the deglacial warming. There was an abrupt change in all proxy records at around 4 ka BP which may indicate a weakening summer monsoon indicated by the speleothem δ18O records.

Development rules of mouth bar in shallow-water delta——A case of Chang 1 Formation in Zizhou area, Ordos Basin

2018-10-24 00:00:00.0

The Ordos Basin during the Late Triassic Yanchang Formation was a large depression basin with the characteristics of gentle slope and shallow water, which is conducive to the formation of shallow-water delta. Through field observation, it is found that the along the Dali River in the Zizhou area of the Ordos Basin develops the mouth bar. And it is also proved that mouth bar can develop in shallow-water delta in some literatures. However, some scholars believe that the prominent feature of the typical shallow-water delta front is dominated by underwater distributary channel, and the mouth bar is not developed. Firstly, this paper analyzes the characteristics of typical mouth bar in Zizhou area, and points out that there are three upward-crossing cycles in the mouth bar and the thickness of argillaceous interlayer in each cycle has an upward trend, which indicates that the accommodation is increasing. Next, the development rules of mouth bar in shallow-water deltas are summarized. This paper argues that the formation of the mouth bar is determined by the accommodation and sediment supply, and its development rules are summarized into three: First, in the case where there is sediment supply and the accommodating space becomes large, the formation of the mouth bar is determined by the amount of sediment supply, forming a retrograding sequence; Second, in the case where there is sediment supply and the accommodating space becomes small, the formation of the mouth bar is determined by the remaining accommodation, forming a progradation sequence; Third, the mouth bar does not develop when there is no accommodation. The variations in the accommodation can be identified by mud thickness, vertical sedimentary facies, mudstone color, and special rock formations or interfaces. Each of them is applicable on different scales.

Study on the Causes of Silicification of ooid-Example from the Cambrian zhangxia Formation at Xiaweidian outcrop in Beijing

2018-10-24 00:00:00.0

As a very important phase particle in carbonate rocks, the research on it is mainly focused on the cause of the formation, and there is less research on the diagenesis of ooid. The Cambrian Zhangxia Formation at Xiaweidian outcrop in Beijing is characterized by the development of large-scale Oolitic limestone. In this paper, we studied the silicification mechanism and siliceous sources of by means of field observations, thin-slice observations, XRD test and combined with geochemical parameters such as organic carbon and pyrolysis. The results show that the recrystallization of the ooid results in the enrichment of organic matter at the edge of the ooid, organic acids released from the evolution of organic matter are the main factors for siliceous precipitation,the source of the silica is mainly the input of the terrestrial source and the transformation of the clay mineral. The organic matter is mainly concentrated on the edge of the ooid, As a result,siliceous deposits mainly occur along the edge of the ooid, forming a siliconized sheath that is characteristic of the ooid edge. This result also reflects that organic matter plays an important role in the formation of ooid.

2018-10-24 00:00:00.0

Study on Sedimentary Features and Facies Modeling of Xiaoerblak Formation in Xiaoerblak Area, Tarim Basin

2018-10-24 00:00:00.0

The dolomite reservoir of Xiaoerblak formation in Tarim Basin is controlled by sedimentary facies, mounds and shoals are the potential zone of reservoir, therefore, study on features and distribution laws of mounds and shoals is significant to exploration of Lower Cambrian. This study takes Xiaoerblak area as an example, measured 7 outcrops, and based on outcrop descriptions and microscopic thin section observation, analyzed the sedimentary features systematically, and established microfacies model. The thickness of Xiaoerblak Fm. is about from 158m to 178m, Laminite dolomite, thrombolite dolomite, spongiostromata stromatolite dolomite, stromatolite dolomite, Oncolites dolomite, arenite dolomite and dolomicrite are the main types of rock, Bottom-up lithofacies combination indicate Xiaoerblak fromation is an upward shoaling 3rd succession. The study confirmed Keping area is a carbonate ramp which with "microbial mat-mound and shoal- tidal flat" sedimentary system in Xiaoerblak sedimentary period. Along the Wensu ancient uplift to the basin, it develops inner ramp, middle ramp and outer ramp in turn; Middle-high energy mounds and shoals are distributed in middle ramp. The thickness of mounds and shoals is about 70m-85m, the ratio of mounds and shoals up to 44%-51%, viewed from favorable facies zone, it supports that Xiaoerblak formation has a good exploration potential.

Three element sand control models of river-dominated delta

2018-10-24 00:00:00.0

Delta sand body was one of the most important reservoir types for oil and gas exploration, and the lacustrine delta type was basically a river-dominated delta. To make clear the development mechanism, migration law, distribution characteristics and combination structure of sand body in river-dominated delta not only has significance of science, but also important guiding significance for oil and gas exploration. There are many factors affecting the river-dominated delta sand bodies, and tectonic activities control the type, formation and evolution of the basin, the form of the sedimentary bottom type, the slope and the source of the sediment macroscopically. In the period of relative stability, the sand body of river-dominated delta was mainly controlled by three factors: the power supply of the source (the source), the slope of the sediment (slope) and the position of the lakeshore line (shoreline). The scale of the sand body was controlled by the power supply capacity of the source, it was reflected in grain size, sand body thickness and range; the bottom slope controls the size of the accommodation space, It was manifested in the angle of the front layer and the delta shape; The estuaries of the lakeshore were the main unloading areas of the sediments and the position and the migration amplitude of the shoreline control the position and continuity of the sand body. The combination of three factors and different combinations forms the distribution pattern of delta sand bodies with different characteristics.

Provenance analysis of Wanbao Formation in Longjiang Basin, central Great Xing’an Range, NE China: Constraints from Detrital Zircon Ages and Geochemistry Characteristics

2018-10-24 00:00:00.0

Longjiang basin is one of the newly established Meso-Cenozoic basins in the periphery area of the Songliao basin. Provenance analysis is an important part of basin research. The analysis aimming to clastic sandstone detrital composition, heavy mineral combination, rock geochemistry and zircon U–Pb ages, and related comprehensive research of clastic rocks from Wanbao Formation in Longjiang Basin were carried out in this paper. Analysis results show that the provenance rocks of Wanbao Formation mainly includes basaltic andesite and andesite, rhyolite, quartzite, vein rocks, and a small amount of argillaceous rocks and small amounts of low-medium metamorphic rocks, indicating a relatively complex rock provenance; Geochemical characteristics of sediment materials from Wanbao Formation show that they are enrichment in LREEs and deplete in HREEs, with a right-dipping signature. Meanwhile, they are enrichment in HFEs (e.g., Cs, Th and U), but depletion in Nb, P, and Ti. Detrital zircon show four age peaks, the main peak is 167.5 Ma, the secondary peak ages are 236.4 Ma ,309.1Ma and 309.1Ma., reflecting multiple provenance of sediment rocks in Wanbao Formation. They are mainly come from the Middle Jurassic volcanic rocks, and secondly from the Triassic-Late Devonian magmatic activity products. The primitive materials source of Wanbao Formation featured by both felsic and intermediate volcanic rocks,, which mainly comes from the upper crust. They were formed in continental island arc environment, and some of which with active continental margin features, indicating the characteristics of the coeval regional rock provenance.

The structure of the Permian Middle Guizhou rift trough basin and its control effect on the Zunyi manganese mine（新稿件）

Zhi-Chen LIU — 2018-10-24 00:00:00.0

Permian Zunyi manganese mine is the earliest industrial manganese deposit discovered in Guizhou. It has been found that 1.5 million tons of rhombohechite deposit has been found. It is an important manganese resource base in China. Through the research on the system of the Permian stratigraphic system and the partition of Maokou, proposed in the Mount Emei plume rise, background of the Southern China massif occurred cracking regularity, Guizhou aulacogen basin consists of rift basin Shuicheng Zunyi rift basin, 2 grade II unit, the Zunyi secondary rift basin (II control level) and formed Zunyi manganese metallogenic belt, including Guizhou, Sinpo, Bozhou, Honghuagang, the distribution of a number of famous - large manganese deposit, consists of 3 grade 3 (graben) faulted basin, 2 grade uplift (Horst) and at least 13 VI in faulted basin (graben), 3 third grade rift basin formed respectively control Tongluojing - Deep Creek, turn Dragon Temple - Xie Jiaba, Zhangjiawan is, monk field - five Longxi manganese metallogenic belt. The metallogenic sub zone of Tongluo well deep deep manganese mine is the center of Zunyi secondary rift basin. The manganese mineralization is strong, forming 3 large manganese deposits: Tongluo well, deep stream, and Zhuan long Miao Yongan. The sixth grade fault depression (graben) basin controls the various manganese deposits in the formation area. It is proposed that the Qixia Makou synsedimentary fault is the key to control the formation of manganese ore, and it is the ascending channel of deep manganese containing hydrothermal solution. 14 synsedimentary faults in the study area and the faulted (graben) basins and main deposits formed in the study area have been restored.

Sedimentary facies evolution of Neoproterozoic in Qingbaikou area of Jingxi Depression

2018-10-24 00:00:00.0

The Jingxi Depression is one of the major depressions in the Yanshan area, but the research on the Neoproterozoic strata facies is still insufficient. On the basis of thorough investigation of previous studies, this paper combines the lithologic characteristics and sedimentary structure of the Qingbaikou formation in the Qingbaikou area through field measurements and the identification of thin sections of rock,and uses the method of sequence stratigraphy to study the area,a detailed division of the sedimentary facies of the Qingbaikou Formation in this area has been made and a sedimentary facies model consistent with its sedimentary evolution has been established.Studies have shown that the Xiamaling Formation is a shallow-sea sedimentary system of terrigenous debris,mainly in the deeper continental shelf-like sediments,sandy clastic flow deposits were found for the first time in this area;The Changlongshan Formation is a land-based coastal litter deposition system.Large sets of nearshore and offshore sand bodies are mainly controlled by the reconstruction of waves and coastal currents;The Jingeryu Formation is a typical tidal-carbonate mixed tidal flat,due to relative changes in ancient latitudes,the sedimentary environment is relatively limited to drought and low energy,the lower and upper parts are mainly purple mudstone sediments,and the middle part develops a large set of thick carbonate rocks.The deposition of detrital material from the terrestrial source input of the Xiamaling and Changlongshan Formations was the main transition to the environment of the endogenous clear water carbonate deposits of the Jingeryu Formation,indicating that the tectonic conditions and the paleogeographic environment gradually stabilized.

Carbonate sedimentary microfacies of the Lower Cambrian Xiaoerbulak Formation in Keping area，Tarim Basin

2018-10-24 00:00:00.0

The Xiaoerbulak formation dolomite is a key stratum for exploration and development of the Cambrian under the salt in the Tarim Basin. Based on the macroscopical study of field geologic profiles and the analysis of thin sections under indoor microscopes, refer to Flugel's carbonate ramp common microfacies type division scheme, identify 11 types of microfacies: bioclastic silt-sized dolomite, lamellar argillaceous dolomicrite, lamellar micro-silt-sized dolomite,lamellar silt-sized dolomite, clot - fine crystal dolomite,crustose clot - fine crystal dolomite , algal arenaceous fine crystalline dolomite, foam cotton layer dolomite, micritic arenaceous dolomite, algal cladding arenaceous dolomite, algal laminated dolomite. Combined with the evolution of the lithological microfacies combination sequences and sedimentary facies analysis, Xiaoerbulak formation is considered as ramp sedimentary environment,Carbonate ramp is divided into three kinds of large-phase and its sub-facies:back ramp, shallow ramp and deep ramp , sedimentary facies model is also established.

The Feature and origin of the grooves in the Liwan depression during the early Miocene

2018-10-24 00:00:00.0

The groove and its origin are the research hotspots in sedimentology and paleoceanography in recent years. Based on the high resolution 3D seismic data in Liwan Depression of the northern part of the South China Sea, multi-kilometer scale grooves are identified firstly in the early Miocene of study area. These grooves located in deep water basin away from the shelf slope break, which lies roughly parallel to the strike of northern South China Sea slope during the ealy Miocene, can be subdivided into four sub-zones. They are straight or arched, or ripple-like in shape and its geometry parameters have different characteristics in different sub-zones. In addition, there are large bands of high amplitude anomalies at the bottom of some grooves, which may correspond to coarse grain deposition or rich natural gas. According to its feature, it is inferred that its origin may be related to the bottom current, which influenced by Intermediate Water Circulation basin-widely. The bottom current, which was mainly control by paleo-geomorphy during the early Miocene, eroded the seabed and formed the grooves. This study not only contributes to the exploration of oil and gas in the ultra-deep water area in the northern part of the south China sea, but also provides new evidence for early Miocene paleo-oceanographic research in the south China sea, which is of great practical and theoretical value.

Characteristics and evolution of lithofacies palaeogeography, Jizhong Depression, China

2018-10-24 00:00:00.0

The Jizhong Depression is a Mesozoic-Cenozoic sedimentary Depression that developed on the North China platform. It mainly develops marine carbonate rocks in Cambrian. Based on the outcrop section and drilling strata of the Cambrian, a stratigraphic contrast framework for outcrop and drilling is established. The studies of single well facies, seismic facies, and correlation profile facies indicate that Cambrian tectonic movements in the Jizhong depression are small, and the difference of strata thickness in each area is small, indicating that they are in a quasi-plainization palaeogeographic pattern. Through the outcrop section measurements, core observations and sample analysis,the lithology content was statistically analyzed. Based on this, the three types of sedimentary facies were identified, they are platform facies, gentle slope facies, and shelf facies. The platform facies can be divided into five types of subfacies, including tidal flat, restricted platform, open platform, oolitic bank, and gravel bank. From the tidal flat subfacies identified on mudstone flat submicrofacies, dolostone flat submicrofacies, limestone flat submicrofacies, etc. Based on the analysis of these types of lithofacies, the Cambrian sedimentary model of the Jizhong depression was established, and 9 sets of lithofacies paleogeographic maps were compiled. The seawater in the Early Fujunshan Age invaded from the northeast, and formed a restricted sea environment in Beijing. At the end of the Fujunshan Age, there was exposure, resulting in an unconformity. Subsequently, in Mantou Age and Maozhuang Age, tidal flat sediments were developed in the entire depression, and the lithology were purple-red mudstones and mud-silt-sized crystalline dolomites. At the beginning of the Xuzhuang Age, seawater became deeper, and the sea level reached its highest level during the Zhangxia Age. This period was dominated by Oolitic bank. In the early Gushan Age, the tidal flat reappeared, and coexisted with bamboo leaf-shaped gravel bank.

Lithofacies Characteristics and Sedimentary Environment of Fine-grained Sedimentary Rock in Dongying Sag

Shu-Jun LIU — 2018-10-24 00:00:00.0

Lithofacies is the basis of the study of fine-grained sedimentary rocks. The exhaustive study of lithofacies is beneficial to the further study of sedimentation and reservoir forming process，and then contributes to the exploration and development of this kind of oil and gas reservoir. Fine-grained sedimentary rocks are well developed in Dongying Sag. By means of core observation, X-ray diffraction of whole rock and analysis methods, we know that carbonate minerals, clay minerals and silty minerals are the main mineral components of fine-grained sedimentary rocks in Donying Sag. According to mineral content and sedimentary structure mainly, the fine-grained sedimentary rocks of the lower submember of Es3 and the upper submember of Es4 in Dongying Sag can be divided into 9 kinds of lithofacies. Among them, the laminar mixed fine-grained sedimentary rocks, the massive mixed fine-grained sedimentary rocks, the laminar limestone, the laminar silty limestone and the laminar argillaceous siltstone are relatively developed.According to the vertical variation of the characteristic element ratio including Ca/ Mg, Na /Al, Fe/ Mn, Sr / Ba, V/(V+Ni) and the element content including Ti and Al , it can be seen that there were obvious evolution stages of fine-grained sedimentary rocks in Dongying Sag in paleoclimate, paleowater depth, paleosalinity, oxidative or reductive ptoperties of the water, and the content of terrigenous clastics input. Climate change has an important impact on other environmental conditions.What\s more, differdnt lithofacies and their combinations with distinguished characteristics.The paleoclimate changed from dry and cold to warm and humid in the upper submember of Es4 member, and developed from warm and humid to relatively cold and humid to warm and humid to relatively hot and humid in the lower submember of Es3 member. Warm and humid climate together with the increase of terrigenous clastics contributed to deposit large amounts of laminar mixed fine-grained sedimentary rocks. However, the laminar silty limestone tended to deposit in relatively cold and dry climate as well as less terrigenous clastics input.

A Preliminary Study of the Tidal disasters in The Qiantang River estuary in the Ming dynasty and its Environmental Background

Shen WANG — 2018-10-24 00:00:00.0

The magnificent and thunderous bore of the Qiantang Estuary has been famous in China since the ancient time and is among the world’s wonders. Plains on both sides of the Qiantang Estuary has a long history of development, rich economy and dense population. However, the frequent occurrence of tidal disasters in the historical period has a great influence on local natural geography, economic society and custom culture. Based on the historical documents, this paper systematically analyzes the tidal bore records of Qiantang estuary in Ming dynasty and analyzes the spatial and temporal distribution characteristics of tidal disasters. The conclusion is as follows: Firstly, in terms of the number of tidal disasters in Qiantang estuary, the north shore is more than south bank, and the upstream of Haimen is basically the same as that of its downstream, but all less than Hangzhou Bay. Secondly, The site of the tidal disaster always change between the south bank and the north bank, each has its steady phrase and outbreak period. Thirdly , the frequency of tidal disasters gradually decreases in the Ming dynasty, and there is more steady phrase of tidal disasters after the middle of the Ming dynasty. In addition, the paper also discusses the factors that influence the spatial and temporal distribution of tidal disasters according to the natural environment of the time, like historical climate, and underwater topography etc.

Sedimentary Paleogeographic Evolution in Paleogene Coal-Bearing Rock Series in Huangxian Basin

2018-10-24 00:00:00.0

It is difficult to reconstructed Palaeogeographic of Lacustrine facies of Huangxian Fault Basin, due to the varied material, sedimentary facies changed fast and transgression, so far none of people map the paleogeography of the mainral deposites. Based on the multidisciplinary research methods of sedimentology, stratigraphy, coal geology, this paper mainly studied the depositional environments of Paleogene in Huangxian Basin Lijiaya Formation. Based on the study of sequence stratigraphy of formers, single factor analysis and multifactor comprehensive mapping method are adopted in reconstracting lithofacies palaeogeography of different system tracts. In sequenceⅠ, the lowstand systems tract is mainly braided fluvial delta facies, lake extension system is mainly fan delta facies and lacustrine facies, highstand system tract is mainly fan delta facies. In sequenceⅡ, the lowstand systems tract is mainly braided fluvial delta facies, lake extension system tract is mainly fan delta facies and lacustrine facies, hightstand system tract is mainly lacustrine facies. It revealed the formation and evolution of Huangxian Basin Lijiaya Formation. In sequenceⅠ, the basin formed during the lowstand system, expanded during the lake extension system and shrank during the highstand system. In sequenceⅡ, the basin slowly expanded in lowstand system again, expanded in lake extension system and shrank in hightstand system. The tectonics in southeastern edge of the basin is the driving machanisms of the basin evolution and formation. The depositional environments formed resulting in the transgression, regression and tectonics. This is also the main factor controlling the development of the oil shale and coal.

The depositions of deep-water contour currents channel in the lower part of Kelimoli Formation in Middle Ordovician of Zhuozishan area, western of Ordos basin

2018-10-24 00:00:00.0

Dark gray thin-bedded limestones intercalated with very thin-bedded grayish black shales as well as the depositions of contour currents are very developed in the lower part of Kelimoli Formation in Middle Ordovician of Zhuozishan area of western Ordos basin. And the Shixiagu section is an ideal one for studying sedimentary processes of contour currents because of its perfect preservation of thin-bedded limestones with slight lenticular shapes which have little post-depositional effects. Based on the detail fieldwork, we further ascertain deep-water slope depositional environments and contour current depositions from sedimentary structures, characteristic and association of sedimentary rocks. Apart from these, this article focus on the depositional mechanisms and hydrodynamics of thin-bedded limestone from its characteristics of fillings and shapes. The results showing that: ① the differential textures and slight cycles are common in single thin-bedded limestone and between them in the section respectively; ② limestones are mainly developed grain-size (crystal grain of calcites) related sedimentary structures which include bigradational grading, banded structure and parallel- uniform-parallel succession; ③ multi limestone beds could be formed lenticular shape with symmetric pinch in single beds and the hole lens are pinching out in both shale and high topography; ④ Thinning-upward packages and its amalgamated beds are developed in the study section; ⑤ comparatively thin limestone bed (thin bed) commonly consists of micrites with continuous small-scale lenses and incomplete uniform-parallel succession; ⑥ comparatively thick limestone bed (thinly medium bed) commonly consists of microcrystalline limestone with long lenses and complete parallel-uniform-parallel succession. Using the previous research, we propose for the depositional environment of thin-bedded limestones in the lower part of Kelimoli Formation is deep-water contour currents channel, and their depositional mechanisms can be divided into 3 stages which include clear water deposition of calcites before contour currents action, re-deposition during contour currents action and the mixing water deposition of mud.