摘要： 准噶尔盆地南缘白垩纪—新近纪发育大型陆相浅水湖盆,干湿与冷暖气候频繁交替,形成了多套色彩斑斓的“五彩”地层,如灰色、灰绿色、灰白色、酱红色、红褐色、砖红色、紫红色、土黄色等。研究表明: 地层颜色具有很好的沉积环境指示意义,如颜色指标L^*(黑白),a^*(红绿)以及b^*(蓝黄)可以明显区分不同的水下与水上沉积环境(如水上河流—三角洲相、泛滥平原、山麓—冲积扇相等,水下半深湖相、滨浅湖相等);地层颜色演化序列可以很好地指示白垩纪—新近纪古气候的演化过程。红色沉积物既可以形成于干旱炎热的陆上氧化环境,也可以形成于相对还原的水下环境: “陆上红”如东沟组砖红色砂泥岩、紫泥泉子组紫红色泥岩、沙湾组褐红色—土红色泥岩等,40>L^*>52,8>a^*>18,12>b^*>22;“水下红”以呼图壁河组酱红色块状泥岩为特征,35>L^*>45,2.5>a^*>4.5,5>b^*>9。早白垩世准噶尔盆地相对温暖湿润,湖泊广泛分布,颜色指标L^*(黑白)最低值接近15,a^*值介于-5~5之间,指示深灰色—灰黑色泥岩形成于还原环境。晚白垩世地层颜色指标中a^*达到了最高峰(15~25),表明准噶尔盆地气候开始出现干旱炎热趋势;古近纪始新世—渐新世,a^*与b^*值同步变化,出现了明显的负漂趋势(7~15),表明气候逐渐变冷;新近纪a^*值出现新低(5~9),而L^*值也接近70,表明气候持续变冷。综上所述,白垩纪末期以来,准噶尔盆地受全球气候变冷和青藏高原隆升共同影响,干旱化程度不断加强,地层颜色比较完整地保留和记录了古环境与古气候的发展演化过程。因此,系统的颜色测量和分析可以为恢复与重建中新生代沉积环境与古气候演化提供重要依据,对于探究新生代以来全球气候变化规律也具有重要意义。

关键词: 准噶尔盆地, 中生代, 新生代, 颜色指标, 古环境, 古气候

Abstract: The southern margin of the Junggar Basin in the Cretaceous-Neogene developed large continental shallow￣water lacustrine basins with frequent alternation of dry and wet,cold and warm climate,forming a series of “multicolor” strata,such as gray,grey-green,grey-white,maroon red,red-brown,brick-red,purple-red,and earthy yellow. The study shows that the color of the strata has a good indicator of sedimentary environment. For example,the color index L^*(black and white),a^*(red and green)and b^*(blue and yellow)can clearly distinguish the different subaquatic(semi-deep lacustrine facies,shore-shallow lacustrine facies)or subaerial(river-delta facies,floodplain facies,alluvial fan facies)sedimentary environments. Stratigraphic color evolution sequence can indicate the evolution of Cretaceous-Neogene palaeoclimate. The red sediments can be formed in both the dry and hot land oxidation environment and the relatively reduced underwater environment: “subaerial red”,such as brick red sandy mudstone of the Donggou Formation,purple red mudstone of the Ziniquanzi Formation,and maroon to earth red mudstone of the Shawan Formation,40>L^*>52,8>a^*>18,12>b^*>22;“subaquatic red” is characterized by the thick red blocky mudstone of the Hutubihe Formation,35>L^*>45,2.5>a^*>4.5,5>b^*>9. In the Early Cretaceous,the Junggar Basin was relatively warm and humid with wide distribution of lakes. The minimum value of the color index L^*(black and white)was close to 15,and the value of a^* was between -5 and 5,indicating that dark gray to gray dark mudstone was formed in a relatively reducting environment. In the Late Cretaceous,the color index a^* reached the highest peak(15-25),indicating that the climate of the Junggar Basin began to show a trend of drought and heat. During the Eocene to Oligocene,the values of a^* and b^* changed synchronously,and there was an obvious trend of negative drift (7-15),and the climate gradually cooled. In the Neogene,the color index a^* was relatively low(5-9),however,the L^* value was close to 70,indicating that the climate continued to be cool. The research shows that since the end of Cretaceous,the drought-stricken Junggar Basin has been increasingly affected by the global climate cooling and the uplift of Qinghai-Tibet Plateau. The stratigraphic color recorded evolution of paleoenvironment and paleoclimate. Systematic color measurement and analysis can provide an important basis for reconstruction of Mesozoic-Cenozoic sedimentary environment and paleoclimate evolution. It also has a great significance for exploration of global climate change since the Cenozoic.

Key words: Junggar Basin, Mesozoic, Cenozoic, color index, palaeoenvironment, palaeoclimate

中图分类号: 

• P588.2

• P46