Abstract: The Haojiagou section， located in the southern margin of the Junggar Basin， is of great significance in studying the Triassic-Jurassic Boundary events. The lower part of the section(bed 4 to bed 44)belongs to the Haojiagou Formation that is assigned to the Upper Triassic， and the interval of bed 45 to bed 102 is the Badaowan Formation that is considered to be the Lower Jurassic. The palynological data show that the gymnosperm pollen grains dominate all the Haojiagou Formation， and fern spores have higher proportion than the gymnosperm pollen grains in the lower member of the Badaowan Formation. Taking into account that most ferns adapt to warm and humid climatic environment， we believe that it was warmer and more humid in the Early Jurassic than in the Late Triassic. Organic carbon isotope data from the Haojiagou section demonstrate that δ¹³C curve has an obvious negative excursion(less than -24.5‰)in the interval of bed 44 to bed 68， while the underlying and overlying strata have similar δ¹³C values(greater than -24.5‰). Analyses of charcoal samples show a similar negative excursion in bed 44 to bed 59. According to the results of ecological research， sedimentary organic matter has lighter carbon isotope values when the climate is warm and humid. Therefore， it is concluded that at the beginning of the Early Jurassic the climate was warmer and more humid than before and afterward.

Key words: Junggar Basin, Haojiagou section, Late Triassic, Early Jurassic, palaeoclimatic change

摘要： 准噶尔盆地南缘的郝家沟剖面三叠系—侏罗系连续发育，是研究三叠系—侏罗系界线及相关地质问题的重要剖面。孢粉分析发现，上三叠统郝家沟组以气候适应范围较宽的裸子植物花粉占优势，而在下侏罗统八道湾组下部主要适应温暖湿润气候的蕨类植物孢子含量明显增高，在组合中常占据优势地位，说明研究区早侏罗世气候比晚三叠世更为潮湿。沉积岩有机碳同位素分析结果显示，在剖面八道湾组下部的δ¹³C值总体低于-24.5‰，形成两次明显的负向偏移，同时采集的丝炭样品的分析结果也证明δ¹³C在八道湾组下部具有明显负向偏移。根据现代湖泊沉积有机质碳同位素与气候关系的研究成果，沉积有机质稳定碳同位素负偏是气候温暖潮湿化的反应，支持了孢粉研究的结果。以上表明，研究区侏罗纪之初的气候比晚三叠世更加炎热潮湿。

关键词: 准噶尔盆地, 郝家沟剖面, 晚三叠世, 早侏罗世, 古气候变化

CLC Number: 

• Q913.84