摘要:
鄂尔多斯盆地西南部陇东地区延长组长8段和长7段分别发现以Aratisporites- Punctatisporites和Asseretospora-Walchiites为代表的孢粉组合,时代分别为中三叠世晚期与晚三叠世早期。通过现生主要植物类型生态环境分布规律的讨论和孢粉植物群已知亲缘关系类型的地层分布特征研究,推测陇东地区中晚三叠世气候温暖潮湿,雨量充沛,植被茂盛。孢粉植物群反映的古气候为温带—亚热带暖湿或湿热气候。孢粉植物群特征与孢粉化石分异度曲线都表明,本地区长8—长7段沉积时期为持续温暖潮湿的适宜期, 与湖泊发展的长8期大规模湖进和长7期的最大湖泛相一致。孢粉植物群具有北方植物群的明显特征,由于本地区当时濒临大型湖泊,而且长8—长7段沉积时期正处于湖泊扩张的鼎盛期,因此显示出更为湿润的古环境特征。正因为长期稳定温暖潮湿气候和广大的深水湖泊环境为水生藻类的大规模发育创造了条件,从而为本地区长7期优质烃源岩的形成提供了母质来源。
Abstract:
A great number of sporopollen fossils have been discovered in Chang 8 and Chang 7 intervals of Yanchang Formation from drilling cores of Longdong area in the southwestern Ordos Basin, and they were named as AratisporitesPunctatisporites assemblage and AsseretosporaWalchiites assemblage,respectively. Their characteristics are similar to the sporopollen assemblages of Tongchuan Formation and Yanchang Formation discovered in the southeast of the basin, and the geologic times of the assemblages are Ladinian of the late Middle Triassic and Carnian of the early Late Triassic. Based on the environmental distribution of main plant types at present and the analysis of the content of types to recognize the relationship between palynological flora and the characteristics of stratagraphic distribution, we can infer that the climate was warm and moist then, rainfall was plentiful, and the vegetation was luxuriant during Middle Triassic and Late Triassic in Longdong area. The paleoclimate reflected by palynological flora was warmwet or hotwet in temperate to subtropical. The ecological types of palynological flora and the diversity curves of palynoflora indicate that the Chang 8 and Chang 7 phases were suitable period of continuously warm and humid in the area, and the extensive lacustrine transgression occurred in Chang 8 phrase during the development of lake as well as sustaining maximum flooding in Chang 7 phase. It was semihumidity temperate to subtropical climate during Middle Triassic and Late Triassic in northern China. The palynological flora discovered from the Chang 8 and Chang 7 intervals in Longdong area is obviously characteristic of the northern China flora. However, because the area was close to the large-scale lake at that time, and the Chang 7 and Chang 8 phases were the great prosperous period that lake was being expanded, so the characteristics of moister paleoenvironment was indicated. It was just because of longterm stable warm and wet climate and the extended deep lake environment that created conditions for largescale growth of hydrophilous alga, consequently they provided organic matter for the highquality source rocks of Chang 7 section in the area.
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