摘要:
早寒武世下扬子陆块与华夏陆块均向北漂移并拼合成南方古陆,发生褶皱隆升,但对下扬子陆块北部(现今下扬子地区)影响不大,总体处于浅海台地相。因为早寒武世早期受上升流等因素的影响,下扬子地区早寒武世有机质来源丰富,在缺氧还原的沉积环境形成了优质烃源岩。下扬子地区下寒武统烃源岩呈NE向展布,受"一台两盆"构造格局影响存在2个沉积中心:一个在安吉—休宁深水陆棚区,厚度100~300 m;另一个在泰州—盐城深水陆棚区,厚度50~150 m。海侵主要来自东北方向,烃源岩向东北方向减薄。从陆域烃源岩厚度分布趋势看,南黄海盆地烃源岩厚度应在50~200 m之间。中生代南方古陆与华北陆块拼合形成中国大陆时,对下扬子古生代形成的油气藏产生了严重的破坏。台缘相烃源岩厚度大、埋深大、生烃早,生成的油气藏在中生代南北陆拼贴期遭到破坏,是现今古油藏的烃源供给者。我们推测南黄海下寒武统为台地相沉积,埋藏相对较浅,热演化程度相对较低,大部分烃源岩可能在燕山中—晚期发生过二次生烃,有利于常规油气藏的保存。
Abstract:
The Lower Yangtze block and the Cathaysian block drifted towards the north during Early Cambrian and then the paleo-continent of South China(OCSC) formed. The Northern Yangtze block (or the Lower Yangtze area), however, remained unaffected as a shallow marine carbonate platform. It was rich in organic matter in Early Cambrian due to some factors, such as the prevailing upwelling current. As the result, a set of hydrocarbon source rocks was formed in an anoxic marine environment. There were two Early Cambrian depocenters for hydrocarbon source rocks in the region along the north-east direction, one in Anji-Xiuning deep-water shelf area, where the source rocks were about 100~300 m in thickness; and another one in Taizhou-Yancheng deep-water shelf area, with a thickness within 50~150 m. Transgression was in NE direction together with the thinning out of the source rocks. It was estimated that the source rocks were around 50-200m in thickness in the South Yellow Sea. Most of the Paleozoic oil reservoir had been probably damaged when OCSC collided with the North China paleo-land in Mesozoic. The Auxi Formation was deposited in the slope area around the platform, which were favorable for hydrocarbon generation, but the oil and gas reservoirs were destroyed in Mesozoic. The South Yellow Sea was then deposited with shallow marine carbonate facies, which were not good enough for hydrocarbon generation, but survived from the collision. It could make contribution to the formation of reservoirs in later stage. We speculated that the Lower Cambrian hydrocarbon source rocks in the South yellow sea, which were shallowly buried during the continental margin stage to the collision stage, could experience the second hydrocarbon-generation in the middle-late Yan Shan movement, and very likely formed a substantial oil and gas reservoirs.
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