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    东濮凹陷北部古近系沙河街组特征

    Features of the Paleogene Shahejie Formation in the northern Dongpu Sag

    • 摘要: 提要:从古生物、岩石、测井等方面综合探讨了东濮凹陷北部古近系沙河街组的特征及其划分与对比。沙四下亚段和沙二段以红色砂泥岩为主,沙四上、下亚段之间为一假整合面,沙二段底部存在一较大的沉积间断面;沙四上亚段、沙三段和沙一段为灰色砂泥(页)岩夹4套盐岩,其中,沙一段和沙三段中的稳定灰质泥页岩是东濮凹陷较好的区域地层对比标志层。沙四下亚段化石稀少;沙四上亚段地方性介形类开始发育,为Cyprinotus altilis组合;沙三段以介形类Huabeinia和Candona的大量出现为特征,介形类为Huabeinia chinensis组合、沟鞭藻类为Bohaidina-Parabohaidina组合;沙二段以轮藻的空前繁盛为特征,轮藻为Charites producta组合、介形类为Cyprinotus xiaozhuangensis组合;沙一段以腹足类极其丰富为特征,腹足类为Valvata (Cincinna) rehetaiensis组合、介形类为Phacocypris huiminensis组合。前人对东濮凹陷北部古近系沙河街组各段的划分所依据的标准相同,但在确定具体界线时分歧较大,尤其是沙三段与沙四段的分界线。虽然前人均是以Cyprinotus altilis组合的上限和Huabeinia属顶峰带的下限为依据进行划分的,但因以古生物为标准划分地层的精度有限,加之当时钻井地质资料较少和断层错综复杂等,致使同一研究者在东濮凹陷的不同地区所划分的界线也不统一。本文研究指出通过层序地层学及沉积相变规律等沉积学问题的详细研究是解决该问题的关键。

       

      Abstract: Abstract:Based on paleontology, petrology and well-logging, the authors have studied the stratigraphic features, division and correlation of the Paleogene Shahejie Formation in northern Dongpu Sag. Member 2 and lower Submember of Member 4 of Shahejie Formation are mainly composed of a set of red sandstones and mudstones. There is an unconformity surface between the lower Submember and the upper Submember of Member 4 of Shahejie Formation. There exists a hiatus at the bottom of Member 2 of Shahejie Formation. Member 1, Member 3 and upper Submember of Member 4 of Shahejie Formation are mainly composed of a set of gray sandstones, mudstones and shales with four sets of salt rocks. The stable calcareous mudstones and shales of Member 1 and Member 3 of Shahejie Formation constitute fairly ideal key beds for regional stratigraphic correlation in the Dongpu Sag. Fossils are rare in the lower Submember of Member 4 of Shahejie Formation. The local ostracodes, called Cyprinotus altilis assemblage, began to develop in Member 4 of Shahejie Formation. Member 3 of Shahejie Formation is characterized by very flourishing ostracodes, such as Huabeinia and Candona, called Huabeinia chinensis assemblage. The dinoflagellates of Member 3 of Shahejie Formation are called Bohaidina-Parabohaidina assemblage. Member 2 of Shahejie Formation is characterized by the most prosperous stonewort called Charites producta assemblage. The ostracodes of Member 2 of Shahejie Formation are called Cyprinotus xiaozhuangensis assemblage. Member 1 of Shahejie Formation is characterized by the most prosperous gasteropods called Valvata (Cincinna) rehetaiensis assemblage. The ostracodes of Member 1 of Shahejie Formation are called Phacocypris huiminensis assemblage. The standards adopted by previous researchers were the same as those in dividing each Member of Shahejie Formation in northern Dongpu Sag. However, there existed remarkable differences in determining the specific boundary. What is more, the previous researchers adopted the standards of extinction of Cyprinotus altilis and the lower boundary of Huabeinia acme-zone in dividing the boundary of Member 3 and Member 4 of Shahejie Formation. However, because of the limited accuracy of palaeontologic standards in dividing the strata, the lack of geological data from wells at that time and the existence of complex faults in the Dongpu Sag, the boundaries of different areas defined by the same researcher are different. It is pointed out in this paper that strengthening researches on sedimentology in such aspects as the sequence stratigraphy and variation regularity of sedimentary facies constitute the key to resolving the problems of stratigraphic division and correlation in the Dongpu Sag.

       

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