Abstract
The Songliao Basin (SLB) is a large terrestrial petroliferous basin located in northeastern China. The Nenjiang Formation represents excellent hydrocarbon source rocks for the Daqing oil field. Previous studies have indicated that the oil shale intervals from the first (K2n1) and second (K2n2) members of the Nenjiang Formation were formed in different depositional settings. In this study, we provide a new high-resolution (1 m interval) record from SK-1s core and compile three sets of published datasets from two drilling holes (Zk3389 and LY-1) and a composite outcrop section. According to the total organic carbon (TOC) chemostratigraphy, we have divided three variation cycles spanning from K2n1 to K2n2 and detected three potential oil shale intervals in the Nenjiang Formation. Combined with the productivity, salinity, and oxygenation proxies, we discuss the paleolimnological environmental changes during deposition of the Nenjiang Formation. Our new and compiled records support the model that excellent preservation conditions were associated with the formation of organic-rich sediments in the K2n1, while the productivity was the major controlling factor for organic matter enrichment in the K2n2.
Highlights
The continental basin is an important carbon reservoir, playing a vital role in modulating the carbon cycle at multiple time scales [1,2]
The Nenjiang Formation have been conducted comprehensive research on geology, sedimentology, geochemistry, paleontology, and paleoclimate, but there is a lack of highresolution geological records and spatial correlation research, understanding of the mechanism of oil shale formation in Nenjiang Formation is still insufficient
We provided a new high-resolution total organic carbon (TOC) record from SK-1s core and compiled another three records from two drilling holes and a composite outcrop section to discuss the organic carbon burial mechanisms in the Nenjiang Formation
Summary
The continental basin is an important carbon reservoir, playing a vital role in modulating the carbon cycle at multiple time scales [1,2]. These geological archives provide invaluable information associated with the regional continental climate changes and the massive formation of lacustrine petroleum source rocks within the Cretaceous greenhouse world [1,3,4,5,6,7,8,9,10]. The Qingshankou and Nenjiang Formations represent organic-rich sediments mainly deposited under a warm and humid climate background and provide a solid materials foundation for oil and gas exploration in Songliao Basin [4]. Previous studies widely discussed sedimentary environments during the deposition of the organic-rich intervals and simultaneously established a series of sedimentary models for interpretation of the oil shale development in the Qingshankou and Nenjiang Formations [1,4,8,12,13,14,15,16,17,18,19]. Prior studies have shown that two large marine transgressions occurred in the lower Qingshankou
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