Journal
INTERNATIONAL JOURNAL OF EARTH SCIENCES
Volume 102, Issue 6, Pages 1717-1734Publisher
SPRINGER
DOI: 10.1007/s00531-013-0903-7
Keywords
Songliao Basin; Oil shale; Biomarker; Paleo-lake environment; Climate and tectonics
Categories
Funding
- Basic Outlay of Scientific Research Work from the Ministry of Science and Technology of China [J1220]
- National Natural Science Foundation of China [40972076]
- Austrian Exchange Service (OAD)
- Austrian Science Fund (FWF) [J1220] Funding Source: Austrian Science Fund (FWF)
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Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C-14-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high beta-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K(2)qn(1)) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract-TST, highstand system tract-HST, and regressive system tract-RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST.
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