A biomarker study of depositional paleoenvironments and source inputs for the massive formation of Upper Cretaceous lacustrine source rocks in the Songliao Basin, China

https://doi.org/10.1016/j.palaeo.2012.12.007Get rights and content

Abstract

The abundance and composition of total organic carbon, aliphatic and aromatic hydrocarbons including biomarkers, and the δ13C composition of total organic matter and individual compounds in core samples of the Nenjiang Formation from the SK-1 borehole of the Songliao Basin provide information on the paleoenvironmental conditions of lacustrine sediments formed during the Upper Cretaceous. The distribution of n-alkanes, and their δ13C composition, and 4-methylsteranes and dinosteranes in the first member of the Nenjiang Formation (K2n1) indicate that the organic matter largely originated from algal organisms and is dominated by types I and II kerogen. The occurrence of gammacerane, aryl isoprenoids isorenieratane and low pristane/phytane and diasterane/sterane ratios further suggest a salinity stratified water column associated with anoxic bottom waters, as well as possible photic zone oxygen depletion conditions during major source rock deposition of the K2n1. The organic geochemical data also indicate significantly different depositional environments for the second member of the Nenjiang Formation (K2n2) sediments, which are interpreted to have been deposited under a uniform salinity (non-stratified) oxic water column. Consequently, although the organic matter in the K2n2 sediments was largely derived from algal and bacterial sources, the kerogen types are dominantly IIb and III due to the oxidative degradation of organic matter, combined with a gradual increase in land–plant input. Furthermore, the occurrence and shift of two saw-toothed distribution patterns of the δ13C composition of C29 to C33 n-alkanes, with “W” and “M” patterns being isotopically heavy odd- and even-numbered alkanes, respectively, is suggestive of organic input shift or an unknown mechanism of carbon uptake or isotopic fractionation. In particular, the heavy even carbon numbered high molecular weight n-alkanes is rare and needs further investigation.

Highlights

► The occurrences of biomarker in the Cretaceous lacustrine sediments are investigated. ► The source rocks were formed under salinity and anoxic stratified water column. ► The type and quality of OM are largely controlled by palaeodepositional conditions. ► An unusual heavier δ13C composition pattern of n-C30 and n-C32 alkanes is identified.

Section snippets

Background

The Songliao Basin in China is the largest continental petroliferous basin in the World and contains a continuous series of lacustrine sediments formed during the Upper Cretaceous. This succession of lacustrine sediments preserves abundant information regarding the paleoclimate and depositional environments, which are very important for the understanding of the regional continental climate and the massive formation of lacustrine petroleum-prone source rocks within the Cretaceous greenhouse

Sample collection and experimental procedure

The Songliao Basin is located in north-eastern China and covers a vast area of 260,000 km2, with a total thickness of up to 10 km of Cretaceous lacustrine sediments (Feng et al., 2007) (Fig. 1). The SK-1 boreholes are situated on the Qijia–Gulong Depression, which was one of the major depositional centers in the basin. During the Upper Cretaceous, two major sedimentary settings of organic rich source rocks developed in the basin associated with the K2q1 + 2 members of the Qingshankou Formation and

Abundance and types of organic matter

The TOC content of samples from K2n1 (member 1) and the lower part of K2n2 (member 2) of the Nenjiang Formation from the SK-1 borehole are tabulated in Table 1 and depicted in Fig. 2. According to the depth variation of TOC, the K2n1 profile can be divided into three sections. Section I from 1116 to 1125 m has a high TOC content (4.1–8.0%). The section from 1099 to 1116 m is assigned as section II and has the lowest TOC of the whole profile (0.24–0.84%). Section III from 1016 to 1099 m is an

Conclusions

The occurrence and distribution of hydrocarbons, and the carbon isotopic composition of n-alkanes and isoprenoids, for lacustrine samples from the Nenjiang Formation in the SK-1 borehole mainly reflect the variation in source input of organic matter and the depositional conditions. The organic matter in the major source rocks of the K2n1 member were mainly derived from algal and bacterially-sourced aquatic organism inputs, while a salinity stratified water column associated with strong anoxic

Acknowledgment

This research was supported by the State “973” Project (grant no. 2006CB701404) and the NSFC (grant no. 40973033) and the earmarked fund of the State Key Laboratory of Organic Geochemistry (grant no. SKLOG2008A01). Managing guest editor, Prof. Chengshan Wang, an anonymous reviewer and Dr. P. Greenwood (AGSO) are thanked for their supportive revising suggestions.

References (47)

  • A. Riboulleau et al.

    Environmental change during the Early Cretaceous in the Purbeck-type Durlston Bay section (Dorset, Southern England): a biomarker approach

    Organic Geochemistry

    (2007)
  • L. Schwark et al.

    Geochemical characterization of Malm Zeta laminated carbonates from the Franconian Alb, SW-Germany (II)

    Organic Geochemistry

    (1998)
  • H.L. ten Haven et al.

    Organic geochemical studies of a Messinian evaporitic basin, northern Apennines (Italy). I: hydrocarbon biological markers for a hypersaline environment

    Geochimica et Cosmochimica Acta

    (1985)
  • H.M.E. Van Kaam-Peters et al.

    A molecular and carbon isotope biogeochemical study of biomarkers and kerogen pyrolysates of the Kimmeridge Clay Facies: palaeoenvironmental implications

    Organic Geochemistry

    (1997)
  • M. Wagreich et al.

    Causes of oxic–anoxic changes in Cretaceous marine environments and their implications for Earth systems — an introduction

    Sedimentary Geology

    (2011)
  • X. Wan et al.

    Late Cretaceous stratigraphy, Songliao Basin, NE China: SK1 Cores

    Palaeogeography, Palaeoclimatology, Palaeoecology

    (2013)
  • L. Wang et al.

    Paleosalinity significance of occurrence and distribution of methyltrimethyltridecyl chromans in the Upper Cretaceous Nenjiang Formation, Songliao Basin, China

    Organic Geochemistry

    (2011)
  • S. Xie et al.

    Molecular and isotopic stratigraphy in an ombrotrophic mire for paleoclimate reconstruction

    Geochimica et Cosmochimica Acta

    (2004)
  • Y. Zhou et al.

    Biosynthetic origin of the saw-toothed profile in d13C and d2Y of n-alkanes and systematic isotopic differences between n-, iso- and anteiso-alkanes in leaf waxes of land plants

    Phytochemistry

    (2010)
  • M.A. Arthur et al.

    Marine black shales: depositional mechanisms and environments of ancient deposits

    Annual Review of Earth and Planetary Sciences

    (1994)
  • M.A. Arthur et al.

    Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary

    Nature

    (1988)
  • M. Blumer et al.

    Hydrocarbons of marine phytoplankton

    Marine Biology

    (1971)
  • C.P. Chamberlain et al.

    Stable isotopic evidence for climate and basin evolution of the Late Cretaceous Songliao Basin, China

    Palaeogeography, Palaeoclimatology, Palaeoecology

    (2012)

    • Cited by (0)

    View full text
    Copyright © 2012 Elsevier B.V. All rights reserved.