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@PHDTHESIS{Wu:981477,
author = {Wu, Zhongrui},
othercontributors = {Littke, Ralf and Sachsenhofer, Reinhard},
title = {{G}eochemistry and organic petrology of lacustrine
petroleum source rocks: implications for paleo-depositional
environment and organic matter accumulation},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2024-03065},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2024},
abstract = {Lacustrine organic matter (OM)-rich shale has historically
served as an important source and reservoir rocks for
conventional and unconventional hydrocarbon production. This
thesis is dedicated to studying the characteristics of
lacustrine petroleum source rocks in China and Europe,
placing particular emphasis on aspects such as hydrocarbon
generation potential, depositional environments, the origin
of OM, paleoclimatic conditions, and mechanisms of OM
accumulation. Chapter 1 contains the objectives of the
thesis, geological information on the three study areas, and
an overview on each of the three main chapters. In Chapter
2, data on core samples from the CY1 well in the Yuqia Sag,
northern Qaidam Basin, are presented and discussed; these
samples were subjected to analysis, including organic
petrography, inorganic geochemistry, as well as bulk and
molecular organic geochemistry. The objective was to
evaluate the thermal maturity of the rocks, assess
hydrocarbon generation potential, reconstruct the
paleoclimate, and understand the depositional environments
during the deposition of the seventh member of the Dameigou
Formation (J2d7). Moreover, the connection between these
factors and OM accumulation was explored. The dominant
source of OM is lake plankton, including halophilic algae
and cyanobacteria. Three distinct source rock units were
identified, exhibiting varying total organic carbon (TOC)
contents. The lower unit was deposited in an oxic freshwater
column under warm, humid climatic conditions and intense
weathering along the lake margin. The OM in this unit is
inferred to originate primarily from terrestrial higher
plants. In contrast, overlying units 2 and 3 were deposited
in sub-oxic to oxic freshwater and anoxic saline
environments, respectively. The deposition of units 2 and 3
reflects progressive aridification in the hinterland,
evidenced by the decreasing chemical index of alteration
(CIA) values. Unit 2's OM was sourced from a combination of
terrestrial higher plants and algal biomass. Conversely,
unit 3 shows a decrease in terrigenous OM content. The
primary source of OM in unit 3 was lake plankton, including
halophilic algae and cyanobacteria. In Chapter 3, bulk and
molecular organic geochemistry alongside major and trace
element data for the first member of the Qingshankou
Formation (K2qn1) in the Songliao Basin are presented,
utilizing 38 core samples. The primary objectives of the
study are to unravel the depositional environments during
the K2qn1 sedimentation and elucidate the key factors
influencing the mechanisms of OM accumulation. All studied
rocks are thermally oil-mature. Within the examined well,
two distinct types of lacustrine source rocks (units 1 and
2) are identified, with unit I further featuring two OM-rich
layers. Essentially, the older unit 1 is characterized by
lower TOC content and the younger unit 2 is characterized by
higher TOC content. Additionally, thin marine transgressive
layers of approximately 1–2 meters were detected within
unit 1. Unit 1 is marked by the lowest TS contents,
averaging 0.56 $wt\%.$ In contrast, unit 2 samples exhibit
significantly higher TS contents (average 1.24 $wt\%).$
Samples representing the presumed marine transgressive
events display the highest TOC (average 2.82 $wt\%)$ and TS
contents (average 2.01 $wt\%).$ Unit 1 was primarily
deposited under oxic-dysoxic and freshwater-brackish water
conditions, as evidenced by multiple organic and inorganic
geochemical indicators. Conversely, unit 2 and the marine
transgressive layers were deposited under less oxygenated
and more saline bottom water. Source rocks from the K2qn1
generally show minor input of terrestrial OM. However, unit
1, containing type II-III kerogen, indicates a slightly more
pronounced contribution from terrigenous higher plants
compared to unit 2 and the marine transgressive layers,
where the kerogen is predominantly derived from
planktonic/algal and microbial biota. In Chapter 4, data on
organic petrology, stable carbon isotopes, as well as bulk
and molecular geochemistry, along with elemental
geochemistry, are presented and discussed based on analysis
of 36 outcrop samples of Early Permian lacustrine shale from
the Usclas-St. Privat (USPF), Tuilières-Loiras Formation
(TLF), and Viala Formation (VF) in the Lodève Basin,
southern France. The study mainly unravels the alterations
in the environmental conditions of the paleolake during the
deposition of these formations and establishes an OM
accumulation model for the lacustrine fine-grained
sediments. All analyzed samples are thermally oil-mature.
The lower section of the USPF exhibits TOC and TS contents
of 4.28 $wt\%$ and 1.09 $wt\%$ on average, respectively. In
contrast, the upper section of the USPF, TLF, and VF show
considerably lower TOC and TS contents. The lower section of
the USPF was deposited in an oxygen-depleted and saline
lacustrine environment, likely associated with more humid
climatic conditions and potential marine influence. In
contrast, the upper section of the USPF, TLF, and VF were
deposited in oxic-dysoxic and freshwater-brackish bottom
water conditions with a significant shift towards arid
conditions. Biomarker analysis suggests that the OM in most
samples primarily originates from planktonic/algal biomass
with additional microbial OM. Only the lower section of the
USPF shows a slightly increased contribution of terrestrial
OM input and a higher detrital influx. It is inferred that
the basin's structural evolution from a narrow, deep setting
to a wider, shallower configuration, along with postulated
marine transgressive events during the early stages, played
a pivotal role in shaping the deposition environments of
these two distinct lacustrine shale sets, influencing OM
accumulation mechanisms. Conversely, substantial climatic
aridification appears to have a relatively minor impact on
OM sources and water column conditions. Chapter 5 exhibits
and compares the geochemistry characteristics of the typical
lacustrine shales with different depositional settings in
China and Europe. In addition, the depositional models for
different types of lacustrine OM-rich source rocks are
summarized.},
cin = {532410 / 530000},
ddc = {550},
cid = {$I:(DE-82)532410_20140620$ / $I:(DE-82)530000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2024-03065},
url = {https://publications.rwth-aachen.de/record/981477},
}
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