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The AAPG/Datapages Combined Publications Database
Journal of Petroleum Geology
Abstract
Journal of Petroleum Geology, vol.
UPPER TRIASSIC-MIDDLE JURASSIC STRATIGRAPHY AND SEDIMENTOLOGY IN THE NE QAIDAM BASIN, NW CHINA: PETROLEUM GEOLOGICAL SIGNIFICANCE OF NEW OUTCROP AND SUBSURFACE DATA
* Department of Petroleum Geology, Research Institute of Petroleum Exploration & Development, PO Box 910, Beijing 100083, China. email: [email protected] **Department of Geology, Utah State University, Logan, UT 84322-4505, USA.
email: [email protected] +Northeast Asia, IHS Energy Group, Houston, TX 77056, USA.
email: [email protected] ++ Research Institute of Exploration and Development of Qinghai Petroleum Company, Dunhuang, Gansu 736202, China. Although Mesozoic source and reservoir rocks are known to occur at oilfields in the
northern Qaidam Basin (NW China), the precise identification and distribution of Mesozoic
rocks in the subsurface are outstanding problems. The Dameigou locality has in the past
been considered as the type section for Lower-Middle Jurassic strata in northern Qaidam.
Previous studies have concluded that the onset of non-marine sedimentation here took
place in the Early Jurassic; and that Mesozoic strata penetrated by wells in the Lenghu
structural zone are Middle Jurassic. In this paper, we present new data from the Lengke-1 well, drilled in the Lenghu
structural zone in 1997. This data indicates the existence of a more extensive pre-Middle
Jurassic stratigraphy than has previously been recognized. Biostratigraphic data together
with regional seismic mapping suggest that the pre-Middle Jurassic succession at
Lengke-1 includes both Late Triassic and Early Jurassic deposits. The Late Triassic
sedimentary rocks appear to have been deposited in local half graben, some of which
were later inverted during Jurassic, Cretaceous and Cenozoic tectonism. Lower and Middle Jurassic strata (lacustrine and fluvial deposits) are present in the
SW and NE parts of the Lenghu structural zone, respectively. Extensive organic-rich
intervals are present in both successions. Lower Jurassic lacustrine mudstones may
represent a previously under-appreciated, and potentially large, source rock sequence.
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