Abstract
Abstract A petroleum system originating from Jurassic source rocks exists in Altyn piedmont. However, the Jurassic formation in this system is deformed by Yanshan-Himalayan tectonic movement, and related studies about its spatial distribution and sedimentary system are still highly controversial. In general, a systematic research on the provenance system helps precisely restoring the prototype basin. Based on the methods of seismic characterization, sedimentary analysis, and detrital zircon U-Pb dating (samples from several Altyn piedmont outcrops), this paper studied the provenances of Jurassic formation in Altyn piedmont and characterized their distribution from different aspects: (1) Lacustrine rift basin developed in the study area at early Jurassic, while the formation showed a saucer shape with its thickness decreasing and vanishing towards the center of the basin in the middle Jurassic; in summary, the Jurassic formation in Altyn piedmont could be divided into several parts due to their different characteristics in different periods. (2) The south part of the Jurassic deposition (south of Qingshuigou) could come from the east Kunlun terrain; the middle part (Yueya mountain to Dongping area) however could be from several provenances, including the east Kunlun terrain, the surrounding plutons, and the Altyn fault; the north part (Niudong to north Lenghu area) is mainly related to the Altyn fault. (3) The Altyn fault, a regional fault system containing several strike-slip faults, is highly active since late Triassic and controls the current spatial distribution of the Jurassic formation; the faulted area in the piedmont could be separated into several parts with several different sources. (4) Compared to the southern and middle parts, the northern Jurassic deposition is relatively flat and contains wider and thicker source rock beds, which makes this area an important gas exploration target.
Highlights
The Qaidam Basin, surrounded by Altyn, Qilian, and Qunlun Mountain [1], is located in the northeastern Qinghai-Tibet Plateau
Seismic profiles here show several separate small-scale early Jurassic rifted lake basins in the south part of Altyn piedmont, such as the small basins in Qingshuigou, Yihaogou, and northern Yueyashan. These basins are graben or half-graben controlled by deep faults, and in seismic profiles, they appear as wedges with larger thickness at Altyn piedmont and getting smaller towards basin center
The sample was collected in middle Jurassic formation, and 110 effective measurements were selected (Figure 6)
Summary
The Qaidam Basin, surrounded by Altyn, Qilian, and Qunlun Mountain [1], is located in the northeastern Qinghai-Tibet Plateau. The Altyn Mountain is located to the northwest of the Qaidam Basin, and natural gas accumulation distributes in a large area in its southeastern piedmont. Middle-giant gas fields in this region such as Dongping, Niudong, and Jianbei have been explored since 2012, which are mainly supplied by Jurassic source rocks [3]. Regional tectonic movement from Mesozoic to Quaternary lifted the Jurassic formation and led to heavy erosion and strong deformation. This makes it difficult to portray the stratigraphy, Jurassic prototype basin, and source rock development in Jurassic, resulting in restriction on further oil and gas exploration
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