The Jurassic basin prototypes and episodic sedimentary characteristics of the Hongshan Sag in the eastern segment of the Northern Qaidam Basin, NW China

The Middle Jurassic Aalenian–Bajocian stages represent the tectonic transition period for the group of Jurassic sedimentary basins in northwestern China and include accumulation of the most important recoverable coal seams. Geological data from borehole cores, well loggings and rock‐mineral determination in the Aalenian to Bajocian‐aged Dameigou Formation in the Yuqia coalfield, Northern Qaidam Basin were employed to unveil the relationship between coal accumulation and changes in palaeoclimates and provenance tectonic activity. The results identify six kinds of lithofacies from fluvial and lacustrine sedimentary systems, and allow the Dameigou Formation to be divided into two third‐order sequences (SIII1–SIII2) and their corresponding system tracts by regional unconformity surfaces, forced regression surfaces and their correlative conformity surfaces, and the abrupt shift surfaces of depositional facies. The main coals, the #7 and #6 seams, were deposited in a lake and swamp environments during lake transgression system tracts of SIII1 and SIII2, respectively. The varying trend of the Tectonic Index values indicate that the source area experienced strong tectonic activity from the SIII1 to the lowstand system tract of SIII2, and then gradually stabilized. The Mineral Alteration Index reveals that the climate during SIII1 was from dry‐hot to humid‐warm, and there is a climate cycle from dry‐hot to humid‐warm then a return to dry‐hot in SIII2. During the faulting stage, the occurrence and termination of coal accumulation was in response to weakening and strengthening periods of tectonic activity respectively, while during the depression stage it was in response to the humid‐warm and dry‐hot climate respectively.

Section: Discussionsupporting

confidence: 85%

Section: Sequence Stratigraphy and Palaeogrographymentioning

confidence: 99%

Jurassic continental coal accumulation linked to changes in palaeoclimate and tectonics in a fault‐depression superimposed basin, Qaidam Basin, NW China

Zhou

Yang

et al. 2020

“…Provenance interpretations of Jurassic sediments can provide data for surrounding mountains tectonic evolution of Qaidam Basin, thus enhancing the understanding of the uplift events in north‐eastern Tibetan Plateau. In recent years, research based on petrography (Feng et al, ; Tang et al, ; Wu et al, ), geochemistry (Cao et al, ; Jian et al, ), and heavy mineral (Shu et al, ) were carried out, but the detailed and systematic provenance studies of the sediments are relatively scarce. Dameigou profile sandstone detrital zircon geochronological studies were reported both by Yu et al () and Qian et al (), but the results indicate different Jurassic primary source areas.…”

Section: Introductionmentioning

confidence: 99%

Jurassic sediments geochemical constraints on provenance, weathering process, and palaeoclimate variation of the north margin of Qaidam Basin, north‐eastern Tibetan Plateau

et al. 2019

The Jurassic sequence in the northern Qaidam Basin can be represented by the lower coal‐bearing swamp‐lacustrine sediments unit and the upper reddish clastic deposits suite, which recorded dramatic transition of deposit environment changes. Whole‐rock geochemical data of this succession in Dameigou profile were used to reconstruct the provenance and chemical weathering history. Based on the major element discrimination diagrams, trace element ratios and chondritenormalized REE patterns, most sediments were derived from a similar source area with felsic‐intermediate rocks as dominant contributors. Multiple geochemical parameters and index displayed good correlation, via vertical variations sequence, Jurassic chemical weathering history of northern Qaidam Basin was established, and four stages were recognized from the profile. Phases I and III experienced intense chemical weathering, while Phases II and IV are characterized by mild to moderate chemical weathering. Based on this, long‐term Jurassic climatic evolution of the Qaidam Basin was reconstructed. Early‐middle period of Early Jurassic and middle period of Middle Jurassic developed warm and humid climate. On the contrary, late Early Jurassic‐early Middle Jurassic and late Middle Jurassic‐Late Jurassic was deposited under relatively semiarid to arid climatic conditions.

“…The Northern Qaidam Basin (NQB) is located in the northwest and northeast parts of the Qaidam Basin. It is surrounded by the ATF to the northwest, Qilian Range to the northeast and Mengbei-Lingjian-Dahuo Fault to the south (H. W. Feng et al, 2017Feng et al, , 2022.…”

Section: Characteristics Of Jurassic Sedimentary Migration In the Nor...mentioning

confidence: 99%

Jurassic sedimentary migration characteristics and their geodynamic implications in the Dunhuang Basin and adjacent regions, Northwestern China

Feng,

Xu,

Xubo

et al. 2024

The Dunhuang Basin, situated in western China along the Altyn Tagh Fault (ATF) zone, intersects the Tethys and Paleo‐Asian Ocean tectonic domains. Influenced by both the ATF system and the far‐field effects of the Qiangtang‐Lhasa‐Eurasia collision during the Mesozoic, the mechanism of the Jurassic sedimentary migration of the basin in response to tectonic movements is unclear so far. The paper uses a comprehensive approach, including field geological surveys, lithologic and lithofacies discern, stratigraphic relationships analysis and 2D seismic profile interpretation, to examine the distribution of Jurassic residual strata in the basin. The comprehensive results of our study suggest that the Dunhuang Basin exists as an isolated block with unique tectonic and sedimentary evolution characteristics. In the Early Jurassic, the Dunhuang Basin underwent initial rifting, leading to the formation of small segmented intermontane sags. This phase was marked by the coarse particle sedimentary system of alluvial fans and braided rivers, represented the near source rapid deposition in the initial formation period of the basin. Stratigraphic distribution was primarily influenced by pre‐Jurassic basement topography and was not significantly constrained by faulting during this period. The formation of these isolated discontinuous small intermontane sags indicates the segmented activities of the ATF in the Early Jurassic period. In the Middle Jurassic period, influenced by the ATF dextral strike‐slip faulting, sedimentation extended eastward and the depocenter migrated clockwise compared with the distribution of the Middle Jurassic strata within the Dunhuang Basin. This period witnessed the development of coal measure strata at the basin's margins and lacustrine fine‐grained clastic deposition in the centre. The segmented fracture of the ATF gradually initiated a unified dextral strike‐slip tectonic movement. In the Late Jurassic period, sedimentary strata were locally present in the Wanyao Sag but absent in other sags. The depocenter migrated counterclockwise compared with the distribution of Middle Jurassic strata within the Dunhuang Basin, due to regional uplift accompanied by the ATF sinistral strike‐slip faulting caused by the collision between the Lhasa Block and the Eurasia Plate. The depocenter migration of the Dunhuang Basin constrained within the ATF system from the Early to Middle and Late Jurassic can be attributed to the transition of the ATF strike‐slip faulting in context of the stress relaxation and compression between the collision of the Qiangtang and Lhasa blocks to the Eurasia Plate, respectively.