Chromaticity of Cretaceous strata reveals astronomically driven lake-level changes in the southern margin of Junggar basin, NW China

The Fengcheng Formation (P1 f) source rock, which was deposited in an alkaline water body, is one of the most significant source rocks in the Mahu sag, Junggar Basin. However, its evolution and mechanism of organic matter accumulation are still not understood. Using seismic, core, and log data, P1 f is divided into 3 third-order sequences, i.e., SQ1, SQ2, and SQ3, from bottom to top. Pyrolysis data of core samples shows that SQ1 and SQ3 mainly are characterized by poor to fair source rocks, with Type III to Type II2 kerogen, while SQ2 mainly are characterized by fair to good to excellent source rocks, with Type II2 to Type I kerogen. The biomarker parameters of 40 source rock samples from different sequences suggest that the reducibility of sedimentary water is characterized by SQ2 > SQ1 > SQ3. The organic matter contribution in different sequences is obviously different. SQ1 organic matter contain more bacteria and algae than that of SQ2 and SQ3, and terrigenous higher plants may have contributed to SQ3 organic matter. Lake level changes and water salinity dominate organic matter origin, accumulation, and preservation. During SQ1 deposition, the lake level was the highest, the salinity of sedimentary water was moderate, and the organic matter contained more conventional algae sources. During SQ2 deposition, the lake level was the lowest and the salinity was the highest, and the organic matter contained special algae characterized by C29 regular steroids. The lake level of SQ3 was higher than that of SQ2, the salinity was the lowest, and terrigenous higher plants may have contributed to organic matter during this period.

The Junggar Basin in NW China contains lacustrine hydrocarbon source rocks which are among the highest quality of hydrocarbon potential in the world. Oil reservoirs in the basin are very substantial: target reservoirs span Carboniferous to Tertiary strata and include Permo-Triassic lacustrine and fluvial sandstones. The Junggar Basin was a foreland basin during the late Permian to Cenozoic, possibly with strike-slip tectonics at the southern margin during Mesozoic time. The Cangfanggou Group, as one of the major reservoirs, is well-exposed in the eastern part of the southern Junggar Basin. A measured outcrop section and a number of borehole logs coupled with resistivity logs were used to attempt sequence stratigraphic analysis. Detailed sedimentological studies on the outcrops and borehole cores have demonstrated that the Cangfanggou Group is characterized by alternating lacustrine and fluvial deposits. Four depositional sequences have been recognized. For each sequence, the basal boundary is marked by erosional truncation of fluvial channel conglomeratic sandstones in sharp contact with underlying lacustrine or floodplain mudstones. The top of each lowstand systems tract is normally overlain by the transition to lacustrine or maximum flooding surface. The transgressive systems tract is normally not identifiable at the basin margin, but was developed in the basinward area and characterized by interbedded fining-upward distal fluvial and shallow lacustrine deposits. The highstand systems tract at the basin margin is characterized by very thick floodplain mudstones or shallow lacustrine deposits, and by typical coarsening-upward parasequences of shallow lacustrine deposits in more basinward areas. Sediment input to the basin was controlled by tectonics and climate. Depositional sequences were probably controlled by fluctuating change of lake level: this was in turn controlled by climate (runoff), modified by tectonics in specific areas.

Middle Permian environmental changes and shale oil potential evidenced by high-resolution organic petrology, geochemistry and mineral composition of the sediments in the Santanghu Basin, Northwest China

Variability in precipitation, temperature and river runoff in W Central Asia during the past ~ 2000 yrs

Carbon and nitrogen signatures of sedimentary organic matter from Dali Lake in Inner Mongolia: Implications for Holocene hydrological and ecological variations in the East Asian summer monsoon margin

The spatial extent of the East Asian summer monsoon in arid NW China during the Holocene and Last Interglaciation

Conglomerate to mudstone lacustrine cycles revealed in Junggar Basin, Northwest China: Middle Permian Lucaogou and Jingjingzigou formations

A Late Quaternary lake record from the Qilian Mountains (NW China): lake level and salinity changes inferred from sediment properties and ostracod assemblages

A study on two closed salt lake basins, Tal Chapar and Parihara in the eastern margin of the Thar Desert, Rajasthan, was carried out to unravel late Quaternary geomorphic evolution of these saline lakes. Both lakes are elliptical in shape bordered by stabilised dunes, and are oriented in a NE-SW direction, i.e., in the direction of the prevailing summer monsoon wind. Both lakes have been formed in the wind-shadow zones of isolated hills of Precambrian quartzite. Our study indicates that the late Quaternary sediments in the lakes began with the cyclic deposition of laminated fine silt layers (0.5 m thick), rich in organic matter, alternating with ripple cross-bedded sand layers (each ∼1.5–2 m thick). Sand layers that are moderately sorted are separated by laminated silt-clay layers with gypsum/calcite and this unit occurs in the upper most 4 m sequence in deeper sections. The presence of gypsum crystals within the laminated sediments suggests a high concentration of Ca in the inflowing water. At Parihara Lake the organic carbon-rich sediments at 95 cm depth was dated to 7,375 + 155/−150 year BP. At Tal Chapar radiocarbon dates of 7,190 + 155/−150 and 9,903 + 360/−350 was obtained from the sediments rich in organic carbon occurring at a depth of 1.35 m and 1.80 m, respectively. The study reveals strong hydrologic oscillations during the past ∼14,000 year BP (13,090 + 310/−300 year BP). Quaternary geomorphic processes, especially the strong aeolian processes during dry climatic phases, played a major role in the formation of the lake basins, as well as the fringing linear dunes. Geochemical and mineralogical analyses of the lacustrine sediments, supported by radiocarbon dates indicate the existence of an ephemeral lake earlier than ∼13,000 year BP as sediments began to be deposited in a lacustrine environment implying sustained runoff in the catchments. A freshwater lake formed between 9,000 year and 7,000 year BP. The lake dried periodically and this strong fluctuating regime continued until about ∼7,000 year BP. Mid-Holocene was wet and this was possibly due to higher winter rains A saline lake existed between 6,000 year and 1,300 year BP and finally present day semi arid conditions set in since 1,200 year BP. Remnants of a habitation site (hearth and charred bones) on stabilised dune at Devani near Tal Chapar were dated to 240 ± 120 year, while that at Gopalpura was dated to 335 ± 90 year. These historical sites on stabilised dunes were, according to the local accounts, settlements of people who used the lake brine for manufacturing salt.

The parameters Sr/Cu, Sr/Ba, and the lake-level changes of the oil shale and mudstone from the oil shale measures reveal that the oil shale mainly formed in the humid climate and fresh water-brackish water environment in the lake-level rising stage. However, mudstone mainly formed in the arid climate and brackish water-salt water environment in the lake-level decline stage. In addition, the lake sealing of the oil shale measures is better.

Sequence stratigraphy, sedimentary systems and petroleum plays in a low-accommodation basin: Middle to upper members of the Lower Jurassic Sangonghe Formation, Central Junggar Basin, Northwestern China

Lithospheric structure beneath the eastern Junggar Basin (NW China), inferred from velocity, gravity and geomagnetism

Carbon isotope stratigraphy across the Triassic-Jurassic boundary in the high-latitude terrestrial Junggar Basin, NW China

Societal Impact StatementIn rapidly changing environments species conservation can be hindered by uncertainties in distinguishing closely related species. Cryptic ongoing hybridization can add further uncertainty and could be beneficial or destructive. Here, we show that a declining birch tree species is hybridizing with a more widespread relative in the Junggar basin, NW China, and their hybrids have been previously named as rare sub‐species. Given the declining numbers of this birch tree, we suggest that conservation effort should aim to slow the rate of anthropogenic habitat loss at this hybrid zone and preserve its pure populations away from the hybrid zone.Summary In areas where closely related species meet, the possibility that they may hybridize must be taken into account by conservationists. Hybridization may have positive or negative consequences for the long‐term future of species. If present, its dynamics need to be understood. Betula microphylla is a declining wetland tree species in NW China that forms a continuum of leaf morphology and geographic distribution with its relative Betula tianshanica. We use ecological niche models to predict the distribution of B. microphylla and B. tianshanica. We use restriction site‐associated DNA sequencing and SSRs to resolve their genetic structure and patterns of allele sharing. Ecological niche models predict an expansion of the range of B. tianshanica into that of B. microphylla since the Last Glacial Maximum and the contraction of B. microphylla's range in the future. Genetic data suggest that the two species have hybridized in the Junggar basin and in the Tianshan Mountains where the two species have co‐occurred in the recent past and in the Altay Mountains where there are no records of B. tianshanica occurrence. Rare populations previously identified as sub‐species of B. microphylla were shown to be of hybrid origin. Further research is needed on the costs and benefits of hybridization between B. microphylla and B. tianshanica in the changing environment of NW China. Our current data suggest that conservation effort should aim to slow the rate of anthropogenic habitat loss at the hybrid zone in the Junggar basin and preserve pure populations far away from the hybrid zone in the Altay Mountains.

Petrogenesis of early Carboniferous bimodal-type volcanic rocks from the Junggar Basin (NW China) with implications for Phanerozoic crustal growth in Central Asian Orogenic Belt