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The Late Jurassic - Early Cretaceous tectonic evolution of SE Siberia was marked by the closure of the Mongol-Okhotsk ocean. While this geodynamic event led to compressive deformation and denudation in a wide area encompassing the North-Altay, Sayan and Baikal Patom ranges, it was contemporaneous to widespread extension from the Transbaikal region situated immediately north of the suture zone to the Pacific plate, affecting eastern Mongolia and northeastern China. In this study we review the paleontological and sedimentological data available in the Russian literature and provide new macro-floral and palynological data from the Mesozoic sediments of three Transbaikal basins. These data are used to describe the paleoenvironmental and paleoclimatic evolution of the Transbaikal area in order to assess the topographic evolution of the region in relation with the closure of the Mongol-Okhotsk ocean. We establish that the Transbaikal basins evolved in a continuously extensional tectonic setting from at least the Early-Middle Jurassic to the Early Cretaceous. The associated sedimentary environments are characterized by retrogradation from alluvial fan–braided river dominated systems prevailing during the Early to Middle Jurassic initial opening of the basins to meandering river– lacustrine systems that developed during the Late Jurassic - Early Cretaceous interval. No evidence of high relief topography was found and we conclude that, while compression and denudation occurred in the North Altai, Sayan and Patom ranges, in the Transbaikal region, the docking of the Mongolia-North China continent to Siberia was a “soft collision” event, possibly involving a major strike-slip displacement that did not lead to an orogenic event implying strong compressive deformation, crustal thickening and topography building.

Cenozoic uplift in the Tianshan played an important role in driving Proto‐Paratethys Sea retreat and Asian aridification. However, most paleoclimate studies have focused on the Pamir‐Tianshan corridor, and frequently overlook the role of the entire Tianshan range in modifying the Central Asian climate during Cenozoic uplift. When and how Cenozoic deformation of Tianshan was initiated and propagated are intensively debated which makes its role in contributing to climate change in Central Asia more ambiguous. To address this issue, this study presents new detrital zircon U‐Pb and detrital apatite U‐Pb and fission track age data from Cenozoic sedimentary successions (54–0 Ma) in the northern margin of the Tarim Basin and integrates these data with published provenance data from adjacent regions. Our results show that deformation/uplift of the Baicheng‐Kuqa Depression and the South Tianshan occurred at ∼41–37 Ma and ∼24 Ma, when topographic growth of South Tianshan began to block the flow of sediment from the north. Continued uplift of the South Tianshan completely blocked fluvial transport from the Central Tianshan‐Yili Block by ∼10 Ma, as shown by the paucity of 380–310 Ma detrital zircons/apatites. Far‐field, north‐directed compressive stress resulting from the India‐Asia collision began to propagate toward the South Tianshan and its foreland during the Late Eocene, and continued to propagate into the South Tianshan and northward at the ∼24 Ma and 10 Ma. Finally, we suggest a two‐stage of aridification in the Tarim Basin which can be linked to two stages (∼24 and 10 Ma) of growth of the Tianshan. Plain Language Summary: The Tarim Basin and the Taklimakan Desert are located in Central Asia, between the Tibetan Plateau to the south and the Tianshan orogenic belt to the north. This region is a crucial area for exploring the primary drivers of Cenozoic desertification. We performed a systematic zircon and apatite provenance study (including detrital apatite and zircon U‐Pb dating, and detrital apatite fission track analysis) in Cenozoic strata from the northern margin of the Tarim Basin. Our results reveal pulsed deformation of the South Tianshan that initiated at ∼41–37 Ma with two subsequent pulses at ∼24 Ma and ∼10 Ma, the timing of which suggests a close link to the two‐step aridification (∼24 and 10 Ma) of the Tarim Basin. We suggest that the pulsed Cenozoic rise and growth of the South Tianshan played a crucial role in blocking westerly winds, restricting moisture from reaching the Tarim Basin, and driving Cenozoic aridification of the Tarim Basin. Key Points: Initiation of the Cenozoic uplift of the South Tianshan occurred in the Late EoceneFurther uplift of the South Tianshan completely blocked fluvial transport from the north by ∼10 MaPulsed growth of Tianshan play a dominant role in the two‐step aridification of the Tarim Basin [ABSTRACT FROM AUTHOR]

Aridification of Central Asia in the Late Mesozoic led to drastic environmental changes characterized by widespread aeolian deposits. We systematically investigated fluvial‐aeolian deposits in the Middle Jurassic Toutunhe Formation, Upper Jurassic Kalazha Formation, and Lower Cretaceous Tugulu Group in the Junggar Basin to the north of the Tianshan Orogenic Belt via unmanned aerial vehicle‐based photogrammetry, scanning electron microscope, grain‐size analysis, and detrital zircon geochronology. Paludal and deltaic environments transitioned to a fluvial‐aeolian environment from the late Middle Jurassic to the Late Jurassic. Fan delta and incisive braided river deposits accumulated in the earliest Cretaceous and evolved into a lacustrine environment with aeolian deposits in the lakeshore. Aeolian deposits are characterized by moderate‐ to well‐sorted and subangular to subround sandstones with large‐scale, high‐dip cross‐bedding, inversely graded lamination, dominant saltation grains, crescent‐shaped, and dish‐shaped impact structures. Aeolian deposits contain heavy minerals including more ilmenite, zircon, garnet, and, tourmaline and less magnetite and epidote than the fluvial deposits. The preserved aeolian sediments of the Kalazha Formation extend west–east for more than 100 km, suggesting a wide desert area during the latest Jurassic. The detrital zircon age patterns indicate that the provenance of the aeolian deposits was similar to that of coeval fluvial deposits. The cooccurrence of fluvial and aeolian deposits and the similar provenances but orthogonal flow directions indicate that the aeolian deposits were mainly sourced from the nearby fluvial material within the basin. The evolution of the fluvial‐aeolian system responded to a complete base‐level cycle controlled by the aridification and tectonics. Due to decreased sediment supply caused by aridification, the base level rose, leading to the change from braided rivers to meandering rivers, along with the deposition of aeolian sediments. Due to the tectonic reactivation in the Late Jurassic, the base level fell, causing the occurrence of alluvial fans and the expansion of the aeolian sediments. Previous studies revealed that the Tianshan in the Jurassic exhibited low relief. The fluvial‐aeolian system played an important role in maintaining the limited relief in southern Central Asia. [ABSTRACT FROM AUTHOR]

This study details the procedures developed between 2021 and 2023 at the Géosciences Rennes lab (GeOHeLiS plateform, Rennes University, France) for obtaining precise (U–Th)/He thermochronological data on apatite. The methodology involves crystal selection, measuring helium (4He) content by heating crystals, and analyzing them using noble gas mass spectrometry. Additionally, determining U, Th, and Sm contents is achieved through crystal dissolution and subsequent solution analysis with triple-quadrupole mass spectrometry (QQQ-MS). Emphasis is placed on a new approach to quadrupole 4He sensitivity calibration based on Durango apatite, ensuring a precision of ~3.9 % in 4He content determination. The study also highlights the development of a 'ramped heating – direct analysis' protocol used to screen apatite diffusion behaviour. In addition, a new quantification protocol for major and trace elements measured in apatite is presented, employing a standard concentration range approach rather than the isotopic spiking technique commonly used for (U-Th)/He studies. [ABSTRACT FROM AUTHOR]

The Early Cretaceous topographic evolution of Transbaikalia was largely governed by the tectonic evolution of the Mongol-Okhotsk orogen. The collapse of the Mongol-Okhotsk orogen triggered the formation of metamorphic core complexes and associated extensional basins, widespread throughout Transbaikalia, North Mongolia, and North China. Numerous lithofacies and biostratigraphic studies have been carried out from the sedimentary deposits of the Transbaikalia basins. However, the absence of absolute ages for the sedimentary series, as well as sediment source-to-sink analysis do not allow to accurately characterize the regional topographic evolution. We focused our study on the Gusinoozersk Basin of Western Transbaikalia, where extensive sedimentary sections of Lower Cretaceous deposits have been preserved. We provide new U/Pb (LA-ICP-MS) data on detrital zircons from sedimentary series and 40Ar/39Ar data on intruding rocks. We review the paleontological data to clarify the age of the paleogeographic events associated with the collapse of the Mongol-Okhotsk orogen, as well as to correct the age of faunal complexes in Western Transbaikalia. Our geochronological results show that the formation of the Cretaceous basins of Transbaikalia began around 136–130 Ma, accompanying the main episode of extension associated with the exhumation of the metamorphic core complexes. The lowest coarse-clastic formation characterizes the rapid subsidence and the predominance of proximal sediment sources. Distal provinces also made a contribution to sedimentation indicating the rise of a positive topography characterizing the exhumation of the metamorphic core complexes. Overlying fine-grained formations indicate a significant smoothing of the topography, suggesting that from middle Aptian, Western Transbaikalia developed in a relatively calm tectonic regime. We also show that the basins of Transbaikalia were formed both in conjunction with the exhumation of metamorphic cores complexes and reactivated structural sutures. Revised data on dinosaur fauna and palynology, together with the dating of host deposits, provide insights on the Early Cretaceous paleoenvironmental evolution. [ABSTRACT FROM AUTHOR]