Many large paleo-lakes in North China were formed after the Triassic Era. Seawater incursion events (SWIEs) in these lakes have been extensively discussed in the literature, yet lack reliable methodology and solid evidence, which are essential for reconstructing and confirming SWIEs. The present study employs specific marine biological markers (24-n-propyl and 24-isopropyl cholestanes) to trace SWIEs in a dated core taken from the Songliao Basin (SLB). Two SWIEs were identified. The first SWIE from 91.37 to 89.00 Ma, was continuous and variable but not strong, while the second SWIE from 84.72 to 83.72 Ma was episodic and strong. SWIEs caused high total organic carbon (TOC) and negative δ13Corg values in the sediments, which were interpreted as an indication of high productivity in the lake, due to the enhancement of nutrient supplies as well as high levels of aqueous CO2, due to the mixing of alkaline seawater and acidic lake water. The SWIEs in SLB were controlled by regional tectonic activity and eustatic variation. Movement direction changes of the Izanagi/Kula Plate in 90 Ma and 84 Ma created faults and triggered SWIEs. A high sea level, from 90 to 84 Ma, also facilitated the occurrence of SWIEs in SLB.

Hainan Island lies near the Red River Fault, a prominent tectonic feature produced by the India‐Asia collision. There, we carried out a geochronologic and paleomagnetic study on Cretaceous rocks in order to better understand the kinematic history of the region. U‐Pb zircon dating of tuff intercalated in red bed sedimentary rocks yielded a concordant age of 106.6 ± 0.3 Ma; a mafic dyke intruding the red beds yielded a concordant age of 104.6 ± 0.7 Ma. Stepwise demagnetization experiments on 448 sedimentary rock samples and 191 dyke samples isolate solely normal polarities. Paleomagnetic directions of the dykes cluster in two distinct populations in geographic coordinates, indicating that dyke intrusion occurred in two pulses of limited duration (secular variation was not averaged) after tilting of the sediments. Baking of the sediments from the dykes only occurred near the contacts. Together with published data, the mean directions of 104 sites most tightly group at 58.3 ± 3.2% unfolding, indicative of a synfolding remagnetization, which can be constrained to have occurred within a 2 Myr period between sedimentation and dyke intrusion. We suggest that warm (50–100°C) fluid interaction during basin development led to new mineral growth spawning chemical remagnetization. The corresponding paleomagnetic pole at 81.5°N, 145.2°E (A95 = 2.4°) is indistinguishable from the coeval Eurasian reference pole, suggesting the South China Block has remained fixed to Eurasia since 105 Ma. A contour map of paleomagnetic rotations from 115 studies in the region shows that the Red River Fault roughly demarcates rotation magnitudes/signs, suggestive of a major tectonic boundary.

Carbon cycling in subduction zones remains poorly constrained due to the lack of relevant geological records. Here we report magnesium isotope data (δ26MgDSM3) from calcium‐silicate rocks (rodingites) from the Xigaze ophiolite, southern Tibet, which is thought to represent remnants of Neo‐Tethyan oceanic lithosphere. Behaviors of immobile trace elements in rodingites resemble those of their mafic dike protoliths, showing subduction‐related signatures. The majority of rodingites exhibits low δ26Mg values of −0.72‰ to −0.33‰ with a weighted average of −0.47 ± 0.11‰ (2 SD), significantly lighter than that of their protoliths (−0.31 ± 0.03‰). This difference likely reflects the interaction of the protolith with isotopically light carbonate fluids. Modeling indicates that this hypothesis requires the input of 5 to 15 wt % carbonates during rodingitization. Our study suggests that rodingite may represent a previously unrecognized reservoir of dissolved Ca from subducted carbonates.

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The western Tibetan Plateau (TP) is characterized by low relief with high elevation separated by deep river valleys. When and how this characteristic topography developed remains ambiguous. Here, we present apatite (U‐Th)/He and fission‐track ages from three groups of samples with different geomorphic and geological settings. Thermal histories and exhumation rates were extracted from the thermochronological data. An early stage of exhumation (ca. 0.1 km/Ma) during 70–40 Ma was recorded by all samples, followed by slow exhumation (0.03–0.06 km/Ma) since the Eocene for the sample farthest away from faults and incised valley. The second stage of faster exhumation (ca. 0.13–0.15 km/Ma) during 30–23 Ma was revealed by samples from the hanging wall of thrust faults, whereas the third stage of exhumation during 15–12 Ma (ca. 0.1 km/Ma) was identified from samples in the Dingzi Zangbo valley. Combined with the regional geological setting, we propose that (a) the Late Cretaceous‐Early Eocene exhumation in the western TP was related to regional thrust‐induced crustal thickening and led to the formation of the proto‐TP; (b) the proto‐TP was modified by local structures and river incision. The Oligocene exhumation might be caused by local thrust activity, whereas the Miocene exhumation might be related to the transition from internal to external drainage. The continuous activity of the Karakoram fault resulted in another reorganization of drainage which led to the slow exhumation since 9 Ma. Our results highlight that tectonic and drainage network reorganization play an important role in shaping the geomorphology of the western TP.