Late Triassic initial closure of the Mongol-Okhotsk Ocean in the western segment: Constraints from sedimentological,detrital zircon ages and paleomagnetic evidence

The Mesozoic evolution of the Mongol-Okhotsk Ocean (MOO) has significantly affected the configuration of the modern Asian continent. Although a scissor-like closure of the MOO has long been proposed, when and how the MOO closed are still hotly debated, especially the timing of initial closure of the MOO in its western segment, hindering our understanding of both the evolution of the MOO and tectonics of the northern Asian continent. In order to uncover the timing of initial closure of the MOO, we performed a multidisciplinary study in sedimentology, detrital zircon U-Pb dating and paleomagnetic on the Late Triassic clastic strata from the Tarvagatay Block and the Amuria Block (AMB) on the both sides of the Mongol-Okhotsk Suture. The upper Triassic strata on both sides of the suture were dominated by plant fossil-bearing alluvial-fluvial facies sediments, which unconformably overlain pre-Triassic geological units, indicating a terrestrial setting after the closure of the MOO. Detrital zircon U-Pb dating results revealed consistent age distribution patterns for samples from both sides of the suture with a predominant peak at ∼253–251 Ma and a secondary peak at ∼359–357 Ma, representing two main arc magmatic events during the bidirectional subduction of the MOO in the Late Devonian-Early Carboniferous and Late Permian-Early Triassic. Coeval Late Triassic paleomagnetic poles were obtained from the northern AMB and Tarvagatay Block, revealing a comparable paleolatitude of the AMB (∼31–33°) and Tarvagatay Block (∼32–34°) in the Late Triassic, arguing for that the western segment of the MOO should have closed at the Late Triassic. The compilation of sedimentology, detrital zircon U-Pb dating, magmatic and paleomagnetic evidence provides integrated constraints on the Late Triassic initial closure of the MOO in its western segment.     

A back analysis scheme for refined soil stratification based on integrating borehole and CPT data

Utilizing both borehole and Cone Penetration Testing (CPT) data in soil stratification helps to get more convincing soil stratification results. However, the soil classification results revealed by borehole (Unified Soil Classification System, USCS) and CPT tests (soil behavior type, SBT) are commonly not consistent. This study proposes a feasible solution to integrate the borehole and CPT data with the tree-based method. The tree-based method is naturally suitable for soil stratification tasks as it aims to divide the subsurface space into several clusters based on the similarities of the soil types. A novel boundary dictionary method is proposed to enhance the model performance on complex soil layer conditions. A probabilistic mapping matrix between the USCS-SBT system is built based on a collected municipal database with collocated borehole and CPT data. The optimal soil stratification results can be selected based on considering multiple borehole information and pruning the structure of trees. The structure of the trees can be optimized in a back analysis perspective with the Sequential Model-Based Global Optimization (SMBO) algorithm which aims to maximize the possibility of observing the borehole information based on the USCS-SBT probabilistic mapping matrix. The uncertainties of the optimal soil stratification results can be estimated based on a weighted Gini index method. The performance of the proposed method is validated based on a real case in New Zealand with a cross-validation method. The results indicate that the proposed method is robust and effective.