Chenglin Gong

Bio: Chenglin Gong is an academic researcher from University of Texas at Austin. The author has an hindex of 1, co-authored 1 publications receiving 23 citations.

Classification, formation, and transport mechanisms of mud clasts

Abstract: Mud clasts are common in non-marine to marine sedimentary records, however, why lack a widely accepted classification scheme? We propose that it is the relative balance of volumetric abundance, sor...

Late Triassic sedimentary records in the northern Tethyan Himalaya: Tectonic link with Greater India

Abstract: The Upper Triassic flysch sediments (Nieru Formation and Langjiexue Group) exposed in the Eastern Tethyan Himalayan Sequence are crucial for unraveling the controversial paleogeography and paleotectonics of the Himalayan orogen. This work reports new detrital zircon U-Pb ages and whole-rock geochemical data for clastic rocks from flysch strata in the Shannan area. The mineral modal composition data suggest that these units were mainly sourced from recycled orogen provenances. The chemical compositions of the sandstones in the strata are similar to the chemical composition of upper continental crust. These rocks have relatively low Chemical Index of Alteration values (with an average of 62) and Index of Compositional Variability values (0.69), indicating that they experienced weak weathering and were mainly derived from a mature source. The geochemical compositions of the Upper Triassic strata are similar to those of graywackes from continental island arcs and are indicative of an acidic-intermediate igneous source. Furthermore, hornblende and feldspar experienced decomposition in the provenance, and the sediment became enriched in zircon and monazite during sediment transport. The detrital zircons in the strata feature two main age peaks at 225–275 Ma and 500–600 Ma, nearly continuous Paleoproterozoic to Neoproterozoic ages, and a broad inconspicuous cluster in the Tonian–Stenian (800–1200 Ma). The detrital zircons from the Upper Triassic sandstones in the study area lack peaks at 300–325 Ma (characteristic of the Lhasa block) and 1150–1200 Ma (characteristic of the Lhasa and West Australia blocks). Therefore, neither the Lhasa block nor the West Australia blocks likely acted as the main provenance of the Upper Triassic strata. Newly discovered Permian–Triassic basalt and mafic dikes in the Himalayas could have provided the 225–275 Ma detrital zircons. Therefore, Indian and Himalayan units were the main provenances of the flysch strata. The Tethyan Himalaya was part of the northern passive margin and was not an exotic terrane separated from India during the Permian to Early Cretaceous. This evidence suggests that the Neo-Tethyan ocean opened prior to the Late Triassic and that the Upper Triassic deposits were derived from continental crustal fragments adjacent to the northern passive continental margin of Greater India.

Spatial distribution and sources of tsunami deposits in a narrow valley setting - insight from 2011 Tohoku-oki tsunami deposits in northeastern Japan

Abstract: Sedimentary processes and spatial distributions of tsunami deposits in valleys have poorly been understood despite many paleo-tsunami deposits have recently been discovered from sedimentary sequences in valleys. We conducted an exhaustive investigation of 2011 Tohoku-oki tsunami deposits in a narrow valley at the south end of Sendai Plain, northeastern Japan, to collect sedimentological data of the tsunami deposits in the valley and to correlate them with tsunami inundation and associated sedimentary processes. The tsunami deposits were investigated at 174 sites to cover the entire inundation area of the narrow valley. We analyzed thickness, sedimentary structures, and grain size of the tsunami deposits to correlate their spatial variation with tsunami flow hydrodynamics and topographic features. The tsunami deposits, composed of sand and mud layers, were found to be 0–40 cm thick. Sand thickness generally decreased inland with local fluctuation. The sand layer was mostly composed of single unit on the upper main valley and sub-valleys, although it was mainly composed of 2–6 sub-units on the lower main valley and in the pond. Mud thickness is strongly controlled by local sources, namely, the rice paddy and the pond. The depositional area of the mud layer coincides with the distribution of the rice paddies and the pond location. The mud layer also considerably thicker in and around the pond. These results indicate that sediment thickness and sedimentary structures are highly varied on a local scale, but they are generally controlled by local topography. Sediment budget in the valley was estimated, and it may provide implications to general sedimentary process. Total depositional volume of the tsunami sand deposited on land is half of the volume of sediments disappeared from the sandy beach and sand dune, suggesting the rest must have been discharged into the sea by the backwash. Spatial distribution of sediment thickness and sedimentary structures as well as sedimentary processes inferred from 2011 Tohoku-oki tsunami deposits will benefit searching and identification of paleo-tsunami deposits in valleys of other coastal environments.

Gravity-flow deposits caused by different initiation processes in a deep-lake system

Abstract: Gravity flows may be triggered by different initiation processes in both marine and lacustrine basins. Recognizing the different initiation processes of gravity flow based on their deposits is vital to accurately establish gravity-flow sandstone distribution, which is important for defining paleogeography and for efficient oil and gas exploration. Gravity-flow deposits in the Dongying sag were analyzed using three-dimensional seismic, well-log, grain size, and porosity and permeability data, along with core descriptions. Eleven lithofacies, nine bed types, and six bed-type associations were recognized in the gravity-flow deposits in the Dongying sag. Gravity-flow deposits around well Niu-110 were caused by delta-fed sediment failure. These deposits are characterized by medium to very fine-grained sandstone, abundant liquefaction and soft-sediment deformation structures, and thick laminae rich in plant debris. They formed massive sandstones accompanied by normally graded sandstone and lenticular-shaped sandbodies and are composed of chaotic deposits and tongue lobes. The above features collectively are indicative of typical collapsed-sediment transport to deep water by slumping and poorly cohesive debris flow to low-density turbidity current. Gravity-flow deposits around well Shi-100 are interpreted to have been caused by flooding river-fed hyperpycnal flows. These deposits are characterized by gravel to very fine-grained sand, abundant erosional structures and climbing ripples, and thin laminae rich in plant debris. They formed massive sandstone with some space stratification accompanied by inverse-then-normal grading sandstone and elongate or fan-shaped sandbodies and are composed of channel-levee systems and lobes. Stratified hyperpycnal flow is prone to form a hydraulic jump at the slope break. After the hydraulic jump, coarse-grained sediments were transported to the basin under the drag and shear of the upper part of the suspension flow. Gravity-flow deposits caused by flooding river-fed hyperpycnal flow are better reservoirs than those caused by delta-fed sediment failure under the same conditions. This study offers insight into the recognition criteria and flow processes of gravity flows caused by the different initiation processes in a lacustrine basin.