Publications
2024
- GSA PosterStatistical Analysis of the Thickness of Deepwater Sedimentary Deposits from IODP Expedition 354: Climatic Insights Gained Using a Data-Driven ApproachIn Proceedings of Geological Society of America Annual Meeting, Anaheim, CA, USA, 2024
The deep-sea Bengal Fan and linked Ganges-Brahmaputra River system forms Earth’s largest source-to-sink sediment-dispersal system, offering a unique opportunity to examine large-scale sediment transfer from the Himalaya to the Indian Ocean. International Ocean Discovery Program (IODP) Expedition 354 (2015) drilled a seven-site transect at 8oN in the Lower Bengal Fan, recovering abundant Pleistocene-aged sands. Medium to coarse sands at such a distal point (~1400 km from the shelf edge) raises questions about the drivers and processes that transported these sands. To investigate these deepwater depositional mechanisms, we did centimeter-scale lithological descriptions of cores from all seven IODP 354 sites, focusing on grain size and sedimentary structures to identify the preserved thickness of individual events. We noted sedimentary structures indicative of sediment gravity flows (SGFs), including normal grading, dewatering and load structures, and convolute bedding suggestive of syn-depositional seismic events. The thickness distribution of the observed beds (< 790 ka) follows an asymmetrical lognormal pattern (n = 1271, mean = 31 cm, std = 82 cm, max = 917 cm, skewness = 5.28), with most values centered around thin beds composed of very fine sands. Coarse-grained outsized SGFs (thickness > 2 m, mean + 2 std), although outliers, account for 47% of the total thickness of all clastic deposits in the seven cores as a whole. There is a strong correlation between grain size and increasing bed thickness for sandy deposits. However, silty beds exhibit an inconsistent trend, possibly due to the rework by bottom currents. Further facies analysis is required to fully understand the complexity of these finer-grained beds. The lognormal distribution of sandy SGFs in Bengal Fan cores may be linked to the frequency and magnitude of floods from the terrestrial source area, with outsized SGFs likely resulting from very infrequent, high-magnitude floods generated in the Himalaya. This data-driven approach employs grain size and thickness statistics for depositional facies analysis, providing insights into the forces that transporting clastic sediments recovered during IODP 354 to the deepwater sink. These results quantify the preservation of rare but substantial events in the stratigraphic architecture and explore signal propagation from the Himalaya to the distal Bengal Fan.
- IAS OralUnveiling Sedimentary Dynamics in the Distal Bengal Fan: Insights from IODP Expedition 354 Core Site U1454bIn Proceedings of the International Association of Sedimentologist Annual Meeting, Aberdeen, Scotland, UK, 2024
The Himalayan-sourced Ganges-Brahmaputra river system and the deep-sea Bengal Fan represent Earth’s largest sediment-dispersal system. IODP Expedition 354 (2015) drilled a 7-site transect in the lower Bengal Fan, ~1400 km south of the shelf margin. The work reported here focuses on quantifying physical characteristics of turbidites through time, so as to reconstruct past sedimentary dynamics, and address questions about triggering mechanisms. We have conducted centimeter-scale description and statistical evaluation of IODP 354 core U1454b, which was collected from a channel-levee system deposited ca. 600-34 Ka. We recognize 137 high-density turbidites (HDTs) with thicknesses up to 3.53 m. We subdivide this core into five units based on discernible depositional patterns, and the assumption that glacial periods of low sea level are necessary for fluvial-to-deep-sea transport of coarser sand. Unit 1 consists of 4% HDTs interbedded with thin low-density turbidites (LDTs) and muddy intervals, and represents an intermittently active levee during high sea level. By contrast, Unit 2 contains 75% HDTs with an average thickness of 0.90 m, which are interbedded with LDTs, and suggest an active levee complex during a glacial period. Similar scenario for Unit 3. Unit 4 features LDTs interbedded with mud, whereas Unit 5 features a predominant silty to muddy layer with limited HDTs. Units 4 and 5 are interpreted to represent a time of sea-level rise and trapping of sands on the shelf, or migration of the channel-levee complex away from the core location. The absence of a discernible cyclic pattern and the presence of large clasts within these ‘megaturbidites’ intimate potential triggering mechanisms such as seismic activity or slope failures. We plan to improve geochronological control on turbidite deposition using optical luminescence dating, thereby constraining our interpretative framework in time, and helping us unravel the intricate relationships between climatic influences and triggers for these extraordinary turbidites.
2021
-
Investigating the Fate of Mg-Bearing Calcium Carbonates during Early DiagenesisMaster theisis at the University of Kansas, 2021The formation of dolomite at low temperature (< 80 °C) is uncommon in modern environments, however dolomite is abundant in the geologic record. The paradox between the scarcity of modern dolomite and abundance in ancient dolomite has been of long-term interest to geologists. Further, because dolomite comprises many prolific carbonate reservoirs, there are practical needs for understanding dolomite formation as it benefits petroleum exploration and development. Dolomite abundance in geologic history also reflects the secular variation of seawater through time and is a key mineral in probing past change in climate. This study investigates whether dolomite can form from seawater in the presence of carboxylated organic matter (COM), and if the presence of COM further facilitates Mg incorporation into calcium carbonates under conditions that approximate early diagenesis and burial. The study compares Mg-incorporation in carbonate precipitated from a solution with the composition of an idealized Silurian seawater in the presence of functionalized (–COOH) organic matter followed by moderate increases in temperature (T) and pressure (P), typical of diagenesis. Three series of experiments were conducted to explore carbonate precipitation at surface conditions (T = 40 °C, and P = 15 psi), followed by rapid sedimentation and burial during early diagenesis (T = 40 °C, and P = 160 psi, 200 psi, 550 psi and 900 psi), and simulated diagenesis (calculated based on thermobaric gradient 1 °C/122 psi; T = 40 °C, 40.5 °C and 47 °C; P = 100 psi, 160 psi and 900 psi). High Mg-calcite (mol% MgCO3 11.5%) and aragonite were identified by XRD in all the vessels after incubation at surface conditions (T = 40 °C, and P = 15 psi). As pressure increased apparent dissolution of calcite and spherulitic aragonite was observed based on analysis by SEM. During the simulation of diagenesis (additional increases in pressure and temperature), saturation indices for carbonate minerals increased, but mol%MgCO3 of calcite slightly decreased. Regrowth of calcite and new fabric of aragonite were observed under SEM, suggesting possible reprecipitation. Generally, there were few differences in bulk fluid geochemistry and mol%MgCO3 of calcite precipitates between experimental and control vessels, which is probably due to the slow incorporation rate and the short incubation time (4 months). However, amorphous calcium carbonates nucleated on the surface of COM exhibited solid Mg:Ca ratios slightly larger than calcite that precipitated homogeneously from solution. This suggests that COM may facilitate Mg incorporation into calcite but under experimental conditions in this study, does not facilitate detectable dolomite nucleation nor formation. Aside from COM, the effect of temperature and pressure on carbonate precipitation are also investigated here. Based on Phreeqc modeling of Silurian seawater composition, the saturation indices (SIs) of calcite, aragonite and dolomite increase with increasing temperature (< 65 °C), and slightly decrease with increasing pressure. While detectable dolomite was not formed in experiments that simulated precipitation under sea surface conditions nor during subsequent simulated diagenesis, changes in mol%MgCO3 of calcite was observed as a function of pressure and COM. While pressure may play a role in the incorporation of Mg into the calcite structure, it is not clear from this study that its effect is large. Given adequate time for nucleation and precipitation, however, which may not have occurred due to the brevity of the experimental protocol, it is hypothesized that high Mg-calcite or dolomite is most likely formed through COM-mediated processes.
2020
- Geological JournalOrigin and tectonic implications of granitoids from the eastern segment of the South Altyn Block, North‐western China: Constraints from petrogeochemistry, zircon U–Pb datingGeological Journal, 2020
The South Altyn Block (SAB), located along the southern margin of the Altyn Tagh in Qaidam Basin, has a significant relationship with the tectonics of the Qaidam Basin basement. This study presents the petrological features, geochemical compositions, and zircon U–Pb and Hf isotope data of four granitic plutons from the eastern segment of the SAB to constrain the petrogenesis and tectonic setting of this region during the Palaeozoic. Basing on previous U–Pb dating results, the zircon U–Pb analysis in this study suggests that Palaeozoic magmatic events can be subdivided into four episodes: Late Cambrian (approximately 502 Ma), Late Ordovician (approximately 444 Ma), Early Devonian, and Middle Permian (approximately 271 Ma). The Palaeozoic granitoids were derived mainly from Neoproterozoic juvenile crustal components, with minor palaeoproterozoic ancient materials. The S- and I-type granitoids in Late Cambrian indicate a compressional tectonic environment with respect to subduction, and A-type granitoids suggest post-collision regime. The Late Ordovician granodiorites of A-type imply typical magmatism within a post-collision extensional setting. Ascribing to the subduction of Palaeo-Tethys Ocean during the Devonian, S-type granites were emplaced in the Early Devonian accompanied with the crust thickening. The Middle Permian magmatic events include a series of S-type granitoids, demonstrating the setting of oceanic subduction along with the closure of the Palaeo-Tethys Ocean.
2018
- DolomiteControlling Factors of the Ordered Index of DolomiteScience and Technology Innovation Herald, 2018
Through compiling and analyzing a dataset on the ordering index of dolomite, formed by three types of dolomitization mechanisms: synsedimentary dolomitization, mixed-water dolomitization, and burial dolomitization, this data-driven research shows that the ordering index of burial dolomite is the largest and increases with increasing burial temperature, followed by mixed-water dolomite, with synsedimentary dolomite having the lowest average ordering index. Referring to previous researches on factors affecting the ordering of dolomite and experimental results on synthesizing high-temperature dolomite, this study further explores the relationship between Mg²⁺ and Ca²⁺ ratios, MgCO₃ content, dolomite content, impurity metal ion content, burial temperature, and the ordered index of dolomite formed by the three processes: synsedimentary, mixed-water, and burial.
2017
- Earth ScienceShallow Water Delta Sedimentation and Source to Sink Process in the South Slope Belt, Dongying SagEarth Science, 2017
The study of Source-to-Sink system is a hot topic in geology research. During the sedimentary period of the second member of the Shahejie Formation (Es2), the structural stable south slope belt in the Dongying sag and its source area Guangrao uplift constituted a complete Source-to-Sink system. In this study, we analyze the paleogeomorphy, the characteristics of sediment transfer pathways and the braided shallow-water delta depositional system based on cores, logging, analytical experiment data and 3D seismic data. This paper presents in detail the sedimentary system distribution, the spatial and temporal relationship, the dominant factor of sedimentary process and sediment-dispersal patterns of the Source-to-Sink system in study area by the seismic attribute and lithology analysis. The results show there are three (i-iii) catchments, four (V1-V4) paleo-valleys from west to east in the source area. The clastic sediments supply to the deposition area, which is shore-shallow lake deposit environment gentle slope (0.52°-1.29°), by the transportation of paleo-valley. This process contributes to a moderate sorted, well rounding pebbly sandstone braided shallow-water delta system that river channel diverges frequently in the plane, several positive rhythm sediments overlay vertically. The sedimentary bodies increase from lower Es2 to upper Es2. The vertical evolution of the sedimentary system is mainly controlled by the lake-level fluctuation resulted from the paleoclimatic change. In the plane, the form and scale of the lobes body in I-III sedimentary area are controlled by the geomorphology vertical elevation difference of the source area, the area of the catchments, the form and scale of the pathways. It shows a positive correlation among the area of the lobes body, the vertical elevation difference and the area of the catchment.
