Collaborative Research: On how the Bengal-Nicobar fan deposition influenced carbonate cementation in the incoming sediment to the Sumatra subduction zone (IODP Exp 362)

GSTDTAP

项目编号	1833269
	Collaborative Research: On how the Bengal-Nicobar fan deposition influenced carbonate cementation in the incoming sediment to the Sumatra subduction zone (IODP Exp 362)
	Kitty Milliken
主持机构	University of Texas at Austin
项目开始年	2018
	2018-09-01
项目结束日期	2020-08-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	65453(USD)
国家	美国
语种	英语
英文摘要	The precipitation of carbonate cements, like calcite, changes the physical and mechanical properties of sediments. Depending on the nature of the sediment and its location relative to zones of seismic activity, like subduction zones, carbonate cementation may decrease porosity and permeability and increase sedimentary section rigidity. It can also impact the slip on faults and earthquake rupture processes. Precipitation of carbonate during the alteration of sediments in subduction zones with burial and increasing temperature (i.e., diagenesis) can also provide an important sink for carbon, which may be released from rocks undergoing alteration deeper in the section or by devolatilization and other water-rock interaction processes. Thus, carbonate precipitation in subduction zone sediments can have a significant impact on the carbon cycle. This research examines the formation of carbonate cements in siliciclastic rocks in a major submarine fan deposit within the Sumatra subduction zone. Processes related to the alteration of siliciclastic sediments and their cementation by carbonate will be studied as will processes related to microbially-mediated carbon cycling. Research activities include petrographic investigation of mineral and textural relationships of sediment and cement grains using state-of-the-art imaging technologies. The geochemistry of samples, including stable isotope analyses of carbon, oxygen, and strontium and trace metal compositions of the sediments and their constituent materials will be carried out to try and identify signatures of different processes leading to the formation of carbonate cements. The study will also include work to characterize intergranular pore spaces and grain boundary relations, especially with regard to changes in porosity, permeability, and mineral dissolution features. Project goals include (1) determining the role of carbonate cements in porosity reduction and rock property evolution in subduction zone siliciclastic sediment packages; (2) evaluating the impact of carbonate cement precipitation on the carbon cycle; and (3) determining the thermal and chemical conditions that lead to carbonate cement formation in subduction zone sediments. Broader impacts of the work include student training and incorporation of research into courses. The investigators will work with organizations associated with their home institutions to attract members of groups underrepresented in the sciences and engage them in the research. The investigators will work with students and educators to develop materials to be used in secondary education settings. The project supports two investigators whose genders are underrepresented in the sciences, one of whom serves as a role model for minority students. Whereas we have a solid understanding of carbonate formation driven solely by carbon cycling, either recrystallization of biogenic carbonate or precipitation of methane-derived authigenic carbonate, another mechanism that may significantly influence the formation of sediment cements is where silicate mineral alteration during diagenesis produces bicarbonate and cations that favor precipitation of carbonate minerals. Diagenetic carbonate precipitation efficiently sequesters carbon. Because carbonate in sediments may be released during diagenesis from subducted rocks by devolatization and/or fluid-induced dissolution of calcium carbonate, knowledge of carbonate-carbon inventories in input sediment sequences to subduction zones is important to constrain the inputs to Earth's surface carbon reservoirs. Furthermore, the formation of diagenetic carbonate cements changes the physical and mechanical properties of the hosting sediment, altering its permeability and mechanical strength. The cementation process and the role of silicate weathering on authigenic carbonate formation in marine systems is not well understood. This work documents the relative roles of the coupled carbon-silica system in generating carbonate cements and depositing carbon-bearing minerals in cores of subduction-related siliciclastic sediments. Sediment samples from the Nicobar Fan from the Sumatra subduction zone were selected because they exhibit significant carbonate cementation, having been recently collected on an International Ocean Discovery Program (IODP) drilling expedition to the Indian Ocean. The research focuses on testing the hypothesis that Nicobar Fan carbonate cements formed at depth during burial and diagenesis due to the generation of alkalinity from the alteration of non-carbonate siliciclastic material. Research tasks include (1) comparing the relative roles of carbonate formation through traditional carbon cycling pathways with those via the proposed coupled silicate-carbonate system; (2) identifying chemical reactions in the sediments that lead to carbonate formation; and (3) understating conditions that promote carbonate precipitation from subsurface marine silicate alteration. Sediment samples will be examined petrographically and subjected to X-ray elemental mapping and cathodoluminescence imaging by field-emission scanning electron microscopy. Samples will also be analyzed geochemically. High-resolution carbon, oxygen and strontium isotopes and clumped stable isotope analyses will be carried out in addition to analyses of trace element composition. Data will be used to determine the role of subsurface marine silicates in carbonate cement formation and identify sediment fabric/porosity changes associated with it. Results will contribute to our understanding of the interdependence among fluid-rock reactions, element cycling, and porosity reduction in siliciclastic-dominated systems that experience methanogenesis and will improve our understanding of global carbon budgets, sediment rheology, and faulting in subduction zones. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/73166
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Kitty Milliken.Collaborative Research: On how the Bengal-Nicobar fan deposition influenced carbonate cementation in the incoming sediment to the Sumatra subduction zone (IODP Exp 362).2018.