Determining how Heterogeneous Sediments Accommodate Diagenesis

Open Access
Author:
Bose, Priyanka
Area of Honors:
Geosciences
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Matthew S Fantle, Thesis Supervisor
  • Maureen Feineman, Honors Advisor
Keywords:
  • Site 1171A
  • Grain Size
Abstract:
Carbonate proxies, specifically trace element ratios, were used to measure diagenesis in carbonate sediments from Site 1171A, located in the South Tasman Sea, from an Ocean Drilling Project. Diagenesis is known to occur in the sediment at this site, and this paper explores how a heterogeneous sediment accommodates diagenesis, and if grain size affects the extent of diagenesis. Three elemental proxies were measured in prior work: Sr/Ca, Mg/Ca, and Na/Ca, to elucidate the long-term evolution of both the climate and the ocean. Understanding constraints on these proxies are critical in both paleoclimatic and paleoceanic studies. Trace element analysis was used to analyze sediment samples to determine the molar elemental ratios for Na/Ca, Mg/Ca, and Sr/Ca for grains ranging from less than 63 μm to those measuring between 125-250 μm. For the Na/Ca and Mg/Ca molar ratios, the 63-125 μm size fraction had the most significant difference from the bulk sediment composition, while for the Sr/Ca molar ratios, the clay fraction was the most altered from the bulk sediment composition. When the molar ratios for each size fraction, and samples, were averaged together, the average value was different from the molar ratios found in the bulk sediment. Thus, some alteration is seen in the size fractions but is not seen in the bulk sediment. This alteration is proven to be diagenetic, as Sr only remains in the ocean for a small residence time, while both Na and Mg remains in the ocean for longer periods of time. These residence times indicate that the elements remain in the ocean for long periods of time, and thus, the only method for these elements to be incorporated into the core is through the pore fluid advection, as proven by Fantle (2015).