Sea-Level versus Bottom-Current Influenced Diagenesis

• Main Author: Prince, Kieron Caleb
• Other Authors: Laya Pereira, Juan Carlos, Pope, Michael, Grossman, Ethan, Alvarez Zarikian, Carlos
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Subaerial exposure; sea level; dolomite; calcite; stable isotopes; Maldives; Kardiva; carbonate; Antarctic; East Antarctic Ice Sheet; Indian; Antarc*; Ice Sheet
• Online Access: https://hdl.handle.net/1969.1/191825

This study presents the diagenetic evolution of the Kardiva Platform, Maldives, located in the tropical region of the Indian Ocean off the southwest coast of India. This drowned carbonate platform was susceptible to high amplitude sea-level variation as well as intense climate events during the Neogene. International Ocean Discovery Program Expedition 359 Sites U1465, U1466, U1468, U1469, and U1470 were situated in waters between 400 and 522 meters with the study interval covering over 1400 m of core. These cores were studied using stable isotopes of C and O, strontium isotope dating, x-ray diffraction and petrographic methods. The Kardiva Platform was impacted by subaerial exposure due to glacially controlled changes in sea-level during the expansion of the East Antarctic Ice Sheet (EAIS). The evidence of exposure and meteoric alteration is restricted to the platform sequences (PS) which show a major exposure surface, characterized by negative excursions in values of δ¹⁸O and δ¹³C, and low strontium and magnesium elemental concentrations for carbonate cements. This represents the first identification of subaerial platform exposure for Miocene carbonate sediments in the Maldives and provides a record of sea-level in an area where this is not well constrained. Dolomite samples showed a series of characteristics including decreasing crystal size from margin to slope, a flat-topped geometry to the ~50 m subsea dolomite body, cool dolomite formation temperatures (~14°C), and non-stoichiometric dolomite compositions (39-44 mole% MgCO₃) that are incompatible with the commonly invoked Kohout Convection model. We propose a new model whereby oceanic bottom-currents created the “current pumping” of seawater through the upper ~100 meters of the older platform and younger periplatform deposits to create subsurface dolomite. At Site U1468, inflections from decreasing to increasing crystal sizes occur at or below the interglacial surfaces. This trend suggests the presence of an up to 20 - 25 m deep advective zone in the ...