Sea Level and Current Dominated Diagenetic Regimes of the Kardiva Platform, Maldives.

Abstract

While the role of fluid flow has been well qualified as critical to dolomite formation, less attention has been given to the role of bottom-currents and their ability to act as a seawater pump. Dolomite has long been of interest to petroleum geologists as significant reserves are contained in dolostones (Sun, 1995) and dolomitization can be a significant control on reservoir quality (Sun, 1994; Rahimpour‐Bonab et al., 2009). Using stable isotopes, strontium isotope dating, x-ray diffraction and petrographic methods, we sought to categorize the diagenetic signature of both sea level and bottom-current induced flow at IODP Expedition 359 Sites U1645, U1466, U1468, U1469, and U1470. Stable isotope values show evidence for subaerial exposure and alteration by meteoric fluids prior to drowning. The drift deposits overlying and adjacent to the platform show a consistent change in mineralogy characterized by the disappearance of aragonite and high magnesium calcite coupled with increased dolomitization. The interstitial water chemistry at U1465, U1469 and U1470 showed relatively constant values over the first 65-150 mbsf at these sites reflecting pore water with values similar to that of mean seawater. Prior to the drowning of the platform ~13 Ma, sea level was the major driver of diagenetic events. This is best demonstrated by the exposure of the platform between 14.3 – 14.7 Ma. Following drowning, bottom currents enhanced an advective flow regime, which appears to be linked to dolomitization events and possibly dissolution involving mean seawater. This multi-phase diagenesis of the Kardiva Platform suggests a complex paragenetic history that has direct implications for the diagenetic histories of isolated carbonate platforms during the Miocene in the Indo-Pacific region.

AAPG Datapages/Search and Discovery Article #90351 © 2019 AAPG Foundation 2019 Grants-in-Aid Projects