Exploration of Shallow-Marine Carbonate Micritization Styles: Arabian Plate Coasts (Red Sea, Arabian Sea, and Arabian Gulf)

Abstract

In numerous Middle Eastern carbonate reservoirs, peloidal wackestone, packstone, and grainstone facies deposited in shallow-marine environments are rock types with excellent pore storage potential in microporous and micritized grains. While the origin of microporosity has been studied extensively, the process of early marine micritization remains unclear. One hypothesis suggests that early marine micritization first alters carbonate microtextures, which then facilitates the formation of micro spar and micropores in the micritized sediments during later subsurface diagenesis. Therefore, a better understanding of the origin and spatial distribution of micritized sediments is essential for accurately predicting the distribution of microporosity in limestones. This study examines micritization products in shallow-marine carbonate sediments from four lagoons on the Arabian plate coast: the Red Sea, the Arabian Sea, and the Arabian/Persian Gulf. Micritized grains are identified and characterized using optical and backscattered scanning electron microscopy. Petrographic observations are compared and correlated with oceanographic and environmental parameters to identify micritization styles and environmental conditions at a regional scale. The findings present several key insights: i) cryptocrystalline micritic microtextures are heterogeneous, characterized by a combinations of microborings and various microborings infill materials, ii) Red Sea and Arabian Gulf sediments are primarily made up of micritized grains, with about 60% of the grains being micritized grains or peloids, whereas Arabian Sea coast sediments are mainly microbored with minimal infill of endolithic tunnels and rare cryptocrystalline microtextures, and iii) the arid climate and warm, restricted oligotrophic seawater of the Red Sea and Arabian Gulf promote micritization. Conversely, the cooler seawater of the Arabian Sea relative to Red Sea and Arabian Gulf, largely open to the Indian Ocean and influenced by the southeast Asian monsoon and associated upwelling currents, promotes intense endolithic activity but limited boring infilling (incomplete micritization). Hence, we show for the first time that the early marine and microbial diagenetic process of micritization relate to a well-defined set of parameters of a regional environmental and oceanographic settings, corresponding to those that also promote the tropical-biochemical carbonate factory.