Micritization and Other Taphonomic Processes at the Origin of Peloids in Shallow Marine Carbonates (Arabian Gulf, Arabian Sea, Red Sea)

In numerous carbonate reservoirs in the Middle East, peloidal wackestone-packstone-grainstone facies are rock types with excellent pore storage potential in microporous grains. However, the origin of the micro-porosity and associated micro-spar remains unclear. Our hypothesis is that both micro-spar and porosity originate from early marine miciritization later altered during subsequent diagenesis. This study examines and compares the micritization products and internal structure of peloids in different shallow marine carbonate environments around the Arabian Plate using optical microscopy and backscattered scanning electron microscopy (BS-SEM). First, we noted the close and systematic relationships between the cryptocrystalline microtextures, microborings and the various phases filling in microborings. We reported high level of micritization along the western (Saudi Arabia) and the southeastern (UAE) coasts of the Arabian Gulf, and in the lagoonal settings of the Red Sea (Saudi Arabia). In the Abu Dhabi section of the UAE coast, the most common taphonomic sequence that produces peloids involves: (1) a moderate endolithic activity, (2) the rapid filling of microborings by radial banded cements and (3) mechanical erosion and transport. This sequence occurs preferentially in subtidal to lower intertidal zones, moderate in energy and free of vegetation (i.e., ooids, sandy shoals, tidal channels, lagoonal terraces). The processes seem to be similar to what occurs on modern sediment of the Great Bahamas Bank (i.e., concurrent micritization). On the other side, along the Arabian Sea coast (Oman) grainy sediment only shows intense endolithic activity but lack cement filling in microborings (ie., only microbored grains).