--> Depositional Pattern in the Lower to Middle Miocene Succession From Subsurface of North Kuwait

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Depositional Pattern in the Lower to Middle Miocene Succession From Subsurface of North Kuwait

Abstract

The Lower to Middle Miocene succession in North Kuwait was deposited along the southwestern margin of the NW-SE extended Mesopotamian foreland basin in the northern part of the Arabian Plate. The succession in here is dominantly clastic in nature as compared to its coeval strata in north and east where it consists of conspicuous evaporitic facies. Present sedimentological and biostratigraphic study is based on more than 800 feet of core from five recent shallow exploratory wells. Five generalized lithofacies i.e. conglomerate and pebbly sandstone, coarse to fine grained sandstone, muddy sandstone and siltstone, dolomitic siltstone, and shale are present. The facies association ideally displays stacking of these lithofacies in ascending order. These are channelized deposits where some of the channels are fluvial in origin and others show signs of marine influence, such as the presence of burrowing and fossiliferous horizons in their upper parts, and are interpreted as coastal plain and estuarine in origin. The succession is made up of four repeated fining upward cycles representing high frequency sequences. Each sequence is developed by filling in the incised valleys carved into the older bed during successive sea level drops. The proceeding rise in base level resulted in flooding in the low lying coastal areas by marine water developing into estuaries, coastal bay and lakes where fine grained facies were deposited making upper parts of the sequences. These flooding events are independently confirmed by the biostratigraphic analysis using foraminifera, ostracoda and palynology. The absence of nannofossils in these strata may indicate the presence of a barrier separating this depositional area from the open marine setting in the east. The understanding developed from this study can help in modeling the distribution of reservoir facies within the succession. Additionally, regional MFS Ng30 of the Arabian Plate is suggested to lie in the uppermost cap shale zone where the presence of Miogypsina remains is reported and the regional MFS Ng20 may lie within the lowermost shale zone of the formation.