Sequence stratigraphic architecture, evolution, and geological controls of an Eocene isolated carbonate platform, NE Sirte Basin, Libya

Abstract

The sequence stratigraphic architecture, evolution, and controlling mechanisms of a lower and middle Eocene isolated carbonate platform in the Sirte Basin in north-central Libya were interpreted from two- and three-dimensional (2D and 3D) seismic and well data. The platform contains six stratigraphic surfaces that divide the platform sedimentary successions into two stratigraphic sequences, namely Sequence 5 and Sequence 6, and five systems tracts. The five systems tracts vary in thickness and differ in depositional systems. The lowstand systems tract (LST) of Sequence 5 forms at the base of the focus interval and is composed of a basin floor fan system with hummocky to undulated seismic facies. The highstand systems tracts (HST) of Sequence 5 has the greatest thickness and comprises a well-defined slope system showing a funnel-shaped trend and suggesting progradational stacking pattern. The LST of Sequence 6 contains a middle ramp system formed during the lowest sea-level. The two transgressive systems tracts (TST) are the thinnest, several meters thick, and separating the LST from the HST. Log curves show an overall funnel-shaped motif through all three depositional systems, indicating a progradational stacking pattern. The main factor controlling the platform growth and demise is sea-level fluctuations. Additional factors, such as, subsidence, antecedent topography, and prevailing currents have also contributed to the evolution of the platform. Sea-level changes coupled with subsidence create accommodation for the platform growth and terminate deposition by drowning. The pre-existing topography creates a topographic relief and influences the growth pattern of the platform. Prevailing local currents influence the direction of platform progradation. This study provides insights on the evolution of isolated carbonate platform in a rift setting, which can help predict the lithofacies and depositional systems of economic significance.