Progradation of a Middle Eocene Carbonate Slope System, Assamoud Field, Sirte Basin, North Central Libya – Implications on the Dynamics of Lateral Growth of Isolated Carbonate Platforms

Abstract

This study investigates the internal configuration and stacking patterns of well-defined prograding clinothems within the middle Eocene Gialo Formation in the Assamoud Oilfield of the Sirte Basin through an integrated analysis of wire-line log and three-dimensional seismic data. The clinothem interval forms a highstand systems tract that is bounded by a downlap surface at the base and a sequence boundary at the top. The prograding clinothems occur over an area of at least 8 km wide along strike and at least 9.5 km along depositional dip. They range in height from 240 to 330 m and have a N progradation direction. Nine clinothems were identified on the basis of stacking patterns of log facies. Individual clinothems are 47–139 m thick and consist of a thin shale unit at the base overlain by thick limestone units. The clinothem interval is interpreted as a slope system and can be divided into two packages on the basis of their log facies, seismic characteristics, and position along the platform: a proximal package composed of high-angle sigmoidal clinothems and a distal package with low-angle sigmoidal pattern. The maximum slope angle of the proximal package is 24° and that of the distal package is 16°. The decrease of slope angle may be caused by an increased amount of siliciclastic mud. The progradation direction indicates that the major sediment source, which is most likely the platform top and margin, was located to the south of the study area. The sediments entered the slope from the platform margin and were redistributed downslope by surface currents driven by southerly probably Sirocco-like winds. The evolution of the platform was controlled by several factors. A pre-existing isolated platform to the south generated the topographic relief between the platform top and slope. Sea-level rise generated accommodation space, whereas sea-level fall caused subaerial exposure and terminated progradation. Subsidence caused a sea-level rise and enhanced accommodation space for platform expansion. Prevailing currents determined the direction of platform lateral growth. The results provide insights on the dynamics of carbonate platform lateral growth and may serve as an analog for future studies on carbonate slope systems.

Department(s)

Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Carbonate; Clinothem; Isolated Platform; Libya; Sirte Basin; Slope

Geographic Coverage

Libya

Time Period

Middle Eocene

International Standard Serial Number (ISSN)

0264-8172

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2021 Elsevier, All rights reserved.

Publication Date

01 Jul 2021

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