Facies Analysis of Remobilised Carbonate Sediments in the Eocene Thebes Formation, Hammam Faraun Fault Block, Gulf of Suez

The Hammam Faraun fault block on the western Sinai Peninsula, Egypt, records excellent pseudo-3D exposure of the Eocene Thebes Formation, a 500 m thick succession of remobilised slope and basinal carbonates. This succession has been partially dolomitised, and the overall aim of this study is to determine the influence of pre-dolomitisation stratigraphy and lithofacies on patterns of diagenesis. Although palaeoflow indicators suggest sediment supply from a northerly platform margin, the architecture of the platform to basin transition remains poorly constrained. A critical objective of this project is therefore to reconstruct the local and regional palaeogeography in order to build a predictive model of facies distribution within the study area.

Sedimentary logging, field mapping and microfacies analysis reveals four principal facies associations:

(i) Matrix-supported debris flows that are characterised by poorly sorted, angular to subrounded clasts (2 cm to 1 m) of Nummulites grainstone or dolomitised foraminiferal pack/wackestone. The matrix surrounding the clasts is a Nummulites wackestone. The angular, poorly sorted nature of the debris flows implies deposition during rapid, chaotic flow on the platform slope.

(ii) Clast-supported conglomerates that infill scours that dissect the debris flows and contain clasts of subrounded to rounded foraminiferal algal grainstone. The high degree of rounding and lack of matrix in these conglomerates implies channelised flow over significant distance with deposition at toe of slope.

(iii) Grain flows of benthic foraminiferal grainstone that contain delicate dasyclad algae, red algae, and foraminifera characteristic of a quiet shallow shelf environment. Preservation of such delicate material was most likely facilitated by marine phreatic calcite cementation.

(iv) Laterally continuous beds of skeletal wackestone and mudstone, dominated by planktonic foraminifera, are interpreted to be pelagic sediments deposited within an outer slope to basinal environment.

A model will be presented by which the spatial distribution of remobilised deposits will be described, and body geometry quantified within the context of the regional platform to basin transition. This will then provide the framework for an assessment of the importance of depositional rock texture on subsequent diagenetic modification, and consequently the role of sedimentary architecture on controlling permeability distribution within this succession.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California