MALPAS, JACQUI A., University of Manchester, Dept. of Earth Sciences, Manchester, UK

ABSTRACT: Integrated Sedimentological and Palaeontological Analysis of Marine Flooding Surfaces: A Case Study of the Miocene, Nukhul Formation, Gulf of Suez

Breaks in sedimentation are commonly recorded within sedimentary successions as distinctive stratal surfaces. These surfaces form as a result of the interaction of depositional, biological and diagenetic processes. In ramp settings there are gradual along-strike and down-dip changes in facies. In contrast, where tectonics exert a major control on accommodation, rapid changes in stratal surface characteristics are common.

A study of the well-exposed marine flooding surfaces within the Miocene, syn-rift Nukhul Formation sediments, Gulf of Suez, has identified rapid variations in surface character associated with tectonic faulting. The regionally correlatable marine flooding surfaces show considerable changes over 12 km².

In proximal settings, the sandstones have calcite-cemented upper surfaces colonised by oysters with Thalassinoides networks. Down-dip, the sandstones rapidly shale-out into bioturbated mudstones, with the unit tops marked by concretions. The cements are both ferroan and non-ferroan calcite, and pyrite with dolomite concretions within the basinal mudstones.

Based on this evidence, the marine flooding surfaces are interpreted as resulting from a sedimentary hiatus allowing time for colonisation by both epi- and infaunal organisms and time for bacterially-mediated carbonate cement precipitation processes to proceed.

The variation indicates that along-strike and down-dip changes in accommodation have a direct influence on the sedimentological, biological and early diagenetic processes operating during marine flooding to create rapidly changing, distinctive stratal surfaces.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid