Sequence Stratigraphy of Mixed Siliciclastic-Carbonate Deposits of Burdigalian Dam Formation in Eastern Saudi Arabia

Abstract

Siliciclastics and carbonates show great differences during their formation within a sequence, as a result of the different factors and processes controlling their deposition. Consequently, the mixed siliciclastic-carbonate systems are considered to be more difficult to interpret sedimentologically and in term of theirsequence stratigraphy. This makes the exploration and development within these systems much more complex. This study aims to investigate, in detail, these heterogeneities using outcrop analogues of the Miocene Dam Formation in Eastern Saudi Arabia. The Dam Formation generally consists of carbonates been bounded by two continental lithostratigraphic formations. Consequently, it represents a regional transgression event in the Burdigalian stage. It was interpreted by Sharland et al., 2001 as a 3rd order sequence. The investigated outcrops of the Dam Formation display three sequences, most probably of the fourth order. The oldest and youngest sequences are both incomplete, showing only their upper and lower sequence boundary (SB), respectively, whereas the middle sequence is complete. Because of that, the interpretation is mainly related to the mid complete sequence. The (SB) identified in the studied outcrops have some subaerial exposure criteria. The facies heterogeneity indicates a great sea-level variation. The lower SB lies below a succession of sabkha deposits (dolomitic mud interbedded with evaporites) with traces of Rhizolith. Over that, an intertidal zone composed of three thickening upward sequences of mud-sandstone infers an increase in the accommodation space, which goes parallel with the criteria of the late LST. Estuarine and carbonate tidal channels cut through previous facies indicating the initiation of transgression. Upward in the sequence, wacke-packstone massive layers cover the whole older succession, and are based by an erosive sharp base, and associated, occasionally, with intraformational lag pebbles, mainly of stromatolite heads and mud clasts. An increase in the accommodation space could be interpreted because of the abrupt shift in facies from intertidal siliciclastic and estuarine channelized sandstone to channelized intertidal oolitic grainstones and subtidal lower shoreface wacke-packstone. Therefore, this facies association mainly represents a transgressive systems tract (TST) and its erosive base is mainly the transgressive surface (TS). The highstand systems tract (HST) is composed of shallowing-upward purely carbonate cycles. These cycles get thinner upwards inferring a relative decrease in the accommodation space to the sediment supply which goes parallel with the characteristics of the HST.

AAPG Datapages/Search and Discovery Article #90370 ©2020 AAPG Middle East Region Geoscience Technology Workshop, 3rd Edition Carbonate Reservoirs of the Middle East, Abu Dhabi, UAE, January 28-29, 2020