Source to Sink of the Sarah Formation, Latest Ordovician, Northwest Saudi Arabia

Abstract

A key question that sedimentologists and stratigraphers face is, what controls sedimentary facies and grain-size trends in a depositional basin? Crucial parameters that control grain-size trends are the sediment discharged into the basin, the characteristic grain size mix of the supply, and the spatial distribution of accommodation. In this paper we present an outcrop case study of the latest Ordovician Sarah Formation, in Saudi Arabia, that represents the proximal part of a glacigenic sedimentary system or a pro-glacial outwash fan where these parameters are quantified. In this study, we examine outcrops and glacigenic valley fill deposits of the Sarah Formation in the Northwest of Saudi Arabia. The Sarah Formation is a glacigenic sedimentary unit of latest Ordovician age deposited along the palaeo-Gondwana Margin and as part of the an extensive, but discontinuous belt of outcrop deposits that extend from Saudi Arabia to westernmost North Africa. This is a 600 km sedimentary system and stretches from the northern outcrop belt of Saudi Arabia to at least the borders with Iraq. This source to sink system spans a great range of depositional environments from proximal coarse sand to pebble pro-glacial outwash fan deposits to distal diamictites and offshore fine deep marine deposits. The proximal part is an extraordinary sedimentary unit that is preserved along an elongated and complex network of palaeo-valley fill deposits. It is represented by coarse to medium sand and pebbly deposits of around 250 m thick deposited in a short time span of around 250 ky (mean sedimentation rate of 1 mm/yr). We attribute this large feature to high sediment load and bypass during the interglacial periods. We apply a source to sink approach to calculate the volume of bypassed sediment from specific regions to deposit and preserve the high abundance of coarse grained sediment. We consider controls on the sedimentary architecture with respect to observed grain sizes. We present a model of the evolution of this sedimentary system based on sedimentological and provenance work that includes petrography, heavy mineral analysis and zircon U/Pb geochronology, both in outcrop and core from wells. In addition to provenance, we try to map out sedimentary fairways from seismic regional lines. In this study we teleconnect, reconstruct and calculate sediment budgets for the sedimentary system from the outcrop to the subsurface.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015