Holocene Sabkha and Coastal Systems of Qatar: Process Models for the Interpretation of Ancient Arabian Plate Carbonate-Evaporite Reservoirs
Authors: Jameson Jeremy , Puls David , Kozar Michael G. 
Published: March 2015

Introduction

Facies tracts, sediment types, stacking patterns, and diagenetic histories of Holocene sabkhas and coastal systems of Qatar provide compelling analogues for the interpretation of ancient, carbonate-evaporite sequences of the Arabian Plate. The use of modern analogues to aid in the interpretation of geological and engineering data is well established in the petroleum industry. Analogue data are used in aid of recognition of time lines and depositional cycles, environmental interpretation, dimensional data, and continuity. Comparison of sabkhas from different physiographic regions of Qatar that formed during the latest Holocene cycle of sea level rise reveals new insights into the characterization of ancient rocks. These observations provide a basis for a substantial update of the definition and characteristic features of facies tracts described in the geological literature as sabkhas.

Much of the understanding of sabkhas comes from extensive studies of the United Arab Emirates. These works are well documented by Alsharhan and Kendall (2003). While sabkhas of Qatar have been well studied (Al-Yousef, 2003), their features are seldom incorporated into depositional models. This paper reports on some of the more fundamental aspects of Qatar sabkhas that differ from common perception.

Database

One of the consequences of the commercial construction boom in Qatar has been unprecedented exposures of the Holocene in the form of construction pits, excavations for major industrial projects, geotechnical borings, and pipeline excavations. Over the past eight years the authors have visited these sights as they became available and logged cross sections that have never been available previously. Large exposures reveal sedimentary structures in a manner that is impossible to capture in hand-dug pits or cores. This study is part of an on-going mapping of the coast of Qatar. To date, 1:10,000 to 1:20,000 scale maps have been made of the surface sediments of Dukhan, Messaieed, Al Thakhira, and Al Ruwaiys. During these studies, over 500 samples were collected, 100 thin sections were described, and 150 C14/12 radiometric age data were obtained.

Physiographic Provinces

The state of Qatar is a peninsula approximately 25 degrees north of the equator and measures 120 km north-south by 60 km east-west. The coastline varies in orientation to prevailing winds, sediment supply, and elevation profile. These factors create four major physiographic areas of sabkhas; each distinguished by variable facies types and facies proportions. All have common sea level history of rapid rise over the last 10,000 years, followed by high frequency oscillations (Al Sharhan and Kendall, 2203, Puls et al, 2008). Comparison of sabkha features between physiographic provinces provides an insight into the variability that might be expected in an ancient sabkha.

With an annual mean temperature of 25 °C, and summer means between 30–35 °C, protected coastal waters are mesosaline. High summer temperatures, low rainfall, and low humidity contribute to high rates of evaporation, particularly inland where the water table is typically within 1–2 m of the land surface.