Resolving Eustasy from Neotectonics in the Sea-Level History of the Pliocene to Holocene of Qatar
Authors: Jameson Jeremy , Strohmenger Christian J. 
Published: May 2016

The evolution of coastal plains, their inhabitation patterns, present day shape, and surface hydrology of Qatar are related to changes in relative sea-level. Several factors, acting on different time scales, have contributed to sea-level changes. These include tectonism, glacio-eustasy and possibly isostatic rebound. The peninsula shape is the surface expression of the Qatar Arch, one of the largest structural features of the Arabian Plate. It plunges northward into the Zagros foredeep. Tertiary age, compressional flexure of the foredeep and plate tilting associated with Red Sea rifting are likely tectonic forces.

Previous studies indicate the Arabian Gulf was a fluvial plain during the last glacial maximum 18,000 years before present (yr BP). The Gulf began flooding 14,000 yr BP in response to ice melting. The period between 14,000–9,000 yr BP is marked by a rapid rise (2m/100yr). Age dating of coastal deposits indicates that sea-level was about 2–4 meters higher than present between 8,000-3,000 years BP. Most coastal deposits are relicts of this sea-level highstand. During this period coral reefs formed a discontinuous fringe around the windward and oblique coastlines. A sea-level drop approximately 2,000 yr BP may account for the demise of the fringing reefs. Similar beaches are found elsewhere along the Gulf.

The occurrence of Pliocene age fluvial gravel deposits of the Hofuf Formation on hill tops 30 to 90 meters above sea-level are interpreted as related to long term tectonic uplift, associated with the evolution of the Zagros foredeep and structural tilting of the Arabian Plate. Pleistocene shoreline deposits may be part of the same structural flexural event or reflect the marine isotope stage 5e.

Data from Pliocene to present suggest that the sea-level history of Qatar reflects relatively high-frequency changes in seal-level driven by eustasy superimposed on a long term pattern of tectonic uplift.

Introduction

Relative changes in sea-level are a primary control on the sedimentological evolution of coastal plains, climate and human habitation. Coastal plains along the southern margin of the Arabian Gulf have been of particular interest to the oil and gas industry as an analogue to ancient evaporitic carbonate ramps in the subsurface (Jameson and Puls, 2009, Tucker and Wright, 1990). The influence of plate tectonics on Holocene sedimentation patterns in Qatar and elsewhere along the southern Gulf has not been well documented. The presence of beaches stranded well above present sea-level along the southern margin of the Gulf has been well known for over 40 years (Kassler,1973). However, little attempt has been made to establish the origins for these events or examine the impact of relative sea-level changes on depositional patterns.

The 11,700 year span of the Holocene is simply too short to capture longer range tectonic processes. This paper derives tectonic data from surface geology from the Miocene-Pleistocene Hofuf Fm. (Al-Saad et al, 2002) and Pleistocene outcrops along the present day coast. Holocene sedimentation patterns are compared to both the long term tectonic trends and well-established, post glacial eustatic sea-level changes in order to document the relative influences tectonics and eustasy on sedimentation.