The Structural and Geomorphic Evolution of the Persian Gulf

Abstract

The origin of the present-day morphology of the Persian Gulf has been studied and is summarized in figure 3. The Gulf is a tectonic basin of late Pliocene to Pleistocene age, whose morphology is greatly influenced by the tectonic style. The topography of Iran and the Iranian coastal islands is controlled by the intense folding of the Zagros orogeny, on NW-SE to E-W trends. The much more subdued relief of the Arabian side is the result of gentler tectonic movements: Plio-Pleistocene folding, faulting and salt diapirism, superimposed on older, predominantly north-south-trending growth structures (“Arabian folds”). There is evidence over much of the Gulf of interference between Arabian and Zagros folds.

This tectonically controlled morphologic pattern was subdued by sedimentation of Pleistocene limestones, but locally rejuvenated by Quarternary tectonic adjustments.

The sea level fell by as much as 120 m during the Pleistocene, emptying the Gulf; river valleys were eroded down the slopes. The sea then cut a series of platforms, at its level of maximum retreat and at times of relative standstill during the post-glacial rise. However, in spite of these Pleistocene physiographic modifications, the underlying tectonic control of morphology is still apparent, and there is a partial correlation between bathymetric and structural highs and lows.

The topography controls the type and the thickness of the marine sediments. Sediment type is largely a function of the biological communities which give rise to skeletal material; these vary in character from shoals to depressions. Sediment thickness is shown by sparker records to be least on topographic highs, and greatest in depressions.

The Recent unconsolidated sediments are the product of the post-glacial Flandrian transgression, which, according to Fairbridge (1961), began about 18 000 years B.P. and reached its present level about 5000 years B.P. These sediments are expected eventually to smooth out the pre-Recent topography by filling up the depressions and extending over the highs. The thickest Recent sediments are found in the Gulf axis.

The essence of this paper, with P. Kassler’s agreement, was presented by M.W. Hughes Clarke at the 1971 International Geological Congress at Heidelberg. P. Kassler is now with N.V. Turkse Shell, Ankara, but was with Shell Research B.V. Rijswijk in 1967–1968.