JASSIM, SAAD Z., School of Earth Sciences, Leeds University, and CHRIS M. GREEN, GETECH, Leeds University, UK

Abstract: The Basin Configuration, Tectonic History and Hydrocarbon Potential of Northern Arabia

Introduction

Northern Arabia, the NE corner of the Afro-Arabian plate, covers N Saudi Arabia, Qatar, Kuwait, SW Iran, Iraq, Jordan, Syria and SE Turkey. For this study, data from over 400 wells, gravity, magnetic and seismic data, geological maps and over 200 published papers and unpublished reports were used. Structural and isopach maps were constructed, which, along with 2D and 3D modelling of gravity data and Euler deconvolution of magnetic data were used to compile a depth map to the Precambrian basement, a 3D of which is shown in Fig.1. Using structural maps of the various units,Time Temperature Index was calculated to important source levels within the sedimentary column.

Tectonic Framework

A new tectonic map has been compiled from gravity and satellite images, known anticlines, basins and uplifts. The interpreted tectonic zones reflect the tectonic and depositional history of the blocks they represent; tectonic zones and faults are shown in Fig.2. The tectonic history of the zones has been influenced by four major tectonic events that left characteristic signature on their trends, internal structure and sedimentary column, these are:
1. The Late Precambrian Idsas Orogeny (N-S) largely influenced the Early Paleozoic history in central Arabia.
2. The Late Silurian to Middle Devonian "Caledonian" event, characterised by NE-SW oriented uplifted and depressed blocks, resulting in partial removal of the Early Paleozoic sequence from the elevated blocks. Two elevated blocks, the Aleppo and the Tanf-Khlesia zones, are representative of this event.
3. The Late Carboniferous-Early Permian "Hercynian" event, characterised by N-S blocks with characteristic intra-block horst and graben development.Two elevated blocks, the Salman-Summan and the Risha-Tabuk Zones are evident; the earlier Aleppo and the Tanf-Khlesia blocks were also re-activated during this event.
4. The Cretaceous-Neogene Alpine events ( NW-SE and E-W trend) were superimposed on the older blocks and largely affected the eastern and northern parts of N Arabia, masking previous tectonic trends.The Mesopotamian, the Foothill, the High Folded and the Mardin zones are representative of this orogenic event.

Geological History and Hydrocarbon Potential

Infracambrian sediments were deposited in two basins separated by the remnants of the Idsas Orogeny, a western basin with thick synrift volcano-sedimentary sequence overlain by sheet clastics and an eastern basin characterised by saliferous sabkha-type sediments. The Cambro-Ordovician started with fluvial then marine sedimentation terminating with glacial event.The Silurian was characterised by worldwide sea level rise and deposition of open marine shale followed by fluviomarine sands.The late Silurian to Middle Devonian "Caledonian" epiorogenic event resulted in the deposition of terrestrial to shallow water marine clastics only on the depressed blocks. Late Devonian and Early Carboniferous marine shale and carbonate were unconformably laid down over the "Caledonian" surface and in the whole region.

The Late Carboniferous and Early Permian represented the period of the syn-Hercynian block disturbance, the most important of which is the elevated Salman-Summan block of Central Arabia. The Risha-Tabuk block was tilted towards the east; its western part was stripped to the basement. On the depressed blocks some limnic, locally coaliferous, clastics were deposited.

During the Late Permian to Triassic the elevated Salman-Summan block was depressed while the depressed block of W Iraq was uplifted to form the Rutba Uplift.Triassic deposition was centred on the Salman-Summan block, N Iraq and the Palmyrides and characterised by alternation of shallow marine carbonates and shale.The Rutba Uplift dominated W Iraq and SE Syria during the Jurassic and Cretaceous, and sedimentation shifted to the Unstable Shelf. The Jurassic-Cretaceous basins were strongly influenced by NE-SW blocks resulting in variations in thickness and facies along the axis of the basin. The Late Cretaceous was characterised by strong Intra-Shelf grabens with phosphorite-rich sediments.

The Tertiary, especially the Neogene, was strongly influenced by the Alpine collision of the Arabian and the Iranian-Turkish plates and the deposition of a thick molasse sequence in NE and E Iraq, SW Iran and the Gulf. Thick Tertiary sequence was laid down within the Dead Sea graben.

Maturity calculations and organic matter distribution have been used to identify potential hydrocarbon systems. Significant hydrocarbon potential has been identified in the Silurian, the Devonian-Carboniferous, the Permian and throughout the Mesozoic, with more local potential in the Ordovician and Tertiary. Generally the older systems are more significant in the west and the younger systems in the east.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England