THE LOWER PALEOZOIC OF OMAN AND ITS CONTEXT IN THE EVOLUTION OF A GONDWANAN CONTINENTAL-MARGIN

The Lower Palaeozoic Haima Group of the Sultanate of Oman comprises a sequence dominated by siliciclastic rocks up to several kilometres thi ck and broadly divisible into two groups. The sequence is known in out line from subsurface exploration, but recent field work on outcrops in the isolated Huqf area in east-central Oman has allowed a more detail ed environmental interpretation of the succession. At the base coarse continental deposits of the Lower Haima Group rest unconformably on Pr ecambrian-Lower Cambrian Huqf Group sediments (mainly carbonates and e vaporites). The overlying Upper Haima Group comprises from base to top the aeolian dominated Amin Formation, the non-marine (coastal plain) to shallow marine (intertidal-subtidal) sediments of the Andam Formati on, the non-marine to marginally marine Ghudun Formation, and the comp lex cyclical deep to shallow water deposits of the Safiq Formation. Co rrelation of the Haima Group of Oman with the Lower Palaeozoic of the Arabian Peninsula, North Africa and Iran allows the evolution of the G ondwanan margin to be modelled. A widespread Lower Cambrian sequence o f coarse alluvium, resting on peneplained Upper Precambrian-Infracambr ian Huqf Group strata, represents the final stage of uplift and basin fill associated with the Late Proterozoic suturing of Arabia and adjac ent plates which resulted in the formation of the Gondwanan continent. The overlying thick sequence of continental (fluvial and aeolian) sed iments was deposited in a series of stable intracratonic basins across the Gondwanan landmass. In the Mid- and Late Cambrian an overall sea- level rise led to the repeated development of shallow marine shelf car bonates across the margin. The subsequent replacement of this marginal carbonate sequence with a thick marginal to non-marine, sand dominate d sequence may reflect the interplay of several events: the drift of G ondwana towards more southerly latitudes, a phase of strong tectonic r ejuvenation during the latest Cambrian-Early Ordovician, and/or a eust atic fall in sea-level. Organic-rich marine mudrocks were deposited ov er much of the Gondwanan platform during a series of marked eustatic s ea-level rises during the Mid-Late Ordovician and Early Silurian. In O man no evidence has yet been found for the significant Late Ordovician glacial event recorded from North Africa and Saudi Arabia.