Biostratigraphy of the Lower Palaeozoic Haima Supergroup, Oman : its application in sequence stratigraphy and hydrocarbon exploration

The siliciclastic Haima Supergroup (Cambrian-Silurian) on the west flank of the Ghaba Salt
Basin in Oman is currently a target for gas exploration following the discovery of significant
gas reserves. An understanding of stratigraphical and facies relationships within the Haima
is crucial for their exploration and exploitation, and biostratigraphy is one of the more
powerful and cost-effective tools that can be deployed to aid such understanding. The
biostratigraphy of the Haima Supergroup is based primarily on palynomorphs. The preexisting
biozonation, comprising conventional interval zones, is of low resolution and
incorporates misconceptions over the ranges of key species. The work reported here
explicitly considered the biostratigraphy of the Haima Supergroup in the context of genetic
sequence stratigraphy. It shows that each of the postulated marine flooding events in the
Haima Supergroup is characterised by a unique assemblage of marine palynomorphs.
Intervening strata are characterised by low diversity and sometimes sparse marine
palynomorph assemblages, often comprising only sphaeromorph acritarchs, accompanied by
terrestrial cryptospores. These low diversity assemblages indicate proximal marine to nonmarine
conditions, consistent with progradation following each marine flood. The sandy
prograding deposits in the Haima Supergroup form reservoirs, which are sealed by the shales
and mudstones deposited by the succeeding marine flooding event. Lateral changes in
marine assemblages indicate onshore-offshore relationships, and have contributed towards
mapping the extent of each marine flooding event, critical for evaluation of the potential areal
extent of seals. The result is improved biostratigraphical resolution, which enables more
precise correlation between wells, and which has contributed to more detailed
palaeogeographical maps and to a better assessment of the distribution of reservoir-seal pairs.