Abstract: Sedimentological Study of the Hamra Quartzites in Ghadames Basin: A Sequence Stratigraphy Approach

ZERIOUL, ABDELLAH

The sequence analysis of the Ordovician formations in the Ghadames Basin, using sequence stratigraphy concepts, allows one to distinguish two second order eustatic cycles: A first cycle S1, of Tremadocian age, consists of two depositional systems tracts (TST and HST). A second cycle S2, attributed to Arenigian, Llanvirian, Llandeilian and Caradocian stages, consists of three depositional systems tracts (LST, TST and HST).

The Hamra Quartzites Member corresponds to a lowstand systems tract (LST) of Arenigian age. It is bounded by a sequence boundary (SB) at the base and a transgressive surface (TS) at the top. These prograding deposits form a relatively homogeneous bed set of quartzites and compacted quartzic sandstones, showing a cylindrical shape on gamma ray curves.

The Hamra Quartzites are generally fine-to medium-grained, bioturbated and containing at the base some thin sandstones and silty shales. They are distinguished by the abundance of tigillites and planar cross-bedding indicating shallow-marine environment and strong surface hydrodynamics.

From a reservoir point of view, the Hamra Quartzites is a fractured and compacted reservoir, with low porosities, between 3 and 6%. Indeed, the compaction phenomena caused a strong reduction of the primary porosity. The interest of the Hamra Quartzites reservoir is related to the fracturing which is related to important improvement of the permeability, enhancing the production potential, and to the consistency of the sandstone thickness and properties all over the basin.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria