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