Anatomy and
Weather Induced Internal Heterogeneities of a Pleistocene Carbonate Coastal
Dune (Rejiche Formation,
Hasler, Claude-Alain1, Gregory
Frébourg1, Eric Davaud1 (1)
Carbonate wind deposits (eolianites) form
large porous bodies, which are of significant economic interest as they may
constitute aquifer or hydrocarbon reservoirs. The Rejiche formation is
characterized by shallow-water to eolian, ooid-rich carbonate deposits. In the
el Bibane lagoon area (southeast Tunisia), this formation builds a coastal belt
over 40 km long and several hundred meters wide, and restricts access to the
open sea from the shallow-water lagoon. These Pleistocene deposits (istotopic
stage 5e) have not been submerged by the sea and have been cemented early under
vadose conditions. The Rejiche formation has been used for building stones
since the Roman times.
The unused quarry of Slob ech-Chergui has
ideal outcrop exposures in the eolian facies that reveal numerous vertical
(both perpendicular and parallel to the coastal belt) and horizontal sections.
They allowed the precise mapping of the microfacies that comprise these fossil
dunes. Microfacies were defined according to depositional processes such as
grainflow, grainfall or wind ripples, which relative abundance depends on
weather conditions. These Facies have their own diagenetic evolution as well as
specific ranges of porosity (primary or secondary) and permeability.
Using geographic information system
software, a 3D distribution of microfacies was obtained, which enabled us 1) to
reconstruct the dunes' evolution through time in order to use it as a
paleoclimatic record (wind directions, rain occurrences, vegetal cover) 2) to
quantify the microfacies relative abundance and the internal petrophysic
heterogeneities for this kind of deposit, 3) to predict the internal
heterogeneity variations due to weather changes.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California