Pleistocene neotectonics and Fe-mineralizations in the Ahnet-Mouydir area (northern margin of the Hoggar Massif, Algerian Sahara)

Abstract

Strongly mineralized lithologies were found in 4 different depositional settings along the northern margin of the Hoggar Massif in southern Algeria: (1) Pleistocene fluvial terraces, (2) pebble-filled erosional furrows in marine Silurian and Upper Devonian shales, (3) sedimentary dykes in Givetian mud buildups and (4) tectonic faultfissures and cracks in Upper Devonian shales. In spite of the contrasting sedimentary environment, all these rocks display very similar properties and are considered as contemporaneous. They are characterized by high porosities, intense Fe-mineralization and a great variety of accompanying, secondary minerals formed in a subrecent continental regime under pluvial to arid conditions. The dykes, faults and cracks are direct evidence of tensional stress during the early and middle Pleistocene which has not been observed so far. The complex sedimentary and diagenetic history of conglomerates, breccias, sandstones, ferricretes, calcretes and claystones in these settings was analyzed using SEM, EDX-microprobe, XRD, transmitted and reflected light petrography and is documented in hitherto unknown details.