Palaeoclimatic events during the Middle-Upper ordovician time of the hawaz formation in the Murzuq Basin, SW Libya

الملخص EN

The Murzuq Basin of SW Libya is an immature exploration area, which has attracted extensive interest in the last few years since the discovery of recoverable of oil reservoirs.

The basin has sedimentary units forming the stratigraphic column with good correlation in the subsurface and outcrops.

The late Palaeozoic age in SW Libya is showing a critical importance change; as it is one of few records of environment glacial activity in the region.

During early Cambrian-Ordovician time, deposition of clastic sediments, mainly fluvial to shallow marine conditions sandstones occurred.

This was followed by a marine transgression during the upper Ordovician, and the subsequent deposition of transgressive marine mudstones.

The lower Ordovician sequence was deposited in shallow to fluvial environments with a cool climate during the upper Ordovician time (Melez Chograne and Memouniat Formations), and poly-thermal mountain or valley-type glaciers; showing glacial deposits occurred in all the area.

However, the first major marine transgression covering the greater part of North Africa started in early Silurian period as a result of the melting of ice sheet that covered the massifs of Hoggar, Tibesti, Jabal Al Uwaynat and probably Jabal Al Hasawnah.

The ice cap melting starts definitively prior to the onset of the Silurian transgression.

This glaciation material was mostly eroded or non-deposited at “H” Oil Field Murzuq Basin.

As documented by XRD analysis and well log interpretation.

The Early Silurian is indicative of significant warming after glacial intervals; and a global sea-level change, this is documented by thick deposition of Tanezzuft Formation charged by an organic rich, radioactive (hot) shales interval at the base of the Silurian.

(Keeley et al.

1989, Lüning et al.

2000, Badalini et al.2002) as sea level rose at the end of the glacial episode, the North Africa platform was flooded and blanketed by transgressive marine shale dominated facies.