Palynology of the Middle Ordovician Hawaz Formation in the Murzuq Basin, south-west Libya

摘要

Twenty-nine core and seven cuttings samples were collected from two boreholes penetrating the Middle Ordovician Hawaz Formation in the Murzuq Basin, south-west Libya. The samples were palynologically analysed in order to determine age and depositional environment. The palynological assemblages contain abundant sphaeromorphs, rare but diverse acritarchs, rare chitinozoans, and relatively abundant cryptospores. A total of 26 acritarch species, five chitinozoan species and 17 cryptospore species have been identified. The acritarch and chitinozoan assemblages provide biostratigraphical age dating and indicate that the Hawaz Formation is Mid Ordovician and most likely mid Darriwilian (Llanvirn) in age. The cryptospore assemblage is typical of those from the Mid Ordovician-earliest Silurian and does not permit further age refinement. Based on palynofacies analysis, the depositional environment of the Hawaz Formation is interpreted as shallowing upward from nearshore marine inner shelf to marginal marine. The cryptospores provide rare evidence for Middle Ordovician terrestrial vegetation at this very early stage in its development.