Print this pageThird-Order Sequence Stratigraphy of the Upper Ordovician (Llanverian -Ashgill) of Arabian Plate and North 
Africa
The upper Ordovician sedimentary successions within Arabian Plate and North Africa basins are considered to be part of second order sequences (AP2 and NA2). In this study, sequence stratigraphic and plate tectonic concepts are used to delineate possible high frequency third order sea level events within Northern Gondwana upper Ordovician regression and transgression successions.
Newly released upper Ordovician biostratigraphic data from Arabian Plate and North Africa basins are used to correlate upper Ordovician regression and transgression cycles with those of Baltica’s high frequency third-order sea level events. Correlations show that the upper Ordovician transgressive and regressive successions within Arabian Plate and North Africa basins were deposited during two lowstands and highstands third-order cycles. The regressive successions represent two lowstand third-order cycles that developed as result of tectonically and glacially induced sea level falls during middle Caradoc and early Ashgill respectively. The transgressive successions were deposited during gracilis and linearis eustatic sea level rise that took place during Llanverian and late Caradoc respectively.
Preservation of the Arabian Plate and North Africa upper Ordovician third-order sequences are controlled by Caradoc, Taconic and Hercynian tectonic, and Ashgillian glaciation events. Multiple reservoir intervals are most likely to be encountered basinward were the effect of glaciations and tectonically induced erosions are minimal.
Since Caradoc and Ashgill sandstone intervals are major hydrocarbon reservoirs within North Africa
basins, the result of this investigation will help to define new hydrocarbon plays within the Arabian Plate upper Ordovician successions.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009