Valanginian-Turonian Second-Order Sequences from the Southern Tethys and Their Exploration Significance
Alexis Godet*, Roger B. Davies, Duncan Macgregor, Peter R. Sharland, Michael D. Simmons, Owen E. Sutcliffe, Alice R.A. Thomas, and Joanne Wyton
Neftex Petroleum Consultants Ltd., UK
The Valanginian-Turonian stratigraphic sequences described from Arabia by Sharland et al. (2001, 2004) can be grouped into two second-order sequences recognisable in successions from Morocco to Yemen. The analysis of sequences from outside the Arabian Plate has improved the biostratigraphic resolution with which the sequences can be dated and correlated, whilst improvements have also been made to the criteria used for the physical placement of the surfaces in any given succession. Within both sequences the second-order MFS is coincident with an Oceanic Anoxic Event – a time of enhanced production and preservation of organic carbon. Early Aptian MFS K80 calibrates to OAE1a, whilst basal Turonian MFS K140 calibrates to OAE2. Where these MFS occur in intra-shelf basins, they are linked to locally important source rocks - intra-Shu’aiba in the United Arab Emirates, Oman and Iran (K80); Natih B (Oman), Bahloul (Tunisia) (K140). Key second-order sequence boundaries occur in the Early Valanginian (K40 SB) and latest Aptian (K90 SB). Biostratigraphic calibration of these boundaries from correlative conformity locations demonstrates that they are also present in basins across the globe. They must therefore be primarily eustatic in origin. However, across the southern Tethys these sequence boundaries were also tectonically enhanced (primarily in response to increases in Atlantic spreading rates). This drove pronounced clastic sediment supply from the shield and the consequential presence of clastic reservoirs, associated with the lowstand and transgressive systems tracts, overlying these sequence boundaries. Source rocks may also have developed because of freshwater overhang in front of the deltas so formed.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain