The Development of Rich, Effective Source Rocks in the Mesozoic of Western Tethys / Central Atlantic Province

Abstract

Enhanced potential for source rock development is recognised at numerous stratigraphic levels through the Mesozoic of the Western Tethys / Central Atlantic Region. Specific levels that are proven effective include, in the Cretaceous; Cenomanian-Turonian, Aptian and in the Jurassic; Kimmeridgian, Toarcian and Hettangian-Pliensbachian.

These source prone levels are typically associated with sea level high stands and in several instances are linked to global anoxic events. In the subject area it seems that, whilst source potential is regionally enhanced in these stratigraphic levels, the development of commercially significant source rocks is more local in distribution. This presentation looks at a range of proven productive source rock basins in the Western Tethys / Central Atlantic region to identify common themes for their development. These examples include the Bahloul Formation (Tunisia), the Aptian (N. Tunisia), Kimmeridgian (Aquitaine Basin), Toarcian (Paris Basin), Hettangian-Sinemurian (Wessex Basin, UK, Paris Basin, France and Lusitanian Basin, Portugal).

The most significant common element amongst these various source basins (besides sea level highstand / global anoxia) is active subsidence at time of source rock deposition. This may be active rifting or other fault driven subsidence, post rifting sag or salt withdrawal. It appears that relatively localised subsidence can be crucial to the evolution of source rocks both rich and thick by providing a persistent sea floor setting with restricted circulation and consequently high levels of organic carbon preservation in the sediment.

Recognising this phenomenon would suggest that effective oil exploration in the region requires identification not only of a trapping configuration, reservoir facies and a mature kitchen area but also evidence of local subsidence during source rock deposition within the kitchen area. Some untested examples with appropriate configurations are described.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015