Evidence of Cretaceous Plate Collisions Along the Falkland Plateau Basin – Ramifications to Petroleum Systems and Reservoir Quality Risk

Abstract

In frontier basins, heat flow predictions often rely on crustal thickness estimates derived from gravity inversion. Such analyses on the Falkland Plateau conclude that the continental crust must thin to zero, based on >12 kms of post rift fill. A basin with no continental crust is inherently cooler than one in which continental crust still exists, thus heat flow predictions conclude the sub-basins along the Plateau are relatively cool. However, recent exploration wells have shown that these basins are significantly warmer than predicted. Evidence for a previously unidentified plate collision event has been recognized along the eastern margin of the Falkland Islands. In the Late Cretaceous, sediments derived from the Falkland Islands and deposited in the offshore Mesozoic basins, are forcibly inclined down to the east. Updip of these inclined beds is a significantly eroded hinge zone. All sedimentation derived from the Falkland Islands ceased, presumably routed away from the uplifted hinge. Offshore, a deepwater trough developed parallel to the shelf margin, between the Falkland Islands and Maurice Ewing Bank. This trough was initially filled by two fine-grained units that onlap both the Falkland and Maurice Ewing Bank margins and thicken to the southeast. We interpret these observations as indications of a collision between the Falkland Islands and another plate, possibly Maurice Ewing Bank. This event plays an important role in reservoir quality and petroleum systems risk evaluation along the Falkland Plateau, and actually explains the inconsistency between the predicted and observed thermal conditions. In this area, Late Cretaceous accommodation was created by tectonic loading of the Falkland plate, not by subsidence resulting from crustal thinning, the assumption used in gravity inversion. Ignoring or being unaware of this tectonic loading results in models with cool temperatures. In reality, the significantly thicker crust makes the basins warmer, raising the level of the oil window, and elevating quartz cementation risk. This presentation will examine the impact of this new tectonic interpretation on petroleum systems and reservoir quality risk.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017