The impact of the Messinian crisis on petroleum systems
The Messinian crisis has been the subject of many recent papers. The origin of this crisis, the timing of events, the magnitude of water drop and the sedimentology of this period are now better constrained. But its consequences in terms of petroleum systems efficiency and trap integrity are poorly developed. The entire Para-Tethys was affected by the Messinian Crisis (Mediterranean Sea, Black Sea and South Caspian Sea).
The Messinian crisis started at 5.96 Ma with transient water transfer through the Gibraltar strait. From 5.5 Ma up to 5.33 Ma, water transfer ceased due to ocean level drop related to Antarctic ice period (glacial cycles TG 12-14). As a consequence, the Para-Tethys sea level drops between 1700 m and 2200 m, for Mediterranean Sea and Black Sea. These values are deduced from river canyons and from DSDP drill-holes at 1700m-2000m water depth which found sedimentation characteristics of shallow marine deposit (50m water depth). In the South Caspian, the sea level fall is much less controlled, but the deep Paleo-Volga canyons north of Bakou are indicators of important sea level change.
At 5.33 Ma, the Atlantic waters found their way through the present Gibraltar Strait and rapidly refilled the Mediterranean, also known as the Zanclean flood. Erosion over 250 m deep on both sides of the Gibraltar Strait is proof of this fast refill. Based on recent papers, the complete refill could have only lasted a few years. The Black Sea water recharge was a bit slower. At 5.15 Ma, both sea levels were identical again.
During the Messinian Crisis, tectonic stresses and aquifer pressure regimes of the underlying sediments had experienced significant changes, depending on the geological context: the sedimentary section which was under shallow water (platform areas) before the Messinian crisis had only small stress and pressure perturbations during the period of sea level drop while the main impact on stress and pressure happened in the deep offshore areas where 150-200 bars of overburden suddenly disappear.
In this paper, we discuss the consequences of different pressure and connectivity scenarios on overburden stresses, seal integrity and faulting. These may have had a significant impact on the petroleum systems and on trap fill and HC type. This will be illustrated with examples and modeling from the Western Black Sea.
AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015