Impact of the late Cenomanian sea-level rise on the south Tethyan coastal ecosystem in the Middle East (Jordan, Egypt, and Tunisia): A quantitative eco-biostratigraphy approach

Sea-level rise can cause changes in coastal ecosystems. To understand the link between sea-level rise and the coastal ecosystems during the late Cenomanian of the southern Tethys, five exposed sections from three Middle East countries were quantitatively analyzed. The Unitary Association (UA) method allowed a two-fold increase in the resolution of zones compared to the Oppel method. Five UAs were obtained from analyses of both ammonite and benthic fauna. However, they were grouped into 3 UA Zones (UAZ) to enable basin-wide correlation. These zones were linked to one and half 3rd-order depositional cycles. During the Neolobites vibrayeanus/ Calycoceras guerangeri ammonite zone (95.5-94.4 Ma), high-energy shallow subtidal environments were formed by the transgression that followed the global sequence boundary 'KCe 4'. They were dominated by stationary epifauna and suspension-feeders (mainly oyster bivalves). During highstand, a restricted lagoonal environment prevailed, where oyster bivalves, which have well-known adaptive strategies, were still dominant. No ammonites were recorded in this zone. Upward, the fauna has underwent a major shift, which documents the beginning of a new depositional sequence above a regional sequence boundary 'KCe 5' with a gradual increase of hemipelagic organic-rich sediments and planktic/nektic fauna in addition to infaunal deposit-feeders and mobile benthos, which have lived in a deeper subtidal environment (Vascoceras cauvini/Pseudospidoceras pseudonodosides ammonite zone; 94.4-93.8 Ma). This dramatic change in the character of the macrofauna at the Cenomanian/ Turonian boundary (maximum flooding of KCe 5) can be attributed to the hydrodynamic changes associated with the eustatic sea-level rise. Therefore, the sea-level-based faunal changes can be integrated in sequence stratigraphic analyses. The geographic reproducibility of the UA mirrors the delay of the transgressive onlap in proximal sections, and thus, can be used to define transgressive and maximum flooding surfaces. This ecobiostratigraphic scheme can be implemented in reliable large-scale correlations.