Abstract

This study presents a detailed micropaleontological analysis of the Cenomanian/ Turonian shallow water carbonate system of the Ajlun Group in a regionally defined sequence stratigraphic framework. Two outcrop sections were studied with a total thickness of 700m representing proximal (Bustani) to distal (Mujib) settings. Over 300 thin sections and disaggregated analyses were produced and integrated with existing sedimentological, nannopaleontological, and isotopic data. The Early/Middle Cenomanian boundary interval is marked by the highest abundance and diversity of benthic foraminifera including index fauna, Praetaberina bingistani and Nummufallotia apula in the Bustani section and Meandropsina vidali in the Mujib section. Benthic foraminiferal diversity declines significantly at the K130 sequence boundary surface corresponding to a sealevel drop. It marks the change from a rimmed carbonate platform to a shallow ramp dominated by oyster shells and small planktic foraminifera interbedded with faverina and ostracods. Larger benthic foraminifera reappear briefly in Late/Middle Cenomanian Hummar. Formation prior to Oceanic Anoxic Event 2, marked by the abundance of dwarf heterohelicids and buliminids coinciding with the positive carbon isotope excursion.Following OAE2, the Turonian interval shows a partial recovery of planktic foraminiferal size and diversity including the First Appearance of Planoheterohelix praenuttali. This was followed by the development of carbonate platform settings with large gastropods and rare small benthic foraminifera. The Middle/Late Turonian boundary is represented in a thin interval dominated by Cuneolina ex. gr. pavonia in peloidal grainstone facies. In addition to the age dating contribution, this study illustrates how micropaleontological information can document subtle environmental changes that refine the sequence stratigraphic model.