Pithonellid calcitarch record in the middle? Cenomanian Derdere-A Member, SE Turkey: palaeoenvironmental changes and stratigraphic significance

Abstract

: Pithonellid calcitarchs are studied in the organic-rich limestones of the Derdere-A Member from the middle? Cenomanian deposits of SE Turkey for the first time. Little is known about the distribution of pithonellid calcitarchs in the Cretaceous strata of Turkey. Three morphogroups of pithonellid calcitarchs are distinguished: they are represented by Pithonella sphaerica (Kaufmann, 1865) and P. ovalis (Kaufmann, 1865), both dominating the pithonellid assemblages, and by Bonetocardiella conoidea (Bonet, 1956), this latter being less abundant. Compared to the relative abundance of Upper Cretaceous pithonellid calcitarchs in the study area, the diversity is extremely low. The significant increase in abundance of pithonellid calcitarchs is particularly noticeable in the Cenomanian. We observed a significant increase in abundance of pithonellid calcitarchs in the Derdere-A Member, which is associated with an early transgressive phase of the middle? Cenomanian Arabian Platform. They are present in relative abundance and could therefore represent a potentially useful correlative marker horizon in SE Turkey. Pithonellid calcitarchs have been interpreted as indicators of increased nutrient input. A positive correlation exist between pithonellid calcitarchs abundance and nutrition input in the Derdere-A Member which is a sequence of carbonates deposite under eutrophic conditions, as evidenced by the low diversity and very low abundance of benthonic and planktonic foraminifers, and the high abundance of pithonellid calcitarchs. As a result, the increase of pithonellid calcitarchs indicates the increase of nutrient input in the Derdere-A Member. We noticed that a comparable trophic change also occurred throughout the SE Turkey carbonate platform in the middle? Cenomanian. The increase in the pithonellid abundance reported here may be a possible indicator of such a change.