Planktonic and benthic foraminiferal biostratigraphy of the Middle Eocene-Lower Miocene successions from the Sivas Basin (Central Anatolia, Turkey)

摘要

Planktonic and benthic foraminifera are described from the Middle Eocene-Lower Miocene successions in the Sivas Basin, Central Anatolia. An integrated foraminiferal zonation provides new age assignments in terms of a great number of taxa for the studied sections. Four biostratigraphical intervals are first recorded based on the concurrent ranges of sporadically occurring but well preserved planktonic foraminiferal assemblages. The first interval characterized by the co-occurrences of Acarinina bullbrooki, Truncorotaloides topilensis and Turborotalia cerroazulensis is referable to the E11 Zone of late Lutetian-early Bartonian. An assemblage yielding Paragloborotalia opima accompanied by Globigerinella obesa forms a basis for the late Chattian O5 Zone. The successive interval corresponds to the late Chattian O6 Zone indicated by the presence of Globigerina ciperoensis and Globigerinoides primordius along with the absence of Paragloborotalia opima. The early Aquitanian M1 Zone can be tentatively defined based mainly on the assemblage of Globigerina, Globigerinella, Globoturborotalita and Tenuitella. The biostratigraphical data obtained from the benthic foraminifera assign the studied sections to the SBZ 21-22, SBZ 23 and SBZ 24 ranging in age from Rupelian to Aquitanian. The SBZ 23 and 24 are well constrained biozones by the occurrences of Miogypsinella complanata and Miogypsina gunteri, respectively, whereas the SBZ 21-22 defined by nummulitids and lepidocylinids in the Tethyan Shallow Benthic Zonation is characterized dominantly by peneroplids, soritids and miliolids in the studied sections. Benthic foraminiferal assemblages suggest different paleoenvironments covering lagoon, algal reef and shallow open marine whereas planktonic foraminifera provides evidence for relatively deep marine settings on the basis of assemblages characterized by a mixture of small-sized simple and more complex morphogroups indicative for intermediate depths of the water column.