Biostratigraphic and Environmental Analysis of the Upper Jurassic- Lower Cretaceous Carbonate Sequence in the Baßoba Yayla Area

Abstract: In the Baßoba Yayla (Trabzon, NE Turkey) area, which is located in the Eastern Pontides northern zone, platform carbonates were deposited during the Late Jurassic-Early Cretaceous time in environments varying from intertidal / supratidal to outer shelf. The carbonate sequence begins with a thick dolomite unit of the Late Jurassic to Early Cretaceous age. The following unit is rich in benthic foraminifers and pelecypoda shells. The foraminiferal assemblage comprising Vercorsella laurentii/camposaurii and Pseudolituonella gavonensis indicates a Late Hauterivian to Early Aptian age for this unit. The Late Aptian-Albian facies is characterized by bioclastic wackestones containing benthic foraminifers typical of outer platform environment, such as Spirillinidae and Lenticulinidae. Late Aptian transgression produced a deepening upward sequence, resulting in the deposition of a very fine-grained mudstone/wackestone with hemipelagic organisms: abundant hedbergellids and rare calcispheres. Probably after the Late Albian time, sedimentation took place in slope environments, now represented by graded bioclastic cal-carenites intercalated with hedbergellid and radiolaria-bearing marls and sandstones which fill up and level off the irregularities on the surface of the underlying outer platform limestone with hedbergellids. There is no evidence for emersion of the Eastern Pon-tides carbonate platform portion in the study area. In contrast to this, submarine erosive processes such as gravity-sliding and ero-sional reworking by currents caused this erosional unconformity. Until the Albo-Cenomanian time, both zones of the Eastern Pontides were characterized by the same stratigraphic and tectonic fea-tures. Subsequently during the Late Cretaceous and the Early Cenozoic, in the northern zone a subduction-related magmatic arc com