Biostratigraphic and Environmental Analysis of the Upper Jurassic- Lower Cretaceous Carbonate Sequence in the Başoba Yayla Area (Trabzon, NE Turkey)

Authors: KEMAL TASLI, EROL ÖZER, CEMİL YILMAZ

Abstract: In the Başoba 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 finegrained 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 calcarenites 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 Pontides carbonate platform portion in the study area. In contrast to this, submarine erosive processes such as gravitysliding and erosional 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 features. Subsequently during the Late Cretaceous and the Early Cenozoic, in the northern zone a subduction-related magmatic arc complex developed while in the southern zone the deposition of siliciclastic turbidites took place. The appearance of such a change, following the breaking up of the platform, led to the subdividing of the Eastern Pontides into the northern and southern zones.

Keywords: Biostratigraphy, Depositional environment, Carbonate platform, Upper Jurassic-Lower Cretaceous, Eastern Pontides, Turkey.

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