Upper Campanian calciclastic turbidite sequences from the Hac?mehmet area (eastern Pontides, NE Turkey): integrated biostratigraphy and microfacies analysis

摘要

The upper Campanian (Cretaceous) of the Hac?mehmet area (south of the city of Trabzon; Eastern Pontides) is mainly?composed of calciclastic turbidites. The basinal unit of the 119 m thick succession includes thin red pelagic limestone interlayers?and conglomerates dominated by volcanic clasts. The overlying upper slope and lower slope units of the sequence?consist of an alternation of allochthonous calcarenite /calcirudite beds and pelagic marls and mudstones. Calcarenite / calcirudite?beds dominate the upper slope unit of the succession and are composed of transported material, including benthic?foraminifers, red algae, bryozoan, crinoid and rudist fragments, inoceramid bivalve prisms and neritic and pelagic?carbonate lithoclasts. The occurrence of Helicorbitoides boluensis (Sirel) extracted from the calcarenite/calcirudite beds?indicates a Campanian age. Identifiable rudists such as Joufia reticulata Boehm, Bournonia cf. anatolica ?zer, Biradiolites? cf. bulgaricus Pamouktchiev and ? Biradiolites sp. from the upper slope unit of the succession indicate a late Campanian–Maastrichtian age. The planktonic foraminifers within the red pelagic limestone beds, marls and mudstones throughout?the succession consist mainly of Campanian–Maastrichtian forms and suggest mainly basinal depositional conditions.?The presence of Radotruncana cf. calcarata (Cushman) accompanied by Globotruncanita elevata (Brotzen) in the basinal?unit of the succession indicates an early late Campanian age for the lower part of the succession. Inoceramid bivalves?have been collected from the upper part of the succession. The fauna is dominated by ‘ Inoceramus ’ tenuilineatus Hall?and Meek, 1854 and Cataceramus haldemensis (Giers, 1964); other taxa recognised are: ‘ Inoceramus ’ algeriensis? Heinz, 1932, Platyceramus vanuxemi (Meek and Hayden, 1860), ‘ Inoceramus ’ cf. nebrascensis Owen, 1852, Cataceramus? aff. barabini (Morton, 1834), Cataceramus gandjaensis (Aliev, 1956), and ‘ Inoceramus ’ sp.; the assemblage indicates?the ‘ Inoceramus ’ tenuilineatus Zone; corresponding to the middle–late Campanian boundary interval. The uppermost?part of the succession is characterized by the presence of the trace fossils Scolicia strozzii and Scolicia isp., indicating?a mixed Skolithos-Cruziana ichnofacies. This ichnofacies suggests a well-oxygenated environment.