Upper Turonian-lower Campanian planktonic foraminifera from southern mid-high latitudes (Exmouth Plateau, NW Australia): biostratigraphy and taxonomic notes

A planktonic foraminiferal zonal scheme is presented for subdivision of the Upper Cretaceous pelagic carbonate sequence from southern mid-high latitud es. Definition of the zones is based on first and last occurrences of plank tonic foraminifera from Ocean Drilling Program Holes 762C and 763B (Leg 122 ; Exmouth Plateau, south Indian Ocean). During the Late Cretaceous the stud ied holes were located close to 50 degrees S and for the first time a compl ete sedimentary record for the mid-high latitudes was obtained. A detailed biostratigraphic analysis has allowed recognition of two new zones (Falsotr uncana maslakovae Zone and Marginotruncana marianosi Zone) for the interval extending from the last occurrence of Helvetoglobotruncana helvetica to th e first occurrence of Dicarinella asymetrica (upper Turonian-lower Santonia n). From this study it is apparent that some low latitude (Globotruncana ve ntricosa, Hedbergella flandrini, Marginotruncana marianosi) and high latitu de (Globigerinelloides impensus and Hedbergella sliteri) marker taxa displa y a vertical distribution at mid-high latitudes which is different from tha t known from low latitudes; moreover, one species (Heterohelix papula), ove rlooked at low latitudes, exhibits a restricted range that seems to be usef ul for chrono-biostratigraphic correlations: its appearance is suggested to coincide with the Coniacian/Santonian boundary. The proposed biozonation, which is integrated with calcareous nannofossil and magnetostratigraphic da ta available for the sections studied, is compared with both the low-latitu de standard zonation and the planktonic foraminiferal zonal scheme for the circum-Antarctic region, in order to define a bio-chronostratigraphic scale that is useful for mid-high latitudes of the southern oceans. (C) 2000 Aca demic Press.