Abstract:
Deep-water benthic foraminifera have been studied in 443 samples from the Lower Cretaceous of Deep-Sea Drilling Project Holes 256, 257, 258, 259, 260 & 263, and Ocean Drilling Program Holes 762, 763, 765 & 766 in the Indian Ocean. Altogether, 260 species have been recognised in our samples, 132 agglutinated and 128 calcareous. Two hundred thirty-five species are illustrated in this book. The agglutinated genus Gaudryinopsis is emended herein, and the genus Kadriayina is here reinstated as valid. The succession of benthic foraminifera in the studied cores allows the establishment of a new biostratigraphical zonation based on the ranges of distinctive species. The following six zones are recognised as regionally applicable to the deep-water sediments of the Indian Ocean: (1) a Valanginian to Hauterivian Lenticulina heiermanni Zone (Partial range zone) the base of which is defined by the First Occurrence (FO) of Lenticulina heiermanni; and top defined by the FO of Gavelinella barremiana. (2) an early to late Barremian Gavelinella barremiana Zone (Interval zone) with its base defined by the FO of Gavelinella barremiana, and top defined by the FO of Saracenaria spinosa. (3) a latest Barremian to early Aptian Praedorothia ouachensis Zone (Partial range zone), whose base is defined by the FO of Saracenaria spinosa, and top is defined by the Last Occurrence (LO) of Praedorothia ouachensis. (4) a late Aptian to late early Albian Kadriayina gradata/Saracenaria spinosa Zone (Partial range zone) with the base defined by LO of Praedorothia ouachensis, and top defined by the FO of Pleurostomella reussi. (5) a late early Albian to early late Albian Pleurostomella reussi Zone (Interval zone), whose base is defined by the FO of Pleurostomella reussi, and top defined by the FO of Spiroplectinella gandolfii. (6) a late Albian to early Cenomanian Spiroplectinella gandolfii Zone (Interval zone) with its base defined by the FO of Spiroplectinella gandolfii. The chronostratigraphy of DSDP Holes 256, 257, 258, 259, 260 & 263 and ODP Holes 762, 763, 765 & 766 has been revised herein. New ages have been determined from benthic foraminiferal data, thereby improving the biostratigraphic resolution of selected intervals from the Lower Cretaceous DSDP and ODP cores. An Aptian age is here assigned to sequences from Hole 260 previously dated as middle Albian. An older Valanginian to Barremian age has also been established for the base of Hole 263, in contrast with the Aptian age published previously.