Danian Calcisphaerulidae of DSDP Leg 35, Site 323, Southeast Pacific Ocean

Abstract

Site 323 of Leg 35 was drilled in the Southeast Pacific Basin (lat 63°40.84'S, long 97°59.69'W) in a water depth of 4993 meters. The hole penetrated 731 meters of sediments and basalt of which the uppermost 500 meters are diatomaceous clay and claystone of Miocene and Pliocene age. The underlying gray claystones and siltstones are barren of biogenic silica. Cores 11 to 13 (550-626.5 m) are ?Oligocene to early Miocene in age based on determinations from arenaceous foraminifera. No age determination was made on Core 14 (636-645.5 m). Within this core the lithology changes downhóle from claystones and siltstones to brown Fe-claystone. The upper part of Core 15 yields a fauna of Paleogene arenaceous foraminifera. An age assignment within the Paleogene is not possible. The lower part of Core 15 to the upper part of Core 16 (662-667 m) contains calcareous foraminifera and a rich occurrence of Calcisphaerulids.1 This unit is a 5-meter layer of brown Danian nannofossil claystone. The underlying brown claystone down to basement at 701 meters subbottom yields only fish teeth, a sparse fauna of arenaceous foraminifera, and in the lower part, Cretaceous radiolarians and a Maestrichtian nannoflora. The Danian sediments in Cores 15 and 16 have a fairly rich fauna of calcareous and arenaceous benthonic foraminifera and contain more than 50% planktonic foraminifera. In some samples, a large part of the residue coarser than 44 μm consists of Calcisphaerulidae. The plankton/benthos ratio and the composition of the benthonic fauna indicate deposition in upper to middle bathyal depths of about 1500-2000 meters. The stratigraphic position of the section is early Paleocene, Danian. According to Haq (this volume), the section falls in the upper part of the nannoplankton Cruciplacolithus tenuis and Chiasmolithus danicus zones. The planktonic foraminifera are of the Globigerina edita Zone (Rögl, this volume). The samples were washed through a 325-mesh (44 μm) sieve and the isolated Calcisphaerulidae were investigated under the scanning electron microscope (SEM) as described by Bolli (1974). The figured specimens are deposited at the Museum of Natural History, Basel, under the numbers C31278-31314.