The pre-Pleistocene stratigraphy and palaeontology of the Palmer Ridge area (northeast Atlantic)

Abstract

One core and ninety dredge samples of Tertiary sediments and volcanic ash have been selected for study from a total of 135 sediment samples obtained at eleven northeast Atlantic deep-sea core and dredge stations by R.R.S. “Discovery” during 1965 and 1966. The area sampled extends from approximately 43°10′N to 42°50′N, and from 19°40′W to 20°20′W; eight of the dredge stations are restricted to a small area (18 × 18 km) of Palmer Ridge. A lithological and micropalaeontological description is given for the sediments from each dredge station, and photographs of selected dredge samples have been included to illustrate the various lithologies. The planktonic Foraminifera and calcareous nannoplankton were investigated. Stratigraphical interpretations are based on both groups and are supported by lists of species of Foraminifera and calcareous nannoplankton compiled in most instances from several samples. The micropalaeontological and stratigraphical interpretations of individual samples are tabulated separately. The sediments recovered range in age from Lower Eocene to Pliocene, and consist of “normal” and winnowed pelagic ooze; zeolitised volcanic ashes are confined to Eocene samples. On the basis of the present results and an earlier study by Cann and Funnell (1967) the following events are postulated in the geological evolution of this area: 1. ( 1) About 60 · 10 6 year: the formation of a complex igneous and metamorphic basement at the then crest of the Mid-Atlantic Ridge. 2. ( 2) 60—21 · 10 6 year: pelagic sedimentation, with intermittent deposition of volcanic ash during the Eocene. 3. ( 3) About 21 · 10 6 year: uplift of the Palmer Ridge accompanied by the emplacement of a serpentinite intrusion. 4. ( 4) 21—0 · 10 6 year: accumulation of winnowed pelagic sediments near the crest of the Palmer Ridge. Stratigraphical variations in the species diversity of the planktonic assemblages are comparable with changes recorded in similar assemblages from other areas, and may reflect climatic variations during the Tertiary. A conspicuous decline in species diversity is recorded in Upper Eocene, Oligocene and Lower Miocene samples. The very high percentage of planktonic species among the Foraminifera, and the absence of members of the family Braarudosphaeraceae in the calcareous nannoplankton suggests that the Palmer Ridge was always situated in an oceanic environment.