Paleomagnetic stratigraphy and micropaleontology of three deep sea cores from the Central North Atlantic Ocean

Abstract

The paleomagnetic stratigraphy of 3 deep sea cores from the central North Atlantic ocean indicates that sediments as old as 2 m.y. were recovered. In one of the cores, CHAIN 61 (171), the phylogenetic transition between Globorotalia tosaensis and Globorotalia truncatulinoides was observed within the Olduvai Normal Event. This evolutionary transition also occurs at the base of the Pleistocene in the holostratotype Calabrian of Italy. Assuming a constant sedimentation rate within the Olduvai polarity section of the core, an age of 1.85 m.y. for Plio/Pleistocene boundary is estimated. The major disappearance of discoasters occurs just above the base of the Pleistocene about 1.6 m.y. ago; discoasters were also found in a single sample within the Jaramillo Normal Event about 0.9 m.y. ago and are interpreted to result from sediment reworking. In all three cores a marked increase in abundance of Globorotalia inflata and Globorotalia hirsuta (cool water species) and a corresponding decrease of Globigerinoides ruber and Globigerinoides sacculifer (warm water species) is noted within the Jaramillo Normal Event at about 0.9 m.y. ago. This faunal change probably corresponds to a major cooling trend and may mark the initiation of Pleistocene glaciation in Europe and North America. These ‘absolute’ dates fit well in the recently estimated chronometric time scale of the Pleistocene in the type area.