Distinct latitudinal control of the distribution of marine microfaunas in the North Atlantic Ocean began in the early part of the Tertiary (Paleogene) and is related to the opening of the North Atlantic to the Arctic region about 60 m.y. ago when the present deep-water circulation pattern was probably initiated. At that time a boreal zoogeographic province was established in the Atlantic Ocean for the first time. Caribbean and Mediterranean benthonic foraminiferal faunas exhibit a marked degree of similarity during the early Tertiary. The gradual displacement of west-east current migration routes into higher latitudes and the compression of Spain against North Africa brought an end to this amphiatlantic distribution pattern about 15 m.y. ago. Initiation of glaciation abou 3 m.y. ago had a marked effect on circulation in the North Atlantic and temperature may have been the primary factor responsible for the many extinctions in planktonic Foraminifera.

Sediment cores and bottom photographs provide evidence of measurable bottom circulation within the Western Boundary undercurrent in the western North Atlantic. This contour current has played a major role in controlling fine-grained sediment deposition since the early Tertiary. Data from recent deep drilling suggest that during middle Cretaceous to early to middle Tertiary times extensive unconformities occurred, and during the early Tertiary a sudden onslaught of deep circulation coupled with wholesale erosion and redeposition of deep-sea sediments may have occurred. Currents gradually diminished in strength during the late Tertiary and are now flowing at moderate velocities apparently sufficient to transport and deposit sediment with only local erosion.

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