SEDIMENTATION IN THE VENEZUELAN BASIN, CIRCULATION IN THE CARIBBEAN SEA, AND ONSET OF NORTHERN-HEMISPHERE GLACIATION

Currents of the equatorial Atlantic and Tethys Sea migrated westward t hrough the Caribbean Sea and Panama seaway from Cretaceous to Oligocen e time. At about 25 Ma currents reversed direction, allowing cool Paci fic waters (Peruvian current) to enter the Caribbean. Almost coinciden t with the reversal was a dramatic increase in Central American explos ive volcanism, which resulted in development of large volcanic centers , and an abundance of suspended volcanic detritus in Pacific and south ern Caribbean waters. The detritus was transported by Pacific currents across the Caribbean to be deposited as pelagic mud in the Venezuelan Basin during 25 to 15 Ma. These cool, turbid Pacific waters led to a dramatic reduction in the diversity of hermatypic corals. At about 15 Ma Venezuelan Basin pelagic sediments record a dramatic change in prov enance, with derivation of highly weathered detritus from the South Am erican continent, probably the result of renewed uplift of the norther n Andes. Exceptionally abundant kaolinite, reflected in high CIA value s of the pelagic mud, indicates that materials of the Andean hinterlan ds suffered intense chemical weathering from at least 15 Ma to the pre sent, with the most intense weathering occurring during Pliocene time. Weathering was somewhat less intense during the cool Pleistocene Peri od. These findings bear on Northern Hemisphere glaciation. With the Pa nama Seaway open, cool Pacific waters entered the Caribbean between 25 and 12 Ma, and probably mixed with warm equatorial Atlantic waters to form the Gulf Stream. Closure of the seaway commenced about 12 Ma and finally closed about 3.5 Ma. This resulted in a warmer Gulf Stream, d erived entirely from equatorial Atlantic waters. Dramatically increase d pelagic sedimentation rates in the Venezuelan Basin since 4 Ma sugge st intensification of the Atlantic equatorial current and strengthenin g of equatorial Atlantic summer storms (hurricanes), both of which str engthened the Gulf Stream current. Resultant northward heat transport by a warm, intensified Gulf Stream led to increased precipitation and promoted glaciation in the Northern Hemisphere.