Currents of the equatorial Atlantic and Tethys Sea migrated westward through the Caribbean Sea and Panama seaway from Cretaceous to Oligocene time. At about 25 Ma currents reversed direction, allowing cool Pacific waters (Peruvian current) to enter the Caribbean. Almost coincident with the reversal was a dramatic increase in Central American explosive volcanism, which resulted in development of large volcanic centers, and an abundance of suspended volcanic detritus in Pacific and southern 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 provenance, with derivation of highly weathered detritus from the South American continent, probably the result of renewed uplift of the northern Andes. Exceptionally abundant kaolinite, reflected in high CIA values of the pelagic mud, indicates that materials of the Andean hinterlands suffered intense chemical weathering from at least 15 Ma to the present, with the most intense weathering occurring during Pliocene time. Weathering was somewhat less intense during the cool Pleistocene Period. These findings bear on Northern Hemisphere glaciation. With the Panama 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, derived entirely from equatorial Atlantic waters. Dramatically increased pelagic sedimentation rates in the Venezuelan Basin since 4 Ma suggest intensification of the Atlantic equatorial current and strengthening of equatorial Atlantic summer storms (hurricanes), both of which strengthened 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.