Deep Sea hiatuses in pelagic sequences are largely determined by surface productivity and the rate of sediment removal by bottom currents and corrosiveness of deep waters with respect to calcite and silica. In regions of high biotic productivity, sedimentary

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sequences are typically free of hiatuses or contain very short hiatuses. Hence, hiatus distribution maps can outline regions of high paleo-productivity. Analyses of Miocene deep-sea cores reveal eight intervals of widespread hiatuses and four distinct sediment distribution changes in the world's oceans. These maps reveal major paleo-oceanographic changes affecting the biotic productivity in the Miocene ocean. Four main episodes in the evolution of oceanic circulation and paleo-productivity are apparent leading to the establishment of present-day high productivity regions.

(1) Circum-equatorial flow persisted to about 18 Ma with calcareous sedimentation in low and middle latitudes and predominantly siliceous sedimentation in the North Atlantic and Antarctic south of 60°S.

(2) Closing of the deep-water connection across Central America by 16 to 15 Ma initiated the "proto" Gulf Stream by diverting Atlantic deep and intermediate waters northward. Siliceous sedimentation increased in the Indian and Pacific Oceans at this time particularly in the eastern equatorial and marginal North Pacific. Coincident with the establishment of these high siliceous productivity regions is a decrease and eventual disappearance of biologic silica in the middle latitude North Atlantic presumably owing to the introduction of Norwegian Overflow Water.

(3) The main aspects of the present circulation and sediment distribution pattern were established by 12 Ma when major production of Norwegian Overflow Water displaced Antarctic deep water from the North and South Atlantic basins and enhanced siliceous sedimentation in the North Pacific.

(4) An essentially modern oceanic circulation system and high biotic productivity pattern were established by 6.5 Ma, possibly as a result of major production of Antarctic Bottom Water associated with the establishment of the West Antarctic ice sheet.

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