Print this pageGlobal Miocene Tectonics and the Modern World
n amazing congruence of seemingly unrelated, diverse global events began in the Middle and Upper Miocene and established our modern world. Two global orogenic belts were active, mostly in the Middle and Upper Miocene, while back arc basins formed along the eastern margin of Asia. Coincident with these events global temperatures cooled in both the ocean and atmosphere, desertification occurred from Central Asia into and across most of northern Africa and also in Australia, and in southern South America. Coincident with the expansion of the Antarctic ice cap at 14 Ma, there was initial widespread deep sea erosion and changes in patterns of deep sea sedimentation. Muddy pelagic sedimentation increased six fold in the North and Central Atlantic and Pacific Oceans and global changes in circulation lead to more diatomites in the Pacific and fewer in the Atlantic. By the end of the Miocene most of the Mediterranean Sea had evaporated. Broadly coincident with these events, many old, large river systems were destroyed and new ones formed as much of the world’s landscape changed. Collectively, these global on-shore tectonic and ocean-atmospheric events provide the foundation for our modern world—a mixture of new and rejuvenated orogenic belts and their far field effects (distant epiorogenic uplift, rain-shadow deserts, large alluvial aprons, and distant deltas) as inherited Gondwanan landscapes persisted remote from plate boundaries. Thus at the end of the Miocene much of the world’s landscape, except for that changed by Pleistocene continental glaciation, would be recognizable to us today.
We argue that all of these events had the same ultimate common cause—an internal Earth engine—that drove plate motions in two broad ways: first, the opening and closing of seven key gateways to deep water oceanic currents radically altered global heat transfer and changed a lingering Greenhouse to an Icehouse world; secondly, these events were in part coincident with renewed heat flow in the African and Pacific Superplumes that energized global plate motions in the Middle and Upper Miocene. We hope this global synthesis will stimulate more research on the many global events of the Miocene—to understand better both our modern world and earlier global orogenies.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil