The global Middle and Late Miocene and the deep earth: Model for earlier orogenies
Abstract The 11 Ma Middle and Late Miocene interval forms only 2% of Phanerozoic time but includes two broadly contemporaneous global orogenies—one reaching across southern Eurasia and the other spanning the Circumpacific. These two global orogenies caused many global events, and because they are close to us in time, causality links between these orogenies and these far scattered events are much more apparent than in older orogenies. These teleconnections include establishment of the present world oceanic current system; the beginnings of oceanic cooling at 14 Ma; an increase in hemipelagic mud bordering the continents; changes in continental tilts and river systems; great biological changes; increased desertification; replacement of C 3 by C 4 grasses; a major shift in siliceous microfossils from the Atlantic to the Pacific at 15 Ma; and first development of the earliest hominids in East Africa starting at 10 Ma. In addition, spreading rates of oceanic ridges increased, volcanism increased, there was movement along many transform faults, and continental elevations increased. Short, bulleted statements set forth these near and far field events. Immediate causes were increased rates of plate motions and/or changes of directions. Only a strong, short 11 Ma pulse of heat from the Earth's core provides the logical ultimate source of this energy. Only such a pulse of heat from the core has sufficient magnitude and acts globally. Thus the deep Earth cycle is a plausible, easy-to-understand, overarching explanation that should be increasingly considered by geologists and geophysicists studying the outer crust. A flow diagram links major earth surface features on the continents to the deep earth. Alternative explanations for these events are considered and seem totally inadequate.