Cycles in Neogene paleoceanography and eustatic changes

Abstract

A characteristic indicator of Antarctic and Arctic waters today is the sinistrally-coiled Globigerina pachyderma. By tracing this indicator back through the Neogene, it is possible to demonstrate major expansions of cold-water isotherms not only during the Quaternary, but also during the Middle Pliocene and the later Miocene. Expansions of cold-water isotherms of the Quaternary are correlated with the classic expansions of ice masses during the Pleistocene; those cold-water expansions of the Middle Pliocene and later Miocene suggest increases in ice masses with associated lowered sea levels, although perhaps not of the same magnitude as those of the Pleistocene. The Antarctic and Greenland ice masses were likely much more extensive during all of these colder cycles than now. Major cycles of expanded cold-water isotherms were almost certainly associated with eustatic reductions in sea level, that in turn produced marine regressions in paralic environments. Thus, there should be regressive cycles associated with the expansion of cold-water isotherms within the later Miocene, the Middle Pliocene, and those of the classic Quaternary. In the absence of complications due to variable rates of sedimentation and tectonism, shallow water depositional sites may show an Upper Miocene nonmarine phase or unconformity, a Lower Pliocene marine phase, a Middle Pliocene nonmarine phase or an unconformity, an Upper Pliocene marine phase, and a major regression at the beginning of the Quaternary. A re-evaluation of Neogene marine sections is suggested. It may be possible that the transgressive facies of the Calabrian of Italy correlates with the later Pliocene of California and is older than 3 × 10 6 years.