The Terminal Miocene Event
- Kenneth J. Hsü
Published Online: 15 MAR 2013
Copyright 1986 by the American Geophysical Union.
Mesozoic and Cenozoic Oceans
How to Cite
Cita, M. B. and McRenzie, J. A. (1986) The Terminal Miocene Event, in Mesozoic and Cenozoic Oceans (ed K. J. Hsü), American Geophysical Union, Washington, D. C.. doi: 10.1029/GD015p0123
- Published Online: 15 MAR 2013
- Published Print: 1 JAN 1986
Print ISBN: 9780875905150
Online ISBN: 9781118669914
- Geology, Stratigraphic—Mesozoic—Congresses;
- Geology, Stratigraphic—Cenozoic—Congresses;
- Ocean circulation—Congresses
The terminal Miocene paleoceanographic event is most certainly connected with the salinity crisis that affected the Mediterranean, although the cause/effect relationships are still debated. The hydrologic budget of the Mediterranean is, and presumably was, strongly negative. Therefore, when permanent connections with the Atlantic were interrupted due to relative motions between Africa and Europe and/or eustatic sea-level lowerings, the Mediterranean basins became evaporitic. The Mediterranean paleogeography underwent drastic changes; the basin margins were subject to subaerial erosion, and the main rivers in an attempt to adapt their thalweg to the rapid fall in base level incised deep and narrow canyons, which were subsequently filled by Plio-Pleistocene marine sediments. Calculations show that over one million cubic kilometers of halite and other evaporitic minerals were laid down in the Mediterranean, lowering the salinity of the oceans by 2 per mil.
Looking for oceanographic expressions of the Messinian Mediterranean salinity crisis in deep-sea sediments, paleoceanographers have found (a) an extended regression on continental margins, (b) a sudden global lightening of the isotopic composition of carbon in oceanic sediments and (c) oxygen-isotopic evidence for several periods of lowered sea level. The regression is well expressed and results in the interruption of carbonate buildups; however, it is not well dated in most cases. On the other hand, the “carbon shift” is well calibrated. Its numerical age is 5.9–6.1 m.y., occurring just after (above) the FAD of Amaurolithus primus in the lower part of paleomagnetic Epoch 6, (Haq et al., 1980). Its significance is still in part obscure but is possibly related to the partial restriction of Mediterranean waters during the non-evaporative Messinian. During Epoch 5 and the lowermost Gilbert Epoch (the evaporative Messinian), high frequency changes interpreted as glacial maxima and minima have been recorded in the oxygen-isotope record of pelagic sediments from both the North and South Atlantic and southwest Pacific Oceans (Cita and Ryan, 1979; McKenzie and Oberhansli, 1985; Hodell et al., 1986; and Keigwin et al., in press). The maxima may represent significant eustatic sea-level drops which could have restricted entirely or partially the inflow of sea water from the Atlantic to the Mediterranean. The flow of water from the Mediterranean to the Atlantic was undoubtedly terminated during the evaporative Messinian. An exact correlation of the various intra-Messinian events recorded in the Mediterranean and the open ocean remains only tentative awaiting better stratigraphic control from both realms.