About This Item
Share This Item
The Quaternary is characterized by 2 climatic signatures: that of the last 800,000 yr, the upper Pleistocene climatic signature (UPCS), and that of the period from 900,000 to 1,800,000 yr ago, the middle Pleistocene climatic signature (MPCS). Glacial cycles within the UPSC are about 100,000 yr long with interglacials of 10,000-12,000 yr duration and a "full" glacial period of 20,000-30,000 yr. The cycles of the MPSC range from 20,000 to 40,000 yr duration. Interaction between the 3 planetary orbital parameters of eccentricity, tilt, and precession are believed to cause the observed climatic signatures.
From DSDP cores, 8 major Miocene hiatuses have been described. There is a roughly equal duration of hiatuses and deposition, with periods ranging from 0.5 to 2 m.y. ± 0.5 m.y. The deep-ocean hiatuses correlate well with the seismically determined lowered sea levels of P. Vail. The hiatuses are interpreted to be caused by increased activity of ocean-bottom currents, in turn initiated by increased glacial activity. Thus, it is geologically reasonable that within each period of increased glacial activity there are 100,000-yr long UPSC-type cycles. The UPCS cycles have been tentatively identified in seismic data on the Louisiana, east Greenland, and Caribbean shelves and on the Indus Cone. Miocene glacial cycles should be sought in seismic data using innovative data processing techni ues.
End_of_Article - Last_Page 281------------