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Discoveries from Deep Ocean Drilling
N. Terence Edgar (1)
The drilling vessel Glomar Challenger is completing six years of drilling at over 300 sites in the Atlantic, Pacific and Indian Oceans as well as the Gulf of Mexico, Caribbean Sea, Labrador Sea, Mediterranean Sea, Bering Sea, Red Sea and Antarctic waters. Significant achievements from drilling in the deep marine environment have been accomplished in the fields of global tectonics, micropaleontology, paleo-oceanography, chemistry of interstitial water, diagenesis, mineralogy and sedimentology.
One of the most outstanding results from the drilling is that the oldest sediment recovered from any ocean basin is only Late Jurassic (or about 166 m.y. old). This fact coupled with the systematic geographic distribution of the ages, constitutes powerful support for the concept of sea-floor spreading and continental drift. In addition to horizontal tectonics, the drilling has revealed areas of uplift and subsidence.
Increased core recovery allowed the study of paleoenvironments on an ocean-wide basis. A major period of stagnation occurred in the Early and Late Cretaceous in the North Atlantic and Caribbean resulting in the deposition of carbonaceous sediments. Circulation was renewed in the Late Cretaceous, and aerobic conditions prevailed to the present. Bottom water circulation became increasingly vigorous causing hiatuses in sedimentation of up to 70 million years in the Cretaceous-Paleogene section. Recently completed voyages into Antarctic waters traced glaciation on Antarctica to early Miocene (20 m.y.b.p.).
Another important application of drilling is the identification of seismic reflectors in the deep ocean sediments. The nature of these reflectors is varied but commonly includes chert, limestone layers, ash layers, basalts, and unconformities.
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