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Scientific Ocean Drilling, from AMSOC to COMPOST
Pages 117-127

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From page 117...
... The program has tested major hypotheses such as seafloor spreading, provided the material basis for a increasingly fine-grained geologic time scale, delivered otherwise unattainable data on compositions and processes from levels deep beneath the seafloor, including the oceanic crust, and made possible the elaboration of a detailed global paleoceanographic history, extending back about 180 million years. Early mistakes and fumbles about responsibilities for oversight, funding, management, science operations, and scientific advice were corrected.
From page 118...
... AMSOC chartered an industry vessel, CUSS-1, which, after some preliminary tests in soft sediments of a Neogene turbidite basin in waters about 1,000 m deep west of San Diego, then drilled a hole 183 m deep in 3,570 m of water off the Mexican island of Guadalupe. The dynamic positioning scheme and the coring of both pelagic sediments and basaltic basement there were successful, opening the way to the CREATING INSTITUTIONS TO MAKE SCIENTIFIC DISCOVERIES POSSIBLE more ambitious stage, a hole all the way to the Moho.
From page 119...
... In principle, these two simple facts opened the possibility of working out not only the paleoceanographic history of the ocean basins over the past 100 million years (the age of the then-oldest known samples from the ocean floor) , but also the age of oceanic crust in all the oceans.
From page 120...
... JOIDES planners had by now devised a nine-leg plan of drilling: a beginning leg in the Gulf of Mexico, partly to explore one of the Sigsbee Knolls (a group of buried salt domes) ; then one leg each across the North and South Atlantic, mainly to date oceanic crust; a leg in the Caribbean; then five legs in the Pacific, including a northsouth transect of the thick pile of pelagic sediments close to the Equator; and a long loop westward to explore the possibly very old crust farthest from the active East Pacific Rise spreading ridge.
From page 121...
... Recognition of the abundance of well-preserved microfossils and of the near-continuous record of sedimentation in the Pacific equatorial zone led to several later coring legs that provided us with the material basis for an extraordinarily detailed biostratigraphic time scale combining all three major groups of planktonic microfossils: foraminifera, coccolithophorids (nannofossils) , and radiolarians.
From page 122...
... A breakdown of the $1 billion expended by NSF and its international partners on the various ocean drilling projects, from Mohole to the present day, is shown in Table 1. DETOUR: TH E OCEAN MARC IN DRILLING PROGRAM In the late 1970s and early 1980s, paced by improvements in seismic reflection systems available in academia, scientific interest in the JOIDES community began to focus very seriously on thickly sedimented continental margins such as the Atlantic margin of North America and the margins of Africa.
From page 124...
... The continuous cores also provide material for determination of magnetic-reversal sequences, which can in turn be linked to the sequence of seafloor magnetic anomalies. The direct radiometric dating of volcanic ash beds in the sediments and of drilled oceanic crust, using laser technology that can yield 0.1 million-years resolution, plus radiometric dating of biostratigraphically constrained ash beds and igneous rocks on the land, has improved resolution by an order magnitude since the Ocean Drilling Program began.
From page 125...
... The KIT halide story has depended as much on data obtained from land outcrops as from the ocean drill cores, which have served mainly to provide an especially detailed record of the sequence of events in regions relatively close to the impact site, on the Yucatan Peninsula. The discovery of the Mediterranean events, on the other hand, was almost purely the result of drilling on DSDP Legs 13 and 42A, which showed that the salt deposits that accumulated in shallow salt marshes and brine basins at the bottom of several Mediterranean depressions are both underlain and overlain directly by deep-sea biogenic sediments.
From page 126...
... Beginning with the clean test of seafloor spreading on Leg 3, the determination of the age of oceanic lithosphere has been made at many of the 1100 sites drilled, giving us a set of ties between the biostratigraphic scale and magnetic anomalies, back to the mid-Jurassic, and enabling the interpretation of magnetic anomaly patterns in terms of plate tectonic evolution. Mantle Plumes, Hotspots, and Early Cretaceous Volcanism The ruling theory for the formation of linear seamount chains is that they result from motion of a plate over a fixed melting anomaly, or hotspot, in the underlying mantle.
From page 127...
... Cores from sedimentary strata of the upper plate showed strong evidence of tectonic kneading of sediments in the accretionary prism and also the presence of fluid escape channels carrying waters squeezed from the deforming sediments upward to the seafloor. Several transects across the entire active margin complex (trench, forearc, volcanic arc, backarc basin, and remnant arc)


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