Oceanic layer

Layer 1 has been extensively sampled by coring and drilling. Seabed surface materials comprise unconsoli-dated deposits including terrigenous sediments carried into the deep oceans by turbidity currents, and pelagic deposits such as brown zeolite clays, calcareous and silicic oozes, and manganese nodules. These deep-sea sediments are frequently redistributed by bottom currents or contour currents, which are largely controlled by thermal and haline anomalies within the oceans. The dense, cold saline water produced at the poles sinks and underflows towards equatorial regions, and is deflected by the Coriolis force. The resulting currents give rise to sedimentary deposits that are termed contourites (Stow & Lovell, 1979).

Figure 2.17 P and S wave velocity structure of the oceanic crust and its interpretation in terms of layered models proposed in 1965 and 1978. Numbers refer to velocities in km s~'. Dashed curve refers to gradational increase in velocity with depth deduced from more sophisticated inversion techniques (after Spudich & Orcutt, 1980 and Harrison & Bonatti, 1981).

Figure 2.17 P and S wave velocity structure of the oceanic crust and its interpretation in terms of layered models proposed in 1965 and 1978. Numbers refer to velocities in km s~'. Dashed curve refers to gradational increase in velocity with depth deduced from more sophisticated inversion techniques (after Spudich & Orcutt, 1980 and Harrison & Bonatti, 1981).

Layer 1 is on average 0.4 km thick. It progressively thickens away from the ocean ridges, where it is thin or absent. There is, however, a systematic difference in the sediment thicknesses of the Pacific and Atlantic/Indian oceans. The former is rimmed by trenches, that trap sediments of continental origin, and the latter are not, allowing greater terrestrial input. The interface between layer 1 and layer 2 is considerably more rugged than the seabed, because of the volcanic and faulted nature of layer 2. Within layer 1 are a number of horizons that show up as prominent reflectors on seismic reflection records. Edgar (1974) has described the acoustic stratigraphy in the North Atlantic, where up to four supra-basement reflectors are found (Fig. 2.18). Horizon A corresponds to an Eocene chert, although deep sea drilling indicates that it maintains its reflective character even when little or no chert is present. In such locations it may correspond to an early Cenozoic hiatus beneath the chert. Horizon A* occurs beneath A, and represents the interface between Late Cretaceous/Paleogene metal-rich clays and underlying euxinic black clays. Horizon B represents the base of the black clays, where they overlie a Late Jurassic/Lower Cretaceous limestone. Horizon B may represent a sedimentary horizon, although it has also been identified as basalt similar to that at the top of layer 2.

Reflectors similar to A and B have been identified in the Pacific and Caribbean, where they are termed A', B' and A", B", respectively.

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How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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