. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 2] MICROTOPOGRAPHY 457. Fig. 27. 35° 07'N, 13° 04'W. Depth 2008 m. Ampere Bank. Area of picture li by 2| m. (Photo by ) Ridges of low-density shingle, thought to be organic in origin, lying on a level bed of Globigerina sand. The ridges are about 1 m between crests and are probably formed by currents perpendicular to the crests. Note the scaphopod-like shells top and bottom. c. Scour pits and depositional drifts Evidence of currents on the bottom is often found where a loose boulder or an attached benthic fauna
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 2] MICROTOPOGRAPHY 457. Fig. 27. 35° 07'N, 13° 04'W. Depth 2008 m. Ampere Bank. Area of picture li by 2| m. (Photo by ) Ridges of low-density shingle, thought to be organic in origin, lying on a level bed of Globigerina sand. The ridges are about 1 m between crests and are probably formed by currents perpendicular to the crests. Note the scaphopod-like shells top and bottom. c. Scour pits and depositional drifts Evidence of currents on the bottom is often found where a loose boulder or an attached benthic fauna, such as a sponge, creates scouring and drifting of the sedinient. Sometimes this is observed in conjunction with ripple marks (Figs. 28 and 29), where it confirms the unidirectional nature of the current, but in other places no ripples are seen. Photograj)hs of manganese nodules at a depth of 5834 m in the northwest Atlantic have shown scour pits on one side of the nodules (Fig. 12). The existence of currents can sometimes be deduced from the lack of sediment cover on rocks, or from the way the sediment is lodged in cracks and crevices. Occasionally a rock face is seen where it has been abraded smooth by the passage of sediment-laden currents. This has been observed on seamounts where it is improbable that turbidity currents have been effective. d. Orientation of benthic fauna Certain filtration-feeding benthic fauna, such as gorgonians, crinoids, etc., have developed a planar shape that is suitable for the interception of maximum quantities of water, and they orient themselves perpendicular to the current. Some species, such as the common sea fan Gorgonia, are anchored rigidly to the bottom and are unable to change their orientation except by the slow process. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original wo
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
