. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT, 2] MICROTOPOGRAPHY 463 is that they are sometimes grouped in regvilar patterns such as straight hnes or circles, six or eight holes comprising the group (Figs. 31 and 32). Among the most spectacular features in the sediment of the sea floor are the tracks made by mobile fauna. The largest track so far observed is 15 cm wide showing a central ridge, parallel lines of small depressions on either side, and transverse markings on the ridge (Fig. 33). It seems likely that these tracks were made by a mud feeder such as a h
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT, 2] MICROTOPOGRAPHY 463 is that they are sometimes grouped in regvilar patterns such as straight hnes or circles, six or eight holes comprising the group (Figs. 31 and 32). Among the most spectacular features in the sediment of the sea floor are the tracks made by mobile fauna. The largest track so far observed is 15 cm wide showing a central ridge, parallel lines of small depressions on either side, and transverse markings on the ridge (Fig. 33). It seems likely that these tracks were made by a mud feeder such as a holothurian, the transverse marks being made by scooping the mud into suspension, and the depressions by its « •"<• Fig. 33. 41° 18']Sr, 14° 'W. Depth 5341 m. Iberia abyssal plain. Area of picture 1 by 1 m. (Photo by ) Broad tracks (15 cm wide) in Globigerina ooze made by a mud-feeding animal on the surface. Note the regular indentations (5 cm apart) either side of the tracks and the transverse markings (top left) suggesting a mud-scooping action resulting in a central ridge. Smaller but more numerous tracks have been identified as having been made by smaller holothurians and sea-urchins (Fig. 34). Unidentified animals with long thin conical shells (resembling scaphopods), with two extended arms, have often been photographed at the end of thin and rather angular tracks (Fig. 35). Occasionally fish feeding near the bottom leave marks where the lower tip of the tail touches the sediment surface. The greatest contribution to the disturbance of the sediments is due, how- ever, to the galleries and dwelling holes of burrowing worms and other infauna which are visible to the camera only where they come to the surface. However, they are shown up well in cross-sections of cores in the region where the sedi- ment colour changes. Galleries bored in the lower material become filled subsequently with the upper material and this constitutes a mixing process.
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
