. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography AUTOCHTHONOUS PATTERNS OF SEDIMENTATION 331 ® PRIMARY RIDGE PRIMARY TROUGH PRIMARY RIDGE â HOLOCENE SILTY CLAY -^-PLEISTOCENE SAND :':>?:? ::>â -'^ ' â ' T- â "' ^m* -«- PLEISTOCENE SILTY CLAY PRIMARY RIDGE. DEVELOPMENT OF RIDGE TOPOGRAPHY FIGURE 21. Ridge evolution on the central New Jersey shelf. (A) Ridge nuclei are formed during the process of ridge detachment and shoreface retreat, or by other means in the nearshore zone. Sand cont
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography AUTOCHTHONOUS PATTERNS OF SEDIMENTATION 331 ® PRIMARY RIDGE PRIMARY TROUGH PRIMARY RIDGE â HOLOCENE SILTY CLAY -^-PLEISTOCENE SAND :':>?:? ::>â -'^ ' â ' T- â "' ^m* -«- PLEISTOCENE SILTY CLAY PRIMARY RIDGE. DEVELOPMENT OF RIDGE TOPOGRAPHY FIGURE 21. Ridge evolution on the central New Jersey shelf. (A) Ridge nuclei are formed during the process of ridge detachment and shoreface retreat, or by other means in the nearshore zone. Sand continues to be swept out of troughs onto ridges as water column deepens during the course of the Holocene transgression. (B) Seafloor scour during storms locally penetrates the Early Holocene lagoonal clay carpet, and a secondary trough forms, initially by downcutting. (C) Downcutting in the secondary trough decreases and lateral erosion increases as second silly clay layer is exposed. Secondary trough widens by undercutting of upper clay in "blowout" fashion. Sand from similar excavations upcurrent forms secondary ridges. From Stubblefield and Swift (in press). The trough axis tends to climb toward a low sill on the southern side of the massif; beyond this the seafloor drops off rapidly to the adjacent shelf valley. The valley floor commonly consists of fine to very fine featureless sand. The topography and grain-size pattern suggest that south-trending flows converge with the rising sea- floor and accelerate up the northern flanks of the massifs. Fine sand swept out of the troughs is deposited in the zone of flow expansion and deceleration over the shelf valley south of the massif. TEXTURAL AND MORPHOLOGIC PATTERNS ON A TIDE- DOMINATED shelf. The tide-swept shelf around the British Isles (Stride, 1963) provides an interesting con- trast with the storm-induced sedimentation of the Middle Atlantic Bight. Surges are at least as frequent here as in the Middle Atlan
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