Abstract

Ripple marks formed in consolidated sediments without movement of the constituent particles occur in the Lower Ordovician Garden City Formation in the Stansbury Mountains, 40 mi W. of Salt Lake City. These marks were cut in lithified limestone pebble conglomerates. The symmetric ripple marks have wave lengths of 2-3 in. and amplitudes up to 1/2 in. The overlying beds are argillaceous limestones braided with siliceous silty laminae. The evidence indicates that the first silty sediment was set in wavy motion on the floor of a body of water, and the loose silt scoured the troughs and rounded the crests. The position of the troughs did not change or did not change fast enough to erase the marks. The braided lamination, as viewed in cross section, probably was caused by similar wavy motion of the water acting on unconsolidated clay and silt size sediments. Ripple marks in these sediments could not be retained completely and the remnants of such marks were further distorted during compaction. Another type of bedding surface mark in which the uppermost pebbles have been truncated by eroding silt is also present. These marks are rounded ridges up to 4 in. high, 18 in. wide, and from 23-57 in. from crest to crest. These ridges have sinuous trends and are discontinuous. They are formed of well-rounded limestone pebbles cemented by calcareous muds. The overlying beds are limestone braided with siliceous silt. The truncation of the uppermost pebbles in this case may have been a final modifying process on pre-existing ridges.

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