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The AAPG/Datapages Combined Publications Database
CSPG Bulletin
Abstract
Carbonate Concretions in the Upper Cretaceous Cedar District Formation, British Columbia
ABSTRACT
The Upper Cretaceous Cedar District Formation of British Columbia, composed of alternating sandstones, siltstones, and shales, contains carbonate concretions of varied shapes and sizes. Calcite is the essential component, but detrital grains are abundant where the concretions are located in silty or sandy beds.
Several features suggest that the concretions were formed immediately after deposition of the host sediments or shortly after shallow burial: (1) animal borings or burrows in the concretions filled with sediment from the host beds; (2) thickening of the host beds around the concretions; (3) the random orientation of some concretions with respect to bedding and lamination, and the stretching and folding of others where present in beds showing soft-sediment deformation; (4) undeformed bivalved shells enclosed in the concretions; and (5) the scarcity of grain to grain contacts among the included detrital grains, and the undeformed mica plates. The concretions probably grew by precipitation of CaCO3 near decomposing organic matter in reducing and high pH environments.
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