Sedimentology of the Late Cretaceous Judith River Formation, "Cathedral" area, Dinosaur Provincial Park, Alberta
LccQE 688 W66 1987
LcshGeology, Stratigraphic - Cretaceous
Geology - Alberta - Dinosaur Provincial Park
Geology - Alberta - Judith River Formation
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AbstractVirtually continuous, three-dimensional exposure of the Late Cretaceous, Judith River Formation in "The Cathedral" area of the Dinosaur Provincial Park badlands provides a rare opportunity to analyse the sedimentological architecture of an ancient coastal plain succession. Four major lithofacies have been recognized in this 60 m thick sequence, namely: 1) an erosionally-based, 2.5-11 m thick, trough cross-bedded sandstone facies (TX); 2) large-scale inclined heterolithic strata (IHS) with original dips of 1-21°. This facies is 3-13 m thick and is comprised of decimetre-scale thick interbeds of either sandstone and mudstone , or intraformational conglomerate and sandstone; 3) a 1-5 m thick sandstone facies (IBS) with large-scale inclined bedding showing original dips of 1-200, and (4) a 0.1-12 m thick, massive shale facies (SH). The study sequence has been divided into six erosionally-based, coarse-to-fine rhythms. Three rhythms have the upward lithofacies sequence TX-IHS-SH, one has TX-IBS-SH, and another has IHS-SH. The sixth rhythm is incompletely preserved . Trough axes indicate unidirectional palaeoflow sub-parallel to the strike of associated IHS or IBS bedding planes. The coarse member of each rhythm (comprised of one or more of TX, IHS or IBS) is interpreted to be a product of iii the lateral migration of a single, fluvially-dominated, meandering channel. TX sequences are regarded as channel bottom and lower point bar deposits, and IHS and IBS sequences are interpreted to be products of contemporaneous point bar lateral accretion. SH sequences are considered to be floodplain deposits laid down during, or after, associated active-channel migration. Palaeochannel reconstructions suggest bankfull depths of 7 m to 25 m and widths of 56 m to over 120 m. An upper delta plain or distal alluvial plain physiographic setting is envisaged for these palaeochannels. Occasional marine influence in the palaeochannels, as suggested by previously reported fossil occurrences, is considered to have resulted from infrequent hydraulic backwater effects rather than daily tidal cycles. Heterolithic point bar sequences (IHS) were deposited under conditions of fluctuating discharge, whereas the sand-dominated point bar sequence (IBS) was laid down in a more steady, generally higher-energy hydrological regime. The spatial and temporal distribution of these different discharge regimes was probably controlled by the combined effects of autocyclic and tectonic mechanisms. Taphonomic modes of occurrence of vertebrate and plant fossils are readily explained in te~ms of the meandering channel models proposed. The first volcanic ash bed reported from Dinosaur Provincial Park strata was discovered during this study.
Bibliography: p. 200-213.
CitationWood, J. M. (1985). Sedimentology of the Late Cretaceous Judith River Formation, "Cathedral" area, Dinosaur Provincial Park, Alberta (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/11958
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