Wright, Amelia M., Ratcliffe, Kenneth T., Zaitlin, Brian A. and Wray, David S. ORCID: 0000-0002-0799-2730 (2010) The application of chemostratigraphic techniques to distinguish compound incised valleys in low-accommodation incised-valley systems in a foreland-basin setting: an example from the Lower Cretaceous Mannville Group and Basal Colorado Sandstone (Colorado Group), Western Canadian Sedimentary Basin. In: Ratcliffe, Kenneth T. and Zaitlin, Brian A., (eds.) Application of Modern Stratigraphic Techniques: Theory and Case Histories. SEPM Special Publications (94). SEPM (Society for Sedimentary Geology), Tulsa, USA, pp. 93-107. ISBN 978-1-56576-199-5

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Abstract

Changes in the bulk inorganic geochemical composition of both sandstones and silty mudstones taken from conventional cores are used to subdivide the Lower Cretaceous Mannville Group and the overlying Colorado Group into chemostratigraphic packages and geochemical units. The chemostratigraphic packages are broadly equivalent to lithostratigraphic formations whereas the geochemical
units are represent finer-scale informal stratigraphic subdivisions that occur within the formations.
The chemostratigraphic packages are equivalent to the Lower Mannville Formation, the Upper Mannville Formation, the Basal Colorado Sandstone (an informal unit at the base of the Colorado Group), and the overlying Joli Fou Formation. The changes, which enable each lithostratigraphic unit, or chemostratigraphic package, to be geochemically fingerprinted, are primarily related to changes in mineralogy,which in turn appear to coincide with changes in sediment provenance and basin architecture. These chemostratigraphic packages, which are broadly equivalent to lithostratigraphic formations, can be considered to result from first-order changes in whole-rock geochemistry.
The geochemical units are equivalent to incised-valley-fill sequences within the lithostratigraphic units, and here it is shown that the incised-valley-fill sequences of the Upper Mannville and Basal Colorado Sandstone each have a unique geochemical signature. Three incised-valley-fill sequences are present in the latter intervals, the oldest of which lie within the Upper Mannville Formation. Valleys at the base of the Basal Colorado Sandstone incise Upper Mannville deposits and are termed the lower Basal Colorado sandstones. The youngest valleys lie at the top of the Basal Colorado Sandstone and are termed the upper Basal Colorado sandstones. The sedimentary deposits in each of these incised valleys can be chemically distinguished from one another, even where a sandstone-on-sandstone contact is present in a single wellbore. The geochemical changes that enable each incised-valley fill to be recognized can be considered as second-order variations and are referred to as geochemical units. Stacked valleys observed in the Lower Mannville Formation have been the subject of previous chemostratigraphic work, and all of these have a unique geochemical signature and are also considered here to be geochemical units.
The base of each incised-valley-fill succession, or geochemical unit, is a sequence boundary. By enabling clear identification of the geochemical unit above and below a sequence boundary, the technique of chemostratigraphy has direct application to aiding both lithostratigraphic and sequence stratigraphic correlations in low-accommodation basin settings.

Item Type:	Book Section
Uncontrolled Keywords:	chemostratigraphy, incised valleys, Mannville Group, Colorado Group
Subjects:	Q Science > QD Chemistry Q Science > QE Geology
Faculty / School / Research Centre / Research Group:	Faculty of Engineering & Science > School of Science (SCI)
Related URLs:	Publisher Organisation Organisation
Last Modified:	08 Dec 2016 12:40
URI:	http://gala.gre.ac.uk/id/eprint/7173

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