Sequence Stratigraphy and Paleotectonics, Denver Basin Area of Lower Cretaceous Foreland Basin, U.S.A.
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A sequence stratigraphic analysis of the Lower Cretaceous in the Denver basin area shows 100 m of intertonguing marine and nonmarine detrital strata punctuated by unconformities. The magnitude of erosion, thicknesses and facies distribution are influenced by subtle penecontemporaneous tectonics characteristic of the cratonic portion of the large Western Interior foreland basin.
These Albian-age strata contain 3 sequences related primarily to sea level changes but also influenced by fault block movement. Although several types of unconformities can be recognized only one type can be used as a sequence boundary. This type has a subaerially exposed surface of erosion with incisement of paleovalleys (up to 50 m deep) caused by a sea level lowstand. A second type unconformity within a depositional sequence is a submarine erosional surface related to the transgression of the shoreline over coastal plain deposits during a rising sea level. Minor erosional surfaces (diastems) also occur within the depositional facies.
Two messages from this study are: a) because many erosional surfaces occur within the Lower Cretaceous strata, care must be taken to select the correct surfaces as sequence boundaries; b) tectonic movement controls the location of paleovalleys, the erosional relief on unconformity surfaces, and the preservation of shallow water facies.
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