Abstract

Cross-stratified sedimentary layers have been referred to as cross-stratified beds or strata by some geologists. The term "bed," when applied to cross-stratified layers produced by climbing bedforms, is in conflict with the term "pseudobed," which has also been applied to such layers. It is proposed that this conflict be resolved by excluding any necessary isochronism from the terms for sedimentary layers and for their bounding surfaces. The sedimentological definition of "bed" is thus made essentially the same as its rock-stratigraphic definition, and a cross-stratified layer produced by the climbing of a bedform can then be properly called a cross-stratified bed or stratum. A new name, "translatent stratum," is proposed for a stratum that is generated by the dominantly translational movement of a depositional surface and whose bounding surfaces are generated wholly or in major part by the dominantly translational movement of linear features on or bounding the depositional surface. The most useful characteristic for recognizing a translatent stratum is that the former depositional surfaces within the stratum meet both bounding surfaces of the stratum. Translatent strata may be classified as laterally translatent and climbing translatent, depending on whether the direction of translation is parallel to or at an angle to the generalized depositional surface; a climbing translatent stratum is what has previously been called a pseudobed. Climbing-ripple structure is composed potentially of climbing translatent strata and of wavy laminae or crosslaminae whose bounding surfaces are former rippled depositional surfaces. The wavy laminae are here called "rippleform laminae." Rippleform laminae are not detectable in some climbing-ripple structures, especially those formed by wind ripples. The characters of climbing translatent strata and of rippleform laminae vary with the angle of ripple climb and change abruptly at the critical angle of climb, which is defined here as the angle at which the vector of ripple climb is parallel to the steepest part of the ripple stoss slope.

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