An investigation of primary features present in recent ephemeral braided stream deposits, Southern High Plains, Texas



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Texas Tech University


The uniformitarian approach to the interpretation of ancient sedimentary environments has been employed for over a century, however it has only been within the last two decades that serious attention has been given this type of investigation. Textural studies have yielded much significant information, but no attempt has been made to investigate the textural aspects of individual sedimentary features. It appears that interest in the interpretation of primary sedimentary features as a guide to ancient environments is rapidly gaining momentum. This type of investigation has an advantage over a textural approach in that the data can be collected rapidly and interpretations rendered without returning to the laboratory

Ephemeral braided stream deposits on the southern High Plains are characterized by numerous primary features, many of which are duplicated in other environments^ but the assemblage of features is seemingly unique^ Ripple marks that have been noted include cuspate or barchanoid current ripples, lobate current ripples, linear or transverse current ripple of linear or transverse wave ripples with parallel crests, rhombeid ripples, linear or transverse eolian ripples with parallel crests, linear or transverse eolian ripples with sub-parallel crests, ad eolian pinnate ripples. Other features include algal structures of various kinds, rill marks, scours graded bedding, chute-deltas> mud cracks, and clay chips and pebbles.

The data collected during this investigation indicate that cuspate^ lobate^ and eolian ripples can be distinguished on the basis of inclination of foreset laminae and value of the obtuse angle between the foreset and backset laminae. Ripple index is not a criterion for distinguishing between eolian and fluviatile ripples in ephemeral braided stream deposits It is important to be able to identify the type of ripple mark in ancient sediments because early cuspate, linear or transverse current ripples, and rhombeid ripples are good indicators of true channel trend.

An understanding of flooding in braided streams is important because most of the sedimentary features that are produced and topographic changes that occur are the result of flood stages.

The role of eolian processes is important because (1) the wind reworks part of the material deposited by the water^ thus^ forming new ripples; (2) a considerable portion of bar growth is the result of lateral accretion produced by the wind; (3) other previously formed features are covered by wind blown sand and may thus be preserved.

Cuspate, lobate^ and eolian ripple marks in a given locality can be distinguished on the basis of their textural characteristics^ The CM pattern of ephemeral braided stream deposits is similar to that of tractive currents as reported by Passega (1957)*



Sedimentation and deposition -- Texas, Geology -- Texas