ABSTRACT

Analysis of 690 asymmetric ripple mark and 40 cross-stratification paleocurrent directions from 37 localities in the Red Peak Formation of Wyoming indicates three major current directions: northeast, southwest, and northwest. These are interpreted to respectively represent wave drift, rip, and longshore currents moving on, off, and along a northwest-southeast oriented coast that bordered the shallow, open marine, Wyoming shelf embayment during the Early (?) Triassic.

Commonly used interpretive techniques based on calculated vector means of paleocurrent directions are inadequate for the polymodal distributions in the Red Peak. Instead, the major directions at each locality are determined and the resulting pattern interpreted visually. The use of vector means and moving averages would not define and could possibly mask the complex current patterns to be expected in the shallow, open marine environment.

Ripple marks have been used infrequently as paleocurrent direction indicators. The long standing misconception equating external shape with mode of formation has inhibited their use. Evidence from the Red Peak supports other studies which have suggested that "symmetric" and "asymmetric" ripple marks are not wave-and current-formed respectively. Rather, most ripple marks possess some degree of asymmetry, either in shape or internal structure, and are formed by currents (including most waves in shallow-water). Truly symmetric ripple marks formed by standing oscillatory waves are probably rare. Being current-formed, asymmetric ripple marks should prove increasingly important in reconstructing paleocurrent systems and paleogeography.