Tidal signatures in an intracratonic playa lake

Abstract

Studies of modern sediments from tide-dominated marine coastal environments in the 1970s and 1980s led to the recognition of what were suggested to be unique sedimentary features formed by tidal currents. These features could be directly related to astronomical forcing by the Sun and Moon. Sedimentary structures formed by marine tidal processes are now frequently described in modern and ancient deposits. Here, we detail similar sedimentary features from shoreline deposits of Lake Eyre, Australia, a present-day, intracratonic playa lake setting, thus challenging the current paradigm that these structures are indicative of marine tidal influence. We attribute the formation of these features in Lake Eyre to meteorological tides generated by daily changes in wind direction and velocity, along with weekly to monthly discharge variations in the feeder river system. This is the first time such sedimentary features have been documented together in a continental setting. A key implication of this is that the classic "tidal" sedimentary structures recognized in ancient rock successions should not automatically be attributed to astronomical or marine tidal currents, since similar structures can be generated by meteorological processes in continental environments. Some interpretations of ancient marine tidal deposits without other lines of evidence supporting a marine depositional environment may therefore require reevaluation. Playa lakes and shallow perennial lacustrine settings should also be considered in the interpretation of strata containing what have formerly been considered classic marine tidal indicators. © 2012 Geological Society of America.