Tidal Rhythmites; Why We Should Be Looking For Them

Erik P. Kvale and Allen W. Archer

Finely laminated sediments that preserve distinct tidal periodicities (tidal rhythmites) occur in a variety of modern and ancient depositional settings. These settings include tide-dominated delta fronts, abandoned tidal channels, tidal flats and bars found within estuaries, tide-dominated deltaic distributary channels, and tidal embayments. Many examples of ancient tidal rhythmites are found in successions once thought to be totally nonmarine. Thus, their recognition has obvious implications for the understanding of local depositional environments and paleogeographies. Because the best documented modern examples of tidal rhythmites are restricted to those settings where tidal ranges are meso- to macro-tidal, estimates of paleotidal ranges for ancient examples may be infe red. With enough regional rhythmite data, basinal reconstructions of paleotidal dynamics might be possible. Similar regional data consisting of several months of tidal deposition in different geological series may reveal changes in paleotidal dynamics over time. These changes might be related to changes in basinal geometry, caused by tectonic uplift or subsidence or changes in coastline configurations caused by the migration of depositional systems. Finally, multi-year tidal-rhythmite records have been documented from Cenozoic, Paleozoic, and Precambrian deposits and could form the basis for estimating rates of lunar-retreat through time and for site-specific determinations of seasonal climatic variability.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California