Paleoshoreline
Shoreline which existed in the geologic past / From Wikipedia, the free encyclopedia
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A paleoshoreline (ancient shoreline) is a shoreline that existed in the geologic past. (Paleo is from an ancient Greek word meaning "old" or "ancient".)[1] Paleoshorelines are driven by changes in sea level over geological time. "Sea level" refers to the average level of a marine water body over a relatively long period of time (years). [2] Fluctuations in sea level is largely due to the melting and freezing of ice sheets. [3] The position of paleoshorelines differed greatly from modern shorelines and can be used to reconstruct past sea levels, environments and ecological communities. Paleoshorelines exist due to unique preservation processes and give insight into the formation and understanding of prominent marine structures. [2] Lakes may also have paleoshorelines.[4] The reconstruction of paleoshorelines also aid in the understanding of species migration, modern ecological assemblages, and paleoclimates.
Average sea level can advance and recede over much longer periods (thousands or millions of years), causing paleoshorelines which may be difficult to identify, but are often found in long lasting coastal structures such as beaches, sand dunes, and coral reefs.[5] Tides cause the ocean to advance and recede in a very short time scale, in most places about twice per day. Weather conditions can also cause short-term variations. Coastlines can also move by coastal erosion without a change in sea level. A perched coastline is an ancient (fossil) shoreline positioned above the present shoreline.
Just off the coast of parts of North America, in the last 21,000 years, sea level has varied from over 130 meters (430 ft) below present level to over 130 meters (430 ft) above present level.[6][7] Within those 21,000 years, humans have lived in North America the entire time.[8] In regions Regions where the continental shelf has a low relief, the paleoshoreline could be over 100 miles from the modern coastline.[9]