Ancient Shorelines as Indicators of Sea Level

Abstract

Abandoned shorelines mark former sea levels in only the broadest sense because they only indicate a range of water levels. Careful investigation is necessary to pinpoint the actual position of the water boundary. To this end, aggradational relief forms that can be positively identified as such may be used. Indicators of abandoned shorelines may be categorized as either geological, biological, or archeological. This paper deals with major geological and biological features of abandoned shorelines in relation to the position of contemporary shorelines. Relict abrasion and accumulative relief types such as abrasion terraces, wave-cut notches, beach ridges, and aggradational terraces are related to former sea levels and can provide useful data for these reconstructions. Erosional scarps and coastal solution holes can also be useful indicators of former sea stands. In tropical and sub-tropical areas, beach-rock formation and deposits ofoolite are often useful indicators of abandoned shore-lines, as are peats and marsh and mudflat deposits. Organic materials such as peat and mollusc shells can be dated by radiometric methods.