Microfossil-Based Reconstructions of Holocene Relative Sea-Level Change

Abstract

Fossil microorganisms are valuable sea-level indicators if modern populations can be precisely related to tidal heights. The vertical position of microorganisms in the modern environment relative to sea level is known as their ‘indicative meaning.’ Foraminifera, diatoms, testate amoebae, and, to a lesser extent, ostracoda are groups of microorganisms that occupy distinct vertical niches in the intertidal zone, have quantifiable indicative meanings and can therefore be used as sea-level indicators in Holocene sedimentary coastal sequences. Pollen analyses are also used in sea-level studies, but only as chronological markers, as indicators of coastal vegetation or to demonstrate the continuity of stratigraphic sequences. Along isostatically uplifting coasts, sea-level changes can be reconstructed from microfossils preserved in sediments in isolation basins. Along isostatically subsiding coasts, microfossils preserved in estuarine, salt-marsh and coastal lagoonal facies can be used to reconstruct relative sea-level changes. Microfossils are also useful to estimate vertical displacement from sediments along tectonically active coasts. The most precise paleosea-level estimates are derived from microfossils preserved in sediments that were deposited in the uppermost part of the intertidal zone. Specialized software is available to quantify the indicative meaning of microorganisms using regression analyses. Transfer functions can be applied to microfossils preserved in sediments to obtain high-resolution sea-level histories with error bands. A range of radiometric dating and stratigraphic marker techniques are available to provide accurate chronologies for microfossil-based sea-level reconstructions.