Late-Holocene sea-level changes in south and southwest Iceland reconstructed from littoral molluscan stratigraphy

Abstract

Sediments deposited during late-Holocene rise in sea level have been found in the Stokkseyri Eyrarbakki (Flói) area of south Iceland. At Stokkseyri, marine littoral sediments containing a thermophilic intertidal faunal assemblage, mainly consisting of gastropods, bivalves and barnacles with a few polychaets, bryozoans and echinoids, have been encountered behind the present storm beach a short distance from the sea. The shell layers are up to 4 m in thickness and reach up to 6 m above the present sea level and 300 m inland. During the late-Holocene sea-level rise, the sea brought sediments and shell material from the coast into a lagoon behind the ridge where it accumulated on former bog layers, during two transgressive tendencies separated by a short regressive tendency. The ages of the two transgressive tendencies are apparently 2600-2800 and 2200-2400 'C years BP, respectively. Then, after the sea retreated, a thin soil layer formed on top of the marine series. Marine sediments of late-Holocene age containing thermophilic littoral species, which have been found in peat layers in the tidal zone of Gardskagi, Reykjanes, southwest Iceland, were deposited during a sea-level rise 3200 years ago. Thus, there are sporadic occurrences of sediments with thermophilic marine fauna of late-Holocene age along the Icelandic south and southwest coast, especially in sheltered places. The mollusc stratigraphy reveals three short periods with a rise in sea level during the late Holocene, 3200-2200 cal. years BP. The calculated sea-level index points indicate an average 'long-term' trend of sea-level rise as high as 2.11 mm/yr during this period in south and southwest Iceland. There are no indications of crustal subsidence occurring in the area at the same time.