The lithostratigraphy and biostratigraphy of a holocene coastal sediment sequence in Marazion Marsh, west Cornwall, U.K. with reference to relative sea-level movements

Abstract

A Holocene sedimentary sequence at Marazion Marsh, Mount's Bay, west Cornwall, U.K. is examined with reference to coastal evolution and relative sea-level change. A sample core analyzed in this paper shows the base of the sedimentary sequence rests on weathered bedrock material. Basal organic-rich deposits are overlain by minerogenic materials dominated by sand. A sharp contact separates these two sedimentary units. Changing coastal conditions are reconstructed using lithostratigraphic, biostratigraphic and Chronometric data from this sequence. The lower organic-rich unit accumulated between ca. 5420 ± 60 and 4380 ± 55 yrs B.P. Substantial changes in the marsh environment, involving vegetation succession from initial herb domination to mesophytic woodland and eventually to fen-carr/reed-marsh development, is indicated by pollen records from this unit. Diatom data show increased salinity within the basal sequence as arboreal pollen values decline and fen-carr/reed-marsh becomes established. Radiocarbon dates from this and other cores from west Cornwall are used to construct a local time/altitude plot of relative sea level (RSL). It is concluded that the sediment sequence at Marazion Marsh appears to have accumulated in an embayed environment. The sequence was both indirectly and directly affected by changes in relative sea-level position and the influence of protective/transgressive coastal morpho-sedimentary structures and associated processes of sedimentation during the mid-Holocene period.