Variability of Holocene sealevel history along the southwestern coast of Australia — Evidence for the effect of significant local tectonism

Abstract

Holocene sealevel records for the interval 7400 14C yrs B.P. to the present were determined from accretionary sequences at three separate localities within the Perth Basin of southwestern Australia. The three records all differ dramatically despite an overall separation of sites of only 170 km. At the northernmost site the record shows sealevel was ca. 1.0 m below present MSL 7415 14C yrs B.P. and that it gradually rose to reach its present position ca. 5100 14C yrs B.P. with no evidence for a raised sealevel nor for significant oscillations. The record at the middle site shows a steadily declining sealevel from an initial high of ca. 2.5 m at 6400 14C yrs B.P., and is consistent with eustatic-hydroisostatic interpretations. The southernmost site shows the most complex sealevel history of the three with a still-stand at 2 or 3 m below present between 7000 and 5500 14C yrs B.P., an abrupt rise to 3 or 4 m above present MSL between 4800 and 3800 14C yrs B.P., followed by a decline with sealevel reaching its present position ca. 2800 14C yrs. B.P. Considered jointly the three differing sealevel records imply significant local tectonism during the Holocene along the southwestern coast of Australia. The data further indicate that this coast can no longer be considered as tectonically stable as previously assumed and consequently the sealevel evidence can no longer be considered to reflect only eustatic and eustatic-hydroisostatic influences.