Elevations of sulfurous layers in acid sulfate soils: What do they indicate about sea levels during the Holocene in eastern Australia?

Abstract

This study is the first large scale examination of the stratigraphic relationships of acid sulfate soils in Australia. Field and laboratory data from 346 excavated acid sulfate soil profiles for an extensive soil survey undertaken to map their extent were classified into non acid sulfate soil (NASS), potential acid sulfate soil (PASS), and actual acid sulfate soil (AASS) layers, and the elevation of these layers within different geomorphic environments was examined. Layers containing sulfurous materials were found at 0.35 m below mean sea level in intertidal swamps, around mean sea level in areas subject to intermittent water logging, and greater than 0.40 m above mean sea level in other areas. Sulfurous materials in intertidal swamps represent present day formation while in other landforms are evidence for a sea level that was once higher than at present. The division of sulfurous sediment elevations into two groups above present day sea level could be explained by two processes. Firstly, two periods of higher sea level during the Holocene could result in sulfurous materials at different levels. Secondly, the barrier system which developed along the NSW coast during the Holocene and impounded a series of estuarine mud basins could have resulted in the formation of sulfurous materials at higher elevations along the edge of the lakes and at lower elevations on the lake beds themselves.