Carbonate eolianites, quartz sands, and Quaternary sea-level cycles,Western Australia: A chronostratigraphic approach

摘要

Marine and eolian carbonate deposits, grouped under the name ‘‘Tamala Limestone’’, have been investigated along thousands of kilometers of coastal Western Australia (WA). Relative-age diagenetic features of carbonate sand dunes or ‘‘eolianites’’ indicate that coastal ridges decrease in age seaward, reflecting coastal accretion during successive sea-level stands. Yellow- to red-stained quartz sands are associated with eolianites as pits, lenses, extensive beds, and even 40-m-high dunes. A regional survey using whole-rock and land snail amino acid epimerization geochronology confirms the eolianite succession and provides a means of correlating widespread deposits along a steep climatic gradient and 161 of latitude. AMS 14C and uranium–thorium (U/Th) ages provide independent radiometric calibration of the amino acid ratios, and eolianite ages can be estimated using a parabolic kinetic model. Over 90% of the sampled eolianite deposits comprise Aminozones A, C, E (125 ka), F?, G, and H, and correlate with interglacials from o10 ka (Holocene) to ca. 500 ka. In contrast, at the type locality of the Tamala Limestone along the Zuytdorp Cliffs, the upper eolianitepaleosol units are characterized by advanced stages of cavernous weathering, pedogenesis, and recrystallization. In the same units, sediment and snail samples generally yield very low or non-detectable levels of amino acids. These factors along with the stratigraphic complexity of the deposits reflect an age much greater than a large majority of sites along the WA coastline. These findings encourage a revision of the existing classification and nomenclature of Quaternary carbonate deposits in WA, as well as a reexamination of the underlying mechanisms related to the formation and emplacement of both carbonate and quartz dunes.