The Sydney duricrusts: their terminology and nomenclature

Abstract

Two main duricrust types - laterites and ferricretes - and their underlying materials are mapped and described for the northern parts of the Sydney district, New South Wales. Laterites are by far the more widespread, being found both in the Wainamatta-Shales and in the Hawkesbury-Sandstone areas, particularly on the broad hilltops and interfiuves of the major divide between the three drainage systems - the north-flowing Hawkesbury-Broken Bay, the south-flowing Parramatta-Port Jackson and the east-flowing Pacific Ocean systems. The ferricretes occur mainly in the drier parts of the northwest, especially in the conglomeratic river gravels of the Maroota area. The two materials have similar profile characteristics but they are different in hand specimen, in textural and structural characteristics, and also in mineralogical composition. The duricrusts and their profiles have been widely destroyed and differentially truncated, so that their various zones and subzones are presently exposed at different places. These materials, especially in respect of laterites, are classified from field and laboratory evidence, according to their recognised, or assigned, position in the typical deep weathering profile. Names are assigned, depending on the area where the best examples were found.