Publication Details

Haredy, R., Jones, B. G. & Hutton, A. C. (2003). Heavy minerals in modern sediments of the Minnamurra estuary and shelf environment, NSW, Australia. 35th Sydney Basin Symposium on Advances in the study of the Sydney Basin (pp. 171-179). Wollongong, Australia: School of Geosciences, University of Wollongong.


Provenance and sediment distribution have been investigated in the Minnamurra estuary and the adjacent shelf in NSW, Australia. Heavy mineral assemblages in the sand fractions (63-250 f.lm) of 110 surficial sediment samples were assessed using microscopic and microprobe analyses. In addition to the dominant opaque minerals, twelve translucent heavy mineral species were identified. The translucent assemblage is dominated by pyroxene, zircon, tourmaline and hornblende. Statistical cluster analysis of heavy mineral percentages in the surficial sediments revealed the existence of five mineralogical facies: the upper fluvial part of the estuary, the Minnamurra spit and elevated inner sand terrace, the estuary inlet and inner part of the inner-shelf, a combined group consisting of the outer part of the iriner-shelf and the midestuary (Rocklow Creek), and the mid-shelf facies. The main factors that control the distribution of the surficial sediments and their contained heavy minerals are transport and hydraulic sorting processes, together with minor coastal erosion. This can be seen clearly on the shelf area with denser heavy minerals concentrated in shallow water deposits whereas the lighter platy heavy minerals become more prominent in the deeper water lower energy areas. The mid-estuary facies is a mixed zone that has a similar heavy mineral assemblage to the outer part of the inner-shelf; possibly resulting from reworking of marine-influenced sand sheets in the Rocklow Creek catchment. The Minnamurra spit (aeolian dune) and elevated inner sand terrace facies is distinctive with its high concentration of total heavy minerals, resulting from winnowing by wind and storm wave influences. The heavy mineral assemblage also identifies multiple sources. The occurrence of heavy minerals from non-local source rocks reflects reworking of quartz sand from the outer-shelf to the inner-shelf and coastal environments during the post-glacial marine transgression. These minerals were originally derived from the Precambrian craton in southeastern and central Australia, and from the Lachlan Fold Belt. The fold belt would have contributed both reworked older grains of ultrastable heavy minerals as well as some primary minerals from the igneous rock units. Fluvial and coastal erosion of the locallatite units and their associated volcaniclastic sedimentary succession has liberated pyroxene and epidote to the Minnamurra estuary and shelf. Fluvial erosion of a Mesozoic tinguaite (containing aegerine augite) and the Tertiary basalts at Robertson (containing titanaugite) have added to the mineralogical complexity, especially in the upper fluvial portion of the estuary.