Australia: The Land Where Time Began

A biography of the Australian continent 

Molecap Greensand & the Overlying Gingin Chalk

A continuous weathered sequence of shallow marine strata is comprised of the Molecap Greensand and the overlying Gingin Chalk. Around the townships of Dandaragan and Gingin in the Perth Basin of southwestern Western Australia the strata outcrop extensively. The Molecap Greensand is mostly comprised of glauconitic sandstones with no distinct bedding, the authors1 suggesting there may be considerable amounts of reworked material contained in them. The extremely fine chalky sediments of the overlying Gingin Chalk is composed of compacted planktonic skeletons. Shallow coastal marine conditions with bottom water that was poorly oxygenated are believed to have been the Palaeoenvironment in which both units were deposited.

The age of the Molecap Greensand has been disputed. An unusual mixed assemblage of plankton from the Cenomanian-Coniacian is indicated by rich palynomorph assemblages. The authors1 suggest this may have resulted from a sediment slump, possibly associated with the formation of the Yallalie impact structure, a buried crater that resulted from an asteroid impact in the Late Cretaceous. A number of ages have been proposed for the Gingin Chalk, from the Santonian to the lowermost Campanian. The fossil record in the Molecap Greensand/Gingin Chalk, though fragmentary, contains evidence of marine reptiles - mosasaurs, plesiosaurs and ichthyosaurs, sharks, bony fish and dinosaurs. In the Gingin Chalk the invertebrate record is dominated by benthic molluscs.

Sources & Further reading

  1. Kear, B.P. & Hamilton-Bruce, R.J., 2011, Dinosaurs in Australia, Mesozoic life from the southern continent, CSIRO Publishing.
Author: M. H. Monroe
Last Updated 17/12/2011

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