WEST KIMBERLEY PLACE REPORT - Department of Sustainability ...

post-deposition deformation and lack of dolomitisation that the area has experienced
is integral to this reconstruction (Johnson and Webb 2007; Playford et al 2009). As
noted by Playford et al. (2009) 'the present-day topography mimics that of the
Devonian sea floor, so that from the air it might appear that the sea has only recently
withdrawn from the area'. This allows interpretation at multiple scales. From the air or
in plan view, the topography preserves regional spatial relationships of the ancient
tropical ramp environment, from deeper water pinnacle reefs on the outer shelf,
through basins and platforms, slopes and reef margins to fringing reefs, islands and
lagoons. Finer resolution allows the reconstruction of detailed local palaeoecologies,
as demonstrated by John Long and others at the intrabasin Gogo localities, which
occur as deeper water slope communities. Johnston and Webb (2007) reconstructed
hydrodynamics, prevailing wind directions and local faunas from sediments and
spatial relationships around the palaeoislands of the Mowanbini Archipelago to yield
'a multifaceted and unparalleled portrait of marine biofacies dispersal in an ancient
tropical island group'.
Around the world, such long term preservation of large scale geographic relationships
in the rock record is rare (Johnson and Webb 2007). Relics of former shorelines are
more common, but tend to be very limited in exposure, and often subject to later
deformation. Devonian rocky shores are poorly documented in the literature.
Palaeoislands have been noted at several sites in North America but the retention of
rocky shores circumscribing entire archipelagos, as in the Mowanbini Archipelago
(represented by the palaeoproterozoic rocks of the Oscar Range) and intervening
undisturbed Pillara Limestone strata, is extraordinary and provides an exceptional
opportunity to reconstruct the spatial relationships of fossil communities and features
under the influence of a variety of depositional, mechanical and climate factors.
The much more recent Pliocene Loxton–Parilla sands (approximately 5,000,000–
2,000,000 years ago) in the upper part of the Murray Basin sequence are part of a
prograding shelf environment which formed as 400 kilometre long barrier complexes
in the Miocene 'Murravian Gulf' under the action of long-period ocean swell waves.
The sequence preserves a series of shore line ridges, formed in response to sea level
fluctuations linked to Milankovitch cycles in the Pliocene epoch. These strand lines
can be used to date and reconstruct sea level advance and regression in response to
climate forcing and demonstrate inshore hydrodynamics at a gross level. Although
minimally deformed (aside from localised uplift), in most areas, the resulting 400
kilometre wide barrier strand plain is now entirely overlain by fluvial, aeolian, and
lacustrine deposits and does not provide the same resolution, variety of shelf
environments or possibilities for elucidation of former spatial/geographic
relationships as the Lennard Shelf complexes (Roy et al. 2000). They are also 370
million years younger. The Ediacara sites at Nilpena, South Australia, are thought to
represent an ancient sea floor on the edge of a submarine canyon, undisturbed enough
to preserve the softbodied organisms that make up the fauna at that time in life
positions. This site, however, preserves a single environment at a much older time
than that represented in the Kimberley and on a smaller scale. At the only comparable
Devonian shelf environments in Australia, the Devonian Wee Jasper/Taemas (New
South Wales) and Buchan (Vic) reef sites, the tropical ramp environments preserved
have been deformed by later tectonic events and only biohermal and bistromal reefs
are preserved, without the excellent preservation and the suite of shelf environments
represented in the Kimberley (Yeates 2001).
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