Outer Rocky Shores of the Mowanbini Archipelago, Devonian Reef Complex, Canning Basin, Western Australia

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. A B S T R A C TThe Oscar Range in Western Australia's Canning Basin features inliers of folded Paleoproterozoic quartzite, quartzitic conglomerate, and phyllite that formed islands during the Late Devonian. Undisturbed strata of the Pillara Limestone (Upper Devonian, Frasnian Stage) surround individual paleoislands that rise above the former seabed with a maximum topographic relief of 90 m. On average, the Mowanbini Archipelago (aboriginal name for the Oscar Range) lies 15 km off the granitic and metamorphic mainland represented by the Kimberley Block to the north. Devonian facies on outer rocky shores were studied at three localities near the southeast end of the Oscar Range. At the west end of the study area, a Devonian reef margin sits unconformably on Paleoproterozoic phyllite, but to the east, the reef is separated from rocky shores by a wide lagoon. Massive clast-supported conglomerate and sandstone beds interfinger with backreef carbonates where the reef is closest to land. Across the lagoon 2.5 km eastward, differential erosion between steeply dipping quartzite layers interbedded with softer phyllite resulted in low sea stacks, or skerries. Tabular quartzite cobbles and quartz sand were shed by the skerries as a unidirectional apron of "breccia" under shoal water conditions. Nearby offshore stromatoporoid thickets reflect growth orientation aligned with paleocurrents compatible with the breccia apron. On a smaller island 2.5 km farther east, lateral transport of debris from a quartzite shore to a contiguous phyllite sector of the coast conforms to the same pattern of water circulation. Overall, the physical geography of outer rocky shores in relation to the lagoon and barrier reef suggests that waves crashed over the reef to energize a longshore current that moved west to east at one end of the Oscar Range. A rapid rise in sea level probably promoted the burial and preservation of the Mowanbini Archipelago, characteristics shared with other examples of quartzite paleoislands that date from Cambrian to Cretaceous times.

Transgressive Eocene clastic-carbonate sediments from the Circum-Rhodope belt, northeastern Greece: implications for a rocky shore palaeoenvironment

“…This conclusion is reinforced by the principally unstable nature of carbonate rock fragments with respect to long transport, e.g. Tropeano and Sabato, 2000;Johnson, 2002;Clifton, 2003;Johnson and Webb, 2007;Corcoran, 2008). The lack of red stained or rimmed lithic grains also precludes remoteness of the sourceland and well-developed surface drainage.…”

“…Clifton, 2003). Such a general inference is drawn from the following important facts: (a) homogeneous lithology and subspherical shape (see Bluck, 1999) Tropeano and Sabato, 2000;Johnson, 2002;Clifton, 2003;Johnson and Webb, 2007;Corcoran, 2008).…”

Stratal architecture and platform evolution of an early Frasnian syn‐tectonic carbonate platform, Canning Basin, Australia

“…Furthermore, diurnal heating and cooling of the adjacent Kimberley Block landmass would have generated strong onshore winds and accompanying waves (cf. Johnson & Webb, ). On the Hull platform, the extent of lateral facies variation related to palaeowind direction is difficult to assess because of complete erosion of the windward (now south‐western) margin and limited exposure of leeward (now north‐eastern) margin facies only towards the top of the thicker measured sections (Figs and ).…”

Shoal-water dynamics and coastal biozones in a sheltered-island setting: Upper Devonian Pillara Limestone (Western Australia)

“…Earlier studies were conducted by this group at localities 1 (Johnson et al . ), 2 and 3 (Johnson & Webb ). Star denotes main study site.…”

“…This study is the third in a series of papers on Devonian rocky shores and coastal palaeoecology from the eastern sector of the Oscar Range in Western Australia. Previous contributions focused on biozones and long‐shore currents along the exposed, outer shores of quartzite islands (Johnson & Webb ) and the dynamics and sequence stratigraphical relationships of an island fluvial system that fed a shoal‐water delta within a narrow lagoon behind the inner reef margin (Johnson et al . ) (Fig.…”