Phillip E. Playford

Iridium anomaly in the upper devonian of the canning basin, Western australia.

A moderate iridium anomaly, about 20 times the local background, has been found in Upper Devonian rocks in the Canning Basin. It occurs at or near the Frasnian-Famennian boundary, which is known to be associated with a major massextinction event of global extent. The anomaly occurs in an extremely condensed limestone sequence laid down under quiet deepwater conditions. Its occurrence suggests a causal link with some form of meteoroid impact. Moreover, carbon isotope data indicate that a large reduction in biomass could have occurred at this level. However, the anomaly coincides with a stromatolite bed containing the fossil cyanobacterium Frutexites; iridium, platinum, iron, manganese, cobalt, arsenic, antimony, and cerium are preferentially concentrated in filaments of this organism, with concentrations ranging from two to five times that of the matrix. It is possible that Frutexites extracted these elements directly from seawater, without the need for their derivation from an extraterrestrial source.

Marine Diagenesis in Devonian Reef Complexes of the Canning Basin, Western Australia

Marine diagenesis is widely recognized as a critical process in the development of reef complexes, both ancient and modern (James and Choquette 1983, James and Ginsburg 1979, Krebs 1969, Mountjoy and Krebs 1983, Playford 1980, 1984, Purser 1969, Schroeder 1972, Walls and Burrowes 1985). Marine cementation, together with frame-building reef organisms, is largely responsible for building reefs into rigid, wave-resistant structures with positive relief above the seafloor. Indeed, it has been suggested for some reefs that cementation was the dominant reef-building process and that they should therefore be regarded as inorganic “reefs” (Schmidt 1977).

Sedimentary and faunal changes across the frasnian/famennian boundary in the canning basin of Western Australia

The Canning Basin of northwestern Australia is a key area for understanding global changes at the “Kellwasser Events” and the Frasnian‐Famennian boundary. Frasnian stromatoporoid‐coral‐cyanobacterial reef platforms stretched out for enormous distances along the palaeoshelf but in the early Famennian they were completely replaced by cyanobacterial reef platforms. An iridium anomaly in the sequence was formerly believed to be at or close to the boundary and was interpreted as possible evidence for an asteroid impact. Recent field work and detailed biostratigraphy in the area east and southeast of Fitzroy Crossing has given dating relevant to the timing and extent of sea level changes, hypoxic incursions and reef backstepping. Goniatites and conodonts provide correlations with the international biostratigraphy. In the Horse Spring area the stage boundary falls within the Virgin Hills Formation which normally has a rich pelagic goniatite, nautiloid and conodont fauna. In the latest Frasnian (Zone 13 of Klappe...

Late Devonian Radiolaria from the Gogo Formation, Canning Basin, Western Australia

Fifteen taxa of polycystine radiolarians are described and illustrated from calcareous nodules in the Frasnian Gogo Formation. Because of poor preservation most taxa are placed in open nomenclature. The fauna includes Palaeoscenidium and entactiniids common in the Late Devonian of North America and the USSR. Spongentactinella windjanensis is described as new.

Algal stromatolites: deepwater forms in the devonian of Western australia.

A diverse assemblage of algal stromatolites occurs in Devonian reef complexes of the Canning Basin, Western Australia. Some forms grew on fore-reef depositional slopes down to at least 45 meters below sea level and are believed to be products of deepwater nonskeletal algae. It is concluded that algal stromatolites in the stratigraphic record are not to be regarded as diagnostic evidence for deposition in very shallow water.

Upper Devonian iridium anomalies, conodont zonation and the Frasnian-Famennian boundary in the Canning Basin, Western Australia

Abstract Two iridium anomalies have been identified near the Frasnian-Famennian boundary (Upper Devonian) in the Canning Basin of Western Australia. Both anomalies are associated with the cyanobacterium Frutexites and are located in marginal slope facies. The first was identified in the Virgin Hills Formation on the west flank of McWhae Ridge near the southeastern end of the Devonian outcrop belt. This anomaly, initially identified as being from the Famennian Upper Palmatolepis triangularis Zone, is now known to be from the Early Palmatolepis crepida Zone, on the basis of the presence of Palmatolepsis crepida in the bed. The second anomaly, found in drill core from the Napier Formation just south of the Napier Range, is older than the first and is from the Frasnian Montagne Noire Conodont Zone 12 or 13 of Klapper (1989) = the Palmatolepis rhenana Zone of Ziegler and Sandberg (1990). These two iridium anomalies are thus significantly below and above the Frasnian-Famennian boundary and are not associated with the extinction event in the Palmatolepis linguiformis Zone. In the Canning Basin the association of two iridium anomalies with beds containing abundant Frutexites microstromatolites indicates that the concentrations of iridium are probably associated with a process of organic concentration. There is no evidence that either example is directly associated with an impact event.

Platform-margin collapse during Famennian reef evolution, Canning Basin, Western Australia

Sedimentological investigations of well-exposed slope strata in the Upper Devonian reef complexes of the northern Canning Basin lead to a sequence-stratigraphic interpretation that differs from others based on predictive models in which coarse carbonate debris deposits are regarded as lowstand deposits. In the upper Frasnian–Famennian Napier Range slope succession, we recognize an important phase of platform-margin collapse during a sea-level highstand in the middle Famennian. At this time the reef-rimmed margin was rapidly prograding, and the platform was producing carbonate grains (notably ooids and peloids) that were being transported by turbidity currents to the slope and basin floor. Periodic collapse of the platform margin led to deposition on the slope of allochthonous blocks of reefal limestone and channelized debris-flow units, intercalated with the ooid-peloidal turbidites and quartzo-feldspathic sandstones. Collapse of the early-cemented margin was probably triggered by gravitational instability caused by oversteepening during rapid progradation and/or tectonic activity, with falling blocks initiating some of the debris flows.

Burial diagenesis in the Upper Devonian reef complexes of the Geikie Gorge region, Canning basin, Western Australia

The Devonian carbonates of the Geikie Gorge region, Canning basin, have undergone a long and complex diagenetic history that began in Devonian seawater with extensive marine cementation of platform-margin lithologies. Devonian-Lower Carboniferous burial diagenesis was the most important porosity occluding episode because almost all primary porosity was destroyed by equant calcite cements (nonluminescent to brightly luminescent to dully luminescent) during this interval. Dolomitization and consequent secondary porosity development also occurred during early burial diagenesis. The distribution and geochemistry of the major calcite cements and dolomite types are consistent with these phases having been precipitated from connate marine or basinal brines. Karstification and mi or calcite cementation took place during Late Carboniferous subaerial exposure. Minor calcite cementation occurred during Permian-Cenozoic burial, predominantly in secondary porosity within pervasively dolomitized lithologies. Karstification, dedolomitization, and calcite recrystallization took place in association with Cenozoic meteoric diagenesis. Secondary moldic and intercrystalline porosity within the completely dolomitized lithologies were the longest lived porosity types in the carbonates. Some secondary porosity escaped both Devonian-Carboniferous and Permian-Cenozoic burial cementation, probably due to a lack of nucleation sites for calcite cements within completely dolomitized lithologies.

ENVIRONMENTAL PRESSURES INFLUENCING LIVING STROMATOLITES IN HAMELIN POOL, SHARK BAY, WESTERN AUSTRALIA

Abstract: Environmental parameters in Hamelin Pool, Shark Bay were investigated to characterize extrinsic factors that may be affecting stromatolite morphogenesis. Hamelin Pool, which evolved into a restricted environment during the last few millennia, sustains the worlds most extensive and diverse assemblage of modern marine stromatolites. These stromatolites occur in a shallow nearshore facies belt covering over 100 km of coast. Temperature, salinity, water level, and current data collected between 2012 and 2014 have revealed previously undocumented regional and seasonal trends. Regional trends include increasing salinity, greater temperature range, and decreasing energy moving southward from Faure Sill and to the Nilemah Embayment. Seasonal trends reveal paradoxically increased salinities in wet winter months and decreased salinity in dry summer months. When paired with annual tidal cycles, these trends suggest the influx of low salinity groundwater along the Hamelin Pool shelf. Speculation on how the documented environmental parameters may affect stromatolite growth suggests potential impact on morphology, internal fabric, and stromatolite-building microbial communities. These insights into environmental pressures within a living stromatolite system provide a framework for understanding extrinsic factors affecting microbial communities and stromatolite development throughout Earth history.

Novel paleoecology of a postextinction reef: Famennian (Late Devonian) of the Canning basin, northwestern Australia: Comment and Reply

[Rachel Wood (2000)][1] discussed changes in the Devonian reef- building biota across the Frasnian-Famennian (F-F) boundary in the Canning basin. This boundary coincides with a major mass extinction of metazoans, yet Wood concluded that the Famennian reef-building community shows “no noteworthy