We describe the thecideid brachiopod Praelacazella wetherelli (Morris, 1851) from the lower Maastrichtian Korojon Formation in the Carnarvon Basin, Western Australia. This is the first documented ...record of Praelacazella wetherelli from the Southern Hemisphere, suggesting that the species was cosmopolitan in distribution during the Late Cretaceous. Three possible long-distance migration routes are discussed.
•This is the first documented occurrence of Praelacazella wetherelli in Australia.•Until now, it was known only from Europe where it is mainly known from chalk facies.•Praelacazella wetherelli thus appears to be a cosmopolitan species.•Three possible migration routes of P. wetherelli are put forward.
The Western Australian margin is a unique coral reef province, with modern coral reef development occurring at latitudes as far south as 29°S. The genesis of this coral reef province may go back to ...the Oligo-Miocene, since geological features ~30 million-year-old and younger interpreted as coral reefs are known from offshore seismic surveys. The nature of these seismic reefs is, however, uncertain, as they are only sparsely sampled, and as time-equivalent outcrops are only present in a few remote and understudied locations. This study investigates middle Miocene shallow-water limestones with tropical fauna formed along the North West Shelf (NWS) between ~13 Ma and ~15 Ma, when the southward extension of the seismic reefs was at its maximum. The outcrops and cores investigated are dominantly composed of peloidal packstones and micritic floatstones containing larger benthic foraminifera, Halimeda sp. and scleractinian corals, including reef-building genera, that accumulated in a protected and oligotrophic, warm-water lagoonal environment. Climate was therefore warm during the middle Miocene acme of seismic reefs development, despite the NWS being located ~7° further south than its present position at that time. Results of this investigation also support the existence of a strong southward flowing Leeuwin-current-style oceanic circulation during the middle Miocene, which could have transported fauna from south-east Asia along the Western Australian margin. Development of the lagoon and seismic reefs may have also been promoted by middle Miocene aridification of the coast bordering the NWS, and by repeated eustatic-driven exposures of the NWS.
Display omitted
•Lagoon 15–13 Ma with taxa characteristic of tropical oligotrophic reef environments•Facies with micrite, scleractinian corals, Halimeda and larger benthic foraminifera•Outcrops time-equivalent to offshore Middle Miocene Western “Great Barrier Reef”•Time-equivalent to Miocene Climatic Transition, post-date Miocene Climatic Optimum•Climatic, paleoceanographic (proto-Leeuwin current), eustatic or tectonic controls
Shallow-marine methane seeps, described here for the first time from the Australian Upper Paleozoic, are among few reported globally from the Carboniferous–Permian. Carbonate-cement fabrics, δ13C ...values and biota indicate that concentrations of nodules scattered in a narrow stratigraphic interval within the lower Holmwood Shale in the Irwin Basin formed in methane seeps. Based on ammonoids, this zone belongs within the Sakmarian. The Holmwood Shale overlies the glaciogenic Nangetty Formation that sits on crystalline Precambrian basement. The Holmwood is little deformed, shows low thermal maturation and has been covered by less than 1000 m of Permian and Neogene strata. The nodules are cementstone with complex multiphase cement fabric and δ13C values (mostly, ‐25 – -45‰ VPDB) below the ranges for normal-marine limestone and carbonate nodules common in marine shale elsewhere. A biota preserved in nodules of the seep deposits includes representatives of three ecosystems: seep, pelagic, and coastal plain. The seep biota, new to the Australian Permian, consists of small thickets with a framework of tubeworms, less common algal-like Tubiphytes, and problematica (? algae or sponges). Other components include microbial mats, macrophyte alga Litostroma (first report from Gondwana); foraminifers; sponges with siliceous monaxon spicules; a new group of small, lightly ornamented rostroconchs; microgastropods and rare larger types; ostracods and minute scolecodonts from polychaete jaws. Elements of the pelagic ecosystem are ammonoids (abundant in enclosing shale) and marine microphytoplankton. Probable vertebrate bone (possibly amphibians) and diverse spores and pollen from land plants come from the adjoining coastal plain. The surrounding mudstone lacks benthic macrofauna but includes an unusual assemblage of siliceous agglutinated foraminifers. The seeps were oases of high organic productivity on an otherwise barren muddy seafloor. The Holmwood Shale's seep carbonates have close similarities to modern seep deposits in shallow-marine settings. They more closely resemble the modern deposits than some of the few others interpreted elsewhere from the Carboniferous–Permian, but seem close to equivalents in shale of latest Pennsylvanian (Gzhelian) age overlying glaciogenic deposits in the Namibian sector of East Gondwana. In both regions, deglaciation of Pennsylvanian ice sheets that covered large parts of East Gondwana, dewatering of melt-water from the glaciogenic sediment pile after burial, and associated release of probable biogenic methane seems to have coincided with formation of seeps.
•First reported methane seeps in Australian Upper Paleozoic.•Among few Permian methane-seep occurrences recognized globally.•Concentrations of carbonate nodules in thick marine mudstone above glaciogenic unit.•Post-glacial shallow marine conditions in interior sea with flat seafloor.•Nodules with cement fabrics, biota, and δ13C values similar to those in modern seeps.
Although carbonate ramps are widely described from the geological record, there is still a debate on the relative influence of water temperature, trophic conditions and type of carbonate factories on ...their development. The ca 2400 km long Australian North West Shelf is among the largest Cenozoic carbonate provinces worldwide, and records a transition from an early Miocene ramp to a middle Miocene rimmed platform. This change is observable on publicly available seismic data, giving the opportunity to investigate environmental influences on platform evolution. This study combines macroscopic and petrographic descriptions of early Miocene strata cropping out in the Cape Range Anticline (North West Cape, southern end of the North West Shelf) and of time‐equivalent well cuttings from the adjacent, offshore Exmouth Sub‐basin. Particular emphasis is placed on the identification of larger benthic foraminifera at a broad generic level, because differing taxa have a limited range of habitable conditions that serve as environmental proxies. The results show that early Miocene strata are dominantly composed of larger benthic foraminifera with minor coralline algae in the proximal platform, grading to micropackstones in the more distal platform. A ramp margin is inferred from the lithological data on the basis of the lack of framework builders and the presence of open oceanic indicators. Facies shallow upward through individual outcrops, with a proximal to distal trend towards the north‐west. These trends along outcrops are consistent with the seismic interpretations. Identification of taxa with warm, oligotrophic water affinity suggests that the ramp was formed in an oligotrophic and warm ocean, despite the absence of coral reefs. Changes of carbonate facies with depth do not seem to be associated with changes in ramp morphology, and the latter may have been controlled by physical oceanic parameters, such as offshore currents and waves.
A fossil cave and associated sediments and fossil fauna located on the Greek island of Rhodes in the eastern Aegean Sea is reported here, and the depositional history discussed. The sediments were ...deposited during the late Pliocene, in the interstitial space between basement boulders of up to 1500 tons. The depositional history of the cave comprises eight stages. From initial flooding, the basin experienced a continuous transgression with sea‐level rise in excess of 500 m, followed by a rapid, forced regression of similar magnitude. The recognition of a succession of fossil communities illustrates this transgression, with a seemingly abrupt shift from endolithic to epilithic biota dominance late in the transgressive cycle. The communities recording the increasing water depth from 0 to >150 m are: The Gatrochaenolithes torpedo (bivalve boring) and Entobia gonioides (sponge boring) ichnocoenosis, with peak distribution between 0 and 1 m water depth; the E. gonioides – E. magna ichnocoenosis, with 1–5 m depth peak distribution; the exclusive E. magna ichnocoenosis, with 5–40 m depth peak distribution; and the E. gigantea ichnocoenosis, with a peak distribution approaching 150–200 m. Below this depth, an epilithic community without boring organisms takes over, characterized by the calcareous sponge Merlia cf. normani, and the inarticulate brachiopod Novocrania turbinata. Simultaneously with the succession of the endo‐ and epilithic cave wall fossil communities, skeletal calcarenite accumulated on the cave floor; the erosional remnants of this sediment are insufficient to further expand the overall transgression–regression model.
Late Sakmarian to early Artinskian (Early Permian) carbonate deposition was widespread in the marine intracratonic rift basins that extended into the interior of Eastern Gondwana from Timor in the ...north to the northern Perth Basin in the south. These basins spanned about 20° of paleolatitude (approximately 35°S to 55°S). This study describes the type section of the Maubisse Limestone in Timor-Leste, and compares this unit with carbonate sections in the Canning Basin (Nura Nura Member of the Poole Sandstone), the Southern Carnarvon Basin (Callytharra Formation) and the northern Perth Basin (Fossil Cliff Member of the Holmwood Shale). The carbonate units have no glacial influence and formed part of a major depositional cycle that, in the southern basins, overlies glacially influenced strata and lies a short distance below mudstone containing marine fossils and scattered dropstones (perhaps indicative of sea ice). In the south marine conditions became more restricted and were replaced by coal measures at the top of the depositional sequence. In the north, the carbonate deposits are possibly bryozoan–crinoidal mounds; whereas in the southern basins they form laterally continuous relatively thin beds, deposited on a very low-gradient seafloor, at the tops of shale–limestone parasequences that thicken upward in parasequence sets. All marine deposition within the sequence took place under very shallow (inner neritic) conditions, and the limestones have similar grain composition. Bryozoan and crinoidal debris dominate the grain assemblages and brachiopod shell fragments, foraminifera and ostracod valves are usually common. Tubiphytes ranged as far south as the Southern Carnarvon Basin, albeit rarely, but is more common to the north. Gastropod and bivalve shell debris, echinoid spines, solitary rugose corals and trilobite carapace elements are rare. The uniformity of the grain assemblage and the lack of tropical elements such as larger fusulinid foraminifera, colonial corals or dasycladacean algae indicate temperate marine conditions with only a small increase in temperature to the north.
The depositional cycle containing the studied carbonate deposits represents a warmer phase than the preceding glacially influenced Asselian to early Sakmarian interval and the subsequent cool phase of the “mid” Artinskian that is followed by significant warming during the late Artinskian–early Kungurian. The timing of cooler and warmer intervals in the west Australian basins seems out-of-phase with the eastern Australian succession, but this may be a problem of chronostratigraphic miscorrelation due to endemic faunas and palynofloras.
•North to south comparison shows similar dominance of bryozoan–crinoidal debris.•Tropical biogenic components are absent; Tubiphytes is present far south.•Temperate conditions with very gradual N–S temperature gradient are suggested.•Discrepancies between west and east Australian successions may be miscorrelation.
Fluctuations in the marine environment just prior to the K–T extinction event have been inferred from several geological sections around the world. Most previous studies have employed isotope or ...trace element proxies. This study uses morphological changes in erect and free-living cheilostome bryozoans as a proxy to investigate environmental change through the final stages of the Maastrichtian at the Nye Kløv section in Denmark. The metrics used are: (1) mean zooid size as a proxy for temperature; (2) intracolony variation in zooid size as a proxy for degree of seasonality; (3) density of defensive avicularia as a proxy for palaeoproductivity; and (4) colony size and asymmetry as proxies for unfavourable environmental conditions. Three semi-distinct phases in the benthic environment are evident: The lowest 3.5
m of the roughly 4.5
m section experienced apparently normal marine conditions. Next, low estimates of benthic seasonality, and highly symmetrical and large colonies with many avicularia indicate a time of increased environmental stability. Subsequent to this quiescence, the uppermost ~
20
cm of the section witnessed environmental volatility and deterioration with mean zooid sizes in all species falling dramatically suggesting a rapid warming or dysoxic event, sharply increasing seasonality estimates implying unusual oceanographical states, and the growth of small, asymmetrical colonies with few avicularia all suggesting unfavourable conditions. These data therefore indicate that strong environmental perturbations occurred just prior to the K–T boundary in the Danish Basin. Such events may have contributed to biotic turnover at the K–T boundary because cause and effect in macroevolution can be delayed. However, potential mechanisms of turnover need to be robustly tested within a detailed palaeoenvironmental framework construct from a suite of independent proxies.
► We examine pre K–T boundary environmental changes in Denmark. ► Various morphologies in bryozoans are used as proxies. ► Data suggest highly stable conditions persisted for most of the section. ► Synchronous shifts starting at 20
cm below the boundary imply rapid deterioration. ► Major environmental change preceded the K–T boundary in the Danish Basin.
A range of physical and biological factors influence species distributions and community structure in marine ecosystems. Benthic assemblages on subtidal rocky reefs in southwestern Australia are ...characterized by a high diversity and coverage of macroalgae and a relatively low abundance and diversity of large, conspicuous invertebrate herbivores. Here, we examined distribution patterns of key benthic organisms (sea urchins, predominantly Heliocidaris erythrogramma, and the canopy-forming macroalgae Ecklonia radiata and Sargassum spp.) and related these patterns to a suite of environmental variables, including geological measures, at 20 sites distributed across 5 rocky reef locations off Perth, Western Australia (WA). Abundance patterns varied at multiple spatial scales and no clear relationship between the abundance of sea urchins and the cover of large macroalgae was observed. The abundance of sea urchins was negatively related to 'substrate cohesion strength' (a measure of limestone reef integrity), which was positively correlated with the percentage cover of E. radiata. The cover of Sargassum spp. was negatively related to fetch. Our results indicate that the distributions of key benthic organisms in temperate WA exhibit considerable spatial variability that appear to be largely driven by physical habitat structure and bottom-up factors rather than through any trophic interactions.
PDF
