John S. Jell

Inferred syngenetic textural evolution in Holocene cryptic reefal microbialites, Heron Reef, Great Barrier Reef, Australia

Cryptic microbialites in the Heron Reef framework occur as crusts of fingerlike microcolumns or branching dendrolites, rarely more than 1 cm long. Microstructure of the most recently growing microbialite surfaces consists of coalesced, 3 µm scalenohedra that are indistinguishable from previously described Mg-calcite “abiotic” cement. The transformation from submicrometer, anhedral crystallites to >3 µm scalenohedra is inferred to have occurred only during active microbialite accretion beneath a biofilm. This syngenetic change from primary, biologically induced microstructures to microstructures that are indistinguishable from abiotic cement has important implications for the recognition and interpretation of early marine microcrystalline carbonates and cements.

Holocene sediments of Wistari Reef: towards a global quantification of coral reef related neritic sedimentation in the Holocene

Wistari Reef. within the southern Great Barrier Reef. is a shallow coral reef platform featuring a very clearly defined leeward accretionary wedge of carbonate sediments. The total global area of shallowly submerged coral reef has been quantified as 255 000 km(2). The question then becomes: What additional area of sediment of significant thickness is associated with the measured shallow reef areas T At Wistari Reef, the leeward sedimentary wedge has an area and a thickness that are roughly equal to the Holocene sediments that have accumulated on the platform. Several important observations can be made from these data. Firstly. the area of significant neritic carbonate sedimentation ( > 1 m/ka) associated with coral reefs is near 500000 km(2). Secondly, the production rate of neritic carbonates at Wistari Reef is almost 50%, less than the accumulation rate needed to obtain the volume of Holocene reef sediments observed. This implies that both production and accumulation neritic carbonate must have been more than a factor of two higher in the early to mid Holocene

Early Middle Cambrian corals from western New South Wales

Three forms, Cothonion sympomatum gen. et sp. nov. with a bi-radially septate operculum, and the new species lissa and daseia of the genus Lipopora gen. nov., are described from the early Middle Cambrian Coonigan Formation in the Mootwingee district of western New South Wales, Australia. They may be representatives of hitherto unknown groups of organisms, but they are tentatively interpreted as coelenterates that reached a level of development comparable with the Anthozoa. Cothonion is placed in the new family Cothoniidae and questionably referred to the Rugosa. Lipopora is considered to be similar to Coelenteratella Korde; both are grouped in die new family Lipoporidae and tentatively referred to the Tabulata.

Recent Developments on a Nearshore, Terrigenous-Influenced Reef: Low Isles Reef, Australia

Abstract Low Isles Reef is the most southerly located of 46 coral reef platforms unique to the inner shelf of the northern Great Barrier Reef Province, Australia, which support both sea grass and mangrove growth. Such reefs develop in areas that are influenced by river flood plumes and where interreef sediments are dominated by terrigenous mud. Low Isles Reef has long been a popular tourist destination. Informal reports of decreasing visibility, a decline in scleractinian corals, and increases in soft coral and macroalgae have sparked speculation that agricultural activities in coastal catchments are affecting the reef. Comparison of the modern surface of Low Isles Reef with historical surveys and photographs dating back to 1928 allows quantification of modern sedimentary processes, rates of change, and factors influencing reef development. Results indicate that changes on Low Isles Reef are related to remobilization of coarse sediment during storm events and gradual shoreline retreat associated with rising sea level. Retreat of shingle ramparts and elongate ridges of coral debris toward the reef interior has led to the infilling of subtidal ponds on the reef top, which supported hard coral colonies in 1928. The gradual development of a composite shingle rampart along the windward margin has promoted an increase (∼150%) in the area of the reef top covered by mangroves. On the leeward margin, a decrease in hard corals since 1950 may reflect a rising contribution of organic debris from the expanding mangrove swamp. Results suggest that recent changes on Low Isles Reef can be explained in the context of natural processes. Further study is needed before the effects of agricultural activities in coastal catchments on reef health can be confirmed.

γ-Carboxyglutamic acid in invertebrates: Its identification in hermatypic corals

Abstract The presence of a γ-carboxyglutamate-containing protein in hermatypic corals has been established. γ-Carboxyglutamate has been isolated from the alkaline hydrolysate of protein extracted from the coral Lobophyllia corymbosa , by chromatography of the hydrolysate on Dowex AG 1-X8 (formate form), followed by chromatography on an amino acid analyzer column. This procedure achieves complete separation of γ-carboxyglutamate from an acid-stable compound which is also present in the alkaline hydrolysate of coral protein, and which has proved difficult to separate from γ-carboxyglutamate by other methods. The identity of the γ-carboxyglutamate thus isolated has been established unequivocally by determining the yield of glutamic acid after acid treatment (2 M HCl, 6 h, 110°C). The color factor for the γ-carboxyglutamate isolated from Lobophyllia is 0.45 4 times the value for glutamic acid, in good agreement with the value determined for authentic γ-carboxyglutamic acid (0.45 8 ) under exactly the same conditions. Virtually identical results have been obtained for the coral, Acropora cuneata . These experiments provide the first secure evidence for the presence of γ-carboxyglutamate in an invertebrate species, and they clearly have important implications for our understanding of invertebrate mineralization.

Jurassic Invertebrates from the Himalayan Central Gneiss

Poorly preserved scleractinian corals and cephalopod molluscs occur in metamorphosed and foliated limestones in the Himalayas of northwest India. The nautiloid Cenoceras and macrocephalitid ammonites indicate a Middle Jurassic age. The fossils occur within a zone of high grade metamorphic rocks known as the Central Gneiss, previously regarded as an axial massif of Precambrian basement. Most palaeogeographic reconstructions feature this zone as a prominent topographic arch or ‘Himalayan Ridge’ which arose in the late Precambrian or early Palaeozoic and, through periodic rejuvenation, persisted throughout the Phanerozoic. Many workers believe that the ‘Himalayan Ridge’ constituted an effective barrier to north-south faunal migration because the terrains of sedimentary rock which flank the Central Gneiss contain quite different faunas. The Jurassic fossils provide new stratigraphic evidence that the tectonic events which generated the Central Gneiss are relatively young, and this, together with structural co...

High frequency sea‐level fluctuations in the Pillara Limestone, Guppy Hills, Lennard Shelf, Northwestern Australia

The Frasnian back‐reef Pillara Limestone from Guppy Hills, Lennard Shelf, northwestern Australia consists of 267 m of biostromal limestone. Seven facies are described and these form seventy‐six interpreted shallowing‐upward cycles, with an average thickness of 3.47 metres. These cycles differ only slightly from cycles described from Menyous Gap, but more markedly from those described from Windjana Gorge. The duration of the Guppy Hills cycles is estimated to be between 26 and 33 ka. This estimate is not well constrained, but falls in the band for estimated Milankovitch frequencies, and is probably influenced by precession. The Menyous Gap and Windjana Gorge cycle durations also fall into Milankovitch frequencies, but are thought to be influenced by obliquity. A Fischer plot for the Guppy Hills cycles, shows a negative shift, suggesting an overall shallowing trend. However, there is evidence of a rapid deepening implying contemporaneous tectonic activity. Correlation between this plot and one of a similar ...

Oxygen isotope variation on a lagoonal platform reef, Heron Island, Great Barrier Reef.

A survey of temperature, salinity and oxygen isotope ratio was conducted on the reefal waters of a lagoonal platform reef, Heron Reef, situated near the southern end of the Great Barrier Reef. The oxygen isotope ratio of the water changed by nearly 2‰ during a 3-week period. Daily variations of 1.4‰ were detected. As the maximum oxygen isotope ratios occurred at low tide, during times of high temperature and high salinity, temperature-induced variation in oxygen isotope ratios of skeletal material was masked. Such a phenomenon can easily explain why previous workers have failed to detect the full range of oxygen isotope ratios in coral skeletons and other calcareous organisms.

Rugose coral diversifications and migrations in the Devonian of Australasia

The occurrence of approximately 100 rugose coral genera has been confirmed in the Devonian carbonate dominated successions of Australasia. Their temporal distribution shows that the largest faunal turnovers were in the Pragian and Givetian, with profound extinction events at or near the ends of the Emsian, Givetian and Frasnian. The evolutionary innovation and diversification of the Early Devonian rugose corals of eastern Australia are characterized by a high turnover rate in the late Lochkovian—Pragian and strong dynamism of radiation from late Pragian to medial Emsian, implying considerable dispersal to South China, central Asia and Europe. After a high intensity of origination in the Pragian, maximum diversity was reached in the Emsian. Phillipsastreids and endophyllids appeared late in the Pragian and became common in the Emsian; stringophyllids appeared in the Emsian. As elements of these families are recorded mainly from the Middle, or even Upper Devonian of other provinces of the Old World Realm, it appears that they may have originated in eastern Australia during the Early Devonian. Following a marked decrease in generic richness in the Eifelian, faunal diversity reached another high peak in the early mid‐Givetian as a result of immigration of coral genera, probably from South China, central Asia, Europe and northwestern Canada in the Old World Realm.

New graptolite faunas from the Llandovery, lower Silurian of the Graveyard Creek Subprovince, Broken River region, Queensland, Australia

A continuous biostratigraphic sequence has been established, possibly from as low as the sedgwickii Biozone but certainly throughout the Telychian Stage (? sedgwickii, turriculatus, ?crispus, griestoniensis and crenulata biozones). Thirty-three taxa have been recorded, including the new genus Wandograptus wandovalensis sp. nov., the new species Pseudostreptograptus queenslandensis and the new subspecies Dictyonema paululum australis and Stimulograptus sedwickii loydelli . A number of species have been recorded from Australia for the first time: Dictyonema cf. geniculatum Bulman, Petalolithus kurcki (Rickards), Pristiograptus initialis (Kirste), Monoclimacis directa Zalasciewicz, Monograptus aff. distans (Portlock), Monograptus sartorius Tornquist, and Torquigraptus pragensis (Boucek). Nine forms have been left under open nomenclature. The type section for the Poley Cow Formation yields a griestoniensis biozone fauna close to the top, and this level can be correlated with a griestoniensis Biozone fauna in the Broken River crossing section, again just below the top of the formation. Further north, griestoniensis Biozone faunas have also been recognized, beyond Diggers Creek, and in the Quinton Formation at Top Hut, enabling a reliable time plane throughout the region. At Top Hut, the highest graptolitic strata yield a crenulata Biozone fauna; and stratigraphically lower sequences, referable to the ?sedgwickii, turriculatus and ? crispus biozones, have been established on the Broken River section. It is likely that a full Telychian (Upper Llandovery) sequence occurs in the Poley Cow and Quinton formations enabling accurate correlation with other parts of the world.