Stephen McLoughlin

Tectonic significance of the Lambert graben, East Antarctica: Reconstructing the Gondwanan rift

Antarcticas Lambert graben, Australias North West Shelf, and the eastern Indian Peninsula all host thick, fault-bounded Permian-Triassic successions. These terranes were adjacent to each other in Gondwana. The Lambert graben intersects the modern coastline, strikes oblique to shelf architecture, and has a geophysical signature that can be traced >1000 km inland. Vitrinite reflectance data from the graben margins record Permian-Triassic infill. Australias North West Shelf is the relict of an intracontinental Carboniferous-Permian rift that was infilled during the Permian-Triassic then driven to oceanic completion during Jurassic-Cretaceous Gondwana breakup. This rift was compartmentalized over length scales of ∼650 km, corresponding to accommodation zones, margin-normal geophysical lineaments, and long-lived crustal weaknesses. In eastern India, similar compartmentalization is marked by extensive coal-bearing graben systems. Gondwana reconstructions indicate that the Lambert graben corresponds to the orientation and length scale of Carboniferous-Permian rift compartmentalization. The Lambert graben represents an accommodation zone of a wide intracontinental rift that extended from Australias North West Shelf, between India and Antarctica, to southern Africa. This rift collected Gondwanas thick Permian-Triassic sedimentary blanket and rich alluvial coal deposits.

Some Morphological Features of Wollemi Pine (Wollemia nobilis: Araucariaceae) and Their Comparison to Cretaceous Plant Fossils

Morphological details of Wollemia nobilis (Wollemi pine) are described and illustrated, and compared with the extant genera Agathis and Araucaria and with selected araucarian fossils from the Cretaceous of Australia. Adult and juvenile shoots of Wollemia differ in leaf arrangement, leaf shape, and cuticular features; in these features they are most similar to Araucaria. The cone scales have a long, distal spine reminiscent of Araucaria section Eutacta, but the winged seeds that are ontogenetically free from, and shed independently from, the cone scale are similar to Agathis. Shoots with variable leaf types, Araucaria-like cone scales, and Agathis-like winged seeds are found in several plant fossil assemblages from the Cretaceous of Australia; these fossil conifers, which had been recognized as araucarian, can now be favorably compared with Wollemia. Pollen of Wollemia is indistinguishable from the fossil pollen form-genus Dilwynites, which has a fossil record extending back to the Late Cretaceous in Australia and New Zealand. Reexamination of Mesozoic and Tertiary paleofloras will most probably reveal an important contribution of Wollemia to the fossil record of Araucariaceae.

Intraspecific Variation of Taeniate Bisaccate Pollen Within Permian Glossopterid Sporangia, from the Prince Charles Mountains, Antarctica

Permineralized sporangia from Late Permian sediments of the Amery Group in the Prince Charles Mountains, East Antarctica, are assigned to Arberiella sp. cf. A. africana Pant and Nautiyal. These sporangia contain between 2000 and 3000 taeniate, saccate pollen grains that are predominantly haploxylonoid bisaccate and referable to the palynotaxon Protohaploxypinus limpidus (Balme and Hennelly) Balme and Playford. However, the sporangia also contain greater than 4% of diploxylonoid bisaccate forms comparable to Striatopodocarpidites cancellatus (Balme and Hennelly) Hart 1963, together with sporadic monosaccate and trisaccate grains that, if found dispersed, would be assigned to several different pollen form genera. Morphometric analysis of in situ bisaccate pollen grains and taeniate bisaccate pollen in the dispersed palynoflora indicates that in situ grains occupy only the smaller end of the total size range. The tendency for in situ grains to cluster into two different size groups may reflect differential predispersal expansion of the corpus. The in situ pollen grains are variable in most qualitative and quantitative features used for taxonomic discrimination of dispersed taeniate bisaccate pollen, and this may lead to unreliable estimates of Late Permian floristic diversity if an overly restrictive species delimitation scheme is used.

Ptilophyllum muelleri (Ettingsh.) comb. nov. from the Oligocene of Australia: Last of the Bennettitales?

Several small pinnate leaves of early Oligocene age from Cethana, Tasmania, are newly described and found to be conspecific with Anomozamites muelleri Ettingsh. recorded from coeval strata at Emmaville, northern New South Wales. These fossils are most probably referable to the Bennettitales on the basis of leaf size, leaflet shape, and venation patterns, in the absence of diagnostic cuticular details. They are transferred to Ptilophyllum on the basis of leaflet morphology and represent the youngest putative bennettitalean remains yet documented. Their occurrence reinforces previous arguments that the highest-paleolatitude fragments of southeastern Gondwana provided moist temperate refugia for the survival of Mesozoic gymnosperm taxa well into the Cenozoic.

A new Maastrichtian-Paleocene Azolla species from of Bolivia, with a comparison of the global record of coeval Azolla microfossils

A new heterosporous fern species, Azolla boliviensis sp. nov., is described from latest Maastrichtian (latest Cretaceous) to Paleocene (earliest Palaeogene) terrestrial sediments of the Eslabón and Flora Formations, Subandean belt, Bolivia. The species is represented by dissociated but abundantly co-preserved megasporocarps, megaspores, microsporangia, massulae and microspores. The genus consistently characterizes warm-climate lacustrine settings. Fossil Azolla is first identified around the Early to mid-Cretaceous but the genus apparently underwent dramatic radiation during the Late Cretaceous. Abundant Azolla remains in Bolivia add to this portrait of rapid geographie dispersai and diversification near the close of the Cretaceous. The ranges of many Azolla species span the Cretaceous- Palaeogene boundary and the potential of Azolla to withstand altered environmental conditions, such as periodic frost damage, drought, and salinity change, and its ability to undergo rapid vegetative regeneration in association with nitrogen-fixing cyanobacterial symbionts, suggest that the survival of this group was favoured during the adverse conditions of the end-Cretaceous event.

Permian plant macrofossils from Fossilryggen Vestfjella Dronning Maud Land

A low diversity plant macrofossil assemblage described from the northern section of Fossilryggen, Vestfjella, Dronning Maud Land, Antarctica, is dominated by matted leaf impressions of Glossopteris sp. cf. G. communis Feistmantel and Glossopteris sp. cf. G. spatulata Pant & Singh, and in situ finely branched Vertebraria indica Royle rootlets. Equisetalean stems, rhizomes and leaf whorls (Phyllotheca australis Brongniart emend. Townrow), isolated seeds, scale-leaves, and fragmentary gymnosperm axes represent minor components of the assemblage. The fossils are preserved in fine-grained, floodbasin sediments and dark palaeosols. Although lacking definitive biostratigraphical indices, the flora is considered to represent a Middle Permian assemblage based principally on lithological and palynological correlation with the southern section at Fossilryggen and broad similarities to mid-Permian plant assemblages elsewhere in Gondwana.

BAIKALOPHYLLUM LOBATUM AND REHEZAMITES ANISOLOBUS: TWO SEED PLANTS WITH "CYCADOPHYTE" FOLIAGE FROM THE EARLY CRETACEOUS OF EASTERN ASIA

Two fossil seed plants with “cycadophyte” foliage, Baikalophyllum lobatum and Rehezamites anisolobus, are reinvestigated and described on the basis of new material from Lower Cretaceous strata of Liaoning and Inner Mongolia, China, and previously published material from China and Transbaikalia, Russia. The new fossils demonstrate that the Baikalophyllum plants were slender-stemmed, loosely branched, and shrublike. Yixianophyllum jinjiagouensis, described from the Zhuanchengzi beds of the Yixian Formation, Liaoning, is determined to be a junior synonym of B. lobatum. Rehezamites anisolobus, informally described from the Lower Cretaceous Yixian Formation in previous studies, is validated here, and its foliage is compared with that of Baikalophyllum. Baikalophyllum and Rehezamites have leaf morphologies and venation patterns that, in terms of general architecture, resemble those of leaves traditionally assigned to extinct members of Cycadales, Bennettitales, and Pentoxylales, but because of ambiguous circumscription and the need for thorough revisions of these groups, leaves of Baikalophyllum and Rehezamites are retained unassigned.

Groundwater mixing in a sand-island freshwater lens: density-dependent flow and stratigraphic controls

This paper focuses on a small back-barrier sand-island on the southeast coast of Queensland. The freshwater lens in the study area exhibits anomalously high short-range salinity gradients at shallow depths, which cannot be explained using a standard seawater intrusion model. The island groundwater system consists of two aquifers: a semiconfined aquifer hosting saline to hypersaline groundwater and an overlying unconfined freshwater aquifer. The deeper aquifer is semiconfined within an incised paleovalley, and groundwater flow is restricted to an eastxa0–xa0west direction. Tidal response observations show that the tidal signal propagates far more rapidly and is of much higher magnitude in the semiconfined aquifer than the unconfined aquifer. The tidal wave-pulse amplitude is also subject to greater attenuation in the unconfined aquifer. A conceptual hydrogeological model illustrates how upwelling of hypersaline groundwater, induced by density-dependent flow and tidal pumping, has contaminated the shallow groun...

Habit and ecology of the Petriellales, an unusual group of seed plants from the Triassic of Gondwana

Premise of research.u2003Well-preserved Triassic plant fossils from Antarctica yield insights into the physiology of plant growth under the seasonal light regimes of warm polar forests, a type of ecosystem without any modern analogue. Among the many well-known Triassic plants from Antarctica is the enigmatic Petriellaea triangulata, a dispersed seedpod structure that is considered a possible homologue of the angiosperm carpel. However, the morphology and physiology of the plants that produced these seedpods have so far remained largely elusive. Methodology.u2003Here, we describe petriellalean stems and leaves in compression and anatomical preservation that enable a detailed interpretation of the physiology and ecology of these plants. Pivotal results.u2003Our results indicate that the Petriellales were diminutive, evergreen, shade-adapted perennial shrubs that colonized the understory of the deciduous forest biome of polar Gondwana. This life form is very unlike that of any other known seed-plant group of that time. By contrast, it fits remarkably well into the “dark and disturbed” niche that some authors considered to have sheltered the rise of the flowering plants some 100 Myr later. Conclusions.u2003The hitherto enigmatic Petriellales are now among the most comprehensively reconstructed groups of extinct seed plants and emerge as promising candidates for elucidating the mysterious origin of the angiosperms.

Drainage patterns in southeast Queensland: the key to concealed geological structures?

Southeast Queenslands geomorphology is characterised by northwest – southeast-trending trunk drainage channels and highlands that strongly correlate with the distribution of geological units and major faults. Other geomorphological trends strongly coincide with subsidiary faults and geological domains. Australia is presently under compressional stress. Seismicity over the past 130 years records 56 earthquakes of >2 magnitude indicating continuing small-scale earth movements in the Moreton region. Highlands in this region are dominated by Paleozoic to Triassic metamorphic and igneous rocks, and are generally 20 – 80 km from the coastline. Coastal lowlands are largely dominated by Mesozoic sedimentary basins and a veneer of surficial sediments. The eastern coast of Australia represents a passive margin; crustal sag along this margin could be expected to produce relatively short, high-energy, eastward-flowing drainage systems. We performed a geomorphological analysis to characterise the drainage patterns in southeast Queensland and identify associations with geological features. Anomalous channel, valley and escarpment features were identified, which failed to match the anticipated drainage model and also lacked obvious geological control. Despite their proximity to the coast (base level), these features include areas where drainage channels flow consistently away from, or parallel to, the coastline. Although many channels do coincide with geological structures, the drainage anomalies cannot be directly related to known structural discontinuities. Anomalous drainage patterns are suggested to indicate previously unidentified structural features and in some cases relatively young tectonic control on the landscape. Recent seismicity data have also been analysed to assess spatial correlations between earthquakes and geomorphological features. Our results show that structure largely controls drainage patterns in this region, and we suggest that a presently unmapped and potentially active, deep-seated structure may exist parallel to the coast in the northern coastal region. We propose that this structure has been associated with uplift in the coastal region of southeast Queensland since mid-Cenozoic times.