Eucla Basin Research Articles

A new Bothriembryon from the Nullarbor Plain, Western Australia, with insights on the age of Bothriembryon praecursor from Kangaroo Well, Northern Territory

Fossil Bothriembryon specimens were recovered from the northwestern edges of the Nullarbor Plain, Western Australia, ∼300 km inland from the current southern coastline. This locality is significant because extant species of Bothriembryon from the Nullarbor are confined to within 50 km of the coastline. Principle component analysis (PCA) was used to compare the Nullarbor Bothriembryon species with a morphologically comparable extant species from the Eucla Basin, Bothriembryon barretti, and geographically closest fossil species: Bothriembryon kremnobates and Bothriembryon praecursor. Results showed strong support for a new fossil species herein described as Bothriembryon pilkiensis sp. nov. Specimens were found as internal moulds within pisolitic calcrete overlying the early Miocene Colville Sandstone. The chronology of the pisolitic calcrete is poorly studied; here we discuss the results of palynological and U–Th disequilibrium investigations which attempted to constrain the time of deposition and fossilization, with palynology results suggesting the late Pliocene. The type locality of B. praecursor, Kangaroo Well, Northern Territory, was also re-evaluated in age to the early Miocene, using biocorrelation of two balbarid species to taxa found within Riversleigh World Heritage Area assemblages. http://zoobank.org/urn:lsid:zoobank.org:pub:E33B1587-1023-419D-AFE8-11FD8C443A27 Helen E. Ryan [ helen.ryan@museum.wa.gov.au ], Collection and Research Centre, WA Museum, 49 Kew Street, Welshpool, WA, 6106; Kenny J. Travouillon [ Kenny.travouillon@museum.wa.gov.au ], Collection and Research Centre, WA Museum, 49 Kew Street, Welshpool, WA, 6106; Lynne A. Milne [ L.Milne@curtin.edu.au ], School of Earth and Planetary Sciences, Curtin University, Kent Street, Bentley, WA, 6102; Sarah K. Martin [ sarah.martin@dmirs.wa.gov.au ], Geological Survey of Western Australia, Department of Energy, Mines, Industry Regulation and Safety, 100 Plain Street, East Perth, WA, 6004; Kailah M. Thorn [ Kailah.thorn@museum.wa.gov.au ], Collection and Research Centre, WA Museum, 49 Kew Street, Welshpool, WA, 6106; Corey S. Whisson [ corey.whisson@museum.wa.gov.au ], Collection and Research Centre, WA Museum, 49 Kew Street, Welshpool, WA, 6106.

Patterns of gastropod predation on middle Eocene echinoids from the western Eucla Basin, Western Australia

Patterns of gastropod predation on middle Eocene echinoids from the western Eucla Basin, Western Australia

Modelling geochemical indices from hyperspectral drill core data from the Eucla Basin basement

Whole rock geochemical analysis of drill core is crucial for rock classification and understanding the evolution of a geological province. This becomes even more important when access to fresh rock samples is hindered by considerable overburden, such as in the case of the basement to the Eucla Basin sediments in Australia. A partial least squares (PLS) regression method was trialled to model geochemical indices, commonly applied for classification of igneous rocks, from hyperspectral visible-near infrared (VNIR; 350 to 1200 nm), shortwave infrared (SWIR; 1200 to 2500 nm) and thermal infrared (TIR; 6000 to 14,500 nm) reflectance spectra of three drill cores intersecting the basement of the Eucla Basin. Modelling of the Mg# (Mg/Mg + Fe) achieved a high correlation between the calculated and predicted values (i.e. R2 > 0.9) at an RMSE of about 10 %. The 2200 to 2400 nm wavelength region of the SWIR was key in modelling the Mg#, with amphibole and chlorite-related absorption features overlapping with the most important input bands in the PLS model. Modelling of the silicon, calcium, iron, magnesium index (SCFM; SiO2/(SiO2 + CaO + FeO + MgO)) required the TIR wavelength range, where diagnostic spectral signatures of silicates are located. PLS-based modelling of the SCFM achieved even a high correlation (i.e. R2 > 0.8) when the model was developed for one drill core but applied to another drill core that intersects the same lithologies. The third geochemical index trialled was the aluminium saturation index (ASI; Al2O3/(Na2O + K2O + CaO), producing high correlation between calculated and predicted ASI when using either, the VNIR-SWIR and the TIR wavelength ranges as input. Our study demonstrates how PLS regression can utilise hyperspectral data to determine geochemical indices, without the cost of full geochemical analysis of every sample in a wide array of rock types. The higher spatial resolution of the modelled geochemistry and the extrapolation of the modelling results to intervals that haven't been sampled for geochemistry supports stratigraphic correlation between drill cores. Furthermore, the combined analysis of geochemical and hyperspectrally-derived mineralogy helps mapping the intensity of weathering of basement as well as mineralogical and physicochemical gradients potentially related to hydrothermal systems.

One size does not fit all: Refining zircon provenance interpretations via integrated grain shape, geochronology, and Hf isotope analysis

Sediment provenance studies commonly utilize isotopic signatures to resolve detrital mineral sources and routing. However, non-unique ages and geochemical characteristics across geographically distinct crystalline source regions can lead to significant ambiguities in mineral provenance interpretations. Such ambiguity is apparent in southern Australia’s Cenozoic Eucla Basin, which hosts world-class heavy mineral sand resources. Here, new Hf isotope data are provided from four heavy mineral prospects (N = 8, n = 844 [N = samples, n = grains]). Zircon grain shape data are also presented for a suite of detrital Eucla Basin samples (N = 22, n = 35,604) and the basin’s underlying basement, the Coompana Province (N = 13, n = 824). The data are integrated with published detrital and non-detrital primary zircon data to investigate the efficacy of grain shape analysis to better resolve the basin’s mineral provenance. Zircon Hf isotope compositions indicate a primary Mesoproterozoic juvenile source for zircon melts (∼1250–1000 Ma, −2.5 <ɛHf > ∼+5) with additional contributions from a range of juvenile to evolved late Archean to Phanerozoic-aged zircon bearing magmas (−28.0 <ɛHf > +11). U–Pb geochronology and Hf isotopes are incapable of differentiating Mesoproterozoic-aged source rocks bounding the region for the majority of heavy mineral deposits analyzed as potential sources express overlapping crystallization ages and similarities in Hf-isotope characteristics. However, distinct zircon grain shapes (i.e., perimeter, major axis and circularity) facilitate improved differentiation across these Mesoproterozoic sources. Filtering of U–Pb age, Hf isotope and shape data implicate the underlying Madura and Coompana provinces as dominant sediment sources for Eucla Basin detritus aged ∼1400–1000 Ma. The lack of direct sediment pathways between the underlying basement provinces and placer sediments analyzed demonstrates the significance of zircon reworking from intermediate sedimentary basins in the formation of the economically significant Eucla Basin beach placers. Zircon grain shape represents a cheaply acquired and readily incorporated grain characteristic that can enhance provenance investigations.

Stratigraphic architecture of the Cenozoic Dugong Supersequence: implications for the late post-breakup development of the Eucla Basin, southern Australian continental margin

ABSTRACTThis study presents an appraisal of the Middle Eocene–Quaternary Dugong Supersequence of the Eucla Basin, offshore southern Australia. It combines details of the rock record with seismic-stratigraphical information, and the resulting stratigraphic framework provides constraints on the nature of the late post-breakup development of the southern Australian continental margin. It is well established that the onshore-to-mid-shelf succession comprises a predominantly aggrading-to-prograding unconformity-bounded succession of carbonate platform deposits; however, our analysis of the outer shelf–upper slope section challenges the widely held view that this shelf-margin wedge represents a distally steepened prograding carbonate ramp primarily modulated by global eustasy. Instead, our results show that the Middle Eocene–Quaternary succession is punctuated by a series of unconformities that reflect a persistent tectonic instability and differential vertical movements throughout the late post-breakup period, the genesis of which is most closely related to tectonic events. Moreover, the upper slope clinoform succession was constructed and shaped predominantly by alongslope processes, and four different contourite drift types are recognised based on their seismic-stratigraphic expression: elongate mounded drift (Quaternary); infill drift (Pliocene); plastered drift (Oligocene); and separated drift (Middle–Upper Eocene). The Quaternary drift – herein termed the ‘Eyre Terrace Drift’ – is a spectacular basin-scale deposit, over 500 m thick and traced for up to 200 km along the upper slope Eyre Terrace. Upslope-migrating sediment waves are associated with this drift. Key sedimentary attributes consistent with a contourite origin include fine-grained sediment, multi-scale gradational bed contacts and pervasive bioturbation. There is also evidence of episodic downslope mass-movement processes ranging from the large-scale Late Neogene Slide, which extends downslope for 15–20 km, to sporadic slumped beds and turbidites recovered in boreholes. The interaction of alongslope and downslope processes indicates a more dynamic sedimentary setting than previously assumed along the outer margin of the Eucla Basin.

Middle Eocene echinoids from the western Eucla Basin, Western Australia

– The oldest carbonate sediments in the western Eucla Basin in south-western Australia are a series of cool-water bryozoan-dominated bioclastic grainstones, packstones and marls that represent deposition during the Tortachilla Transgression during the Bartonian (middle Eocene) planktonic foraminiferal zones 14–15.

Detrital Zircon Perspectives on Heavy Mineral Sand Systems, Eucla Basin, Australia

Abstract Southern Australia’s Cenozoic Eucla basin contains world-class strandline heavy mineral deposits. This study links detrital zircon U-Pb geochronology and heavy mineral compositions from four mineral sand prospects, and a suite of published deposits, to bounding Archean to Neoproterozoic crustal areas. A variable number of distinct sediment sources is recorded from each prospect’s detrital zircon age spectrum. This variability in zircon ages, quantified using a Shannon-Weaver test, serves as a metric of source region heterogeneity. Greater zircon age heterogeneity correlates with heavy mineral enrichment. Enhanced heavy mineral yields reflect retention of resistate over labile minerals—a function of greater sediment transport, reworking, and upgrading processes that parallel those that result in detrital zircon age polymodality. In this case study, greater reworking in intermediate storage sites and transport by longshore processes, eastward along the ~1,000 km spanned by the study sites, corresponds to the direction of progressive heavy mineral enrichment identified in zircon ages and mineral compositions. This approach is a proxy for the duration minerals have spent in the sedimentary system and provides an important perspective for understanding heavy mineral sands.

Widespread seagrass meadows during the Early Miocene (Burdigalian) in southwestern Australia paralleled modern seagrass distributions

The Trealla Limestone, which forms a veneer of foraminiferal-rich limestone and covers over 4000 km2 of the tectonically stable Southern Carnarvon Platform, contains the oldest evidence for seagrass meadows known in Western Australia. It belongs to Lower Tf1 Letter Stage (based on larger benthic foraminifers) of the Burdigalian, within interval 19–16 Ma, and is the only Miocene unit on the platform. The Trealla Limestone here is coeval to the deeper water lower part of the much thicker Trealla Limestone in the Exmouth Sub-basin to the northwest. A seagrass-meadow depositional environment is indicated by most of the studied microfacies based on comparisons with modern sediment composition and foraminiferal assemblages found in innermost shelf seagrass banks between 23°S and 32°S on the present Western Australian coast. Some levels in the Trealla Limestone on the platform (e.g. with abundant miliolid foraminifers, and absence of coral debris) probably were deposited in and around dense seagrass meadows similar to those present today in the metahaline (40–55 ppt salinity) reaches of Shark Bay; whereas other levels (e.g. coral floatstone) were deposited under normal-marine conditions. Based on comparisons with modern carbonate sediment and biota in the region, the biogenic composition of the Trealla Limestone on the platform suggests winter minimum sea-surface temperatures within the range of 17–22 °C. The Nullabor Limestone in the Eucla Basin, at 10° further south on the southern Australian margin, is similar, at least in part, in composition and age to the Trealla Limestone on the Southern Carnarvon Platform. Both may have been deposited during a Burdigalian sea-level rise, and during part of the Miocene climate optimum recognized elsewhere. Sediment composition and foraminiferal assemblages (including epiphytic types) found in the Trealla and Nullabor limestones are similar to those in the modern seagrass banks of the region. This suggests that seagrasses similar to the extensive Posidonia and Amphibolus stands, which are dominant today between 25°S and 35°S along the Western Australian coast, were widespread during the Burdigalian.

Synchrotron X-ray tomographic imaging of embedded fossil invertebrates in Aboriginal stone artefacts from Western Australia: Implications for sourcing, distribution and chronostratigraphy

Eocene fossiliferous chert is a distinctive rock used in the manufacture of stone artefacts commonly found in archaeological sites in southwestern Western Australia (WA). In this study, we employ non-destructive high-resolution X-ray computer tomographic (CT) imaging at the Australian Synchrotron to map and identify embedded bryozoan (and other) fossils within archival artefact samples and potential source material from offshore drill cores in the Perth Basin and from the Nullarbor Plain to the east. Analysis of synchrotron data confirmed the presence of Cellaria, Porina, Quadricellaria, Reteporella, Siphonicytara, Trigonopora, and Idmonea species in chert samples from as far afield as Exmouth Gulf in the north west of WA, Esperance in the south and inland as far as the Goldfields region of WA. This widespread distribution of fossiliferous chert over 1800 km is significantly greater than previously documented and the bryozoan fingerprinting of geological source and artefact material indicates that a potential source within the Eucla Basin located in the SW corner of WA cannot be discounted. In addition, the association of one chert artefact on Doole Island (Exmouth Gulf) with shell midden material dated between 2500 and 770 yr BP also questions the use of fossiliferous chert as a late-Pleistocene-early Holocene chronological marker. The advantages and limitations of synchrotron CT imaging for characterising and sourcing fossiliferous chert are also discussed, with further research warranted on the distribution and probable long-distance trade of this idiosyncratic material.

Insights into the procurement and distribution of fossiliferous chert artefacts across southern Australia from the archival record

Following from previous research in Western Australia, this study explores the use of embedded microfossils—including bryozoan and foraminiferal fossil assemblages—to help identify source and distribution of fossiliferous chert artefacts from South Australian archives. Artefacts from key archaeological sites include Allen’s Cave, Koonalda Cave, Wilson’s Bluff, Ooldea and Kongarong. Preliminary analyses indicate a possible differentiation of fossiliferous chert types east and west of the Eyre Peninsula, from Otway Basin and Eucla Basin limestones, respectively. The widespread distribution and trade of fossiliferous chert is supported by ethnographic descriptions of the sources, procurement and trade as recorded by Daisy Bates, Thomas Draper Campbell and Norman Tindale. Further work combining biostratigraphy and lithology with archaeology and ethnography is needed to explore these ideas further.

Using surface regolith geochemistry to map the major crustal blocks of the Australian continent

Multi-element near-surface geochemistry from the National Geochemical Survey of Australia has been evaluated in the context of mapping the exposed to deeply buried major crustal blocks of the Australian continent. The major crustal blocks, interpreted from geophysical and geological data, reflect distinct tectonic domains comprised of early Archean to recent Cenozoic igneous, metamorphic and sedimentary rock assemblages. The geochemical data have been treated as compositional data to uniquely describe and characterize the geochemistry of the regolith overlying the major crustal blocks across Australia according to the following workflow: imputation of missing/censored data, log-ratio transformation, multivariate statistical analysis, multivariate geospatial (minimum/maximum autocorrelation factor) analysis, and classification. Using cross validation techniques, the uniqueness of each major crustal block has been quantified. The ability to predict the membership of a surface regolith sample to one or more of the major crustal blocks is demonstrated. The predicted crustal block assignments define spatially coherent regions that coincide with the known crustal blocks. In some areas, inaccurate predictions are due to uncertainty in the initial crustal boundary definition or from surficial processes that mask the crustal block geochemical signature. In conclusion, the geochemical composition of the Australian surface regolith generally can be used to map the underlying crustal architecture, despite secondary modifications due to physical transport and chemical weathering effects. This methodology is however less effective where extensive and thick sedimentary basins such as the Eromanga and Eucla basins overlie crustal blocks.

Proterozoic crustal evolution of the Eucla basement, Australia: Implications for destruction of oceanic crust during emergence of Nuna

The crystalline basement beneath the Cretaceous to Cenozoic Bight and Eucla Basins, in Western Australia has received comparatively little attention even though it lies on the eastern margin of one of the most mineral resource endowed regions on the planet. This basement is characterized by a complex geological evolution spanning c. 2billionyears, but paucity of outcrop and younger basin cover present a daunting challenge to understand the basement geology. In this work the composition of the unexposed Proterozoic crystalline basement to the Bight and Eucla Basins is investigated through zircon Hf isotopes and whole rock geochemistry from new drillcore samples. This region includes two geophysically defined basement entities: The Madura Province, containing: 1) c. 1478Ma Sleeper Camp Formation, which has variable isotopic signatures including evolved values interpreted to reflect reworking of rare slivers of hyperextended Archean crust, 2) 1415–1389Ma Haig Cave Supersuite, with mantle-like isotope values interpreted as melting of subduction-modified N-MORB source, and 3) 1181–1125Ma Moodini Supersuite, with juvenile isotopic signatures interpreted to reflect mixed mafic lower-crustal and asthenospheric melts produced at the base of thinned crust. The Coompana Province, to the east of the Madura Province, has three major magmatic components: 1) c. 1610Ma Toolgana Supersuite, with chemical and isotopic characteristics of primitive arc rock, 2) c. 1490Ma Undawidgi Supersuite, with juvenile isotope values consistent with extensional processes involving asthenospheric input and 3) 1192–1140Ma Moodini Supersuite, with strong isotopic similarity to Moodini Supersuite rocks in the Madura Province.This new isotopic and geochemical data shows that the Madura and Coompana regions together represent a huge tract of predominantly juvenile material. Magma sources recognised, include; 1) depleted mantle, producing MORB-like crust at c. 1950Ma, but also contributing to younger magmatism; 2) recycled c. 1950Ma crust reworked in primitive arcs and in intra-plate settings and; 3) minor evolved material representing fragments of hyperextended continent. The observed isotopic evolution pattern is comparable to that of other central Australian Proterozoic provinces, including the Musgrave Province, the northern margin of the Gawler Craton, and components within the Rudall Province. Linking these isotopic signatures defines the Mirning Ocean, and its subducted and underplated equivalents. In a global context we suggest c. 1950Ma crust production reflects the onset of ordered oceanic spreading centres, which swept juvenile crustal fragments into Nuna.

Three new species of the echinoid genus Monostychia Laube, 1869 from Western Australia

Sadler, T., Martin, S.K. & Gallagher, S.J., February 2017. Three new species of the echinoid genus Monostychia Laube, 1869 from Western Australia. Alcheringa 41, 464–473. ISSN 0311-5518Three new species of the extinct echinoid genus Monostychia Laube, 1869 are described from Western Australia. All are from the middle Miocene Colville Sandstone of the Eucla Basin and have historically been referred to this genus without description. These new taxa differ from previously described Monostychia species in several morphological features, such as size and shape but also in the number of post-basicoronal interambulacral plates developed in the oral paired interambulacrum, a feature considered taxonomically important at both genus and species level for clypeasteroids. The number of ambulacral plates in the paired and unpaired oral regions is also considered a potentially diagnostic taxonomic feature for this genus; it is concluded that the oral ambulacral plate count, particularly that of the unpaired ambulacrum III, is at least as useful a taxonomic feature as the oral interambulacral plate count.Tony Sadler [t.sadler@student.unimelb.edu.au] and Stephen J. Gallagher [sjgall@unimelb.edu.au], School of Earth Sciences, University of Melbourne, Victoria 2010, Australia; Sarah K. Martin [sarah.martin@dmp.wa.gov.au], Geological Survey of Western Australia, Department of Mines and Petroleum, Western Australia, 6004.

Further Mollusca from the late Eocene Pallinup Formation, Eucla Basin, Western Australia

Further Mollusca from the late Eocene Pallinup Formation, Eucla Basin, Western Australia

Looking into a ‘Blue Hole’ - Resolving Magnetization and Structure from the Complex Negative Coompana Anomaly, South Australia

A large (c. 2000nT amplitude, 50 km diameter) negative amplitude TMI anomaly under the Eucla Basin in southwestern South Australia, long known and referred to as the “Coompana Anomaly” has been well resolved by a new high resolution (200 metre line spaced, 80 metre ground clearance) survey flown for the Geological Survey of South Australia. We use parametric inversion to simultaneously derive magnetization direction and spatial distribution of magnetizations giving rise to satellite anomalies both above and around the main anomaly. For the two most prominent satellite anomalies these magnetization estimates agree well with estimates derived from the historic data, but the new survey data provides greater confidence, and reliable mapping of many smaller bodies. The improvement in resolution has allowed us to attempt isolation of the anomaly due to the more voluminous, deeper magnetization, but to date we have not yet been able to recover repeatable results for that deeper magnetization. Magnetization intensity estimates for all investigated anomalies are very high, ranging from about 5 A/m to over 20 A/m (equivalent in intensity to magnetizations from susceptibilities of 0.1 to 0.5 SI). The deeper magnetization is well correlated with a negative gravity anomaly, suggesting that the material generating the main magnetic anomaly has a relatively low density.

Basement influences on structural styles in the Bremer and Eyre Sub-Basins, southern Australia

The Bight Basin on the southern margin of Australia is nearly 2000 km wide from west to east and overlies a number of different basement terranes (Figure 1). Major basement terrane divisions occur between the basement of the Ceduna delta and the Eyre and Bremer sub-basins, resulting in changes in structural styles in the overlying basin successions. The Eyre Sub-Basin overlies the boundaries of the Proterozoic Madura and Coompana basement provinces, which are separated by the Mundrabilla shear zone. The shear zone is a N-S trending, continent-wide structure visible in magnetic data which appears to extend offshore in the Eyre Sub-Basin and is also visible as a north-trending present-day fault scarp in the onshore Eucla Basin. Seismic data interpretation suggests that the shear zone steps to the east in the region of the Jerboa-1 well. Differential movement across the shear zone during Jurassic-Cretaceous rifting may have influenced the location of depocentres within the Eyre Sub-Basin. Overlying the Albany Fraser Orogen’s northern foreland, the Bremer Sub-Basin is dominated by WSW-ENE trending half graben structures and large rollover anticlines associated with Jurassic-Cretaceous rifting. The basin is divided by a N-S trending basement structure, visible in gravity data, and in the overlying sedimentary succession as a broad zone of subsidence with several periods of reactivation. Similarities between this structure and the shear zone in the Eyre Sub-Basin suggest they may have a similar origin.

Molecular systematics and biodiversity of oniscidean isopods in the groundwater calcretes of central Western Australia

Groundwater calcrete aquifers of central Western Australia have been shown to contain a high diversity of stygobiont (subterranean aquatic) invertebrates, with each species confined to an individual calcrete and the entire system resembling a ‘subterranean archipelago’ containing hundreds of isolated calcretes. Here, we utilised alternative sampling techniques above the water table and uncovered a significant fauna of subterranean terrestrial oniscidean isopods from the calcretes. We explored the diversity and evolution of this fauna using molecular analyses based on one mitochondrial gene, Cytochrome C Oxidase Subunit I (COI), two Ribosomal RNA genes (28S and 18S), and one protein coding nuclear gene, Lysyl-tRNA Synthetase (LysRS). The results from 12 calcretes showed the existence of 36 divergent DNA lineages belonging to four oniscidean families (Paraplatyarthridae, Armadillidae, Stenoniscidae and Philosciidae). Using a combination of phylogenetic and species delimitation methods, we hypothesized the occurrence of at least 27 putative new species of subterranean oniscideans, of which 24 taxa appeared to be restricted to an individual calcrete, lending further support to the “subterranean island hypothesis”. Three paraplatyarthrid species were present on adjacent calcretes and these exceptions possessed more ommatidia and body pigments compared with the calcrete-restricted taxa, and are likely to represent troglophiles.The occurrence of stenoniscid isopods in the calcretes of central Western Australia, a group previously only known from the marine littoral zone, suggests a link to the marine inundation of the Eucla basin during the Late Eocene. The current oniscidean subterranean fauna consists of groups known to be subtropical, littoral and benthic, reflecting different historical events that have shaped the evolution of the fauna in the calcretes.

Cenozoic surface uplift from south Western Australian rivers

SUMMARY Embedded within Earth’s topography is a constantly evolving fluvial network sensitive to variations in horizontal and vertical motions, driving sediment transport from elevated sources to sedimentary basins. The notion that a river acts as a ‘tape recorder’ for positive vertical displacements suggests that changes in spatial and temporal characteristics of surface uplift can be deduced through the analysis of longitudinal river profiles. The relative tectonic quiescence of the Australian continent during the Cenozoic makes it an excellent natural laboratory to study recent large-scale variations in surface uplift, often linked with mantle convective processes. Here, we analyse X longitudinal river profiles from south Western Australia. Major knickzones in the longitudinal profiles of rivers in southwest Australia suggest recent surface uplift. Given the lack of recent large-scale tectonic activity in that region, this uplift requires an explanation. Applying an inverse algorithm to river profiles of south Western Australia reveals that this surface uplift started in the Eocene and culminated in the mid-late Neogene. The surface uplift rates deduced from this river profile analysis generally agree with independent geological observations including preserved shallow-marine sediment outcrops across the Eucla Basin and south Western Australia. The timing of this event is also to be compared with offshore stratigraphic sections to link onshore surface uplift to offshore sedimentation. We show that the interplay between global sea level and long-wavelength dynamic topography associated with south Western Australia’s plate motion path over the remnants of an ancient Pacific slab is a plausible mechanism driving this surface uplift.

Molecular systematics and biogeography of Logania R.Br. (Loganiaceae)

The angiosperm genus Logania R.Br. (Loganiaceae) is endemic to the mainland of Australia. A recent genetic study challenged the monophyly of Logania, suggesting that its two sections, Logania sect. Logania and Logania sect. Stomandra, do not group together. Additionally, the genus has a disjunct distribution, with a gap at the Nullarbor Plain in southern Australia. Therefore, Logania is a favourable candidate to gain insight into phylogenetic relationships and how these might intersect with Earth-history events. Our phylogenetic analyses of DNA sequences of two chloroplast markers (petD and rps16) showed that Logania sect. Logania and L. sect. Stomandra were each resolved as monophyletic, but the genus (as currently circumscribed) was not. Based on our Bayesian estimates of divergence times, the disjunct distributions within Logania sect. Stomandra could have been caused by flooding of the Eucla Basin. However, this biogeographical process cannot account for the distribution of Logania sect. Logania, with long-distance dispersal and establishment seeming more likely.

Cenozoic uplift of south Western Australia as constrained by river profiles

The relative tectonic quiescence of the Australian continent during the Cenozoic makes it an excellent natural laboratory to study recent large-scale variations in surface topography, and processes that influence changes in its elevation. Embedded within this topography is a fluvial network that is sensitive to variations in horizontal and vertical motions. The notion that a river acts as a 'tape recorder' for vertical perturbations suggests that changes in spatial and temporal characteristics of surface uplift can be deduced through the analysis of longitudinal river profiles. We analyse 20 longitudinal river profiles around the Australian continent. Concave upward profiles in northeast Australia indicate an absence of recent surface uplift. In contrast, the major knickzones within longitudinal profiles of rivers in southwest Australia suggest recent surface uplift. Given the lack of recent large-scale tectonic activity in that region, this uplift requires an explanation. Applying an inverse algorithm to river profiles of south Western Australia reveals that this surface uplift started in the Eocene and culminated in the mid-late Neogene. The surface uplift rates deduced from this river profile analysis generally agree with independent geological observations including preserved shallow-marine sediment outcrops across the Eucla Basin and south Western Australia. We show that the interplay between global sea level and long-wavelength dynamic topography associated with south Western Australia's plate motion path over the remnants of an ancient Pacific slab is a plausible mechanism driving this surface uplift.