Nullarbor Region Research Articles

A Meteor Spectroscopic Survey in the Nullarbor

We report the start of science operations of a meteor spectroscopic survey in the Nullarbor region, Western Australia. The observation program consists of well-proven observatories developed as part of the All-Sky Meteor Orbit System (AMOS) project. These comprise high-sensitivity all-sky imaging units, as well as spectroscopic instruments observing brighter meteors. They are co-located with Desert Fireball Network (DFN) instruments, which themselves provide high-resolution astrometry for fireballs. There are two goals for this program. One is to keep a constant watch on meteor activity by always having one AMOS sub-network in the dark. The second is to provide spectroscopic coverage for recovered meteorites by the DFN, establishing essential calibration points between meteoritic samples and fireball spectra.

Review of the fossil record of the Australian land snail genus Bothriembryon Pilsbry, 1894 (Mollusca: Gastropoda: Bothriembryontidae): new distributional and geological data

The land snail genus Bothriembryon Pilsbry, 1894, endemic to southern Australia, contains seven fossil and 39 extant species, and forms part of the Gondwanan family Bothriembryontidae. Little published data on the geographical distribution of fossil Bothriembryon exists. In this study, fossil and modern data of Bothriembryon from nine Australian museums and institutes were mapped for the first time. The fossil Bothriembryon collection in the Western Australian Museum was curated to current taxonomy. Using this data set, the geological age of fossil and extant species was documented. Twenty two extant Bothriembryon species were identified in the fossil collection, with 15 of these species having a published fossil record for the first time. Several fossil and extant species had range extensions. The geological age span of Bothriembryon was determined as a minimum of Late Oligocene to recent, with extant endemic Western Australian Bothriembryon species determined as younger, traced to Pleistocene age. Extant Bothriembryon species from the Nullarbor region were older, dated Late Pliocene to Early Pleistocene. Cave environments proved an excellent source of fossil Bothriembryon material, where shells often showed signs of predation. The dataset from this study provided insights into the origin and radiation of Bothriembryon, and will enable future phylogenetic dating.

Total evidence analysis of the phylogenetic relationships of bandicoots and bilbies (Marsupialia: Peramelemorphia): reassessment of two species and description of a new species.

The phylogenetic relationships of bandicoots and bilbies have been somewhat problematic, with conflicting results between morphological work and molecular data. This conflict makes it difficult to assess the taxonomic status of species and subspecies within this order, and also prevents accurate evolutionary assessments. Here, we present a new total evidence analysis, combining the latest cranio-dental morphological matrix containing both modern and fossil taxa, with molecular data from GenBank. Several subspecies were scored in the morphological dataset to match the molecular data available. Both parsimony and Bayesian analyses were performed, giving similar topologies except for the position of four fossil taxa. Total evidence dating places the peramelemorphian crown origin close to the Oligocene/Miocene boundary, and the radiations of most modern genera beginning in the Late Miocene or Early Pliocene. Our results show that some species and subspecies require taxonomic reassessment, and are revised here. We also describe a new, extinct species from the Nullarbor region. This suggests that the number of recently extinct peramelemorphian species is likely to further increase.

An 57Fe Mössbauer study of three Australian L5 ordinary-chondrite meteorites: dating Kinclaven–001

Three L5-type ordinary chondrite meteorites recovered from the Nullarbor Region of Western Australia were studied by 57Fe Mossbauer spectroscopy: Kinclaven–001, Camel Donga–007 and Gunnadorah–002. The relative amounts of the various Fe-bearing phases including the primary minerals (Olivine, Pyroxene, Troilite and Fe-Ni metal) and the ferric alteration products (Goethite, Maghemite/Magnetite) were obtained to determine the percentage of iron converted to Fe3 + by weathering processes. These data allow us to estimate the terrestrial age of Kinclaven–001 at 1,700 ± 1,300 yrs.

The Australian Desert Fireball Network: a new era for planetary science

Through an international collaboration between Imperial College London, the Ondřejov Observatory in the Czech Republic and the Western Australian Museum, the installation of the Australian Desert Fireball Network in the Nullarbor Region of Western Australia was completed in 2007. Currently, the Network, which is the first to be established in the southern hemisphere, comprises four all-sky autonomous observatories providing precise triangulation of fireball records to constrain pre-atmospheric orbits and fall positions of meteorites over an area of approximately 200 000 km2. To date, the Network has led to the successful recovery of two observed meteorite falls. The first recovery was three fragments (174, 150 and 14.9 g) of the same meteorite fall recorded on 20 July 2007 at 19 h 13 m 53.2 s±0.1 s UT that were found within 100 m of the predicted fall line. Named Bunburra Rockhole, the meteorite is a basaltic achondrite with an oxygen isotopic composition (Δ17O = −0.112 ‰) distinguishing it from basaltic meteorites belonging to the Howardite–Eucrite–Diogenite clan thought to be derived from asteroid 4Vesta, and therefore must have come from another differentiated asteroid in the terrestrial planet region. Bunburra Rockhole was delivered to Earth from an Aten-like orbit that was almost entirely contained within the Earth's orbit. The second recovered fall was detected by the Network on 13 April 2010 and led to the recovery of a 24.54 g meteorite fragment that is yet to be fully described. To date, the Network has recorded ∼550 fireballs. Records from which precise orbits and trajectories can be determined number ∼150. In addition to the two recovered falls twelve fireballs are considered to have resulted in meteorite falls. Of these, four are probable falls (10's–100 g), and five are certain falls (>100 g). Having proved the potential of the Network, ultimately a large dataset of meteorites with orbits will provide the spatial context for the interpretation of meteorite composition that is currently lacking in planetary science.

Terrestrial ages of meteorites from the Nullarbor region, Australia, based on 14C and 14C–10Be measurements

Abstract– We have investigated the terrestrial ages, or residence times, of 78 meteorites (representing 73 discrete falls) recovered in Western Australia, and one from South Australia, using both 14C measurements and also 14C/10Be. The samples studied included two ureilites, one CK and one EL chondrite. We have included 10Be measurements from 30 meteorites, including some meteorites for which the 14C terrestrial age was previously determined. We find that the 14C/10Be terrestrial ages are more precise than 14C alone, as we can correct for shielding effects. In general, the two different age determinations age by 14C–10Be are precise to 0.5–1 ka and 14C alone within 1–2 ka. However, measurement of the 14C age alone gives good agreement with the 14C–10Be for most samples. The study of the terrestrial ages of meteorites gives us useful information concerning the storage and weathering of meteorites and the study of fall times and terrestrial age. We have compared the terrestrial ages to weathering, degree of oxidation (estimated from Mössbauer studies) and Δ17O. In this study, we found that weathering is not well correlated with terrestrial age for Nullarbor meteorites. However, there is a good correlation between degree of oxidation and Δ17O. The implications for the study of terrestrial ages and weathering from other desert environments will be discussed.

Second representative of the order Misophrioida (Crustacea, Copepoda) from Australia challenges the hypothesis of the Tethyan origin of some anchialine faunas

A new species of the genus Speleophria is described from a cave in the Nullarbor region in southern Western Australia. Its congeners include species from the Balearics, Croatia, Bermuda, Yucatan peninsula and north-western Western Australia, all considered to be Tethyan relicts. However, the discovery of the new speleophriid in the Nullarbor region has important biogeographic and ecological implications. From the biogeographic perspective, it either suggests dispersal as the process determining the current distribution pattern of the aquatic fauna found on the Roe Plains or significantly extends the Tethyan track across Australia, from the north-western coastal margin of the continent to the southern coastal margin. From an ecologic perspective, the new speleophriid suggests the possible existence of anchialine habitats in southern Australia. Speleophria nullarborensis sp. nov. can be distinguished from its four congeners by its plesiomorphic 3-segmented endopod of the first swimming leg (2-segmented in other species) and unusually long innermost apical seta on the caudal ramus. Another character that easily distinguishes our new species, and seems to be an autapomorphic feature, is its constricted preanal somite.

A troglobitic cryptopid centipede (Chilopoda: Scolopendromorpha) from western Queensland

Cryptops (Trigonocryptops) camoowealensis sp. nov. from Five O'Clock cave in the CJmooweal district of Queenslillld, is the second troglobitic species of the subgenus Trigonocnptops to be described from Australia. 'n1e new species is less troglomorphic than is a recently described congener from caves in the Nullarbor Region of Western Australia.

Noble gases in ten Nullarbor chondrites: Exposure ages, terrestrial ages, and weathering effects

Abstract— We present concentration and isotopic composition of He, Ne, and Ar in ten chondrites from the Nullarbor region in Western Australia as well as the concentrations of 84Ke, 129Xe, and 132Xe. From the measured cosmogenic 14C concentrations (Jull et al. 1995), shielding-corrected production rates of 14C are deduced using cosmogenic 22Ne/21Ne ratios. For shielding conditions characterized by 22Ne/21Ne >1.10, this correction becomes significant and results in shorter terrestrial ages. The exposure ages of the ten Nullarbor chondrites are in the range of values usually observed in ordinary chondrites. Some of the meteorites have lost radiogenic gases as well as cosmogenic 3He. Most of the analyzed specimens show additional trapped Ar, Kr, and Xe of terrestrial origin. The incorporation of these gases into weathering products is common in chondrites from hot deserts.

A troglomorphic species of the centipede Cryptops (Trigonocryptops) (Chilopoda: Scolopendromorpha) from Western Australia

– Among the 152 named species of the cosmopolitan centipede genus Cryptops Leach, 1815, a few troglomorphic species have been described from caves in Europe, the Canary Islands, and Cuba. Caves in the Roe Plains in the Nullarbor Region of Western Australia have yielded a new troglomorphic species, C. (Trigonocryptops) roeplainsensis sp.

Gold Basin meteorite strewn field, Mojave Desert, northwestern Arizona: Relic of a small late Pleistocene impact event

Abstract— Over 4450 meteorite specimens with a total mass of 168 760 g have been found in the Gold Basin (L4) strewn field over an area of 225 km2. The meteorite is a breccia, composed only of fragments of L‐chondrite materials. The parent meteoroid had a kinetic energy equivalent to ∼5 to 50 ktons when it hit the top of the atmosphere. Cosmogenic nuclide studies indicate the meteorite has a terrestrial age of 15 000 ± 600 years, corresponding to the Late Pinedale portion of the Wisconsin Glaciation. Conditions in the Gold Basin, which is now part of the Mojave Desert, were wetter and cooler at the time of the fall. Mössbauer analyses indicate the sample is 30 to 35% oxidized. This is less than that in meteorites with similar ages found in eastern New Mexico, but comparable to that found in meteorites from the Sahara and the Nullarbor Region. Oxidation is likely to have occurred soon after the fall, when exposure to precipitation was at its maximum. Four other new meteorites were also found in the Gold Basin strewn field.

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Phylogenetic structure of unusual aquatic microbial formations in Nullarbor caves, Australia.

The nature of unusual aquatic microbial formations in flooded passages of cave systems in the Nullarbor region of Australia was investigated using electron microscopy and DNA analysis. The caves are located in a semiarid region but intersect the watertable at depths of approximately 100 m below the surface. Throughout submerged portions of the caves divers have noted the presence of unusual microbial formations. These 'microbial mantles' comprise sheets or tongues of mucoid material in which small crystals are embedded. Examination of the biomass revealed it to be primarily composed of densely packed, unbranched filaments, together with spherical-, rod- and spiral-shaped cells, and microcrystals of calcite in a mucoid matrix. Molecular phylogenetic analysis of the community structure revealed approximately 12% of clones showed high similarity to autotrophic nitrite-oxidizing bacteria (Nitrospira moscoviensis). The remainder of the clones exhibited a high proportion of phylogenetically novel sequence types. Chemical analysis of water samples revealed high levels of sulphate and nitrate together with significant nitrite. The community structure, the presence of nitrite in the water, and the apparent absence of aquatic macrofauna, suggest these microbial structures may represent biochemically novel, chemoautotrophic communities dependent on nitrite oxidation.

Classification of ten new Nullarbor Region meteorites

Abstract— We classified ten new ordinary chondrites found in 1993 in the Nullarbor Region of Western Australia, seven of which were found in the Reid area (Reid 018–024) and three in the Hughes area (Hughes 027–029). Six of these are H and four are L chondrites, with petrologic types ranging from 4 to 6 and shock classifications from S2 to S4. All of the samples are small and, in most cases, heavily weathered, making pairing difficult.

Workshop on extraterrestrial materials from cold and hot deserts

The workshop was held July 6-8, 1999 before the Meteoritical Society meeting in Johannesburg, South Africa. The venue was Kwa Maritane Resort in the Pilanesburg Game Reserve. Conveners were Ludolf Schultz (Chair, MPI fur Chemie), Ian Franchi (Open University), Arch Reid (University of Houston), and Mike Zolensky (NASA JSC). Extended abstracts will be published as an LPI Technical Report. In the first session, Marvin discussed three African iron meteorites: Cape of Good Hope, Gibeon, and Hoba. Grady presented a statistical analysis of meteorites from hot and cold deserts. Wasson discussed types of Antarctic iron meteorites. Several presentations characterized populations of meteorites from individual desert areas: Libyan Desert (Weber et al.), Nullarbor Region (Bevan et al.), and Mojave Desert (Kring et al. and Verish et al). Pairing among EET87503-group howardites was discussed by Buchanan et al. Based on 14C terrestrial ages of Allan Hills ordinary chondrites, Bland et al. suggested that ice flow may be the principal sink for Antarctic meteorites. The effects of preterrestrial and terrestrial alteration were considered in the second session. Nakamura et al. and Lipschutz discussed asteroidal metamorphism of carbonaceous chondrites. Zolensky presented evidence for preterrestrial halide and sulfide in meteorites. Crozaz and Wadhwa described terrestrial alteration of Dar al Gani 476. Welten and Nishiizumi discussed terrestrial weathering of chondrites from Frontier Mountain, Antarctica. Most of the third session dealt with terrestrial meteorite ages. Based on 14C-10Be ages, Jull et al. discussed the exponential decay in numbers of meteorites with increased age. Nishiizumi et al. concluded that some Allan Hills meteorites have much older terrestrial ages than any meteorites from Lewis Cliffs. Welten et al. discussed terrestrial ages determined by 41Ca/36CI of metal separates from hot desert meteorites. Based on a comparison with large IDPs, Flynn et al. suggested that polar micrometeorites, lost a water-soluble sulfate phase by terrestrial alteration. Nyquist suggested that Type I cosmic spheres from deep sea sediments and polar ice were derived from carbonaceous chondrite-like asteroidal sources. The final session considered noble gases, cosmic ray effects, and thermoluminescence. Calculations presented by Reedy indicate that cosmic ray-produced nuclides are more likely to be preserved in small objects than in larger objects. Murty and Mohapatra. reported that trapped gas in Dar al Gani 476 includes a Martian atmospheric component. Wieler et al. and Scherer et al. reported noble gas abundances in different types of desert meteorites. Patzer and Schultz discussed the influence of terrestrial weathering on cosmic ray exposure ages of enstatite chondrites. Franchi et al. suggested that it is difficult to discriminate whether differences in gas release profiles of lunar meteorites from hot deserts and returned lunar samples are the result of terrestrial weathering or shock metamorphism. Benoit and Sears surveyed natural and induced thermoluminescence of Antarctic ordinary chondrites. Merchel et al. analyzed Saharan meteorites with short or complex exposure histories.

Climate and rock weathering: a study of terrestrial age dated ordinary chondritic meteorites from hot desert regions

Ordinary chondrites (OC) recovered from the desert areas of Roosevelt County, New Mexico, the Nullarbor Region of Western Australia, and the Algerian and Libyan Sahara, for which 14C terrestrial ages have been determined, were examined by 57Fe Mössbauer spectroscopy. OC were chosen as a standard sample to investigate weathering processes as their well constrained trace and bulk element chemistry, normative mineralogy and isotopic composition define a known, pre-weathering, starting composition. Given that terrestrial ages are known, it is possible to compare (initially very similar) samples that have been subsequently weathered in a range of climatic regimes from the present day to > 44 ka BP. In addition, recently fallen equilibrated OC contain iron only as Fe 0 and Fe 2+, thus the abundance of ferric iron is directly related to the level of terrestrial weathering. Mössbauer spectroscopy identifies two broad types of ferric alteration: paramagnetic phases (akaganéite, lepidocrocite, and goethite), and magnetically ordered (principally magnetite and maghemite). OC finds show a range in the percentage of total Fe existing as Fe 3+ from zero to over 80%. However, oxidation is comparable between fragments of the same OC separated since their time of fall (i.e., paired meteorites). Our results indicate several features of meteorite weathering that may result from climatic or geomorphologic conditions at the accumulation site: (1) Saharan samples are, overall, less weathered than non-Saharan samples, which may be related to the relatively recent age (ca. 20 ka) of the Saharan accumulation surface; (2) broad differences between sites in the rate of weathering, arising from regional differences in climate; (3) consistent differences in the weathering products between samples that fell during humid periods and those that fell during more arid periods (those falling during humid periods contain a higher proportion of magnetically ordered ferric oxides); (4) one region (the Nullarbor) that shows a variation in the total amount of ferric species that closely matches the climatic record for this area of Australia for the last 30 ka. Points (3) and (4) may be related to the identification of a rapid initial weathering phase: the majority of weathering occurs in the first few hundred years after fall, followed by passivation of weathering by porosity reduction. Porosity reduction, and the associated restriction in the ability of water to penetrate the sample, appears to be the mechanism whereby a weathering assemblage formed during the brief initial period of oxidation is preserved through subsequent climatic cycles over the terrestrial lifetime of the sample.

The Meteoritical Bulletin, No. 82, 1998 July

Abstract— Meteoritical Bulletin No. 82 lists information for 974 new meteorites, including 521 finds from Antarctica, 401 finds from the Sahara, 21 finds from the Nullarbor region of Australia, and 7 falls (Ban Rong Du, Burnwell, Fermo, Jalanash, Juancheng, Monahans (1998), and Silao). Many rare types of meteorites are reported: counting pairing groups as one, these include one CR chondrite, two CK chondrites, two CO chondrites, four CV chondrites, one CH chondrite or Bencubbin‐like, six C2 (unclassified) chondrites, two EH chondrites, two EL chondrites, three R chondrites, thirty unequilibrated ordinary chondrites, one un‐grouped chondrite, three eucrites, six howardites, one diogenite, eleven ureilites, nine iron meteorites, one mesosiderite, two brachinites, one lodranite, one winonaite, and two lunar meteorites (Dar al Gani 400 and EET 96008). All italicized abbreviations refer to addresses tabulated at the end of this document.

Meteorite flux on the Nullarbor Region, Australia

Abstract The Nullarbor Region of Australia is one of the most prolific sites for meteorite recoveries outside of Antarctica. Reported 14 C terrestrial ages for chondritic meteorites from the Nullarbor indicate an age range from present day to c. 35 ka. There is good evidence to suggest that meteorites are lying on, or close to the surfaces on which they fell and that, physiographically, the region has remained essentially undisturbed for at least the last 30 ka. The Nullarbor can thus provide important data on the flux of meteorites over the period of accumulation. One significant factor influencing flux calculations based on meteorite accumulation sites is the determination of the number of falls represented in the recovered population. In the case of the Nullarbor, a general lack of transportation processes in the region and careful documentation of the distribution of finds allows confident ‘pairing’ of meteorites. For example, strewn fields of showers that have remained undisturbed for thousands of years are easily recognized and mapped today. Mass distribution statistics confirm that there are few undetected pairs in the population of meteorites so far described from the Nullarbor, and there is no evidence of selection of meteorites of a specific terrestrial age. The Nullarbor is the largest accumulation of meteorites nearest to Antarctica with a terrestrial age range (0–35 ka) that overlaps the Antarctic population (0 to >1 Ma). Analysis of the well-documented population of meteorites from the Nullarbor compared with Antarctica suggests that there are many unrecognized paired meteorites in the Antarctic population and the abundance of small meteorites at that site can be accounted for, at least in part, by the presence of large shower falls of common chondrites. The data suggest that there may also be many unrecognized paired meteorites in collections from the Sahara.

The flux of meteorites to the Earth over the last 50 000 years

98 ordinary chondrite finds, terrestrial age-dated using 14C analyses by Jull et al., from three arid/semi-arid meteorite accumulation sites (New Mexico, the Sahara, and the Nullarbor Region, Australia) have been examined by Mössbauer spectroscopy to determine quantitatively the terrestrial oxidation for each sample. A comparison of weathering over time, and its effect in ‘eroding’ meteorites, allows a calculation of a decay constant for meteorites from each hot desert site. This, together with the number and mass distribution of paired meteorites in each region, enables us to derive estimates of the number of meteorite falls over a given mass per year: we calculate between 36 and 116 falls over 10 g per 106 km2 yr−1. In addition, we constrain the total mass flux to the Earth's surface over the 10 g to 1 kg interval to between 2900 and 7300 kg yr−1. We find remarkable agreement in our estimates from each accumulation site, and also with the estimate of the present flux made from MORP camera network data presented by Halliday, Blackwell & Griffin, suggesting that the flux of meteorites to the Earth has remained essentially constant over the last 50 000 yr. This work is the first independent confirmation of the MORP estimate, and indicates that meteorite accumulation sites provide an alternative method of calculating flux. We suggest that the application of a similar methodology to the Antarctic meteorite population may be used to explore the possibility that the flux of meteorites to the Earth has varied over the 1-Ma time-scale sampled by these meteorites.

Formation of opaque minerals in CK chondrites

The opaque minerals of 19 CK chondrites from Antarctica and the Nullarbor Region, Australia were studied mineralogically by optical and analytical methods. The most striking feature of the CK chondrites—indicating the oxidized nature of these meteorites—is the presence of magnetite as the most abundant opaque phase. It occurs in modal abundances between 1.2 and 8.1 vol.%, averaging about 4 vol.%. Magnetite occurs in two different populations: as tiny micronsized grains dispersed throughout the meteorite; and as rounded aggregates up to 1 mm in size. In the latter type exsolution lamellae of ilmenite and spinel were observed. Chemically, the magnetites contain small amounts of MgO, Al 2O 3 and TiO 2 (usually below 1 wt.%), and an average of about 4 wt.% Cr 2O 3. Sulphide phases occur in abundances below 1 vol.% (except Karoonda 1.3 vol.%). However, six different phases were found: pentlandite ((Fe,Ni) 9S 8), pyrite (FeS 2), pyrrhotite (Fe 1− x S), monosulphide solid solution (MSS; (Fe,Ni) 1− x S), millerite (NiS), and chalcopyrite (CuFeS 2). Usually, the parageneses pentlandite-pyrrhotite/MSS-pyrite and pentlandite-pyrite were found. The chemical compositions of the observed pentlandites vary substantially regarding the Fe Ni ratio. In all phases various amounts of Co and, in some cases Cr were detected. Associated with magnetite and/or sulphides, micron-sized noble metal-rich sulphides, tellurides and arsenides were found. Among the sulphides the most frequently occurring phase is (Os,Ru,Ir)S 2. In addition, PtS, (Au,Fe,Ag) 2S, and (Fe,Au,Co) 2S 3 were identified. Among the tellurides and arsenides, chengbolite (PtTe 2), in some cases containing dissolved Fe and Au, and a phase (Ir,Pt,Fe,Os)(As,S) 2 were discovered. For the formation of the observed opaque phases and assemblages a multistage process under increased oxygen fugacities is proposed. Magnetite is formed from Fe,Ni-metal during a metamorphic event under oxygen fugacities on the order of the NiNiO oxygen buffer. Ni became disengaged, oxidized and diffused into olivine. The observed exsolution of ilmenite and spinel was established during cooling. Based on stability conditions the observed sulphide parageneses must have been formed by subsolidus reactions under low temperatures from MSS. The noble metal elements which were either dissolved in the Fe,Ni-metal or in the MSS, formed noble metal-rich phases by exsolution during the oxidation of the metal phases or during the subsolidus breakdown of MSS.