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The Phanerozoic sedimentary record documents a diverse series of cyclic patterns of sedimentation that reflect multiple drivers of change (e.g. climate, eustasy, tectonics, biotic evolution) operating over a range of time scales (days to hundreds of million years). While short-term cycles can be easily identified within the rock record and have frequently been related to the Milankovitch cycles, medium-term (a few tens of million years) and long-term (hundreds of million years) cycles are less-well-resolved. Notably the identification of medium- and long-term cycles are reliant upon global scale studies, which are typically hampered by low stratigraphic resolution or address sedimentary changes indirectly through proxies (e.g. sea-level models, geochemical trends). Moreover, such difficulties have resulted in uncertainties as to the drivers and durations of medium- and long-term cycles.To adequately address this challenge, an integrated approach is required, combining 1) large sedimentary and global events datasets, 2) a high-resolution sequence stratigraphic model, and 3) plate tectonic and digital palaeo-elevation modelling.We present the preliminary results of an industry-led study of medium- to long-term Phanerozoic cycles in global sedimentation and an assessment of the drivers of these cycles. Our study is based upon a spatially- and temporally-enabled global dataset of sedimentary records, obtained from over 8,500 wells. The sedimentary data contained within the wells have been standardised using a hierarchical classification of sediment types and divided into time slices based upon sequence stratigraphic interpretations, and the identification of age calibrated maximum flooding surfaces derived from the Neftex Global Sequence Stratigraphic Model. This approach allows the Phanerozoic sedimentary record to be subdivided into 132 time slices and the proportion of different sedimentary compositions preserved for each time slice can be reported as a percentage. The resultant analysis identifies medium- to long-term cycles in the proportions of siliciclastics, carbonates and evaporites.There are two long-terms trends apparent from our data, and these have been analysed by a palinspastic reconstruction of each time slice using our digital palaeo-elevation and tectonic models. The first trend is a progressive decrease in the proportion of carbonates relative to siliciclastics, such that carbonates represent ~50% of Cambrian sediments and ~30% of Neogene sediments. This appears linked to early Palaeozoic low latitude continental configurations favouring carbonate sedimentation. The second trend is a notable increase in evaporites from the Late Permian to Late Jurassic (5% to 10%, from a Phanerozoic average of Medium-term cycles are identifiable as significant shifts in the global proportions of siliciclastics relative to carbonates. There is a hierarchical arrangement to these cycles, both in terms of duration and severity of change, suggestive of multiple drivers. An initial comparison with known glaciations, major biotic events impacting carbonate producers and orogenies appears to explain many of these cycles.

We report results of Canberra-ATCA Doppler-only continuous wave (CW) radar observations of near-Earth asteroid (163899) 2003 SD220 at a receiving frequency of 7159 MHz (4.19 cm) on 2018 December 20, 21, and 22 during its close approach within 0.019 au (7.4 lunar distances). Echo power spectra provide evidence that the shape is significantly elongated, asymmetric, and has at least one relatively large concavity. An average spectrum per track yields an OC (opposite sense of circular polarisation) radar cross section of 0.39, 0.27, and 0.25 km$^{2}$, respectively, with an uncertainty of 35 \%. Variations by roughly a factor of two in the limb-to-limb bandwidth over the three days indicate rotation of an elongated object. We obtain a circular polarization ratio of 0.21 $\pm$ 0.07 that is consistent with, but somewhat lower than, the average among other S-class near-Earth asteroids observed by radar., Comment: 15 pages, 4 figures, accepted for publication in Icarus

We describe the first demonstration of a southern hemisphere planetary radar system to detect two near-Earth asteroids (NEAs). The demonstration was conducted in a bistatic manner, with the 70 m antenna of the Canberra Deep Space Communications Complex transmitting at 2.1 GHz and reception at the Parkes Radio Telescope, outfitted with multiple receivers, and the Australia Telescope Compact Array. This initial system was used to detect the NEAs (43577) 2005 UL5 and (33342) 1998 WT24 during their close approaches in 2015 November and 2015 December, respectively. We describe the performance of the system and consider future possibilities using other antennas of the Canberra Deep Space Communications Complex as transmitters.

A dual beam, dual polarization, low noise receiver has been installed at a Cassegrain focus of the NASA 70[Formula: see text]m antenna near Canberra, Australia. It operates in five pairs of 1[Formula: see text]GHz bands from 17 to 27[Formula: see text]GHz simultaneously. The receiver temperature measured at the feed is 21–22[Formula: see text]K at 22[Formula: see text]GHz and, during dry winter night-time conditions, zenith system temperatures as low as 35[Formula: see text]K have been observed in the 21–22[Formula: see text]GHz band. The native polarization is linear but can be converted to circular prior to down-conversion. The downconverters have complex mixers, followed by quadrature hybrids which can be bypassed or used to convert the quadrature phase channels into an upper and lower sideband, each 1000[Formula: see text]MHz wide. For spectroscopy, four ROACH1 signal processors each currently providing 32[Formula: see text]K channel spectra across four 1000[Formula: see text]MHz bands, for 0.4[Formula: see text]km/s velocity resolution at 22[Formula: see text]GHz. Using both beam- and position-switching, the receiver achieved a noise level of 5[Formula: see text]mK r.m.s. in an hour of integration and 31[Formula: see text]kHz resolution. The NASA 70[Formula: see text]m antennas have a 45 arcsec beamwidth at 22[Formula: see text]GHz and an aperture efficiency of 35.5% giving a sensitivity of 0.49[Formula: see text]K/Jy.

The origin of moderate magnitude (tens of metres), short-term Cretaceous eustatic cycles remains enigmatic. The historical view of ubiquitous Cretaceous warmth casts doubt on the presence of significant terrestrial ice caps and the role of glacio-eustasy. As such, aquifer-eustasy is increasingly advocated as the primary driver of Cretaceous short-term sea-level change. Here, we analyse the role of aquifer-eustasy in driving Cretaceous short-term cycles by assessing the spatio-temporal pattern of aridity and humidity under differing CO2 forcing in new climate simulations for the Valanginian, Turonian, and Maastrichtian. Elevated CO2 forcing acts to increase the spatial extent of fully arid land areas, while resulting in only a marginal expansion of fully humid zones. Consequently, the greatest aquifer charge is more likely during lower CO2/cooler intervals, indicating that aquifer-eustasy works in phase with both glacio- and thermo-eustasy in contrast to the current aquifer-eustasy paradigm. Modern data indicate that climate is a primary control on water table depth. Using this constraint, the hydrological response in our Cretaceous simulations to large changes in atmospheric CO2 are insufficient to generate reported eustatic magnitudes. Our most likely aquifer-eustasy estimates are decimetre scale. Even using optimistic values for the impact of lakes and assuming the water table depth was reduced from the modern average to 0 m globally, the total aquifer-eustasy response remains smaller than 5 m. Our results indicate that glacio-eustasy was the most likely driver of Cretaceous short-term cycles, consistent with a growing body of evidence that challenges the ubiquitously warm Cretaceous notion.

No consensus currently exists regarding the magnitude of Cretaceous short-term (less than 3 Ma in duration) eustatic sea-level change. The lack of a consensus limits the ability to predict sedimentary facies and architecture and to assess the potential drivers of eustasy during a period of Earth history considered as significantly warmer than today. Consequently, this review documents, weighs, synthesises, and summarises records of short-term relative sea-level change and evaluates the observed trends in magnitude within the context of potential climatic drivers and their eustatic expression. Although Cretaceous sea-level change is addressed in many publications, estimates of absolute values are relatively limited, often cover short time intervals, and use different methods. Based upon integrated geological and statistical analyses, four broad episodes of magnitude change have been identified. Three of these episodes reflect trends of increasing magnitudes of sea-level change from the Berriasian to early Hauterivian, late Hauterivian to Aptian, and Santonian to Maastrichtian. The fourth episode reflects a decreasing magnitude trend from the Albian to Coniacian. In addition, the maximum magnitude of sea-level change, at an approximate stage level, has been identified and categorised as slight (less than 10 m), modest (10 to 40 m), or significant (41 to 65 m). Significant magnitudes are inferred for the Valanginian, Aptian, Albian, and Maastrichtian; exclusively slight magnitudes are restricted to the Berriasian. Such an assessment casts doubt on the repeated and stratigraphically widespread episodes of very large magnitudes (more than 75 m) advocated by some workers, and instead defines distinct periods and magnitudes of sea-level change that should be globally reflected in sedimentary facies patterns. For example, intervals of sea-level fall of significant magnitude are commonly associated with the increased delivery of sediment into basinal settings, including the marked progradation of shallow-marine sediments, whilst up-systems tract there can be enhanced development of karst and erosional features. Because climatically driven eustasy is the likely cause of short-term sea-level change, an assessment of the characteristic maximum magnitude limits of the principal climatic drivers (thermo-, aquifer-, and glacio-eustasy) has been made. Such a comparison argues for glacio-eustasy as the driver of significant short-term sea-level change. In addition, climate proxy data demonstrates that the Valanginian, Aptian, Albian, and Maastrichtian are intervals of cooling within the Cretaceous, thereby supporting the link between significant magnitudes and glacio-eustasy.

The Mt Painter Province of northern South Australia is a site of exceptional suite of Mesoproterozoic high heat producing (HHP) granites and felsic volcanics. These rocks have very high heat production values of > 5 μW m − 3 . The HHP granites, including the Mt Neill, Box Bore, Terrapinna, Wattleowie and Yerila granites, form part of a broadly coeval association of mafic and felsic volcanic rocks that also include the Pepegoona Volcanics, lamprophyres and mafic–intermediate dykes. U–Pb LA-ICPMS zircon dating and Hf-in-zircon isotopic data are used to constrain both the timing and source of these magmatic rocks. U–Pb zircon LA-ICPMS crystallization ages range from ~ 1596 to 1521 Ma and imply a protracted sequence of magmatic events. Initial Hf isotopic compositions of these zircons from both dykes and felsic rocks have overlapping compositional ranges, with e Hf values mainly from + 4 to − 2. These Hf values are significantly higher than contemporary crustal values which are likely to have been in the range − 4 to − 20. These data imply that the magmatic suite has both mantle and crustal sources.

The Archaean to Mesoproterozoic basement of northern South Australia is almost completely overlain by thick Neoproterozoic and younger basins (<< 1% outcrop), yet is likely to preserve an important record of the interactions between the Archean-Proterozoic Gawler Craton and the Proterozoic Musgrave Province during the amalgamation of Australia in the Proterozoic. However, constraints on the location and geometry of the boundary between these provinces are poor. We use potential field data to determine the 3D basement architecture and so constrain where this Palaeo-Mesoproterozoic boundary may be located beneath the Eastern Officer Basin. We establish the geometry and properties of the overlying basins and explicitly include them during forward and inverse modelling of potential field data to highlight the structure of the underlying basement. Our analysis identifies three crustal domains. (1) Southeast of the steep northeast-southwest Middle Bore Fault, positive gravity and magnetic anomalies are co-located and sourced from bodies in the upper crust, these bodies overlie middle to lower crust that is apparently uniform. (2) Between the Middle Bore Fault and the southern edge of the Munyarai Trough, the highest amplitude gravity and magnetic anomalies are not co-located and are sourced from large northwest dipping bodies. (3) To the northwest, the crust underlying the Munyarai Trough has similar properties to the Musgrave Province, suggesting that the Musgrave Province extends at least 50 km beneath the Eastern Officer Basin. Although details of the geology in the second (central) domain are poorly constrained, the domain preserves large crustal-scale Precambrian structures and is interpreted to mark the boundary between the Gawler Craton and the Musgrave Province. In particular, the multiply reactivated Middle Bore Fault forms a major crustal boundary and is interpreted to mark the northern limit of the Gawler Craton. The Middle Bore Fault may have formed as early as the Kimban Orogeny (similar to 1.7 Ga), although substantial reactivation and modification of the crustal architecture could have occurred between the Kimban Orogeny and intrusion of the cross-cutting Gairdner Dolerite Dykes (827 Ma). Refereed/Peer-reviewed

Absolute ages of plutonic rocks from mid-ocean ridges provide important constraints on the scale, timing and rates of oceanic crustal accretion, yet few such rocks have been absolutely dated. We present 206Pb/238U SHRIMP zircon ages from two ODP Drill Holes and a surface sample from Atlantis Bank on the Southwest Indian Ridge. We report ten new sample ages from 26–1430 m in ODP Hole 735B, and one from 57 m in ODP Hole 1105A. Including a previously published age, eleven samples from Hole 735B yield 206Pb/238U zircon crystallization ages that are the same, within error, overlap with the estimated magnetic age and are inferred to date the main period of crustal growth, the average age of analyses is 11.99 ± 0.12 Ma. Any differences in the ages of magmatic series and/or tectonic blocks within Hole 735B are unresolvable and eight well-constrained ages vary from 11.86 ± 0.20 Ma to 12.13 ± 0.21 Ma, a range of 0.27 ± 0.29 Ma, consistent with the duration of crustal accretion observed at the Mid-Atlantic Ridge. An age of 11.87 ± 0.23 Ma from Hole 1105A is within error of ages from Hole 735B and permits previous correlations made between zones of oxide-rich gabbros in each hole. Pb/U zircon ages > 0.5 Ma younger than the magnetic age are recorded in at least three samples from Atlantis Bank, one from Hole 735B and two collected along a fault scarp to the East. These young ages may date one or more off-axis events previously suggested from thermochronologic data and support the interpretation of a complex geological history following crustal accretion at Atlantis Bank. Together with results from the surface of Atlantis Bank, dating has shown that while the majority of Pb/U SHRIMP zircon ages record the short-lived ( 1 Ma suggesting a complex and prolonged magmatic/tectonic history for the crust at Atlantis Bank.

The rates of slip on oceanic detachment faults and how those rates compare to sea-floor spreading rates constitute fundamental data required to constrain how oceanic core-complexes form and their role during crustal accretion. We combine sea-surface magnetic data, with the magnetic polarity of shallow-core samples and Pb/U SHRIMP ages of igneous zircon to determine the time-averaged half-spreading rate during oceanic detachment faulting at Atlantis Bank, 100 km south of the ultraslow-spreading Southwest Indian Ridge (SWIR). The Pb/U zircon ages correlate well with the magnetic ages and so highlight that magmatic accretion and faulting were coeval for over 2 Myr, creating and exposing a > 1.5-km-thick layer of gabbro for > 35 km parallel-to-spreading. We use bivariate linear regression of distance–age data and forward modeling of magnetic anomaly data to calculate a half-spreading rate during detachment faulting of 14.1 + 1.8/− 1.5 km/Myr (95% confidence limits). When integrated with regional constraints on spreading history, we note that detachment faulting coincided with a short-lived regional increase in the full-spreading rate along the SWIR and, for the ridge segment containing Atlantis Bank, spreading was highly asymmetric with ~ 80% of plate-motion accommodated by detachment faulting. Consequently, the detachment fault effectively formed the plate-boundary at the surface in this spreading segment. Highly asymmetric spreading was confined to the spreading segment containing Atlantis Bank and to the duration of detachment faulting. So the ridge segment containing Atlantis Bank migrated northward relative to its symmetrically spreading eastern neighbour, such that the intervening non-transform discontinuity shortened. We suggest that the highly asymmetric spreading may be a characteristic feature of oceanic detachment faulting, an inference supported by more poorly constrained half-spreading rates determined at several other oceanic core-complexes.

The cooling history and therefore thermal structure of oceanic lithosphere in slow-spreading environments is, to date, poorly constrained. Application of thermochronometric techniques to rocks from the very slow spreading SW Indian Ridge provide for the first time a direct measure of the age and thermal history of in situ lower oceanic crust. Crystallization of felsic veins (f850jC) drilled in Hole 735B is estimated at 11.93F0.14 Ma, based on U–Pb analyses of zircon by ion probe. This crystallization age is older than the ‘crustal age’ from remanence inferred from both sea surface and near-bottom magnetic anomaly data gathered over Hole 735B which indicate magnetization between major normal polarity chrons C5n.2n and C5An.1n (10.949–11.935 Ma). 40 Ar/ 39 Ar analyses of biotite give plateau ages between 11 and 12 Ma (mean 11.42F0.21 Ma), implying cooling rates of >800jC/m.y. over the first 500,00 years to temperatures below f330–400jC. Fission-track ages on zircon (mean 9.35F1.2 Ma) and apatite reveal less rapid cooling to 700 m below sea floor at 8–10 Ma (i.e. 2–4 m.y. off axis). We offer two hypotheses for this thermal anomaly: (i) Off-axis (or asymmetric) magmatism that caused anomalous reheating of the crust preserved in Hole 735B. This postulated magmatic event might be a consequence of the transtension, which affected the Atlantis II transform from f19.5 to 7.5 Ma. (ii) Late detachment faulting, which led to significant crustal denudation (2.5–3 km removed), further from the ridge axis than conventionally thought. D 2004 Elsevier B.V. All rights reserved.

The Superfast Spreading Crust campaign, echoing long-standing ocean lithosphere community endeavors, was designed to understand the formation, architecture, and evolution of ocean crust formed at fast spreading rates. Integrated Ocean Drilling Program (IODP) Expedition 335, “Superfast Spreading Rate Crust 4” (13 April–3 June 2011), was the fourth scientific drilling cruise of the Superfast Spreading Crust campaign to Ocean Drilling Program (ODP) Hole 1256D. The expedition aimed to deepen this basement reference site several hundred meters into the gabbroic rocks of intact lower oceanic crust to address the following fundamental scientific questions: Does the lower crust form by subsidence of a crystal mush from a high-level magma chamber (gabbro glacier), by intrusion of sills throughout the lower crust, or by some other mechanism? How does melt percolate through the lower crust, and what are the reactions and chemical evolution of magmas during migration? Is the plutonic crust cooled by conduction and/or hydrothermal circulation? What are the role and extent of deeply penetrating seawater-derived hydrothermal fluids in cooling the lower crust and the chemical exchanges between the ocean crust and the oceans? What are the relationships among the geological, geochemical, and geophysical structure of the crust and, in particular, the nature of the seismic Layer 2–3 transition?

Expedition 335 of the riserless drilling platform Puntarenas, Costa Rica, to Balboa, Panama Site 1256 13 April-3 June 2011

The Superfast Spreading Crust campaign, echoing long-standing ocean lithosphere community endeavors, was designed to help us understand the formation, architecture, and evolution of ocean crust formed at fast spreading rates. Integrated Ocean Drilling Program (IODP) Expedition 335, "Superfast Spreading Rate Crust 4" (13 April-3 June 2011), was the fourth scientific drilling cruise of the Superfast Spreading Crust campaign to Ocean Drilling Program (ODP) Hole 1256D. The expedition aimed to deepen this basement reference site several hundred meters into the gabbroic rocks of intact lower oceanic crust to address the following fundamental scientific questions: Does the lower crust form by subsidence of a crystal mush from a high-level magma chamber (gabbro glacier), by intrusion of sills throughout the lower crust, or by some other mechanism? How does melt percolate through the lower crust, and what are the reactions and chemical evolution of magmas during migration? Is the plutonic crust cooled by conduction or hydrothermal circulation? What are the role and extent of deeply penetrating seawater-derived hydrothermal fluids in cooling the lower crust and the chemical exchanges between the ocean crust and the oceans? What are the relationships among the geological, geochemical, and geophysical structure of the crust and, in particular, the nature of the seismic Layer 2-3 transition? What is the magnetic contribution of the lower crust to marine magnetic anomalies?

The Adelaide Basin in Australia is a complex of late Neoproterozoic to Early Cambrian rift and sag basins which was inverted during the Cambro-Ordovician Delamerian Orogeny. The deposition of evaporitic sediments during the earliest stage of basin development in the late Neoproterozoic (Willouran age) played a major role in the subsequent tectonic evolution of the basin. Previous studies have shown that early mobilization, vertical transport and withdrawal of the evaporites influenced the sedimentation during the late Neoproterozoic and Early Cambrian. The evaporites also influenced deformation during the inversion of the basin and the development of the Delamerian fold and thrust belt. However, the control exerted by basement structures in the deposition of the evaporitic beds and the role of these tectonic structures in the later inversion of the basin have been poorly constrained. In this work, we use a combination of published and original geological observations along with the interpretation of potential field datasets (total magnetic intensity and Bouguer anomaly data) to better constrain the geology of the basin at depth. We construct two and a half dimensional forward models of the potential field data along selected profiles across the Adelaide Basin. These models are constrained by the geology at the surface, drill hole data and measured petrophysical properties (specific gravity and magnetic susceptibility). We achieved the best fit between observed and modelled potential fields with a model favouring thick-skinned deformation, where the diapirs are not randomly distributed, but located directly above basement-penetrating normal faults. Furthermore, these normal faults were probably active during the sedimentation of the late Neoproterozoic and Early Cambrian sediments, and underwent partial or total inversion during the Cambro-Ordovician Delamerian Orogeny. Mobilisation and withdrawal of the evaporites was therefore initiated and facilitated by the extension coeval with the opening of the basin, and continued during the subsequent Delamerian Orogeny. Refereed/Peer-reviewed

[1] We report 26 (U-Th)/He zircon ages from Atlantis Bank, Southwest Indian Ridge, which constrain time scales and rates of lower crustal cooling in ultraslow spreading oceanic crust in this setting. Samples from the detachment fault surface indicate that denuded oceanic crust cooled rapidly ( 1200°C/Ma, consistent with existing models for the cooling of oceanic crust. (U-Th)/He zircon ages from samples collected along N–S and E–W trending faults scarps record young ages inconsistent with standard cooling models for lower oceanic crust. These samples have a mean (U-Th)/He zircon age 2.6 Ma younger than their corresponding igneous crystallization ages and record cooling through 200°C well outside the rift valley. Similar anomalously young ages are recorded by zircon, sphene, and apatite fission track data from ODP Hole 735B. We interpret these young ages as recording an off-axis thermal/heating event associated with localized high-temperature (>300°C) hydrothermal fluid flow resulting from underplated mafic magmas.

From 55°45′E to 58°45′E and from 60°30′E to 62°00′E, the ultraslow-spreading Southwest Indian Ridge (SWIR) consists of magmatic spreading segments separated by oblique amagmatic spreading segments, transform faults, and nontransform discontinuities. Off-axis magnetic and multibeam bathymetric data permit investigation of the evolution of this part of the SWIR. Individual magmatic segments show varying magnitudes and directions of asymmetric spreading, which requires that the shape of the plate boundary has changed significantly over time. In particular, since 26 Ma the Atlantis II transform fault grew by 90 km to reach 199 km, while a 45-km-long transform fault at 56°30′E shrank to become an 11 km offset nontransform discontinuity. Conversely, an oblique amagmatic segment at the center of a first-order spreading segment shows little change in orientation with time. These changes are consistent with the clockwise rotation of two ∼450-km-wide first-order spreading segments between the Gallieni and Melville transform faults (52–60°E) to become more orthogonal to spreading. We suggest that suborthogonal first-order spreading segments reflect a stable configuration for mid-ocean ridges that maximizes upwelling rates in the asthenospheric mantle and results in a hotter and weaker ridge-axis that can more easily accommodate seafloor spreading.

Atlantis Bank is an anomalously uplifted oceanic core complex adjacent to the Atlantis II transform, on the southwest Indian Ridge, that rises >3 km above normal seafloor of the same age. Models of flexural uplift due to detachment faulting can account for ∼1 km of this uplift. Postdetachment normal faults have been observed during submersible dives and on swath bathymetry. Two transform-parallel, large-offset (hundreds of meters) normal faults are identified on the eastern flank of Atlantis Bank, with numerous smaller faults (tens of meters) on the western flank. Flexural uplift associated with this transform-parallel normal faulting is consistent with gravity data and can account for the remaining anomalous uplift of Atlantis Bank. Extension normal to the Atlantis II transform may have occurred during a 12 m.y. period of transtension initiated by a 10° change in spreading direction ca. 19.5 Ma. This extension may have produced the 120-km-long transverse ridge of which Atlantis Bank is a part, and is consistent with stress reorientation about a weak transform fault.