Early Pliocene ostracod faunas of the Jemmys Point Formation, onshore Gippsland Basin, yield a rich and well-preserved marine ostracod fauna of mixed shallow marine and deep marine origins. The ostracod faunas evidence a marine continental shelf palaeoenvironment that, during the deposition of one stratigraphic interval, was influenced by a strong, persistent upwelling current. This upwelling current allowed the migration of deep-sea Ostracoda (Philoneptunus sp.) onto the continental shelf. The deeper marine aspect of this early Pliocene fauna, and of modern ostracod faunas from the Bass Strait region, evidence the adaptation of deep shelf taxonomic clades to shallow cool temperate shelf environments and highlights one unusual evolutionary mechanism that has contributed to modern Bass Strait shallow marine biodiversity. Four species are newly described: Neonesidea chapminuta sp. nov., Tasmanocypris salaputia sp. nov., Oculocytheropteron jemmyensis sp. nov., and Philoneptunus plutonis sp. nov.Abbey P. McDonald* [a.mcdonald@deakin.edu.au], School of Life and Environmental Sciences, Deakin University, Burwood, Victoria 3125, Australia;Elizabeth A. Weldon [l.weldon@deakin.edu.au], School of Life and Environmental Sciences and Deakin Marine Research and Innovation Centre, Deakin University, Burwood, Victoria 3125, Australia;Mark T. Warne [mark.warne@deakin.edu.au], School of Life and Environmental Sciences and Deakin Marine Research and Innovation Centre, Deakin University, Burwood, Victoria 3125, Australia, and Museums Victoria, GPO Box 666, Melbourne, Victoria 3001, Australia.

The Lower Devonian (Emsian) Norton Gully Sandstone contains rich invertebrate fossil faunas including ostracods. Seven ostracod taxa are recognized and illustrated herein: Bungonibeyrichia copelandi, Bungonibeyrichia wooriyallockensis, Bungonibeyrichia treslata sp. nov., Bungonibeyrichia australiae, Bairdiocypris sp., and two indeterminate genera. The ostracods are preserved in sandstone and mudstone as natural moulds. There are two distinct biofacies identified within the Norton Gully Sandstone: one dominated by ornate ostracods belonging to Bungonibeyrichia; and the other by smooth species of Bairdiocypris. We also conclude that most southeast Australian species previously placed in Velibeyrichia are more appropriately placed in Bungonibeyrichia on the basis of lobe morphology. Consequently, both these genera can be recognized as having discrete Silurian-Devonian palaeobiogeographical distributions, with Velibeyrichia spp. occurring in the shallow seas of Laurentia, while Bungonibeyrichia spp. was restricted to shallow seas around eastern Gondwana.

Magmatic sills emplaced at shallow-levels are commonly associated with bending and uplift of the overburden. Such phenomena result into domed-shaped structures, known as forced folds whose structural architecture is chiefly controlled by the geometry of underlying intrusions. Several models for host-rock deformation have been proposed and are based on elastic bending-related uplift of the associated overburden. However, the importance of inelastic compaction of overburden for accommodating intruded magma volume has remained underestimated. In this study, we document a forced fold developed above magmatic sills intruded at shallow levels into the sedimentary layers of the offshore Otway Basin, southeastern Australia, from high-quality 3D reflection seismic data. The intruded sills S1 and S2 have an average thickness of 81 m and 223 m, and its emplacement uplifted the paleo-seabed to an average amplitude of 93 m. The intruded sill S2 possess larger contribution in bending the overburden, however, the discrepancy (similar to 65%) between the sill thickness and vertical uplift observed at the paleo-surface, indicates the occurrence of localized host rock deformation caused by pore space collapse and fluidization of shallow buried consolidated sediments. In addition, we assume that the imaged igneous sill may include flakes of sedimentary rocks, which caused an overestimation of the sill thickness, using the widely accepted seismic velocity for mafic intrusions. Our observations imply that porosity reduction due to compaction of both proximal syn-emplacement and post-emplacement sediments, could play a vital role in accommodating this intrusion within the associated stratigraphic succession. Thus, our study provides critical insights into the compaction-related mechanism involved in overburden deformation as a result of sill intrusion.

Magmatic rocks are frequently encountered during hydrocarbon exploration in rift-related sedimentary basins. As magmatic rocks may contribute both positively and negatively to the hydrocarbon systems, their spatio-temporal distribution and structural elements are crucial for exploration in frontier basins. With the proliferation and increased density of seismic reflection data, various subsurface magmatic features can be discriminated and illuminated via conventional interpretation approaches, such as attribute extraction, opacity rendering or geo-body extraction. However, these manual interpretation techniques are labor-intensive, subject to interpreter bias and often bottleneck with respect to time data delivery. A supervised machine learning approach could efficiently resolve these issues by amalgamating suitable seismic attributes, such as energy, reflection strength, texture, and similarity, and automatically delineating these magmatic features in 3D seismic reflection data. Our machine learning neural network classified igneous features from non-igneous features in two different seismic surveys within the natural laboratory of the offshore Otway Basin, SE Australia. This multi-layer perception neural network designed in this study resulted in an optimized igneous probability meta-attribute cube that could effectively reveal the extension and distribution of igneous features and several structural elements in the study area. We presented the detailed workflow of this artificial neural network and observed the efficiency of this approach in different seismic surveys. These results illustrate the potential of neural network in imaging other complex igneous features from 3D seismic data in the Otway Basin and worldwide.

The uppermost Miocene Bookpurnong Formation within the Murray Basin of southeastern Australia overlies a regionally extensive subaerial unconformity formed by relatively low late Miocene eustatic sea levels, and the initial phase of the Kosciuszko Uplift tectonic event. A diverse marine fossil ostracod fauna has been recovered from the Bookpurnong Formation, and is associated with a marine transgression that flooded inland regions of southeastern Australia to form a shallow epicontinental sea. Many of the Bookpurnong Formation ostracods represent immigrant taxa, with species such as Puriana lubbockiana, evidencing a subtropical range expansion of thermophilic warm water forms into southern mid-latitudes. We attribute this to warm plumes from the East Australian Current, which would have impacted southeastern Australia at that time. In general, the Bookpurnong Formation ostracod assemblages indicate low to moderate energy shallow offshore palaeoenvironments subject to warm-temperate and subtropical conditions. One new genus and five new species are described: Fortistriginglymus gen. nov., Bradyleberis praecristatella sp. nov., Callistocythere bookpurnongensis sp. nov., Callistocythere mchenryi sp. nov., Callistocythere zigzaga sp. nov., and Parakeijia notoreticularis sp. nov.

Pockmarks are morphological expressions of seabed fluid escape along continental margins. Identifying the underlying controls on their formation and spatial distribution is crucial for understanding substrate fluid plumbing systems and has important implications for hydrocarbon exploration, seafloor stability and seabed release of greenhouse gasses. Here, we use 3D seismic reflection dataset and a machine learning approach to present the first evidence for paleo-pockmarks in the Bass Strait, southeast Australia. The paleo-pockmarks are identified in the Bass Basin, within an interval between 250 and 310 m below present-day seafloor, corresponding to the Miocene carbonate-dominated Torquay Group. The paleo-pockmarks have depths ranging from-29 to 74 m and areas between-0.01 and 0.8 km2, with diameters varying between-0.1 and 1.1 km. The absence of an underlying seal-bypass system such as pipes and faults associated with these paleo-pockmarks discounts a deeper thermogenic source or a potential magmatic-driven fluid system. Rather a biogenic fluid system derived from the degradation of organic-rich layers and pore water expelled during early-stage compaction is hypothesised to drive paleo-pockmark formation. The seismic interval comprising these paleopockmarks demonstrates a distinctive seaward progradation and stepping-down configuration, indicating a forced regression. We propose this resulted in the destabilization of hydrostatic pressure triggering the creation of the paleo-pockmarks.

The 'Illaenus' band of the Costerfield Siltstone in the Costerfield-Heathcote area contains pockets of Silurian (lower Wenlock) deposits that contain a rich invertebrate fauna. Several assemblages from the 'Illaenus' band have been described and include ostracod species referable to 13 genera. These specimens were housed at the Australian Government Bureau of Mineral Resources in Canberra, which was damaged by fire in 1953. Of the documented ostracod specimens, only three remain, but are in a degraded state. We reinterpret this historically important material as representing the types of Ctenobolbina proxima and Kayatia prima.

Spatially and volumetrically extensive igneous rocks are exposed onshore in southeastern Australia and provide important information about the Cenozoic evolution of the region. However, the morphology and distribution of igneous rocks are still not well constrained in the similar to 70 km wide continental shelf of the central Otway Basin. Within this region, we present seismo-geomorphological characteristics of 30 volcanoes and 27 hydrothermal vents, as well as several lava flows and magmatic sills, based on 2D and 3D seismic reflection data. Hydrothermal vents formed mainly during the mid-Eocene, while igneous complexes developed between the mid-Eocene to late Miocene, both post-dating continental break-up in the basin. The distribution and morphology of igneous rocks and hydrothermal vents is influenced by rift-related faults, as most of these features are linked to the underlying faults by near-vertical zones of disruption and are elongated in an NW-SE direction that parallels the primary fault trend. Magma for volcanoes and heat sources for hydrothermal vents within the study area are likely supplied by deep-sourced dykes, as magmatic sills only have a scattered distribution in this region. This implies a dyke-dominated plumbing system for magmatism in the Otway Basin. In comparison, the nearby Bight Basin, which has a thin basement but a relatively thick sedimentary sequence, displays magma propogation more prone to forming igneous sills. There are significant lithological and tectonic similarities between the Otway and Bight basins; thus, we propose that a relatively thin sedimentary sequence over a thick basement in the Otway Basin produced sufficient magma pressure for a predominantly dyke-dictated igneous plumbing system. This work highlights the critical role of basin structures, such as the thickness of basement and overlying strata, in the control of igneous plumbing styles and the distribution of post-rift igneous complexes along magma-poor continental margins. Our work, therefore, aids the estimation of different magmatic components within the sedimentary basins and facilitates the understanding of their diverse impacts on the exploration of frontier basins. This result also provides some constraints on the prediction of possible future eruption centres within active volcanic fields.

Volcanic rocks occur in different types of sedimentary basins, especially those evolving from lithospheric stretching. While volcanoes and other igneous rocks are widespread in the onshore Otway Basin, well-preserved volcanoes have not been documented in the offshore portion of the basin. Here, we analysed high-quality 2-D and 3-D seismic reflection datasets to investigate the origin and distribution of the enigmatic, kilometre-scale buried mound-shaped structures in the Prawn Platform, offshore Otway Basin. Detailed seismic characterisation enabled the identification of 19 mounds, ranging from similar to 90-400 m in height and 1.8-6 km in diameter. Relatively small (similar to 0.2-11 km(2)) igneous sills are associated with these mounds. Based on their external geometries and internal seismic architectures, we interpret these mounds as dyke-fed shield volcanoes. Distinct seismic facies characterise the buried volcanoes, including the main volcanic eruption centre, tuff cone, and pyroclastic mass-wasting deposits. Interbedded extrusive and sedimentary rocks are mainly observed within volcanoes over 250 m high, and are associated with gullies along their flanks, indicating these volcanoes may have been subject to erosion. The volcanoes occur at three stratigraphic levels: late Eocene (similar to 37 Ma), mid-Oligocene (similar to 27-29 Ma), and early Miocene (similar to 20 Ma), within the age of the Older Volcanics of the southern Australian margin. We propose that this newly discovered volcanism in the offshore Otway Basin was caused by edge-driven convection (similar mechanism to adjacent onshore volcanism), associated with the fast spreading rate of the Southern Ocean since the late Eocene (similar to 40 Ma). The discovery of these buried volcanoes extends our understanding of magmatism in the Otway Basin, especially regarding the offshore extension of the Older Volcanics.y

The Plio-Pleistocene Whalers Bluff Formation (WBF) of the offshore Otway Basin is composed of mixed siliciclastic-carbonate sediments. In seismic cross sections, this formation includes an interval that consists of higher amplitude seismic reflections that display alternating depressional ponds and raised ridges. This interval is shallowly buried and lies between 40 and 150 ms two-way traveltime below the present-day seafloor. In this study, we have used 2D and 3D seismic data sets in combination with the available shallow subsurface well logs to characterize the geomorphology and investigate the origin of these enigmatic features. The ponds are expressed as densely packed, circular to polygonal, and in some cases, hexagonal-shaped features in time-slice maps, and they closely resemble previously documented honeycomb structures. In our study area, the honeycomb-like structures (HS) are comprised of large (200–800 m diameter range) depressed ponds that are separated by narrow (approximately 20 m at the top) reticulate ridges. In total, these HS cover an area of 760 km2. Geospatial analysis shows that the ponds of HS, especially those in the northeast of the study area, are aligned along the northwest–southeast trend lines. There are several possible origins for the HS. The most probable mechanism is that the HS resulted from the bulk contraction of soft sediment, associated with shallow-burial diagenesis processes such as subaqueous dewatering of the fine-grained successions within the WBF. Interestingly, irregular furrows of various lengths on the seafloor correspond to the ridges of the HS, and we hypothesize that these furrows may have formed due to differential compaction of the underlying alternating ponds and ridges. Our results demonstrate the benefits of using seismic reflection data sets in combination with geospatial analysis to investigate the buried paleogeomorphologic features and their impact on the present-day seafloor physiography.Geological feature: Honeycomb-like, soft sediment deformation associated with shallow-burial diagenesis, Otway Basin, southeastern Australia Cross-section appearance: Alternating depressional ponds and raised ridges Map view appearance: Densely packed, oval to polygonal-shaped features Features with a similar appearance: Acquisition footprints, carbonate mounds/dissolution features, polygonal faults, pockmarks, opal-A to opal-CT transition Formation: Whalers Bluff Formation, offshore Otway Basin Age: Pliocene to recent Location: Continental shelf of the Otway Basin, southeastern Australia Data sets: 2D and 3D seismic reflection data, borehole data, from Geological Survey of Victoria, Australia Analysis tools: Interpretation and visualization (Petrel 2019 and DUG Insight, v.4.7, 2020), Geospatial analysis (ESRI‘s ArcMap 10.5)

A new fossil paracypridine ostracod, Tasmanocypris lochardi sp.nov. is described from late Miocene shallow marine strata of southeastern Australia. It has morphological features similar to a number of modern southern Australian and southwest African Tasmanocypris species, here termed the dartnalli-group. This species group was likely present in early Cenozoic temperate, shallow seas around Antarctica. The first appearance of Tasmanocypris lochardi in late Miocene marine strata of the Bass Strait hinterland of SE Australia, equates to a late Miocene (9-7 Ma) intensification and northward latitudinal shift of the Antarctic Circumpolar Current (ACC). Late Miocene occurrences of Tasmanocypris lochardi in southeast Australia were likely associated with temperate eastward flows of the ACC north of the Subantarctic Front. During the early Pliocene, the warm Zeehan Current (aka Leeuwin Current) replaced the ACC as the dominant easterly flowing current across Bass Strait, and this 4.4 Ma palaeoceanographical event correlates with the temporary, but widespread disappearance of T. lochardi from southeast Australian marine waters. However, the presence of refugia populations of T. lochardi along the east Australian continental shelf between 4.4 and 3.4 Ma, likely enabled the brief re-establishment of T. lochardi in the east of Bass Strait during the late Pliocene (3.2-3.0 Ma). Tasmanocypris lochardi became permanently extinct in this region during the latest Pliocene to early Pleistocene ( < 2.6 Ma), broadly correlating with the onset of the global Quaternary glaciation, and inception of the cold Bass Cascade winter current within Bass Strait.

A continental shelf to upper continental slope ostracod fauna is documented from the late Cretaceous (late Turonian to Santonian) Belfast Mudstone in Voluta-1 of the Otway Basin, southeastern Australia. The fauna has palaeobiogeographical affinities with mid-late Cretaceous ostracod faunas of Western Australia, New Zealand, the Antarctic Peninsula and the Falklands Plateau. This distribution pattern probably reflects dispersal influenced by the opening of the Australo-Antarctic Gulf, and by clockwise gyre currents in the proto Southern Ocean. The presence of Philoneptunus sp. in this fauna suggests that the Australo-Antarctic Gulf was an important locus for deep sea colonization by Gondwanan neritic ostracod clades.

Camilleri, T.A., Warne, M.T., Holloway, D.J. & Weldon, E.A., 10 May 2019. Revision of the ostracod genus Velibeyrichia Henningsmoen, 1954 from the Silurian and Lower Devonian of North America. Alcheringa XXX, X–X. ISSN 0311-5518. Known occurrences of the ostracod genus Velibeyrichia are restricted to a number of Silurian to Lower Devonian geological strata in North America: the McKenzie Member of the Mifflintown Formation of Maryland and West Virginia; the Tonoloway Limestone of Maryland, West Virginia, Virginia and Pennsylvania; the Bloomsburg Formation of Maryland, Virginia and Pennsylvania; the Manlius Limestone of New York; and the Decker Limestone of New Jersey and New York. The genus includes six species: V. moodeyi (type species), V. mesleri, V. paucigranulosa, V. reticulosaccula, V. tonolowayensis and V. tricornia. The diagnostic combination of characters for this genus are: distinct deflection of the velum where it crosses the crumina in heteromorphs (adult female specimens), dorsal nodes on lobes L1 and L3, sexual dimorphism of the velum, and in tecnomorph specimens, either a shallow sulcus on lobe L3 or a zygal ridge (in adult tecnomorph specimens) extending from lobe L2 to lobe L3. The presence of one or the other of the latter two characters defines two distinct species groups. Tamara T.A. Camilleri* [tamara.camilleri@deakin.edu.au], Mark T. Warne* [mark.warne@deakin.edu.au] and Elizabeth A. Weldon [l.weldon@deakin.edu.au], Deakin University, Geelong, School of Life and Environmental Sciences & Centre for Integrative Ecology (Melbourne Campus), 221 Burwood Highway, Burwood, Victoria 3125, Australia; David J. Holloway [dhollow@museum.vic.gov.au], Museums Victoria, GPO Box 666, Melbourne, Victoria 3001, Australia. *Also affiliated with: Museums Victoria, GPO Box 666, Melbourne, Victoria 3001, Australia.

The concept of the thaerocytherid ostracod genus Neohornibrookella was established by Jellinek (1993) on valve and carapace specimens from Kenyan coastal waters, identified by him as belonging to the species Cythere lactea Brady, 1866. Thus, Jellinek (1993) nominated Cythere lactea as the type species for Neohornibrookella. However, he misidentified these Kenyan specimens, which are here interpreted to belong to the broadly distributed, thermophilic shallow marine species, Hermanites transoceanica Teeter, 1975. In accordance with Article 70.3 of the International Code of Zoological Nomenclature, 1999, either the species originally nominated as the type species (Cythere lactea Brady, 1866), or the species represented by the Kenyan specimens on which the genus was described (Hermanites transoceanica Teeter, 1975), may be accepted as the type species for Neohornibrookella Jellinek, 1993. In accordance with Article 70.3.2 of the International Code of Zoological Nomenclature, 1999 I choose Hermanites transoceanica Teeter, 1975 as the types species for Neohornibrookella Jellinek, 1993 because it conforms with the established concept of the carapace morphology for this genus, as per discussion below.

Camilleri, T.T.A., Warne, M.T. & Holloway, D.J., March 2017, Review and clarification of Bungonibeyrichia Copeland, 1981 (Ostracoda) from the upper Silurian–Lower Devonian of New South Wales, Australia. Alcheringa xx, xx.The abundant and diverse beyrichioid ostracod faunas preserved in Silurian and Devonian silisiclastic strata of the Lachlan Orogen in southeastern Australia include specimens of the genus Bungonibeyrichia. Bungonibeyrichia copelandi sp. nov. is proposed for the fossil material, originally misidentified at species level, on which the description of this genus was based. The new species is nominated as the type species for Bungonibeyrichia in accordance with Article 70.3 of the International Code of Zoological Nomenclature. Bungonibeyrichia is distinguished from other beyrichioid genera on the basis of a distinctive combination of lobe, velum and crumina features.Tamara T.A. Camilleri* [tamara.camilleri@deakin.edu.au] and Mark T. Warne* [mark.warne@deakin.edu.au], Deakin University, Geelong, School of Life and Environmental Sciences & Centre for Integrative Ecology, (Melbourne Campus), 221 Burwood Highway, Burwood, Victoria 3125, Australia; David J. Holloway [dhollow@museum.vic.gov.au], Museums Victoria, GPO Box 666, Melbourne, Victoria 3001, Australia. *Also affiliated with Museums Victoria, GPO Box 666, Melbourne, Victoria 3001, Australia.

Three closely allied shallow marine taxa, Neohornibrookella sorrentae (Chapman and Crespin), Neohornibrookella glyphica (Neil), and Neohornibrookella nepeani sp. nov. are recorded from latest early Miocene to late Pliocene strata in southeastern Australia. These taxa, together with Neohornibrookella quadranodosa (Holden) from the Miocene of Midway Island (Northwestern Hawaiian Islands), form a morphologically distinct group of relatively large species (the sorrentae-group) within the genus Neohornibrookella Jellinek. Latitudinal expansion of the subtropical and warm-temperate climatic belts together with the influence of warm western boundary surface currents associated with the North and South Pacific gyres, are likely to have played key roles in the Miocene dispersal of this species group. Species of the sorrentae-group first migrated south from equatorial west Pacific regions into southeastern Australia during the early Miocene, under the influence of the East Australian Current. During three time intervals (i) latest early Miocene, (ii) latest late Miocene and (iii) earliest late Pliocene, forceful pulses of the East Australian Current played a significant role in propelling the widespread distribution of thermophilic Neohornibrookella species across southeast Australian shallow marine realms. During intervening middle and late Miocene times, Neohornibrookella species are only sporadically present across the Bass Strait region of southeast Australia, indicating a weaker East Australian Current influence and the cooling influence of coastal upwelling. During the mid early Pliocene Neohornibrookella species disappeared from the western Bass Strait region, suggesting the complete exclusion of East Australian Current waters from this region. This was probably due to the counteracting influence of the eastward flowing Zeehan Current (extension of the Leeuwin Current) impinging on the western Bass Strait region. This mid early Pliocene palaeobiogeographical partition in Bass Strait, defined by the distribution of sorrentae-group species, is here termed the Bassian Gateway. The two species, N. sorrentae and N. glyphica, occur concurrently during the mid Miocene in southeast Australia, but are associated with different lithofacies. It is hypothesised that there is a heterochronic evolutionary relationship expressed in the ornament of these two species. The thaerocytherid genera Neohornibrookella Jellinek, Tenedocythere Sissingh and Bosasella Bonaduce are here included in the new ostracod subfamily Tenedocytherinae.