Academic literature on the topic 'Otway Region'

The Otway Basin formed during the Mesozoic separation of Antarctica and Australia. A study of apatite fission track (FT) analysis and vitrinite reflectance (VR) data from borehole samples in the western Otway Basin was initiated to elucidate some of the thermal and structural complexities of this region.Interpretation of results suggest that some areas experienced regionally elevated palaeotemperatures, however, much of the region is at present-day maximum temperatures. Where cooling from maximum palaeotemperatures is observed, the timing may be grouped over three main intervals as follows; mid-Cretaceous, Late Cretaceous to Early Tertiary, and Tertiary. Cooling was facilitated by a decline in geothermal gradient, uplift and erosion, or both. Evidence for a decline in geothermal gradient from values >55°C/km in the mid- Cretaceous is recognised in several wells. Elevated mid- Cretaceous palaeogeothermal gradients (50−60°C/km) have been reported for the eastern Otway Basin, suggesting that these high temperatures were a regional phenomena. Cooling by uplift and erosion at this time was minimal throughout the western Otway Basin in contrast to the kilometre scale uplift and erosion reported for the eastern Otway Basin and adjacent basement inland of this section of the rift.The relative early maturation of the Otway Supergroup during mid-Cretaceous regionally elevated geothermal gradients, and subsequent basin restructuring, are key factors affecting hydrocarbon preservation in the western Otway Basin. Strategies for identification of prospective areas include identification of regions that have remained at moderate temperatures during the Early Cretaceous, and have not undergone burial under a thick Upper Cretaceous to Tertiary section.

Recent advances in cross-section balancing software have simplified the application of basic geometric constraints to the analysis of basin development. Geometric analysis of field and seismic data allows the user to verify initial interpretations and also elucidates important information about the structural evolution of a basin. Principally, computerised balancing and restoration of cross-sections assists in constraining:the amount of crustal extension;trap geometries, particularly fault geometries through time;the geometry of key horizons at any time, revealing basin morphology and migration paths;the time and amount of maximum burial and hence hydrocarbon migration; andthe likely mechanisms involved in basin evolution. In turn, these parameters can be used to further assess hydrocarbon prospectivity by providing useful data for lithospheric modelling.This study utilises 2D cross-section balancing software (Geosec™) to decompact, balance and restore a series of regional onshore-offshore cross-sections based on both reflection seismic data in the Torquay Embayment and field mapping in the Otway Ranges. The thickness of eroded strata has been constrained by Apatite Fission Track and Vitrinite Reflectance analyses. The resulting section restoration suggests that the eastern Otway Basin experienced extension of 26 per cent in the Early Cretaceous and that the Otway Ranges were subjected to −8 per cent shortening during mid-Cretaceous inversion and −4 per cent shortening during Mio-Pliocene inversion.The structural style of the Otway Ranges and Torquay Embayment is typified by steep, relatively planar, en echelon, N and NE-dipping Early Cretaceous extension faults that were subsequently inverted and eroded during the Cenomanian and Mio-Pliocene. The structural style of the region shows strong similarities with oblique- rift analogue models suggesting that the extensional history of the region was strongly controlled by prevailing basement fabric.Lower Cretaceous source rocks in the eastern Otway Basin reached maximum maturity prior to mid-Cretaceous inversion with the exception of parts of the Torquay Embayment which may not have experienced significant uplift and erosion at this time. The lack of subsidence in the eastern Otway Basin prevented the deposition of significant amounts of Upper Cretaceous sediments which are proven reservoirs in the western Otway Basin and Gippsland Basin. Subsequent Tertiary burial was insufficient, in most regions, to allow the source rocks re-enter the oil generation window.

Since the offshore discoveries of economic gas accumulations at Geographe and Thylacine, the Otway Basin has become the focus of an exploration resurgence. Its proximity to major markets ensures the discoveries will be commercially valuable. The latest successes in the basin are mainly due to modern 3D-seismic techniques. While the upper sedimentary succession has been imaged at high resolution, details of the deeper successions, however, remained obscure.An integrated study of magnetic, gravimetric, bathymetric and deep seismic data-sets has outlined the way that pre-existing basement fractures controlled much of the later basin-evolution, the structural style and the distribution of hydrocarbon bearing structures.The Otway Basin formed by the profound interaction between crustal fabric in the Proterozoic and Palaeozoic basement and the extensional stresses during Gondwana break-up. Overall, three different rift systems can be distinguished:Early ENE-trending Jurassic to Early Cretaceous rifts are an extension of the E-W rift system in Western Australia and South Australia, Early WNW Late Jurassic to Early Cretaceous rifts are connected to the ENE set and include the western Otway Basin east of the Robe Trough and the Torquay Sub-basin, and Early Cretaceous NNW transtensional rifts in the southern part of the Shipwreck Trough. These control the La Bella, Thylacine and Geographe discoveries, all of which overlie the Neoproterozoic to Cambrian Selwyn Block.Within these rift systems, the Jurassic to Cretaceous rifts along the continental shelf break coincide with the northern edge of the Voluta Trough, whilst the mid-slope rifts are part of the deep Voluta Trough and were possibly generated during the Late Cretaceous.Although the potential field data do not directly delineate hydrocarbon accumulations, when integrated with other data they provide powerful tools for exploration. For instance, it is possible to map the distribution of Paleocene channels that overlie the basement and represent likely reservoir facies, while data integration with palaeoenvironmental interpretations can highlight areas in which source rock facies developed.Regionally, the way the rifts have formed with respect to the basement fabric suggests that the dominant extension direction in the basin was N to NNW. Integrating the interpretation with regional studies in the western Tasmanian region supports the proposition that the western part of the south Tasman Rise was once the outer part of the upper plate adjacent to the deepwater parts of the Otway Basin SW of Cape Otway.

A well-dated pollen record from Chapple Vale in the north of the Otway region provides a detailed history of vegetation and environments through the last c. 7000 years. From the commencement of the record, a stand of cool temperate rainforest, dominated by Nothofagus cunninghamii (Hook.) Oerst., grew on or around the site and was surrounded by eucalypt-dominated tall open forest. Between c. 5200 and 4600 years BP (before present), the rainforest declined and tall open forest predominated. Some time after 4400 years BP there was a major and consistent increase in charcoal values, suggesting an increase in burning, the progressive development of scrub–heath vegetation on site and the replacement of tall open forest vegetation by eucalypt woodland surrounding the site. The fossil evidence for N. cunninghamii on the site and its present restriction to wetter areas and gullies of the Otway Ranges indicate, from the application of the present bioclimatic range of the species, a mean annual temperature and winter temperatures that were c. 1˚C cooler than present, and summer temperatures that were possibly slightly cooler than present, together with a much higher effective precipitation from the commencement of the record until c. 4600 years BP. These climatic estimates are in accord with those derived from a similar study of changing distributions of N. cunninghamii in the Central Highlands of lower mean annual and cooler summer temperatures and higher effective precipitation over this time span. However, for winter, the evidence is equivocal. While the Otway estimates suggest lower temperatures, the Central Highlands findings show slightly higher temperatures. Taking into account additional present-day records for N. cunninghamii, it is likely that the Otway estimates are the most reliable.

Evaluation of Early Cretaceous source rocks within the onshore Victoria Otway Basin has revealed that thick, mature shales containing predominantly gas-prone and in local concentrations, oil-prone macerals exist northwest of Portland, in the Tyrendarra Embayment, and around the Port Campbell region.Current results of Rock-Eval, bulk composition, gas chromatography, and biomarker analyses, coupled with geohistory and hydrocarbon generation interpretations, indicate that at least three phases of oil generation and expulsion occurred within the basin. The earliest phase, which coincided with the maximum heatflow in the crust around 100 Ma, resulted in the charging of the existing stratigraphic/shoestring traps of the basin. The second and third phases occurred in the eastern end of the basin at around 85 and 60 Ma. There is also evidence to suggest that structural traps of the eastern areas were formed later, during Oligocene time, and that these traps are probably still receiving late-stage charges of hydrocarbons.Although the sparse well density in the basin has resulted in limited, non-uniforin sampling opportunities, several regions with good Early Cretaceous source rocks can be recognised. Some of these good source rock areas are in close proximity to the several known hydrocarbon shows and producing fields. These current studies, which also include a source rock risk analysis indicating source rock adequacy, show that locations for future exploration could include the Casterton-Portland-Mt Gambier western region, the Peterborough-Port Campbell eastern region, and the prospective close peripheries and offshore extensions of these regions.

The Otway Basin is one of the best known and most actively explored of a series of Mesozoic basins formed along the southern coastline of Australia by the rifting of the Antarctic and Australian plates during the Cretaceous. The basin offers a diversity of play types, with at least three major sedimentary sequences forming conventional targets for petroleum exploration in the onshore basin. The Penola Trough in South Australia has enjoyed over 20 years of commercial hydrocarbon production from the sandstones of the Early Cretaceous Otway Group comprising the Crayfish Subgroup (Pretty Hill Formation and Katnook sandstones) and Eumeralla Formation (Windermere Sandstone Member). Lithostratigraphic characterisation and nomenclature for these sequences are poorly constrained, challenging correlation across the border into the potentially petroleum prospective Victorian Penola Trough region. The Geological Survey of Victoria (GSV), as part of the Victorian Gas Program, commissioned Chemostrat Australia to undertake an 11-well chemostratigraphic study of the Victorian Otway Basin. The South Australia Department for Energy and Mining, GSV and Chemostrat Australia are working collaboratively to develop a consistent, basin-wide schema for the stratigraphic nomenclature of the Otway Basin within a chemostratigraphic framework. Variability in the mineralogy and hence inorganic geochemistry of sediments reflects changes in provenance, lithic composition, facies changes, weathering and diagenesis. This geochemical variation enables the differentiation of apparently uniform sedimentary successions into unique sequences and packages, aiding in the resolution of complex structural relationships and facies changes. In this paper, we present the preliminary results of detailed geochemical analyses and interpretation of 15 wells from across the Otway Basin and the potential impacts on hydrocarbon prospectivity.

There have been several studies, both published and unpublished, of the present-day state-of-stress of southeast Australia that address a variety of geomechanical issues related to the petroleum industry. This paper combines present-day stress data from those studies with new data to provide an overview of the present-day state-of-stress from the Otway Basin to the Gippsland Basin. This overview provides valuable baseline data for further geomechanical studies in southeast Australia and helps explain the regional controls on the state-of-stress in the area.Analysis of existing and new data from petroleum wells reveals broadly northwest–southeast oriented, maximum horizontal stress with an anticlockwise rotation of about 15° from the Otway Basin to the Gippsland Basin. A general increase in minimum horizontal stress magnitude from the Otway Basin towards the Gippsland Basin is also observed. The present-day state-of-stress has been interpreted as strike-slip in the South Australian (SA) Otway Basin, strike-slip trending towards reverse in the Victorian Otway Basin and borderline strike-slip/reverse in the Gippsland Basin. The present-day stress states and the orientation of the maximum horizontal stress are consistent with previously published earthquake focal mechanism solutions and the neotectonic record for the region. The consistency between measured present-day stress in the basement (from focal mechanism solutions) and the sedimentary basin cover (from petroleum well data) suggests a dominantly tectonic far-field control on the present-day stress distribution of southeast Australia. The rotation of the maximum horizontal stress and the increase in magnitude of the minimum horizontal stress from west to east across southeast Australia may be due to the relative proximity of the New Zealand segment of the plate boundary.

Mesozoic extension along Australia's southern margin and the evolution and architecture of the Otway Basin were probably controlled by three factors: 1) changes in global plate movements driven by mantle processes; 2) the structural grain of Palaeozoic basement; and, 3) changes in subduction along Gondwana's Pacific margin. Major plate realignments controlled the Jurassic onset of rifting, the mid-Cretaceous break-up and the Eocene onset of rapid spreading in the Southern Ocean.The initial southern margin rift site was influenced by the northern limit of Pacific margin (extensional) Jurassic dolerites and the rifting may have terminated dolerite emplacement. Changed conditions of Pacific margin subduction (e.g. ridge subduction) in the Aptian may have placed the Australia-Antarctic plates into minor compression, abating Neocomian southern margin rifting. It also produced vast amounts of volcanolithic sediment from the Pacific margin arc that was funnelled down the rift graben, causing additional regional subsidence due to loading. Albian orogenic collapse of the Pacific margin, related to collision with the Phoenix Plate, influenced mid-Cretaceous breakup propagating south of Tasmania and into the Tasman Sea.Major offsets of the spreading axis during breakup, at the Tasman and Spencer Fracture zones, were most likely controlled by the location of Palaeozoic terrane boundaries. The Tasman Fracture System was reactivated during break-up, with considerable uplift and denudation of the Bass failed rift to the east, which controlled Otway Basin facies distribution. Palaeozoic structures also had a significant effect in determining the half graben orientations within a general N-S extensional regime during early Cretaceous rifting. The late Cretaceous second stage of rifting, seaward of the Tartwaup, Timboon and Sorell fault zones, left a stable failed rift margin to the north, but the attenuated lithosphere of the Otway-Sorell microplate to the south records repeated extension that led to continental separation and may be part of an Antarctic upper plate.

The Otway Basin is one of three sedimentary basins in the Bass Strait region and is situated west of the Bass and Gippsland Basins. It trends NW-SE, straddling the southern Australian coastline for 500 km between the Mornington Peninsula in Victoria and Cape Jaffa in South Australia. It has an average width of 200 km and an average offshore width, in water depths of less than 200 m, of 50 km.The offshore basin consists of three main tectonic units: the Mussel Platform in the east, the Voluta Trough, which occurs in the centre of the basin, and the Crayfish Platform in the west. Structures are formed predominantly by Cretaceous normal faults, downthrown to the continent-ocean boundary, and displacing landward-dipping Cretaceous strata. The sedimentary sequence can reach 10 km in thickness and consists of terrestrial Early Cretaceous sediments of the Otway Group, Late Cretaceous transgressive-regressive terrigenous sediments of the Sherbrook Group, Paleocene-Eocene transgressive-regressive, terrigenous and carbonate sediments of the Wangerrip and Nirranda Groups, and Oligocene-Miocene shelf carbonates of the Heytesbury Group.Since the early 1960s, about 50 exploration wells have been drilled onshore and 17 offshore. Shows of oil, gas and condensate have been widespread in both onshore and offshore wells, though only two small economic fields have so far been discovered; both are onshore. Exploration, particularly during the 1960s and 1970s, was hampered by poor seismic data quality, due primarily to the presence of shallow carbonates.

This thesis is involved with changes that have occurred to small mammal populations following a major disturbance in the Anglesea region as a result of the 1983 Ash Wednesday fires. Fire, with its effects on spatial and temporal heterogeneity, was found to be an important factor in the maintenance of vegetation and small mammal community structure and diversity in the region. Successional changes in vegetation and small mammal communities were described by multivariate analyses, using data collected annually from 22 study sites. The use of factor analysis techniques, in reducing the annual capture data content, enabled long-term changes in the structure of mammal communities to be interpreted. The small mammal communities in the coastal heath and forest vegetation in the Anglesea region show evidence of a general resilience, (the degree and speed of recovery), to disturbance. Two phases of successional response to fire by mammal species have been proposed; a ‘re-establishment’ phase which occurs in the initial 5-6 years post-fire and is accompanied by rapid increase in species’ abundance, and a subsequent ‘maintenance’ phase accompanied by relatively minor changes in abundance. Habitat Suitability Indices were produced relating to these phases. Vertical density measures of understorey shrubs and herb layers showed significant relationships with small mammal species abundance at the study sites. Long term studies following major disturbances are needed to distinguish between short term recovery of plant and animal species and long term changes in these species. Studies extending over a number of years enable a better directional view of changes in small mammal communities than can be determined from . observations made over a short period. As a part of the investigation into temporal change, it was proposed to undertake trial reintroductions of the Swamp antechinus, Ant echinus minimus, a marsupial dasyurid species which was trapped in the area prior to the 1983 fire, but rarely subsequently. Other more commonly observed native small mammal species (e.g. Rattus fuscipes,R. lutreolus, Antechinus stuartii, Sminthopsis leucopus) had re-invaded the proposed reintroduction site after this fire. Failure of A. minimus to re-establish may have been due to spatial separation of the pre-fire populations coupled with the extensive area burnt in 1983, A source population of the species was located about 100km to the west and habitat utilization and interspecific and niche relationships between the species making the small mammal community explored. Discriminant analysis revealed some spatial separation of species within a habitat based on structural vegetation factors rather than floristic factors. Temporal separation of species was observed, asA. minimus were more active than Rattus species during daylight periods. There was evidence of micro-habitat selection by species, and structural vegetation factors were most commonly identified in statistical analyses as contributing towards selection by small mammal species. Following a theoretical modelling study three reintroduction trials were carried out near Anglesea during 1992-94. Individuals were subsequently radio tracked, and habitat relationships between the species in the small mammal community investigated. Although successful breeding of A, minimus occurred during the latter two trials, the subsequent fate of offspring was not determined. Invasive techniques required to adequately monitor young animals were considered potentially too damaging. Telemetry studies indicated a preference of A. minimus for short, wet heath vegetation. Structural vegetation factors were identified as being significant in discriminating between capture locations of species. Small scale and inexpensive trial reintroductions have yielded valuable additional data on this species and may be viewed as a useful tool in the conservation of other small native mammals.

This visually superb and informative field guide is the second volume of Flora of the Otway Plain and Ranges, and covers more than 480 species of Daisies, Heaths, Peas, Saltbushes, Sundews, Wattles and other shrubby and herbaceous Dicotyledons. The illustrated family key is unique and covers 75 families and over 200 genera. Each species is illustrated and labels provide a clear key to identification for botanists and amateurs alike. The Otway region of Victoria, with its temperate rainforests, mountain ash forests, heathlands, plains and coastal dunes, has an extraordinarily rich and diverse flora.

The Otway region of Victoria, with its temperate rainforests, mountain ash forests, heathlands, plains and coastal dunes, has an extraordinarily rich and diverse flora. The first volume of Flora of the Otway Plain and Ranges covers the orchids, irises, lilies, grass-trees, mat-rushes and other petaloid monocotyledonous plants. Enid Mayfield's exquisite colour illustrations of more than 200 species reveal tiny botanical details which enable the untrained botanist to identify each species with ease. The section on orchids describes and illustrates more than 130 species, highlighting their fascinating adaptations for attracting specific pollinating insects. The clear text and illustrations frequently draw attention to the relationship of plants to the broader environment, the impact of fire, the role of pollinators and the importance of fungi.

The Otways and Shipwreck Coast is known for its natural beauty and attracts millions of visitors each year, particularly along the Great Ocean Road. The value of the region's rich biodiversity is recognised at the national and global level and its wildlife is markedly different to other regions, including eastern Victoria which supports similar vegetation types. Wildlife of the Otways and Shipwreck Coast is a photographic field guide to the vertebrate wildlife of Victoria’s south-west. It covers all the mammals, birds, reptiles and frogs that occur in the region, including on land and in coastal waters. Each of the 288 species profiles includes a description and information on identification, range, conservation status, habitat use and ecology and is complemented by an exquisite colour photograph and a detailed distribution map. The book also includes chapters on habitat types, conservation and management, and on 14 key places in the region to view wildlife. This book will allow those interested in wildlife, including residents and visitors, to identify vertebrate animals found in the region. Readers will also become more familiar with the distinct role the Otways has in conserving Australia’s biodiversity.

Rainforest Restoration Manual for South-Eastern Australia is the definitive guide to the recovery and restoration of Subtropical, Warm Temperate, Cool Temperate, Gallery, Dry, Dry Gully and Littoral Rainforests from south-eastern Queensland to Tasmania. All of these rainforest types were inherently rare prior to settlement, and today with depletion, feral animals, weeds and climate change, all are threatened – with many listed under state and federal legislation. The manual presents detailed restoration methods in 10 easy-to-follow steps, documenting the research and trials undertaken during rainforest restoration over more than two decades. These experiments and their results will empower readers to uncover answers to many of the problems they could encounter. The manual is supported by a CD that provides important background information, with 32 appendices, a propagation manual for the region's 735 rainforest plants, an illustrated glossary and resources for teachers. Species lists and specific planting guides are provided for the 57 rainforest floristic communities that occur from the coast to the mountains between Durras Mountain in New South Wales and the Otways in Victoria. Extensively illustrated with colour photographs, this book will empower you or your group to be able to restore, manage, protect and conserve the magnificent rainforests that are in your care. The general principles and techniques described will meet the needs of students and teachers, novices, experienced practitioners, community groups and agencies alike.