The advent of the Paleocene-Eocene Thermal Maximum (PETM), a similar to 200 kyr period of global warming ca. 56 Ma, caused sea-levels to rise, transgressing near-coastal environments in southeastern (SE) Australia over >55,000 km(2). During the PETM, warming tropical climates may have extended south to >= 60 S-degrees paleolatitude. The PETM in SE Australia is corroborated primarily by stable carbon isotope chemostratigraphy and detailed palynology records in four geological basins. Previous work showed that, in addition to the globally recognised carbon isotope excursion, the PETM interval in coastal SE Australia can be identified using the dual occurrence of the tropical mangrove Nypa palm pollen ( Spinizonocolpites prominatus ) accompanied by thermophilic marine dinoflagellate cysts (mainly Apectodinium hyperacanthum ). We here document a total of twenty-six Gippsland Basin wells that record this Nypa - A.hyperacanthum association in the earliest Eocene Kingfish Formation (Lower Malvacipollis diversus Zone). In the Bass Basin, eight wells record Nypa-A.hyperacanthum association within the Eastern View Group basal Koorkah Formation, or lower part of the Lower M. diversus Zone (earliest Eocene). In the Bass Basin a further thirteen wells with Nypa occurrences near the top of the Cormorant Formation are found, which might be associated with the longer -term warmth of the Early Eocene Climatic Optimum (EECO, similar to 53-49 Ma). Government bores and petroleum wells across the Otway Basin record the Nypa-A. hyperacanthum PETM association within the Pember Mudstone Lower M. diversus Zone in twenty-one bores. Nine horizons with Nypa occurrences occur within the Burrungule Member (EECO) at the top of the Dilwyn Formation. In western Tasmania, Nypa occurs in the Sorell Basin and Macquarie Harbour area within the Lower M. diversus Zone. Together, these observations show the remarkable extent of the mangrove-coasts that were established across the mid-high paleolatitudes in SE Australia during the warmest intervals of the Cenozoic, the PETM and EECO.

To assess zonal temperature and biogeographical patterns in the Southern Ocean during the Paleogene, we present new multi-proxy air-and sea-surface temperature data for the latest Paleocene (similar to 57-56 Ma) and the Paleocene-Eocene Thermal Maximum (PETM; similar to 56 Ma) from the northern margin of the Australo-Antarctic Gulf (AAG). The various proxy data sets document the well-known late Paleocene warming and, superimposed, two transient late Paleocene pre-cursor warming events, hundreds of kyr prior to the PETM. Remarkably, temperature reconstructions for the AAG and southwest Pacific during the latest Paleocene, PETM and Early Eocene Climatic Optimum (similar to 53-49 Ma) show similar trends as well as similar absolute temperatures east and west of the closed Tasmanian Gateway. Our data imply that the exceptional warmth as recorded by previous studies for the southwest Pacific extended westward into the AAG. This contrasts with modeling-derived circulation and temperature patterns. We suggest that simulations of ocean circulation underestimate heat transport in the southwest Pacific due to insufficient resolution, not allowing for mesoscale eddy-related heat transport. We argue for a systematic approach to tackle model and proxy biases that may occur in marginal marine settings and non-analog high-latitude climates to assess the temperature reconstructions.

We present a composite terrestrial pollen record of latest Eocene through Oligocene (35.5-23 Ma) vegetation and climate change from the Gippsland Basin of south-eastern Australia. Climates were overwhelmingly mesothermic through this time period, with mean annual temperature (MAT) varying between 13 and 18 degrees C, with an average of 16 degrees C. We provide evidence to support a cooling trend through the Eocene-Oligocene Transition (EOT), but also identify three subsequent warming cycles through the Oligocene, leading to more seasonal climates at the termination of the Epoch. One of the warming episodes in the Early Oligocene appears to have also occurred at two other southern hemisphere sites at the Drake Passage as well as off eastern Tasmania, based on recent research. Similarities with sea surface temperature records from modern high southern latitudes which also record similar cycles of warming and cooling, are presented and discussed. Annual precipitation varied between 1200 and 1700 mm/yr, with an average of 1470 mm/yr through the sequence. Notwithstanding the extinction of Nothofagus sg. Brassospora from Australia and some now microthermic humid restricted Podocarpaceae conifer taxa, the rainforest vegetation of lowland south-eastern Australia is reconstructed to have been similar to present day Australian Evergreen Notophyll Vine Forests existing under the sub-tropical Koppen-Geiger climate class Cfa (humid subtropical) for most of the sequence. Short periods of cooler climates, such as occurred through the EOT when MAT was similar to 13 degrees C, may have supported vegetation similar to modern day Evergreen Microphyll Fern Forest. Of potentially greater significance, however, was a warm period in the Early to early Late Oligocene (32-26 Ma) when MAT was 17-18 degrees C, accompanied by small but important increases in Araucariaceae pollen. At this time, Araucarian Notophyll/Microphyll Vine Forest likely occurred regionally.

Relationships between terrestrial formations in the central Latrobe Valley of southeastern Australia and coeval terrestrial and marine formations further to the east have been elucidated over the past several decades. In the Gippsland Basin's Latrobe Valley and Seaspray depressions, Eocene to Miocene fossils including rare foraminifera and more common dinoflagellates have been recovered from all five interseam sediments in the Morwell Formation, six interseam splits within the Traralgon Formation that includes age diagnostic Gippslandia extensa, and three interseams in the Alberton coal measures. The dinoflagellate assemblages generally are species-poor but do provide some age control and indicate episodic marine conditions within the Latrobe Valley Coal Measures. Some dinoflagellates may tolerate lower salinity near-shore waters, but above the Eocene acme of Gippslandia extensa are interpreted to indicate offshore conditions. The occurrence of dinoflagellates between seams of the Latrobe Valley and Alberton coal measures within the Gippsland Basin provides useful paleogeographic information, constraining paleo-shorelines.

Current knowledge of terrestrial ecosystem response to the Paleocene-Eocene Thermal Maximum (PETM; ca. 56 Ma) is largely based on the midlatitudes of the Northern Hemisphere. To more fully reconstruct global terrestrial ecosystem response to the PETM, we generated vegetation and biomarker proxy records from an outcrop section on the southern coast of Australia (∼60°S paleolatitude). We documented a rapid, massive, and sustained vegetation turnover as a response to regional PETM warming of ∼1–4 °C, abruptly transitioning from a warm temperate to a meso-megathermal rain forest similar to that of present-day northeastern Queensland, Australia. The onset of this vegetation change preceded the characteristic PETM carbon-isotope excursion (CIE) by several thousand years. The reconstructed ecosystem change is much stronger than in other Southern Hemisphere records, highlighting the need for consideration of regional paleoceanographic, paleogeographic, and biogeographic characteristics to fully understand the global terrestrial ecosystem response to PETM climate forcing.

When you are missing pieces from the jigsaw, the result may be attractive and even comprehensible, but it is incomplete. The conventional geological picture of the 'Traralgon Formation' in the Gippsland Basin includes a variety of ages, uses and concepts, and the formation's type section at Loy Yang has never been dated by palynology. The inclusion of new palynological data from bores at Loy Yang and elsewhere in the onshore part of the Gippsland Basin presents a more complete picture that reinterprets the age and distribution of the coal seams. The new data indicate that the Traralgon Formation coal seams in the Loy Yang area of the Latrobe Valley and the Lake Wellington Depression mostly comprise the youngest T0 coal seams, with Upper Nothofagidites asperus Zone (early Oligocene) ages. The Traralgon Formation coals in the Gormandale Syncline and Seaspray Depression, however, are mainly T1 and T2 coal seams of Middle and Lower Nothofagidites asperus Zone (late and middle Eocene) ages. The Rosedale Monocline, situated between the Latrobe Valley-Lake Wellington and Gormandale-Seaspray depressions, acted as a hinge that reversed movements at the Eocene-Oligocene boundary. Using quantitative palynology, the paleoclimates of the T0 seam are examined where it straddles the transition between the Eocene 'greenhouse' and the Oligocene 'icehouse'. In the Seaspray and Lake Wellington depressions below the T0 coal is an up to 150 m-thick regressive barrier sand of the upper Eocene Dutson Sand Member. The regression indicates that the climate transition began before end-Eocene and continued into the lower T0 coal. Mean annual temperatures (MATs) fell sharply from 16-17 degrees C to 14-16 degrees C to be <= 14 degrees C in the latest Eocene-earliest Oligocene. The lower T0 coal seams comprise a semi-continuous terrestrial record through the earliest Oligocene (the Oil glaciation event), marking the first significant glaciations in Antarctica. The upper part of T0 seam indicates a warmer, mesothermal climate, and MATs generally within the range of 14-16 degrees C.

Multiple stable isotope investigations from upper Eocene to lower Oligocene deep-water marine sequences record the transition from global greenhouse to the icehouse conditions (Oi-1 glacial). While Southern Ocean high latitude deep sea records of this transition are well known, their shallow marine equivalents are rare and have the potential to record the eustatic and oceanic consequences of Paleogene glacial variability. The well-known high paleolatitude (similar to 55 degrees S) neritic carbonate sequence at Browns Creek and Castle Cove in the Otway Basin in southeast Australia spans the Eocene-Oligocene boundary. During this time the area lay on the northeastern margin of the Australo-Antarctic Gulf facing the evolving Southern Ocean. The importance of this record has been hampered by a lack of a consistent stratigraphy and contradictory microfossil interpretations. To reconcile these issues we combine new bio-, chemo- and lithostratigraphic analyses of the outcrops and a new core (Colac-2) with pre-existing data to revise the stratigraphy. This confirms the middle/upper Eocene boundary is near the base of the section. The overlying upper Eocene siliciclastic strata are truncated by an unconformity (of similar to 0.8 Ma in duration) and overlain by glauconitic sand (the Notrostrea greensand) deposited after similar to 35.9 Ma. Subsequently deepening to middle to outer neritic depths deposited cyclic carbonates. Shallowing after similar to 35 Ma deposited laterally variable calcareous siliciclastic facies. These strata were tilted and eroded prior to 34 Ma leading to shallow water facies that may have been subaerially exposed during uplift. Brachiopod strontium isotope dates and an 0.5 parts per thousand carbon isotope excursion above this unconformity suggests the top of the Browns Creek and the base of the Castle Cove section correlate to Eocene-Oligocene transition (EOT-1) at similar to 34 Ma. The subsequent persistence of positive C/O isotope values above this level records the transition to the Oi-1 glaciation at similar to 33.7 Ma. Strong cyclicity in the inner shelf Castle Cove limestone is interpreted to record the commencement of obliquity dominated glacio-eustacy during the Oi-1 glacial phase. The shallowing from outer to inner shelf palaeodepths from the late Eocene to the early Oligocene is likely related to the onset of cryosphere expansion, however, palaeodepth estimates are complicated by the onset of regional compressional tectonism at the Eocene/Oligocene boundary that caused localized tilting and an unconformity with possible antisiphoning effects in this near-field site.

Reducing the uncertainty in predictions of future climate change is one of today’s greatest scientific challenges, with many significant problems unsolved, including the relationship between pCO2 and global temperature. To better constrain these forecasts, it is meaningful to study past time intervals of global warmth, such as the Eocene (56.0–33.9 Ma), serving as climatic analogues for the future. Here we reconstructed pCO2 using the stomatal densities of a large fossil Lauraceae (laurel) leaf database from ten sites across the Eocene of Australia and New Zealand. We show that mostly moderate pCO2 levels of ∼450–600 ppm prevailed throughout the Eocene, levels that are considerably lower than the pCO2 forcing currently needed to recreate Eocene temperatures in climate models. Our data record significantly lower pCO2 than inferred from marine isotopes, but concur with previously published Northern Hemisphere Eocene stomatal proxy pCO2. We argue that the now globally consistent stomatal proxy pCO2 record for the Eocene is robust and that climate sensitivity was elevated and/or that additional climate forcings operated more powerfully than previously assumed.

Detailed, stratigraphically well-constrained environmental reconstructions are available for Paleocene and Eocene strata at a range of sites in the southwest Pacific Ocean (New Zealand and East Tasman Plateau; ETP) and Integrated Ocean Discovery Program (IODP) Site U1356 in the south of the Australo-Antarctic Gulf (AAG). These reconstructions have revealed a large discrepancy between temperature proxy data and climate models in this region, suggesting a crucial error in model, proxy data or both. To resolve the origin of this discrepancy, detailed reconstructions are needed from both sides of the Tasmanian Gateway. Paleocene-Eocene sedimentary archives from the west of the Tasmanian Gateway have unfortunately remained scarce (only IODP Site U1356), and no well-dated successions are available for the northern sector of the AAG. Here we present new stratigraphic data for upper Paleocene and lower Eocene strata from the Otway Basin, southeast Australia, on the (north) west side of the Tasmanian Gateway. We analyzed sediments recovered from exploration drilling (Latrobe-1 drill core) and outcrop sampling (Point Margaret) and performed high-resolution carbon isotope geochemistry of bulk organic matter and dinoflagellate cyst (dinocyst) and pollen biostratigraphy on sediments from the regional lithostratigraphic units, including the Pebble Point Formation, Pember Mudstone and Dilwyn Formation. Pollen and dinocyst assemblages are assigned to previously established Australian pollen and dinocyst zonations and tied to available zonations for the SW Pacific. Based on our dinocyst stratigraphy and previously published planktic foraminifer biostratigraphy, the Pebble Point Formation at Point Margaret is dated to the latest Paleocene. The globally synchronous negative carbon isotope excursion that marks the Paleocene-Eocene boundary is identified within the top part of the Pember Mudstone in the Latrobe-1 borehole and at Point Margaret. However, the high abundances of the dinocyst Apectodinium prior to this negative carbon isotope excursion prohibit a direct correlation of this regional bio-event with the quasi-global Apectodinium acme at the Paleocene-Eocene Thermal Maximum (PETM; 56 Ma). Therefore, the first occurrence of the pollen species Spinizonocolpites prominatus and the dinocyst species Florentinia reichartii are here designated as regional markers for the PETM. In the Latrobe-1 drill core, dinocyst biostratigraphy further indicates that the early Eocene (similar to 56-51 Ma) sediments are truncated by a similar to 10 Myr long hiatus overlain by middle Eocene (similar to 40 Ma) strata. These sedimentary archives from southeast Australia may prove key in resolving the model-data discrepancy in this region, and the new stratigraphic data presented here allow for detailed comparisons between paleoclimate records on both sides of the Tasmanian Gateway.

Australia's Gippsland Basin contains a semi-continuous Eocene-Oligocene (41.5-28.4 Ma) near-coastal coal record that formed adjacent to Pacific Ocean. Traralgon and Morwell Formation brown coals include 4 main seams (T2, Tl, TO, M2). Coal seam palynology records show late Middle Eocene (T2) coals formed under megathermic conditions characterized by high-gymnosperm contents, Late Eocene (T1) coals formed under mesothermic conditions characterized by reduced-gymnosperm contents and earliest indications of palaeoclimate cooling. Earliest Oligocene TO coal record (33.9-31.5 Ma) contains high-gymnosperm palynology profile, very similar to the T2 coals. The earliest indication of cooler climes only begins after this coal formed as indicated by low-gymnosperm high-Nothofagus (southern beech) pollen proportions. We suggest in Gippsland the earliest evidence for major glacial cooling (by inference the Oil event) be placed immediately above the TO coal seam where Early to Late Oligocene Morwell Formation sands, clays and coals contain low counts of gymnosperms (<10%) but high average proportions of Nothofagus (50%). This is the main definitive indicator that palaeoclimates had cooled between the Eocene and Oligocene. This agrees with the current ocean drilling position of the earliest (Oil) glacial event shortly above the Eocene-Oligocene boundary.A number of contemporaneous Middle to Late Eocene brown coals occurred in near-coastal settings across 1200 km of southern Australia. Palaeogeographically, all these coal basins faced the Australo-Antarctic Gulf and have a much lower gymnosperm proportion (<10%), low Nothofagus proportion (<10%), but very high (non-Nothofagus) angiosperms proportion. This suggests a different climatic regime separated a cooler and wetter Gippsland Basin flora that responded to the cooler Proto-Ross Sea Gyre rotating around a wide Pacific Ocean, and a warm-wet climate associated with a warm proto-Leeuwin current of the Australo-Antarctic Gulf. (C) 2017 Elsevier B.V. All rights reserved.

The Holocene and pre-Holocene sediments and stratigraphy of the Yarra Delta have been examined using nearly 600 geotechnical bores. The oldest Holocene unit is the Coode Island Silt that has two depocentres, each up to 20.0-25.0m thick, separated by a NW-SE belt of older pre-Holocene units. The northern depocentre represents estuarine infill to the Yarra and Maribyrnong, a river system, whereas the southern depocentre appears to be an offshore bay facies. The youngest unit is the Port Melbourne Sand, which is largely restricted to the area south of the present Yarra River. It is between 5.0 and 28.0m thick, and is diachronous with the underlying Coode Island Silt. New C-14 shell dates from the Coode Island Silt and Port Melbourne Sand have shown an age range between 8341 and 2760 yrs BP. These sediments infill former swamplands covering low-stand river valleys of the Yarra and Maribyrnong rivers across West Melbourne, Fishermans Bend and South Melbourne. After ca 2760 yrs BP active sedimentation in the delta ceased as base-levels fell, and Yarra and Maribyrnong river sediments bypassed the delta because of falling bay levels. The Yarra and Maribyrnong river courses also shifted progressively westwards behind growing beach barriers of the Port Melbourne Sand. A comparable stratigraphy exists between the Yarra Delta and the adjacent Port Phillip Bay, i.e. marine and lagoonal shelly sediments of the Coode Island Silt and barrier sands of the Port Melbourne Sand infill last-glacial channels cut into the middle Pleistocene Fishermans Bend Silt.

A detailed examination of the brown coal facies preserved in the Latrobe Valley Morwell 1B seam indicates that the type of peat-forming environment and the associated hydrological regime are the main factors influencing the development of lithotypes in brown coal deposits. New palynological data from the Morwell 1B seam suggests that each respective lithotype in the lightening-upwards lithotype cycles was deposited in a particular depositional environment that was characterised by a distinct floral community. The laminated dark lithotype represents a fire-prone emergent marsh that grew on the margins of a coastal lagoon and/or freshwater swamp. This facies grades into the dark lithotype, representing the transition from a meadow marsh to a periodically flooded ombrogenous forested bog. The medium and lighter lithotypes are interpreted as being deposited in an angiosperm-dominated ombrogenous forest bog that was intolerant of fire. These peat-forming environments are interpreted as being largely controlled by moisture and relative depth to water table. Each environment produces distinct lithotypes and lightening-upwards cycles are interpreted as terrestrialization cycles. As the peat grew upwards and above the water table, less moist conditions prevailed and lighter lithotypes were produced. The observed change in colour, from darker to lighter lithotypes, results from the environment evolving from anaerobic/inundated to less anaerobic/less moist settings via terrestrialization. The thin and laterally extensive light and pale lithotypes that top the cycles are interpreted to represent a residual layer of concentrated, oxidation resistant peat-forming elements that result from intense weathering and aerobic degradation of the peats. At a generic level, modern lowland bogs of South Westland in New Zealand have remarkably similar floral/ecological gradients to those of the Oligo-Miocene Morwell 1B brown coal cycles in Australia. This suggests that modern New Zealand bogs can be used as floral/ecological analogues in order to better understand these Oligo-Miocene peatland environments.

The Late Oligocene to Mid-Miocene (25–13 million years ago) brown coals of the Gippsland Basin in southern Victoria, Australia, were deposited in peat mega-swamps, unlike any in the world at the present day. The swamps preserve a rich botanical suite of macro- and microfossils, many of which can be identified with plant genera and families present today in Australia, New Caledonia, New Zealand and New Guinea. The peat-forming environments also preserve evidence of past burning in the form of micro-charcoal as well as macro-charcoal, the latter being evident as regional lenses or layers of fusinite, generally in coals of the darkest colour termed dark lithotypes. The presence of micro-charcoal in dark and some other lighter lithotypes indicated that fires also burnt locally, although they may have been extinguished before regional-scale burning occurred. It is also feasible that some peat mega-swamp plant communities dominated by rainforest angiosperm plants may have been fire excluders and prevented widespread fires from developing. Pollen and macrofossil evidence is presented of a distinctive southern conifer and angiosperm flora with an open canopy, primarily associated with the darkest coals that formed in the wettest parts of the peat-forming environment. Elsewhere, swamp forests with a large rainforest component grew on swamps raised appreciably above the regional groundwater table in a structural context akin to the ombrogenous peats of tropical coastal Sumatra and Sarawak. These vegetation types were not fire prone, but may have occasionally burnt at a local scale or at forest margins. Evidence is presented for the existence of seasonal climatic conditions that would appear to have facilitated a drying-out of the peat swamps in the warmest months of the year. A mesothermal climate was invoked where mean annual precipitation was at least 1500 mm, and possibly as much as 2000 mm, and mean annual temperatures were ~19°C.

The cyclic succession of brown coals in the Latrobe Valley, Gippsland Basin, Australia, records an exceptional floral and charcoal record from the Late Oligocene to Middle Miocene. New palynological, geological and charcoal data are consistent with existing colourimetry, carbon isotope, and organic geochemical and palaeobotanical data, indicating that the repeated lithotype cycles represent relative drying (terrestrialization). Based on this detailed palynological study, the vegetation succession within the Latrobe Valley peatlands is interpreted to have begun with a fire-prone emergent marsh of bulrushes (Typhaceae), which grades landward into a fire-prone meadow marsh of rushes (Restionaceae), heaths (Ericaceae) and coral-ferns (Gleicheniaceae). This marsh environment then developed into a forested bog, with gymnosperms (e.g. the Podocarpaceae Dacrycarpus and Dacrydium) as the dominant trees, until an ombrogenous forest bog developed, predominantly consisting of angiosperms (e.g. Nothofagus, Quintinia).The similarity between vegetation successions in New Zealand and the lightening-upwards cycles from the Latrobe Valley coals suggests that New Zealand's modern vegetation communities represent a floral analogue for the successions preserved in the Latrobe Valley coals. High abundances of micro and macro charcoal recorded in the darker lithotypes, within the lithotype cycles of the M1B and M2A seams, suggest that the Latrobe Valley peatlands were subject to repeated fires during the Late Oligocene to Early Miocene. (C) 2016 Elsevier B.V. All rights reserved.

Brown coal colour lithotype cycles range from 10 to 30m thick in Oligo-Miocene coals of the Latrobe Valley, Gippsland Basin, Australia. Similar colour lithotype cycles occur in the Lusatia German Miocene brown coals. In both the Latrobe Valley and Germany, the cycles often display well-developed colour-lightening-upward trends as defined by new colourimetry measurement. The typical lithotype cycle boundary is abrupt between light below and dark lithotype above. Geological, geochemical, palynological and macrofossil evidence is consistent with a relative drying (terrestrialisation) upward depositional model for each cycle, and the overlying dark lithotype represents renewed peat accretion. The dark lithotype may include charcoal near the cycle base, explained by the fire-prone and highly flammable nature of the herbaceous/reed wetlands. In both the German and Australian coals, wetter (darker) lithotypes are characterized by a gymnosperm paleoflora, while drier (lighter) lithotypes are characterized by angiosperms.In the German (Rhenish) Miocene brown coal exposed in large open cut mines at Garzweiler and Hambach, a 1.0m spaced sampling and colourimetry measurement program shows lightening-upwards cycles for the Morken seam, Frimmersdorf-A seam, Frimmersdorf-B seam and for the Garzweiler-II seam. At Hambach where the 60m thick ‘Main Seam’ includes amalgamations of Frimmersdorf-A, Frimmersdorf-B and Garzweiler-I, II & III seams, the lightening-upwards trends, provides a means of stratigraphic subdivision.The palaeogeographic setting for Latrobe Valley and German brown coals is similar – in Latrobe Valley the seams split and thin to the east into marine facies. In the Rhenish and Lusatia brown coals they also split and thin to the north into marine facies. The two Rhenish mines at Hambach and Garzweiler respectively typify end members of this palaeogeography – the Hambach mine is located in a distal location where sulphur content is negligible; the Garzweiler mine is located in a proximal location to the marine boundary where sulphur content is higher. The colourimetry and facies succession suggest German brown coal deposition followed a similar cyclic depositional succession to the Latrobe Valley, and that this succession may be fundamental in all thick coal seams.

In 2010–2011, a well on the uplifted northern edge of the Latrobe Valley (Yallourn North-1A) cored a 550 m section of mostly arenaceous sediments from the Lower Cretaceous Tyers River Subgroup. A follow-up core-hole (Yallourn Power-1) aimed at extending the Tyers River Subgroup section some 5 km south into the Latrobe Valley instead encountered Paleozoic basement rocks immediately below Cenozoic coal measures. From a re-examination of earlier coal and groundwater bore results, and new interpretations from gravity, seismic and magneto-telluric (MT) surveys, there is a significant area of Paleozoic basement rock that may underlie the whole northern Latrobe Valley area. The uplifted Yallourn North Lower Cretaceous sediments are a separate basin entity herein named the Monash trough. It appears they are separate from the main Lower Cretaceous Strzelecki Group Basin sediments on the southern side of the Latrobe Valley. Attributes of the Monash trough may underlie the main Strzelecki Basin, but this remains to be substantiated by further drilling. The intervening subcrop of Paleozoic basement rocks is herein named the Glengarry basement block. It shows characteristic gravity, MT and seismic features covering some 200 km2 of the northern Latrobe Valley area. The boundary between the Glengarry basement block and Strzelecki Basin approximates to the Princes Highway. It is uncertain whether structural separation of the Monash trough from the main Strzelecki Basin always existed, or whether uplift and stripping of Cretaceous rocks over the Glengarry basement block occurred in post-Cretaceous but pre-Cenozoic times. Comparative rank and maturity indices indicate a greater depth of burial of the Glengarry basement block than what exists today, whereas less stripping and loss of section have occurred to the Monash trough. Cretaceous sediments of the Tyers River Subgroup (Rintouls Creek Formation, Tyers Conglomerate) in the Monash trough are dominated by mudstones, siltstones with lesser quartzose sandstones, conglomerates and thin coals. The sediments are over 300 m thick and are conformably overlain by 100 m of volcaniclastic sediments typical of the main Strzelecki Group, in turn overlain by nearly 100 m of Cenozoic coal measures. New detailed spore–pollen dating of Yallourn North-1A cores indicates that all Cretaceous sediments in the Monash trough are Barremian in age. This revises the traditional Neocomian age assigned to the formation. High total organic carbon levels in the 100 m-thick mudstones of the Locmany Member in the Rintouls Creek Formation constitute a mature petroleum source rock worthy of future hydrocarbon exploration.

Cook Strait separates North Island and South Island of New Zealand. It contains the Wairau and other sedimentary basins, which have sedimentary thicknesses of up to 4 km. The Strait overlies part of the Australia-Pacific plate boundary where subduction below the North Island changes to strike-slip motion through the South Island. Strike-slip faults are well documented in the South Island and less so in the North Island. Cook Strait has been surveyed by a variety of shallow penetration seismic in the past, and this has resulted in various models and uncertainty about how major faults join across the strait. The shallow-penetration data image numerous fault traces close to the sea bed, most of which can be traced for only a short distance. Gaps between individual fault traces are common. In recent years, a growing body of research, government and oil company seismic data has imaged structures much more deeply and is the subject of this paper. The Wairau Basin structural style is one dominated by normal faulting, with expansion of basin area and progressive eastwards shift in depocentres with time. A steep structural gradient or faulted margin to basement subcrop and outcrop on the North Island margin indicates a significant north-northwest to northwest component of fault control in this area of Neogene development. The seismic interpretation of this deeper data suggests there are continuous seismogenic zones underlying the discontinuous young seafloor fault scarps. Such discontinuities have led to a perception that Cook Strait faults are not connecting through, that fault rupturing across Cook Strait is improbable. Fault connections across Cook Strait along seismogenic zones have recently been interpreted from historical records. These indicate that the October 1848 earthquakes involved mainshock (M-w 7.4-7.7) displacement on the Awatere Fault in the South Island and probable aftershock displacement on the Ohariu and Wellington faults in the North Island. The January-February 1855 earthquakes (mainshock M-w similar to 8.2-8.4) occurred on the Wairarapa Fault in southern North Island, Wharekauhau, Nicholson Bank faults in Cook Strait, Vernon and Awatere faults in the South Island, and Needles Fault off the NE Marlborough coast. These interpretations are supported by recent seismic data that indicate underlying basin-defining seismogenic zones connect across Cook Strait, with movements that date back at least to the top Paleogene.

The 1848 and 1855 earthquakes provide examples of clustered earthquake sequences involving several faults. Historical evidence indicates that fault rupturing and ground deformation on both sides of Cook Strait occurred over periods of several days during the October 1848 earthquakes on the Awatere, Ohariu and possibly the Wellington faults, with shallowing in Lambton Harbour, Wellington. The January–February 1855 earthquakes occurred on the Wairarapa, Wharekauhau, Nicholson Bank, Vernon, Awatere and Needles faults. The pattern of faulting suggests the existence of distinct seismogenic zones across Cook Strait, within which mainshock triggering of aftershock displacement on major faults can occur.