The Polda Basin is a narrow, east–west striking intracontinental basin that extends ~400 km from the onshore Eyre Peninsula in South Australia to the offshore Great Australian Bight and contains up to 5 km of strata, with a thick sequence of Neoproterozoic rocks overlain by unconformably-bound sequences of Carboniferous-Permian, Jurassic and Cenozoic strata. Though the Polda Basin has witnessed limited exploration for hydrocarbons, it is attracting renewed interest due to the potential for underground hydrogen storage in Neoproterozoic halites, whilst surrounding regions of the Gawler Craton are considered prospective for natural hydrogen. To date however, knowledge of the tectonic history of the Polda Basin, which is critical to assessing its potential role in the energy transition, is limited. Here we present results from a regional apatite fission track analysis study of the Eyre Peninsula, focussing on data from the onshore Kilroo-1A borehole, which provide insights into the burial and exhumation history of the Polda Basin. Results indicate that the preserved Upper Jurassic sequence was thicker prior to Late Cretaceous exhumation, which may have supplied sediment to the adjacent Ceduna Sub-basin. Our results highlight a complex history of Phanerozoic vertical motions in this region, which have implications for both resource and energy storage potential.

<p>The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides limited documentation of the post-Caledonian history. But a more complete understanding can be obtained by also considering evidence of rocks that were formerly present but have since been removed (‘missing section’).</p> <p>We report apatite fission-track data and associated thermal history constraints in 331 samples of Precambrian basement, Phanerozoic sediments and igneous rocks from outcrops and boreholes (up to 6 km depth) from Norway, Sweden and Finland, which define multiple episodes of cooling over the last billion years.</p> <p>We are therefore able to establish a post-Caledonian history of Fennoscandia involving repeated episodes of kilometer-scale burial and exhumation with key episodes of exhumation beginning during late Carboniferous, Middle Triassic, Middle Jurassic, mid-Cretaceous and early Miocene. The effects of these episodes are documented in the stratigraphic record and as prominent peneplains. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasizing the tectonic nature of the history.</p> <p>Results from Finland record events also recognized in Norway and Sweden (though less pronounced) and are thus not consistent with long-term cratonic stability. We interpret the lack of preserved Phanerozoic sedimentary cover in Finland to be due to complete removal during multiple episodes of denudation. For example, our results show that about 2 km of Cambrian to Middle Triassic sediments covered the Sub-Cambrian Peneplain in southern Finland prior to the onset of Middle Triassic exhumation. In southern Scandinavia, Miocene exhumation led to formation of a peneplain which in Pliocene times was uplifted and dissected, producing the modern landscape, also by exhuming older peneplains from below their protective cover rocks.</p> <p>The Carboniferous to Cretaceous exhumation episodes affected Fennoscandia as well as East Greenland, however, post-breakup episodes affected the conjugate margins of the NE Atlantic differently. Whereas Neogene uplift began in the early Miocene in Fennoscandia, it began in the late Miocene in Greenland. Pliocene uplift affected both margins at about the same time. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here.</p> <p> </p> <p>References</p> <p>Bonow & Japsen, 2021, Peneplains and tectonics in North-East Greenland after opening of the North-East Atlantic. GEUS Bulletin.</p> <p>Green et al., 2022a, Episodic kilometre-scale burial and exhumation and the importance of missing section. Earth-Science Reviews.</p> <p>Green et al., 2022b, The post-Caledonian thermo-tectonic evolution of Fennoscandia. Gondwana Research.</p> <p>Japsen & Chalmers, 2022, The Norwegian mountains: the result of multiple episodes of uplift and subsidence. Geology Today. https://doi.org/10.1111/gto.12377</p> <p>Japsen et al., 2018, Mountains of southernmost Norway: uplifted Miocene peneplains and re-exposed Mesozoic surfaces. Journal of the Geological Society, London.</p> <p>Japsen et al., 2021, Episodic burial and exhumation in North-East Greenland before and after opening of the North-East Atlantic. GEUS Bulletin.</p> <p>Lidmar-Bergström et al., 2013, Stratigraphic landscape analysis and geomorphological paradigms: Scandinavia as an example of Phanerozoic uplift and subsidence. Global and Planetary Change.</p>

Quantifying the thermal histories of rift basins is important for evaluating their resource and CO2 storage potential because temperature controls hydrocarbon generation, and the diagenesis of reservoir rocks. However, in many rift basins, it is difficult to obtain evidence for elevated heat flow accompanying rifting, since paleotemperature data from drilled sections typically record heating related to post-rift burial. Here we integrate geochemical, geophysical and petrophysical data from the Duntroon Sub-basin, Great Australian Bight, that show how strain-migration during multiphase extension can preserve the signature of syn-rift elevated geothermal gradients. During the late Jurassic–early Cretaceous, rifting was focussed along ~ESE-striking normal fault systems in the northern part of the Duntroon Sub-basin. During the late Cretaceous, strain migrated to the southwest through the development of normal faults which accommodated the deposition of Upper Cretaceous strata. The Echidna-1 well was drilled into a basement high, in the footwall of a late Cretaceous fault system, penetrating ~2.5 km of Lower Cretaceous strata. Paleotemperature proxies define an early Cretaceous paleogeothermal gradient of ~60°C km−1, substantially higher than the present-day gradient. Our results indicate that preserved Lower Cretaceous strata were more deeply buried by ~1 km of additional section, which was likely eroded during an episode of mid-Cretaceous exhumation associated with the migrating locus of rifting; this enabled the preservation of thermal signature of elevated syn-rift heat flow. Similar evidence is also observed in the Otway Basin, demonstrating the regional extent of elevated syn-rift heat flow along the southern Australian margin.

We thank Lovell for his comments on our paper describing events in which kilometre-scale thicknesses are deposited and removed, resulting in the phenomenon of "missing section". Lovell proposes that these events can be explained by mantle convection and dynamic topography, based on examples of domal uplifts interpreted to represent dynamically supported swells with a vertical deflection of up to 2 km at the centre. However, while mantle-driven processes may contribute, in part, to kilometre-scale exhumation the examples cited by Lovell do not accurately reproduce the events described by Green et al. (2022), which involve burial and exhumation, often in multiple episodes, and affect regions over vast distances broadly synchronously. Thus, detailed understanding of the underlying mechanisms remains elusive.

The incompleteness of the stratigraphical record is well documented, and the concept of "missing time" has attracted renewed attention in recent years. However, the importance of "missing section", comprising rock sequences that were deposited and removed within time intervals for which no rock is now preserved, is not so widely appreciated. We focus here on studies showing that in diverse regions, many of which are regarded as free of tectonic influences over intervals of 10s to 100 s of millions of years, kilometre-scale thicknesses of rock have been deposited and subsequently removed, typically within a few tens of Myr, leaving little or no trace of their former presence in the preserved rock record. Much of the evidence for these episodes comes from low tem-perature thermochronology (LTT) studies of basement regions including passive continental margins, ancient orogens and cratons. Such studies have commonly been carried out within a framework of continuous slow cooling, on the assumption that denudation of these supposedly tectonically stable regions is mainly a response to changes in climate and isostatic response to erosion. In many regions, integration of LTT results with geological evidence, principally the presence of remnants of sedimentary cover and erosion surfaces, shows that histories involving long-term slow cooling/denudation are not appropriate. Instead, histories involving repeated episodes of burial and exhumation/ heating and cooling, appear to be common in these supposedly tectonically inactive regions. During these episodes, thicknesses of several kilometres may be deposited and subsequently removed, returning the underlying rock to the surface or close to it. These events affect areas of many 1000s of km2, and may affect neighbouring regions on a continental scale more or less synchronously. They may affect both basement regions and adjacent sedimentary basins. The resulting unconformities, including erosion surfaces in basement, are often very low angle in nature, reflecting the spatial scale of the affected regions, and are often mistakenly regarded as representing periods of stability. Apparent long-term preservation of elevated topography and preservation of exposed ancient landscapes have been regarded by many as enigmatic. However, both can be understood in terms of vertical motions similar to those revealed from LTT. A number of studies point to the conclusions that regions of supposedly long-lived elevated topography have been uplifted relatively recently and ancient surfaces have been preserved by burial and uncovered as a result of relatively recent exhumation. The concept of km-scale "missing section" has been regarded with scepticism by many geologists, on the basis that there is no evidence that a significant cover was ever present. But the evidence exists in the form of data from a variety of paleo-thermal and paleo-burial techniques. Some of the earliest geologists recognised the importance of former geological sequences that are no longer present. We suggest that serious consideration should be given to explaining this behaviour, rather than dismissing it as unrealistic. Intra-plate stresses from far-field plate boundary interactions and/or processes related to mantle circulation may explain the processes involved in producing episodic kilometre-scale burial and exhumation.

The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides only partial documentation of the geological evolution. A more complete understanding is obtained by also considering evidence of rocks that were formerly present but have since been removed. We report apatite fission track data and associated thermal history constraints in 331 samples of Precambrian basement, younger sedimentary cover, Paleozoic and Mesozoic igneous rocks from outcrops and boreholes (up to 6 km depth) across Fennoscandia, which define thirteen phases of cooling (each representing kilometre-scale exhumation) over the last 1100 Myr. Key post-Caledonian episodes began in the intervals 311-307 Ma (late Carboniferous), 245-244 Ma (Middle Triassic), 170-167 Ma (Middle Jurassic), 102-92 Ma (mid-Cretaceous) and 23-21 Ma (early Miocene). These episodes, varying in magnitude, are recognised across Fennoscandia, and their effects are documented in the stratigraphic record and as prominent regional peneplains. The results define a history involving repeated episodes of regional burial and exhumation. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasising the tectonic nature of the history. Results from Finland record the same events recognised in Norway and Sweden (though less pronounced), and are not consistent with long-term cratonic stability. The lack of preserved Phanerozoic sedimentary cover in Finland is interpreted to be due to complete removal during multiple episodes of denudation. In southern Norway and Sweden, early Miocene exhumation led to creation of a peneplain, which in Pliocene times was uplifted and dissected, producing the modern landscape. Post-Caledonian exhumation episodes defined here are broadly synchronous with similar events in Greenland, the British Isles and North America. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here. (C) 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

The antiquity of the Australian landscape has long been the subject of debate, with some studies inferring extraordinary longevity (>10 8 myr) for some subaerial landforms dating back to the early Paleozoic. A number of early Permian glacial erosion surfaces in the Fleurieu Peninsula, southeastern Australia, provide an opportunity to test the notion of long-term subaerial emergence, and thus tectonic and geomorphic stability, of parts of the Australian continent. Here we present results of apatite fission track analysis (AFTA) applied to a suite of samples collected from localities where glacial erosion features of early Permian age are developed. Our synthesis of AFTA results with geological data reveals four cooling episodes (C1-4), which are interpreted to represent distinct stages of exhumation. These episodes occurred during the Ediacaran to Ordovician (C1), mid-Carboniferous (C2), Permian to mid-Triassic (C3) and Eocene to Oligocene (C4). The interpretation of AFTA results indicates that the Neoproterozoic − Lower Paleozoic metasedimentary rocks and granitic intrusions upon which the glacial rock surfaces generally occur were exhumed to the surface by the latest Carboniferous − earliest Permian during episodes C2 and/or C3, possibly as a far-field response to the intraplate Alice Springs Orogeny. The resulting landscapes were sculpted by glacial erosive processes. Our interpretation of AFTA results suggests that the erosion surfaces and overlying Permian sedimentary rocks were subsequently heated to between c. 60 and 80°C, which we interpret as recording burial by a sedimentary cover comprising Permian and younger strata, roughly 1 km in thickness. This interpretation is consistent with existing thermochronological datasets from this region, and also with palynological and geochronological datasets from sediments in offshore Mesozoic − Cenozoic-age basins along the southern Australian margin that indicate substantial recycling of Permian − Cretaceous sediments. We propose that the exhumation which led to the contemporary exposure of the glacial erosion features began during the Eocene to Oligocene (episode C4), during the initial stages of intraplate deformation that has shaped the Mt Lofty and Flinders Ranges in South Australia. Our findings are consistent with several recent studies, which suggest that burial and exhumation have played a key role in the preservation and contemporary re-exposure of Gondwanan geomorphic features in the Australian landscape.

Here we present apatite fission-track analysis (AFTA) data and thermal history interpretations in 332 samples from outcrops and boreholes at elevations between +2 and -6 km relative to sea level across Fennoscandia. The data define episodes of burial and exhumation which involved deposition and removal of kilometre-scale thicknesses of sediment as well as denudation of the underlying basement rocks that resulted in the formation of peneplains of different age and characteristics. Many of these episodes correlate with similar episodes over a much wider region, and this argues for regional tectonic control, related to plate-tectonic processes.Post-Caledonian development of Fennoscandia involved five dominant episodes of exhumation, beginning in late Carboniferous, Middle Triassic, Middle Jurassic, mid-Cretaceous and early Miocene times. These episodes affected not only the present-day Atlantic margin but also the continental interior which is considered by many to represent a stable cratonic region because of the low relief and limited remnants of sedimentary cover. Pronounced offsets in the magnitude of the pre-Cenozoic episodes over short distances occur close to the Atlantic margin, and around the Oslo Rift, attesting to the tectonic origin of these episodes. In contrast, the Middle Triassic and mid-Cretaceous episodes display little variation over vast regions in the interior. Yet even here, our results show that the vertical movements involved deposition and removal of substantial sedimentary covers.The late Carboniferous, Middle Triassic and Middle Jurassic episodes can be linked with the break-up of Pangaea. The mid-Cretaceous episode correlates with a global plate reorganization. The early Miocene episode appears to be earlier than analogous episodes in Greenland, and it is not yet clear how these episodes fit into the pattern of plate-tectonic forces. The youngest tectono-thermal episode to affect Fennoscandia began in the early Pliocene and is only revealed by AFTA data from a few deep boreholes. But this episode had a major impact in shaping the present-day topography on both sides of the Atlantic and may have been driven by dynamic support from the Iceland Plume.A key aspect of the paleo-thermal episodes identified in this study is that they involve both deposition and removal of kilometre-scale thicknesses of sediment (i.e. subsidence and uplift), rather than progressive emergence and monotonic cooling of the continents as assumed in many studies. Dynamic topography and far-field transmission of stress thus appear to be likely candidates for driving the ups and downs of both marginal and interior regions.

Recent exchanges concerning methods for extracting thermal histories from low temperature thermochronology data do not address key limitations imposed by the nature of system response. Thermochronology data in isolation cannot define periods when samples were cooler and subsequently reheated. This can only be defined with the aid of constraints from geological evidence. The common assumption of slow continuous cooling is clearly not appropriate in many situations, and cooling rates derived from such studies have little relevance to geological processes. We suggest a revised approach, which focuses on the information contained in the data.

The antiquity of the Australian landscape has long been the subject of debate, with some studies inferring extraordinary longevity (>10^8 Myr) for some subaerial landforms dating back to the early Palaeozoic. A number of late Palaeozoic glacial erosion surfaces in the Fleurieu Peninsula, southeastern Australia, provide an opportunity to test the notion of long-term subaerial emergence, and thus tectonic and geomorphic stability, of parts of the Australian continent. Here we present results of apatite fission-track analysis (AFTA) applied to a suite of samples collected from localities where glacial erosion features of early Permian age are developed. Our results indicate that the Neoproterozoic-Lower Palaeozoic metasedimentary rocks and granitic intrusions upon which the glacial rock surfaces generally occur were exhumed to the surface by the latest Carboniferous-earliest Permian, possibly as a far-field response to the intraplate Alice Springs Orogeny. The resulting landscapes were sculpted by glacial erosive processes. AFTA results suggest that the erosion surfaces and overlying Permian sediments were subsequently heated to between ~60 and 80°C, which we interpret as recording burial by a Permian-Mesozoic sedimentary cover, roughly 1 kilometre in thickness. This interpretation is consistent with existing thermochronological datasets from this region, and also with palynological and geochronological datasets from sediments in offshore Mezozoic-Cenozoic-age basins along the southern Australian margin that indicate substantial recycling of Permian-Cretaceous sediments. AFTA suggests that the exhumation which led to the contemporary exposure of the glacial erosion features probably began during Paleogene, during the initial stages of intraplate deformation that has shaped the Mt Lofty and Flinders Ranges in South Australia. Our findings are consistent with several recent studies, which suggest that burial and exhumation has played a key role in the preservation of Gondwanan geomorphic features in the contemporary Australian landscape.

The incompleteness of the stratigraphical record is well documented, and the concept of “missing time” has attracted renewed attention in recent years. However, the importance of “missing section”, comprising rock sequences that were deposited and removed within time intervals for which no rock is now preserved, is not so widely appreciated. We focus here on studies showing that in diverse regions, many of which are regarded as free of tectonic influences over intervals of 10s to 100 s of millions of years, kilometre-scale thicknesses of rock have been deposited and subsequently removed, typically within a few tens of Myr, leaving little or no trace of their former presence in the preserved rock record. Much of the evidence for these episodes comes from low temperature thermochronology (LTT) studies of basement regions including passive continental margins, ancient orogens and cratons. Such studies have commonly been carried out within a framework of continuous slow cooling, on the assumption that denudation of these supposedly tectonically stable regions is mainly a response to changes in climate and isostatic response to erosion. In many regions, integration of LTT results with geological evidence, principally the presence of remnants of sedimentary cover and erosion surfaces, shows that histories involving long-term slow cooling/denudation are not appropriate. Instead, histories involving repeated episodes of burial and exhumation/ heating and cooling, appear to be common in these supposedly tectonically inactive regions. During these episodes, thicknesses of several kilometres may be deposited and subsequently removed, returning the underlying rock to the surface or close to it. These events affect areas of many 1000s of km2, and may affect neighbouring regions on a continental scale more or less synchronously. They may affect both basement regions and adjacent sedimentary basins. The resulting unconformities, including erosion surfaces in basement, are often very low angle in nature, reflecting the spatial scale of the affected regions, and are often mistakenly regarded as representing periods of stability. Apparent long-term preservation of elevated topography and preservation of exposed ancient landscapes have been regarded by many as enigmatic. However, both can be understood in terms of vertical motions similar to those revealed from LTT. A number of studies point to the conclusions that regions of supposedly long-lived elevated topography have been uplifted relatively recently and ancient surfaces have been preserved by burial and uncovered as a result of relatively recent exhumation. The concept of km-scale “missing section” has been regarded with scepticism by many geologists, on the basis that there is no evidence that a significant cover was ever present. But the evidence exists in the form of data from a variety of paleo-thermal and paleo-burial techniques. Some of the earliest geologists recognised the importance of former geological sequences that are no longer present. We suggest that serious consideration should be given to explaining this behaviour, rather than dismissing it as unrealistic. Intra-plate stresses from far-field plate boundary interactions and/or processes related to mantle circulation may explain the processes involved in producing episodic kilometre-scale burial and exhumation.

Despite the increasing application of apatite (U-Th-Sm)/He thermochronology in a range of settings, the technique suffers from two major unresolved problems which preclude reliable thermal history interpretations on a routine basis. One problem is the common but unexplained over-dispersion of single grain ages compared to predictions based on accepted models of diffusion systematics (including enhanced He retentivity due to the buildup of radiation damage in the apatite crystal lattice). A second related problem is that the widely adopted "RDAAM" model does not provide an accurate representation of the degree to which helium retentivity is enhanced as a result of the accumulation of radiation damage. Until these problems are resolved and eliminated, thermal history interpretations derived from this method cannot be regarded as reliable. Routine application of the technique requires a more rigorous quantitative understanding of these factors. Further experimental studies are required to identify all significant sources of variation in measured ages and to develop more accurate models of the thermal response of the system, combined with rigorous calibration and validation against independent methods in well-constrained natural settings. Only once this is achieved will the technique be capable of producing robust and reliable interpretations.

Abstract We present a consistent synthesis of palaeothermal (apatite fission track analysis (AFTA) and vitrinite reflectance) data from UK Southern North Sea wells with the regional pattern of exhumation defined from sonic velocity data. Cenozoic exhumation across most of the region began in the Paleocene between 63 and 59 Ma. Amounts of removed section are around 1 km across the offshore platform, increasing to 2 km or more on the Sole Pit axis. Neogene exhumation within this area began between 22 and 15 Ma, and led to removal of up to 1 km of section. Along the eastern flank of the Sole Pit axis, sonic data define a pre-Chalk event, and AFTA data from these wells show that exhumation began between 120 and 93 Ma. This timing correlates with events defined from AFTA data in the Sorgenfrei–Tornquist Zone, further east, presumably reflecting a response to regional tectonic stresses. East of the Sole Pit axis, AFTA and sonic velocities suggest that Neogene exhumation dominates, while further east towards the central parts of the North Sea Mesozoic sediments appear to be at maximum burial today except for local effects related to salt movement. The multiple episodes of exhumation and burial defined here have important implications for exploration.

Despite many years of study, the processes involved in the development of the continental margin of southern Africa and the distinctive topography of the hinterland remain poorly understood. Previous thermochronological studies carried out within a monotonic cooling framework have failed to take into account constraints provided by Mesozoic sedimentary basins along the southern margin. We report apatite fission track analysis and vitrinite reflectance data in outcrop samples from the Late Jurassic to Early Cretaceous sedimentary fill of the Oudtshoorn, Gamtoos and Algoa Basins (Uitenhage Group), as well as isolated sedimentary remnants further west, plus underlying Paleozoic rocks (Cape Supergroup) and Permian-Triassic sandstones from the Karoo Supergroup around the Great Escarpment. Results define a series of major regional cooling episodes. Latest Triassic to Early Jurassic cooling which began between 205 and 180 Ma is seen dominantly in basement flanks to the Algoa and Gamtoos Basins. This episode may have affected a wider region but in most places any effects have been overprinted by later events. The effects of Early Cretaceous (beginning between 145 and 130 Ma) and Early to mid-Cretaceous (120-100 Ma) cooling are both delimited by major structures, while Late Cretaceous (85-75 Ma) cooling appears to have affected the whole region. These cooling events are all interpreted as dominantly reflecting exhumation. Higher Late Cretaceous paleotemperatures in samples from the core of the Swartberg Range, coupled with evidence for localised Cenozoic cooling, are interpreted as representing Cenozoic differential exhumation of the mountain range. Late Cretaceous paleotemperatures between 60 degrees C and 90 degrees C in outcropping Uitenhage Group sediments from the Oudtshoorn, Gamtoos and Algoa Basins require burial by between 1.2 and 2.2 km prior to Late Cretaceous exhumation. Because these sediments lie in depositional contact with underlying Paleozoic rocks in many places, relatively uniform Late Cretaceous paleotemperatures across most of the region, in samples of both basin fill and underlying basement, suggest the whole region may have been buried prior to Late Cretaceous exhumation. Cenozoic cooling (beginning between 30 and 20 Ma) is focussed mainly in mountainous regions and is interpreted as representing denudation which produced the modern-day relief. Features such as the Great Escarpment are not related to continental break up, as is often supposed, but are much younger (post-30 Ma). This history of post-breakup burial and subsequent episodic exhumation is very different from conventional ideas of passive margin evolution, and requires a radical re-think of models for development of continental margins.

Despite many years of study, the processes involved in the post-breakup development of passive margins remain poorly understood. Integration of apatite fission track analysis (AFTA) and stratigraphic landscape analysis (SLA) at a number of margins has provided new insights into the development of elevated passive continental margins (EPCMs). In particular, by integrating evidence from the preserved rock record and landscape with information on the deposition and erosional removal of rock units which are no longer present ("missing section") these studies have highlighted the importance of episodic positive and negative vertical km-scale crustal movements. Based on these studies we present seven propositions regarding the formation of EPCMs and the nature of the controlling processes, viz: 1: EPCMs are not the inevitable consequence of rifting and breakup 2: Elevated topography at present-day EPCMs developed long after breakup 3: Similar EPCM landscapes at different margins suggest similar controlling processes 4: EPCMs have undergone episodic km-scale burial and exhumation rather than slow monotonic denudation, both before rifting and after breakup 5: Post-breakup km-scale exhumation at continental margins is not restricted to presently elevated onshore regions 6: Post-breakup km-scale burial and exhumation have affected presently low lying margins as well as EPCMs 7: Exhumation events show a broad level of synchroneity over continents and across oceans and correlate with plate boundary events and changes in plate motions. These propositions imply that positive and negative vertical motions at passive margins are controlled by plate scale processes. Another key conclusion is that present-day elevation alone provides no clue to the earlier history of a margin. Many of the key aspects of these propositions are absent from current geodynamic models of passive margin development. Understanding the processes that control vertical movements at passive continental margins requires development of realistic geodynamic models that honour these propositions. (C) 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

This study provides the first record of the high diversity and abundance of Victoria's earliest angiosperms from outcrops in the non-marine upper Eumeralla Formation of the Otway Basin. The biostratigraphic schemes established for the Albian of Australia are re-evaluated using more reliable and widespread index species, resulting in the construction of a high-resolution Albian biostratigraphy in the Otway Basin. New localities in the uppermost outcrop of the Eumerella Formation contain spore–pollen assemblages that cannot be placed in the existing scheme and a new Upper Phimopollenites pannosus Subzone is recognised. The correlation of the P. pannosus Zone to the geochronological timescale was re-assessed and shows that it is 103–101.51Ma, giving a late Albian age. In contrast to previous studies that record low diversity angiosperm assemblages in the Albian, this study identifies twenty-three angiosperm species, including one new species, Tricolpites tortuous. The high diversity and abundance of angiosperm pollen in the Otway Basin provides further evidence that angiosperms probably migrated into eastern Gondwana via South America and Antarctica.

The Ceduna Sub-basin is the main depocentre of the frontier Bight Basin, which formed as a result of the late Jurassic-Cenozoic separation of Australia and Antarctica. The sedimentary fill of the Ceduna Sub-basin is dominated by two structurally distinct deltaic lobes of Cenomanian and Santonian-Maastrichtian age with combined thickness >12 km. This region is the focus of growing exploration interest, and thus improved knowledge of its origin and evolution is essential for reducing exploration uncertainty. However, because the Ceduna sub-basin is located completely offshore in water depths up to 5 km, to date there has been little exploratory drilling in this region. With primary data from the sub-basin itself lacking, we have collected a variety of new thermochronological and geochronological datasets from the onshore margins and hinterland to the Ceduna sub-basin, which have a bearing on the evolution of the offshore region. These datasets include:1. Zircon U-Pb ages from several samples of drillcore from the Lower Cretaceous Loongana Formation, which is preserved in the Denman Basin, a shallow depression that underlies the onshore Eucla Basin. Age populations within these data suggest that sediment input at this time was predominantly from the N and W.2. Zircon U-Pb ages from several samples of drillcore from the Winton Formation, an Albian-Cenomanian-age fluvial-lacustrine sequence from the Eromanga Basin. This sequence has been proposed as an analogue for the Cenomanian deltaic lobe in the Ceduna sub-basin, which has yet to be penetrated by drilling.3. AFTA and VR data from outcropping rocks in the Eyre Peninsula, and subsurface rocks retrieved by drilling in the Polda sub-basin, to the NE of the Ceduna sub-basin. These data point to substantial exhumation of this region during the late Cretaceous.4. Zircon U-Pb and fission track ages from the Turonian-Maastrichtian sequence penetrated by the offshore Gnarlyknots-1 well. Interpretation of these ages suggests that this sequence was largely sourced from recycled Permian-Early Cretaceous cover and underlying basement rocks eroded from the proximal, NE basin margin. The integration of these onshore and offshore datasets provides new, valuable insights into the Cretaceous palaeogeography of the Ceduna sub-basin, the tectonic processes controlling the input of clastic sediments, and the prospectivity of this frontier exploration region.

In basins with complex histories, conventional basin modelling invariably combines burial histories based on the preserved stratigraphic section with variable heat flow to match calibration data (usually vitrinite reflectance). However, numerous studies involving application of low temperature thermochronology (principally apatite fission track analysis) combined with VR have shown that thermal history is often controlled not by variation in heat flow but by deeper burial and subsequent exhumation, in which km-scale section is deposited and subsequently removed typically within 30 Myr or less. These episodes are not restricted to basins, but also affect adjacent basement regions across areas of several 104 km2. The origin of such events has long been debated. Due to the regional extent, the resulting unconformities are often very low angle, and the corresponding time intervals are often erroneously interpreted as periods of stability and non-deposition. The notion of deeper burial and subsequent exhumation during these intervals is sometimes questioned because of the lack of an accepted mechanism. Nevertheless, a large body of data points to the reality of these events. It has also become clear that these exhumation episodes are broadly synchronous over vast regions. Three phases of Cenozoic exhumation are recorded in areas from Alaska to Greenland, Norway and Svalbard, while exhumation episodes ranging in time from Carboniferous to Cenozoic appear to be broadly synchronous in Brazil, South Africa and Australia. The lack of attention to missing section contrasts starkly with the effort devoted to the preserved section. Yet in many basins hydrocarbon prospectivity is controlled by deposition and removal of the missing section rather than elevated heat flow. Deeper burial leads to enhanced maturity levels while mistaking the effects of deeper burial for elevated heat flow can lead to incorrect discounting of deep source potential. Exhumation can lead to remigration and loss of charge due to seal breach and phase change. Understanding the controlling processes is essential in order to accurately define the variation of maturity in time and space so as to identify more prospective regions, and geodynamic models are required that can provide a mechanism. Meanwhile, basin modelling studies should focus more on deposition and removal of km-scale thicknesses of section instead of elevated heat flow.