Basin Research - Volume 32, Issue 5, 2020

This study presents the discovery of four giant canyons along the northern portion of the Davie Ridge (western Indian Ocean). Three canyons are now inactive, supra‐elevated relative to the adjacent sea floor and disconnected from the modern slope systems offshore the Rovuma and Rufiji River deltas. The chronological constraints available suggest that the tectonic activity driving the uplift of the Davie Ridge in this area has started during the middle‐upper Miocene. Our findings contribute to placing the Kerimbas Graben and the Davie Ridge offshore Tanzania in the regional geodynamic context of the western Indian Ocean and show how the tectonics of the offshore branch of the EARS modified the physiography of the margin, re‐routing the deep‐water drainage network.

The East African Rift System (EARS) exerted a major influence on river drainage basins and regional climate of east Africa during the Cenozoic. Recent studies have highlighted an offshore branch of the EARS in the western Indian Ocean, where the Kerimbas Graben and the Davie Ridge represent its sea floor expression. To date, a clear picture of the impact and timing of this EARS offshore branch on the continental margin of the western Indian Ocean, and associated sediment dispersal pathways, is still missing. This study presents new evidence for four giant canyons along the northern portion of the Davie Ridge offshore Tanzania. Seismic and multibeam bathymetric data highlight that the southernmost three canyons are now inactive, supra‐elevated relative to the adjacent sea floor of the Kerimbas Graben and disconnected from the modern slope systems offshore the Rovuma and Rufiji River deltas. Regional correlation of dated seismic horizons, integrated with well data and sediment samples, proves that the tectonic activity driving the uplift of the Davie Ridge in this area has started during the middle‐upper Miocene and is still ongoing, as suggested by the presence of fault escarpments at the sea floor and by the location and magnitude of recent earthquakes. Our findings contribute to placing the Kerimbas Graben and the Davie Ridge offshore Tanzania in the regional geodynamic context of the western Indian Ocean and show how the tectonics of the offshore branch of the EARS modified the physiography of the margin, re‐routing the deep‐water drainage network since the middle Miocene. Future studies are needed to understand the influence of changing sea floor topography on the western Indian Ocean circulation and to evaluate the potential of the EARS offshore tectonics in generating tsunamigenic events.

Using geological information and a basin modelling approach the deep biosphere of the Shimokita coalbeds has been modelled over deep geological time. This required coupling metabolic and geochemical processes to far field geological and tectonic events. Viewed in this light sedimentary basins become living breathing entities that operate on geological time scales.

Basin models can simulate geological, geochemical and geophysical processes and potentially also the deep biosphere, starting from a burial curve, assuming a thermal history and utilizing other experimentally obtained data. Here, we apply basin modelling techniques to model cell abundances within the deep coalbed biosphere off Shimokita Peninsula, Japan, drilled during Integrated Ocean Drilling Program Expedition 337. Two approaches were used to simulate the deep coalbed biosphere: (a) In the first approach, the deep biosphere was modelled using a material balance approach that treats the deep biosphere as a carbon reservoir, in which fluxes are governed by temperature‐controlled metabolic processes that retain carbon via cell‐growth and cell‐repair and pass it back via cell‐damaging reactions. (b) In the second approach, the deep biosphere was modelled as a microbial community with a temperature‐controlled growth ratio and carrying capacity (a limit on the size of the deep biosphere) modulated by diagenetic‐processes. In all cases, the biosphere in the coalbeds and adjacent habitat are best modelled as a carbon‐limited community undergoing starvation because labile sedimentary organic matter is no longer present and petroleum generation is yet to occur. This state of starvation was represented by the conversion of organic carbon to authigenic carbonate and the formation of kerogen. The potential for the biosphere to be stimulated by the generation of carbon‐dioxide from the coal during its transition from brown to sub‐bituminous coal was evaluated and a net thickness of 20 m of lignite was found sufficient to support an order of magnitude greater number of cells within a low‐total organic carbon (TOC) horizon. By comparison, the stimulation of microbial populations in a coalbed or high‐TOC horizon would be harder to detect because the increase in population size would be proportionally very small.

Reverse displacements during inversion mirror normal displacements during extension. Inversion occurred by coeval reverse reactivation of normal faults and dextral strike‐slip faulting. The throw profiles are stepped where they intersect the larger strike‐slip faults increases in throw across the branchpoints with the dextral strike‐slip faults.

The Celtic Sea basins lie on the continental shelf between Ireland and northwest France and consist of a series of ENE–WSW trending elongate basins that extend from St George’s Channel Basin in the east to the Fastnet Basin in the west. The basins, which contain Triassic to Neogene stratigraphic sequences, evolved through a complex geological history that includes multiple Mesozoic rift stages and later Cenozoic inversion. The Mizen Basin represents the NW termination of the Celtic Sea basins and consists of two NE–SW‐trending half‐grabens developed as a result of the reactivation of Palaeozoic (Caledonian, Lower Carboniferous and Variscan) faults. The faults bounding the Mizen Basin were active as normal faults from Early Triassic to Late Cretaceous times. Most of the fault displacement took place during Berriasian to Hauterivian (Early Cretaceous) times, with a NW–SE direction of extension. A later phase of Aptian to Cenomanian (Early to Late Cretaceous) N–S‐oriented extension gave rise to E–W‐striking minor normal faults and reactivation of the pre‐existing basin bounding faults that propagated upwards as left‐stepping arrays of segmented normal faults. In common with most of the Celtic Sea basins, the Mizen Basin experienced a period of major erosion, attributed to tectonic uplift, during the Paleocene. Approximately N–S Alpine regional compression‐causing basin inversion is dated as Middle Eocene to Miocene by a well‐preserved syn‐inversion stratigraphy. Reverse reactivation of the basin bounding faults was broadly synchronous with the formation of a set of near‐orthogonal NW–SE dextral strike‐slip faults so that compression was partitioned onto two fault sets, the geometrical configuration of which is partly inherited from Palaeozoic basement structure. The segmented character of the fault forming the southern boundary of the Mizen Basin was preserved during Alpine inversion so that Cenozoic reverse displacement distribution on syn‐inversion horizons mirrors the earlier extensional displacements. Segmentation of normal faults therefore controls the geometry and location of inversion structures, including inversion anticlines and the back rotation of earlier relay ramps.

Detrital zircon U/Pb age and Hf‐isotopes facilitate a robust understanding of sediment source to sink relationships on the southern margin of Australia. Provenance analysis tracks complete reorganisation of sediment systems associated with the rifting of Australia and Antarctica during Gondwana break‐up.

Understanding the development of sedimentary systems during continental rifting is important for tracking environmental change and lithospheric processes. Conceptual models have been developed for the sourcing, routing and facies architecture of sediments in rift‐settings, driven in part by quantitative sediment tracking. Here, we present laser ablation split‐stream detrital zircon U/Pb geochronology and Hf‐isotopes for post‐rift (Cretaceous‐Paleogene) clastic sediments from Ocean Drilling Program (ODP) wells and Plio‐Pleistocene palaeoshoreline material, from the southern margin of Australia. Provenance results are contextualized through comparison with well‐characterized source regions and regional pre‐ and syn‐rift sediment reservoirs to track changes associated with Australia‐Antarctica separation during East Gondwana break‐up. The provenance character of the post‐rift sediments studied are distinct from pre‐existing sediment reservoirs and demonstrate termination of previously stable sediment routing systems and a dominance of local basement of the Proterozoic Madura and Coompana provinces (~1.2 Ga and CHUR‐like Hf‐signatures; Moodini Supersuite) in offshore ODP wells. A composite post‐rift Cretaceous?‐Eocene sample in the easternmost well expresses characteristic Phanerozoic zircon age signatures associated with source regions in eastern Australia that are interpreted to reflect inversion in the Ceduna Sub‐basin to the east. Detrital zircon signatures in Plio‐Pleistocene palaeoshoreline sediment are also relatively distinct, indicating derivation from coastal erosion in the Leeuwin Complex (~0.5 and 0.7 Ga subchondritic grains) and Albany–Fraser Orogen (~1.2 Ga subchondritic grains) several hundred, to over a thousand kilometers to the west. Collectively, results highlight the fundamental geological processes associated with rifting that dramatically change the character of sediment provenance via (a) isolation of pre‐existing primary and secondary sources of detritus, (b) development of new source regions in basin compartmentalized highs and localized fault scarps, and (c) establishment of marine and coastal currents that redefine clastic sediment transport.

Salt tectonics is an important part of the geological evolution of many continental margins, yet the four‐dimensional evolution of the minibasins, the fundamental building block of these and many other salt basins, remains poorly understood. Using high‐quality 3D seismic data from the Lower Congo Basin, offshore Angola we document the long‐term (>70 Myr) dynamics of minibasin subsidence. We show that, during the Albian, a broadly tabular layer of carbonate was deposited prior to substantial salt flow, diapirism, and minibasin formation. We identify four subsequent stages of salt‐tectonics and related minibasin evolution: (i) thin‐skinned extension (Cenomanian to Coniacian) driven by basinward tilting of the salt layer, resulting in the formation of low‐displacement normal faults and related salt rollers. During this stage, local salt welding led to the along‐strike migration of fault‐bound depocentres; (ii) salt welding below the eastern part of the minibasin (Santonian to Paleocene), causing a westward shift in depocentre location; (iii) welding below the minibasin centre (Eocene to Oligocene), resulting in the formation of a turtle and an abrupt shift of depocentres towards the flanks of the bounding salt walls; and (iv) an eastward shift in depocentre location due to regional tilting, contraction, and diapir squeezing (Miocene to Holocene). Our study shows that salt welding and subsequent contraction are key controls on minibasin geometry, subsidence and stratigraphic patterns. In particular, we show how salt welding is a protracted process, spanning > 70 Myr of the salt‐tectonic history of this, and likely other salt‐rich basins. The progressive migration of minibasin depocentres, and the associated stratigraphic architecture, record weld dynamics. Our study has implications for the tectono‐stratigraphic evolution of minibasins.

We use 3D seismic data from the Lower Congo Basin to show that minibasin subsidence is largely controlled by salt weld as the associated depocentres migrate along‐ and across‐strike under thin‐skinned extension (a and b) and sedimentary loading (c). Notably, the salt weld processes formed the salt‐core structure (c) under the minibasin are protracted and diachronous, contrasting to the one‐time weld model in current literature.

We present detrital apatite and zircon (U‐Th)/He data from late Cretaceous–Cenozoic sedimentary rocks of the Hoh Xil Basin (HXB). These data, combined with regional geological constraints and interpreted with inverse and forward model of sediment deposition and burial reheating, suggest that ~4–2.7 km vertical exhumation initiated at 30 Ma in the eastern HXB. A simple model of uplift and exhumation would predict a maximum of 0.8 km of surface uplift after upper crustal shortening during 30–27 Ma, which is insufficient to explain the high elevations currently observed. One way to increase elevation without changing exhumation rates and to decouple uplift from upper crustal shortening is through the combined effects of continental subduction, mantle lithosphere removal and magmatic inflation.

The uplift and associated exhumation of the Tibetan Plateau has been widely considered a key control of Cenozoic global cooling. The south‐central parts of this plateau experienced rapid exhumation during the Cretaceous–Palaeocene periods. When and how the northern part was exhumed, however, remains controversial. The Hoh Xil Basin (HXB) is the largest late Cretaceous–Cenozoic sedimentary basin in the northern part, and it preserves the archives of the exhumation history. We present detrital apatite and zircon (U‐Th)/He data from late Cretaceous–Cenozoic sedimentary rocks of the western and eastern HXB. These data, combined with regional geological constraints and interpreted with inverse and forward model of sediment deposition and burial reheating, suggest that the occurrence of ca. 4–2.7 km and ca. 4–2.3 km of vertical exhumation initiated at ca. 30–25 Ma and 40–35 Ma in the eastern and western HXB respectively. The initial differential exhumation of the eastern HXB and the western HXB might be controlled by the oblique subduction of the Qaidam block beneath the HXB. The initial exhumation timing in the northern Tibetan Plateau is younger than that in the south‐central parts. This reveals an episodic exhumation of the Tibetan Plateau compared to models of synchronous Miocene exhumation of the entire plateau and the early Eocene exhumation of the northern Tibetan Plateau shortly after the India–Asia collision. One possible mechanism to account for outward growth is crustal shortening. A simple model of uplift and exhumation would predict a maximum of 0.8 km of surface uplift after upper crustal shortening during 30–27 Ma, which is insufficient to explain the high elevations currently observed. One way to increase elevation without changing exhumation rates and to decouple uplift from upper crustal shortening is through the combined effects of continental subduction, mantle lithosphere removal and magmatic inflation.

Palaeogeographical evolution sketch of the Betic seaway during Late Miocene.

The Lorca and Fortuna basins are two intramontane Neogene basins located in the eastern Betic Cordillera (SE Spain). During the Late Tortonian—Early Messinian, marine and continental evaporites precipitated in these basins as a consequence of increased marine restriction and isolation. Here we show a stratigraphic correlation between the evaporite records of these basins based on geochemical indicators. We use SO4 isotope compositions and Sr isotopic ratios in gypsum, and halite Br contents to characterize these units and to identify the marine or continental source of the waters feeding the evaporite basins. In addition, we review the available chronological information used to date these evaporites in Lorca (La Serrata Fm), including a thick saline deposit, that we correlate with the First Evaporitic Group in Fortuna (Los Baños Fm). This correlation is also supported by micropalaeontological data, giving a Late Tortonian age for this sequence. The Second Evaporitic Group, (Chicamo Fm), and the Third Evaporitic Group (Rambla Salada Fm) developed only in Fortuna during the Messinian. According to the palaeogeographical scheme presented here, the evaporites of the Lorca and Fortuna basins were formed during the Late Tortonian—Early Messinian, close to the Betic Seaway closure. Sulphate isotope compositions and Sr isotopic ratios of the Ribera Gypsum Mb, at the base of the Rambla Salada Fm (Fortuna basin), match those of the Late Messinian selenite gypsum beds in San Miguel de Salinas, in the near Bajo Segura basin (40 km to the East), and other Messinian Salinity Crisis gypsum deposits in the Mediterranean. According to these geochemical indicators and the uncertainty of the chronology of this unit, the assignment of the Rambla Salada Fm to the MSC cannot be ruled out.

Conceptual model of growth basins and their development in prodelta/ lower front of a tidally influenced delta. Heterolithic and sand deposits are redistributed by tidal bars and dunes, detached from the delta‐ front/ delta top.

World‐class examples of fault‐controlled growth basins with associated syn‐kinematic sedimentary fill are developed in Upper Triassic prodelta to delta‐front deposits exposed at Kvalpynten, SW Edgeøya in East Svalbard. They are interpreted to have interacted with north‐westerly progradation of a regional delta system. The syn‐kinematic successions consist of 4 to 5 coarsening‐upward units spanning from offshore mudstones to subtidal heterolithic bars and compound tidal dunes, which were blanketed by regional, post‐kinematic sandstone sheets deposited as laterally continuous, subaqueous tidal dune fields. The rate of growth faulting is reflected in the distribution of accommodation, which governs sedimentary architecture and stacking patterns within the coarsening‐upward units. Fully compartmentalized basins (12, 200–800 m wide and c. 150 m high grabens and half grabens) are characterized by syn‐kinematic sedimentary infill. These grabens and half‐grabens are separated by 60–150 m high horsts composed of pro‐delta to distal delta‐front mudstones. Grabens host tabular tidal dunes (sandwaves), whereas half‐grabens bound by listric faults (mainly south‐dipping) consist of wedge‐shaped, rotated strata with erosive boundaries proximal to the uplifted fault block crests. Heterolithic tidal bars (sand ridges) occur in narrow half‐grabens, showing migration oblique to the faults, up the dipslope. Structureless sandstone wedges and localized subaqueous slumps that formed in response to collapse of the block crests were only documented in half‐grabens. Late‐kinematic deposition during the final stages of faulting occurred in partly compartmentalized basins, filled with variably thick sets of continuous sandstone belts (compound tidal dunes).

Although the trajectory and geometry of clinoforms in different types of basins have been described in many studies, few studies discuss the influence of halokinesis on clinoforms in salt‐related basins. In this study, we analyse the Lower Cretaceous clinoforms in the Tiddlybanken Basin, Norwegian Barents Sea to evaluate the impact of salt mobilization on the geometry and trajectory of clinoforms as well as its implications on sediment partitioning. To accomplish this objective, we use a multidisciplinary approach consisting of seismic and well‐interpretation, 3D structural restoration, and forward stratigraphic modelling. The results show that salt mobilization affects prograding clinoforms by: (a) causing lateral variations in progradation rates, resulting in complex palaeogeography, (b) increasing slope angles, which affect the equilibrium of the clinoform profile and can trigger slope‐readjustment processes and (c) producing lateral and temporal variations in accommodation space, leading to different clinoform trajectories, stacking patterns and reservoir distribution along the basin. Forward stratigraphic modelling shows that in salt‐related basins and other tectonically active basins, the isolated use of conventional methods for clinoform analysis might lead to potential interpretation pitfalls such as misinterpretation of trajectories and overestimation of foreset angles, which can have negative consequences for exploration models.

Salt mobilization causes drastic vertical and lateral changes in relative sea level, which in turn induce lateral variations in clinoform trajectory, foreset angle, relief and progradation rates. Salt withdrawal and uplift produces complex spatial and temporal stacking patterns of depositional environments resulting in different palaeogeographies through time.This study has implications in understanding sediment partitioning of salt‐bearing basins filled by prograding overburdens.

Most source‐to‐sink studies typically focus on the dynamics of clastic sediments and consider erosion, transport and deposition of sediment particles as the sole contributors. Although often neglected, dissolved solids produced by weathering processes contribute significantly in the sedimentary dynamics of basins, supporting chemical and/or biological precipitation. Calcium ions are usually a major dissolved constituent of water drained through the watershed and may facilitate the precipitation of calcium carbonate when supersaturating conditions are reached. The high mobility of Ca²⁺ ions may cause outflow from an open system and consequently loss. In contrast, in closed basins, all dissolved (i.e. non‐volatile) inputs converge at the lowest point of the basin. The endoreic Great Salt Lake basin constitutes an excellent natural laboratory to study the dynamics of calcium on a basin scale, from the erosion and transport through the watershed to the sink, including sedimentation in lake's waterbody. The current investigation focused on the Holocene epoch. Despite successive lake level fluctuations (amplitude around 10 m), the average water level seems to have not been affected by any significant long‐term change (i.e. no increasing or decreasing trend, but fairly stable across the Holocene). Weathering of calcium‐rich minerals in the watershed mobilizes Ca²⁺ ions that are transported by surface streams and subsurface flow to the Great Salt Lake (GSL). Monitoring data of these flows was corrected for recent anthropogenic activity (river management) and combined with direct precipitation (i.e. rain and snow) and atmospheric dust income into the lake, allowing estimating the amount of calcium delivered to the GSL. These values were then extrapolated through the Holocene period and compared to the estimated amount of calcium stored in GSL water column, porewater and sediments (using hydrochemical, mapping, coring and petrophysical estimates). The similar estimate of calcium delivered (4.88 Gt) and calcium stored (3.94 Gt) is consistent with the premise of the source‐to‐sink approach: a mass balance between eroded and transported compounds and the sinks. The amount of calcium deposited in the basin can therefore be predicted indirectly from the different inputs, which can be assessed with more confidence. When monitoring is unavailable (e.g. in the fossil record), the geodynamic context, the average lithology of the watershed and the bioclimatic classification of an endoreic basin are alternative properties that may be used to estimate the inputs. We show that this approach is sufficiently accurate to predict the amount of calcium captured in a basin and can be extended to the whole fossil record and inform on the storage of calcium.

This study implemented a source‐to‐sink approach for the Great Salt Lake (GSL) hydro‐geosystem of the calcium dynamics, highlighting the dissolved pool in both the waterbody and the watershed. Major and minor pathways of calcium inputs were evaluated in order to quantify calcium delivered to the GSL during the Holocene. The value resulting from the hydrologic data was compared to the amount of calcium stored in the water column and sediments of the lake during the same period. The similarity between these two estimates is consistent with the premise of the source‐to‐sink approach: a mass balance between eroded and transported compounds and the sinks. The amount of calcium deposited in the basin can therefore be predicted indirectly from the different inputs. Alternative properties can be used to estimate the inputs in the fossil record when monitoring is unavailable.

Pleistocene glaciations have promoted important landscape transformations as a result of high rates of erosion and rapid sediment evacuation to adjacent marine basins. In the Patagonian Andes the role of the Patagonian Ice Sheet on landscape evolution, in particular the spatial patterns of glacial erosion and its influence on sediment fluxes, is poorly documented. Here, we investigate the Middle and Late Pleistocene sedimentary record of the continental slope from Ocean Drilling Program (ODP) Site 861, offshore Patagonia (46°S), to evaluate the link between glaciations, mountain range erosion and continental margin strata formation. Petrographic analysis of the sand‐size fraction (0.063–2 mm) and ɛNd and ⁸⁷Sr/⁸⁶Sr measurements in the silt‐size fraction (10–63 µm) indicate that glacial erosion over the last 350,000 years has focused within the Patagonian Batholith, with a minor influence of a proximal source to the drilling site, the Chonos Metamorphic Complex. This shows that erosion has focused in the core of the northern Patagonian Andes, coinciding roughly with the location of the Liquiñe‐Ofqui Fault Zone and the zone of concentrated precipitation during glaciations, suggesting a combined climatic and structural control on glacial erosion. Temporal variation in the provenance signal is contemporaneous with a marked change in the stratigraphy of ODP Site 861 that occurred after the glaciation of MIS 8 (~240 kyr ago). Before MIS 8, a restricted provenance signal and coarse lithofacies accumulated on the continental slope indicates spatially restricted erosion and efficient transfer of sediment towards the ocean. In contrast, very high provenance variability and finer continental slope lithofacies accumulation after MIS 8 suggest a disorganized expansion of the areas under erosion and a more distal influence of ice sediment discharge to this site. We argue that this change may have been related to a re‐organization of the drainage patterns of the Patagonian Ice Sheet and flow of outlet glaciers to the continental margin during the last two glaciations.

Sediment provenance analysis of the sand and silt size fractions of ODP site 861 (46ºS, offshore Patagonia) provides insights into erosion and ice drainage of the Patagonian Ice Sheet during the Middle to Late Pleistocene. Focus of erosion during this time period is related to a combined climatic and structural influence on glacial erosion. Temporal variations in sediment provenance contemporaneous with a change in the stratigraphy of this site suggest a re‐organization of ice extent and drainage towards the ocean around 240 kyr ago. These results contribute to constrain ice dynamics of the western side of the Patagonian Ice Sheet during the Pleistocene.

Five 3rd‐order depositional sequences are interpreted from the early Albian to late Campanian interval in the Potiguar Basin. An integrated analysis of seismic interpretations, well logs, cores and biostratigraphic data provides a stratigraphic framework composed by stratigraphic surfaces, systems tracts and sequences. Depositional Sequence 1 and 2 are, respectively, Albian and early to mid‐Cenomanian aged and are composed by the falling stage, low stand, transgressive and high stand systems tracts. Depositional Sequence 3 is late Cenomanian to mid‐Turonian aged and is composed by the transgressive and high stand systems tracts. Depositional sequences 4 and 5 are, respectively, late Turonian to mid‐Santonian and late Santonian to mid‐Campanian aged and are composed only by transgressive and high stand systems tracts. The lack of falling stage and low stand systems tracts in depositional sequences 3, 4 and 5, as well the increasing in transgressive and highstand systems tracts thickness as depositional sequences get younger, are reflection of an overall transgressive trend of a 2nd‐order sequence. The interpretation proposed in this paper correlates onshore with offshore deposits within a seismic scale (3rd‐order) sequence stratigraphy framework. This approach allows a better understanding of the Açu Formation, the primary oil‐bearing formation of the Potiguar Basin. The Açu Formation is part of depositional sequences 1, 2 and 3 and is characterized by lateral and vertical variations of depositional systems instead of being associated to a specific depositional system. This sequence stratigraphy analysis can be used as a low‐resolution framework for future high‐resolution (4th‐order scale) studies.

The five 3rd order depositional sequences interpreted in Albian do Campanian interval of Potiguar Basin, as well the system tracts, and its relation with the lithostratigraphic units. The Açu Formation, main oil‐bearing formation of the basin, in inserted in the Depositional Sequences 1 to 3 context.

We present a photogrammetry‐based 3D reconstruction of Hjörleifshöfði in southern Iceland which provides an exceptional outcrop exposure of an emergent hyaloclastite sequence. By incorporating detailed facies interpretations and laboratory petrophysical analyses into the model, we have produced pseudo‐wireline logs and property distribution maps to demonstrate the variability of physical properties at seismic scale. Our study provides an improved understanding of the petrophysical property distribution within hyaloclastite sequences and forms a valuable step towards improving the understanding of similar subsurface sequences and their implications for imaging and fluid flow.

Hyaloclastites develop where lava interacts with water resulting in deposits that have a unique and often complex range of petrophysical properties. A combination of eruptive style and emplacement environment dictates the size, geometry and distribution of different hyaloclastite facies and their associated primary physical properties such as porosity, permeability and velocity. To date, links between the 3D facies variability within these systems and their petrophysical properties remain poorly understood. Hjörleifshöfði in southern Iceland presents an exceptional outcrop exposure of an emergent hyaloclastite sequence >1 km wide by >200 m high and enables an investigation of the distribution of the hyaloclastite deposits at seismic scale. Within this study we present a photogrammetry‐based 3D model from part of this recent hyaloclastite delta and incorporate previous work by Watton et al. (Journal of Volcanology and Geothermal Research, 2013, 250, 19) to undertake detailed facies interpretation and quantification. Laboratory petrophysical analyses were performed on 34 core plugs cut from key field facies samples, including P‐ and S‐wave velocity, density, porosity and permeability at both ambient and confining pressure. Integration of the 3D model with the petrophysical data has enabled the production of pseudo‐wireline logs and property distribution maps which demonstrate the variability of physical properties within hyaloclastite sequences at outcrop to seismic scale. Through comparison of our data with examples of older buried hyaloclastite sequences we demonstrate that the wide‐ranging properties of young hyaloclastites become highly uniform in older sequences making their identification by remote geophysical methods for similar facies variations more challenging. Our study provides an improved understanding of the petrophysical property distribution within hyaloclastite sequences and forms a valuable step towards improving the understanding of similar subsurface sequences and their implications for imaging and fluid flow.

Deep‐water syn‐rift systems develop in partially‐ or transiently‐linked depocentres to form complicated depositional architectures, which are characterised by short transport distances, coarse grain sizes and a wide range of sedimentary processes. Exhumed systems that can help to constrain the tectono‐stratigraphic evolution of such systems are rare or complicated by inversion tectonics. Here, we document a mid‐Pleistocene deep‐water syn‐rift system fed by Gilbert‐type fan deltas in the hangingwall of a rift margin fault bounding the West Xylokastro Horst block, on the southern margin of the Gulf of Corinth, Greece. Structural and stratigraphic mapping combined with digital outcrop models permit observations along this syn‐rift depositional system from hinterland source to deep‐water sink. The West Xylokastro Fault hangingwall is filled by two distinct sediment systems; an axial system fed by coarse‐grained sediment gravity flows derived from fault‐tip Gilbert‐type fan deltas and a lateral system dominated by mass transport deposits fed from an evolving fault‐scarp apron. Abrupt changes in stratigraphic architecture across the axial system are interpreted to record changes in relative base level, sediment supply and tectonics. Locally, depositional topography and intra‐basinal structures controlled sediment dispersal patterns, from bed‐scale infilling of local rugose topography above mass transport complexes, to basin‐scale confinement from the fault scarp apron. These acted to generate a temporally and spatially variable, heterogeneous stratigraphic architecture throughout the basin‐fill. The transition of the locus of sedimentation from a rift margin to a fault terrace through the syn‐sedimentary growth of a basinward fault produced regressive surfaces updip, which manifest themselves as channels in the deep‐water realm and acted to prograde the system. We present a new conceptual model that recognises coeval axial and transverse systems based on the stratigraphic architecture around the West Xylokastro fault block that emphasizes the lateral and vertical heterogeneity of rift basin‐fills with multiple entry points.

Deep‐water syn‐rift depocentres are characterised by short transport distances, coarse grain sizes and variety of sedimentary processes, all of which interact with complex intra‐basinal topography and structural evolution (a). This axial depositional system interacts with coeaval, mass‐transport dominated transverse systems sourced from the growing West Xylokastro Fault to shift the locus of sedimentation in the axial system far from the immediate hangingwall region in what is ultimately a relatively narrow (5‐6 km) fault terrace. Abrupt changes in stratigraphic architecture across the axial system record relative base‐level, sediment supply and subsidence variability which is complicated by local depositional topography and intra‐basinal structures (b). Exhumed systems can help constrain the tectono‐stratigraphic evolution of such systems, however these are rare or often complicated by inversion tectonics. However, the West Xylokastro Fault Block (Gulf of Corinth, Greece) offers superb exposures of an Early‐Mid Pleistocene Gilbert‐type fan delta and downdip, axial deep‐water depositional system in the hangingwall of a rift margin fault (c). Here we provide new conceptual models for the evolution of multi‐input, deep‐water syn‐rift depocentres and characterise the scale and nature of the variability of depositional systems within them.

We utilized carbonate clumped isotope thermometry to explore the thermal history of the Delaware Basin, West Texas, USA. Carbonate wellbore cuttings from five oil/gas wells across the basin yielded clumped isotope temperatures (T(Δ47)) ranging from 27°C to 307°C, interpreted to reflect a combination of initial precipitation/recrystallization temperature and solid‐state C‐O bond reordering during burial. Dolomite samples generally record lower apparent T(Δ47)s than calcite, reflecting greater resistance to reordering in dolomite. In all five wells, clumped isotope temperatures exceed modern downhole temperature measurements, indicating higher heat flow in the past. Using modelled burial curves based on sedimentological history, we created unique time‐temperature histories by linearly applying a geothermal gradient. Applying two different thermal history reordering models, we modelled the extent of solid‐state C–O bond reordering to iteratively find the time‐averaged best‐fit geothermal gradients for each of the five wells. Results of this modelling suggest that the shallower, southwestern portion of the study area experienced higher geothermal gradients throughout the sediment history (~45°C/km) than did the deeper, southeastern portion (~32°C/km), with the northern portion experiencing intermediate geothermal gradients (~35–38°C/km). This trend is in agreement with the observed gas/oil ratios of the Delaware Basin, increasing from east to west. Furthermore, our clumped isotope temperatures agree well with previously published vitrinite reflectance data, confirming previous observations and demonstrating the utility of carbonate clumped isotope thermometry to reconstruct basin thermal histories.

We used clumped isotope thermometry to explore past geothermal gradients for five wells in the Delaware Basin, West Texas, USA. Measured Δ47 temperatures range from 27–307°C, with most temperatures significantly higher than the modern geothermal gradient. We calculated past geothermal gradients using clumped isotope reordering models, revealing a range of past geothermal gradients from 32°C/km in the eastern portions of the basin to 45°C/km in the western portion.

Understanding continental‐slope morphological evolution is essential for predicting basin deposition. However, separating the imprints and chronology of different seafloor shaping processes is difficult. This study explores the utility of bathymetric spectral decomposition for separating and characterizing the variety of interleaved seafloor imprints of mass wasting, and clarifying their role in the morphological evolution of the southeastern Mediterranean Sea passive‐margin slope. Bathymetric spectral decomposition, integrated with interpretation of seismic profiles, highlights the long‐term shape of the slope and separates the observed mass transport elements into several genetic groups: (1) a series of ~25 km wide, now‐buried slide scars and lobes; (2) slope‐parallel bathymetric scarps representing shallow faults; (3) slope‐perpendicular, open slope slide scars; (4) bathymetric roughness representing debris lobes; (5) slope‐confined gullies. Our results provide a multi‐scale view of the interplay between sediment transport, mass transport and shallow faulting in the evolution of the slope morphology. The base of the slope and focused disturbances are controlled by ~1 km deep salt retreat, and mimic the Messinian base of slope. The top of the open‐slope is delimited by faults, accommodating internal collapse of the margin. The now‐buried slides were slope‐confined and presumably cohesive, and mostly nucleated along the upper‐slope faults. Sediment accumulations, infilling the now‐buried scars, generated more recent open‐slope slides. These latter slides transported ~10 km³ of sediments, depositing a significant fraction (~3 m in average) of the sediments along the base of the studied slope during the past < 50 ka. South to north decrease in the volume of the open‐slope slides highlight their role in counterbalancing the northwards diminishing sediment supply and helping to maintain a long‐term steady‐state bathymetric profile. The latest phase slope‐confined gullies were presumably created by channelling of bottom currents into slide‐scar depressions, possibly establishing incipient canyon headword erosion.

The southeastern mediterranean continental slope bathymetry is impacted by interleaved imprints of mass transport processes. These are delineated, classified and mapped through semi‐automatic bathymetric spectral decomposition, appraising their role in sediments bypassing and maintenance of a long‐term shelf‐to‐basin equilibrium profile.

Our current understanding on sedimentary deep‐water environments is mainly built of information obtained from tectonic settings such as passive margins and foreland basins. More observations from extensional settings are particularly needed in order to better constrain the role of active tectonics in controlling sediment pathways, depositional style and stratigraphic stacking patterns. This study focuses on the evolution of a Plio‐Pleistocene deep‐water sedimentary system (Rethi‐Dendro Formation) and its relation to structural activity in the Amphithea fault block in the Corinth Rift, Greece. The Corinth Rift is an active extensional basin in the early stages of rift evolution, providing perfect opportunities for the study of early deep‐water syn‐rift deposits that are usually eroded from the rift shoulders due to erosion in mature basins like the Red Sea, North Sea and the Atlantic rifted margin. The depocentre is located at the exit of a structurally controlled sediment fairway, approximately 15 km from its main sediment source and 12 km basinwards from the basin margin coastline. Fieldwork, augmented by digital outcrop techniques (LiDAR and photogrammetry) and clast‐count compositional analysis allowed identification of 16 stratigraphic units that are grouped into six types of depositional elements: A—mudstone‐dominated sheets, B—conglomerate‐dominated lobes, C—conglomerate channel belts and sandstone sheets, D—sandstone channel belts, E—sandstone‐dominated broad shallow lobes, F—sandstone‐dominated sheets with broad shallow channels. The formation represents an axial system sourced by a hinterland‐fed Mavro delta, with minor contributions from a transverse system of conglomerate‐dominated lobes sourced from intrabasinal highs. The results of clast compositional analysis enable precise attribution for the different sediment sources to the deep‐water system and their link to other stratigraphic units in the area. Structures in the Amphithea fault block played a major role in controlling the location and orientation of sedimentary systems by modifying basin‐floor gradients due to a combination of hangingwall tilt, displacement of faults internal to the depocentre and folding on top of blind growing faults. Fault activity also promoted large‐scale subaqueous landslides and eventual uplift of the whole fault block.

Tectono‐sedimentary models of the evolution of the Rethi‐Dendro Formation depositional environment in the Amphithea fault block. Plio‐Pleistocene syn‐rift of the Corinth Rift, Greece.

Previous work has demonstrated the presence of a number of exhumed hydrocarbon traps in central East Greenland. Re‐evaluation of the stratigraphy alongside detailed investigation of the occurrence of bitumen within the Mols Bjerge and Laplace Bjerg exhumed hydrocarbon traps provides new perspectives on these structures, as well as the petroleum geology of East Greenland and the wider North Atlantic. Sedimentological and stratigraphic studies, augmented with palynological and provenance investigations, have constrained the dating and correlation of the strata exposed in the Mols Bjerge and Laplace Bjerg. Petrographic analysis, alongside analysis of the bitumen identified, has highlighted a much wider distribution of hydrocarbon than previously recognized. It was previously considered that Jurassic strata formed the main reservoir interval within the Mols Bjerge and Laplace Bjerg exhumed hydrocarbon traps. It is shown here that the reservoir intervals in the Laplace Bjerg trap lie within the Late Triassic Ørsted Dal and Vega Sund members, which contain up to 18% pyrobitumen and were previously misidentified as Jurassic. The Jurassic Bristol Elv Formation is the most extensively bitumen stained unit in the Mols Bjerge trap. However, occurrences of pyrobitumen (up to 3%) are recorded throughout the Triassic stratigraphy, including the Early Triassic Wordie Creek Formation. Faults, thick calcrete development and regionally continuous mudstone units play an important role in compartmentalizing the palaeohydrocarbon accumulations.

The Laplace Bjerg exhumed hydrocarbon trap in East Greenland. Superb exposures of both this fault bounded horst and the tilted fault block of the Mols Bjerge have allowed detailed mapping to be carried out. Both of these exhumed hydrocarbon traps were sealed, at depth, by Cretaceus mudstones, which blanketed much of East Greenland. The identification of pyrobitumen, resulting in a dark staining in the sandstones, has allowed the distribution of the palaeohydocarbon accumulation to be assessed and intra reservoir compartmentalisation by thick, mature calcretes to be recognised. Palynological analysis has determined a Triassic age for the main reservoir units providing evidence for a further potential play in the North Atlantic petroleum system.

In a recent study, Andrews et al. (2020) describe “exhumed hydrocarbon traps” in North‐East Greenland. The basic premise for their interpretation is that dark‐coloured, pyrobitumen‐bearing sandstones represent the remnants of once buried petroleum reservoirs. We do not see the necessary field or analytical evidence to support a model that has strong implications for resource evaluations. Andrews et al. (2020) have not considered previous published information on diagenetic and thermal maturity history of the area. A more probable model would include the intrusion of dykes and sills into a sedimentary succession with immature petroleum source rocks and reservoir‐quality sandstones. The heating caused rapid generation of petroleum components and local hydrothermal circulation systems in adjacent porous sandstones. Any petroleum was rapidly destroyed leaving essentially only black grain‐coatings and minor particles of pyrobitumen—essentially in one short‐lived continuous process. The existence of new plays in the North Atlantic as proposed by Andrews et al. (2020) is in our opinion not substantiated as this requires analytical data from unaltered oils from the less mature parts of the sedimentary succession and considerations of thermal maturity and basin evolution. To draw conclusions that have a serious impact on resource evaluations based on the dark colouration of sandstones without comprehensive analytical data is, in our opinion, ill advised.