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Glacio-eustatic cycles lead to changes in sedimentation on all types of continental margins. There is, however, a paucity of sedimentation rate data over eustatic sea-level cycles in active subduction zones. During International Ocean Discovery Program Expedition 375, coring of the upper ∼110 m of the northern Hikurangi Trough Site U1520 recovered a turbidite-dominated succession deposited during the last ∼45 kyrs (Marine Isotope Stages (MIS) 1–3). We present an age model integrating radiocarbon dates, tephrochronology, and δ18O stratigraphy, to evaluate the bed recurrence interval (RI) and sediment accumulation rate (SAR). Our analyses indicate mean bed RI varies from ∼322 yrs in MIS1, ∼49 yrs in MIS2, and ∼231 yrs in MIS3. Large (6-fold) and abrupt variations in SAR are recorded across MIS transitions, with rates of up to ∼10 m/kyr occurring during the Last Glacial Maximum (LGM), and

Turbidite palaeoseismology has produced arguably the most comprehensive multimillennial scale records of subduction-zone earthquakes but is underpinned by techniques that are vigorously debated in earthquake science. Resolving this argument requires new direct observations that test the approach’s essential assumptions. Here we present measurements from turbidites triggered by the 2016 M 7.8 Kaikōura earthquake in New Zealand, one of the most well-instrumented earthquakes in history. This natural experiment provides an ideal test for turbidite palaeoseismology because fault source, ground motions and turbidite deposition in discrete canyons are well-resolved by analysis of sediment cores combined with physics-based ground-motion modelling. We find that the Kaikōura earthquake triggered flows in ten consecutive canyon–distributary systems along a 200 km segment of the Hikurangi subduction margin where long-period (>2 s) peak ground velocities exceeded turbidity-current-triggering thresholds between 16–25 cm s. Comparison between ground motions and turbidite deposition confirm that there is a predictable relationship between earthquake source, ground motions and deposition of coseismic turbidites. We demonstrate that the patterns of triggering and resultant turbidite character may preserve evidence of fault-rupture direction along with the radiating patterns and amplification of earthquake ground motions.

This is the articlesSupplementary Appendix 1. Measured foraminiferal data for 2016 Kaikōura turbidite samples used in analyses. It contains information on all the foraminiferal samples studied from the 2016 turbidite in cores at bathyal and abyssal depths down the canyons and abyssal Hikurangi Channel, test size distribution, planktic percentage, absolute number of tests, planktic foraminiferal fragmentation index and census counts on key benthic foraminiferal genera. &nbsp

This is the first of a two-part New Zealand Journal of Geology and Geophysics Special Issue that focuses on improving our understanding of sedimentary systems of the Hikurangi Subduction Margin, Aotearoa-New Zealand. It is amongst the world’s youngest and most accessible active subduction margins and its sedimentary basins preserve a rich history of inception and ongoing evolution, spanning trench to back-arc positions. These sediments and sedimentary rocks provide a record of surface processes from the latest Paleogene to today, and reflect the spatio-temporal variability of the effects of subduction, seismicity, volcanism, evolving sediment sources, routing systems and processes, all imprinted upon by glacio-eustatic sea-level changes. The papers in this volume focus on the interplay between controlling mechanisms and the dynamics of these systems, from both onshore and offshore sedimentary environments. This issue is divided into two themes, distinguished by geological age: 1. Miocene Sedimentary Systems and intra-slope basin evolution, and 2. Insights from Quaternary Sedimentary Systems from the trench to the inner margin. Collectively, these papers represent significant advances into our understanding of sedimentary systems within the Hikurangi Subduction Margin, with innovative results that may find applications to other convergent settings.

This study uses a combination of regional ocean modelling systems (ROMS), a sediment transport model (sedtrans05) and detailed grainsize data with the aim of determining the hydrodynamics and prima...

The Australian Government Research Training Program Scholarship funded Craig’s Ph.D. candidature. An International Association of Sedimentologists Postgraduate Award Grant funded Craig’s visit to Bangor University (Bangor, UK). The UK Natural Environment Research Council grant NE/1027223/1 (COHBED project) enabled this research to be undertaken using the flume facility built by Rob Evans (Bangor University). Sediment gravity flows are the primary process by which sediment and organic carbon are transported from the continental margin to the deep ocean. Up to 40% of the total marine organic carbon pool is represented by cohesive extracellular polymeric substances (EPS) produced by microorganisms. The effect of these polymers on sediment gravity flows has not been investigated, despite the economic and societal importance of these flows. We present the first EPS concentrations measured in deep-sea sediment, combined with novel laboratory data that offer insights into the modulation of the dynamics of clay-laden, physically cohesive sediment gravity flows by biological cohesion. We show that EPS can profoundly affect the character, evolution, and runout of sediment gravity flows and are as prevalent in deep oceans as in shallow seas. Transitional and laminar plug flows are more susceptible to EPS-induced changes in flow properties than turbulent flows. At relatively low concentrations, EPS markedly decrease the head velocity and runout distance of transitional flows. This biological cohesion is greater, per unit weight, than the physical cohesion of cohesive clay and may exert a stronger control on flow behavior. These results significantly improve our understanding of the effects of an unrealized biological component of sediment gravity flows. The implications are wide ranging and may influence predictive models of sediment gravity flows and advance our understanding about the ways in which these flows transport and bury organic carbon globally. Publisher PDF

Both the duration and severity of deep-water anoxic conditions across the Permian-Triassic mass extinction (PTME) are controversial. Panthalassa Ocean circulation models yield varying results, ranging from a well-ventilated deep ocean to rapidly developing northern-latitude, but not southern-latitude, anoxia in response to Siberian Traps–driven global warming. To address this uncertainty, we examined a southern-paleolatitude pelagic record. Trace metal and pyrite framboid data suggest bottom-water euxinic conditions developed in the southern Panthalassa Ocean at the PTME, coincident with enhanced volcanic activity indicated by Hg geochemistry. While a global ocean euxinic event at the PTME placed extraordinary stress on marine life, southern surface waters appear to have recovered more quickly as radiolarian populations returned several million years before they did in northern Panthalassa.

The deep-water record of marine anoxia across the Permo-Triassic mass extinction (PTME) is highly controversial; both the length of time and severity of anoxic conditions are uncertain. Panthalassa Ocean circulation models show varying results, ranging from a well-ventilated deep ocean to rapidly developing northern, but not southern, latitude anoxia in response to Siberian Traps driven global warming. To address this uncertainty we examined a southern paleo-latitude pelagic record. Trace metal and pyrite framboid data show bottom water euxinc conditions developed in the southern Panthalassa Ocean at the PTME, coincident with enhanced volcanic activity indicated by Hg geochemistry. While a global deep-ocean euxinic event at the PTME placed extraordinary stress on marine life, southern surface waters appear to have recovered more quickly as radiolarian populations return several million years before they do in northern Panthalassa.

The distribution of benthic ecosystems, dominated by filter-feeding communities, is highly influenced by the seabed geomorphology. However, the spatial variation in settlement of these species is also affected by near-bottom currents and any changes in light, nutrient concentration and food quality often associated with increases of suspended sediment concentrations within the water column. Detailed predictions of the geographic distribution of filter-feeder species and a deeper understanding of the physical processes influencing their distribution patterns is key for effective management and conservation. To date, predictive distribution modelling has been derived essentially from geomorphological parameters, mainly using spatially limited observations. In this study, seabed mapping, oceanographic modelling, hydrographic records and biological observations are integrated to provide high-resolution prediction of filter-feeder habitat distribution within Queen Charlotte Sound/Tōtaranui and Tory Channel/Kura Te Au, South Island of New Zealand. The aim is to evaluate potential suitable habitat areas for filter-feeders to inform where habitat restoration management should focus efforts to recover communities such as the horse mussel (Atrina zelandica) or the green-lipped mussel (Perna canaliculus), both of which have high economic impact in New Zealand. To accomplish this, Maximum Entropy (MaxEnt) predictive modelling was used to produce Habitat Suitability (HS) maps, using geomorphological parameters and seafloor classification information. Final HS maps also incorporated oceanographic and sediment dynamic information, showing that filter-feeder habitat distribution is highly influenced by the hydrodynamics and sedimentary processes apart from the seafloor geomorphology. Filter-feeder communities inhabit quiescent areas, limited by depth, slope and sediment type; and coincide with regions presenting low near-bottom currents and low turbidity levels. Additionally, the obtained results reveal the effects of the coastal settlements and major marine traffic routes, limiting the suitable habitats to areas with less human impact. This study demonstrates that a multidisciplinary approach is crucial to better predict the spatial distribution of benthic communities, which is key to improve benthic habitat restoration and recovery assessments.

To better understand earthquake reoccurrence and hazard, records of ancient earthquakes spanning millennia are routinely generated using seabed turbidite deposits, inferred to be synchronously triggered by strong ground motions over large geographic areas. However, the use of turbidites for paleoseismology is underpinned by untested hypotheses due to the dearth of verified earthquake-triggered turbidite deposits produced by well-characterised earthquakes. The aim of a RV Tangaroa voyage in October 2019 was to use the unique opportunity provided by the widespread and documented occurrences of the 2016 Mw7.8 Kaikōura earthquake-triggered turbidite to determine whether synchronous turbidite deposition can be reconstructed from the sedimentary record alone. Our presentation will summarise insights gleaned from precision short cores and high-resolution sub-bottom profiles collected along and across the axis of submarine canyons that preserve turbidite deposits triggered by the Kaikōura earthquake. Planned detailed laboratory characterisation of the turbidites will include high-resolution core imaging, texture, densitometry, down-core physical properties and geochemical characterisation combined with radioisotope-derived chronology. Through repeat coring at historical sites and future coring campaigns we hope to also quantify the impact of biological mixing on the Kaikōura event deposit to determine its likely preservation potential in the geological record. Our results have the potential to provide the first robust test of turbidite paleoseismology.

Highlights • Sedimentary characteristics and geochemistry of tephra deposits are reported across 21 cores. • Four types of tephra lithofacies are distinguished. • Geomorphic sub-environments play a key role in tephra preservation. • Isolated semi-confined basin settings generally preserve the highest number of tephra deposits. • For eruptions VEI≥6 volcaniclastic sediments may swamp the marine system for centuries. Tephra (volcanic ash) deposits are important isochronous markers for correlating marine sediments or events recorded in marine sediment cores. However, the active tectonics that are commonly associated with volcanic activity at plate tectonicboundaries also drive large-scale deformation, leading to steep and variable local and regional bathymetry (e.g., ridges, basins and canyons systems). This complex bathymetry influences gravity-flow behaviour and paths, which can rework and redeposit tephras, resulting in stratigraphic complexities. Such as, the mis-identification of primary versus reworked tephra deposits, and in turn lead to the development of inaccurate chronostratigraphies. Here we present 36 tephra deposits from 21 shallow marine sediment cores that traverse the length of the southern and central margin of eastern North Island, New Zealand. Using major and trace element geochemical compositions for glass shards from the tephras, we correlate these deposits to three major rhyolitic eruptions from the Taupō Volcanic Zone (TVZ) approximately 200 km west, including; Taupō (1718 cal yrs. BP), Kaharoa (636 cal yrs. BP), and Kawakawa/Oruanui (KOT; 25.4 ka). Based on their morphology, depositional character and inferred emplacement mechanisms, the tephra deposits are grouped into four lithofacies types; (1) primary deposits, (2) volcaniclastic-rich turbidites, (3) blebs/pods of volcaniclastic-rich material, and (4) complex deposits. Primary deposits form syn-eruptively through airfall onto the ocean surface, settling over hours to days through the water column under diffuse vertical gravity currents. Volcaniclastic-rich turbidites are formed through secondary redeposition and entrainment by post-eruptive turbidity currents, while blebs/pods of material are interpreted to have formed by erosion and/or bioturbation. Complex deposits form through the interaction of all these mechanisms producing an overthickened array of primary and redeposited units within a single facies. Herein, we argue that redeposited units of volcaniclastic-rich turbidites or small blebs/pods can be used as tentative chronological markers if the geochemical composition of the glass shards have a homogeneous signature, i.e. a single eruptive source. Where the glass shards in redeposited units have mixed geochemical compositions, and are not stratigraphically associated with a primary deposit source, they cannot be used as chronological marker horizons. This emphasises the need for accurate and rigorous data reduction without overlooking the importance of data points that are statistical outliers. We also show that the highest preservation of tephra deposits is found in semi-confined isolated basin settings, including a wide range of deposit types. Due to erosive sediment flows that bypass through submarine distributary systems, these major sediment dispersal pathways preserve few volcaniclastic deposits. Our findings have important implications not only for identifying primary or redeposited characteristics in marine tephras for building accurate chronostratigraphies, but also as a guide geomorphic sub-environments with the best preservation of tephras in marine sedimentary systems.

Distributive submarine fans contain channel-lobe elements that compensationally stack to build a radially dispersive map pattern. The middle parts of some submarine fans contain juxtapositions of channel elements and lobe elements due to longitudinal and lateral shifts in their channel-lobe transition zones. This article uses an exceptionally well-exposed three-dimensional outcrop of the Ross Sandstone at Bridges of Ross (Ireland) to document the stratigraphic and plan-view manifestation of lateral juxtapositions of channel elements and lobe elements in submarine fans. Observations made herein compare favorably to those in seafloor studies of Navy Submarine Fan (offshore southern California, USA) by William Normark and others, indicating that these systems can be used as paired outcrop-seafloor analogs for distributive fans in which the channel-lobe transition zones are located in longitudinally variable positions. In addition, data from Bridges of Ross and Navy Submarine Fan are integrated to constrain a geometric model that predicts the fractional length of a fan that contains lateral juxtapositions of channel elements and lobe elements. Lateral juxtapositions of channel elements and lobe elements are important because they enhance vertical and lateral connectivity within subsurface reservoirs.

The effect of vertical changes in lithology on cleavage refraction and cleavage fanning is relatively well understood. In contrast, the control that lateral changes in bed thickness and related multilayer characteristics have on cleavage fanning has not been widely documented. Mudstone-dominated Wenlock-age turbidites of the Anglo-Brabant Deformation Belt, Belgium, exhibit pronounced lateral thickness changes, which we attribute to intraslope flow ponding during foreland basin development. The mudstone-dominated nature of the turbidites is considered to reflect a particularly fine-grained source area, rather than a distal origin. Formation boundaries and lateral changes in lithofacies unit thickness are reflected in the amount of cleavage fanning. The degree of convergent cleavage fanning increases with an increase in thickness of the less competent units and with a decrease in thickness and number of the more competent units. As such, a detailed analysis of changes in cleavage–bedding angle aids in the distinction of different lithostratigraphic units of similar appearance, the location of their boundaries and identification of subtle lateral sedimentological changes. The utilization of cleavage and bedding data to recognize and describe vertical and lateral changes in a semi-quantitative way allows the linkage of subtle changes in multilayer rheology to finite strain trajectories. Supplementary materials: Details of position of lithological profiles are available at www.geolsoc.org.uk/SUP18708.

Turbidites from three sedimentary basins data, and probably the A.D. 1826 Fiordland earthquake and the well‐dated A.D. 1717 Alpine fault earthquake. The recurrence intervals are shorter than recently published recurrence data from the Alpine fault on land, reflecting mixed fault‐source earthquake records and potentially increased Alpine fault segmentation offshore. Online Material: Details of the laboratory methods and analytical techniques applied to sedimentrary cores, photos of seafloor substrates and fan core, OxCal codes and results, and sediment transport analysis. [1]: /embed/inline-graphic-1.gif

New, high-resolution lithofacies data from hanging-wall Miocene synrift (Rudeis Formation) exposures of the eastern Suez Rift margin, Egypt, reveal a submarine slope depositional system dominated by coarse-grained (pebble), heterogeneous, lenticular beds, formed by coalescing turbidity currents, slumps, and debris flows deposited on deforming submarine substrate. Flows include prerift clasts and contemporaneous shallow-marine fossil fragments originating from an uplifted eastern hinterland. Multiple terrestrial drainages debouched onto faulted offshore slopes or fed small fan deltas on narrow shelves ( 360 m Rudeis Formation is divided into stratigraphic units R1 and R2, which exhibit upward-coarsening and unordered vertical motifs. Ongoing faulting influenced synrift deposition by controlling the locus of subsidence and gravity base level. Mesoscale faults became inactive during Rudeis Formation times, with strain localized on the large rift border fault system, leading to a wider basin with time. We compare 16 subaqueous rift-margin basin fills from various tectonic and geographic settings and show they generally represent proximal gravity-flow deposits dominated by nongraded beds. We find little commonality in vertical grain-size trends, highlighting the diversity of stratal architectures. Most basin fills show an inverse relationship between maximum clast size and shelf width. We propose a new model to capture the spectrum of sedimentary responses to rifting within rift-margin basins, varying as a function of shelf width, slope gradient, maximum grain size, and textural maturity. Rudeis Formation strata at north Wadi Baba represent a particularly coarse-grained end member, deposited on steep slopes, with a narrow shelf.

Theprocessbywhichslumpstransform intootherflowtypesisanunderstudied phenomenon; generally, sedimentologists have assumed that this is how many debris flows and turbidity currents form, yet there is a paucity of information relating to the specific processes involved. This paper aims to redress this imbalance and investigates the processes of slump flow transformation using a well-exposed example, where the precursor slump and flows to which it was transforming have been preserved in the outcrop. A detailed field investigation of the Lower Miocene, Little Manly Slump, located within the Waitemata Basin, New Zealand, reveals a complex bi-partite deposit, comprised of a lower slumpdebrite unit and an upper turbidite unit, separated from one another by an impersistent contact. Reconstruction of slump evolution, from preserved strain indicators, shows that slump motion was unsteady and non-uniform, and that the slump arrested rapidly. Flow transformation is directly linked to slump evolution and progressed through the multiple processes of body transformation, fluidization transformation and surface transformation. The resultant flow comprised a very dense lower unit with slump and debris flow phases overlain by a turbidity current. This study shows that flow transformation did not result in en masse transformation to a debris flow by a single process, but rather it was characterized by partial transformation of the slump to generate a three-phase flow. Density is thought to be the key parameter in controlling flow transformation efficiency, which appears to have varied rapidly as a function of slump unsteadiness and non-uniformity.

Folds and faults preserved within slump horizons are thought to be the only sedimentary structures that primarily reflect palaeoslope direction. By evaluating methods for the analysis of slump folds, the robustness of many palaeoslope and palaeogeographical reconstructions can be tested. Five methods for estimating palaeoslope direction from slump fold orientation data are tested with reference to the Upper Carboniferous Fisherstreet Slump horizon of County Clare, Ireland. These methods are the Mean Axis Method, the Separation Arc Method, the Downslope Average axis Method, the Axial–planar Intersection Method and the Fold Hinge Azimuth and Interlimb Angle Method. Transport determination techniques have mixed success when applied to this example and reveal a mean downslope transport direction of 067°. This result reflects the varied boundary conditions that are possible during slumping, resulting from variations in initial fold geometries, progressive fold formation, spatial and temporal changes in velocity, material properties, pore fluid pressures and the local slope. Without a comprehensive analysis of slump data – using all available techniques – large errors in interpreted transport direction can exist and may invalidate palaeogeographic reconstructions. It is essential to use as many transport determination techniques as possible to determine slip direction accurately. With this in mind, a general procedure for determining palaeoslope directions is suggested and used to examine existing palaeogeographic models for the Clare Basin.

Remobilization of sandstones can dramatically reconfigure original depositional geometries and results in very unusually shaped sandstones, which resemble little, if any, of the original geometry. A number of deformational sandstone bodies, dykes and volcanoes from the upper part of the Carboniferous Ross Formation are described, which offer the opportunity to examine a suite of field-scale reconfigured sandstones. These structures are located in close proximity to the Ross Slide, which outcrops along a 2-km section on the northern coast of the Loop Head Peninsula, County Clare, Ireland. Dome- and ridge-shaped deformational sandstone bodies, dykes and volcanoes are interpreted to be the product of remobilization of a turbiditic sandstone. Liquification and remobilization were triggered by translation, cessation and loading of the underlying turbiditic sandstone by the Ross Slide. Deformational sand body, dyke and volcano development occurred in an asynchronous fashion with deformational sand bodies formed during slump translation. Sand dykes and volcanoes developed after the cessation of slump movement. During slump translation, the minimum principal stress (σ 3 ) was orientated vertically and the slump behaved in a 'ductile' manner. After slump arrest, the minimum principal stress was oriented horizontally, and the unit regained shear strength to behave in a 'brittle' manner. The relative change in rheological states with changing applied shear stress is indicative of thixotropic-like behaviour within the slump mass. Ridge-shaped deformational sand bodies are aligned parallel to slump folds, and their morphology is inferred to be controlled by compressional slump deformation associated with heterogeneous cessation of slump movement that was initiated by frontal arrest of the translating mass.

New sedimentary geochemistry and petrographic analyses provide the most extensive sedimentary documentation yet of the rapid denudation of the young Timor orogen. The data from three basins including two widely-separated, well-dated sections of the Synorogenic Megasequence of Timor-Leste, and a re-dated DSDP 262, constrain the source and timing of detrital sediment flux during forearc-continent collision along the Timor sector of the Banda Arc. The exhumed synorogenic piggy-back basins formed above a melange unit that developed at the expense of a weak stratigraphic horizon in the Mesozoic stratigraphy, and was exhumed to the sea floor in latest Messinian time. Following an interval of deep marine chalky marl sedimentation, an increasingly muddy sediment flux indicates that the island of Timor became emergent and shed sediment by 4.5 Ma. Comparison of exhumed sections with similar patterns in the DSDP262 chemistry suggests that the sediment source was probably located some 50–60 km distant from the basin, which is consistent with the Aileu region of Timor-Leste that shows an appropriate exhumation history. All sedimentation between 4.5 and 3.2 Ma was probably derived from a low-relief, rapidly eroding, and mudstone-dominated landscape with geochemical affinities to the Triassic-mudstone-derived synorogenic melange. The melange unit overlies and surrounds the Banda Terrane, and was presumably structurally emplaced by propagation of a decollement through the Triassic rocks during the collision. After 3.2 Ma, sedimentation was dominated by hard rock lithologies of the Banda Terrane, consisting of forearc cover and basement, the latter including elements of metamafic rocks and metapelites. This phase of sedimentation was accompanied by rapid uplift, which may have been partly driven by a transient imbalance between rock uplift and denudation as resistant lithologies emerged from below melange-like mudstone. Previous work has suggested that the timing of collision in Timor-Leste and West Timor was substantially different. Our reevaluation of DSDP 262 facies migration history in the context of the re-dating presented here, favours a relatively synchronous onset of uplift in both halves of the island, but with different partitioning of strain between the foreland and hinterland in each half of the island.

[1] The early Miocene Waitemata Basin has long been described as an interarc/intra-arc basin, formed between twin chains of arc volcanoes in Northland, New Zealand. However, deep marine, polymict, volcaniclastic conglomerates within the basin reveal tectonic and magmatic signals that are not evident from neighboring volcanic edifices. The conglomerates were deposited by high-density turbidity currents and debris flows and include single sediment cycle megaclasts of lava. These basaltic lavas have ocean island basalt (OIB)-like geochemical affinities and are precisely dated at 20 Ma by 40Ar-39Ar methods. Their age and the occurrence of subordinate clasts derived from an ophiolitic nappe to the north indicate the basin postdates the initiation of collision in the wider region. Contemporaneous calc-alkaline volcanism did occur some 250 km NW of the basin. However, the conglomerates lack clasts of calc-alkaline/arc affinities indicating an absence of arc-like volcanism in the vicinity of the basin. Recent tectonic models for the SW Pacific region and mantle tomography highlight the importance of wholesale slab detachment in driving early Miocene calc-alkaline volcanism and basin development. Although such models provide a slab window for the eruption of nonarc OIB-like magmas, they would not explain their localized occurrence at the proposed leading edge of the tear (Waitemata Basin), rather than progressively along the entire length of the detachment (Northland), as seen in other detachment settings. In addition, OIB-like volcanism predates the adjacent calc-alkaline volcanism on the margin of the basin, a transition that is the opposite of that found at other slab detachment settings. The occurrence of OIB-like volcanism is better explained by a lateral slab termination in the vicinity of the Waitemata Basin that allowed asthenospheric-derived magmas to erupt. The basin is inferred to have developed in response to asthenospheric upwelling and associated lithospheric extension or deformation associated with a slab termination zone. This study highlights the importance and potential of combined geochemical, geochronological, and sedimentological studies of conglomerates in reconstructing the geodynamic setting of a basin.