The seismically active Australian North West Shelf (NWS) hosts a 170 km-long carbonate platform in the Exmouth Sub-basin, where Cenozoic mass-transport complexes (MTCs) provide a valuable opportunity to investigate slope failure processes in carbonate-dominated margins, which remain underrepresented in global datasets largely derived from siliciclastic systems. Using a high-resolution 3D seismic dataset covering 11,731 km2, interpreted through full-volume seismic interpretation workflows and calibrated to the Ravensworth 1/CH1 well, we establish a high-resolution seismic stratigraphic framework and map in detail four MTCs ranging from 40 to 185 km3 in volume. Geomorphological and quantitative analysis reveals a down-slope continuum of deformation along basal shear surfaces, transitioning from coherent slide blocks up to 3.3 km long near the headscarps to rafted blocks and ultimately amorphous debris flows. Run-out distances of 11 to 80 km are controlled by paleotopography and rheology, highlighting the importance of substrate properties in governing MTC evolution and architectural maturity. Spatial relationships between faulting and headscarps, locally hardlinked to underlying faults, indicate that tectonic processes constitute a key triggering mechanism, while retrogressive failure features suggest on-going slope instability associated with present-day seismicity. Overall, the timing of MTC development reflects the interplay of tectonic and climatic controls, with major failure events coinciding with periods of intensified regional structural activity. These MTCs are associated with proto-slumps, crown cracks, and pockmarks, which in turn can increase slope instability in the future (i.e., development of new MTCs) and represent a significant geohazard risk. Quantitative morphometric relationships demonstrate that these MTCs are broadly comparable to passive margin-attached MTCs globally, including carbonate systems such as the Great Bahama Bank. However, observed differences with global trends infer that the variability of carbonate lithologies (i.e., diverse rheological properties) constitutes a key control parameter on MTC dimensions. By providing a detailed morphometric analysis of MTCs along a carbonate margin, this study helps address a bias in current global databases and offers new hypotheses for evaluating the transferability of slope failure models between siliciclastic and carbonate systems. These results improve our understanding of how sediments are redistributed along carbonate slopes and how the interaction between structural inheritance, sedimentary processes and external forcing governs slope failure on continental margins, with implications for basin evolution and geohazard assessment, which ultimately can help the prediction of MTC occurrence and behavior in analogous settings worldwide.

Mud volcanoes occur in a variety of geodynamic settings, and are common in subduction zones, usually within the accretionary prism. Although mud volcanism occurs along the Ryukyu Trench in southern Japan, no such activity has been documented along the Japan Trench. Sub-bottom profile data from International Ocean Discovery Program Expedition 386 show acoustically anomalous features in the basin-fill stratigraphy consistent with mud diapirism and mud volcanism along the Japan Trench. Unusually these features occur in basins along the trench axis itself, and not primarily as part of the accretionary complex. We present evidence for diapirism along similar to 600 km of the Japan Trench and for mud volcanoes in the central and northern part of the trench. Mud diapirism and nearby igneous volcanic activity shows close spatial relationships to flexural faults on the downgoing plate, which may provide the plumbing system for mobile muds to reach the surface.

Deformation of trench-fill sediments at the central Japan Trench axis confirms that coseismic slip during the 2011 CE Mw 9.1 Tōhoku-oki earthquake extended to the shallowest part of the megathrust fault, contributing to the unexpectedly large tsunami that followed. Understanding the recurrence of “slip-to-the-trench” style earthquakes is therefore essential for diagnosing future hazard at the Japan Trench (and other subduction zones). Thermal biomarkers from the décollement indicate that similar shallow slip has occurred repeatedly, but the timing has not yet been linked to specific past earthquakes. We examine the sedimentary sequence of a trench-fill basin at 38.75°N (just north of the Tōhoku-oki slip zone) to investigate archives of past deformation caused by slip to the trench. Reprocessed seismic reflection and sub-bottom profiler data image several stratigraphic intervals of imbricate thrust wedge formation and paleo-seafloor uplift consistent with compression induced by locally enhanced coseismic slip along the décollement. The uplifted paleo-seafloor topography is onlapped by thick seismoturbidites that have been cored and dated by International Ocean Discovery Program Expedition 386, thus providing chronostratigraphic tie points. With this, we link the youngest coseismic deformation of trench-fill sediments to the 869 CE Jogan earthquake, indicating that rupture extended farther north and closer to the trench than previously estimated. Documenting slip to the trench for this historical megathrust event is proof of concept for our core-to-seismic correlation approach to constrain shallow slip in past earthquakes. Hence, we infer the several deeper intervals of imbricate thrust faulting and turbidites contain the means to unlock an extensive history of slip-to-the-trench style earthquakes and quantify the recurrence of shallow, tsunamigenic slip at the Japan Trench.

Key Messages: (1) Mass-transport complexes (MTCs) developed in the Exmouth Sub-basin exhibit a continuum of downslope deformation along basal shear surfaces that coincide with third-order sequence boundaries. (2) Fault reactivation is a likely trigger for slope failure in several MTCs as suggested by the direct link observed between headscarps and underlying faults. (3) Variations in run-out distance (11–80 km), likely influenced by paleotopography and rheology, affect the architectural maturity of the MTCs, which are morphometrically comparable to other passive margin-attached systems in carbonate settings.

A palynological analysis of the basinal volcaniclastic turbiditic Foura Sandstone Member within the Babulu Formation in Timor-Leste reveals rich assemblages including well-preserved material that correlates with the upper Ladinian-Carnian upper Staurosaccites quadrifidus-?lower Samaropollenites speciosus spore-pollen zones of Australia. The high diversity of conifer pollen in these assemblages indicates an association with microfloras from comparable latitudinal zones within Gondwana and an affiliation with the Onslow paleobiogeographic floral belt. The relationship between pollen and megafloral associations highlights the ecological flexibility of conifers, and their preeminent role in Triassic Gondwanan vegetation. The assemblages from the Foura Sandstone, including the new species Cadargasporites helbyi, Cadargasporites timorensis and Planctonites? comasii, point to the high diversity of vegetation in the area and the need for further studies.

Mass transport deposits have long been known on the Exmouth Plateau, offshore NW Australia, identified in 2D and 3D industry seismic lines. The expedition SO257 in 2017 collected 30 high-resolution, shallow seismic lines along targeted transects on the northern Australian margin. Many of these imaged mass transport deposits, with the top 700-800 m of the section captured in detail not available with industry seismic data. We present nine new high-resolution seismic lines from three separate areas of the North West Shelf. Slides in the Roebuck Basin show complex anastomosing ductile extensional mechanisms, with multiple slip surfaces and no headscarps or adjacent faults. Slides on the Exmouth Plateau have fault control, with surface fault offsets of up to 300 m, indicating seismicity as a likely triggering mechanism. Slumps along the western margin of Western Australia are more limited in extent, associated with surface notches, with indications of previous activity at depth. All areas show a repeated history of mass transport deposits. The area of the active landslide province offshore of NW Australia is far larger than the individual slides recognized on the Exmouth Plateau.

Hadal trenches are unique geological and ecological systems located along subduction zones. Earthquake-triggered turbidites act as efficient transport pathways of organic carbon (OC), yet remineralization and transformation of OC in these systems are not comprehensively understood. Here we measure concentrations and stable- and radiocarbon isotope signatures of dissolved organic and inorganic carbon (DOC, DIC) in the subsurface sediment interstitial water along the Japan Trench axis collected during the IODP Expedition 386. We find accumulation and aging of DOC and DIC in the subsurface sediments, which we interpret as enhanced production of labile dissolved carbon owing to earthquake-triggered turbidites, which supports intensive microbial methanogenesis in the trench sediments. The residual dissolved carbon accumulates in deep subsurface sediments and may continue to fuel the deep biosphere. Tectonic events can therefore enhance carbon accumulation and stimulate carbon transformation in plate convergent trench systems, which may accelerate carbon export into the subduction zones.

This is the source data file of the Nature Communications manuscript 'Earthquake-enhanced dissolved carbon cycles in ultra-deep ocean sediments'.

All depth and thickness estimates in this section are approximate and assume a seismic velocity of 1500 m/s. BathymetryHoles M0094A and M0094B lie in the deepest part of the basin at 7469 m.The acquired bathymetry data do not capture the entire basin but are instead limited to the length of the subbottom profile.The western side of the basin is bound by a series of north-northwest-trending topographic terraces that cause topography to step up to the west, with a maximum slope gradient of 12%-15% at the steepest points.To the east, the topography has a lower slope gradient, rising gently at 6%-8%.Basin width, defined as the extent of the flat bottom basin between sharp topographic boundaries, is less than 1700 m for most of the basin, although it broadens toward the northern end of the profile line.

Restoration of interpreted 2D deep seismic lines across Australia's North West Shelf indicates that rifting style changed significantly during multiple phases of extension and continental breakup. Early phase rifting during the Neo-Proterozoic and Early Paleozoic, characterised by low-angle detachment faults, crustal-scale necking and hyperextension of the crust (Metamorphic Core Complex Mode), was localised over pre-existing Proterozoic orogenic belts formed adjacent to major cratonic blocks. Subsequent extensional events in the Late Paleozoic and Mesozoic reactivated these low-angle rift fault systems. However, a series of narrow rift basins (Narrow Rift Mode), bound by high-angle normal faults that cut into the upper mantle, also began forming due to changes in the rheological architecture of the lithosphere following previous extension, crustal thinning and post-rift cooling. Wide rift mode extension, wherein extensional deformation was distributed over broad areas, may have occurred prior to, or in conjunction with, the development of more localised narrow rifts (dual mode rifting) in areas such as the Northern Carnarvon and Browse basins. Extensional deformation progressively localised into the narrow rift basins, which in some cases, matured into seafloor spreading centres during breakup, typically outboard of the major low-angle detachment fault systems. The resulting general structural architecture evolution is consistent with several other hyperextended margins from around the world. The rift events were punctuated by periods of thermal sag, often in conjunction with pulses of compressional deformation associated with plate-scale tectonic events. Structural restoration of 2D regional seismic lines shows a marked difference in the way the different polyphase rift basin elements responded to shortening. Low-angle detachment faults were relatively well oriented for reactivation under compression, leading to the development of inversion anticlines and associated convergent unconformities towards the inboard basin margin. In contrast, high-angle normal fault systems associated with the pre-existing narrow rift basins were poorly oriented for reactivation during compression and tend to be characterised by minor wrench/flower structures, generally with relatively limited uplift and erosion on the basin margins. Regional in-plane compressional stresses also worked in combination with vertical loading due to thermal decay to downwarp the lithosphere, forming broad rapidly subsiding synclinal basins above axes of the pre-existing rift basins. The evolving structural architecture developed during the compressional events had significant impacts on the associated sequence stratigraphic architecture.

The complicated geology of the Banda region results from complex collision between the Eurasia, Australia and Pacific plates, ongoing in the region since the Late Oligocene but particularly in the study area since the Middle Miocene (from 15 Ma). Regional 2D broadband seismic data have provided improved imaging of Mesozoic and Cenozoic sedimentary successions in the region. The region comprises the deep and ultra-deep Banda Sea enclosed by a magmatic inner arc and an outer deformed zone, comprising a series of orogens. This outer orogenic zone comprises islands with extended and sometimes hyperextended continental crust, a series of marginal foredeeps and intervening fold-and thrust belts. This paper illustrates how the offshore fold-and-thrust belts that bound the fore-deeps change in size, shape and degree of basement reactivation in a clockwise sense around the Banda Arc.

SummarySummaryThe logging and biostratigraphic characterization of the Foura Sandstone type section, Timor-Leste, show it is Carnian–early Norian (Samaropollenites speciosus Zone). Sedimentary structures indicate a turbidite origin and petrographic analysis reveals a high proportion of volcanic lithic grains.Palynological material presents a variable preservation suggesting a complex pre-burial history involving longdistance transport. The presence of prasinophytes suggests anoxic and euxinic depositional settings.Foura SandstoneTimor-LestepalynologyCarnianNorian

•Type Barique Formation contains mainly volcanics plus limited limestone units.•Limestones belong to inner and outer neritic facies.•Limestones are late Middle Eocene and include planktonic foraminiferal zone E10.•This limestone/volcanic association is widespread in Timor but unknown in Australia.•Part of Overthrust Terrane Association emplaced during Late Miocene Collision.

The western margin of Australia has migrated over 30° northward in the last fifty million years. As it progressed, it carried evidence of greenhouse to icehouse climate and ocean transitions in the sedimentary sequences. In the last ten million years Australia collided with the Asian plate to the north, leading to the uplift of the Indonesian archipelago and Papua New Guinea highlands and restricting the interchange between the Indian and Pacific oceans. This created the near “modern” oceanography of the region with the onset of the Indonesian Throughflow and related Leeuwin Current. It also resulted in the ongoing crustal stress along the North West Shelf causing substantial seismicity and faulting. Recent sediment coring by the International Ocean Discovery Program (IODP) and RV Sonne has yielded superb palaeoclimatic and palaeoceanographic archives that will uncover details of the evolution of this margin through the late Neogene to Recent. Knowledge of the past evolution of Australia’s western margin is essential if we are to better predict the consequences of ocean/climate variability for future climate change.