The 66 Ma Chicxulub impact crater, Mexico, is obscured by hundreds of meters thick horizontal carbonate strata, which in age are as young as Pliocene. The spatial density of karst-induced sinkholes, known as cenotes, is maximal at, and aligns with, the onshore portion of the buried crater margin, forming a distinct semicircle, about 170 km in diameter. The causal relationship between the presence of the buried crater margin and the formation of the partial cenote ring has remained elusive since the discovery of the Chicxulub crater, by now some 30 years ago. Earlier hypotheses, by which the cenotes formed due to subsurface collapse of either impact breccia or porous reef complexes lined with the crater margin have received little support. However, it is well known that ground water flow of the northwestern Yucatán aquifer is channelled in post-impact carbonate rock below the cenote ring. This calls for the presence of prominent structural discontinuities in carbonate strata above the buried crater margin. We addressed cenote formation in the realm of the Chicxulub crater by scaled analogue experiments and by mapping the locations and surface outlines of some 6500 cenotes using imagery embedded in ArcGIS Pro. The outlines are mostly elongate, suggesting that cenotes formed by preferential dissolution of carbonate rock at planar structural discontinuities. This interpretation is corroborated by the overall shape-preferred orientation of their outline long axes in E-W direction, throughout the northern portion of the Yucatán peninsula. Interestingly, long axes deviate from this trend for many of the cenotes defining the partial ring. Such directional departure points to local perturbation of deformation, and thus stresses, preceding cenote formation above the crater margin. Physical experiments using photo-elastic materials as analogues for continental crust were designed to explore to what extent far-field compressive stresses, imparted by plate convergence at the Middle-America Trench, may account for the perturbations in carbonate rock above the crater margin. Long-term isostatic relaxation of crust below large impact craters is an alternative hypothesis for the formation of concentric faults, potentially localizing at crater margins and thus, generating the partial cenote ring. Using two-layer analogue experiments scaled to the physical conditions on Earth and modelling the deformational behaviour of lower and upper crust following crater formation, we explored the structural and kinematic consequences of crustal relaxation by systematically varying initial depths and diameters of crater floors. Model results indicate that Chicxulub-size craters do indeed develop concentric faults at crater margins by accomplishing differential displacement between uplifting crater floors and subsiding peripheral areas. Interestingly, crater floors retained structural coherence during uplift, which aligns with the paucity of cenotes within the respective ring at Chicxulub. Based on the scaling of our experiments, the duration of isostatic relaxation translates to natural time scales of at least tens of thousands of years. Although isostatic relaxation of impacted crust may not solely account for the origin of a structurally and karst-controlled cenote ring at Chicxulub, concentric faults generated by this mechanism may propagate with time through post-impact strata, driven by far-field stresses.

Although mechanisms of impact cratering have been studied intensely by numerical modelling and field analyses, an outstanding problem concerns long-term crater modification. Localized deformation in form of radial and concentric crater floor fractures are prominent post-cratering structural vestiges of lunar impact craters. Two mechanisms were proposed to explain the formation of floor fractures: isostatic re-equilibration of crust underlying crater floors, and emplacement of horizontal igneous sheets below craters. Due to thick and cool lunar upper crust, the latter mechanism has been regarded as the more plausible one to account for the presence of floor fractures in lunar craters. However, the structural consequences of magmatic inflation on surface deformation in combination with crater floor morphology has not been analyzed systematically in 3D.We use scaled analogue experiments to model the deformational behavior of upper crust following crater formation to explore the structural and kinematic consequences of sill formation below crater floors with different depths and diameters. Our experiments were scaled to the lunar physical conditions. The initial diameter-to-depth ratios of lunar craters were based on numerical modelling. Granular material simulating the Moon’s brittle upper crust was filled into a 60 cm by 60 cm size tank. Craters with specified morphologies, depths and radii were “drilled” into this material by a rotating blade. Sills were simulated by variably sized flat, circular balloons of plastic foil, emplaced into the granular material below model craters and inflated by a pumped-in fluid. For each experiment, the sill was first inflated and then deflated to model intrusion and evacuation of magma, respectively. Surface deformation within and around the crater was monitored with a 4-D digital image correlation system allowing us to quantify key parameters including surface uplift as well as the distribution and evolution of strain. The results of our scale models enabled us to quantify the geometry and distribution of brittle deformation of lunar upper crust.Our experiments show that inflation of balloons caused radial and concentric dilation fractures in the overlying granular material. Fracture patterns were more controlled by the depth to the top surface of balloons rather than by crater floor morphology. For the duration of fluid inflation into shallow model sills, surface uplift was focused in the crater center and associated with rather prominent fractures. Upon deflation, concentric normal faults developed at the inner crater rim, and this corresponds to the terraced crater margins ubiquitously observed at lunar craters. Interestingly, model craters are characterized by more diverse fracture patterns, compared to lunar craters. This may be due to brittle deformation above sills during inflation, allowing for magma to erupt from natural sill reservoirs. It is, therefore, unlikely that natural sill systems attain the structural maturity of our modelled equivalents. Hence, evacuation during inflation in natural systems can account for the presence of less prominent fracture patterns compared to the ones in modelled, more “mature” sill systems.

Crater floor fractures are prominent post-cratering structural vestiges that are known from large impact craters on rocky celestial bodies. Two mechanisms have been proposed to explain the formation of crater floor fractures: emplacement of horizontal igneous sheets below crater floors and isostatic re-equilibration of crust underlying target rocks, i.e., crustal relaxation. Here, we use two-layer analogue experiments to model the deformation of lower and upper crust following crater formation, scaled to the physical conditions on Earth, to explore the structural and kinematic consequences of crustal relaxation. Specifically, the structural evolution of model upper crust was systematically analysed for various initial depths and diameters of crater floors, gleaned from previous numerical models for average continental crust. The analogue modelling results provide quantitative estimates of the duration, geometry and distribution of deformation zones in the upper crust and, for the first time, a quantitative relationship between the diameter, depth and fracture geometry of crater floors. The experiments also show that crater floor uplift is accomplished by long-wavelength subsidence of the crater periphery, which may operate on time scales of hundreds of thousands of years in nature. We conclude that patterns of natural crater floor fractures, including impact melt rock dikes known from the Sudbury and Vredefort impact structures, can be caused by long-term uplift of the crater floor, compensated by lateral crustal flow toward the crater centre.

Morphology, internal structure, and in situ facies distribution of mesophotic Halimeda bioherms from the Queensland Plateau (NE Australia) are presented based on hydroacoustic and oceanographic data, seafloor observations, and discrete sediment sampling carried out during RV SONNE cruise SO292 in 2022. Halimeda buildups consist of cone-like mounds up to 500 m in diameter and 3–10 m high, with gentle slopes (2°–5° on the top of Tregrosse Bank). Bioherms occur in water depths of 10–70 m, with most bioherm between 50 and 65 m. Their internal structure consists of aggrading low-amplitude reflections at the core of the bioherm interfingering with high-amplitude reflections to the flanks. Surface facies distribution displays one to four facies belts, from distal to proximal: Halimeda rudstone, Halimeda rudstone with living plants, Halimeda rudstone with coralgal debris, and coralgal boundstone (when present, occupied the top of the bioherms). It is proposed that the alternation of two key processes contributes to the formation of these bioherms: (1) in situ accumulation of Halimeda debris and (2) episodic dismantling of the mesophotic coralgal boundstone at the centre of the bioherm by severe storms. These storms may dismantle the mesophotic reef and export coralgal rubble to the flanks. Flanks may be recolonized by Halimeda during fair-weather periods. Due to their different geomorphic expressions, complex internal structure, and surficial facies distribution, we suggest that the buildups of the Queensland Plateau represent a new Halimeda bioherm morphotype, distinct from previously described bioherms on the adjacent Great Barrier Reef and elsewhere globally.

The steep slopes of carbonate platforms frequently display large-scale sediment destabilization features like rockfalls, mass transport complexes, and slope erosion. The processes and factors triggering such instabilities and how they interact are a matter of ongoing discussion. We use hydroacoustic, sedimentological, and seafloor imaging data to map and characterize slope instabilities and potential controlling factors at the flank of the isolated Tregrosse carbonate bank in the Coral Sea, northeast Australia. Erosion of gullies and submarine valleys is concentrated in slope segments with the platform rim at several 10s of meters of water depth, i.e. where there is potential for sediment transfer from the bank interior to the slope. Gravity core data indicate that most sediment export from the platform occurs during sea-level fall. The toe of slopes neighboring segments with a shallower platform rim are mostly characterized by mass-transport complexes of platform rim and upper slope rocks forming extended block fields. Distal slope areas are dismantled through submarine landslides resulting in scalloped head scarps. The basal detachment surface of these submarine landslides appears to be rooted in several 100 s of meters in the subsurface at a lithological heterogeneity, which is documented by a gamma-ray peak in the downhole logging data from Ocean Drilling Program Site 817. Our findings show that (1) canyon erosion, (2) platform rim and upper slope destabilization as well as (3) lower slope dismantling, largely act independently of each other to destabilize the flanks of the carbonate bank. The complexity of the carbonate platform dismantling processes and the corresponding controlling factors shown in this study should also be considered when interpreting seismic morphological data.

Sediment sampling of the seafloor, especially with a box corer, is an important aspect of marine geology and sedimentology. The sediment surface recovered by this tool, however, is of limited extend (10s of cm only) and might be disturbed thru the sampling process. The Box corer Imaging System (BOXIS) is an addon for the box corer allowing for high resolution video recording of the sampling process. It attaches to the box corer main frame and adds lights, batteries and a camera. The system can be adapted to a variety of sampling devices. Its main objective is to capture video of the sample area before and after the sampling of which images can be extracted. The recording is extracted after the sampling process, when the tool is on deck. The system is equipped with LED lights featuring a total of 7000 lumens and built-in redundancy. The separate light units are connected via cable to their corresponding battery unit featuring a custom timer and magnetic activation switch. The special camera housing features a popular action camera recording at 5.3K resolution (19.6 Mpx). The camera field of view features a wide, undistorted, unobstructed view looking down. As a benefit of the camera position, depending on visibility it is possible to gather images from up to 10 m above the seafloor conveying a broader context down to close-ups 25 cm from the seafloor. The BOXIS system is rated to a maximum operation depth of 1750 m. The BOXIS footage can be examined instantly over a wireless connection on a mobile device once the box corer is back on deck to evaluate sampling quality and support discussion and decision making on the proceeding of further sampling operations. Large batteries ensured multiple deployments in a row without service. Even in cases where the box corer does not trigger, the BOXIS provides data not only of the seafloor but also on operational problems such as sediment penetration. It is a system with a minimum of cabling, which therefore is not endangered to interact with the hoisting equipment used for lowering and lifting of the normally analog gear.The BOXIS system has been successfully deployed for the first time on FS SONNE cruise SO292 in spring 2022 to the Queensland plateau, Australia. In total we could record a total of 27 deployments without a single failure. We will present the BOXIS system based on examples from these successful deployments.

The Southern Andes are regarded as a typical subduction orogen formed by oblique plate convergence. However, there is considerable uncertainty as to how deformation is kinematically partitioned in the upper plate. Here we use analogue experiments conducted in the MultiBox (Multifunctional analogue Box) apparatus to investigate dextral transpression in the Southern Andes between 34 °S and 42 °S. We find that transpression in our models is caused mainly by two prominent fault sets; transpression zone-parallel dextral oblique-slip thrust faults and sinistral oblique-slip reverse faults. The latter of these sets may be equivalent to northwest-striking faults which were believed to be pre-Andean in origin. We also model variable crustal strength in our experiments and find that stronger crust north of 37 °S and weaker crust to the south best reproduces the observed GPS velocity field. We propose that transpression in the Southern Andes is accommodated by distributed deformation rather than localized displacements on few margin-parallel faults.

Carbonate platforms are built mainly by corals living in shallow light-saturated tropical waters. The Saya de Malha Bank (Indian Ocean), one of the world's largest carbonate platforms, lies in the path of the South Equatorial Current. Its reefs do not reach sea level, and all carbonate production is mesophotic to oligophotic. New geological and oceanographic data unravel the evolution and environment of the bank, elucidating the factors determining this exceptional state. There are no nutrient-related limitations for coral growth. A switch from a rimmed atoll to a current-exposed system with only mesophotic coral growth is proposed to have followed the South Equatorial Current development during the late Neogene. Combined current activity and sea-level fluctuations are likely controlling factors of modern platform configuration.

The Southern Andes are often viewed as a classic example for kinematic partitioning of oblique plate convergence into components of continental margin-parallel strike-slip and transverse shortening. In this regard, the Liquiñe-Ofqui Fault Zone, one of Earth’s most prominent intra-arc deformation zones, is believed to be the most important crustal discontinuity in the Southern Andes taking up margin-parallel dextral strike-slip. Recent structural studies, however, are at odds with this simple concept of kinematic partitioning, due to the presence of margin-oblique and a number of other margin-parallel intra-arc deformation zones. However, knowledge on the extent of such zones in the Southern Andes is still limited. Here, we document traces of prominent structural discontinuities (lineaments) from the Southern Andes between 39° S and 46° S. In combination with compiled low-temperature thermochronology data and interpolation of respective exhumation rates, we revisit the issue of kinematic partitioning in the Southern Andes. Exhumation rates are maximal in the central parts of the orogen and discontinuity traces, trending predominantly N–S, WNW–ESE and NE–SW, are distributed across the entire width of the orogen. Notably, discontinuities coincide spatially with large gradients in Neogene exhumation rates and separate crustal domains characterized by uniform exhumation. Collectively, these relationships point to significant components of vertical displacement on these discontinuities, in addition to horizontal displacements known from published structural studies. Our results agree with previously documented Neogene shortening in the Southern Andes and indicate orogen-scale transpression with maximal vertical extrusion of rocks in the center of the transpression zone. The lineament and thermochronology data call into question the traditional view of kinematic partitioning in the Southern Andes, in which deformation is focused on the Liquiñe-Ofqui Fault Zone.

The Caviahue–Copahue volcanic complex in the Southern Volcanic Zone of the Andes is composed of the Pliocene–Pleistocene Caviahue depression and the active Copahue volcano. This volcanic complex is located in a zone of profuse volcanic and tectonic activity, and thus, the origin of the depression includes both tectonic and volcanic hypothesis (e.g., formation of a collapse caldera and a pull-apart basin). According to current knowledge, the oldest rocks filling the depression are lavas and ignimbrites of the Pleistocene Las Mellizas Formation. However, clastic sedimentary deposits underlying this unit have been recognized. Here, we document the characteristics of these deposits at the south shore of the Caviahue lake using field data and digital outcrop models (DOM). We have concluded that the deposits are deltaic and alluvial in origin and made up by a prodelta/distal deltaic front, delta front deposits, delta plain sediments and alluvial deposits. An unconformity separates the deltaic deposits from overlying alluvial deposits, indicating the decrease in the stratigraphic base level probably associated with a sudden coarse-grained clastic input and a drop in the lake level. Our study has implications on the timing and evolution of the Caviahue depression and indicates that the depression precedes the Las Mellizas Formation. Thus, Las Mellizas ignimbrite should not be interpreted as the main unit related to the Caviahue caldera as it has been proposed by some authors. If the depression had indeed been formed by a collapse caldera, this event would be previous to the described sediments.

Meteorite impact is recognized as a fundamental geological process of the solar system. Although mechanisms of large impact cratering have been studied intensely, mostly by numerical modelling, an outstanding problem concerns long-term crater modification, which operates on time scales of tens of thousands of years after impact. Localized deformation in the form of radial and concentric floor fractures (FFCs) are known from large craters on all terrestrial planets. On Earth, we can observe the occurrence of radial and concentric impact melt rock dikes in the eroded basement of large impact structures, such as Sudbury (Canada) and Vredefort (South Africa). Two mechanisms were proposed in the past to explain the formation of FFCs: the intrusion and inflation of igneous bodies below the crater floor and long-term isostatic re-equilibration of impacted target rocks. Using two-layer analogue experiments scaled to physical conditions on Earth, we explore to what extent isostatic re-equilibration of crust may account for the observed dike and fracture patterns of FFCs.The structural evolution of model upper crust was examined for a variety of initial depths and diameters of crater floors. The crater diameter-to-depth ratio was scaled according to numerical models for average continental crust. Specifically, a tank, 80cm by 80cm in size, was filled with PDMS, representing the viscous middle and lower crust and granular material, simulating the brittle upper crust. Moreover, we introduce a method, which allowed us to generate any shapes of model impact crater floors.The experiment surfaces were monitored with a 3D digital image correlation system allowing us to quantify key parameters, such as surface motion as well as the distribution and evolution of surface strain. The results of our scale models enabled us to quantify the duration, geometry and distribution of brittle deformation of upper crust. Most importantly, the analogue experiments provided, for the first time, a quantitative relationship between diameter, depth and fracture geometry of crater floors.Our results indicate that FFCs are caused by long-term uplift of the crater floor, compensated by crustal flow toward the crater center. Such radial convergent flow generated radial and concentric dilation fractures. Crater floor uplift is accompanied by long-wavelength subsidence of the crater periphery on the order of 50 minutes, amounting to some 3000 years in nature. The formation of radial versus concentric fractures depends on the ratio between crater diameter and crater depth and, hence, is controlled by isostacy and crustal strength. The geometry and distribution of fractures in analogue experiments are strikingly similar to the geometry of impact melt rock dikes at Sudbury and Vredefort.

Models of intra-arc deformation in the Southern Andean Volcanic Zone (SAVZ) between 42◦S and 47◦S commonly focus on the kinematics of the Liquiñe-Ofqui Fault Zone (LOFZ), which cuts the SAVZ along-strike for more than 1000 km. Northward displacement of the Chiloé Block, a detached fore-arc sliver to the west of the LOFZ, points to an overall dextral displacement on the LOFZ. In this tectonic framework, which is based on limited ground truth, the LOFZ is commonly regarded as the main, if not the only, discontinuity accommodating oblique plate convergence. Recent paleomagnetic and fault-kinematic studies, however, challenge this concept as they provide independent evidence for distributed deformation along a number of additional first-order faults resulting in heterogeneous vertical-axis rotation of upper crustal blocks. Following this concept, we highlight the complexity of deformation in the SAVZ and discuss the role of the LOFZ. Our conclusions are based on detailed lineament analysis and reassessment of compiled kinematic, paleomagnetic and apatite fission track (AFT) data.