Outcrop Examples Research Articles

Inner architecture of fan delta front deposits: An outcrop example from Xiguayuan Formation, Luanping Basin, northeast China

Inner architecture of fan delta front deposits: An outcrop example from Xiguayuan Formation, Luanping Basin, northeast China

Hierarchies of stratigraphic discontinuity surfaces in siliciclastic, carbonate and mixed siliciclastic‐bioclastic tidalites: Implications for fluid migration in reservoir quality assessment

AbstractThe hierarchies of the stratigraphic discontinuity surfaces observed in ancient tidalites are qualitatively assessed, aiming to evaluate their role as possible preferential conduits for fluid migration. Three outcrop examples are presented from microtidal settings of southern Italy: (i) siliciclastic tidalites consisting of quartz‐rich cross‐stratified sandstones generated by strong two‐directional tidal currents flowing along a tidal strait; (ii) carbonate tidalites, which accumulated in a Cretaceous lagoon and tidal flat where peritidal cycles formed vertically‐stacked sequences of biopeloidal and fenestral packstones, wackestones and bindstones during repeated phases of Milankovitch‐scale sea‐level changes; (iii) mixed, siliciclastic‐bioclastic tidalites, deposited in a bay and recording offshore‐transition, to shoreface wave‐dominated and tide‐influenced environments. Observations made during this study suggest that fluid movement can be controlled by the presence of main bounding surfaces that occur at different dimensions, from large (hectometre)‐scale, to medium (decametre)‐scale, to smaller (metre)‐scales. These surfaces produced either by depositional or erosional processes, are characterised by different features and geometries in siliciclastic, carbonate and mixed siliciclastic‐bioclastic tidalites arguably revealing complex internal pathways for fluid flows. These results suggest that fluids propagating along the main discontinuities follow a dominant sub‐horizontal direction of propagation, associated with minor sub‐vertical movements, due to local internal surface geometries and interconnections and a general lack of fractures. This surface‐based approach to the study of fluid‐flow transmission within stratified rocks represents a conceptual attempt to predict fluid mobility and reservoir potential in tidalite‐bearing siliciclastic, carbonate and mixed reservoir rocks.

Did mid‐Ediacaran regional sea‐level drawdown trigger extensive allochthonous salt breakout and the incision of kilometre‐deep palaeocanyons, Flinders Ranges, South Australia?

AbstractThe Ediacaran Period is of interest for the emergence of multicellular life, one or more glaciations, and the occurrence of the largest δ13C excursion in Earth history (the Shuram). The Ediacaran stratigraphic succession in the Flinders Ranges of South Australia is distinctive also for well‐exposed outcrop examples of palaeocanyons and salt diapirs. We present data placing a level of salt‐sheet breakout during deposition of the Wonoka Formation, within the time span of the Shuram, and at a datum indistinguishable from the canyon incision level. We hypothesize that canyon incision and salt breakout were triggered by subaerial erosion and non‐deposition associated with sea‐level drawdown in a temporarily isolated embayment. This mechanism provides support for the idea that the palaeocanyons were fluvially incised, and imposes a new constraint on the palaeoenvironmental setting of Australia at the time of the Shuram and the Ediacara fauna.

The role of antithetic faults in transferring displacement across contractional relay zones on normal faults

Contractional relay zones between pairs of normal faults are sometimes associated with multiple antithetic faults in a geometry similar to that found in Riedel shear zones. Detailed fault displacement profiles of outcrop examples of this geometry demonstrate that the antithetic faults accommodate the transfer of displacement between the synthetic faults that bound the relay zones. The throw on individual antithetic faults, or R′ shears, is typically constant across relay zones while the throw profile on the synthetic faults, or R shears, is stepped; the steps occurring across branchpoints with abutting R’ shears. Transfer of fault displacement occurs by a combination of block rotation and irrotational block translation within the relay zone. As fault throw increases, contractional relay zones are by-passed by the linkage of the synthetic faults, in a manner analogous to the formation of P-shears by the linkage of R shears in classic Riedel shear experiments, but with the original relay zone structure still preserved within the fault zone. With yet further strain bedding may rotate into near-parallelism with the fault surface, with the original geometrical configuration of the relay zone difficult to unravel.

Crust necking of the northeastern South China Sea: Insights from deep seismic data

During rifting, continental crust necks, leading to significant thickness reduction in a few tens of kilometres. However, deformations associated with the necking process remain elusive due to few outcrop examples and a lack of seismic data coverage that clearly images crustal architecture at depth. Here we use deep, high-resolution seismic data across a well-developed necking zone in the northeastern South China Sea passive margin to show the structural style associated with the crustal necking. Seismic stratigraphy in the necking domain can be divided into pre-, syn- and post-rift sequences based on the nature of sequence-bounding unconformities and their relation with faults. Seismic expression of continental crust exhibits two types of reflection characteristics – homogeneous upper crust and layered lower crust. The necking domain shows significant thinning that reduced its thickness from ~30 km to less than over 10 km in a distance of about ~50 km and is characterised by seaward removal of layered lower crust, while the homogeneous upper crust thickness remains largely unchanged in thickness. The necking domain is bounded by inner and outer breakaway complexes that define a portion of flexed crust. Crustal flexure is evidenced by progressive tilting of the necking domain that gradually increases the pre-rift sequence dip from 0° to 10°. Within the tilted necking domain, densely-spaced, landward-dipping minor faults and fractures are organised in a domino configuration, implying a top-to-the-continent movement and a simple shear deformation of the whole continental crust. We suggest that the flexed necking domain could be home to fractured reservoir providing that it is effectively sealed by post-rift sequences.

Broken Beds, but better science; using multiple hypotheses to interpret geological data

AbstractIn this study, we propose a multiple hypotheses approach to improve interpretations of limited remotely sensed datasets, such as sparsely exposed outcrops, subsurface datasets, or planetary objects using semi‐quantitative scoring and ranking of observable features. This method is demonstrated using an outcrop example from the Broken Beds of the Upper Jurassic–Lower Cretaceous Purbeck Limestone Group exposed along Britain's Jurassic Coast. Four published hypotheses regarding their origin are refined, represented in matrix form, scored and ranked based on carefully selected outcrop features. Semi‐quantitative scoring utilises knowledge of likely processes governing the occurrence of a range of features, some of which might be ignored or down‐played to favour a single hypothesis. Furthermore, by integrating expertise from different sub‐disciplines (e.g. basin analysis, sedimentology, diagenesis), we also consider the combined evidence of multiple features. This new method results in an interpretation that favours a multi‐process origin for the Broken Beds due to evaporite dissolution, overpressure release and tectonic folding, with identified uncertainty, all useful to guide further data collection.

The influence of creeping slope failure on turbidity current behaviour

ABSTRACTErosional scars, slumps, slides and debrites (mass‐transport deposits) on submarine slopes form relief that influences turbidity current behaviour. However, the interaction of mass‐transport deposit emplacement kinematics (i.e. rapid emplacement versus creep), the morphology of the evolving seafloor topography and subsequent flow types is complicated. This study describes two outcrop examples of deep‐water, predominantly turbiditic, deposits overlying mass‐transport deposits, from the Eocene slope succession of the Aínsa Basin (Spanish Pyrenees). In both examples, the mass‐transport deposit substrate continued to creep contemporaneously with turbidity current deposition and bypass. In the first case study, structures in the mass‐transport deposits are extensional and oriented parallel to flow. In the second, structures are compressional and oriented perpendicular to flow. Mudstones dominate the slope succession, but deposits overlying mass‐transport deposits form sandstone‐prone accumulations. Lateral confinement by flow‐parallel extensional faults enhanced channel‐formation. Channel incision occurred close to the exhumed fault plane on the hangingwall. Incision ceased as the fault gradually locked‐up, and channels avulsed to the hangingwall of a newly active normal fault, while the abandoned channel was filled by a thinning and fining‐upward succession. Barriers formed where the long axes of compressional anticlines developed in mass‐transport deposits formed perpendicular to flow. Here, turbidites filled the bathymetric lows in the axes of synclines. Continued tightening of synclinal depocentres led to repeated stoss side trapping and upslope accretion of coarse‐grained sediment accumulation. This generated thickening and coarsening‐up, followed by thinning and fining‐upward successions, tracking the decreasing, then increasing flow bypass associated with topographic expression on the mass‐transport deposit. This study shows how post‐emplacement creep, and orientation of topographic features on mass‐transport deposits, influence the routing and deposition of contemporaneous turbidity currents, and illustrates examples of facies successions that could be misinterpreted as the product of other autogenic submarine slope processes, such as lateral migration of sinuous channels, or compensational lobe stacking.

Contourite channels – Facies model and channel evolution

AbstractDespite the rise in published evidence of deep‐marine bottom current processes and associated deposits there are still very few documented outcrop examples. Herein are reported results of a contourite channel system related to the late Miocene palaeo‐Mediterranean Outflow Water in the Rifian Corridor, Morocco. This work aims to unravel the sedimentary evolution and facies distribution based on the study of large morphological features related to contourite channels and their subsequent sandstone dominated infill sequences. It was found that the channel evolution and facies distribution are related to spatiotemporal changes in flow characteristics of the palaeo‐Mediterranean Outflow Water. The recognized channel facies distribution correlates well with previously established bedform stability diagrams. Erosion and upper‐stage flow regime bedforms are associated with the most vigorous bottom currents, generally related to its core. Laterally, following the decrease in flow velocity towards the adjacent drift, bedforms comprise dunes, lower‐stage plane bedforms and more heterolithic facies. Similar facies changes are also observed down‐channel, related to a decrease in flow velocities resulting from turbulent mixing of water masses, associated decreases in density gradients and the subsequent deceleration due to gravity. Results of this work have been used to propose a three‐dimensional facies model for channelized sandy contourites. This study contributes to understanding contourite systems, thus benefitting oceanographic and climatic reconstructions as well as aiding the predictability of contourite channel systems for industry geoscience applications.

Sharp-based, mixed carbonate–siliciclastic shallow-marine deposits (upper Miocene, Betic Cordillera, Spain): The record of ancient transgressive shelf ridges?

Isolated sharp-based sedimentary bodies in shelf settings can develop via the reworking of regressive deposits during transgressions. An example of these are shelf ridges, formed under a wide range of processes, and widely studied due to their high reservoir potential. However, there is still a lack of examples in mixed (carbonate–siliciclastic) successions. This study presents an outcrop example from the Upper Miocene of the Betic Cordillera (Spain), with the aim to propose a model for the development of transgressive sharp-based mixed carbonate–siliciclastic deposits, and to provide criteria to differentiate these from their regressive counterparts. The studied succession is ca. 300 m-thick, and shows a cyclic alternation of coarse and fine-grained mixed deposits. Depositional cycles start with siliciclastic-dominated offshore to offshore transition deposits, progressively replaced by lower shoreface deposits. These are abruptly truncated by sharp erosive contacts bioturbated by passively-infilled large burrows; their ichnological features allow assignation to the Glossifungites ichnofacies. These contacts are interpreted as ravinement surfaces. They are overlain by mixed carbonate–siliciclastic barforms, rich in skeletal fragments and extraclasts, and displaying large-scale cross bedding. These form several m-thick and hundreds of m-long depositional elements interpreted as mixed shelf ridges. These ridges formed in a fine-grained, shallow-water shelf, which occasionally received coarse siliciclastic sediment supply via gravity flows, but had a coeval offshore carbonate factory, which provided the skeletal fragments. The sharp-based, coarser-grained nature and lithological break at the base of these mixed carbonate–clastic deposits could lead to their misinterpretation as forced-regressive wedges. However, the nature of their lower contact, combined with the reworked offshore skeletal fragments, and their stacking pattern are consistent with these mixed units forming during transgression. Other studies in relatively time-equivalent deposits have demonstrated the existence of coeval regressive, coarser siliciclastic-dominated shoreline systems in relatively close localities. These evidence a complex basin configuration in the area during the upper Miocene, with the development of local depocentres and relatively narrow corridors or seaways in the Mediterranean–Atlantic connection, which could have favoured shelf reworking processes, but also promoted the development of diverse stacking patterns, reflecting the differential interaction between active tectonics and sedimentation across the region.

Detailed structural analysis of digital outcrops: A learning example from the Kermanshah-Qulqula radiolarite basin, Zagros Belt, Iran

A digital outcrop example and associated structural analysis of highly deformed sedimentary strata from the Zagros Belt of Iran is presented. By providing this site in open-access, downloadable format, we aim to make this excellent outcrop exposure accessible to a wide range of geoscientists. Digital data extraction techniques are used to constrain structural interpretations and cross section orientation, as well as kinematic restorations of interpreted structures. Structural analysis protocols provided here are well-suited to learning outcomes associated with digital cross section construction, interpretation and restoration. Complex deformation at the study locality and associated uncertainties in horizon and fault mapping yield interpretation and structural restoration results that are likely non-unique. Interpretation uncertainties are discussed in the context of geoscience education, with specific reference to the need for considering and assessing data quality and underlying geological assumptions. Our workflow and results can be used to bridge the gap between field-based training at undergraduate level and the proficiency in 3D digital environments required of professional geoscientists. By using digital outcrops to achieve learning outcomes, knowledge of underlying geological processes and practical skills in digital data handling and treatment can be effectively communicated to future geoscientists within the virtual environment.

Seismic interpretation workflows for deep-water systems: A practical guide for the subsurface

Effective exploration, appraisal and development of deep-water reservoirs requires systematic mapping, description and characterization of the depositional systems that host them. Success in these areas requires that there is a firm understanding of hydrocarbon volumes and uncertainties, facies distributions to locate exploration and appraisal wells, and a framework to build reservoir models. We present a practical seismic interpretation workflow methodology which will be applicable in most cases and with most seismic data sets. The workflows are for channels, sheets and mass transport deposits (MTDs). Each step of the workflow is illustrated with subsurface and/or outcrop examples. The channels workflow guides the interpreter through identification of three hierarchical levels of channel architecture and the recognition of six key seismic facies: channel axis; channel margin; basal lags; slumps; thin-bedded facies (internal levees and terraces); and external levees. The sheet sandstone workflow emphasizes a series of steps including: understanding the regional and local context; understanding the evolution of sea-floor topography at basinal and depositional scales; and generating detailed amplitude maps. Mass transport complexes are rarely reservoirs but can have a major impact on reservoir distribution. The workflow encourages enquiries into these impacts which include: potential erosion of underlying reservoirs; ponding on and around the MTD; diversion and deflection of subsequent reservoir-hosting depositional systems; and their potential as sealing facies. The workflows are designed to be efficient and practical, and will provide an appropriate characterization encompassing exploration and appraisal to early development phases.

The Origin and 3D Architecture of a Km-Scale Deep-Water Scour-Fill: Example From the Skoorsteenberg Fm, Karoo Basin, South Africa

Scours, and scour fields, are common features on the modern seafloor of deep-marine systems, particularly downstream of submarine channels, and in channel-lobe-transition-zones. High-resolution images of the seafloor have improved the documentation of the large scale, coalescence, and distribution of these scours in deep-marine systems. However, their scale and high aspect ratio mean they can be challenging to identify in outcrop. Here, we document a large-scale, composite erosion surface from the exhumed deep-marine stratigraphy of Unit 5 from the Permian Karoo Basin succession in South Africa, which is interpreted to be present at the end of a submarine channel. This study utilizes 24 sedimentary logs, 2 cored boreholes, and extensive palaeocurrent and thickness data across a 126 km2 study area. Sedimentary facies analysis, thickness variations and correlation panels allowed identification of a lower heterolithic-dominated part (up to 70 m thick) and an upper sandstone-dominated part (10–40 m thick) separated by an extensive erosion surface. The lower part comprises heterolithics with abundant current and sinusoidal ripples, which due to palaeocurrents, thickness trends and adjacent depositional environments is interpreted as the aggradational lobe complex fringes. The base of the upper part comprises 2-3 medium-bedded sandstone beds interpreted as precursor lobes cut by a 3–4 km wide, 1–2 km long, and up to 28 m deep, high aspect ratio (1:100) composite scour surface. The abrupt change from heterolithics to thick-bedded sandstones marks the establishment of a new sediment delivery system, which may have been triggered by an updip channel avulsion. The composite scour and subsequent sandstone fill support a change from erosion- and bypass-dominated flows to depositional flows, which might reflect increasingly sand-rich flows as a new sediment route matured. This study provides a unique outcrop example with 3D stratigraphic control of the record of a new sediment conduit, and development and fill of a large-scale composite scour surface at a channel mouth transition zone, providing a rare insight into how scours imaged on seafloor data can be filled and preserved in the rock record.

Integrating outcrop and subsurface data to improve the predictability of geobodies distribution using a 3D training image: A case study of a Triassic Channel – Crevasse-splay complex

Fluvial sandstones deposited by high-sinuosity fluvial systems are one of the most complex reservoirs to predict and model with confidence, a reflection of both the geometries and complex distribution of the component geobodies. By integrating both analogue outcrop data and associated subsurface data, as well as new technical advances in the reconstruction of the outcrop in 3D (Digital Outcrop Models, DOM), the geostatistical parameters, which condition the modelling of these reservoirs, can be better determined. In addition, DOMs also allow us to easily extract the necessary georeferenced input data (digitized outcrop interpretations, geometrical parameters, as well as key surfaces) and so create geocellular outcrop models (GOM); a useful tool with which to contrast the results obtained from geostatistical simulations, as well as to quantify the uncertainty associated with the results.In this study, classical field data, digital data derived from outcrop models and subsurface data were combined in order to carry out a geostatistical modelling of a Channel – Crevasse-splay complex outcrop analogue, located in the Triassic Red Beds of Iberian Meseta (TIBEM). Geostatistical modelling results were obtained by combining Object-based (OBM) and MultiPoint Statistics-based (MPS) modelling techniques.A critical element in this study was the design of appropriate modelling workflows with Petrel® which would best reproduce the distribution of heterogeneities at macroscale. The designed modelling workflow was used to construct a 3D Training Image (TI) of a fluvial reservoir comprising both a meandering channel system and its associated overbank sandstone deposits. The resulting TI represents all geobodies described in the studied outcrop example and is exportable to similar fluvial reservoirs. This TI was then used in MPS simulations, in order to establish how it could assist in the prediction of the reservoir geobodies, as well as confirming to what extent this prediction matched the outcrop.

Freshwater to low salinity expression of Cretaceous Glossifungites-demarcated autogenic stratigraphic surfaces, central Utah

One of the most important contributions that S. George Pemberton made to the field of ichnology was the identification that burrowed firmgrounds associated with the Glossifungites Ichnofacies, commonly demarcate important sequence stratigraphic allogenic surfaces, and more recently described autogenic surfaces. This study considers an outcrop example from the Turonian Ferron Sandstone of central Utah, wherein high and low abundance monospecific suites of Glossifungites isp. are preserved landward of marginal-marine settings, recording colonization in channels under low salinity conditions. High abundances of Glossifungites isp. are associated with sloped areas of the erosional surfaces due to environmental preference, and with clay-rich underlying lithologies owing to either substrate selection or toponomy. These suites of the Glossifungites Ichnofacies demarcate surfaces at the bases of small, stacked channels encased in coastal plain strata. Stacking suggests repeated colonization related to an autogenic process. The enclosing strata and estimated position of the shoreline indicate a more landward affinity than previously reported for the ichnogenus Glossifungites, which is normally related to erosional nearshore processes or, less commonly, to offshore submarine channel development. Glossifungites-like burrows are constructed in modern freshwater settings by subaqueous insects, such as mayfly nymphs, but the trace fossil widths reported from the Ferron Sandstone are up to one and a half times larger than these modern examples. This suggests that the described trace fossils were made by marine-recruited, brackish-water crustaceans that created similar-sized burrows, or if constructed by subaqueous insects, the tracemakers were divergent in size or body plan from known modern tracemakers.

A general model for growth trajectories of linear carbonate platforms

ABSTRACT A key challenge regarding development of carbonate platforms is predicting the temporal pattern of platform-margin progradation, aggradation, retrogradation, and drowning. Numerical forward models of carbonate sedimentation have been widely applied to this problem, shedding substantial light on the roles of sediment production, transport, tectonic subsidence, and eustasy on the evolution of carbonate platforms. However, forward models are typically complex and computationally expensive, preventing comprehensive exploration of parameter space. In addition, the interactions among parameters are often nonlinear, preventing the development of simple expressions relating the position of the platform margin to the governing parameters of the model. To complement the considerable insights derived from numerical forward models, this study presents analytical expressions for the temporal evolution of the position of platform margins using the simplest possible assumptions regarding sediment production and transport. These expressions provide useful null models, deviations from which can be used to identify the particular effects of biology or seawater chemistry on carbonate factories in influencing the development of these important sedimentary deposits. Application of the model to synthetic and outcrop examples demonstrates that these simple equations are useful for parameter estimation that can then be used to guide more detailed, process-based numerical forward models.

The Relationship between Fluid Flow, Structures, and Depositional Architecture in Sedimentary Rocks: An Example-Based Overview

Fluid flow in the subsurface is fundamental in a variety of geological processes including volcanism, metamorphism, and mineral dissolution and precipitation. It is also of economic and societal significance given its relevance, for example, within groundwater and contaminant transport, hydrocarbon migration, and precipitation of ore-forming minerals. In this example-based overview, we use the distribution of iron oxide precipitates as a proxy for palaeofluid flow to investigate the relationship between fluid flow, geological structures, and depositional architecture in sedimentary rocks. We analyse and discuss a number of outcrop examples from sandstones and carbonate rocks in New Zealand, Malta, and Utah (USA), showing controls on fluid flow ranging from simple geological heterogeneities to more complex networks of structures. Based on our observations and review of a wide range of the published literature, we conclude that flow within structures and networks is primarily controlled by structure type (e.g., joint and deformation band), geometry (e.g., length and orientation), connectivity (i.e., number of connections in a network), kinematics (e.g., dilation and compaction), and interactions (e.g., relays and intersections) within the network. Additionally, host rock properties and depositional architecture represent important controls on flow and may interfere to create hybrid networks, which are networks of combined structural and stratal conduits for flow.

Seismic expression of shear zones: Insights from 2-D point-spread-function based convolution modelling

Shear zones are common strain localization structures in the middle and lower crust and play a major role during orogeny, transcurrent movements and rifting alike. Our understanding of crustal deformation depends on our ability to recognize and map shear zones in the subsurface, yet the exact signatures of shear zones in seismic reflection data are not well constrained. To advance our understanding, we simulate how three outcrop examples of shear zones (Holsnøy - Norway, Cap de Creus - Spain, Borborema - Brazil) would look in different types of seismic reflection data using 2-D point-spread-function (PSF)-based convolution modelling, where PSF is the elementary response of diffraction points in seismic imaging. We explore how geological properties (e.g. shear zone size and dip) and imaging effects (e.g. frequency, resolution, illumination) control the seismic signatures of shear zones. Our models show three consistent seismic characteristics of shear zones: (1) multiple, inclined reflections, (2) converging reflections, and (3) cross-cutting reflections that can help interpreters recognize these structures with confidence.

Recognizing the product of concave‐bank sedimentary processes in fluvial meander‐belt strata

AbstractDownstream migration of point bars is an important process in meander belts. Inherent to downstream migration is sediment accumulation in concave channel banks, immediately adjacent to and downstream of convex point bars. Despite this, associated concave bank processes are often overlooked, with depositional products sparsely identified in the stratigraphic record. Counter‐point‐bar deposits are a type of concave‐bank deposit that have been positively identified in subsurface three‐dimensional seismic datasets, yet outcrop examples are not well‐constrained. This study characterizes and establishes recognition criteria of counter‐point‐bar deposits in outcrop using extensive exposure of Late‐Cretaceous meander‐belt deposits in eastern Alberta, Canada. Using a combination of traditional field‐based sedimentological analyses and three‐dimensional outcrop mapping with an Uncrewed Aerial Vehicle and Structure‐from‐Motion photogrammetry, point bar, counter‐point bar, and associated abandoned‐channel deposits, as well as adjacent floodplain deposits are identified. Bed‐scale characteristics of counter‐point‐bar deposits include interlaminated and interbedded siltstone and fine‐grained sandstone, abundant organic detritus, and evidence of deformation and slumping. At the bend scale, accretion packages bounded by internal erosion surfaces are composed of dipping siltstone and minor sandstone beds that extend from the top to the base of the meander belt. At the belt scale, positive identification relies on concave accretion surface mapping, their orientation relative to the meander‐belt edge (i.e. dipping away), and consideration of meander‐bend evolution. These results have implications for recognition of counter‐point‐bar deposits in analogous, less‐constrained data sets, which provides a foundation for more complete palaeoenvironmental interpretations.

Image processing techniques to improve characterization of composite ichnofabrics

Image processing techniques, including the Analyze Particles tool offered by Fiji software and the Intensity Profile by ICY (IP-ICY), were applied in core and outcrop examples to improve characterization of autocomposite ichnofabrics. Analyze Particles gives information about particle shape and size in the studied image. This tool was applied to Chondrites assemblages in composite ichnofabrics in view of selected images of modern marine hemipelagic cores from Site U1385 of IODP Expedition 339. Differences in size, relative abundance, density and distribution of Chondrites were interpreted as related to variations within the population of Chondrites tracemakers. Intensity Profile quantifies pixel values of the infilling material of traces, proving helpful to discriminate between specimens, evaluate the horizon of colonization, and approach the penetration depth. Its application to the analysis of Zoophycos improves characterization of composite ichnofabrics from deep-sea pelagic calcilutites of the Petra Tou Romiou section (Eocene Lefkara Formation; southern Cyprus). Some suites of Zoophycos were interpreted as associated with different phases of colonization from several horizons. Moreover, it was possible to discriminate structures pertaining to different specimens, as opposed to those from the same specimen.

The role of mass transport deposits contributing to fluid escape: Neogene outcrop and seismic examples from north Taranaki, New Zealand

Many sedimentary structures are the manifestation of fluid escape in sedimentary basins. This paper examines outcrop and seismic examples in upper Miocene deep-water sandstones and siltstones of north Taranaki, New Zealand. In outcrop examples of fluid escape features comprise discordant bodies within otherwise uniformly bedded surrounding stratigraphy, features characterized by steep sided, over-hanging, vertical or near-vertical margins, infilled with an assortment of poorly sorted or chaotically arranged sandstone and siltstone. Typically, these features are several metres wide and up to 20 m high in outcrop and always occur stratigraphically below a mass transport deposit (MTD). Examples of similar features from nearby 2D and 3D seismic reflection data consist of localized vertical to sub-vertical zones of disrupted reflectivity and are as much as 300 m in height and 10’s–100’s of metres in width. The structures occur in close association with the basal slide planes of seismic-scale MTDs. The close association of fluid escape structures with MTDs suggests that these features formed by the sudden loading of the sedimentary succession by the emplacement of several metre-thick overlying MTDs. We suggest recurring phases whereby the emplacement of MTDs triggered fluid escape within underlying strata and, in turn, the fluid escape contributed to further instability with potential for mobilization and transport of subsequent MTDs in a dynamic deep-water setting.