ALBERT

Description: The Pramollo Basin (Italy-Austria) is one of the richest body and trace fossil sites of the Alps, and exhibits a well-preserved Permian–Carboniferous fluvio-deltaic to marginal-marine sedimentary succession. Despite the exceptionally abundant and well-preserved ichnological heritage, the trace fossils of the Pramollo Basin are not well studied, particularly those of Permian units. This study focuses on the ichnofauna of the Val Dolce Formation (Permian; partly Asselian to partly Sakmarian), with the goal of documenting its ichnological heritage and reconstructing its paleoenvironment. These research questions are addressed by applying network theory, an emerging field of complexity science that focuses on web-like systems made of interconnected entities. An ichnological system can be seen as a set of interlinked ichnotaxa, the topology of which depends on the organism-environment interactions. In addition, traditional paleontological and sedimentological observations are used to reconstruct the paleoenvironment. The following ichnotaxa are documented from the Val Dolce Formation: Archaeonassa isp., Curvolithus simplex , Cylindrichnus isp., Helminthoidichnites tenuis , Nereites missouriensis , Planolites isp., Phymatoderma isp., Pramollichnus pastae , Psammichnites plummeri , Taenidium isp., and Zoophycos isp. Network analysis indicates that the Val Dolce ichnological system is structured, with ichnotaxa organized in environment-driven ichnoassociations: Cylindrichnus - Planolites (proximal delta front), Phymatoderma - Zoophycos (prodelta with dysoxic porewaters), Cylindrichnus - Helminthoidichnites - Curvolithus - Zoophycos (distal delta front–proximal prodelta), and Helminthoidichnites - Taenidium - Curvolithus - Nereites - Zoophycos (prodelta). Furthermore, the delta front–prodelta gradient is accompanied by increasing bioturbation intensity and diversity, reflecting the decreasing intensity of major environmental stressors (hydrodynamics, freshwater input, turbidity). Centrality measures of network analysis allow the topological position of traces to be discerned within the studied system, detecting the paleoenvironmental resolution of individual ichnotaxa. As intersections of sets can be described by networks, the studied ichnoassociations can be considered as occupying intersecting behavioral niches. In analogy with the concept of a Hutchinsonian niche, an ichnotaxon’s niche exists in a multidimensional abstract space defined by environmental parameters, which are expressed as spatial variables in the paleolandscape. Consequently, ichnoassociations are not just association patterns, but represent spatial, environmental, and topological entities. This approach allows the reconstitution of spatial relationships between the geographical ranges of ichnotaxa and ichnoassociations, providing information on the physical arrangement of different subenvironments, that is, the structure of the paleoenvironment.

Description: A probabilistic method has been devised to assess the geologic realism of subsurface well-to-well correlations that entail the lateral tracing of geologic bodies across well arrays with constant spacing. Models of geo-body correlability (based on the ratio between correlatable and penetrated geo-bodies) are obtained from total probabilities of penetration and correlation, which are themselves dependent on the distribution of lateral extent of the geo-body type. Employing outcrop-analog data to constrain the width distribution of the geo-bodies, it is possible to generate a model that describes realistic well-to-well correlation patterns for given types of depositional systems. This type of correlability model can be applied for checking the quality of correlation-based subsurface interpretations by assessing their geologic realism as compared with one or more suitable outcrop analogs. The approach is illustrated by generating total-probability curves that refer to fluvial channel complexes and that are categorized on the basis of outcrop-analog classifications (e.g., braided system, system with 20% net-to-gross), employing information from a large fluvial geo-body database, Fluvial Architecture Knowledge Transfer System (FAKTS), which stores information relating to fluvial architecture. From these total-probability functions, values can be drawn to adapt the correlability models to any well-array spacing. The method has been specifically applied to rank three published alternative interpretations of a stratigraphic interval of the Travis Peak Formation (Texas), previously interpreted as a braided fluvial depositional system, in terms of realism of correlation patterns as compared to (1) all analogs recorded in FAKTS and considered suitable for large-scale architectural characterization, and (2) a subset of them including only systems interpreted as braided.

Description: Outcrop analogs are routinely used to constrain models of subsurface fluvial sedimentary architecture built through stochastic modeling or interwell sand-body correlations. Correlability models are analog-based quantitative templates for guiding the well-to-well correlation of sand bodies, whereas indicator variograms used as input to reservoir models can be parameterized from data collected from analogs, using existing empirical relationships. This study tests the value and limitations of adopting analog-informed correlability models and indicator variogram models and assesses the effect and significance of analog choice in subsurface workflows for characterizing fluvial reservoirs. A 3.2-km (2-mi)-long architectural panel based on a virtual outcrop from the Cretaceous Blackhawk Formation (Wasatch Plateau, Utah) has been used to test the methodologies. Vertical dummy wells have been constructed across the panel, and the intervening fluvial architecture has been predicted using correlability models and sequential indicator simulations. The correlability and indicator variogram models employed to predict the outcrop architecture have been compiled using information drawn from an architectural database. These models relate to (1) analogs that partially match with the Blackhawk Formation in terms of depositional setting and (2) empirical relationships relating statistics on depositional element geometries and spatial relations to net-to-gross ratio, based on data from multiple fluvial systems of a variety of forms. The forecasting methods are assessed by quantifying the mismatch between predicted architecture and outcrop observations in terms of the correlability of channel complexes and static connectivity of channel deposits. Results highlight the effectiveness of correlability models as a check for the geologic realism of correlation panels and the value of analog-informed indicator variograms as a valid alternative to variogram model parameterization through geostatistical analysis of well data. This work has application in the definition of best-practice use of analogs in subsurface workflows; it provides insight into the typical degree of realism of analog-based predictions of reservoir architecture, as well as the effect of analog choice, and draws attention to associated pitfalls.

Description: A bstract : Mudstone-dominated marine successions are common in the geological record, yet a full understanding of their depositional processes is often hampered by a lack of generally accepted diagnostic criteria to distinguish between hemipelagic settling and deposition from a flowing medium. The Marnoso Arenacea Formation, a turbidite unit of Miocene age cropping out in the northern Apennines of Italy, offers the possibility to address some of these uncertainties. A relatively small (~ 10%) but distinctive portion of the Marnoso Arenacea Formation is composed of white marlstone beds (WM beds) that have frequently been interpreted as due to hemipelagic settling of fine-grained particles (hemipelagites). The analysis of the anisotropy of magnetic susceptibility (AMS) revealed the presence in the WM beds of maximum susceptibility axes clustered within the depositional plane along the average paleoflow direction inferred from flute casts at the bases of the nearest turbidite beds, whereas the minimum susceptibility axes are oriented perpendicular to the bedding plane. This fabric is interpreted as largely sedimentary in origin (albeit a contribution from tectonic shortening cannot be excluded) and due to the alignment within the bedding plane of paramagnetic grains (e.g., muscovite) and possibly also ferromagnetic grains (magnetite) under low-velocity currents. The trend of the maximum susceptibility axes, and hence of the paleoflow direction, is approximately oriented NNW–SSE after correction for Apennines thrust-sheet rotation since the Miocene. These results suggest that the WM beds cannot be entirely due to hemipelagic settling, as often stated in the literature. A discussion of alternative depositional mechanisms leads us to conclude that the WM beds may have been deposited under the influence of contour currents and should therefore be referred to as muddy contourites.

Description: The Miocene Marnoso-arenacea Formation (Italy) is the only ancient sequence where deposits of individual submarine density flow deposits have been mapped in detail for long (〉100 km) distances, thereby providing unique information on how such flows evolve. These beds were deposited by large and infrequent flows in a low-relief basin plain. An almost complete lack of bed amalgamation aids bed correlation, and resembles some modern abyssal plains, but contrasts with ubiquitous bed amalgamation seen in fan-lobe deposits worldwide. Despite the subdued topography of this basin plain, the beds have a complicated character. Previous work showed that a single flow can commonly comprise both turbidity current and cohesive mud-rich debris flows. The debris flows were highly mobile on low gradients, but their deposits are absent in outcrops nearest to source. Similar hybrid beds have been documented in numerous distal fan deposits worldwide, and they represent an important process for delivering sediment into the deep ocean. It is therefore important to understand their origin and flow dynamics. To account for the absence of debrites in proximal Marnoso-arenacea Formation outcrops, it was proposed that debris flows originated within the study area due to erosion of mud-rich seafloor; we show that this is incorrect. Clast and matrix composition show that sediment within the cohesive debris flows originated outside the study area. Previous work showed that intermediate and low strength debris flows produced different downflow-trending facies tracts. Here, we show that intermediate strength debris flows entered the study area as debris flows, while low strength (clast poor) debris flows most likely formed through local transformation from an initially turbulent mud-rich suspension. New field data document debrite planform shape across the basin plain. Predicting this shape is important for subsurface oil and gas reservoirs. Low strength and intermediate strength debrites have substantially different planform shapes. However, the shape of each type of debrite is consistent. Low strength debrites occur in two tongues at the margins of the outcrop area, while intermediate strength debrite forms a single tongue near the basin center. Intermediate strength debrites are underlain by a thin layer of structureless clean sandstone that may have settled out from the debris flow at a late stage, as seen in laboratory experiments, or been deposited by a forerunning turbidity current that is closely linked to the debris flow. Low strength debrites can infill relief created by underlying dune crests, suggesting gentle emplacement. Dewatering of basal clean sand did not cause a long runout of debris flows in this location. Hybrid beds are common in a much thicker stratigraphic interval than was studied previously, and the same two types of debrite occur there. Hybrid flows transported large volumes (as much as 10 km 3 per flow) of sediment into this basin plain, over a prolonged period of time.

Description: Quantitative databases storing analog data describing the geometry of sedimentologic features are commonly used to derive input for geostatistical simulations of reservoir sedimentary architecture; however, geometrical information alone is inadequate for the detailed characterization of sedimentary heterogeneity. A relational database storing fluvial architecture data has been developed and populated with literature- and field-derived data from modern rivers and ancient successions. The database scheme characterizes fluvial architecture at three different scales of observation—recording style of internal organization, geometries, and spatial relationships of genetic units—classifying data sets according to controlling factors (e.g., climate type) and context-descriptive characteristics (e.g., river pattern). The database can therefore be filtered on both architectural features and boundary conditions to yield outputs tailored on the system being modeled to generate input to object- and pixel-based stochastic simulations of reservoir architecture. When modeling heterogeneity with stochastic simulations, the choice of input parameters quantifying spatial variation is problematic because of the paucity of primary data and the partial characterization of supposed analogs. This database-driven approach permits the definition of various constraints referring to either genetic units (e.g., architectural elements) or material units (i.e., contiguous volumes of sediment characterized by the same value of a given categorical or discretized variable; e.g., same lithofacies type, clay and silt content, and others), which permit the realistic description of fluvial architecture heterogeneity. Applications of this database approach include the computation of relative dimensional parameters and the generation of auto- and cross-variograms and transition-probability matrices, which are necessary to effectively model spatial complexity.

Description: Submarine sand-rich slope fans within confined basins have long been recognized as components of deepwater depositional systems and, in some areas, they host important hydrocarbon accumulations. The Bric la Croce-Castelnuovo turbidite system (BCTS) of northern Italy offers an opportunity to study an exposed sand-rich slope fan system, allowing reconstruction of the main architectural elements of a fan, from slope to basin floor. The system belongs to the Langhe Basin, the major depocentre of the TPB (Tertiary Piedmont Basin), an episutural basin set upon a complex of Alpine nappes of the Liguria-Piemonte Western Alps. The system consists of three main erosional and depositional zones from up- to downstream (from SE to NW): i ) a base of slope zone; ii ) a channel-lobe transition zone; iii ) a lobe zone. Downslope and upslope migration of these sectors determines, through time, their superimposition and gives rise to a generation of depositional units of different hierarchical order ranging from metre-thick simple facies sequences to decametres composite facies sequence, expression of single and composite architectural elements as channel and lobe complexes. The vertical organisation of the BCTS reflects its overall forestepping. Thin-bedded turbidites interpreted as distal lobes are overlain by stacked sandsheets and aggradational channels attributed to the mid-fan setting. At the top of the series, coarse-grained sandy channels correspond to the maximum of forestepping. The logged sections and the geological mapping provide a valuable data set that can be used to study the spatial-temporal relationships between facies of channelized and nonchannelized strata (lobe deposits) along a depositional profile, cut roughly parallel to the main palaeocurrent flow. The sands were derived from south and flowed toward the north. The portion of the BCTS which crops out is approximately 160 m thick and extends for about 10–12 km in a SW-NE direction. Research involved a detailed analysis of facies (genetic facies related to depositional processes), physical stratigraphy of stacking and correlation patterns. The detailed correlation panels allowed evaluating how facies changed along the depositional profile and this was considered as the expression of the flow transformation during its movement. Based on these considerations, it has been possible to reconstruct different facies tracts, which are related to flows with different volume and efficiency recording a coeval phase of sedimentation in the channel, channel-transition and lobe zones.

Description: A bstract :  Submarine sediment density flows are one of the volumetrically most important processes for sediment transport across Earth. The sediment concentration of flows that reach the deep ocean has never been measured directly, and understanding these long-runout flows remains a major challenge. The Miocene Marnoso-Arenacea Formation in the Italian Apennines is the only ancient sequence where individual submarine sediment-density-flow deposits (single beds) have been mapped out for more than 100 km down-flow. Here we document the external shape and internal architecture of thirty-two individual beds that record flow evolution and can be compared to deposit shapes in mathematical or experimental models. The large number of beds allows modes of flow behavior to be identified. Larger-volume turbidites are typically dominated by massive (T A ) or planar-laminated (T B ) sandstone intervals that have a broad thickness maximum. This shape is important because it suggests that massive and planar laminated sandstones record hindered settling from dense near-bed layers, which have high (〉 10% by volume) sediment concentrations. Previously, some authors have inferred that planar-laminated sandstones (T B ) are deposited mainly by dilute flows. The position of the broad thickness maximum moves basinward as the volume of sand in the flow increases. This is consistent with mathematical modeling that suggests the position of the thickness maximum depends on flow thickness, flow speed, and sediment settling velocity, as well as sediment concentration, variations in seawater entrainment rate, and local changes in seafloor gradient. Smaller-volume turbidite sandstone intervals are finer grained and dominated by ripple cross-lamination (T C ) and have a near exponential decay in thickness that is consistent with deposition from a dilute sediment suspension. The rate of near exponential thinning is controlled by sandstone volume. In contrast, turbidite mudstone intervals show an approximately linear increase in thickness with distance. Flows that entered the basin in opposite directions produced turbidite mudstone intervals that thicken towards the same location, indicating that muddy turbidity currents can drain back over long distances to basinal lows.

Description: A bstract :  Turbidity currents, and other types of submarine sediment density flow, redistribute more sediment across the surface of the Earth than any other sediment flow process, yet their sediment concentration has never been measured directly in the deep ocean. The deposits of these flows are of societal importance as imperfect records of past earthquakes and tsunamogenic landslides and as the reservoir rocks for many deep-water petroleum accumulations. Key future research directions on these flows and their deposits were identified at an informal workshop in September 2013. This contribution summarizes conclusions from that workshop, and engages the wider community in this debate. International efforts are needed for an initiative to monitor and understand a series of test sites where flows occur frequently, which needs coordination to optimize sharing of equipment and interpretation of data. Direct monitoring observations should be combined with cores and seismic data to link flow and deposit character, whilst experimental and numerical models play a key role in understanding field observations. Such an initiative may be timely and feasible, due to recent technological advances in monitoring sensors, moorings, and autonomous data recovery. This is illustrated here by recently collected data from the Squamish River delta, Monterey Canyon, Congo Canyon, and offshore SE Taiwan. A series of other key topics are then highlighted. Theoretical considerations suggest that supercritical flows may often occur on gradients of greater than ~ 0.6°. Trains of up-slope-migrating bedforms have recently been mapped in a wide range of marine and freshwater settings. They may result from repeated hydraulic jumps in supercritical flows, and dense (greater than approximately 10% volume) near-bed layers may need to be invoked to explain transport of heavy (25 to 1,000 kg) blocks. Future work needs to understand how sediment is transported in these bedforms, the internal structure and preservation potential of their deposits, and their use in facies prediction. Turbulence damping may be widespread and commonplace in submarine sediment density flows, particularly as flows decelerate, because it can occur at low (〈 0.1%) volume concentrations. This could have important implications for flow evolution and deposit geometries. Better quantitative constraints are needed on what controls flow capacity and competence, together with improved constraints on bed erosion and sediment resuspension. Recent advances in understanding dilute or mainly saline flows in submarine channels should be extended to explore how flow behavior changes as sediment concentrations increase. The petroleum industry requires predictive models of longer-term channel system behavior and resulting deposit architecture, and for these purposes it is important to distinguish between geomorphic and stratigraphic surfaces in seismic datasets. Validation of models, including against full-scale field data, requires clever experimental design of physical models and targeted field programs.