1,721,138 research outputs found
Depositional architecture of a confined, sand-rich submarine system: the Bric la Croce–Castelnuovo turbidite system (Tertiary Piedmont Basin, Oligocene, NW Italy)
No full textSubmarine 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 down-stream (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
Processes and facies trends of hybrid event beds in deep-water systems: outcrop case studies and applied significance from the North-Apennine
No full textHybrid event beds (HEBs) are a type of deep-water sediment gravity flow deposit comprising a basal clean (H1) and/or banded (H2) sandstone overlain by a muddier sandy facies (H3) emplaced during the same transport event. They generally have a tabular geometry but an internal complexity in terms of relative thickness and texture of the component divisions. HEBs are increasingly recognised in outcrop and in hydrocarbon reservoirs, requiring an improved understanding of their textural make-up, association, context and impact on reservoir properties.
Although HEBs share the described common characters that allow them to be differentiated from ‘classic’ turbidites, observations from a range of sedimentary basins show great variability in their sedimentological character. The texture of the relatively mud-rich H3 division and the size and shape of substrate clasts within it are key feature for classification and process interpretation. Two important and recurring bed associations are identified: (1) a range of commonly thick beds in which the H3 division can include very large substrate slabs and blocks, evidence of extensive autoinjection and clast break-up, and dense mudclast concentrations, all set in a sandstone with elevated interstitial clay. This association typically is found in outer fan and confined sheet systems in a downdip position. (2) beds in which H3 divisions are characterised by high levels of dispersed clay, floating mudstone clasts and matrices that are enriched in hydraulically-fractionated components (mica, organic matter, clay flocs). Beds with thin H3 divisions typically pass down-dip to those in which H3 is expanded. This association is found in fan lobe successions where it can alternate with turbidites. The two associations are interpreted to reflect different modes of flow transformation. In the first case, the rafts and chaotic textures are related to local substrate delamination processes that culminated in the formation of a linked cohesive debris flow because of intense internal shearing and clast disaggregation. The second association formed by mud entrainment at channel mouths, proximal lobe locations or flow expansion points and developed through progressive longitudinal flow transformation and rapid deceleration and may include deposition from transitional flows
Quantification of the degree of confinement of a turbidite-filled basin : a statistical approach based on bed thickness distribution
No full textBed thickness distribution within turbidite systems is related to basin geometry and to magnitude and duration of depositional events. Cumulative distribution of turbidite bed thicknesses is often interpreted in terms of a power-law. Alternatively, these distributions have been described by a lognormal mixture model. Changes in the power-law exponent can be related to the rheological properties of the gravity-driven flows and to the geometry of the basin.
This study attempts to quantify the degree of confinement of well-exposed turbidite units of the Oligocene Cengio and Bric la Croce - Castelnuovo Turbidite Systems (Tertiary Piedmont Basin, Italy). Focus is on the behaviour of bed thickness distribution. The succession is suitable for this study because it represents the infill of a progressively widening basin, during quiescence of intrabasinal tectonics. In this basin the cumulative frequency distribution of turbidite bed thickness follows a segmented power-law relationship. The deviation from the trend observed for the thickest beds is associated with a deficiency of beds in a certain thickness range. This behaviour suggests existence of a thickness threshold that segregates the deposits of the fully confined flows that could deposit thick aggrading beds, with minor downcurrent flow transitions, from the rest of the bed-thickness population. This threshold decreases from the lowermost (and most confined) to the uppermost units of the Cengio Turbidite System (CTS). No thresholds were identified for the uppermost Bric la Croce - Castelnuovo Turbidite Systems (BCTS) that spread over a wider basin than the CTS, suggesting unconfined deposition. The BCTS was presumably larger than the area that could be covered by the turbidity currents.
When integrated with data on sedimentology and basin morphology (well-log and seismic data), bed thickness statistics can provide a general guidance about interpretation of depositional settings, degree of confinement, erosion/amalgamation and bypass of turbidites, improving and assisting the development of reservoir models
Syndepositional tectonics recorded by soft-sediment deformation and liquefaction structures (continental Lower Permian sediments, Southern Alps, Northern Italy): Stratigraphic significance
Full text linkThe Lower Permian succession of the Central Southern Alps (Lombardy, Northern Italy) was deposited in fault-controlled continental basins, probably related to transtensional tectonics. We focussed our study on the stratigraphic record of the Lower Permian Orobic Basin, which consists of a 1000. m thick succession of prevailing continental clastics with intercalations of ignimbritic flows and tuffs (Pizzo del Diavolo Formation, PDV) resting on the underlying prevailing pyroclastic flows of the Cabianca Volcanite. The PDV consists of a lower part (composed of conglomerates passing laterally to sandstones and distally to silt and shales), a middle part (pelitic, with carbonates) and an upper part (alternating sandstone, silt and volcanic flows). Syndepositional tectonics during the deposition of the PDV is recorded by facies distribution, thickness changes and by the presence of deformation and liquefaction structures interpreted as seismites. Deformation is recorded by both ductile structures (ball-and-pillow, plastic intrusion, disturbed lamination, convolute stratification and slumps) and brittle structures (sand dykes and autoclastic breccias). Both the sedimentological features and the geodynamic setting of the depositional basin confidently support the interpretation of the described deformation features as related to seismic shocks. The most significant seismically-induced deformation is represented by a slumped horizon (about 4. m thick on average) which can be followed laterally for more than 5. km. The slumped bed consists of playa-lake deposits (alternating pelites and microbial carbonates, associated with mud cracks and vertebrate tracks). The lateral continuity and the evidence of deposition on a very low-angle surface along with the deformation/liquefaction of the sediments suggest that the slump was triggered by a high-magnitude earthquake.The stratigraphic distribution of the seismites allows us to identify time intervals of intense seismic activity, which correspond to rapid and basin-wide changes in the stratigraphical architecture of the depositional basin and/or to the reprise of the volcanic activity.The nature of the structures and their distribution suggest that the magnitude of the earthquakes responsible for the observed structures was likely higher than 5 (in order to produce sediment liquefaction) and probably reached intensity as high as 7 or more. The basin architecture suggests that the foci of these earthquakes were located close to the fault-controlled borders of the basin or within the basin itself
Boulders expectation in glacial till tunneling: a T-progs approach (Transition Probability Geostatistics). It.: previsione della presenza di massi nello scavo di gallerie in depositi glaciali: approccio geostatistico mediante T-progs (Transition Probability Geostatistics).
No full textBoulders expectation in glacial till tunneling: a transition probability geostatistical approach.
No full textValidation of Hurst statistics : a predictive tool to discriminate turbiditic sub-environments in a confined basin
No full textTurbidite sequences within confined basins constitute important hydrocarbon reservoirs worldwide; for this reason the discrimination of sedimentary sub-environments based on an objective statistical method is of interest for pure and applied science.
We investigated the potential use of the Hurst test (Chen & Hiscott 1999) as a statistical tool to discriminate sub-environments within geologically complex turbiditic units that fill a confined basin with well exposed facies transitions and onlaps, at the scale of several stacked reservoirs (Cengio and Bric la Croce - Castelnuovo Turbidite Systems in the Tertiary Piedmont Basin, Oligocene, Northern Italy). In vertical stratigraphic sections, the Hurst test determines the degree of clustering of low and high values of sedimentological variables like bed-thickness, grain-size and sand/mud ratio that are dependent on sub-environments of deposition. We applied the Hurst test to depocentral and marginal sub-areas across the basin (parallel and perpendicular to the main palaeo-current direction), documenting a different clustering of thick and thin beds, and of high and low values of the sand/mud ratio, in the depocentre-distal sector with respect to the onlap areas.
A new field (onlap sub-environment) could thus be added to the Chen & Hiscott (1999) classification diagram of turbidite settings based on the Hurst index. The Hurst phenomenon i.e. clustering of high and low values of the selected variables, was also able to distinguish between proximal and distal (depocentral) lobe settings, and to recognize the fingerprint of the different depositional lobes (fully confined aggrading, prograding, backstepping).
The map of turbidite sub-environments obtained by interpolation of the Hurst index is quite comparable to the field-observed facies map, providing impressive robust validation of the Hurst statistics. This method seems to represent a very promising predictive tool for subsurface studies of turbiditic oil fields based on core and log analyses
Expectation of boulder frequency when tunneling in glacial till : a statistical approach based on transition probability
No full textThe aim of this study is the prediction of boulder frequency encountered during the construction of a tunnel in a morainic amphitheatre in northern Italy. This area is characterized by the presence of glacial and fluvioglacial
deposits from the Pleistocene age.
The ability to predict the size and frequency of boulders during construction is essential for assessing the type of machines to be used for tunneling and the related cost. Borehole data from site exploration programs do not provide sufficient information (e.g. frequency, size and location) on boulders embedded in the studied deposits. Statistics regarding boulder sizes, however, can be inferred from borehole data through the
application of geostatistical techniques.
A new estimation method is proposed that utilizes a transition probability-based geostatistical approach (TPROGS)
to model spatial variability of boulders by 3-D Markov chains. T-PROGS has several advantages over traditional geostatistical methods because it has a conceptual framework for incorporating a considerable amount of geological information into the development of simulations. This is accomplished by linking fundamental observable geological attributes (e.g. mean lengths, material proportions, anisotropy, and lithofacies juxtaposition) with Markov chain model parameters.
The geological database used consists of the following: borehole data, geological survey of the excavation,
outcrop measurement of boulder characteristics and an interpretative geological cross-section across the
study area.
The result of geostatistical simulations allowed prediction of the size, frequency distribution and location of boulders during the construction of the tunnel. The higher value of boulder concentration corresponds to glacial deposits, where a concentration of 27 boulders/10,000 m3 of sediments has been simulated.
Furthermore, the variability between different simulations that have been computed allowed quantification
of the uncertainty
Previsione della presenza di massi nello scavo di gallerie in depositi glaciali: approccio geostatistico mediante T-PROGS (Transition Probability Geostatistics)
No full textThe aim of this study is the prediction of boulder (erratic blocks) frequency encountered during the construction of a tunnel in a morainic amphitheatre of the northern Italy. This area is characterized by the presence of glacial and fluvio-glacial deposits of Pleistocene age. The ability to predict the size and frequency of boulders during construction is essential for assessing the type of machines to be used for tunnelling. A geostatistical method is proposed herein that utilizes a transition probability-based geostatistical approach (T-PROGS) to model spatial variability of boulders by 3-D Markov Chains. T-PROGS has several advantages over traditional geostatistical methods because has a conceptual framework for incorporating many geological information into the development of simulations. This is accomplished by linking fundamental observable attributes mean lengths, material proportions, anisotropy, and juxtapositioning with Markov chain model parameters. The geological data base used in this study to compute the geostatistical simulations consist of: borehole data, geological survey in the excavation, measurement on outcrop of boulder characteristics (larger, smaller and intermediate axis, respectively L1, L2 and L3) and an interpretative geological cross-section across the study area. The result of this study allows us to predict the size and frequency distribution of boulders during the construction of the tunnel. The higher value of boulders is in correspondence of glacial deposits, where a concentration of 27 boulders/10000 m3 of sediments has been simulated. The variability between different simulations that have been computed allows us to quantify the result uncertainty
Sedimentological structures as evidence of syndepositional tectonics : liquefaction and convolution structures from continental Early Permian sediments (Southern Alps, Northern Italy)
No full text- …
