192 research outputs found
Sedimentology, architecture, and depositional evolution of a coarse-grained submarine canyon fill from the Gelasian (early Pleistocene) of the Peri-Adriatic basin, Offida, central Italy.
No full textToSCAN -Turbidity currents in Submarine CANyons
No full textTurbidity currents at continental margins are subaqueous density flows, in which the suspension of sediments in seawater produces a water-sediment mixture that is denser than the ambient seawater and hence flows downslope due to gravity along the seafloor. These currents carve submarine canyons in the continental slopes and deliver sediments to the abyssal plains. Deposits from turbidity currents are notably known for being significant hydrocarbon-rich and other minerals reservoirs. Turbidity currents also represent a natural hazard for the growing offshore industry as even small currents can damage the oil and gas pipelines and undersea telecommunications cables scattered on the seafloor (see the review of Meiburg and Kneller, 2010). Understanding the dynamics of such gravity currents is thus crucially needed.
Until now the different scenarios that have been envisaged to explain the geological and geophysical observations on turbidity currents rely on qualitative models. There is no physical model for turbidity currents flowing down complex and erodible topographies. We know that particulate gravity currents flowing horizontally in a fixed V-shaped valley are progressively thinner and deposit predominantly in the centre of the valley compared to its flanks (Monaghan, Mériaux and others, 2009a & 2009b). However we do not know what is the influence of slopes on the deposition, and under which conditions erosion competes with deposition in a V-shaped valley. We know that any current consisting of multiple particles of the same density results in deposits that are vertically stratified with the coarser particles more frequent at the base, and whose grain size thins with distance from the source (Garcia, 1994), but we still do not really understand the particle-particle interactions within those currents (Mériaux and Kurz-Besson, 2012). Furthermore, few turbidity currents in the ocean have provided evidence of their capacity to damage structures laid on the seafloor but there has been no quantification of the forces exerted onto fixed or movable bodies by particulate gravity currents flowing along complex geometries such as a sloping V-shaped valley. Such questions require to be tested by physical and numerical models.
ToSCAN will develop laboratory and numerical models of turbidity currents. In particular we will perform experiments in sloping V-shaped valleys, evaluate the forces on fixed/movable objects exerted by the impact of turbidity currents, and assess the erosional power of currents on pre-existent deposits. The laboratory experiments will be run in parallel with three-dimensional numerical simulations based on the Smooth Particle Hydrodynamics (SPH) method. The experiments and simulations, which we propose to carry out in this application, are all original and innovative. The findings will be compared with modern and ancient natural analogues including canyons of the Portuguese Margin (São Vicente, Lagos, Portimão), and the ancient outcropping turbidity deposits of the Southwest Iberia (e.g. Costa Vicentina, Portugal).
Our analogue and numerical modelling will provide a framework to advance our understanding of 1) the characteristics of the deposits produced by turbidity currents flowing down an inclined V-shaped valley, 2) the conditions for erosion and deposition during a turbidity current event in a V-shaped canyon, and 3) the extent to which turbidity currents can damage or move any solid objects within their path. This study will be a key to the understanding of the complex geomorphology of the Portuguese canyon system as well as ancient turbidity deposits as our results will provide tools to interpret deposits resulting from turbidity currents. This study will also be beneficial to the offshore industry as we provide a reliable evaluation of the risks for pipelines and telecommunications cables when run over by turbidity currents.
The research team has been framed to meet the challenges set for this project with a unique group of Portuguese and international experts in analogue and numerical modelling, and in geology and marine geology disciplines
I depositi pliocenici dell’Unità di Ariano (Monti della Baronia, Appennino meridionale)
No full textMajor controls on architecture, sequence stratigraphy and paleosols of middle Pleistocene continental sediments ("Qc Unit"), eastern central Italy
No full textMiddle Pleistocene continental sediments in central Italy ("Qc Unit") record the oldest fluvial accumulation along the uplifting margin of the Peri-Adriatic basin. The architecture of the sediment body can be divided into two unconformity-bounded, fining-upward cycles interpreted as genetically related depositional sequences. These sequences highlight the systematic adjustment of the fluvial system to changes in the ratio between accommodation space and sediment supply (A/S ratio) and, from base to top, comprise the following surfaces and stratal components: (i) a regionally correlative sequence boundary resulting from an A/S ratio. ≤. 0; (ii) a low-accommodation systems tract characterized by conglomerate-rich, amalgamated channel fills and recording an A/S ratio. [removed]. 1; and (v) a mature red argillic paleosol. To constrain the climatic signal for paleosols formation, the two sequence-capping mature paleosols have been investigated. The results of these studies suggest that they were developed under humid and warm climatic conditions associated with interglacial phases, which have been correlatively attributed to Marine Oxygen Isotope Stages 11 and 9. © 2015 University of Washington
Deformation within the Pisco Basin sedimentary record (southern Peru): Stratabound orthogonal vein sets and their impact on fault development
No full textThis outcrop-based study reports diffuse joints and veins, normal to strike-slip fault zones and minor folds that developed, from Miocene to Quaternary, within the clastic to siliceous sedimentary record of the forearc Pisco Basin of southern Peru. Patterns, orientations, dimensional parameters and other outcrop-scale characteristics of the various deformation features are illustrated and their genetic mechanisms and timing of development are inferred. These new structural data and interpretations allow a better constraint of the structural style and evolution of the Pisco Basin, and can represent useful guidelines for characterizing the outcrop-scale deformation affecting similar forearc basins along the Peruvian coast. Major results of this study are that the development of the documented deformation features, their patterns, dimensional parameters and kinematics seem influenced by local perturbations of the paleostress field by mechanic processes partly independent of plate tectonics forces. These processes include strain localization on both pre-existing and progressively forming new structural discontinuities, and cyclic switches of the horizontal, principal stress axes s2 and s3. In particular, we discuss how different normal fault patterns, from sub-parallel to multidirectional/polygonal, could form in a same deformation phase in response of the local s2/s3 magnitude ratio, as an evolution of stratabound, mutually orthogonal vein set
Marine and nonmarine deposition in a long-term low-accommodation setting: an example from the Middle Pleistocene Qm2 Unit, eastern Central Italy
No full textFacies anatomy and large-scale stratigraphic organization of mid-Pleistocene strata (Qm2 Unit) exposed near the town of Ortona, eastern central Italy, have been defined through an integrated outcrop and subsurface dataset, and record sedimentation within a long-term low-accommodation setting. The studied interval can be subdivided into nine facies associations, reflecting a range of continental, marginal marine, nearshore and innermost shelf environments, and contains a well-preserved record of high-frequency relative sea-level changes in the form of a stack of three unconformity-bounded sequences. Each of the three sequences, designated Qm23, Qm22, and Qm21 from oldest to youngest, consists of a specific subset of the nine identified facies associations as a function of preserved depositional systems and systems tracts. Typically, the following architectural elements occur in ascending stratigraphic order: i) a basal unconformity, molded by fluvial incision and subaerial exposure during sea-level fall and shoreface erosion during subsequent rise; ii) a maximum regressive surface, which is coincident with the sequence boundary; iii) a transgressive systems tract including braided-river conglomerates and floodplain fines within the confines of an incised-valley, palustrine carbonates and back-barrier lagoon mudstones, and a deepening- and fining-upward shoreface to offshore-transition facies succession bounded at the base by a wave ravinement surface; iv) a sharp regressive surface of marine erosion produced by shoreface incision during relative sea-level fall; and v) a prograding, downstepping, and offlapping sharp-based lithofacies assemblage of either beach conglomerates or sandstones, ascribed to the falling stage systems tract, overlain by a rooted paleosol marking subaerial exposure. Sequences were deposited on the uplifting palaeo-Adriatic shelf in response to repeated high-frequency and high-amplitude eustatic changes in sea level that would promote the creation of accommodation space. By subtracting space to deposition, the contemporaneous regional uplift of the basin margin may be accounted for the shingled, downstepping configuration of individual sequences to form a falling stage sequence set of a larger composite sequence. In dip view, the erosional contact at the base of the Qm2 falling stage sequence set is a composite regressive surface, resulting from the downdip convergence and amalgamation of multiple erosional surfaces produced by the progressive basinward translation of successive sequences. Results from this study have direct implications for the oil and gas field development and exploration when making predictions of reservoir and seal geometries within shallow-marine, marginal-marine, and nonmarine sediments emplaced in similar long-term limited-accommodation settings
External controls on internal organization and vertical stacking pattern of Pleistocene shallow-marine and fluvial depositional sequences
No full textThe complex interaction of regional uplift, glacio-eustasy, local tectonics, and sediment supply has a significant impact on the internal
architecture and vertical arrangement of shallow-marine and fluvial depositional sequences and can be documented in well-exposed
successions of Pleistocene strata cropping out along the uplifted margins of Ecuador, northern Chile, and eastern central Italy.
The results stemming from these sediments have important implications for sequence stratigraphic models in tectonically active areas
and lead to the following general conclusions: (i) given that rates of syndepositional regional tectonic uplift were substantially less
than rates of contemporaneous eustatic changes in sea level in all of the study areas, glacio-eustasy appears to have played the main
control on development of high-frequency sequences; (ii) stratal geometries, sedimentary facies, and genetic complexity of sequence
bounding unconformities of these cyclic successions indicate that the internal organization of individual depositional sequences is
directly controlled by the rates of sediment supply and by the occurrence of intrabasinal, short-term normal faults striking obliquely
with respect to paleo-shoreline trends; (iii) the effects of the regional tectonic uplift on these eustatic sequences is on longer term, at
sequence set scale, and is responsible for their distinctive stacking pattern; owing to the progressive, tectonically driven reduction of
accommodation space, high-frequency sequences are nested within a forced regressive sequence set, where each successively younger sequence is displaced basinward and downward respect to the last
Sedimentary features of tsunami backwash deposits in a shallow marine Miocene setting, Mejillones Peninsula, northern Chile
No full textMiocene shoreface sandstones in the Caleta Herradura half-graben, northern Chile, contain an exceptionally coarse deposit that, based on sedimentologic and stratigraphic features, is regarded as having been laid down during a tsunami event by noncohesive and sediment-laden subaqueous density flows. Interpretations of the principal sediment-depositing mechanisms effective in the tsunami surges rely largely on field observations of deposit geometry and internal sedimentary characteristics. This example comprises two erosively based sedimentation units that were probably deposited by successive waves in the tsunami wave train. The Lower Unit consists of a clast-supported, polymodal, boulder-bearing breccia composed mostly of angular clasts and fewer well-rounded clasts. Framework components are mostly chaotic but may also exhibit either inverse-tonormal grading or crude normal grading. Laterally, changes in characters of depositional facies are common and abrupt. The sand-sized, bioclastic-rich matrix is poorly sorted and very similar to the underlying lower shoreface bioclastic sandstone, implying that soft sediments eroded at the lower erosional surface contributed to the tsunami deposit. The bulk of the Upper Unit is a poorly sorted, breccia-bearing sandstone. Pebbles and cobbles are scattered, massive or normally graded. Sporadic outsized boulders, emplaced as debris fall deposits, may occur along the erosional base. An array of signatures, such as unusually coarse grain size in comparison to the surrounding deposits, erosional bases, the mixed sources of sediments, multiple erosional and depositional events, normal size grading or massive texture, are all considered distinctive features of tsunamigenic deposits. Backwash deposition is indicated by the incorporation within the tsunami deposits of sediments derived from mixed sources, such as angular clasts from nearby subaerial settings, rounded clasts reworked from beach gravels, and bioclastic sand eroded from older, and unconsolidated, shoreface deposits. Notwithstanding the absence of soft-sediment deformation features, the marked facies change from a lower shoreface into an upper shoreface environment through the tsunamiites provides directional information about the origin of the tsunami wave. It was most likely produced by a sea floor fault displacement associated with an episode of sudden, probably coseismic coastal uplift
New beaked whales from the late Miocene of Peru and evidence for convergent evolution in stem and crown Ziphiidae (Cetacea, Odontoceti).
No full textThe Ziphiidae (beaked whales) represent a large group of open-ocean odontocetes (toothed cetaceans), whose elusive and deep diving behavior prevents direct observation in their natural habitat. Despite their generally large body size, broad geographical distribution, and high species number, ziphiids thus remain poorly known. Furthermore, the evolutionary processes that have led to their extreme adaptations and impressive extant diversity are still poorly understood. Here we report new fossil beaked whales from the late Miocene of the Pisco Formation (southern Peru). The best preserved remains here described are referred to two new genera and species, the Messinian Chavinziphius maxillocristatus and the Tortonian Chimuziphius coloradensis, based on skull remains from two marine vertebrate-rich localities: Cerro Los Quesos and Cerro Colorado, respectively. C. maxillocristatus is medium sized retains a complete set of functional lower teeth, and bears robust rostral maxillary crests similar to those of the extant Berardius. By contrast, C. coloradensis is small and characterized by large triangular nasals and moderately thickened premaxillae that dorsally close the mesorostral groove. Both species confirm the high past diversity of Ziphiidae, the richest cetacean family in terms of the number of genera and species. Our new phylogenetic and biogeographical analyses depart markedly from earlier studies in dividing beaked whales into two major clades: the Messapicetus clade, which, along with other stem ziphiids, once dominated the southeastern Pacific and North Atlantic; and crown Ziphiidae, the majority of which are found in deep-water regions of the Southern Ocean, with possible subsequent dispersal both globally (Mesoplodon and Ziphius) and to the cooler waters of the northern oceans (Berardius and Hyperoodon). Despite this relatively clear separation, both lineages seem to follow similar evolutionary trends, including (1) a progressive reduction of dentition; (2) an increase in the compactness and thickness of the rostral bones; (3) similar changes in facial morphology (e.g., elevation of the vertex); and (4) an increase of body size.We suggest that these trends may be linked to a convergent ecological shift to deep diving and suction feeding
Sequence response to syndepositional regional uplift: insights from high-resolution sequence stratigraphy of late Early Pleistocene strata, Periadriatic Basin, central Italy.
No full textThis paper deals with the depositional sequences that occur within the uppermost part of the Plio–PleistocenePeriadriaticbasin fill in the southern Marche region, centralItaly. The succession is an EarlyPleistocene, easterly dipping clastic wedge showing an overall shallowing trend from slope clays to shallow-marine and non-marine deposits comprising two major sequences, namely Qmb and Qmc. Analysis has provided new insights into: (i) the nature of sedimentary facies and facies associations occurring within the upper part of Qmb and Qmc; (ii) the gradual contact within Qmb between regressive littoral deposits (RLD) and underlying deep-marine blue clays; (iii) the composite origin of the Emilian surface, which is a widespread erosional unconformity separating Qmb from Qmc; (iv) the cyclothemic pattern of Qmc, composed of downstepping, small-scale depositional sequences; (v) the role played by synsedimentary uplift on the stacking pattern of small-scale sequences and their internal architecture.Up to three small-scale depositional sequences have been recognised within Qmc. They are up to 50 m thick and defined by previously unrecorded. High-frequency sequences display a distinctive stacking pattern and form a tectonically induced forced regressive sequence set underlain by a composite, tectonically enhanced regressive surface of marine erosion formed by the lateral connection of lower-rank sequence boundaries
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