Papers by Rodrigo Perovano
Large-scale mass-transport deposits: a major architectural element in the Cenozoic sedimentary construction of the offshore Amazon basin, Brazilian equatorial Atlantic
HAL (Le Centre pour la Communication Scientifique Directe), Oct 9, 2016
Anomalously shallow bottom-simulating reflections on the upper Amazon deep-sea fan record gas hydrate response to upward fluid/heat flux
HAL (Le Centre pour la Communication Scientifique Directe), Jun 25, 2017
International audienceThe Amazon River supplies one of the world's largest deep sea fans, a s... more International audienceThe Amazon River supplies one of the world's largest deep sea fans, a sedimentary depocentre over 10 km thick that occupies an area of nearly 330,000 km 2 from the shelf-break to water depths greater than 4000 m. Gas hydrates have been inferred to occur within the Amazon fan, based on seismic profiles showing discontinuous bottom simulating reflectors (BSRs) on the upper fan, and the presence of gassy sediments and pore water freshening in sediment cores of ODP Leg 155 on the lower fan. Gas hydrate dissociation during glacial-interglacial changes in sea level has been hypothesized to act as a trigger for slope instabilities within the fan. The Amazon fan is also characterized by remarkably high rates of sedimentation, especially during the late Quaternary when average sedimentation rates reached 50 mm/year during glacial stages. Rapid deposition favours overpressure build-up, which can drive deformation at different scales. On the Amazon fan this includes gravitational collapse above multiple deep detachment surfaces, expressed near the seafloor in a large-scale extensional-and-compressional system characterized by normal faults on the shelf and upper slope (above ~500 mbsl) and thrust-folds at greater depths (from ~1000 mbsl to 2000 mbsl). Some of these structures can reach the seafloor generating scarps up to 500 m in relief attesting to ongoing deformation. Our interpretation of a regional grid of 2D and 3D multichannel seismic reflection data, combined with modeling of the gas hydrate stability zone, provides new information on the distribution and character of discontinuous BSRs on the Amazon fan and their relation to fluid flow through structures within the compressive domain. BSRs are only observed in water depths of 1200-2000 m, mainly on the northwest part of the main depocentre, forming a series of elongate BSR 'patches' up to 140 km long and 10-50 km wide that coincide with the crests of thrust-folds. The BSRs mainly lie at 200-300 mbsf, as strong reflections of negative polarity that cut across deformed strata within the thrust-folds and fade away within intervening basins. In places the BSRs rise to shallower depths, within 150 m of the seafloor, in some cases beneath fluid escape features observed on 3D seismic, including pock-marks and probable mud volcanoes linked to migration pathways within the thrust-folds. The regional methane hydrate stability zone (RMHSZ) was modeled using the phase boundary for pure methane in equilibrium with water of 3.5% salinity and inputs for bathymetry (Gebco08), bottom-water temperatures (World Ocean Database) and geothermal gradients (International Heat Flow Commission, ODP and published sources). The results show the upper limit of the RMHSZ to lie between 500-600 mbsl, its exact position being controlled by bottom-water temperatures that vary over seasonal and longer timescales. The RMHSZ thickens rapidly downslope in response to low geothermal gradients within the upper-central fan (17-20˚C/km), to maximum thicknesses of over 1 km (in 2500-3000 m water depth) but decreases to 305 m on the lower fan (> 4,000 m water depth). On the upper fan, the modeled depth of the RMHSZ (700-900 mbsf) is several times greater than the maximum depths of the BSR observed on seismic sections. Anomalously shallow BSRs could be explained either by highly saline pore fluids, or by higher sub-seafloor temperatures. Modeling of the RMHSZ using a range of constant geothermal gradients shows the BSR patches to correspond to values that vary across their widths (of 10 km or more) from 40˚C/km at their edges to as high as 90˚C/km where shallowest. This variation in gradients corresponds to vertical variations in temperature of up to 7.5˚C across the observed sub-seafloor depth range of the BSRs (150 m). The coincidence of BSRs with thrust-folds versus their absence elsewhere (over water depths of 500-4500 m), suggests that compressive structures are key elements for the migration of fluids from depth. The fact that BSRs are only observed above thrust-folds could be explained in terms of higher fluid flux, in particular by a supply of fre
Gas hydrates are ice-like compounds of water and volatiles (mainly methane) that are stable in de... more Gas hydrates are ice-like compounds of water and volatiles (mainly methane) that are stable in deep-sea sediments due to high pressures and low temperatures. Changes in oceanographic conditions that reduce their stability field (e.g. sea level lowering, bottom water warming) have been suggested to trigger continental slope failures. The Amazon deep-sea fan is a major Plio-Quaternary depocentre associated with large-scale slope instabilities, in which the presence of gas hydrates has been reported from a discontinuous bottom simulating reflection (BSR) on the upper slope. Reductions in gas hydrate stability during lowered sea levels have been argued to trigger megaslides from the upper fan; megaslides have also been linked to tectonism within an extension- compression system on the upper fan recording its collapse above deep detachments. Here we present the first systematic mapping of the Amazon fan BSR using a regional grid of 2D/3D seismic reflection data, and argue the results to ...
BSRs Elevated by Fluid Upwelling on the Upper Amazon Fan : Bottom-up Controls on Gas Hydrate Stability
The stability of natural gas hydrate accumulations on continental margins has mainly been conside... more The stability of natural gas hydrate accumulations on continental margins has mainly been considered in terms of changes in seawater pressures and temperatures driven from above by climate. We present evidence from the Amazon deep-sea fan for stability zone changes driven from below by fluid upwelling. A grid of 2D and 3D multichannel seismic data show the upper Amazon fan in water depths of 12002000 m to contain a discontinuous bottom simulating seismic reflection (BSR) that forms 'patches' 1050 km wide and up to 140 km long, over a total area of at least 5000 km. The elongate BSR patches coincide with anticlinal thrust-folds that record ongoing gravitational collapse of the fan above decollements at depths of up to 10 km. The BSR lies within 100300 m of seafloor, in places rising beneath features that seafloor imagery show to be pockmarks and mud volcanoes, some venting gas to the water column. The BSR patches are up to 500 m shallower than predicted for methane hydrate ba...
Proceedings of the 3 Simpósio Brasileiro de Geofísica, 2008
Proceedings of the 3 Simpósio Brasileiro de Geofísica, 2008
Seafloor instabilities on the southeastern flank of the Amazon Fan and adjacent Area, Foz do Amazonas basin: preliminary results
15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017, 2017
Effects of a regional décollement level for gravity tectonics on late Neogene to recent large-scale slope instabilities in the Foz do Amazonas Basin, Brazil
Marine and Petroleum Geology, 2016
Extra sets of 2D multi-channel seismic and chronostratigraphic data allowed us to undertake analy... more Extra sets of 2D multi-channel seismic and chronostratigraphic data allowed us to undertake analyses of source to sink processes and triggering mechanisms of the gigantic megaslides previously documented off the NW and SE steep slope settings of the Foz do Amazonas basin. As these megaslides comprise two sets of stacked allochthonous masses within the Upper Miocene-Quaternary sedimentary record, they are now described as Mass-Transport Complexes (MTCs) and have been renamed the Amapa Megaslide Complex (AMC) and the Para-Maranhao Megaslide Complex (PMMC). Individual megaslides of both MTCs can mobilize up to kilometre-thick sedimentary series as allochthonous masses with distinct flow directions, degrees of sediment disruption and internal coherence. Megaslides spread downslope over areas as large as thousands of km2, attaining dimensions comparable to the world's largest mass-transport deposits. Among all the megaslides, the basal and largest AM1 megaslide (AMC) stands as a quite unique example of mass-transport deposit in the basin, interpreted as a dominant carbonate allochthonous mass sourced from a mixed carbonate-siliciclastic platform. The instability was probably triggered between the late Miocene and the end of the Early Pliocene by the gravitational collapse of the mixed platform under its own weight, after successive subaerial exposures which generated karstification processes. Siliciclastic-type megaslides, on the other hand, are all sourced from large upslope slide and/or rotated blocks (up to 60 km wide in the case of the PMMC). The detachment of upslope blocks was triggered by structurally-induced seabed movements during the Mid Pliocene-Pleistocene (in the case of the PMMC) and during the Pleistocene (in the case of the AMC). All mapped features support the interpretation of sedimentary blocks which have undergone long lasting deformation, having been variably folded and faulted by the sliding along an overpressured condensed section (H3 horizon). H3 horizon equally acts as the upper decollement level for the gravity tectonic system that operates on the regional scale of the Foz do Amazonas basin. In such a context, the results of this study evidence complex links between variable modes and scales of gravity processes (gravity tectonics and MTCs emplacements), all induced by instability created from a condensed section prone to produce pore fluid overpressure. And yet, seismic attributes of the decollement H3 across the slope, characterized by a reflector of negative polarity of high amplitude, indicate that the potential for similar large scale sediment failures continues to exist across the AMC and PMMC.
Movimentof de massa multiescala na Bacia da Foz do Amazonas- Margem Equatorial Brasileira
The Chuí Megaslide Complex: Regional-Scale Submarine Landslides on the Southern Brazilian Margin
Advances in Natural and Technological Hazards Research, 2016
The Brazilian Continental Shelf Survey Programme (LEPLAC) identified the occurrence of large-scal... more The Brazilian Continental Shelf Survey Programme (LEPLAC) identified the occurrence of large-scale mass-transport deposits on the southernmost limit of the Brazilian margin, based mainly on analyses of acoustic imagery. The mass-transport deposits, named the Chui Megaslide Complex, comprise a stack of large translational slides that spread from the shelf break ~650 km downslope to ~4,900 m water depth, cutting into Pliocene-Quaternary sedimentary successions and strongly affecting both the margin morphology and regional depositional processes. The main headwall scarp is U-shaped, 400–500 m high, and extends c. 80 km downslope as a large elongated evacuated scar, 50–85 km wide. Outside this main failure scar, external scarps evidence a large area of erosion and faulted blocks, indicating ongoing retrogressive sediment disruption. Slide masses occur as a combination of variably deformed failed masses and debris flows, covering an area of ~150,000 km2. Main preconditioning parameters and the possible triggering mechanism for the Chui Megaslide Complex are likely a combination of a series of causative factors such as slope failure structurally-induced by gravity tectonics and high sediment influx into the shelf-edge and upper slope during the Early Miocene-Quaternary.
Multiple Megaslide Complexes and Their Significance for the Miocene Stratigraphic Evolution of the Offshore Amazon Basin
Advances in Natural and Technological Hazards Research, 2016
The interpretation of a new and extended 2D seismic database on the offshore Amazon Basin (Foz do... more The interpretation of a new and extended 2D seismic database on the offshore Amazon Basin (Foz do Amazonas Basin) confirms the widespread presence of regional-scale mass-transport deposits (MTDs) that are important architectural elements of the Amazon Deep Sea Fan. These MTDs were deposited since the late Miocene and extend throughout an area of nearly 315,000 km2. They are grouped into three megaslide complexes: the northwestern Amapa Complex, the Central Amazon Fan Complex and the southeastern Para-Maranhao Complex. Each complex has multiple stacked MTDs with various internal seismic facies that are indicative of large downslope modification and disruption of the original stratigraphy. The majority of the MTDs show chaotic or transparent internal seismic facies that we interpret as indicative of debris flow deposits. Although we cannot determine the exact triggering mechanism(s) for the various sediment failures, these events appear to be related to the gravitational compression of fold-and-thrust belts created by gravity-tectonic processes on the upper Amazon Fan and to structurally-induced mobilization of large blocks on the upper continental slope in response to overpressure along impermeable surfaces. These processes were apparently more active during the Pleistocene in response to increased sedimentation rates on the fan.
Deep-water fold-and-thrust belts in the Amazon deep-sea fan
The Amazon deepsea fan is part of the offshore Amazon Mouth basin. It comprises a thick progradi... more The Amazon deepsea fan is part of the offshore Amazon Mouth basin. It comprises a thick prograding siliciclastic prism (∼ 9 km thick) related to the Amazon River input since Upper Miocene (∼10 Ma). Gravitydriven deepwater foldandthrust belts stand as the most remarkable structures along the margin, deforming both the deepsea fan and the earlier marine sequences (Lower CretaceousMiddle Miocene). Thrust structures, imaged by 2D multichannel seismic profiles, were driven by gravity in a linked extensionalcontractional system gliding on weak overpressured shales, and driven by sedimentary loading and by the bathymetric slope. Extension is characterized by both basinward and landwarddipping normal faults on the shelf and upper slope. Downdip contraction induced detachment folds and reverse/thrust faults leading to the formation of piggyback basins. Sliding of the sedimentary section took place along distinct detachment surfaces and, apparently, at different stages of the margi...
Estratigrafia sísmica da porção NW do Leque Superior do Amazonas
12th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 15–18 August 2011, 2011
The Upper Amazon Deep-sea Fan is strongly affected by families of normal faults and fold-and-thru... more The Upper Amazon Deep-sea Fan is strongly affected by families of normal faults and fold-and-thrust belts that detach along weak basal decollement levels. These structures are significantly more complex at the Northwest part of the upper fan, where a Northwestern Structural Compartment was defined. Seismic analysis of 2D multichannel seismic and well data carried out in the present work provide evidences that the deposition of the fan stratigraphic succession in the Northwestern Structural Compartment took place between the Upper Miocene and the Upper Pleistocene under the influence of variable rates of sediment supply and variable rates of gravitydriven deformation. Three main stages of distinct patterns of structural and depositional interaction could be identified: stage 1 took place during the onset of the fan stratigraphic succession in the Upper Miocene (~10.5-5.3 My), associated to higher terrigenous sediment input, and is characterized by widespread downslope deposition with no evidence of noticeable structurally-conditioned depocenters, pointing rather to a quiescent gravity tectonic structural set; stage 2 comprises the fan deposition during the Pliocene (~5.3-2.6 My) concentrated in a few depocenters distributed close and along planes of main proximal normal faults and along the piggy-back basins developed on the distal fold-and-thrust belts. This stage points to an active syn-depositional structural set. Activation of this structural system may has been triggered by the increasing sedimentary loading exerted by the Pliocene deposition; finally, stage 3 concerns the Quaternary (~2.6-0.0 My) fan deposition and represents a stage of enhanced sediment supply organized as a much wider and continuous depocenter, involving most of the upper fan area between the normal faults and the distal fold-and thrust belts which act as an imposing topographic barrier since then. As a conclusion, the complex structural style of the Northwestern Structural Compartment observed today stems from stage 3 deposition and deformation that occurred during the Quaternary.
Structural Analysis of Multiple Phases of Gravity Deformation in the Foz do Amazonas Basin using Seismic Interpretation and Experimental Modeling
12th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 15–18 August 2011, 2011
The tectonic evolution of passive margins affected by gravity-driven shale tectonics can occur th... more The tectonic evolution of passive margins affected by gravity-driven shale tectonics can occur through episodic events, reflecting critical stages of pore-fluid overpressure in weak lithological levels, which can lead to gravitydriven deformation (gravity gliding/spreading) of the overlying sedimentary package above multiple decollements levels. Based on preliminary results of seismic interpretation, experimental models were developed to replicate possible scenarios for the structural evolution of the gravitational deformation that have affected the marine sequences of the Foz do Amazonas Basin. The resulting structural setting reminds in many aspects the gravity-driven features described in the basin. An initial gravity gliding phase of a flat-layered model resulted in an upslope set of extensional faults and a downslope gravitational fold-and-thrust belt. During the second deformation phase, the gravity spreading of progradational wedges over the sliding sheet previously deformed by gravity gliding was able to promote the gradual reactivation of the compressive belt either in compression or sometimes reactivated in extension, as the shelf progrades. In all experiments, two decollements levels acted at some time or place supporting the gravitational deformation. The mechanical behavior of these decollements (silica microspheres layers) varies in time and space based on the magnitude of pore-fluid overpressure and, thus, resembles the behavior of overpressured shales.
Recurrent Megaslides in the Foz do Amazonas Basin
11th International Congress of the Brazilian Geophysical Society & EXPOGEF 2009, Salvador, Bahia, Brazil, 24-28 August 2009, 2009
A coupled system of gravity tectonics and mass wasting processes in the Amazon Deep-sea Fan
11th International Congress of the Brazilian Geophysical Society & EXPOGEF 2009, Salvador, Bahia, Brazil, 24-28 August 2009, 2009
Models of salt-sediment interactions influencing the architecture of the Plio-quaternary deep-water sedimentary systems, Gulf of Lions-Western Mediterranean
10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007
Arquitetura sedimentar do sistema turbidítico pliocênico do Golfo de Lion, Mediterrâneo Ocidental
10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007
The Gulf of Lion located in the Western Mediterranean has in its basin important deep water turbi... more The Gulf of Lion located in the Western Mediterranean has in its basin important deep water turbidity complexes, like the Rhone Deep-Sea Fan. During the Pliocene, the feeder system of this fan would have been constituted by multiple canyons; while in the Quaternary, the feeder system would have converged for a single canyon - the Petit-Rhone Canyon. However, the analysis of an isopac map of the Pliocene suggested that the pliocene sequence converges for two principal canyons - the Marti and the Petit-Rhone Canyon.
Estruturas halocinéticas indicativas de deformação dúctil: exemplo do Golfo de Lion - Mediterrâneo Ocidental
10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007
The marine sedimentary sequence of the Gulf of Lions (Miocene-Holocene) contains an evaporitic le... more The marine sedimentary sequence of the Gulf of Lions (Miocene-Holocene) contains an evaporitic level of Messinian age (5,6-5,3 Ma), whose gravitational gliding is the motor for the salt tectonics that affects the area. Plio-Quaternary salt tectonic deformations developed characteristic structural zonations: an extensive proximal domain characterized by lystric normal faults, and a distal contractional zone dominated by diapirs, connected by rigid gliding domain – the so-called Rigid Gliding Province. This province is relatively little deformed in relation to both the extensive and the contractional domains. However, we observe the presence of saltcored anticlines forming zones of buckle folds which affect Plio-Quaternary sequences. In the present work we undertake a seismic analysis in order to investigate the nature and mechanisms of deformation involved. Our results show the occurrence of buckle folds along the socalled Rigid Gliding Province. These deformations are concentrated in large area of the southwestern region of the Gulf of Lion, covering the whole area between the upslope extensional faults and the distal diapirs, while to the East, they are limited to a narrow zone close to the distal salt diapirs. The seismic analysis shows as well that the buckle folds are late deformational structures dating from middle Pliocene to Early Quaternary. The formation of salt-cored anticlines is probably due to a late mechanism of ductile layer-parallel shortening. On the other hand, the concentration of buckle folds in the southwestern region of the Gulf is probably due to the concave morphology of the sub-salt relief in the area, which seems to have induced a pattern of convergent radial gliding of both the salt layer and the sedimentary cover. As a result, the area and the mechanical role of the intermediate translational province have changed with time, evolving from a real Rigid Gliding Province (between Early to Middle Pliocene) to a deformation zone that accomodates part of the upslope extension (between Upper Pliocene to Early Quaternary).
Investigação da tectônica gravitacional na Bacia da Foz do Amazonas a partir de análise sísmica e de modelagem experimental
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Papers by Rodrigo Perovano