United States

We present PALEOSTRIPv1.0, a MATLAB open-source software designed to perform 1D, 2D and 3D backtracking of paleo-bathymetries. PALEOSTRIP comes with a Graphical User Interface (GUI) to facilitate computation of sensitivity tests and to allow the users to switch on and off all the different processes and thus separate the various aspects of backtracking. As such, all physical parameters can be modified from the GUI. It includes 3D flexural isostasy, 1D thermal subsidence and possibilities to correct for prescribed sea level and dynamical topography changes. In the following we detail the physics embedded within PALEOSTRIP and we show a few applications on a drilling site (1D), a transect (2D) and a map (3D), taking the Ross Sea (Antarctica) as a case study. PALEOSTRIP has been designed to be modular and to allow users to insert their own implementations.

SGI 2021

A user-friendly 3D backtracking software to reconstruct paleo-bathymetries

The mission of ENASE (Evaluation of Novel Approaches to Software Engineering) is to be a prime international forum to discuss and publish research findings and IT industry experiences with relation to novel approaches to software engineering.

ENASE 2020

technical paper

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In the Northern Ionian Sea, the Calabrian Accretionary Wedge (CAW) is facing directly the subducting Apula plate, mainly made of Mesozoic to Tertiary Carbonate Platform (Del Ben et al., 2010; Volpi et al., 2017). This contribution illuminates the structures and stratigraphic relationships between the frontal part of the orogenic belt, the foredeep and adjacent Apulian foreland. A detailed seismic facies analysis of four multichannel seismic profiles has been carried out to define the tectonic-sedimentary evolution of the study area but without exploration wells not available for these deep offshore area. Seismic interpretation allows to identify four main structural domains: the highly tectonized CAW; the narrow foredeep basin filled by a Pliocene-Holocene subhorizontal succession laying above buried normal faults; the massive carbonate succession of the Apulian Platform showing reef and carbonate platform margin facies; the layered succession of the Apulian Platform characterized by ‘'intra-platform'’ facies in the easternmost portion of the area. Three main regional unconformities with characteristic relationships with structural trends were recognized: i) the Messinian unconformity, related to a regional and significant erosion associated to paleokarst processes on the exposed Mesozoic Apulian Platform, is cut by an array of normal faults in the Apulian foreland and by thrust in the accretionary wedge; ii) the angular and erosive middle Pliocene Unconformity truncates the Lower Pliocene reflectors and is affected by normal faults in the foreland and by compressive tectonics in the CAW; iii) a Jurassic/Cretaceous unconformity in the Apulian foreland is marked by Cretaceous reflectors onlapping the Jurassic carbonate platform. The CAW is characterized by compressive tectonics with several fore-thrusts forming a leading imbricate fan system nearby the orogenic front. The Mesozoic Apulian platform is affected by active extensional tectonics driven by flexural bending since Lower Pliocene (Volpi et al., 2017; Maesano et al., 2020), that probably reactivated old normal faults related to the Permian-Triassic rifting stage. The structural map shows that transpressive and positive inversion tectonics is a common deformational style in the central sector of the foreland, suggesting that the Apulia plate is already part of the Calabrian/Hellenic belt. According to these observations, the compressive tectonics affecting the Apula plate is interpreted as related to shortening processes of both the CAW and Hellenic wedge whose interference plays an important role in defining the tectonic-stratigraphic evolution of the Apula Plate in the Northern Ionian Sea.

The response of the Apula plate to the advancing Calabrian and Hellenic wedges (Northern Ionian Sea): implications for subduction processes and tectono-stratigraphic evolution

The Tertiary Piedmont Basin (TPB) is an episutural basin located on top of the junction between the Western Alps and the Northern Apennines. This work combines geological mapping and interpretation of a seismic line provided by Eni S.p.A. aiming at investigating the sedimentary succession of the Arquata Scrivia-Carrosio area, a key sector separating the Alto Monferrato sector to the west from the Borbera-Curone sub-basin to the east. The seismo-stratigraphic analysis of a 33 km-long SE-NE striking seismic line extending from Carrosio to Alessandria and tied to a well, allowed recognizing seven key stratigraphic surfaces, which define six unconformity-bounded stratigraphic units. These could be tied to the outcrop by identifying component lithostratigraphic units at surface. This works contributes to better understanding of the tectono-sedimentary evolution of this sector of TPB, which can be summarized as follows: during the early Oligocene (Unit 1), coarse-grained deltas (Conglomerati di Savignone and Molare Fms.) established, which passed distally (i.e. to the NE) into turbidites and hyperpycnites (Monastero Fm). Following the swift late Oligocene transgression, these marginal fan deltas were onlapped SE-wards by hemipelagic marlstone, containing isolated channelized turbidites (Unit 2; Gremiasco Fm.). Coarse clastic supply was re-established during the Aquitanian-early Burdigalian, with deposition of confined turbidites, mass transport deposits, and channelized turbidites (Unit 3; Castagnola and Costa Montada Fms). In Unit 4 (Costa Areasa Fm., upper Burdigalian-lower Langhian) a basin plain environment established all over TPB, reflecting an increase of the accommodation space driven by southward tectonic tilting of the basin. A further event of basin inversion is that of the intra-Langhian sea level fall, driven by tectonic uplift to the south and recorded by Unit 5 (upper Langhian-lower Messinian), which comprises a range of shelfal systems (Marne di Cessole, Arenarie di Serravalle and Marne di S.Agata Fossili Fms.) making northward transition into turbidites (Cassinasco Fm.). Lastly, Unit 6 (upper Messinian-Pliocene) encompasses a basal package of conglomerates (Conglomerati di Cassano Spinola Fm.), followed upward by early Pliocene clays (Argille di Lugagnano Fm.), over which the shelf margin prograded depositing the Sabbie d’Asti Fm. In addition, the analysis of velocity data from four additional wells from other sectors of the TPB allowed defining a P-wave velocity and seismic wave propagation model. Besides the increase of velocity with depth, conglomeratic facies were found to show higher velocities (in the range 3500-4200 m/s at depths between 350 and 2800 m) than arenaceous and pelitic facies (in the range 2000-3370 m/s at depths between 350 and 3500 m below surface). Results will help time-depth conversion of seismic lines detailing the subsurface of TPB, contributing to accurate reconstruction of basin fill architecture.

Tectonics and sedimentation interplay in the eastern Tertiary Piedmont Basin (Arquata Scrivia, NW Italy): insights from new seismo-stratigraphic analysis

The Northern Apennines are a seismically active accretionary wedge formed in response to the Late Cretaceous-Eocene closure of the Ligurian-Piedmont Ocean and the Oligocene-Miocene collision between Adria and Europe. The wedge is shaped by WNW-ESE-striking, SW-dipping thrusts accommodating bulk top-to-the NE tectonic transport. Since the Late Miocene, thrusting in the belt external domains acted coevally with extension in the western hinterland domain, where crustal thinning is still being accommodated by NW-SE-striking normal faults. The focal mechanism solutions of earthquakes between 8 and 35 km constrain NE-SW shortening in the frontal part of the wedge, whereas extensional tectonics controls the seismicity along the belt’s axial portion and in the hinterland. Atop the deformed accretionary wedge occur the Epiligurian Units, which consist of middle Eocene-upper Miocene bathyal to shallow-water siliciclastic deposits infilling wedge-top basins. A regional unconformity separates pre- and post-Burdigalian sequences within the Epiligurian succession, with sedimentary facies changing from deep marine-to platform environment. Our mesoscale structural analysis shows compressional, extensional, and strike-slip fault arrays affecting extensively all the Epiligurian Units, with distinct structural features. Top-to-the NE, WNW-ESE-striking reverse faults are defined by commonly slickensided planar surfaces decorated by thin damage zones. Top-to-the SE, WSW-ENE-striking reverse faults are, instead, generally devoid of well-developed damage zones. NW-SE and NE-SW-striking normal and oblique faults systematically cut across the reverse faults and accommodate centimetric to metric throws. Common cataclastic and disaggregation deformation bands are associated with NE-SW striking normal faults cutting through Upper Eocene-Lower Oligocene siliciclastic units. On the other hand, calcite veins and fibres locally decorate NW-SE and NE-SW-striking normal and oblique faults in marly post-Burdigalian sequences, attesting to fluid-rock interaction within dilatant rock volumes during faulting. A remote sensing analysis has been performed on tectonic structures mapped at the regional scale and confirms a variable trend distribution and density for both normal and reverse faults within both the pre- and post-Burdigalian sequences. Our results suggest that these wedge-top basins probably evolved independently, influenced by lateral thickness variations of the stratigraphic sequences, erosion, subsidence rates and tectonics in response to regional and local variations of the stress regime within the underlying orogenic prism. We propose that the present-day framework of the Epiligurian Units can be used as a powerful structural-stratigraphic gauge to track down the variation, through time and space, of the tectonic regime and state of stress of the Apennines wedge, with noteworthy implications on its current seismotectonic setting.

Unveiling the structural architecture of the wedge-top Epiligurian Units in the Northern Apennines

Proofs of synsedimentary tectonics during the Early Permian in the central Southern Alps (cSA, N Italy) are recorded in the volcanic and terrigenous successions of the Laghi Gemelli Group, which are characterized by the occurrence of abrupt facies variations often associated with coarse-grained deposits. These features are generally attributed to syn-sedimentary tectonic activity demonstrated by the local occurrence of sediments deformation (Berra et al., 2011) such as liquefaction or slumping due to seismic shaking. Detailed fieldwork allowed us to recognize dewatering structures and sedimentary dikes, ball and pillars and small slumps, occurring along hundreds of mesoscopic faults showing meter-scale displacement in correspondence of high-angle conjugate systems as well as domino-style faults, often accompanied by growth structures. These structures are mainly concentrated in the fine-grained sediments of the Pizzo del Diavolo Formation, which were deposited on top of the volcaniclastic succession of the Ca’ Bianca Volcanite and crossed by seismogenic synsedimentary faults. The Permian synsedimentary structures of cSA are mostly associated with high-angle Andersonian normal faults which are combined with low-angle normal faults (LANFs) that developed along the interface between the Permian sedimentary cover and the Variscan basement (Zanchi et al., 2019). This LANFs system is relevant for the Permian hydrothermal circulation, resulting in widespread tourmalinites deposition along fault zones, and locally in U mineralization. According to our structural analysis the Permian tectonic setting is characterized by pure extension, dominated by ENE-WSW striking normal faults inverted during the Alpine shortening as high-angle reverse faults (Zanchetta et al., 2015).

Evidence of syndepositional tectonics during the Early Permian in the Orobic Basin (central Southern Alps, N Italy)

Seismic images are fundamental to interpret subsurface setting on both continental and marine environments. However, in carbonate systems, seismic response can be very difficult to be analyzed due to the petrophysical heterogeneities, being the interpretation particularly complicated when faults are present. In fact, faults rocks are generally characterized by different petrophysical properties with respect to the host rocks. Synthetic seismic forward modeling is a powerful tool to quantifying the seismic response associated with fault-related petrophysical changes, since input parameters can be modified. In this study, field and laboratory measurements are used to analyze the spectrum of the carbonate-bearing fault seismic response. Here, we focused on the carbonate ramp setting outcropping in the Majella Massif since it represents an excellent surface analogue of buried porous and faulted carbonate reservoirs worldwide. Density and porosity were measured through a helium pycnometer on representative fault (damage zone) rocks sampled at increasing distances from fault planes. Investigated damage zone samples, show both increased and decreased porosity with respect to the host rock, depending on the single fault characteristics. A 2D (12 km long) synthetic profile from the platform top to the basin, oriented SSE-NNW, was then carried out in Matlab simulating the outcropping architecture and spatial distribution of the sedimentary facies and of the faults. Together with a proper porosity variation related to facies distribution, the porosity along the damage zones (DZ) of the simulated faults was set according to the laboratory measurements. The low-frequency (40Hz) synthetic seismic profile shows marked diffraction hyperbolas in the modeled fault zones for faults characterized by higher porosity DZ where lower seismic velocity is expected. On the contrary, fault zone characterized by lower porosity DZ with respect to the host rock resulted to give a less clear seismic image. Going into the details, faults with decreased porosity and consequent increased seismic velocity of 1000 m/s in the damage zone respect to the host rock, do not show a visible difference in the seismic response if compared with the seismic image without modified petrophysical characteristics within the faults. On the other hand, faults with increased porosity and decreased seismic velocity of just 500 m/s respect to the host rock, show clear diffraction hyperbolas where their apexes correspond to the fault planes. Ongoing laboratory measurements and simulations changing geometries, thicknesses and orientations of the damage zones, are expected to help in improving the knowledge of fault seismic response. This work helps in bridging the gap between forward modeling and actual seismic imaging with large implications for hydrocarbon-reservoir characterization and the identification of potential CO2 or hydrogen storage sites.

Synthetic seismic forward modeling as a tool to assess the seismic signature of carbonate-bearing fault zones

The Eastern Mediterranean Sea results from an alternation between extensional and contractional phases. Although several geodynamic reconstructions have been proposed, its tectonostratigraphic evolution is still a matter of debate. The main tectonic phases that affected the area were the Mesozoic rifting, followed by a Cenozoic contractional phase, due to the inception of the convergence between Africa and Eurasia and the subduction of the oceanic lithosphere. From the Miocene, the opening of the Red Sea induced a rotation and northward migration of the Arabian Plate. At the same time, the rollback of the subducting oceanic lithosphere in the Central Mediterranean area favoured a westward escape of the Anatolian plate squeezed out by the northward migration of the Arabian Plate. Our study area is located in the easternmost portion of the Mediterranean Sea, offshore Turkey, Cyprus and Syria, on the ancient passive margin of the Tethys between the Arabian continental lithosphere and the African oceanic lithosphere. Along the Cyprus Arc, the Neo-Tethys oceanic crust is subducting toward NE. Most of the authors (Symeou et al. 2018 and references therein) suggested that this system is continuous from Cyprus to Syria. In this work, multi-channel seismic reflection profiles have been used to analyze the basement nature (oceanic vs continental), to recognize potential subduction zones and their lateral continuity, and to reconstruct the contractional events. Our data suggest a continental nature of the basement, excluding a continuous ophiolite complex and subduction in eastern Cyprus offshore. Most of the recent structures evidenced in the area derive from transpressional reactivation of inherited extensional fault systems.

Structural inheritance in the Northeastern Mediterranean basin 

Diagnostic morphological features (e.g. rectilinear seafloor scarps) and lateral offsets of the Upper Quaternary deposits are typically used to infer offshore active faults. These structures are not necessarily capable of producing large earthquakes as they could be shallow and formed in response to local stresses. We present a multiscale approach to reconstruct the structural pattern in offshore areas and distinguish between shallow, non-seismogenic, active faults, and deep blind faults, potentially associated with large seismic release. The approach is based on the interpretation of seismic reflection profiles with different resolution/penetration and the quantitative morphometric analysis of multibeam bathymetry. The site chosen for testing the method is the Sant’Eufemia Gulf (south-eastern Tyrrhenian Sea) because it is a natural laboratory to investigate the relationships between regional and local processes associated with a slab tear fault (e.g. Rosenbaum et al., 2008) and crustal structures controlling the Plio-Quaternary tectonic evolution (e.g. Brutto et al., 2016). Data highlights the occurrence of three major tectonic events since the Late Miocene. The first extensional or transtensional phase occurred during the Late Miocene. Since the Early Pliocene, a right-lateral transpressional event caused the positive inversion of deep (> 3 km) tectonic features, and the formation of NE-SW faults in the central part of the gulf. Also, NNE-SSW to NE-SW trending anticlines (e.g. Maida Ridge) developed in the eastern sector. Since the Early Pleistocene (Calabrian), shallow (< 1.5 km) NNE-SSW oriented structures formed in a left-lateral transtensional regime. The results of this work integrated with literature data indicate that the transpressional/transtensional structures developed in an ~E-W oriented principal displacement zone extending from the Sant’Eufemia Gulf to the Ionian offshore. The strike-slip zone likely represents the upper plate response to the development of a slab tear fault.  The quantitative morphometric and bathymetric analyses indicate that NNE-SSW to NE-SW trending anticlines were negatively reactivated during the last tectonic phase. We suggest that the deep structure below the Maida Ridge may correspond to the seismogenic source of the large magnitude earthquake that struck the Calabrian region in 1905. The multiscale approach contributes to understanding the tectonic imprint of active faults with different hierarchical order developed in a strike-slip zone orthogonal to the Calabrian Arc.

Geometry and kinematics of offshore active faults revealed by an integrated multiscale method

The role of sea-bottom topography in the dispersal of shallow water-derived calciturbidites across a submarine rift, as determined by the local extensional architecture, is under-investigated, namely with pelagic settings along ancient passive continental margins. A comparison with modern carbonate platform/basin analogues, or with siliciclastic systems, is not always feasible, as ancient carbonate systems were commonly home to anachronistic environments (e.g. the Western Tethyan Mesozoic). Geological mapping of the Jurassic rift basin exposed in the Apennines of Central Italy revealed a complex pattern of intrabasinal highs (pelagic carbonate platforms) and intervening basins, controlled by the high density, and oddly variable trends, of faults rooted in a shallow detachment layer corresponding to thick Triassic salt. A map pairing the occurrences of resedimented beds in pelagic successions with an updated palaeogeography becomes therefore the natural descriptor of the itineraries followed by sediment gravity flows. This qualitative method represents a companion, or even alternative, approach to the one strictly based on physical stratigraphy, and it greatly improves our knowledge of regional geology and rift-basin analysis. Our study focuses on: i) a reconstruction of the palaeotectonic architecture of the Umbria-Marche Basin in the Jurassic, and on ii) how this architecture produced a submarine topography which governed the dispersal of sediment, shed by the neighbouring Lazio-Abruzzo Carbonate Platform, for >40 million years. Geological mapping, coupled with the measurement and correlation of stratigraphic sections, shows that the marginal palaeoescarpments of pelagic carbonate platforms formed obstacles to the gravity flows as sediment load was discharged in confined basins at their toes and/or flows were deflected and forced along alternative itineraries. While turbidity currents were locally vigorous enough to climb the escarpments, leaving graded and laminated overbank deposits on the pelagic carbonate platform-tops, a “shelter” effect is evidenced by the resediment-free nature of those basins lying downflow, which were shielded by the highs. Our case study potentially represents the analogue of hydrocarbon fields both inland and in the offshore.

Role of Early Jurassic rift architecture in the dispersal of calciturbidites, as revealed by geological mapping in Central and Northern Apennines

A 2D and 3D re-interpretation of vintage seismic profiles acquired during the 1970s in the area of the Northern Tyrrhenian Sea between the Elba Island and the Argentario promontory was performend to build a 3D models of the main structures characterizing the Tuscan shelf. Stratigraphic information were extracted by the Pianosa island surface geology along with the Martina-1 and Mimosa-1 exploration wells. We identified eight seismostratigraphic units separated by eight unconformities. Among these seismostratigraphic units, two represent the pre-Neogenic foundation while six post-orogenic units represent the Neogenic succession covering the Tuscan shelf. The main shallow structures of the area are the narrow, mostly N-S and NE-SW trending Neogenic basins of Montecristo, Punta Ala and Uccellina, where the post-orogenic seismostratigraphic units deposited. Effort has been done to unravel the relationship between the position and evolution of the basins with previous compressive structures, mostly consisting in deep East-verging thrusts belonging to a previous compressional phase. Intringuingly, and partially in contrast with the literature works in the area, no evidence of listric and low angle fault systems were observed. A new evolutionary model of the Tuscany shelf was then proposed. In this view the formation of the Neogenic basins began in the upper Burdigalian initially as intermontane basins developed along the flanks of the antiforms formed during the compressive tectonics. The position of the basins, usually recovered at the forelimb vs. the backlimb of the thrust antiforms, influenced the  asymmetrical or symmetrical shape during their evolution. Starting from the Messinian, we observe a general collapse of the platform, which leads to the deepening of the basins driven by the normal high-angle bordering faults. This process continues up to the lower Pliocene, when the deactivation of all normal faults is recorded, and conditions of widespread subsidence are clear throughout the platform, together with the deposition of the two more post-orogenic units. In this contribution we reviewed the tectonic evolution of the northern Tyrrhenian Sea posing new questions both on the mechanisms responsible for the extensional processes and on the structures which impacted on such arrangement, also establishing a new starting point for a full unravelling of the Tuscan Shelf evolution.A 2D and 3D re-interpretation of vintage seismic profiles acquired during the 1970s in the area of the Northern Tyrrhenian Sea between the Elba Island and the Argentario promontory was performend to build a 3D models of the main structures characterizing the Tuscan shelf. Stratigraphic information were extracted by the Pianosa island surface geology along with the Martina-1 and Mimosa-1 exploration wells. We identified eight seismostratigraphic units separated by eight unconformities. Among these seismostratigraphic units, two represent the pre-Neogenic foundation while six post-orogenic units represent the Neogenic succession covering the Tuscan shelf. The main shallow structures of the area are the narrow, mostly N-S and NE-SW trending Neogenic basins of Montecristo, Punta Ala and Uccellina, where the post-orogenic seismostratigraphic units deposited. Effort has been done to unravel the relationship between the position and evolution of the basins with previous compressive structures, mostly consisting in deep East-verging thrusts belonging to a previous compressional phase. Intringuingly, and partially in contrast with the literature works in the area, no evidence of listric and low angle fault systems were observed. A new evolutionary model of the Tuscany shelf was then proposed. In this view the formation of the Neogenic basins began in the upper Burdigalian initially as intermontane basins developed along the flanks of the antiforms formed during the compressive tectonics. The position of the basins, usually recovered at the forelimb vs. the backlimb of the thrust antiforms, influenced the  asymmetrical or symmetrical shape during their evolution. Starting from the Messinian, we observe a general collapse of the platform, which leads to the deepening of the basins driven by the normal high-angle bordering faults. This process continues up to the lower Pliocene, when the deactivation of all normal faults is recorded, and conditions of widespread subsidence are clear throughout the platform, together with the deposition of the two more post-orogenic units. In this contribution we reviewed the tectonic evolution of the northern Tyrrhenian Sea posing new questions both on the mechanisms responsible for the extensional processes and on the structures which impacted on such arrangement, also establishing a new starting point for a full unravelling of the Tuscan Shelf evolution.

Tectonic-Sedimentary evolution of the Tuscan shelf: seismic-stratigraphic analysis of Neogenic succession in the norther Tyrrhenian sea (Elba Island - Argentario)

The Turkana depression (Ethiopia-Kenya) is a tectonic basin related to the Cretaceous-Early Cenozoic development of the South Sudan and the Anza grabens filled with a thick sequence of Cretaceous-Paleogene sediments reaching up to a thickness of 6–8 km. These two NW-SE trending depressions, which likely resulted from NE-SW extension, were later affected by W-E extension related to the Cenozoic East African Rift System. The influence of crustal thinning related to these NW-SE grabens on later W-E-related extension is testified by the marked change in style of deformation from the narrow rift valleys in Kenya and Ethiopia, to a distributed, basin-and-range-style faulting in the Turkana depression. Despite some local scale reactivation is visible, large scale reactivation of pre-existing NW-SE structures in the Turkana depression is not obvious, as it is extensively masked by the sedimentary and volcanic cover; consequently, contrasting hypothesis on the possible role exerted by discrete pre-existing fabrics have been proposed in the literature. To address this controversy, we performed analogue models to investigate whether inherited structures, largely obscured by sediments in the Turkana depression, might have been reactivated during subsequent tectonic phases. We run 2-layer, brittle-ductile models deformed in two successive phases: a first phase of NE-SW extension, followed by W-E extension. Different models were subjected to different amount of bulk extension during the first phase to investigate the influence of this parameter (and the importance of first-phase structures) on later reactivation. Our models indicate that the amount of deformation in the initial tectonic phase is key for structure reactivation in subsequent tectonic phases: the larger the deformation in the first phase, the higher the probability of reactivation. Comparison of the experimental results with nature suggest that, despite some local fault reactivation, large-scale structures were likely not reactivated in the Turkana depression. These outcomes represent a useful tool to decipher fault reactivation, not only in the Turkana depression but also in tectonic basins worldwide, especially where thick sedimentary covers may mask tectonic structures.

A user-friendly 3D backtracking software to reconstruct paleo-bathymetries

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The response of the Apula plate to the advancing Calabrian and Hellenic wedges (Northern Ionian Sea): implications for subduction processes and tectono-stratigraphic evolution

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