United States

Over the last decade, there has been a resurgence of interest in the climatic and tectonic mechanisms that drove the Messinian salinity crisis (MSC) and the associated deposition of thick evaporites. The MSC represents an unprecedented palaeoceanographic change that led to a very short (c. 630 kyr) ecological and environmental crisis (Andreetto et al., 2021).  However, across the Levantine offshore basin, the sedimentological nature of the top evaporitic units and the mechanisms that controlled the transition from a hypersaline evaporitic unit to brackish deposits (final MSC stage 3) are still disputed. Here,  we re-evaluate the deposits associated with the terminal phase of the MSC (ca. later stage of  3.2 by Meilijson et al.,2019) ,  named in offshore Lebanon as the Nahr Menashe deposits (NM, Madof et al.,2019). We describe the NM seismic facies, characterize and map its internal seismic stratigraphy, and provide a new interpretation of its depositional environment, which persisted during the late Messinian and then evolved through a regional reflooding event. The base of the NM and some of its internal units overlies semi-circular depressions, randomly distributed linear marks and surface collapse features, which are indicative of a period of intense evaporite dissolution. The NMU seismic facies observed from the slope to the deep part of the basin support the interpretation of a layered salt-evaporite-sand depositional system subject to complex reworking, dissolution, deposition, and final erosion. A drainage network of valleys and complex tributary channels incising into the top NM shows marked erosional characteristics, which indicate a dominant southwards sediment transfer following deposition of the NM. This erosional drainage network formed due to the base-level fall associated with the last phase of the MSC. The base of the channel/valley network does not cut below the bottom of the Narh Menashe dissolution surfaces. The channel and valley network was subsequently infilled by layered sediments interpreted here to represent the post-MSC marine sediments deposited during reflooding.  Our analysis point out that the NM may represent a mixed evaporite-siliciclastic affected by karstic processes, deposited or re deposited in a shallow marine or lacustrine during the tilting of the offshore Lebanese basin .  Only subsequently did the NM experience a rapid erosional event followed by swift burial of  transgressive/high-stand sediments.

SGI 2021

Formation, dissolution and fluvial incision of the top evaporite seismic unit (Nahr Menashe) recording the end of the  Messinian salinity Crisis , NE offshore Levant Basin, Eastern Mediterranean

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L'Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS e il Dipartimento di Matematica e Geoscienze dell'Università di Trieste sono orgogliosi di ospitare il 90° Congresso della Società Geologica Italiana a Trieste dal 14 al 16 settembre 2021. La modalità del congresso è interamente online.

Con il motto "Geologia senza frontiere" questo evento mira a promuovere le Scienze della Terra come disciplina scientifica proiettata nel futuro, oltre i confini geografici, politici e disciplinari, per comprendere meglio l'interno del Pianeta Terra e la struttura del sottosuolo, difendere la società da pericolosi eventi geologici, comprendere meglio la variabilità climatica, pianificare l'utilizzo delle georisorse in modo etico e nel rispetto dell'ambiente.


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The National Institute of Oceanography and Experimental Geophysics - OGS and the Department of Mathematics and Geosciences of the University of Trieste are proud to host the 90th Congress of the Italian Geological Society in Trieste on 14-16 September 2021.  The Congress will be held entirely online.

With the motto "Geology Without Borders" this event aims to promote Earth Sciences as a scientific discipline projected into the future, beyond geographical, political and disciplinary boundaries, to better understand the interior of Planet Earth and the structure of the subsurface, defend society from dangerous geological events, better understand climatic variability, plan the use of geo-resources in an ethical way and respecting the environment.


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Earth Sciences should be understood not only as necessary for a better understanding of the interior of the planet Earth, but also as a defense of society from dangerous geological events, for the understanding of climatic variations, for the planning and use of georesources in a ethical and respecting and protecting the environment.

poster

We present a brand new multi-proxy dataset of thermal maturity indicators, which derive from the application of several analytical techniques on surface and subsurface sedimentary successions. The study area spans from the Greater Caucasus to the Adjara-Trialeti fold-and-thrust belt (FTB), comprising the intervening western Kura Basin, in Georgia, and represents a region of continental deformation in the hinterland of the Arabia-Eurasia collision zone. Original and published clay mineralogy, Raman spectroscopy and petrography on dispersed organic matter, and pyrolysis data are integrated for the first time in a coherent tectono-sedimentary scenario. Thermal maturity spans from the low diagenetic realm (60-80°C) in the Upper Miocene section of the Kura sedimentary fill, to the oil window in the Cretaceous to Lower Miocene successions of Adjara-Trialeti FTB, Kakheti ridge and Kura Basin (70-120°C), up to about 400°C in the Greater Caucasus core. Integration of different indicators, besides allowing the estimation of maximum burial temperatures acquired through time, enabled to draw the tectonic evolution of the area. Different maturity trends and thermal histories, coupled with structural and stratigraphic data, highlight that the study area comprises two domains derived from positive tectonic inversion: the E-W Adjara-Trialeti doubly-verging FTB from an Eocene back-arc rift basin and the SSW-verging Georgian Greater Caucasus from a Mesozoic rift basin. Between the two, thin-skinned south-verging thrusts deform the Kura Basin and the Kakheti ridge successions, originally deposited on an extensional structural high which was later flexured during compression. The similar thermal maturity degree in the Adjara-Trialeti FTB and the Kakheti ridge/Kura Basin areas has been acquired in different time spans: during Paleogene extension and during Miocene thin-skinned shortening, respectively. The results indicate that thermal maturation of the sedimentary successions in the Adjara-Trialeti FTB can be ascribed to burial during rift evolution. The same conclusion can be drawn for the axial zone of the Greater Caucasus, whereas tectonic overburden may have contributed to the thermal maturity of the rocks in the southern foothills of the Greater Caucasus: this area needs further work to assess its tectonic evolution.

Using multi-proxy thermal maturity datasets to validate deformation styles from the Adjara-Trialeti fold-and-thrust belt to the Greater Caucasus (Georgia)A

The tide-dominated Messina Strait (southern Italy) is a 3 km wide marine passageway, whose block-faulted borders form steep subaqueous zones incised by canyons and gullies. These erosional features retreat towards the shorelines and are often in direct connection with subaerial valley-bounded river deltas. High-energy density-flows generated by river floods periodically enter the canyon heads, attaining supercritical-flow regime and accreting large, upslope-migrating bedforms. Although these bedforms have been documented in recent studies, little attention has been paid to the definition of the type of delta entering canyon heads, the internal features of river-influenced deposits accumulated in the nearshore zone, and their interplay with tidal currents flowing axially to the strait. This study focuses on a Lower Pleistocene coarse-grained succession exposed along the north-eastern margin of the modern Messina Strait, investigated using conventional facies analysis and sedimentological logging, integrated with photogrammetric techniques and interpretation of drone-acquired imagery. Facies confinement between basement blocks suggests a subaqueous delta complex shed from the tectonically controlled margin of the ancient strait and entering shallowly submerged canyon heads. Basal breccias, conglomerates and pebbly sandstones exhibiting channel-form discontinuities and upslope dipping backsets are interpreted as cyclic-step and antidune deposits. Units composed of these facies are comprised between master erosional surfaces and tidal ravinement surfaces. The tidal ravinements suggest that canyon infill occurred during a major phase of sea-level rise, punctuated by minor falls and stillstands. These surfaces are overlain by mixed bioclastic–siliciclastic, arenitic, trough and planar cross-strata, representing dunes migrating roughly parallel to the palaeo-coastline and originated by tidal currents amplified by the narrowing of the ancient Messina Strait. Tidal-influenced sedimentation dominated over the fluvial-influenced processes during the late transgression, overfilling the canyon relief. The exceptionally good exposure of depositional architectures and facies characteristics is key to outline the general features of a specific type of delta system, fed by valley-bounded rivers and entering canyon heads in the nearshore of tectonically-controlled, tide-influenced steep strait margins. The pre-existing subaqueous incised topography forced the delta front to be split into lobe branches during the canyon infilling, hampering clinoform architectures and preserving large supercritical-flow sedimentary structures. This study suggests these as possible criteria for the recognition of similar systems in outcrop or subsurface.

Coarse-grained deltas approaching shallow-water canyon heads: A case study from the Lower Pleistocene Messina Strait, Southern Italy

Early Palaeozoic represents a crucial period in Earth history, marked by intervals of life spread alternated with short-lasting crisis in biological activity. The Zagros Basin (SW Iran) could be a key area for the study of this time interval, due to the widespread and well-exposed Cambrian-Ordovician successions; nevertheless, these are still poorly constrained from a sedimentological and stratigraphic point of view. This study, carried out through a high-resolution facies and microfacies analysis of the Zard Kuh section, aims to give a contribution to the palaeogeographic evolution of this area. The studied section (296 m thick) includes the upper Mila C Member and Ilebeyk Formation, referred to the late Cambrian (Furongian) based on acritarch assemblages. The upper Mila C Member (23 m thick) is mainly characterized by medium to thin-bedded bioclastic packstones to mudstones grading upward into a nodular limestone unit. A sharp horizon marks the contact with the overlying Ilebeyk Formation, represented by a shale-dominated interval in the lower part. These mudrocks grade upward into heterolithic lithofacies, generating a coarsening upward sequence with an increase of siltstone and sandstone intercalations in the lower-middle part. The coarser-grained layers display scoured basal surfaces, with common gutter casts, capped by plane parallel lamination and hummocky cross-stratification (HCS). In the middle part of Ilebeyk Formation, siliciclastic deposits are alternated with relatively thick carbonatic intervals, showing similar features with Mila C Member. The upper part of the Ilebeyk Formation is dominated by shales, overlain at the topmost by a 28 m thick unit of micaceous sandstone and siltstone. The sandstone layers include plane-parallel bedding, trough cross-stratification and long-wavelength HCS. Based on the facies and microfacies analysis, the depositional system of the studied section is interpreted as a mixed carbonate-siliciclastic ramp. In the Mila C Member and carbonatic unit of Ilebeyk Formation, small cycles characterized by erosive surfaces and fining upward fossiliferous biomicrites suggest deposition in middle ramp setting, affected by storm events. On the other hand, the nodular limestone intervals at the top of the carbonatic units point to deposition below the SWB under a transgressional regime. The shale to heterolithic parasequences from the Ilbeyk Formation are interpreted as autocyclic fluctuations of the depositional system from lower to upper offshore environment. In the uppermost part, the sandstone-dominated interval is attributed to shoreface setting, marking an abrupt change in the bathymetric conditions after a forced regression. The sedimentological features of the studied area can be correlated with other coeval depositional events at both regional (Arabian plate) and global (Laurentia and Baltica) scales, providing new constraints for the lower Palaeozoic evolution of the northeastern Gondwanan margin.

Facies analysis and depositional environment of a late Cambrian mixed carbonate-siliciclastic ramp from the Arabian Plate (Zagros Basin, Southwestern Iran)

An integrated analysis of subsurface dataset and outcropping successions permitted to define a stratigraphic and paleogeographic evolutionary model of the wedge-top Rossano and Crotone Basins during the Messinian Salinity Crisis (MSC). The presence of complete sea-level controlled successions, indicate the dominance of the eustatic signal in the basin evolution, in comparison with the synsedimentary tectonic input, which played only a secondary role consisting in the strong basinward shift of facies caused by fast decreasing in the accommodation space. In particular, during the late Tortonian - early Messinian the studied basins were characterized by open normal marine conditions, as suggested by the widespread deposition of deep-water claystones followed by diatomites (Tripoli Fm). The first basin restriction occurred during the early Messinian at ca. 5.96 Ma, as a consequence of the sea-level relative still stand, that triggered the deposition of a carbonate platform system (Calcare di Base Fm - CdB). The latter was characterized by sabkha to shallow-water environments, dominated by microbial carbonate and evaporite deposition, passing into a gentle slope to basin setting in which resedimented and pelagic deposits occurred. A successive regional sea-level drop, dated at ca. 5.60 Ma, induced a general exposure of the CdB platform system and the creation of a marked erosional surface generally known as the Messinian Erosional Surface (MES). Consequently, during the early LST, a thick prograding wedge deposited and, due to the reduction of the connections with the open sea, new more severe restricted conditions of the basins took place. Later, during the late LST, the massive deposition of salt dominated bodies reshaped the basin paleotopography and the depocentres were filled, thus sealing the previous irregularities of the paleo-seascape and creating roughly flat plains without deep depozones. Afterwards, a renewed transgression phase (TST) inundated again the basins, causing firstly the sedimentation of clay dominated deposits, and later, during a further HST, the reestablishment of evaporitic conditions and the deposition of widespread shallow-water sulphate deposits. Lastly, a new severe relative sea-level drop (LST) exposed again all the previous deposits, as testified by the superimposition of alluvial conglomerates along paleovalleys incised into the underlying HST sulphates. This event marks the transition to the so-called Lago-Mare event that typifies the last stage of the MSC, which definitely terminates with the reflooding of the Mediterranean at the Pliocene transition (ca. 5.33 Ma).

Relative sea-level variations and basin evolution during the Messinian Salinity Crisis (Crotone and Rossano Basins - North Calabria)

Incised valley-fill (IVF) systems play a key role in source-to-sink (S2S) sediment transport towards sedimentary basins (Blum et al., 2013). A buried paleovalley system, about 3.5 km wide and 50 m deep, was reconstructed below the Pescara River coastal plain (central Adriatic). The study area represents an onshore sector of the larger-scale S2S Po-Adriatic system and is located in front of the Mid-Adriatic Depression basin. The paleovalley profile, incised into the marine Upper Pliocene-Lower Pleistocene bedrock, and the 3D IVF facies architecture were reconstructed through a multi-proxy approach based on stratigraphic, sedimentological and palaeontological data. To refine stratigraphic and paleoenvironmental reconstructions, a new continuous core was recovered from the paleovalley depocenter and samples were collected for radiocarbon dating and facies analysis. At different depths below the surface, paleovalley flanks are characterized by fluvial terraces made of gravel bodies with upper flat surfaces. These terraces, most likely incised by the Pescara river during the stepwise sea-level fall that followed the last Interglacial (MIS 5e, about 125 ky BP), are interpreted as falling stage systems tract (FSST) deposits. The valley floor is composed of a laterally extensive gravel body, > 10 m thick, that accumulated during the Last Glacial Maximum (28-20 ky BP, MIS 2). This fluvial deposit represents the lowstand systems tract (LST). Above LST deposits, the transgressive systems tract (TST) shows a deepening-upward trend, from poorly-drained (alluvial) to estuarine facies associations (early to late TST). The estuarine succession is characterized by very soft (< 1 kg/cm²) and organic-rich silty clays, linked to the post-glacial sea-level rise, when the Pescara paleovalley was progressively drowned and an estuary formed in the study area. The uppermost part of the IVF and Pescara coastal plain Holocene succession is composed of coarse-grained (sands and gravels) fluvio-deltaic deposits. The base of this stratigraphic interval coincides with the beginning of deltaic progradation at the onset of the Holocene (MIS 1), and can be interpreted as the Maximum flooding surface (MFS). Thus, prograding fluvio-deltaic sediments are the highstand systems tract (HST). Glacio-eustatic fluctuations (over the last 125 ky) are considered the main driving factor that induced river down cutting during sea-level fall and subsequent valley filling during sea-level rise. This study represents the starting point of a more complex basin-scale study, where onshore data will be correlated to their offshore equivalents to better understand sediment dynamics within the Po-Adriatic S2S system.

The Pescara incised valley system: Insights from an onshore sector of the S2S Po-Adriatic sediment routing

A better understanding of the evolution of bottom current circulation and associated deposits is significant for many applications including paleoclimatology and geological hazard. Besides the large contourite drifts, bottom currents may generate fields of large sediment waves that, depending on their height and velocity of migration, may pose severe risk for infrastructures. Conversely, the time span of their paleoceanographic record is generally relatively short. We use bathymetry data, sub-bottom and seismic reflection profiles and legacy oceanographic data to analyse the sediment waves occurring in a deep environment (from 2400 to 3800 m water depth at the foot of the Malta Escarpment in the Mediterranean Sea) to understand their evolution in time, their significance for paleoceanography, and their relation to present day hydrographic conditions. In the absence of direct stratigraphic information, we use the information from nearby studies and from ODP Site 964 and DSDP Site 374 to constrain the age of the sedimentary successions. We discover that these waves (about 2.5 km in wavelength, 50 m in eight, with crest sub-perpendicular to the continental slope trend) have been steadily growing and migrating northward since about 500 ka, although an irregular growth and unsteady migration is distinguishable since about 1,800 ka. The waves are generated by predominantly alongslope southward flowing bottom currents compatible with modern hydraulic conditions (mean flow speed of ~5 cm s-1, peaks of 15 cm s-1). The rate of crest migration (~ 2.0-3.2 mm a-1) and the average sedimentation rate (0.64 - 0.69 mm a-1) are unusually high for deep sea environments away from turbidity currents paths. We infer that the steady development of sediment waves is produced by a drastic increase in sediment input to the Ionian Basin resulting from the tectonic uplift in NE Sicily and Calabria and the onset of a relatively steady, low energy bottom current regime following the Mid-Pleistocene Transition. We attempt to extract information on orbital cyclicity preserved in the seismic record from the power spectra of virtual seismic traces from the well preserved succession of 5 visually discernible, regularly spaced sub-units consisting of alternation of high-amplitude and low-reflectivity packages within the last 500 ka. Peaks in the power spectra can be identified around orbital obliquity and precession periodicities, while eccentricity appears not to be recorded. We discuss the results of seismic cyclicity analysis relative to uncertainties of stratigraphic and petrophysical constraints. The sediment waves along the foot of the Malta escarpment are an excellent candidate for the extraction of a long, continuous and high resolution sedimentary record of the paleo circulation changes and climate cycles in the Mediterranean Sea since about 500 ka.

Bottom current-controlled Quaternary sedimentation at the foot of the Malta Escarpment (Ionian Basin, Mediterranean)

In the western Ionian Basin, a wedge-shaped seismically transparent to chaotic unit has been mapped at the foot of the Malta Escarpment extending and thinning towards the east on the outer reaches of the Calabrian accretionary wedge. Its thickness, assuming realistic values of seismic velocity, exceed 800 m in the depocenter, and the volume is ~ 1600 km3. Its stratigraphic position has been assigned variably between the upper Messinian (deformed evaporites, mainly gypsum; Butler et al., 2015) and lower Pliocene (olistostrome; Polonia et al., 2011). A number of recent publications (Micallef et al., 2018, 2019; Garcia Castellanos et al., 2020; Spatola et al., 2020; Camerlenghi et al., 2020; Rebesco et al., in review) have proposed the hypothesis that this unit is the sedimentary expression of the Zanclean megaflood of the Mediterranean that ended the Messinian Salinity Crisis (e.g. Garcia-Castellanos et al., 2007). A number of observational, theoretical (numerical modelling) and conceptual arguments support his hypothesis, contributing to the discussion on the role of megafloods in the evolution of Earth terrestrial and marine sedimentary basins, and for comparison, on planets. We review the arguments in favor of the megaflood hypothesis and illustrate how we plan to verify it through scientific ocean drilling, proposing that a cross-disciplinary effort should be made to shed light on what could be the largest megaflood deposit so far identified on Earth and on the role of rapid  sealevel changes in marine sedimentary basin evolution.

Megaflood deposits in sedimentary basins evolution. The case of the Messinian-Zanclean seismic stratigraphic unit in the Ionian basin

Geological mapping of the Longobucco Basin (NE Calabria) revealed the multifaceted nature of the Paludi Formation, an unconformity-bounded, syn-orogenic, turbiditic/megaclastic unit. Sedimentology and lithostratigraphy were merged with nannoplancton and macroforams analysis. The Longobucco Basin belongs to the Calabria Peloritani Arc, an exotic crustal fragment, scraped off from its original paleogeographic position along with other continental ribbons (Kabilie, Alboran, Rif) and accreted to the Apennines during the southeastwards retreat of the Adria-Ionian slab. The Longobucco Basin hosts a Meso-Cenozoic succession overlying the Hercynian basement, and it records polyphase deformation: i) two extensional phases in the Early Jurassic, related to opening of the W Tethys, ii) a compressive phase in the ?late Oligocene/early Miocene followed by a poorly constrained extensional event. The Mesozoic succession ends with Hauterivian Maiolica-like deposits and is unconformably overlain by the Paludi Fm, which exhibits three lithofacies: a) reddish marls and shales (“Scaglia” facies), b) turbiditic sandstones and hybrid arenites, and c) clast- to matrix-supported breccias. The reddish marls are locally cannibalized by megaclastic and turbiditic deposits. Lithofacies (c) includes two mass transport deposits (MTD), >100m thick in the depocentres and with a lateral continuity of 6km. The basal megaclastic interval rests on the basement through a basin-wide SW-dipping onlap surface. Lithofacies (b) bears chaotic intervals, slumped megabeds to debrites, and calcarenites/hybrid arenites bearing macroforams in the form of resedimented loose grains forming biostratigraphically coherent assemblages, suggesting they are penecontemporaneous with the turbidites and thus provide reliable ages. Nannoplancton from the hemipelagites served for cross-checking the ages derived from benthic forams. Both methods produced an early Eocene age (Ypresian) for the basal Paludi and a late Oligocene/?Aquitanian age for the top. The style of basal interaction of the MTD with the substrate varies, with two main modes: i) deep plastic deformation of the substrate paired with sand injections, and ii) erosion, with scours and grooves. Clasts pertain to the Mesozoic succession or to the basement (phyllites, granitoids), ranging in size from pebbles to megablocks (longer axis up to 220m). Semi-consolidated clasts and bedstacks display common ductile/brittle features (asymmetric rootless folds, pseudo sigma structures, boudinage, shear zones). As sedimentation of the Paludi Fm is mainly the product of mass wasting processes, the unit as a whole can be referred to as a Mass Transport Complex. Clast composition, paired with biostratigraphic ages, suggests the Paludi Fm was sedimented in a foredeep setting, receiving the products of the dismantling of an Alpine orogen. This was followed by shortening during a proto-Apenninic phase, and eventually by accretion to the Apenninic orogen.

Sedimentological and biostratigraphic characterization of the Paludi Formation (Longobucco Basin, north-eastern Calabria): proto-Apenninic shortening of an Alpine foredeep?

The terrigenous sediments of the Bengal deep-sea fan (Indian Ocean) represent an archive of Himalayan source-to-sink processes. Mineralogical and geochemical data on silt- and sand-sized sediments of the Bengal Fan turbiditic depositional system allow us to unravel their provenance, to discriminate between pre-depositional and post-depositional processes controlling sediment mineralogy, and to link their depositional history to uplift and erosion of different tectono-stratigraphic Himalayan domains. The IODP Expedition 354 to ~8°N in the Bay of Bengal drilled seven sites along a 320 km transect across the Fan thus providing a spatial overview of the turbiditic depositional system. A complete section of the fan and pre-fan deposits was recovered at the deep-penetration U1451 drill site. Eighteen samples from the shallow drill site U1454 and two deep-penetration drill sites U1450 and U1451 collected down to a depth of 1200 m were analysed, together with four additional samples from drill site U1444 collected during IODP Expedition 353. The mineralogical and geochemical variability among different samples, both collected at different depths within the same core (intra-core) and among cores (inter-core) was investigated. Intra-core mineralogical variability provides information about provenance changes and/or diagenetic effects, wheras inter-core variability helps us to check for potential differences associated with lateral shifts of dispersal patterns through time. The intensity of mineral dissolution in silt versus sand samples will also be analysed to verify whether least stable minerals are prone to be preserved better in less permeable mud-rich layers. In Pleistocene sediments down to 400 m below sea floor, rich heavy-mineral suites include hornblende, epidote and garnet, with subordinate apatite, clinopyroxene, tourmaline, sillimanite, kyanite, zircon, titanite, and rare staurolite and rutile. In Pliocene-Miocene sediments, the heavy mineral concentration decreases, and assemblages are relatively enriched in garnet and epidote at the expense of amphibole. The relative abundance of zircon, tourmaline, and apatite increase progressively in older strata. Mineralogical and geochemical compositions testify to long-distance provenance from the Himalayan Range via the Ganga-Brahmaputra fluvio-deltaic-turbiditic system and confirm that the Bengal Fan was a major sink for Himalaya-derived material since the Miocene. Petrographic and mineralogical data, combined with biostratigraphic, paleomagnetic, and geochemical evidence, allow us to unravel the sedimentary history of the Bengal Fan as related to Himalayan uplift, erosion, and monsoon development during the last 10 Ma.

Mineralogy and geochemistry of Bengal Fan turbidites (IODP 354): Himalayan provenance and depositional history

Basin evolution results from geodynamic and depositional events, but also from the burial history, that may be reflected in the diagenetic history recorded in the sedimentary rocks: the multidisciplinary study of diagenetic phases coupled with basin analyses may provide constraints on the timing of these events. The petrographic, cathodoluminescence (CL), stable isotope, and microthermometry investigation of inner platform facies of the pervasively dolomitized carbonate platform of the Norian (Upper Triassic) Dolomia Principale (Southern Alps, N Italy) identified two major dolomite phases. An early replacement fabric-retentive dolomite (D1 and D2, respectively replacing the sedimentary facies - from fenestral mudstone/wackestone to bioclastic packstone and mudstone and stromatolites- and early marine cements) is followed by a later, vug- and fracture-filling dolomite cement phase (D3, planar-s texture). The fabric-retentive dolomitized carbonates (< 4 µm−30 µm, D1) and marine fibrous cements (30 µm−250 µm, D2) exhibit dull luminescence under CL whereas the burial dolomite cement (200 µm−500 µm, D3) exhibits zoned luminescence. The δ13C values of the investigated dolomites (D1, D2, and D3) show a narrow range of variation (2.0 to 3.1 ‰ VPDB), pointing toward a fluid-buffered system. Differently, the δ18O values largely varies, ranging from −12.8 to +1.9 ‰ VPDB. In this range, D3 values cluster distinctively between −6.0 to −12.8 ‰ VPDB with respect to D1 and D2, which cluster from about −4 to +1.9 ‰ VPDB. The estimated oxygen isotope composition of the parent fluid of D1 and D2 (~0 to −5 ‰ VSMOW) suggests possible contributions from marine to slightly evaporated seawater, which is consistent with the arid climate and some basin restrictions suggested by earlier studies, whereas that of D3 (+1 to +5 ‰ VSMOW) is consistent with burial fluids. Microthermometric measurements of the primary two-phase fluid inclusions in D3 yielded a mean homogenization temperature of 112.4 ± 8.2oC. These results can be famed in the burial history of the studied basin, providing constraints on the timing of the diagenetic events. Supposing a surface seawater temperature of at least 20-25°C and a geothermal gradient of about 40°C/km (during the Early Jurassic rifting that led to the opening of the Alpine Tethys) such temperature might be reached at reasonable burial depth ranging from 2.0 km to about 2.5 km. According to the subsidence curve this depth, compatible with the temperature recorded by the fluid inclusions, was reached during the Early Jurassic, with D3 cement precipitation causing a significant reduction of the porosity. The followed integrated approach highlights the possibility to better characterize the occurrence of multiple diagenetic events in time and space, as well as their feedback effects on the porosity evolution of dolomitized carbonate reservoirs, framing the diagenetic events at basin scale.

Burial history and diagenesis: stable-isotope and fluid inclusion constraints on the timing of diagenetic events in the dolomitized Dolomia Principale Norian, Southern Alps of Italy)

Next from SGI 2021

Using multi-proxy thermal maturity datasets to validate deformation styles from the Adjara-Trialeti fold-and-thrust belt to the Greater Caucasus (Georgia)A

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Relative sea-level variations and basin evolution during the Messinian Salinity Crisis (Crotone and Rossano Basins - North Calabria)