United States

The geological record of deep seismic activity in subduction zones is generally limited due to common rock overprinting during exhumation and only a few regions allow studying well-preserved exhumed deep structures. The Northern Apennines (Italy) are one such area, granting access to continental units (Tuscan Metamorphic Units) that were subducted to high-pressure conditions, were affected by brittle-ductile deformation while accommodating deep tremor and slip and then exhumed back to surface, with only minor retrogression. Our approach is based on detailed fieldwork, microstructural and petrological investigations. Field observations reveal a metamorphosed broken formation composed of boudinaged metaconglomerate levels enveloped by metapelite displaying a pervasive mylonitic foliation. Dilational shear veins occur in both lithologies, but are more common and laterally continuous in the metapelite. They are mostly parallel to the foliation and composed of iso-oriented stretched quartz and Mg-carpholite (XMg&gt;0.5) fibres, which are single-grains up to several centimetres long. These fibres define a stretching direction coherent with that observed in the metaconglomerate and metapelite, which is marked by K-white mica and quartz. Thermodynamic modeling constrains the formation of the high-pressure veins and the mylonitic foliation to ~ 1 GPa and 350°C, corresponding to c. 30-40 km depth in the subduction channel. Dilational shear veins developed in subducted (meta)sediments are a key indicator of episodic tremors and slip events (e.g. 1). We propose that these structures reflect the repeated alternation of localised brittle failure, with dilational shear veins development, and more diffuse viscous deformation. These cycles were probably related to the fluctuation of pore pressure that repeatedly reached lithostatic values. Concluding, these structures can be considered the geological record of episodic tremors and slip events occurring at &gt;30 km of depth in the Apenninic subduction channel.

SGI 2021

Brittle-ductile deformation in high-pressure continental units and deep episodic tremors and slip events

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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.

The geological record of deep seismic activity in subduction zones is generally limited due to common rock overprinting during exhumation and only a few regions allow studying well-preserved exhumed deep structures. The Northern Apennines (Italy) are one such area, granting access to continental units (Tuscan Metamorphic Units) that were subducted to high-pressure conditions, were affected by brittle-ductile deformation while accommodating deep tremor and slip and then exhumed back to surface, with only minor retrogression. Our approach is based on detailed fieldwork, microstructural and petrological investigations. Field observations reveal a metamorphosed broken formation composed of boudinaged metaconglomerate levels enveloped by metapelite displaying a pervasive mylonitic foliation. Dilational shear veins occur in both lithologies, but are more common and laterally continuous in the metapelite. They are mostly parallel to the foliation and composed of iso-oriented stretched quartz and Mg-carpholite (XMg>0.5) fibres, which are single-grains up to several centimetres long. These fibres define a stretching direction coherent with that observed in the metaconglomerate and metapelite, which is marked by K-white mica and quartz. Thermodynamic modeling constrains the formation of the high-pressure veins and the mylonitic foliation to ~ 1 GPa and 350°C, corresponding to c. 30-40 km depth in the subduction channel. Dilational shear veins developed in subducted (meta)sediments are a key indicator of episodic tremors and slip events (e.g. 1). We propose that these structures reflect the repeated alternation of localised brittle failure, with dilational shear veins development, and more diffuse viscous deformation. These cycles were probably related to the fluctuation of pore pressure that repeatedly reached lithostatic values. Concluding, these structures can be considered the geological record of episodic tremors and slip events occurring at >30 km of depth in the Apenninic subduction channel.

technical paper

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.

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

Badenian (lower part of Middle Miocene) sediments are of paramount importance of defining the Central Paratethys in Serbia. The marine deposition in the Neogene of Serbia is limited to the Badenian age. The locality is situated on the easternmost slopes of Fruška Gora Mt., occupying the Koševac ridge. Badenian sediments are confirmed to date in this area at an outcrop along the road leading from Krčedin village to the Krčedin quarry. Coordinates of the outcrop are 45°10'5"N 20°8'15"E. The whole outcrop is not higher than 2m and contains four lithofacies, which is an excellent object for high resolution sequence stratigraphy. These sediements are part of a syn-rift climax system tract, according to the sequence stratigraphic scheme devised by Prosser (1993) and improved by Holz et al. (2017) to fit the rift tectonostratigraphic model. The basin basement is represented by Lower Cretaceous turbidites exposed at the Krčedin quarry, and the rift strata are overlain by Quaternary sediments (Anđelković, 2020). Prosser (1993) defined the syn-rift sediments as belonging to the rift initiation or rift climax system tracts. So can we describe the found Badenian sediments. The lowest part of the series is represented by coarse-grained conglomerates belonging to the lithofacies A. It can be defined as rift initiation system tract because it represents the transgressive surface, probably bounded by the syn-rift unconformity (sensu Holz et al., 2017) at its base. Lithofacies B is represented by microconglomerates, which indicates less water energy and slightly more depth, so it would be convenient to assign it to the early rift climax system tract. Finally, lithofacies C (sandy marl) and lithofacies D (pure marl) can be found. They containt numerous planktonic foraminifera (Orbulina suturalis, Praeorbulina sp., Globigerina sp.), a much lesser amount of benthic foraminifera (Borelis melo, Elphidium sp.) and some ostracoda and gastropod fragments (Anđelković & Batoćanin, 2020). These marls are remnants of a rapidly deepening basin and they can be described as middle rift climax system tract. After the Badenian age, the basin was rapidly inverted.

High resolution rift sequence stratigraphy of Badenian sediments near Krčedin (Northern Serbia, Central Paratethys)

In this study 80 detrital quartz grains coming from 4 sedimentary rocks samples of the Julian Basin (JB) have been analysed. Quartz can incorporate chemical impurities as defects in the crystal lattice, with substitution of Si4+ with H+ and Al+3 or B3+, by 4H+, and with LiOH. These substitutions form specific infrared absorption bands that can be investigated and analysed (Stalder & Konzett, 2012). Fourier Transform Infrared spectroscopy of quartz was used to investigate the sample set with interest to its OH defect speciation and content. OH defects are correlated to petrogenetic conditions, and they may be used as a provenance tool (Stalder, 2014). Polarized IR spectra can identify these different substitutions and allow to separate them from molecular water contained in fluid inclusions. Defect water contents were calculated for every different substitution (if present) by integration of the absorption area in the peaks’ regions. Julian Basin is a syn-orogenic basin in South-eastern Alps across Italian-Slovenian border, developed in the Late Cretaceous-Early Eocene. Quartz from the oldest sample (JB1; Maastrichtian) show a pattern suggesting a mixed source between igneous and non-igneous rocks, with a slight predominance of metamorphic material supply. Grains from sample JB17 (Thanetian) show the greatest variability in both defects and water content amount that suggests a different and more complex source. Quartz crystals from samples JB23 and JB26 (Ypresian) show a pattern of water-poor grains suggesting a mainly metamorphic rock type source. The peculiarity of JB17 is confirmed by several different previous studies based on both heavy minerals and geochemistry which demonstrated a strong difference in the supplies in the corresponding time interval (Lenaz et al., 2000; Lenaz & Princivalle, 2002; De Min et al., 2014; Velicogna, 2020).

Diverse detrital quartz supplies in SE Alps: an FTIR study

The different environmental conditions produced by the progressive restriction at the Mediterranean-Atlantic gateways during the early Messinian are abundantly investigated in the deeper water succession, while the shallow-water record is less explored. Throughout the Mediterranean, the pre-evaporite deposits in the deep-water record display changing lithologies, from hemipelagic marls and limestone alternation to sapropelitic marly limestone and euxinic clays. The shallow water successions are generally characterised by luxurious coral reefs developed in the Mediterranean area, with some, locally restricted, exceptions. During the early Messinian a first record of the progressive decay of trophic conditions in shallow water environment has been reported in the Majella structure (Central Apennines, Italy). Here the lower Messinian is represented by the Lithothamnion Limestone carbonate ramp that constitutes the uppermost carbonate unit of the Bolognano Formation. This ramp developed in the paleo Adriatic sea and it was characterised by a wide middle ramp environment in which coralline algae dominated carbonate production. This facies was associated with seagrass meadows colonizing the inner ramp. The outer ramp was characterized by bioturbated hemipelagic marl with planktonic foraminifera, pectinids and brachiopods in the aphotic zone. In this work we present facies and geochemical data providing evidence for an early, and repeated, onset of a restrictive environmental development, characterising and the Lithothamnion Limestone carbonate ramp. A stratigraphic section of ramp succession was measured in the eastern sector of Majella structure (Taranta Peligna), fourty bulk-rock samples were analysed for carbon isotopes then correlated with Mediterranean stable isotope record. Redox-sensitive elements (ICP-MS) was performed on twenty-five bulk rock samples. On these samples the Total Organic Carbon (TOC) was also measured using the Loss-On-Ignition (LOI) techniques. The foraminiferal content was analysed under a binocular microscope and classified for bio/chronostratigraphic attribution. The general negative carbon isotope trend recorded of the investigated section is interpreted as the record of the final stage of the Late Miocene Carbon Shift. Trends in the redox-sensitive elements are indicative of an evident decrease in bottom-water oxygen content and coinciding with the drowning of Lithothamnion Limestone carbonate ramp. The drowning coincides with the occurrence of Globorotalia nicolae (MMi 13b zone), when a conspicuous terrigenous input marked by a spike of Al and TOC content was recorded in the investigated succession.

Decoding seafloor and paleoclimate conditions from the paleo-Adriatic domain during early Messinian (Majella, Apennines, Italy)

The Cilento Group (Langhian-to-Tortonian) is a thick turbiditic succession (1200-2500 m) of the Southern Apennines foreland region that unconformably overlain the Lucanian oceanic terranes.  It has been divided into four formations from NW to SE: the Pollica, San Mauro, Torrente Bruca and Albidona formations.  Here, the post-depositional history of the upper portions of the Cilento Group, the San Mauro Formation (SMF), is discussed. The SMF consists of 1400-1600 m thick succession characterized by three main turbidite facies associations: outer-fan, middle-fan, and inner-fan. The outer-fan facies association characterizes the lower part SMF and is made by 300-500 m of thin-bedded sandstones and thick mudstones and marlstones. Numerous intrabasinal carbonate turbidite beds paired with a coarse-grained volcaniclastic layer are interbedded with the outer-fan deposits. The middle-fan facies association define the middle part of the SMF and is represented by a section of about 700 m thick sandstone-lobe turbidite beds and thin fan-fringe deposits. Two impressive intrabasinal carbonate megaturbidite beds, 65 m and 35 m in thickness, respectively, are interbedded with sandstone-lobe strata. The inner-fan facies association typify the upper part of the SMF and is characterized by 400-500 m thick succession of channelized coarse-grained sandstone and conglomerate turbidite beds. Sandstones are generally characterized by quartzolithic, volcanolithic and quartzofeldspathic composition, whereas hybrid arenites and calcarenites characterize the carbonate megabeds. Several diagenetic processes reducing porosity and permeability, such as compaction and cementation, occurred within the SMF. In particular, framework grains result deeply compacted, as testified by the common deformation of ductile grains (mainly micas) and detrital matrix. Cementation occurred through the precipitation of different minerals. The main cements are: 1) carbonate, such as calcite and less dolomite, playing an important occluding role along intergranular space, even running a quite replacement in quartz and feldspar grains ; 2) authigenic quartz occurring as little overgrowths or as minor mosaic quartz; 3) phyllosilicates, mainly developing in the upper part of SMF as pore filling chlorite cement or as small and incomplete illite coatings on skeletal grains; 4) Fe-oxides occuring as pathchy or pore-filling cements. The pore system consists of inter-intra-granular pores with a small pore radius and fractures. The relationship between the compactional porosity loss (COPL) and the cementational porosity loss (CEPL) testifies that compaction is the main reduction porosity process for SMF sandstones. Burial analysis suggests two phases of intense subsidence, interpreted as the result of syn-orogenic extension at shallow crustal levels intermitted by periods of low sedimentation rates, linked to gravitational instability of a vertically growing orogen.

Diagenetic destruction of porosity in Quartzofeldspathic sandstones, Miocene Cilento group, Southern Apennines foreland basin system

The Crotone Province (Calabria - South Italy) extends for a total surface of circa 1.736 km² in which a wide spectrum of geological, geomorphological and tectonic configurations alternate from the mountainous hinterland portions towards the coastal plain settings. Through the integrated collection of data coming from separated databases such as Geoportale della Calabria, Geoportale Nazionale, Videpi Project, ARPACAL Multirisk Functional Center, CARG project, CASMEZ, a complete geodatabase which make available a wealth of different spatial and cartographic data useful for the study and monitoring of Province of Crotone was implemented through open source technologies such as Qgis and PostgreSQL. The processed data consist in: 1) A new unified Geological map obtained through the comparison of the CASMEZ 1: 25000 and CARG the 1: 50000 maps and the reinterpretation of the stratigraphies with the adaptation of the old nomenclature with the new standards defined by the CARG project; 2) Geomorphological map obtained through the integration of  the available bibliography with new data coming from geoportale della Calabria; 3) Topographic and land cover maps obtained through the processing of both national and regional data; 4) Aspect, Slope and Curvature maps of the studied territory obtained using the Digital Elevation Models (DEM); 5) Rainfall and drainage density maps obtained through the re-elaboration of the ARPACAL databases; 6) Subsidence and land movements maps obtained though the processing of the ascending and descending orbit of RADARSAT 1 and 2 (Band C) satellites (2013-2018) using PSP-DIFSAR technique, and the ascending orbit of the TerraSarX satellite (X Band) and the descending orbit of the CosmoSkyMED satellite (X Band) (2013-2018)  using SBAS technique. Lastly, using the qgis2web plugin an interactive WebMap was created with the final aim to disclose, query and interactively view as much information as possible from a single database which also allows periodic updating without major investments and with very low maintenance costs.

Development of a unified geographic database from separated existing data through open-source softwares, Crotone Basin, Southern Italy

The Tertiary Piedmont Basin of NE Italy is an episutural basin which lies at the junction between the Alpine and Apennine chains. Its late Eocene to Pliocene sedimentary fill is thus important because it may provide a record of a source to sink system modulated by tectonics. This study focuses on sedimentology and petrography of the sedimentary succession cropping out in the Arquata Scrivia-Carrosio area, a key sector separating the Alto Monferrato area to the west from the Borbera-Curone sub-basin to the east. The litostratigraphic succession indicates initial establishment of a conglomeratic fan-delta (Conglomerati di Savignone and Molare Fms., Rupelian), which is drowned and onlapped by slope hemipelagic marlstone and channelized turbidites (Gremiasco Fm., Chattian). These are followed up section by a suite of confined turbidites, mass transport deposits, and channelized turbidites (Castagnola and Costa Montada Fms., Aquitanian-Early Burdigalian pro-parte), which record a further deepening culminating in the establishment of a basin plain environment (Costa Areasa Fm., Early Burdigalian-Langhian). Lastly, from the late Langhian onward, tectonic uplift resulted in a regional unconformity capped by shelfal marly deposits with storm layers and hyperpycnites (Marne di Cessole Fm., Langhian). Quantitative petrographic analysis of the above succession allowed us to recognise 11 petrofacies, which were compared and contrasted in a stratigraphic perspective. In agreement with previous studies, we identified lithic fragments from the Voltri Group, the Sestri-Voltaggio Zone, the Ligurian Appenine Units and the Mortara Volcanic complex, which can be therefore regarded as the main sediment sources. Results show that quartz and feldspars fractions increase up-section, whereas that of lithics decreases. In the lithic fraction, a decrease in the content of metamorphic lithics is observed in favour of volcanic and sedimentary lithotypes. The increase in quartz and feldspars content requires further investigation to be linked to candidate source terrains (Dora Maira? Cristallino di Valosio?). On the other hand, the increase of the volcanic fraction is partly coeval to the Mortara Volcanic complex (Upper Oligocene-Lower Miocene), now buried about 50 km to the north of the study area, and may thus correlate to an acme of volcanic activity and/or dismantling of its products. Lastly, the increase of the carbonate fraction can be interpreted to reflect the establishment of carbonate platforms of similar age documented at outcrop both to the N and S of the study area (P. da Cantoni Fm. of the Basso Monferrato and Visone Fm. of the Alto Monferrato, respectively) and in the subsurface (Quargnento High) to the N.

Sedimentological and petrographic evolution of the Oligo-Miocene succession in the Carrosio and Arquata Scrivia area (eastern Tertiary Piedmont Basin, NW Italy) 

This work illustrates a combined modelling approach using digital photogrammetry and geological modelling to create a high detailed 3D facies model of the inner environment of the Monte Carrubba carbonate ramp outcropping in the South Sicily. The Monte Carrubba Formation is the youngest marine Miocene carbonate deposit of the Hyblean region, prior to the Messinian crisis of the Mediterranean. In particular, Faro Santa Croce outcrop shows the most proximal sector of this ramp.The Faro Santa Croce outcrop offers the opportunity to investigate and reproduce a highly-detailed facies heterogeneity 3D model for a very narrow and limited area of few squared kilometers, developed in a tectonically stable area. Within this small areal, five facies have been recognized and modelled revealing a high level of facies heterogeneity. In this area marine ooidal shoals (ooidal grainstone to packstone) interfingered with shallow water seagrass environment (green-algal-floatstone facies and bioclastic grainstone-to-packstone) with abundant mollusc fauna. The distal part of this vegetated environment (fine mollusc-packstone facies) pass basinward into coral mounds (coral boundstone). The combination of digital photogrammetry and 3D geological modelling software has allowed to obtain a very high-resolution model of facies heterogeneity, evidencing the complexity of facies associations and, in particular, the development of a facies mosaic that can be underestimated by a classical 1D or 2D field analysis, especially in limitedly-exposed outcrops.

Facies modelling of proximal environment in the upper Tortonian-lower Messinian carbonate ramp of Hyblean domain (Faro Santa Croce, Sicily, Central Mediterranean)

During Permian, the Pangea supercontinent experienced the most critical and dramatic restocking of its configuration. Meanwhile, in the Mediterranean region, the occurrence of late Paleozoic siliciclastic strata experienced peculiar tectonic and climatic environment. Here, we detail the Permian sedimentary succession types displayed in some portions of the circum-Mediterranean region, providing new insights about the composition of Permian siliciclastic strata of the basal Apulian Unit, in Puglia 1 well log, and the Sosio Valley succession in Sicily. Permian sandstones, and related mudrocks, record a synchronously phase of post-Variscan collision and subsequent final closure of Paleotethyan ocean. Sedimentological and stratigraphic framework, also associated to the distribution of mineralogical composition of sandstones and mudrocks, are pivotal factors to reconstruct the sedimentary evolution of the Permian paleogeography. The Apulia Unit played a critical role because it stood relatively still in the Mediterranean paleogeographical contest and received a great Permian sedimentary load. Nowadays these strata were intersected in Puglia 1 well between 7070 m to 6110 m in depth, for 960 m in thickness, with sandstone, mudstone and breccia mostly. Meanwhile a Sicily Permian succession (the San Calogero Formation) is well preserved, outcropping around the Sosio Valley (northwestern Sicily), by few tens of meters of marine sandstones and clays strata. Sandstones of the Puglia 1 Well are quartzolithic, with abundance of quartz and  metasedimentary lithic fragments (mainly phyllite and schist). Feldspars are minor. Sandstones of the San Calogero Fm. in Sicily, are more variable in composition, from quartz-rich sandstone, to hybrid arenites and calclithite, and include abundant extrabasinal carbonate fragments and metasedimentary lithic fragments, as such as important contributions of intrabasinal carbonate grains. Interbedded volcanic and volcaniclastic layers are also present. These siliciclastic strata experienced a diverse burial history. The Puglia 1 succession presents moderate carbonate cements, that are dominant, and consist of crystals of dolomite, ankerite and calcite (related to dedolomitization/calcitization processes of the first carbonates. Mudrocks display K-enrichments, intense paleoweathering under a hot, episodically humid, climate with a prolonged dry season, and sediment recycling processes. Meanwhile Sicily succession is pervaded by carbonatic poikilotopic cements mostly, siliciclastic matrix and less iron cements. Quartz overgrowths are locally present. In terms of provenance, sandstone detrital modes are typical of quartzolithic sandstones, hybrid arenite and calclithite: that should be related to the erosion of upper crustal levels of the Variscan orogenic terranes , with most of metasedimentary and sedimentary rocks occurring in Calabria-Peloritani, southern Alps and in internal domains of the Circum-Mediterranean orogens.

Detrital modes of Permian sandstones in southern Italy

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)

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