In situ brecciation and fluid migration in seep carbonates : the case study of the messinian limestones in the western mediterranean basin

Brecciated fabrics, coupled with authigenic carbonate precipitation, extensively affect the carbonatic units developed during the Messinian Salinity Crisis (MSC) of the Mediterranean Sea. These limestones represent a complex unit in terms of genesis and stratigraphy: they show a rich facies inventory and are intimately related to a major basin-scale unconformity (the MES, Messinian Erosional Surface). The brecciated limestones are known as “Calcare di Base” Fm. (basal limestone) and show sulphur-bearing lithofacies at places. They have been long investigated and the attempt to group them on the basis of sedimentological, mineralogical and geochemical datasets results in still fragmentary models, where the fabric aspects have not been highlighted yet, nor the trigger for the wholesale brecciation hasn’t been clearly defined. Two different triggers for brecciation have been so far claimed: evaporitic collapse and mass wasting processes. The relation between the upper Messinian breccias and fluid migration, to date only speculated, is tested in the present study using a suite of sedimentary techniques (outcrop facies analysis, natural radioactive measurements, facies and fabric investigations) and geochemical techniques (XRD and EDS analyses, stable isotopes δ18O and δ13C, organic geochemistry). The brecciated limestones widely crop out in the Western Mediterranean area: some key-sections located in Italy (Maiella area; Calabrian Arc; Sicily) have been chosen in this thesis to obtain an exhaustive stratigraphic framework and a genetic model for the Upper Messinian breccias. The overall challenge is to validate the role of investigating brecciated fabric as: 1) a sedimentological tool for detecting ancient cold seeps, offering a contribute to the “paleo-seep search strategy”; 2) an opportunity to achieve an outstanding insight into the processes taking place below the seafloor in modern seepage settings. The Messinian breccias are made up of limestones exhibiting high variability in facies and thickness: their geometry varies from a patchy distribution within a host sediment to massive or stratified thick bodies interbedded with pelitic horizons. The carbonatic beds consist of locally brecciated marly lime mudstones, highly cemented, devoid of gravity segregation and any preferential distribution. Generally brecciation overprints the primary fabric, resulting in fabric-retentive breccias (in situ brecciation). Breccias are typified by monomictic subangular clasts, showing scale-invariant fabric and lithology-independent patterns. Brecciation, accompanied by fluid migration pathways occurring at any scale of observation, is a diffused phenomenon at the mesoscale, but localized at the microscale. This possibly accounts for variation in the energy input of the fluids, supposed to have triggered brecciation in such environments. - 2 - The co-occurrence of plastic and brittle behaviour proxies point to fluidification and associated brecciation phenomena taking place in a partly unlithified sedimentary column, typified by differential diagenesis. Both the carbonates and the pelitic fraction show an intense natural radioactivity (up to 63 Cps), mostly related to authigenic 238U. The geochemical dataset is complex and shows wide ranges both in δ18O (+7.74 down to -9.64 ‰ PDB) and δ13C values (+4.14 down to -43.7 ‰ PDB). This is the result of: 1) originally mixed carbon sources involved in authigenesis; 2) a complex fluid-rock interaction; 3) different fluid composition in the different basins (in the Maiella Basin and at Capodarso - in the Caltanissetta basin - they were enriched in hydrocarbons; in the Calabrian Arc and in Centuripe - in the Caltanissetta basin - the nature of the fluids, was possibly saline). In addition, the coupled positive δ18O - negative δ13C widely typifying the Calcare di Base both in Sicily and Calabria, could be related to gas hydrate destabilization processes, since textures resembling gas-hydrate bearing sediments were observed as well. A revisiting of the term “seep limestone” is proposed herein, since the aforementioned facies and fabric association enucleates important sedimentological proxies for the detection of seep limestones: (a) irregular geometries of the geobodies; (b) primary fabric overprinting; (c) peculiar textural characters of breccias; (d) scale-independent and lithology-independent patterns; (e) complex rheology; (f) fabric resembling gas-hydrate infilling sediments. The upper Messinian brecciated limestones occur in correspondence to different phases of the Messinian Salinity Crisis, but are strictly related to the regional unconformity: the MES played a critical role in the brecciation processes. There is no evidence to consider the upper Messinian breccias as a stratigraphic unit: the processes of brecciation and widespread fluid migration took place, involving different stratigraphic levels, according to their rheology and to the structural local setting. The age of this processes is constrained to the early upper Messinian phase, before the development of the Lago-Mare event. The major drawdown of the Mediterranean Sea recorded by the MES corresponds to a huge sea level drop: this most likely represents the primary trigger for fluid migration: the high depressurization experienced by the sedimentary column after the removal of at least 1 km of water column, could have likely favoured a catastrophic migration of overpressured fluids from below

Deep-seated hydrocarbons in the seep “Brecciated Limestones” of the Maiella area (Adriatic foreland basin): Evaporitic sealing and oil re-mobilization effects linked to the drawdown of the Messinian Salinity Crisis

The 13C-depleted “Brecciated Limestones” record a hydrocarbon seep event that occurred between 5.56 and 5.532 Ma in the Maiella area. They unconformably overlie the “Primary Lower Gypsum” and crop out as carbonate buildups and authigenic patches fed by fluid migration pathways filled with flow-mobilized pelites. Tar occurs as solid bitumen shows, corresponding to pore-filling tar in the microfacies, and as a distinctive brown facies, resulting in finely impregnating patterns in thin section. Geochemical rock characterization confirmed that the measured Total Organic Carbon, with values up to 11.07%, mostly consists of migrated hydrocarbons in the carbonate buildups and the authigenic patches, while the flow- mobilized pelites are devoid of oil traces. Bitumen characterization showed an overall homogeneity among the samples, established by their similarities in the tricyclic fraction and their uniform bitumen d13C signals (␣26.3/␣28.66‰ PDB-1). Gas chromatographyemass spectrometry revealed five distinctive markers indicative of an oil that originated and migrated from a carbonate source rock: high C29/C30 hopane ratio; low Ts/Tm ratio; abundant C24 tetracyclic terpane; absence of diasteranes; and occurrence of methylsteranes. Considering the regional source rock setting, the carbonate source rock might pre- sumably be Upper Triassic/Lower Liassic in age. We favor a conceptual model that envisages a step-wise migration of hydrocarbons, which originated from a deep-seated source and migrated through a hydrofractured reservoir (Bolognano Fm.). The Primary Lower Gypsum of the Messinian Salinity Crisis provided an efficient seal until the major evaporative drawdown of the Mediterranean Sea at ~5.55 Ma triggered a renewed hydrocarbons migration, which occurred first with a vigorous gaseous release and then with a seeping oil flow. Oil impregnated the early cemented “Brecciated Limestones” and partly contributed to their precipitation, whereas a self-clogging effect supposedly prevented oil impregnation in correspondence with the feeder channels formed during the first gaseous migration phase

Subsurface seepage dynamics and flow types in a Messinian paleoseep system (Maiella Mts., Central Italy)

The subsurface feeder complexes of mud volcanoes and seepage systems potentially provide valuable information on the evolution of seepage dynamics. Ancient seepage systems in outcrops allow for the observation of expulsion features, which are otherwise commonly beyond seismic resolution. In the Maiella hydrocarbon seep area, the evolution of fluid migration through the sedimentary column during the Messinian Salinity Crisis generated distinctive seep-plumbing features, geological responses, and geochemical signatures in the “Brecciated Limestones” unit. The fluid migration pathways evolved from funnel-shaped feeder channels (Flow-mobilized Sediments) into hydrofractured microbial carbonate buildups (Limestone Buildups), and finally into blow-out micropipes in the host sediment (Patchy Limestones), as overpressure dissipated through the plumbing system. The Flow-mobilized Sediments (δ13C down to − 24.5‰ PDB-1) correspond to the highest flow rates in the whole area, whereas the Patchy Limestones (δ13C down to − 39.3‰ PDB-1) correspond to the slowest flow rates within the intrusive zone. The Limestone Buildups show different degrees of hydrofracturing that reflect different flow rates (δ13C down to − 27.5‰ PDB-1). The fluid transport mechanisms evolved from focused venting through neoformed feeder channels, where sediments elutriated from depths were carried out (the sediment-prone response to fluid migration), to high-rate seepage triggering high hydrofracturation in the microbial buildups. While the hydrocarbon-rich fluids contemporaneously triggered authigenic precipitation (the mineral-prone response to fluid migration), progressive upward and lateral flow deceleration resulted in gradually weaker hydrofracturing of the microbial buildups and finally only local cementation in the form of carbonate patches within the host sediments

The late Messinian Lago-Mare biofacies in central Apennines: the ostracod perspective

""The different phases of colonization of the Palaeo-. Mediterranean by the Paratethyan ostracods during the Lago-. Mare event of the Messinian Salinity Crisis, as recognized in the. whole Palaeo-Mediterranean area, are investigated in the central. Apennines. The studied localities showed the record of the first. colonization (5.59-5.40 Ma) by Loxoconcha mülleri and. Tyrrhenocythere sp. in the Majella Mt. area (Colle di Votta and. Decontra sections) and the arrival of the huge Paratethyan. contingent (5.40-5.33 Ma) made by several species of. Candoninae, Leptocytheridae and Loxoconchidae (among which. Loxocorniculina djafarovi, fig. 1) in the deposits of Latium (Cura. di Vetralla and Mondragone) and Abruzzi (Le Vicenne and. Majella Mt.). The latest phase of the Lago-Mare event (5.35-5.33. Ma) is documented in the Cura di Vetralla, Le Vicenne, Fonte dei. Pulcini and Decontra sections by the presence of Amnicythere. costata, A. litica, A. subcaspia, Pontoniella verrucosa,. Loxoconcha kochi and Tyrrhenocythere ruggierii."

Cyclicity and 87Sr/86Sr stratigraphy of the Primary Lower Gypsum of the Adriatic sub-basin (Italy): insight into oceanic-continental water mixing in the Mediterranean during the early stage of the Messinian salinity crisis

During the Messinian stage, the Maiella area was part of the Adriatic foreland domain of the Apennine orogenic system. Westward of the present Maiella Mts (Queglia-Morrone-Alfedena) a W-dipping ramp characterized theconnection between the Apennine foredeep basin (Marsica–Laga Mts basin), to the west, and the Adriatic foreland domain, to the east (Maiella Mts). The Maiella area was affected by the Apennine orogeny starting from the Early Pliocene. The Messinian interval of the Maiella succession is characterized by deposits related to the Messinian salinity crisis (MSC), mainly Primary Lower Gypsum (PLG), which pass up-section, above a spectacular erosional surface (Messinian erosional surface, MES) to barren shales and carbonates. Above a younger erosional surface (MES2) marls with Paratethyan ostracofauna (late Messinian Lago-Mare event) predate the Early Pliocene flooding of the Mediterranean area, responsible for the deposition of bathyal clays just above oligohaline marls with Paratethyan ostracods. In the Maiella area, the PLG rests conformably above Messinian shallow-water (40-50 m depth) marine clays and marls, sedimented in anoxic conditions. Down-section these anoxic deposits pass to open marine Turborotalia multiloba-bearing marls (Messinian p.p.), which lie on carbonate ramp deposits (Lithothamnium limestones, Tortonian p.p.-Messinian p.p.) containing a rich-Heterostegina level close to the base (middle Tortonian). From this Tortonian-Messinian 145 m-thick section, 69 samples have been collected for 87Sr/86Sr analysis. These include 6 samples from the pre-evaporitic deposits (Lithothamnium limestones, Turborotalia multiloba-bearing marls, and anoxic clays and marls) and 63 samples from the PLG, which are arranged in 19 precessional-forced sapropel/gypsum cycles. From the PLG, different facies have been sampled: selenite, bandedselenite, branching-selenite, gypsarenite, gypsum laminite, and microbial limestone. 87Sr/86Sr values, which range between 0.708674 to 0.709000, show cyclical variations even in the same precessional cycle. At the bottom of the section (9.5 Ma, middle Tortonian) 87Sr/86Sr values plot on the global ocean 87Sr/86Sr curve, whereas up-section in the late Tortonian-Messinian interval, they show departures from the 87Sr/86Sr seawater curve. The major shifts from the global ocean 87Sr/86Sr values are at about 6.0 Ma (just before the onset of the MSC), 5.93 Ma, and 5.86 Ma. Except for three gypsum/sapropel cycles (1st, 3rd, and 7th), which show values similar to the global ocean water, the rest of the PLG precessional-forced cycles are characterized by lower 87Sr/86Sr values. The departure of the measured values from the 87Sr/86Sr global curve could be explained with frequent mixing of continental water with the seawater of the Adriatic sub-basin approaching the closure of the Gibraltar Strait and the onset of the MSC. Because drainage basins in the region encompass Mesozoic carbonates, in the Maiella area we could expect continental run-off with isotopic riverine input between 0.7076 to 0.7077. The major shifts from the 87Sr/86Sr global curve in the Maiella section, at about 6.00 and 5.93 Ma (0.708720 and 0.708674, respectively) could be linked either to riverine outflow increase or to minor inflow of oceanic water into the Mediterranean Basin during temporary closures of the global ocean gateway

Stratigraphic architecture of the upper Messinian deposits of the Adana Basin (Southern Turkey): implications for the Messinian salinity crisis and the Taurus petroleum system

This paper is mainly based on field work carried out on the Messinian deposits of the Adana Basin (southern Turkey), as well as on the interpretation of seismic reflection profiles to understand 3D geometries of the basin filling. Chronostratigraphical constraints for the Messinian deposits are from micropaleontological studies on foraminifera, ostracods, and calcareous nannofossils, recently carried out on the Messinian deposits of the Adana Basin. Our results indicate that this basin developed in a marginal area strictly related to the Mediterranean realm. The Messinian deposits of the Adana Basin record all the main steps of the Messinian Salinity Crisis (MSC) that affected the Mediterranean area at the end of the Miocene. The new stratigraphical model for the Messinian deposits of the Adana Basin provided in this work gives new insights into both the MSC and the Taurus petroleum system. Despite their complete correspondence with the MSC, the Messinian deposits of the Adana Basin show some differences with respect to the current conceptual model for the MSC. For example, in the current conceptual model for the MSC, only one regional erosional surface (MES) characterizes the MSC deposits. In the Adana Basin, two regional erosional surfaces, named MES1 and MES2, separate the Messinian deposits related to the MSC in Lower Evaporites, Resedimented Lower Evaporites (RLE), and upper Messinian continental deposits containing a late Lago-Mare ostracod assemblage (mainly fluvial coarse-grained and fine-grained sediments). In some places, Brecciated Limestones lie just above the MES1 and beneath the RLE. In addition, the RLE are thought to be related to the same step that brought to the Messinian halite deposition throughout the Mediterranean, pointing to a hyperhaline environment. In contrast, the fine-grained deposits of the RLE of the Adana Basin show the occurrence of Parathetyan brakish ostracod fauna (early Lago-Mare ostracod assemblages), which defines an oligohaline depositional environment for the RLE. In terms of hydrocarbon prospecting, the Messinian evaporites of the Adana Basin have been considered as a perfect seal for the active Taurus petroleum system. Our results show that due to the complex stratigraphical architecture of the basin filling and the occurrence of two regional erosional surfaces (MES1 and MES2), the Messinian evaporites are discontinuously present both in surface and in the subsurface of the Adana Basin. However, seal properties in the Adana Basin could be found in the Lower Pliocene deep marine clays of the Avadan Formation. This work leads to suggest a new stratigraphical model for the Messinian deposits of the Adana Basin, allowing us to amend the classical scheme with respect to the Messinian, and to officially define some new formations within the stratigraphy of the Adana Basin

Ancient Roman Mortars from Anfiteatro Flavio (Pozzuoli, Southern Italy): A Mineralogical, Petrographic and Chemical Study

This research is based on the characterization of ancient mortars from the Anfiteatro Flavio (Pozzuoli) dating back to the 1st and 2nd century CE through a multi-analytical approach involving macroscopic, mineralogical, petrographic, and chemical investigations. The goal that has been set is to deepen knowledge about mortar mix design, the provenance of used raw materials, and secondary minerogenetic processes that have occurred within ancient Roman mortars. Results show that: (i) raw materials for mortar preparation have a local provenance, i.e., Phlegraean Fields area; (ii) mortars can be considered as hydraulic; (iii) calcite presence could be due to a non-complete calcination process, an improper slaking or to exposition of materials to the subaerial environment; (iv) gypsum is due to calcite sulfation process; (v) halite presence is due to marine aerosol exposition. The achieved information testifies that, for at least two centuries, Roman builders considered the identified mortar mix as optimal for their buildings, but also contributes to the understanding of their technical skills and represents an important first step to planning future restoration operations