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The end-Triassic mass extinction: A new correlation between extinction events and δ13C fluctuations from a Triassic-Jurassic peritidal succession in western Sicily
No full textA new δ13Ccarb curve was obtained from an expanded peritidal succession in western Sicily and was used to
investigate the relationships between isotopic signatures and biological events on carbonate platforms across
the Triassic-Jurassic boundary (TJB). The resulting curve shows two main negative carbon isotopic excursions
(CIEs) that fit well with the “Initial” and “Main” CIEs that are recognized worldwide and linked to the End-
Triassic Extinction (ETE). In the studied section, the first negative CIE marks the disappearance of the large
megalodontids, which were replaced by small and thin-shelled specimens, while the “Main” CIE corresponds
to the last occurrence (LO) of the megalodontids and, approximately 50m upsection, to the total demise of the
Rhaetian benthic foraminifer community. Upward, the carbon curve shows a positive trend (ca. +1‰) and a
gradual recovery of the benthic communities after an approximately 10 m-thick barren interval populated
only by the problematic alga Thaumatoporella parvovesiculifera.
A comparison between the Mt. Sparagio δ13Ccarb curve and other coeval Ccarb and Corg curves from carbonate
platform, ramp and deep basin successions indicates similar isotopic trends; however, the diverse magnitudes
and responses of benthic communities confirmthat the carbon cycle perturbations have been globally significant,
and were influenced by external forces such as CAMP volcanism. The multiphase nature of the extinction pulses
could have been caused by local environmental changes related to transgression/regression phenomena. Overall,
this study adds new data and a new timing to the effect of the acidification process on carbon productivity and
benthic communities in different environments across the TJB
Evidence of a biodiversity crises documented on a peritidal carbonate succession from western Tethys (Sicily): new data on the End Triassic Mass Extinction
Full text linkA biodiversity crisis was observed in the latest Triassic on both macro-and micro-benthic communities from a western Tethyan carbonate platform. The studied succession represented by the Monte Sparagio section consists of a continuous Upper Triassic to Lower Jurassic peritidal limestones organized in shallowing upward cycles. The subtidal facies in the lower part of this section (Unit A) contains very abundant and highly diverse fossiliferous assemblages consisting of very large megalodontoids (up to 40 cm). Up-section, a reduction of biodiversity, abundance and shell size of megalodontoids (up to 15 cm) tipifies Unit B. Similarly, in this last Unit, the average dimensions of the benthic foraminifer T. hantkeni decreases (ca. 30%). After a short interval marked by a bloom of the problematic alga T. parvovesiculifera, the overlying Unit C accounts for the recovery of the Jurassic benthic community. The geochemical analyses of stable isotopes (C, O and S) seem correlative to the drastic reduction in the Rhaetian biodiversity between Unit A and Unit B. These biodiversity crises in the Rhaetian horizons can be interpreted as a precursor of the End Triassic Extinction and provide new insights into the existence of two extinction pulses at the end of Triassic. These data are in accordance with the environmental parameters of survival in a modern tropical shallow water platform (T-factory). In particular, the sea surface temperature (SST) of a T-factory ranges from 18 degrees C to 30.5 degrees C representing respectively the minimum SST for the carbonate factory persistence and the maximum SST that a T-factory can tolerate
The role of pressure solution in the evolving fracture stratigraphy properties of Mesozoic platform carbonates
Full text linkSlope Failures and MTDs along a Cretaceous Escarpment in Western Sicily (Italy)
Full text linkIn the last decades, many contributions have examined the Mass Transport Deposits (MTDs) in both modern and ancient examples for the comprehension of the sedimentary dynamics along the carbonate escarpments. Such sedimentary bodies have a great economic significance, since they are widely considered prone to the development of petroleum systems. In particular, MTDs from Cretaceous escarpments are well known from many regions of the world, since they are typically rich in rudists aragonite fragments determining high percentages of porosity. In these respect the deep knowledge on the facies architecture of these depositional systems is of broad interest as can offer examples for the prediction of the geometry and distribution of the facies types. Subsurface studies based on seismic data require comparisons with analogues from outcrops that allow the observation of structure and sedimentary characters of the MTDs.
On this topic, we carried out a sedimentological study in northwestern Sicily on a well-exposed Cretaceous escarpment, (Custonaci Cretaceous Escarpment, CCE). At present the original escarpment is dismembered in several tectonic units in the Maghrebian Chain. The biostratigraphic data allow to constrain the beginning of the slope sedimentation at the lowermost Cretaceous. Along the succession, the MTDs formed by huge bodies of megabreccias, alternate to finer grained skeletal rudstone and floatstone emplaced by turbidity currents and grain flows. The presence of pillow basalt intercalations suggests a major role of the tectonics as trigger for the MTDs emplacement. Furthermore, synsedimentary listric faults, slump scars and channel filling megabreccias allow to reconstruct the present day polarity of the slope.
The emplacement of coarse megabreccia beds at Custonaci can be documented until the Santonian. However, upward alternances of Scaglia-type pelagic calcilutites and skeletal turbidites and debrite beds lasted up to the Maastrichtian.
Nevertheless the Tertiary deformations have obscured the relationships of the CCE with the original source areas, there is a tight correlation between the evolution of the Cretaceous Panormide Platform and the studied slope
Correlation between extinction pattern and δ13C fluctuations across the Triassic Jurassic boundary in shallow water settings: a proxy for the present day acidification processes
No full textWith the aim to assess the possible influence of the carbon variations on the benthic communities across the Triassic Jurassic boundary we have carried out sedimentological, biostratigraphic and stable isotope studies on an about 220 m thick peritidal section cropping out in Northwestern Sicily.
The subtidal facies of the lower and middle part of this succession show the common occurrence of large and thick megalodontids and a benthic foraminiferal assemblage with Triasina hantkeni and Aulotuortids that supports a Rhaetian age. In the lower part of the succession, a significative biotic perturbation is evidenced by a sudden reduction of the size, shell thickness and abundance of the large megalodontids. This “Lilliput effect” corresponds to a first severe negative shift of the carbon curve that match a perturbation recorded worldwide known as “initial CIE”.
The “Lilliput effect” does not seems to have any influence on the microbenthic community (e.g. foraminifers and calcareous algae).
Upward, a second negative excursion spans a large stratigraphic interval and consists of at least 4 subtrends. This negative excursion is well comparable to the “main CIE” as defined worldwide in several sections (Hesselbo et al., 2007).
In our section, the lower part of the main CIE corresponds to the disappearance of the megalodontids, while the upper part of the main CIE records the LO of the microbenthic communities and, in particular of the Triasina hantkeni assemblage. Upward, concurrently to a gradual positive trend of the carbon curve (ca. +1‰) a gradual recovery of the benthic communities occurs, as witnessed by oligospecific assemblages of the problematic calcareous alga Thaumatoporella parvovesiculifera and, subsequently, by the appearance of benthic foraminifers such as Siphovalvulina sp.
The obtained carbon signature is comparable to the negative CIE recorded during Late Triassic in many other sections of the world as a consequence of the high CO2 rates related to CAMP volcanism.
Even if the correlation between extinction events and negative shift of the δ13C curve is a few constrained, this study adds new data on the effect of the acidification process on carbon productivity and benthic communities and allow to make a comparison with the present day acidification processes that are involving the carbonate calcifiers organisms
Depositional Setting, Diagenetic Processes, and Pressure Solution-Assisted Compaction of Mesozoic Platform Carbonates, Southern Apennines, Italy
Full text linkPressure solution processes taking place during diagenesis deeply modify the hydraulic properties of carbonates, affecting their mechanical layering and hence the dimension, distribution, and connectivity of high-angle fractures. The formation of stylolites is controlled by the texture of the host rock and therefore by the depositional environment and the diagenetic processes that involve it. This study reports the results of a multidisciplinary study carried out on a Jurassic–Cretaceous carbonate platform in southern Italy. The goal is to unravel the control exerted by single carbonate textures and specific diagenetic processes on the formation of bed-parallel stylolites. Microfacies analyses of thin sections are aimed at obtaining information regarding the composition and texture of the carbonates. Petrographic observations coupled with CL analyses are key to deciphering their diagenetic history. Results are consistent with carbonates originally deposited in a shallow-water realm in which carbonate mud is occasionally abundant. In this environment, early cementation inhibits their chemical compaction. In grain-supported facies, pressure solution is only localized at the grain contacts. During shallow burial diagenesis, precipitation of blocky calcite predates the formation of bed-parallel stylolites in the grain-supported facies. Contrarily, mud-supported facies favor chemical compaction, which results in stylolites showing a good lateral extension and thick sediment infill. A classification of different types of stylolite morphology is attempted in relation to facies texture. In detail, rougher morphology (sharp-peak) characterizes the stylolites nucleated in grain-supported facies, while smoother morphology (rectangular to wave-like) is observed in stylolites on mud-supported facies. Application of this knowledge can be helpful in constraining the diagenetic history of carbonate rocks cored from depth, and therefore predict the fracture stratigraphy properties of carbonates buried at depth
Seismo-stratigraphic and morpho-bathymetric analysis revealing recent fluid-rising phenomena on the Adventure Plateau (northwestern Sicily Channel)
Full text linkThe northwestern region of the Sicily Channel hosts a great number of morphological highs, the widest of which is the Adventure Plateau that is part of the Sicilian Maghrebian Fold and Thrust Belt system, formed since the Neogene. The Adventure Plateau was shaped in the Early Pliocene by an extensional phase that produced high-angle normal faults mostly WNW-ESE to N-S oriented. Through these faults, magmatic fluids ascended and produced widespread volcanic manifestations often associated to fluid flow processes. The interpretation of multibeam echosounder, seismic reflection (sparker, airgun) and well-log data allow us to identify several features related to the presence of fluids in the study area. The morpho-structural analysis showed a NW–SE oriented fault system and a string of pockmarks that follow the same trend. A detailed well-log analysis confirmed the presence of oil traces, at a depth of ~ 250 m, and gas (i.e., CO2) at a depth of ~ 450 m. The seismo-stratigraphic analysis highlighted seismic signals located below the pockmarks, (e.g. seismic chimneys, bright spots) which suggest the presence of fluids that would rise to a few meters’ depth. Based on the observations, two sources and two corresponding rising mechanisms have been identified. Morphometric analysis of pockmarks has been performed to delineate their possible interaction with the bottom currents. A fluids pathway model has been reconstructed, revealing the source of fluids emissions at depth in the Adventure Plateau, and providing new insights into the identification of fluid leakage pathways
Two end-members of carbonate slope evolution during the Late Cretaceous in the peri-Tethyan domain (Western Sicily and Southern Albania)
Full text linkClimatic and tectonic processes are major mechanisms influencing tropical carbonate platform development, sediment production and sediment export. Mass transport deposits (including slides, slumps and debrites) and calciturbidites are some of the sediment export products resulting from the interplay of aforementioned redeposition mechanisms. They reflect distinct variations in both production and export of sediments from the carbonate factories. The gravitary export deposits provide information on their sediment source and result in sedimentary sequences with specific porosity / permeability properties prone to host hydrocarbon resources. Climate-controlled sea-level variations are well-constrained in present day and Quaternary tropical carbonate environments (e.g. Bahamas, Maldives). However, it is still challenging to decipher relative eustatic sea-level variations and to separate them from tectonically-induced control when dealing with flat-topped carbonate platform production and re-sedimentation products within the adjacent basins. During Cretaceous times, multiple wide carbonate platforms prevailed in the peri-Tethyan realm. These sedimentary series are exposed in various outcrops and host important hydrocarbons resources in the subsurface. During the Late Cretaceous, several sectors of the sedimentary platform systems drowned, thus causing the demise of large portions of the carbonate factories. Although reduced in size and extremely localized, some carbonate platforms and associated sediment production persisted, e.g. Panormide Platform (S Italy), Latium-Abruzzi Platform (SW Italy), Adriatic Platform (SE Italy-Albania), Arabian Platform (N Lebanon). The evolution of two Upper Cretaceous carbonate platforms and slopes were analyzed utilizing sedimentary sequences cropping out in Sicily (WSCE - Western Sicily Cretaceous Escarpment, southern Italy) as well as in Albania (SACS – Southern Albania Cretaceous Slope). WSCE is characterized by thick calcidebrites and displays strong tectonic control on the sedimentation patterns as shown by the occurrence of massive megabreccia bodies as well as volcanic intercalations related to deep rooted extensional faults. SACS is dominated by finer grained deposits
(calciturbidites) and slumps. Large-scale tectonics caused massive basin-ward sediment shedding in both the case studies. Nevertheless, an enhanced subsidence favoring platform production and aggradation is highlighted at SACS, while a clear backstepping of the system is observed at WSCE. The two outcrop studies allow for a detailed comparison of the growth and demise of two carbonate factories situated within the peri- Tethyan domain as detailed in the sedimentary records of the individual carbonate slope to basin systems. This comparison will enhance our understanding of the sedimentary response of peri-Tethyan tropical carbonate platforms to tectonic processes
Fluid seepage evidence in the Adventure Plateau (NW Sicily Channel)
Full text linkThe northwestern region of the Sicilian Channel hosts a great number of morphological highs, the widest of which is the Adventure Plateau which is part of the Sicilian-Maghrebian Fold and Thrust Belt system, formed mainly during the Neogene. The complex morphology of the Adventure Plateau was shaped in the Lower Pliocene also by an extensional phase that produced high-angle normal faults mostly NW-SE to N-S oriented. Through these preferential pathways, magmatic fluids ascended and produced widespread volcanic manifestations. The interpretation of MBES (Multibeam Echosounder), seismic (sparker, airgun), well logs, and ROV (Remote Operative Vehicle) data identified several features related to the presence of fluids in the study area. The morpho-structural analysis showed an NW-SE-oriented fault system and a string of depressions that follows the same trend. The seismic-stratigraphic analysis highlighted various seismic signals located below the depressions, such as bright spots, enhanced reflection zones, and chimneys, which also suggest the presence of fluids that would rise to a few meters’ depth. Since all these fluids’ seepage evidence occur along the fault system, we consider this as the main pathway for vertical fluids migration. Further, to understand the fluid’s origin, a detailed well-log analysis has been performed; this showed the presence of oil traces, at a depth of 250 m, and gas (CO2) at a depth of 500 m. So, also considering the magmatic fluids evidence found by literature data, a possible mixed origin of the fluids, both biogenic and magmatic, should be assumed. Therefore, this work allowed us not only to identify new fluid seepage evidence in the Adventure Plateau but also to provide new insights into the identification of fluid leakage pathways
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