Francesco Perri

Compositional and Geochemical Signatures for the Sedimentary Evolution of the Middle Triassic-Lower Jurassic Continental Redbeds from Western-Central Mediterranean Alpine Chains

Compositional and chemical analyses suggest that Middle Triassic–Lower Liassic continental redbeds (in the internal domains of the Betic, Maghrebian, and Apenninic chains) can be considered a regional lithosome marking the Triassic-Jurassic rift-valley stage of Tethyan rifting, which led to the Pangaea breakup and subsequent development of a mosaic of plates and microplates. Sandstones are quartzose to quartzolithic and represent a provenance of continental block and recycled orogen, made up mainly of Paleozoic metasedimentary rocks similar to those underlying the redbeds. Mudrocks display K enrichments; intense paleoweathering under a hot, episodically humid climate with a prolonged dry season; and sediment recycling. Redbeds experienced temperatures in the range of 100°–160°C and lithostatic/tectonic loading of more than 4 km. These redbeds represent an important stratigraphic signature to reconstruct a continental block (Mesomediterranean Microplate) that separated different realms of the western Tethys from Middle-Late Jurassic to Miocene, when it was completely involved in Alpine orogenesis.

Link between thrust tectonics and sedimentation processes of stratigraphic sequences from the southern Apennines foreland basin system, Italy

We discuss here tectonics and sedimentation processes occurring during continent-continent collision and relationships between accretionary processes on overplate, flexural lithosphere on underplate and related controls on clastic sedimentation in developing foreland basin systems. This paper focuses on and clastic sedimentation developed during the sequential history of the southern Italy orogenic system. These clastic trends, covering a large time span from pre-collisional Early Mesozoic to the present, may contribute: (1) to the paleogeographic and paleotectonic reconstructions of the southern Italy portions of the western Mediterranean orogen, and (2) to the general models of complex relationships between clastic sedimentation and paleotectonic history of other major orogens. The evolutionary record of Earth’s processes preserved in the form of sedimentary rocks has been pivotal in paleogeographical and paleotectonic reconstructions of source/basin systems. Compositional trends of clastic strata through space and time are used to infer the structural history of adjacent mountain belts and to monitor the key geodynamic changes during orogenic processes (e.g. Dickinson, 1985, 1988; Critelli & Ingersoll, 1994; Critelli, 1999). The controls on the composition and dispersal pathways of clastic strata along the convergent plate margins have long been debated (e.g. Dickinson, 1988; Ingersoll et alii, 1995). Clastic infilling of sedimentary basins in orogenic systems have been used as important indicators of tectonic activity and climatic changes. In the orogenic systems, clastic sedimentation may record the accretionary processes, the accomodation of the thrust units, and the flexural features of the foreland plate. The development of an orogenic wedge during continental collision results in thickening of the crust. The excess mass of this thickened crust acts as a load on the underthrust plate, causing it to be flexed downwards close to the load, so developing a foreland basin (e.g. Beaumont, 1981; Sinclair and Allen, 1992). During plate convergence, the vertically acting load of the mountain belt migrates over the foreland plate, thus resulting in the migration of the associated foreland basin. The foreland is the region between the front of a thrust belt and the adjacent craton (e.g. Dickinson, 1974; Bally and Snelson, 1980; Allen et alii, 1986; Miall, 1995). Large volumes of clastic sediment are derived from erosion of the thrust belt and deposited in the foreland basin. The foreland basin generally is defined as an elongate trough that forms between a linear contractional orogenic belt and the stable craton, mainly in response to flexural subsidence caused by thrust-sheet loading in the orogen.Foreland basin stratigraphy records tectonic, eustatic, and climatic changes at convergent plate margins (e.g. Miall, 1995). The formation of unconformities is the results of the interplay of temporal variations in the erosion and lateral progradation rates of the orogenic wedge, as well as tectonic and eustatic sea-level changes (e.g. Beaumont, 1981; Jordan, 1981; Schedl & Wiltsc hko, 1984; Peper et alii, 1995).

Clay Mineral Assemblages and Sandstone Compositions of the Mesozoic Longobucco Group, Northeastern Calabria: Implications for Burial History and Diagenetic Evolution

Mesozoic mudrocks and sandstones from the Longobucco Group (Sila Unit, North Calabria) were mineralogically, chemically, and petrographically analyzed for their burial, diagenesis, and sourcearea weathering histories. These sediments mark an important phase of the regional geological evolution along internal domains of the circum-Mediterranean chains from the Gibraltar Arc (Spain and Morocco) to the Calabria-Peloritani orogen (Italy). The effects of diagenesis on quartzose sandstone-mudstone lithotypes in the Mesozoic Longobucco Group succession are quantified. The basal Longobucco Group consists of continental clastic redbeds deposited in a rapidly subsiding rift-valley basin, overlain by shallow-marine to deep-marine carbonate and clastic strata. These sediments were analyzed using thin-section petrography, SEM/EDS, X-ray diffraction (XRD), and fluorescence. Quartzarenites display heterogeneous distributions of authigenic quartz, kaolin, illite, feldspar, and minor carbonate cementation. Authigenic zoned syntaxial overgrowths on detrital quartz represent the principal cement, and interstitial clay is an important component of these lithotypes. The mineralogical assemblage of mudrocks is dominated by illite and illite/smectite mixed layers. This observation, coupled with the CIA index and the A-CN-K plot, suggests post-depositional K-enrichment. Paleoweathering indices (CIW and PIA ratios) suggest that the source experienced intense weathering and that mudrocks likely record recycling from metasedimentary basement rocks. Clay-mineral distributions of sandstone/mudstone lithotypes indicate that mixed-layer illite/smectite with ordered interstratification (from R = 1 to R = 3) dominates mudstone mineralogy. Authigenic clays in sandstone are kaolinite, illite, chlorite, and kaolinite illitization as pore filling and lining. These authigenic clays show a distinct distribution, reflecting differences in burial/temperature history. The illite crystallinity index, the illitization of kaolinite, and the occurrence of high-illite I/S mixed-layer clay minerals suggest burial depths of at least 4-6 km and a temperature typical of the boundary between late diagenesis to low anchizone.

Sandstone petrology and mudstone geochemistry of the Peruc–Korycany Formation (Bohemian Cretaceous Basin, Czech Republic)

We have studied the petrography and the bulk-rock geochemistry of arenites and mudstones of the Cenomanian Peruc–Korycany Formation to characterize their provenance and sedimentary history, as well as the influence of weathering, hydraulic sorting, and recycling of the source rocks. The Peruc–Korycany Formation contains sedimentary facies reflecting both meandering- and braided-river systems and shallow-marine systems. Differences in the three depositional settings did not cause distinctly different modifications of the framework compositions of the arenites. The sand from the fluvial systems is very mature (Qm98F0Lt2). These fluvial arenites were subsequently modified by shallow-marine processes; reworking produced very slight decreases in the abundance of lithic fragments and polycrystalline quartz grains. The Cenomanian strata of the Bohemian Cretaceous Basin were derived dominantly from metasedimentary and crystalline rocks of the Palaeozoic Teplà-Barrandian and Cadomian Moldanubian units, respectively. Periods of low tectonic activity resulted in the deposition of arenites with quartzose framework compositions, indicating that climatic and/or transport/depositional-environmental controls overwhelmed factors such as source-rock compositions. Ultrastable dense minerals are useful indicators of sedimentary recycling within the Peruc–Korycanytarenites. Mudstone samples are characterized by abundant kaolinite, illite, chlorite, and quartz but by negligible amounts of goethite and gypsum. Concentrations normalized to the post-Archaean Australian shale (PAAS) show that the sediments are strongly depleted of Na, K, Ca, Sr, and Ba, probably because of the mobility of these elements during weathering. Chemical indices of alteration (CIA, CIW, and PIA) show that the degree of weathering of the source area was high. The data fall closer to the compositional fields of highly weathered minerals such as kaolinite, gibbsite, and chlorite on an A-CN-K diagram. The indices of compositional variability of the studied samples are much less than 1, suggesting that the samples are compositionally mature and were likely dominated by recycling. The elemental ratios critical of provenance (La/Sc, Th/Sc, Th/Co, Th/Cr, and Cr/Th) are similar to fine fractions derived from the weathering of mostly granitoids rather than mafic rocks.

Provenance signatures for the Miocene volcaniclastic succession of the Tufiti di Tusa Formation, southern Apennines, Italy

The Tufiti di Tusa Formation, a siliciclastic turbidite system of lower Miocene age in southern Italy, is mainly composed of volcaniclastic and quartzolithic sandstones interbedded with mudrocks. Sandstones are subdivided into four distinctive petrofacies, evolving from quartzolithic to volcaniclastic lithofeldspathic and feldspatholithic, reflecting detrital evolution from growing orogen (quartzolithic petrofacies) to active volcanism (volcaniclastic petrofacies). The mineralogical composition of the associated mudrocks is predominantly characterized by phyllosilicates, mainly illite/smectite mixed layers (I/S R1 associated with minor amounts of I/S R0 in the lower part of the succession, and I/S R3 in its upper part), together with illite, detrital micas and chlorite, and minor amounts of chlorite/smectite mixed layers and kaolinite, in addition to quartz, calcite and feldspars. The most abundant phyllosilicates are I/S mixed layers, 10-A minerals (illite and micas) and chlorite, while kaolinite and chlorite–smectite mixed layers are present as a few per cent or in trace amounts. X-ray diffraction patterns show the occurrence of the ordered I/S R1 mixed layers in most samples but, at the top of the succession, some samples are characterized by I/S R3 mixed layers, whilst in the lower part of the succession I/S R1 is associated with a lower amount of I/S R0. These features suggest that the Tufiti di Tusa Formation experienced a medium diagenetic grade, and the occurrence of I/S R3 could be explained by K-availability in samples in the upper part of the succession. The lithic fragments in sandstones are metasedimentary rocks of Palaeozoic age, and andesite to dacite volcanic rocks of early Miocene age. The associated mudrocks also contain trace element ratios (Cr/V, Y/Ni, La/Sc, Th/Sc, Th/Co, Th/Cr, Cr/Th and Eu/Eu*) consistent with a provenance containing intermediate to silicic sources with scarce or absent basic rocks. The chemical index of alteration (63.2 to 71.6) suggests a moderate degree of weathering in the source. Furthermore, the K/Cs ratios of sediments confirm likely moderate rather than intense weathering. The index of compositional variability (ICV) values (from 1.2 to 2.5) are high enough to suggest the mudrocks are first-cycle sediments with little recycling. The Al–Ti–Zr diagram and the Th/Sc v. Zr/Sc plot indicate poor sorting and rapid deposition of the sediments. Detrital and sedimentary evolution of the Tufiti di Tusa Formation provides constraints, in terms of relations between a growing orogenic system and active volcanism in the Central Mediterranean, to contribute to geodynamic and palaeogeographic reconstructions of the earliest collision in the southern Apennines region.

Relationships between Lithospheric Flexure, Thrust Tectonics and Stratigraphic Sequences in Foreland Setting: the Southern Apennines Foreland Basin System, Italy

We discuss here tectonics and sedimentation processes occurring during continent-continent collision and relationships between accretionary processes on overplate, flexural lithosphere on underplate and related controls on clastic sedimentation in developing foreland basin systems. This paper focuses on and clastic sedimentation developed during the sequential history of an orogenic system, in the Mediterranean Region. These clastic trends, covering a large time span from Early Mesozoic to the present, may contribute: (1) to the paleogeographic and paleotectonic reconstructions of the southern Italy portions of the western Mediterranean orogen, and (2) to the general models of complex relationships between clastic sedimentation and paleotectonic history of other major orogens. The evolutionary record of Earth’s processes preserved in the form of sedimentary rocks has been pivotal in paleogeographical and paleotectonic reconstructions of source/ basin systems. Compositional trends of clastic strata through space and time are used to infer the structural history of adjacent mountain belts and to monitor the key geodynamic changes during orogenic processes (e.g. Dickinson, 1985, 1988; Critelli & Ingersoll, 1994; Critelli, 1999). The controls on the composition and dispersal pathways of clastic strata along the convergent plate margins have long been debated (e.g. Dickinson, 1988; Ingersoll et al., 1995). Clastic infilling of sedimentary basins in orogenic systems have been used as important indicators of tectonic activity and climatic changes. In the orogenic systems, clastic sedimentation may record the accretionary processes, the accomodation of the thrust units, and the flexural features of the foreland plate. The development of an orogenic wedge during continental collision results in thickening of the crust. The excess mass of this thickened crust acts as a load on the underthrust plate, causing it to be flexed downwards close to the load, so developing a foreland basin (e.g. Beaumont, 1981; Sinclair and Allen, 1992). During plate convergence, the vertically acting load of the mountain belt migrates over the foreland plate, thus resulting in the migration of the associated foreland basin. The foreland is the region between the front of a thrust belt and the adjacent craton (e.g. Dickinson, 1974; Bally and Snelson, 1980; Allen et al., 1986; Miall, 1995). Large volumes of clastic sediment are derived from erosion of the thrust belt and deposited in the foreland

Chemical and minero-petrographic features of Plio-Pleistocene fine-grained sediments in Calabria, southern Italy

The composition of Plio-Pleistocene fine-grained sediments from different areas of Calabria (southern Italy), have been studied to unravel the interplay of provenance. The use of multivariate statistical methods ( e.g. , PCA) based on biplot, allows for the discrimination of different groups of sediments. The general chemical composition of the fine-grained samples reflects the mineralogical variation observed in the sediments, which are composed of phyllosilicates, quartz, calcite, dolomite and feldspars. The I-S mixed layers, 10 A-minerals (illite and micas) are the most abundant phyllosilicates, chlorite and kaolinite are present in variable amounts, and smectite and chlorite/smectite mixed layers are presents in trace amounts. These chemical and mineralogical variations are also confirmed by SEM analysis, which also demonstrates that phyllosilicates are characterized by open and folded structures with generation of neoformed clay minerals. Provenance proxies and element ratios testify greater input of felsic source rocks, with lack of a marked mafic-ultramafic detritus input for all studied sediments, and the minero-petrographical features of the studied fine-grained sediments. These chemical and mineralogical variations are also confirmed by SEM analysis showing abundant phyllosilicate minerals for Groups 1 (Crotone Basin) and 2 (Crati Graben) and high content of quartz and feldspars grains for Group 4 (Catanzaro Graben) samples, probably due to abundant siliciclastic input coming from plutonic-metamorphic source and associated Mesozoic to Miocene sedimentary sources (Sila and Serre Massifs), and abundant calcium-carbonate phases mainly related to the presence of planktonic calcareous microfossils (Globigerina and coccoliths) for Groups 3 (southern Ionian coast) and 5 (southern Tyrrhenian coast). Furthermore, paleogeographic reconstructions characterized by re-establishment of open-marine conditions in the Mediterranean following the Messinian salinity crisis at the beginning of the Pliocene, play an important role. A progressive increase in the connectivity of Mediterranean sub-basins with the Atlantic ( e.g. , sub-basins at the south of the Catanzaro Strait, characterized by normal water supply) and Paratethys ( e.g. , sub-basins at the north of the Catanzaro Strait, characterized by freshwater supply) can be envisaged during the Neogene period; this paleogeographic reconstruction may also explain the different composition among the studied samples.

Zircon Compositions of Lower Mesozoic Redbeds of the Tethyan Margins, West-Central Mediterranean Area

Typologic study and chemistry of zircon populations from Middle Triassic-Lower Liassic arenitic continental redbeds of the Internal Domains successions of the Mediterranean chains, from the Gibraltar Arc to the Calabria-Peloritani Arc, allow assessment of whether this type of study may be used to obtain more comprehensive inferences on the sedimentary evolution of ancient clastic rocks. Calabria-Peloritani Arc zircons are primarily euhedral, with subordinate rounded and subrounded grains. Rifian Maghrebides samples contain abundant euhedral zircons, with minor rounded and ovoid zircons. Betic Cordillera zircons are rounded or subrounded, with minor euhedral elongate grains; rounded zircons of these samples cannot be typologically classified. Electron-microprobe analyses (Si, Zr, Hf, P, and HREE) indicate homogeneous compositions, suggestive of common source areas characterized by granitoid rocks, whereas typology suggests the existence of two distinct groups. The first group includes arenites from the Calabria-Peloritani Arc and the Rifian Maghrebides. The second group includes arenites from the Betic Cordillera. Differences between the two zircon groups may be related to recycling effects, in agreement with a geochemical study of Triassic to lowermost Jurassic mudrock redbeds. Recycling likely was more significant for the Betic Cordillera samples. These results suggest that zircon typology and mudrock geochemistry can be useful tools for provenance, especially in complex sedimentary contexts where arenite-mudrock couplets occur.

Stratigraphy, composition and provenance of argillaceous marls from the Calcare di Base Formation, Rossano Basin (northeastern Calabria)

The Calcare di Base Formation is a part of the Rossano Basin characterizing the Foreland Basin System of northeastern Calabria. Messinian argillaceous marls from the Calcare di Base Formation have been studied to characterize the sedimentary evolution of this formation during the post-orogenic phases of the Calabria–Peloritani Arc. The mineralogical assemblage of the argillaceous marls is dominated by phyllosilicates (illite, chlorite, illite/smectite mixed layers and traces of kaolinite), carbonate minerals (calcite, aragonite and dolomite), quartz and traces of feldspars (both K-feldspars and plagioclase), gypsum and celestine. The palaeoweathering index records changes at the source, reflecting variations in the tectonic regime as shown in the A–CN–K plot, where the studied samples describe a trend typical of a source area in which active tectonism allows erosion of all zones within weathering profiles developed on source rocks. The studied samples are derived from an environment in which non-steady-state weathering conditions prevailed. This trend could record deformational events that affected the Mediterranean area during the Miocene. The Th/Sc versus Zr/Sc ratios and Al–Zr–Ti plot suggest that the samples likely record a recycling effect from their basement rocks. The geochemical proxies of these samples suggest a provenance from a mainly felsic source. The Messinian argillaceous marls record that deposition probably occurred in a semi-closed marine environment mainly subject to hypersalinity with local episodes of meteoric water influx, during a period characterized by persistent dry and warm/arid conditions alternating with relatively wet conditions.

Sourceland controls and dispersal pathways of Holocene muds from boreholes of the Ionian Basin, Calabria, southern Italy

Deep-marine muds were collected from two boreholes (Crati II and Neto VI) along the Ionian Calabrian Basin. The samples from the Crati II and the Neto VI boreholes show a similar mineralogical distribution; the marine muds contain mostly phyllosilicates, quartz, calcite, feldspars and dolomite. Traces of gypsum are present in a few samples. The Neto muds show higher concentrations of carbonates than the Crati muds; these contents are mainly related to recycling of the Neogene–Quaternary carbonate-rich marine deposits of the Crotone Basin, which mostly influences the composition of the Neto muds. The geochemical signatures of the muds mainly reflect a provenance characterized by felsic rocks with a minor, but not negligible, mafic supply. In particular, the hinterland composition of the Crati drainage area is on average more mafic in composition than the Neto drainage area. The higher mafic concentration of the Crati sample muds is probably related to the ophiolitiferous units that are exposed in the Crati drainage basin. The degree of source area weathering was most probably of low–moderate intensity because the Chemical Index of Alteration values for the studied muds range from 67 to 69. Furthermore, the low and constant Al/K and Rb/K ratios suggest low–moderate weathering without important fluctuations in weathering intensity. The Al 2 O 3 –TiO 2 –Zr ternary diagram and the values of the Index of Compositional Variability indicate that both the Neto and Crati muds are first-cycle, compositionally immature sediments, related to a tectonically active (collision) setting such as the Calabria–Peloritani Arc, where chemical weathering plays a minor role.