Gian Battista Vai

Development of the palaeogeography of Pangaea from Late Carboniferous to Early Permian

Abstract Old and new, well and poorly known lithofacies data of Moscovian and Artinskian age in the area limited by the Arctic Sea and central Africa, the Atlantic Ocean and the Ural Mountains have been plotted on present-day maps. The facies-mapped and related environments allow the recognition of a series of different palaeogeographic/palaeotectonic units including the Late Carboniferous to Early Permian deep sea to Palaeo-Tethyan ocean, west Siberia–Kazakhstan continent and Uralian–Kazakhstan–Tienshan arc, Uralian foredeep up to the closing arms of the Uralian ocean, Precaspian basin, Russian platform, Donets rift basin, Caucasian–Moesian–Dobrogean–Polish–Oslo basinal belt, syn-tectonic Hercynian foreland basin, intramontane post-Hercynian basins, Iran–Anatolian–Hellenic–Dinaric–Carnic basin branching into the Hungarian seaway, Apennine basin branching into the Cantabrian and South Portuguese basins, Oman–Iraq–Levantine–Sicily deep basin and inferred oceanic sea-way, south Peri-Tethyan platform basins, east Arabian cratonic basin, and north African intracratonic basins. The subsidence/sedimentation trends of these units were correlated and compared through lithostratigraphic logs, bathymetric curves and uncorrected cumulative stratigraphic curves. The sets of original and processed data were used to test two different palaeodynamic models, a Pangaea A model, static from Late Carboniferous to Triassic, and a mobile Pangaea B model with different dextral displacements between Laurussia and Gondwanaland in the same time interval. The best fit for our data requires a strike-slip offset of about 800 km from Moscovian to Artinskian time. This model implies a first quasi-Pangaea or Pangaea B assembly at the Carboniferous/Permian transition, an ephemeral Pangaea B break-up driven by an Early Permian oblique rift across the Mediterranean to Caribbean areas, and a final Pangaea A assembly in the Mid-to-Late Permian. The two palinspastic maps describing the model have been cross-checked by comparison with an independent set of biogeographic features of Late Carboniferous and Early Permian. Overall floral, reptile, and marine benthic organism distribution is consistent with the Early Permian trans-Pangaea seaway inferred from facies and palaeodynamic analyses.

Petrography and stable isotope aspects of cold-vent activity imprinted on Miocene-age “calcari aLucina” from Tuscan and Romagna Apennines, Italy

Over 20 occurrences of discontinuous limestone blocks, locally called “calcari aLucina,” were mapped in the Tuscan—Romagna region of the northern Italian Apennines. The limestones, consisting of a variable mixture of authigenic carbonates (calcite, dolomite, and aragonite), sulfides (primarily pyrite), and allogenic silicates, occur in association with turbidite and hemipelagite units that were deposited in foredeep basins during early to late Miocene times. The limestone blocks are interpreted to represent relicts of carbonate buildups formed around methane-rich fluid vents on the basis of their (1) striking petrographic similarities to carbonates from cold vents in the modern oceans; (2) unique chemosynthetic-like fauna, and (3) anomalously negativeδ13C values (δ13C = − 16‰ to − 58‰ PDB). The contemporaneous tectonism of the Apennine orogeny is likely to be the primary cause for the expulsion of the methane-rich fluids to the seabed in a manner analogous to the fluid-flow processes occurring at modern accretionary prisms.

Sequence stratigraphy and correlation of late Carboniferous and Permian in the CIS, Europe, Tethyan area, North Africa, Arabia, China, Gondwanaland and the USA

Abstract Sequence stratigraphy was used to correlate the depositional chronology during Permo–Carboniferous time in various sedimentary basins of Gondwanaland, western Europe, eastern Europe, Tethyan area, North Africa, Arabia, China, and North America. During late Carboniferous and Permian, eleven second-order sequences (SOS) were recognised throughout the whole area. The sequence SI is Serpukhovian pp, Namurian A pp and Chesterian. The sequence SII is Serpukhovian pp–Bashkirian pp, Namurian A pp-B-C–Westphalian A–B pp and Morrowan. The sequence SIII is late Bashkirian–Moscovian, Westphalian B pp-C-D and Atokan–Desmoinesian. The sequence SIV is Kasimovian, early Stephanian and Missourian. The sequence SV is Gzhelian–Orenburgian, late Stephanian and Virgilian. The sequence SVI is Asselian, Autunian and Nealian. The sequences SVII–IX are Saxonian, Sakmarian–Artinskian–Kungurian and Leonardian–Hessian–Cathedralian. The sequences SX–XI are Guadalupian and Lopingian. Depending on the regional setting, different relationships exist between marine transgression and the respective effects of tectonics and of sea-level changes: in western Europe, effects of the glacial processes in Gondwanaland are partly balanced by the late compression in the Hercynian belt during Moscovian. Eastern Europe, Tethyan area, North Africa, China, and North America show a good correlation between glacial (ice melting) processes in Gondwanaland and the intensity of the transgression which is increased by the westward progradation of the orogeny in Urals and Appalachians. In Arabia, Tunisia and Tethyan area, the impact of the Neotethys opening is obvious from the Artinskian and mainly during the late Permian.

A stratigraphic and tectonofacies framework of the “calcari aLucina” in the Apennine Chain, Italy

The Apennine Chain provides the first example of stratigraphic (time) and synsedimentary tectonic (space) distribution of the “calcari aLucina” Miocene equivalents of modern cold-vent carbonates. Chemosynthetic faunal assemblages and related carbonate deposits are found at different stratigraphic levels, with peaks during Langhian-Serravallian and late Tortonian-early Messinian times. A general increase in frequency and volume occurs with time. A “genetic link” between venting and the Messinian Evaporite event is difficult to demonstrate. However,Lucina limestones are limited to preevaporitic times, and their maximum abundance is reached just before the onset of the Messinian Evaporite accumulation.Lucina limestones occur in almost all tectofacies of the orogen, from backland to foreland.

Upper Devonian intraclast parabreccias interpreted as seismites

Abstract Parabreccias found across a Devonian carbonate platform-basin margin, in the Carnic region (NE Italy), coeval to extensional tectonic fragmentation are interpreted as seismites s.l. They are characterized by plate-shaped, edge-smoothed, early lithified intraformational clasts of basinal micritic limestone embedded and usually floating in a calcarenite matrix made of shallow-water debris. Such features are explained as a result of a first seismic autoclastic brecciation, due to shallow-seated earthquakes, of a thin pelagic mud layer lithified at the sediment—water interface; the brecciation was followed by disruption, small-scale transport and embedding of the clasts in a gravity-driven turbidity flow from the shallow-water platform, triggered by the same seismic event. A seismic origin of the clasts is preferred to an erosional one because of composition and morphology of the clasts, as well as of geometry of the layers (length in the order of 10–15 km, model thickness of 0.5–1 m, estimated minimum volume of 0.5–1 km 3 , relative abundance of parabreccias versus all remaining lithofacies about 70%). The suggested interpretation of the parabreccias fits very well the tecto-sedimentary evolution of the Carnic Devonian since the parabreccias appear only associated with independent evidences of synsedimentary palaeofaulting. Parabreccias of this kind, if distinct and mapped separately from polymictic “common” carbonate megabreccias of seismotectonic origin could become an additional tool for detecting timing, spacing, zonation and magnitude of palaeoearthquakes. An uncommon lithofacies of “intraclast parabreccia” interbedded with calcareous turbidites (and/or allodapic beds) within a pelagic carbonate sequence of Upper Devonian age, from the Carnic Alps (NE Italy), has been interpreted as a special type of seismite (Spalletta et al., 1983). Aim of this short note is to summarize the main features of these deposits and to discuss the evidences for such an interpretation.

Palaeozoic strike-slip rift pulses and palaeogeography in the circum-Mediterranean Tethyan realm

Abstract Five main rifting cycles, supported by different types of field evidence (including magmatism, sedimentation and tectonics), have been recognized in the circum-Mediterranean area (western Tethys realm) before the opening of the Jurassic Tethys proper. They occurred roughly in the late Cambrian-early Ordovician, early Silurian, late Devonian-Dinantian, early-mid Permian and mid-Triassic times. Each of these rifting cycles began with intracontinental, mainly shallow-marine conditions, evolving usually to basinal environments of quite different bathymetry (the Palaeozoic CCD has been proved to be much less deep than the post Liassic one). Minor suboceanic seaways cut across and fragmented the Gondwana-South European plate following the early Palaeozoic rifting cycles. The long mid Palaeozoic (Devono-Dinantian) rifting cycle migh possibly have resulted in a wider system of suboceanic sea-ways connecting a Palaeo-Tethys ocean to the east of Gondwana with the Rheic ocean to the west of it. The birth of Palaeo-Tethys, or of its westward extension, would have been directly linked with the gradual death of the Devono-Mississippian Rheic Ocean. A complex, large-scale, dextral transform system is inferred to have connected the two respectively expanding and contracting oceans. Fragmentation and mutual displacement of microblocks in the connection area (the circum-Mediterranea area and Southern Europe) resulted from strike-slip, oblique rift pulses with coeval, local contractional and extensional processes. A major change of the Gondwana rotational vector is believed to have produced the mid-late Carboniferous transpressional strike-slip Hercynian orogen. This is a good explanation of the peculiar thermal regime of the Hercynian diastrophism all over Europe. There is no support for the hypothesis of a very wide (more than 3000 km) Palaeozoic ocean separating Northern Europe from Southern Europe or Gondwanaland. This idea was mainly based on poor palaeomagnetic data and is heavily contradicted by palaeobiogeographical and geological data. Furthermore, it ignores the dramatic shortening of the Hercynian orogen all over Europe. The early Palaeozoic to early Mesozoic history of the circum-Mediterranean area involves the cyclic recurrence of oblique rifts, culminating in the early Jurassic strike-slip rift and subsequent limited opening of the Tethys proper. To avoid confusion in terminology, one should use prefixes referring to age, bathymetry-physiography and geotectonic setting to qualifying the general term “Tethys” (e.g., shallow Cretaceous Tethys, basinal intracontinental Devonian Tethys, oceanic Jurassic Tethys, etc.).

Hydrocarbon-derived imprints in olistostromes of the Early Serravallian Marnoso-arenacea Formation, Romagna Apennines (northern Italy)

Evidence of hydrocarbon venting within slumped bodies associated with the siliciclastic, dominantly turbiditic, Marnoso-arenacea Formation (Umbria-Romagna structural domain, Romagna Apennine, northern Italy) is documented with sedimentological, faunal, and geochemical data. Specifically,13C-depleted carbonate concretions and limestones and clusters of chemosynthetic clams (Vesicomyidae) have been identified in the marls of the Le Caselle Olistostrome and other slumped bodies contained within the Early Serravallian section of the Marnoso-arenacea Fm. Most of the olistostrome marls and limestones are extrabasinal and must have slid from a source area located several kilometers southwest of their present position. Thus, they presumably pertain to the Vicchio Marls Formation of the northeastern (outer) Tuscan structural domain, with possible minor contributions from the epi-Ligurian Bismantova Fm. It is suggested that venting of methane in the source area of the olistostromes permitted the establishment of exotic chemosynthetic communities and promoted the precipitation of carbonate concretions and limestones. According to the field evidence, these materials were later subjected to multistep downslope remobilization and were eventually carried into the Marnoso-arenacea basin through gravity mass transport.

The first geological map: an Italian legacy

Although the popular map by William Smith “ A Delineation of the Strata of England and Wales with Part of Scotland ” is properly celebrated as the first complete geological map of an entire country, the basic principles used by the famous English canal surveyor were epistemologically founded and utilized by the Italian Count Luigi Ferdinando Marsili about a century earlier. Marsili, “ uomo d’arme e scienza ” (“man of army and science”), represents a vitally important pioneer in the fields of geography, cartography, and oceanography, with farther-ranging knowledge that included, for example, the field of archaeological survey. With his geologic map of the Cesenate sulphur mines Marsili was the first geologist to make the quantum leap from simple mineralogical maps – which report the location and access of mines on a topographic background – to a proto-geological map, wherein the areas represented by corresponding lithostratigraphic units are delimited. If Smith’s map is rightly regarded as an ambitious work for the areal extent covered, Marsili’s “ Treatise on the Structure of the Earthy Globe ” (lamentably unfinished) was by far more ambitious. The 200 sheets that come down to us include about 50 pen drawings and more than 35 water-colored plates. These clearly show how the work of Marsili took radical departure from the classic systems or “ Theories of the Earth ” espoused by British contemporaries such as Burnet and Woodward: in the Italian scientist we find the first arguments on the mountain roots and the observations that, much later, led to the principle of isostasy. In the fields of stratigraphy, regional geology, oceanography, and geological mapping, Marsili anticipated scholarly thought by at least a century.

The Search for a Stratotype Section for the Late Pleistocene: Progress from the Fronte Section (Taranto Area, Italy)

We present the results of detailed litho-, bio-, and magnetostratigraphic investigations along the Fronte section (Taranto, Italy), where the facies distribution is interpreted using a combined palaeoecological and sequence-stratigraphic approach. The data obtained so far suggest a continuous sedimentary record at the Fronte site, where the MIS 5e peak and subsequent highstand are documented, thus providing robust evidence for the Last Interglacial sedimentary interval.

The Valle di Manche Section (Calabria, Southern Italy): A Candidate Section for the GSSP of the Ionian Stage (Middle Pleistocene Subseries)

We present the key features of the Valle di Manche section (Calabria, southern Italy) and discuss the pros and cons of this stratigraphic succession as a candidate section for the GSSP of the Ionian Stage (Middle Pleistocene Subseries).