Paleomagnetism of latest Anisian (Middle Triassic) sections of the Prezzo Limestone and the Buchenstein Formation, Southern Alps, Italy

A paleomagnetic study was carried out at six stratigraphic sections (309 specimens) in the latest Anisian (Middle Triassic) Prezzo Limestone and the overlying Buchenstein Formation. These units outcrop over a wide area in the western Southern Alps, although most of the sampled sections are in the vicinity of the Late Eocene-Early Oligocene Adamello batholith. Three sites suffered a complete remagnetization induced by the Adamello, whereas a characteristic component with a positive fold test has been isolated at the three other sites. The mean pole of the characteristic component (Lat. 63.2°N, Long. 229.3°E,N = 3,A95 = 8°,k = 236) is in agreement with the Triassic portion of the West Gondwana apparent polar wander path (APWP), supporting the use of paleopoles from well-dated rocks in the Southern Alps as useful proxies for the African APWP. The characteristic component, where isolated in the sampled sections, is of normal polarity only, corresponding to the latest Anisian on the basis of well-defined ammonoid and conodont biostratigraphy, but the present results suggest that there are good opportunities for extending Middle Triassic magnetostratigraphy in these Southern Alps rock units. The mean pole of the Adamello-induced component (Lat. 74.5°N, Long. 172.1°E,N = 4,A95 = 7.6°,K = 145) lies close to the Early Tertiary portion of the APWP for stable Europe. The post-folding, Adamello-induced directions confirm that the 30–42 Ma Adamello batholith intruded after Alpine deformation and that no further deformation apparently occurred in post-emplacement times

Mobility of Pangea: Implications for Late Paleozoic and Early Mesozoic paleoclimate

Several recent analyses of paleomagnetic data support the concept of Pangea, an assemblage of most of the world‘s continents that was mobile in terms of large-scale internal deformation and with respect to paleolatitude. The main feature of internal deformation involved the transformation from a Pangea B—type configuration in the late Paleozoic, with northwestern South America adjacent to eastern North America, to a more traditional Pangea A—type configuration in the early Mesozoic, with northwestern Africa adjacent to eastern North America. Pangea B thus seems to coincide in time with extensive low-latitude coal deposition and high southern-latitude Gondwana glaciations, whereas Pangea A coincides with generally drier conditions over the continents and no polar ice sheets. Although the configuration of Pangea may have been more stable as an A-type configuration in the Early and Middle Jurassic prior to breakup, the paleomagnetic evidence suggests that there was appreciable latitudinal change of the assembly. Such changing tectonic boundary conditions emphasize the practical importance of age registry of paleoclimate data in making valid comparisons with model results. A simple zonal climate model coupled with the geocentric axial dipole hypothesis for establishing paleolatitudes in precisely controlled paleogeographic reconstructions can explain many of the climate patterns in both the late Paleozoic and the early Mesozoic, but it cannot explain the presence or absence of continental ice sheets

ADRIA AS PROMONTORY OF AFRICA AND ITS CONCEPTUAL ROLE IN THE TETHYS TWIST AND PANGEA B TO PANGEA A TRANSFORMATION IN THE PERMIAN

It has been almost 60 years since the first results from the Early Permian Bolzano Quartz Porphyries from the Trento Plateau of northern Italy (Southern Alps) showed paleomagnetic inclinations steeper than inclinations from broadly coeval units from central Europe. This experimental discrepancy, confirmed ever since at varying levels of magnitude and certitude, implied that northern Italy had paleolatitudes too northerly relative to Europe to be considered part of the European continent. On the other hand, it became progressively more apparent that paleomagnetic data from northern Italy were more compatible with data from Africa than with data from Europe, and this observation revived and complemented Argand’s original concept of Adria as a promontory of Africa. But if Adria was part of Africa, then the paleolatitude anomaly of Adria relative to Europe translated into a huge crustal misfit of Gondwana relative to Laurasia when these landmasses were forced into a classic Wegenerian Pangea as typified by the Bullard fit of the circum-Atlantic continents. This crustal misfit between Gondwana and Laurasia was shown to persist in the ever-growing paleomagnetic database even when data from Adria were provisionally excluded as non-cratonic in nature. Various solutions were offered that ultimately involved placing Gondwana to the east (allowing it to be more northerly) relative to Laurasia and envisaging a dextral shear occurring in the Tethys (Mediterranean) realm between these supercontinental landmasses. This shear or transformation was initially thought to occur as a continuum over the course of the Mesozoic–Cenozoic (the so-called ‘Tethys Twist’) but soon afterwards when plate tectonics came into play and limited the younger extent, as a discrete event during the post-Triassic, Triassic or most probably – as in the latest and preferred reconstructions – the Permian between a configuration of Pangea termed B – with the northwestern margin of Africa against southern Europe – to a configuration termed Pangea A-2, with the northwestern margin of Africa against eastern North America, that is more proximal in shape to the classic Pangea A-1 that started fragmenting in the Jurassic with the opening of the Atlantic Ocean. The Permian timing and presumed locus of the ~2300 km dextral shear is supported by rotated tectonic domains in Sardinia and elsewhere along the interface between Lauarasia and Gondwana. The concept of Pangea B and its transformation into Pangea A developed therefore in close conjunction with the concept and paleomagnetic support of Adria as a promontory of Africa, and has ramifications to many aspects of tectonics, climate change and biogeography yet to be explored

A Novel Plate Tectonic Scenario for the Genesis and Sealing of Some Major Mesozoic Oil Fields

Recent research reveals evidence of a major event of global plate motion during the Jurassic, with a magnitude and tempo hitherto not fully appreciated. Yet, its legacy persists today as the potent Jurassic source-reservoir-seal oil systems in the Persian Gulf region. We suggest that these formed as a consequence of a sweeping tectonic movement whereby Arabia drifted rapidly from the oil- forming Intertropical Convergence Zone along the equator to the arid tropics of the southern hemisphere with rapid deposition of relatively uncemented carbonate reservoirs and anhydrite seals, all during as little as 15 m.y. in the Late Jurassic. The Ghawar super- giant oil field of Saudi Arabia was one of the results. Rapid latitu- dinal change may have influenced the development of some source-reservoir-seal oil systems elsewhere as well

Widespread formation of cherts during the early Eocene climate optimum

Radiolarian cherts in the Tethyan realm of Jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates. However, the widespread occurrence of cherts in the Eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones. In a new survey of the global spatio-temporal distribution of Cenozoic cherts in Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sediment cores, we found that cherts occur most frequently in the Paleocene and early Eocene, with a peak in occurrences at ~50 Ma that is coincident with the time of highest bottom water temperatures of the early Eocene climatic optimum (EECO) when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity. Cherts occur less commonly during the subsequent Eocene global cooling trend. Primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation. This timing of peak Eocene chert occurrence, which is supported by detailed stratigraphic correlations, contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and/or volcanism in a supposedly sluggish ocean of the EECO, followed during the subsequent middle Eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification, with the formation of chert as a result of biosilica transformation during diagenesis. Instead, we suggest that basin-basin fractionation by deep-sea circulation could have raised the concentration of EECO dissolved silica especially in the North Atlantic, where an alternative mode of silica burial involving widespread direct precipitation and/or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling-deficient conditions of the EECO. Cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones

Lower and Middle Triassic foraminifera from the Eros Limestone, Hydra Island, Greece

Abstract. The systematics and stratigraphic ranges (constrained by conodont dating) of abundant and well preserved foraminiferal faunas from six sections in the Lower and Middle Triassic Eros Limestone of central and western Hydra (Argolis Peninsula, Greece) are described. A joint analysis of the conodonts, foraminifera and bivalves has enabled the Scythian and Anisian stages to be recognized with some certainty within the Eros Limestone carbonate platform. The foraminifera have affinities with those of many other Tethyan localities, in particular the Dinarides, Balkans, Carpathians and the Southern Alps

Human migration into Europe during the late Early Pleistocene climate transition

A critical assesment of the available magnetostratigraphic and/or radiometric age constraints on key sites bearing hominin remains and/or lithic industries from southern Europe (Italy, France, Spain) leads us to propose that the main window of early hominin presence in southern Europe is broadly comprised between the Jaramillo subchron and the Brunhes–Matuyama boundary (i.e., subchron C1r.1r, 0.99–0.78 Ma). Within the dating uncertainties, this ~ 200 ky time window broadly coincides with the late Early Pleistocene global climate transition that contains marine isotope stage (MIS) 22 (~ 0.87 Ma), the first prominent cold stage of the Pleistocene. We suggest that aridification in North Africa and Eastern Europe, particularly harsh during MIS 22 times, triggered migration pulses of large herbivores, particularly elephants, from these regions into southern European refugia, and that hominins migrated with them. Finally, we speculate on common pathways of late Early Pleistocene dispersal of elephants and hominins from their home in savannah Africa to southern Europe, elephant and hominin buen retiro. In particular, we stress the importance of the Po Valley of northern Italy that became largely and permanently exposed only since MIS 22, thus allowing possibly for the first time in the Pleistocene viable new migration routes for large mammals and hominins across northern Italy to southern France and Spain in the west

Magnetostratigraphy of a Lower-Middle Triassic boundary section from Chios (Greece)

The Marmarotrapeza Formation at Chios Island (northern Aegean Sea, Greece) is renowned for its Lower-Middle Triassic boundary sections in a marine Tethyan setting. Two sections have been sampled bed by bed to develop a magnetostratigraphic framework for the ammonoid and conodont biostratigraphy. The boundary sections occur within a lower normal (A+)-reverse (B−)-upper normal (C+) polarity sequence. The Lower-Middle Triassic boundary, placed at the first occurrence of the ammonoid genera Aegeiceras ugra Diener, Paracrochordiceras spp., Paradanubites depressus Fantini Sestini and Japonites sp., and close to the first appearance of the conodont species Gondolella timorensis Nogami, occurs in normal polarity zone Chios C+. The overall mean direction of the reversal-bearing characteristic component, whose early acquisition is suggested by a tilt test, is D = 271.2°, I = 33.2° (α95 = 11.7°, k = 112.5, N = 3). The inferred paleolatitude of the sampling sites is about 18°N, consistent with either an African or stable European affinity, although the declinations suggest large-scale counter-clockwise rotations with respect to Africa or stable Europe since the Early-Middle Triassic

Comment on ‘The oldest human fossil in Europe from Orce (Spain) by Toro-Moyano et al. (2013)

A critique of evidence for human occupation of Europe older than the Jaramillo subchron (~1 Ma). The recently dated human tooth from Barranco León, Spain, would seem to indicate that hominins were present in southern Europe as early asw1.4 Ma (millions of years ago) based on electron spin resonance (ESR) ages on quartz grains coupled with magnetostratigraphic and biochronologic correlations (Toro-Moyano et al., 2013). We suggest that the evidence for human occupation of Europe prior to 1 Ma is highly equivocal