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40Ar/39Ar age constraints on MIS 5.5 and MIS 5.3 paleo‐sea levels. Implications for global sea levels and ice‐volume estimates
Get PDFWe integrate 10 new with five published 40Ar/39Ar age determinations, both on primary volcanic deposits and on detrital sanidine, which provide precise geochronologic control on the Marine Isotope Stage (MIS) 5.5 and MIS 5.3 sea-level indicators that occur at three coastal caves in a tectonically stable region of the central Tyrrhenian Sea of Italy. The age of a Strombus-bearing bioclastic conglomerate, associated with a tidal notch occurring at 9.5 m a.s.l. at Cape Circeo, is constrained to between 121.5 ± 5.8 and 116.2 ± 1.2 ka. Moreover, backbeach deposits intercalated in the sedimentary filling of Guattari and Capre coastal caves are directly correlated with a tidal notch at ∼2.5 m associated with another bioclastic conglomerate at Cape Circeo and dated to 110.4 ± 1.4–104.9 ± 0.9 ka. The latter deposit is also correlated with the adjacent marine terrace, occurring at 3–5 m on the coast between Capes Circeo and Anzio, for which a maximum age of 100.7 ± 6.6 ka was previously reported. These data provide evidence for a maximum sea level around 9.5 m above the present sea level and a duration of MIS 5.5 highstand until 116 ka, in agreement with estimates from other regions in the world. In contrast, they suggest a maximum sea level during MIS 5.3 highstand that is similar to the present level, and only ∼7 m lower than the MIS 5.5 highstand, challenging the reconstructions of the MIS 5 ice-sheet volumes and derived global sea levels that are based on benthic oxygen isotope records
New insights on the petrology of the ancient activity of the Roccamonfina volcano (central-southern Italy)
No full textRoccamonfina is an extinct stratovolcano of the Italian peninsula where leucite-bearing ultrapotassic products are generally considered to predate leucite-free shoshonitic products. This relationship is largely based on studies conducted on lavas, while pyroclastic successions have been generally overlooked due to their poor preservation.
Here we report a detailed petrological investigation of the juvenile products from pyroclastic deposits of the oldest stages of the volcano activity (i.e. >350 ka) cropping out on the eastern side of the edifice. Most of the samples are represented by crystal-poor pumice clasts with few clinopyroxene and sanidine microphenocrysts set into a brownish, glassy groundmass with sparse, variably altered to fresh leucite crystals. A smaller number
of samples are relatively crystal-rich and feature clinopyroxene, altered leucite and biotite phenocrysts plus variable amounts of sanidine and plagioclase, depending on the rock composition. Glass compositions range from phonotephritic to phonolitic, in line with the compositions of the oldest Roccamonfina lavas. In addition, leucite-free juvenile clasts were also observed. These clasts are typically crystal-poor, and featuring only rare alkali
feldspar and clinopyroxene phenocrysts set into a trachytic groundmass whose compositions are in line with that of the most recent shoshonitic products. Interestingly, leucite-bearing and leucite-free samples display comparable Sr (0.70900-0.70939 vs. 0.70872-0.70913) and Nd (0.51217-0.51220 vs. 0.51220-0.51224) isotope ratios. These preliminary results indicate that the ancient Roccamonfina activity was significantly more
complex than previously thought, featuring at least two different magma series possibly generated by different partial melting degrees of the same mantle source
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A high resolution tephrochronological record of MIS 14-12 in the Southern Apennines (Acerno basin, Italy).
No full textLithological, mineralogical, and glass chemical analyses on juvenile fragments extracted from 20 tephra layers embedded within the lacustrine sediments of the Acerno basin (Southern Apennines, Italy) were carried out together with four sanidine 40Ar/39Ar age determinations. The measured ages span the interval between 561 and 493 ka. Middle Pleistocene eruptive activity at Roman Province volcanoes was identified as the main possible source of the investigated tephra layers. Some of them were correlated with precise terrestrial counterparts corresponding to large explosive events of the Sabatini (e.g. Tufo Giallo della Via Tiberina) and Alban Hills volcanic districts (e.g. Tufo Pisolitico di Trigoria). The integration of tephrochronology and pollen analyses allowed the Acerno lacustrine sedimentation to be constrained between MIS 14 and 12, which overlaps with several well-studied, lacustrine successions of the Southern Apennines. The correlation with other tephrostratigraphic records from intramontane basins in central-southern Apennines testifies to the wide dispersal of at least three tephra layers that serve as marker layers, thus improving the resolution of the Middle Pleistocene Italian tephrostratotype
Tectonic and cimatic control on Geomorphological and sedimentary evolution of the Mercure basin, southern Apennines, Italy.
No full textThe morpho-tectonic and sedimentary evolution of the Mercure intramontane basin (Calabria- Lucania boundary, southern Apennines) has been assessed through facies analysis, morphostratigraphy and geomorphological correlation with adjacent areas.
The Mercure basin, one of the most active seismogenic zones of the southern Apennines, is a favorable area for reconstructing the main stages of landscape evolution of the axial zone because of its capability to record changes in base level during the Quaternary. In addition, the presence of both erosional and depositional palaeosurfaces is a useful marker for reconstructing tectonic and morphogenetic events, and hence to detect the role played by tectonics and climate in its genesis, evolution and extinction. The present study identifies the key role of tectonics and denudation, combined with highfrequency
floods, as mechanisms controlling alluvial sedimentation in the study area. During endorheic conditions, denudational processes driven by pulses of extensional deformation of he basin margin caused strong alluvial inputs that resulted in the development of alluvial fans. Alluvial facies are mainly characterized by turbulent, subaerial, hyperconcentrated flood flows deposited during the glacial, semi-arid conditions of MIS 14. The retrogradational stacking pattern of the alluvial system indicates decreasing rates of tectonic activity along with declining river gradients.
The Mercure coalescing alluvial fans were inundated by lake transgression during MIS 13 in response to (i) abrupt tectonic subsidence at the basin margins and (ii) large decrease of coarse sediment supply due to the interplay among climate, tectonics and catchment size changes. In this regard, it is suggested that tectonic control on the drainage network along with climate and long-term slope evolution may have caused marked pulses in sediment
supply, thus influencing the arrangement of facies associations in the sedimentary succession.
In addition, the study points out that the main tectonic landforms developed during each period of the landscape evolution well correspond with some active fault segments
A new age within MIS 7 for the Homo neanderthalensis of Saccopastore in the glacio-eustatically forced sedimentary successions of the Aniene River Valley, Rome
No full textField observations as well as borehole, sedimentological and geochronologic data allow us to reconstruct the geologic setting of the Aniene River Valley in northern Rome, framing it within the recently recognized picture of temporally constrained, glacio-eustatically forced aggradational successions of this region. The sedimentary successions cropping out in this area include those described in the literature of the early 20th century in Saccopastore, where two skulls of Homo neanderthalensis were recovered. Based on the geometry, elevation and sedimentologic features of the investigated sedimentary deposits, the stratigraphic record of Saccopastore is correlated with the aggradational succession deposited in response to sea-level rise during glacial termination III at the onset of MIS 7 (i.e. ~250 ka), corresponding to the local Vitinia Formation, as opposed to previous correlation with the MIS 5 interglacial and a locally defined "Tyrrhenian" stage (~130 ka). This previous attribution was based on the interpretation of the sedimentary succession of Saccopastore, occurring between 15 and 21 m a.s.l., as a fluvial terrace formed around 130 ka during the Riss-Würm interglacial, ca. 6 m above the present-day alluvial plain of the Aniene River. In contrast to this interpretation, a 40Ar/39Ar age of 129 ± 2 ka determined for this study on a pyroclastic-flow deposit intercalated in a fluvial-lacustrine sequence forming a terrace ~37 m a.s.l. near the coast of Rome constrains the aggradational succession in this area to MIS 5, precluding the occurrence of an equivalent fluvial terrace at lower elevation in the inland sector of Saccopastore. We therefore interpret the stratigraphic record of Saccopastore as the basal portion of the aggradational succession deposited in response to sea-level rise during MIS 7, whose equivalent fluvial terrace occurs around 55 m a.s.l. in this region. We also review the published paleontological and paleoethnological records recovered in Saccopastore and demonstrate their compatibility with the faunal assemblages and lithic industries occurring in the sedimentary deposits of the Vitinia Formation, while we show the lack of any unequivocal Late Pleistocene (MIS 5) affinity. We therefore propose that the chronostratigraphic position of the Saccopastore deposits containing the two skulls should be around 250,000 years, as opposed to a previously preferred age of 130,000 years. The revised age makes these skulls the oldest Italian occurrences of H. neanderthalensis and provides evidence for a substantially coeval appearance and evolutionary path with respect to central-northern Europe
First evidence for leucite-bearing products in the recent stages of activity of the Roccamonfina volcano (central-southern Italy).
No full textThe Roccamonfina volcano is one of the first Italian potassic volcanoes to be investigated by detailed petrological studies, which revealed an overall time-related progression of magma compositions from leucite-bearing ultrapotassic to leucite-free shoshonitic. However, sparse accounts reported some deviations to this general scheme, suggesting that the petrological evolution of the volcano is more complex than previously thought.
Here we report a detailed investigation of the products of the recent phase of the volcano history (i.e. <305 ka), including both lava and pyroclastic deposits from the eastern side of the Roccamonfina. Along with prevailing leucite-free products, leucite-bearing juvenile clasts and lava samples were also recognised, featuring phenocrysts of clinopyroxene and leucite (olivine) or of leucite only set into a groundmass with clinopyroxene, plagioclase
and leucite or clinopyroxene and plagioclase. Bulk-rock compositions are in line with the that of the leucite-bearing products of the oldest stages (>350 ka), although higher SiO2, Cr and Ni, and lower Ba, Sr and V contents are observed at similar degrees of evolution. Also, the compositions of glass from the pyroclastic deposits are in line with that of the oldest stages, being phonotephritic. Interestingly, the Sr-Nd isotopic compositions of the two
groups of leucite-bearing rocks are strikingly different, with the youngest products showing lower 87Sr/86Sr (0.70653 vs. 0.70872-0.71079) and higher 143Nd/144Nd (0.51250 vs. 0.51211-0.51222). These preliminary results support the idea that leucite-bearing magmas were not confined to the oldest stages of Roccamonfina history and suggest that they were generated at different times from different mantle sources
Chronostratigraphic constraints on Middle Pleistocene faunal assemblages and Acheulian industries from the Cretone lacustrine basin, central Italy
No full textIntegrated 40Ar/39Ar, trace-element, stratigraphic, palaeontological and palaethnological data provide geochronological and biochronological constraints for the sedimentary and tectonic history of a Middle Pleistocene fluvial–lacustrine basin near Rome (Cretone Basin, central Italy), which has yielded a significant record of mammal fossil remains and Palaeolithic industry. This work is a case study of the interplay between tectonics and glacio-eustacy, which strongly influenced the evolution of the Tyrrhenian Sea margin of central Italy. Dating of tephra layers interbedded within the Cretone Basin lacustrine succession and reconstruction of relict terraced surfaces allow correlation with similar, geochronologically constrained, marine isotopic stages (MIS) 15–5 terraced deposits along the coast. Coupled extensional tectonics and regional uplift over the last 600 ka caused the progressive uplifting and westward migration of the main fluvial–lacustrine basin and the formation of a smaller satellite basin at its eastern margin. Here, stable environmental conditions during MIS 13–5 indicated continuous human and large mammal frequentation, as testified by lithic industry and fossil remains ascribable to the Acheulean and later early Middle Palaeolithic technocomplexes and Galerian–Aurelian mammal faunas, respectively. In addition to providing independent age constraints to glacial sea-level oscillations of this region, the reconstructed chronostratigraphic setting for the Cretone Basin provides evidence for one of the oldest Acheulean lithic assemblage of central Italy, as well as new biochronological and palaeobiogeographical data for some Middle Pleistocene mammal species of Italy
40Ar/39Ar single crystal dates from pyroclastic deposits provide a detailed record of the 590-240 ka eruptive period at the Vulsini Volcanic District (central Italy)
No full textWe analyze the age distribution provided by 113 sanidine crystals separated from six samples of pyroclastic products of the Bolsena-Orvieto phase of activity at the Vulsini Volcanic District, which were dated via the 40Ar/39Ar single crystal, total fusion method in a previous study. Moreover, we investigate the compositional and depositional features of the dated products, both at the outcrop scale and at the optical microscope, aimed at discriminating the juvenile vs. antecrystic vs. xenocrystic origin of the dated crystals. Results of this study provide insights on the magmatic process preceding the eruptions, as well as on the eruptive mechanisms of the primary deposits. The data also provide a geochronologic context to the history of eruptive activity of the Vulsini Volcanic District, from 590 to 250 ka with greater detail than previously outlined by direct dating of several primary units. Indeed, most of the six samples analyzed in the present work yielded 19 distinct crystal population ages, 10 of which match those of previously dated eruptive units and the other 9 possibly corresponding to primary deposits so far undated
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