We investigated for magnetostratigraphy the Rio Nigra and Rio Frommer stratigraphic sections from Alpe di Siusi/Seiser Alm (Dolomites, northern Italy) in order to improve the calibration of the ...Triassic time scale. Both sections are characterized by ammonoid and conodont associations typical of Longobardian (late Ladinian, Middle Triassic) age. Moreover, the Rio Nigra section is constrained by a U-Pb zircon date of 237.77 ± 0.05 Ma. Building on the recently verified Newark-Hartford astrochronological polarity timescale for the Late Carnian–Rhaetian (plus the Hettangian) and through magnetostratigraphic correlations of an updated inventory of Tethyan marine stratigraphic sections from the literature, some of which are provided with U-Pb zircon age constraints, we propose a revised Geomagnetic Polarity Time Scale for the entire Triassic.
•New U-Pb constrained Ladinian magnetostratigraphy improves Triassic chronology.•Using recent magnetostratigraphic data to update the Geomagnetic Polarity Timescale•Updated Geomagnetic Polarity Timescale led to a duration of 50.5 Myr for Triassic.
Abstract
The onset of the Acheulean, marked by the emergence of large cutting tools (LCTs), is considered a major technological advance in the Early Stone Age and a key turning point in human ...evolution. The Acheulean originated in East Africa at ~ 1.8–1.6 Ma and is reported in South Africa between ~ 1.6 and > 1.0 Ma. The timing of its appearance and development in North Africa have been poorly known due to the near-absence of well-dated sites in reliable contexts. The ~ 1 Ma stone artefacts of Tighennif (Algeria) and Thomas Quarry I-Unit L (ThI-L) at Casablanca (Morocco) are thus far regarded as documenting the oldest Acheulean in North Africa but whatever the precision of their stratigraphical position, both deserve a better chronology. Here we provide a chronology for ThI
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L, based on new magnetostratigraphic and geochemical data. Added to the existing lithostratigraphy of the Casablanca sequence, these results provide the first robust chronostratigraphic framework for the early North African Acheulean and firmly establish its emergence in this part of the continent back at least to ~ 1.3 Ma.
The latest Triassic was an interval of prolonged biotic extinction culminating in the end-Triassic Extinction (ETE). The ETE is now associated with a perturbation of the global carbon cycle just ...before the end of the Triassic that has been attributed to the extensive volcanism of the Circum-Atlantic Magmatic Province (CAMP). However, we attribute the onset of declining latest Triassic diversity to an older perturbation of the carbon cycle (δ13Corg) of global extent at or very close to the Norian/Rhaetian boundary (NRB). The NRB appears to be the culmination of stepwise biotic turnovers that characterize the latest Triassic and includes global extinctions of significant marine and terrestrial fossil groups. These biotic events across the NRB have been largely under-appreciated, yet together with a coeval disturbance of the carbon cycle were pivotal in the history of the Late Triassic. Here, we present new and published δ13Corg data from widespread sections (Italy, Greece, ODP, Australia, New Zealand, USA, Canada). These sections document a previously unknown perturbation in the carbon cycle of global extent that spanned the NRB. The disturbance extended across the Panthalassa Ocean to both sides of the Pangaean supercontinent and is recorded in both the Northern and Southern Hemispheres. The onset of stepwise Late Triassic extinctions coincides with carbon perturbation (δ13Corg) at the NRB, indicating that a combination of climatic and environmental changes impacted the biota at a global scale. The NRB event may have been triggered either by gas emissions from the eruption of a large igneous province pre-dating the NRB, by a bolide impact of significant size or by some alternative source of greenhouse gas emissions. As yet, it has not been possible to clearly determine which of these trigger scenarios was responsible; the evidence is insufficient to decisively identify the causal mechanism and merits further study.
We provide the magnetostratigraphy of the Ladinian/Carnian Punta Grohmann stratigraphic section (Dolomites, Italy), calibrated with UPb ages from the literature (237.58 ± 0.04 Ma; 237.68 ± 0.05 Ma). ...The FO of ammonoid Zestoceras lorigae, the base of the vigens-densus palynomorphs Zone, and sequence stratigraphy suggest a Carnian age for the upper part of the section, which has been confirmed by the magnetostratigraphic correlation between Punta Grohmann and Prati di Stuores (Carnian GSSP). Additional magnetostratigraphic correlation between Punta Grohmann and key time-calibrated Ladinian–Carnian sections from the literature (e.g., Mayerling, Seceda, Rio Nigra) lead to a more precise age of the Carnian base (∼236.5 Ma) and to a better definition of the Middle–Late Triassic Geomagnetic Polarity Time Scale.
•New magnetostratigraphic data of a UPb constrained Ladinian section improves Triassic chronology.•The Punta Grohmann time-calibrated magnetostratigraphy allowed the update of the Ladinian Geomagnetic Polarity Timescale.•Updated Geomagnetic Polarity Timescale led to a revised age of the Ladinian/Carnian boundary (∼236.5 Ma).
This paper investigates the magnetostratigraphy of the ~750 m-thick Costa Grande Member (lower Miocene) from the Castagnola Basin of NW Italy, which represents the turbidite fill of a structurally ...confined basin where flow ponding resulted in a complete record of deposition from diverse sediment gravity flow types. The magnetostratigraphic profile of the Costa Grande Mb was correlated to the Geomagnetic Polarity Timescale using a well-established statistical method devised to be applied to sedimentary successions with steady accumulation rate. The results of the correlation exercise, validated with the available biostratigraphy, indicate an early Miocene age (from Chron C6AAr.3r to C6Bn.2n) between 21.7 and 22.3 Ma. The obtained age model was then used to calculate accumulation rates and frequencies of small volume and low-density vs. large volume and high-density gravity flows over an estimated 650 kyr time span. Results show that low-density flows contributed at a constant pace of 545 m Myr−1 to sediment accumulation, depositing relatively thin-bedded turbidites with a minimum recurrence time of 1.7 kyr, whereas the high-density flows, which are at least four times less frequent, are clustered in the stratigraphy, and become more abundant up-section. We also show that the minimum sediment volumes discharged by high-density flows suggest triggering by submarine failures whose recurrence and magnitude were probably not random. Lastly, we propose that the statistical method used in this study to correlate the Costa Grande Mb magnetostratigraphy to the GPTS provides best results when the products of episodic but voluminous depositional events are carefully identified and removed.
The Kimmeridgian (Late Jurassic) stage has proven difficult to define in modern timescales essentially because the land sections used to describe it are typically condensed and discontinuous. For ...example, no single land section has been able to replicate the full record of magnetic polarity reversals recorded on the ocean floor as marine magnetic anomalies. Here, we report the magnetostratigraphy of the S'Adde carbonate succession from the Tethyan realm of Sardinia (Italy) that was previously studied for nannofossil biostratigraphy. We applied a statistical approach to correlate this magneto-biostratigraphic record to a recent global stack of M-sequence magnetic anomalies. We found that the base of the Tethyan Kimmeridgian, as approximated by the first occurrence (FO) of nannofossil Faviconus multicolumnatus, falls within M25Ar1n at a nominal age of ~152.8 Ma, while the base of the Tethyan Tithonian (top Kimmeridgian) as approximated by the FO of Conusphaera mexicana minor falls in the lower part of M22n at a nominal age of ~146.5 Ma. A discussion of the relationship between our Tethyan Kimmeridgian and the Sub-Boreal Kimmeridgian as defined in the Flodigarry GSSP candidate section is also provided. By virtue of its continuity, the S'Adde section is a valuable reference section for defining the Tethyan Kimmeridgian in modern Jurassic timescales.
•The Kimmeridgian has historically proven difficult to define in modern timescales.•The S'Adde section provides an expanded record of the Tethyan Kimmeridgian.•A statistical correlation of S'Adde polarity zones with the M-sequence is performed.•The base of the Tethyan Kimmeridgian falls within M25Ar1n at ~152.8 Ma.•The base of the Tethyan Tithonian falls in the lower part of M22n at ~146.5 Ma.
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