The base of the Rhaetian stage (Norian/Rhaetian boundary, NRB) is still awaiting for- mal designation by the International Commission on Stratigraphy. At present, only the 4.30-m-thick Steinbergkogel section (Austria) has been proposed as GSSP (Global Stratotype Section and Point) candidate for the base of the Rhaetian. Here we present data from the 63-m-thick Pignola-Abriola section (Southern Apennines, Italy) that we consider an alternative candidate for the Rhaetian GSSP. The Pignola-Abriola basinal section, represented by hemipelagic–pelagic carbonate successions belonging to the Lagonegro Basin, matches all the requirements for a GSSP: 1, it is well exposed with minimal structural deformation; 2, it is rich in age diagnostic fossils (e.g. conodonts and radiolarians); 3, it yields a geochemical record suitable for correlation (e.g. d13Corg/carb); and 4, it has a robust magnetostratigraphy and is correlated with the Newark APTS for age approximation of the NRB and additional Rhaetian bioevents. In the Pignola-Abriola section, we opt to place the NRB at the 44.4 metre level, coinci- dent with a prominent negative shift of ca. 6& of the d13Corg. This level is located 50 cm below the FAD of conodont Misikella posthernsteini s.s within the radiolarian Proparvicingula moniliformis Zone. Both the negative d13Corg shift and the FAD of Misikella posthernsteini occur within Pignola-Abriola magnetozone MPA-5r, at ~205.7 Ma, according to magnetostratigraphical correlation to the Newark APTS. We also illustrate the coeval Mt. Volturino stratigraphical section deposited below the cal- cite compensation depth (CCD) within the same Lagonegro Basin and characterized by a detailed radiolarian biostratigraphy and strong d13Corg negative shift around the NRB
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-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.
3 February 2015 in Geological Society of America Bulletin
A detailed magnetostratigraphic investigation of the Pignola-Abriola section of Norian to Rhaetian age permits the identification of 22 magnetic polarity reversals grouped in 10 magnetozones. We correlate the magnetostratigraphy of the Pignola-Abriola section with the Newark astrochronological polarity time scale (APTS). In total, 19 correlation options were tested, and only one (option 7) yielded a statistically significant correlation that was consistent with the available information on the stratigraphic age of the Newark APTS. After some adjustments to minimize erratic variations in sediment accumulation rates, a final correlation (option 7.1) was used to generate an age model of sedimentation for the Pignola-Abriola section. The Pignola-Abriola section has been correlated with Rhaetian sections from the literature, notably the current global boundary stratotype section and point candidate for the base of the Rhaetian at Steinbergkogel, Austria, where the Norian-Rhaetian boundary is proposed to be placed at a stratigraphic level containing the first appearance datum (FAD) of conodont Misikella posthernsteini, traced on the Newark APTS to ca. 209–210 Ma. Issues regarding the taxonomy of M. posthernsteini, a species characterized by transitional forms with its ancestor Misikella hernsteini, lead us to propose the alternative option of placing the Norian-Rhaetian boundary at a prominent negative δ13Corg spike observed in the Pignola-Abriola section at meter 44.5, 50 cm below the level containing the FAD of M. posthernsteini sensu stricto and close to the base of radiolarian Proparvicingula moniliformis zone. This level has been magnetostratigraphically correlated to Newark magnetozone E20r.2r at ca. 205.7 Ma. Assuming an age of ca. 201.3 Ma for the Triassic-Jurassic boundary, the Rhaetian Stage would have a duration of ~4.4 m.y.
In an effort to improve the calibration of the Late Triassic time scale, two stratigraphic successions in Italy were investigated for magnetostratigraphy: the Pignola-2 (Southern Apennines) and the Dibona (Dolomites) sections. These sections reveal a sequence of biostratigraphically calibrated (conodonts and palynomorphs) magnetic polarity zones encompassing the Julian/Tuvalian boundary (Carnian). A total of 63 samples have been collected from the Pignola-2 section that helped defining 3 magnetozones. These data are constrained by a published radiometric U/Pb age of 230.91 0.33 Ma from the Aglianico ash-bed (Furin et al. 2006). From the Dibona section, 81 samples have been collected, revealing 2 magnetozones in the Heiligkreuz Fm. (lower part of the succession) and 2 magnetozones in the Travenanzes Fm. (upper part). The Dibona section provided only few high-quality paleomagnetic data in spite of the sampling effort, so we considered only the Pignola-2 section as suitable for the correlation with other Carnian sections from the literature, in order to define the magnetostratigraphy around the Julian/Tuvalian boundary in the Tethys realm. The correlation between the Pignola-2 and the Newark Astrochronological Polarity Time Scale (APTS) provides independent insights on the age of the base of the Newark basin APTS. We found that the U-Pb zircon-dated Pignola-2 level, magnetostratigraphically projected on the Newark APTS, falls within Chrons E5–E4 at around 231 Ma, in agreement with the (extrapolated) astrochronological ages of the Newark APTS.