Palynological and calcareous nannofossil investigation of the Gosau Group deposits from three boreholes in the Vienna Basin, Austria

Palynological and calcareous nannofossil investigations on samples from the basal part of the Gosau Group succession in three boreholes (Glinzendorf T1, Gänserndorf T3 and Markgraf Neusiedl T1) in the Vienna Basin provide calibrated age assessment of late Coniacian to early Campanian age for this thick non-marine to marginal-marine siliciclastic interval.

A multistratigraphic study of the Campanian Postalm section (Northern Calcareous Alps, Austria)

<p>The Postalm section in the Gosau Group (Northern Calcareous Alps) exposes pelagic deposits of northwestern Tethyan origin. We present a magneto-, bio- and chemostratigraphic assessment of this Santonian to uppermost Campanian record, as well as a cyclostratigraphic model for the Tethyan Campanian based on three independently assessed proxies; the δ<sup>13</sup>C signature, the elemental ratio of Fe and the thickness of limestone/marl couplets (Wolfgring et al., 2021).</p><p>The Santonian/Campanian transition is characterised by condensed greyish packstones, the Campanian strata exhibit a succession of limestone-marl couplets that represent orbital precession of an approximate duration of 20ka. A magneto- and biostratigraphic (based on planktonic foraminifera and calcareous nannofossils) framework is supported by carbon isotope and strontium stratigraphy.</p><p>The Sr isotope record matches the data for the Upper Cretaceous and suggests no major gaps in the Postalm succession. A robust cyclostratigraphic assessment of three independently assessed data series (L/M couplets, Fe and δ<sup>13</sup>C) resulted in the identification of eighteen 405 ka eccentricity cycles spanning the middle to upper Campanian (<em>Contusotruncana plummerae</em> to <em>Gansserina gansseri </em>Zones or CC17/UC15 to CC23/UC16 nannofossil zones).</p><p>Carbon isotope stratigraphy identifies the LCE (Late Campanian Event) and possibly the SCBE (Santonian Campanian Boundary Event). Magneto- and biostratigraphic data, in particular the position of the top of the <em>R. calcarata </em>planktonic foraminifera Zone, the position of the LCE and the top of Chron C32r.1r served as primary tie points and constraints to match the floating cyclostratigraphic model to the Laskar solution and to compare it to other cyclostratigraphic solutions and reference sections for the upper Campanian.</p><p>References: Wolfgring, E., Wagreich, M., Hohenegger, J., Böhm, K., Dinarès Turell, J., Gier, S., Sames, B., Spötl, C., Jin, S., 2021. An integrated multi-proxy study of cyclic pelagic deposits from the north-western Tethys: The Campanian of the Postalm section (Gosau Group, Austria), Cretaceous Research, 120, 104704, doi.org/10.1016/j.cretres.2020.104704.</p>

A new reverse subchron (C33n.1r) in the Campanian: astronomical duration estimate and geomagnetic/chronostratigraphic implications

<p>The Cretaceous Normal Polarity Superchron (CNPS, chron C34n, Aptian–Santonian, ~83–118 Ma in CK95 GPTS) is followed in the Campanian by two relatively long chrons (chron C33r, 3.925 My duration and then the normal chron C33n, 5.456 My duration) straddling most of the Campanian stage. The analysis of the geomagnetic reversal history has classically determined two nearly linear segments for the late Cretaceous–Cenozoic interval divided at chron C12r. The length of chrons in the younger interval has no systematic trend and henceforth is considered stationary for statistical analysis with a mean chron length of 0.248–0.219 My while the older segment has 0.749 My mean chron length. The stationarity for this latter interval is attained, however, when the two long polarity chrons C33r and C33n adjacent to the CNPS are omitted. Studies in the weakly magnetized southern England chalk succession and marine Bearpaw Shale in the Canadian Rockies from Alberta have argued about the presence of a number of reversals within C33r and C33n (and C34n). However, all these remain ambiguously established and not incorporated in the standard GPTS despite their significance for theories of geodynamo behavior and potentiality for high-resolution stratigraphic correlations that could notably impact, for instance, the chronostratigraphy of dinosaur-bearing terrestrial Upper Cretaceous of the Western Interior of North America. In any case, no polarity subchrons within C33r or C33n have been reported in any deep-sea record or in the landmark pelagic “scaglia” sections from the Gubbio area in the central Italian Apennines, for which a good integrated biostratigraphy and a thorough paleomagnetic record exists.</p><p>Here, we report on a new reverse subchron in the lower part of C33n, informally named the Postalm Fall Subchron (PFS), retrieved in the Postalm section (Gosau Group, Northern Calcareous Alps of Austria). The Postalm section shows a deepening trend from upper Santonian conglomerates and grey shelf marls to pelagic bathyal red marly limestones of Campanian age. The section has previously been studied in the frame of an integrated multi-proxy stratigraphic study that includes high-resolution calcareous plankton biostratigraphy, magnetostratigraphy, stable isotopes, strontium stratigraphy and Fe content. Robust paleomagnetic data has pinpointed the top of C34n that defines the Santonian-Campanian boundary together with key biostratigraphic markers in the lower part of the red unit. The integrated study extents upwards for about 170 m up to calcareous nannofossil zone UC16 in chron C32 in the late Campanian. The cyclic nature of the pelagic sequence has been studied by means of spectral analysis on the limestone/marl couplet thickness data and geochemical proxies that allows identifying the short and long eccentricity cycles and to establish a cyclostratigraphic framework. From 33 new tightly collected samples in this study, 23 display unambiguous reverse polarity and conform the PFS subchron that straddles 3–4 precession cycles (~70 ky duration) within the UC15b calcareous nannofossil biozone. The average sediment accumulation rate at Postalm (~2 cm/ky compared to ~0.6–1 cm/ky at Gubbio) and the high-quality paleomagnetic signal have favored this discovery. The absolute age calibration and related geomagnetic and chronostratigraphic implications would be discussed.</p>

Geological evolution of the southwestern part of the Veporic Unit (Western Carpathians): based on fission track and morphotectonic data

Zircon and apatite fission track (FT) and morphotectonic analyses were applied in order to infer quantitative constraints on the Alpine morphotectonic evolution of the western part of the Southern Veporic Unit which is related to: (1) Eo-Alpine Cretaceous nappe stacking and metamorphism of the crystalline basement in the greenschist facies. (2) Exhumation phase due to underthrusting of the northerly located Tatric-Fatric basement (~ 90–80 Ma), followed by a passive en-block exhumation with cooling through ~ 320–200 °C during the Palaeocene (ZFT ages of ~ 61–55 Ma). (3) Slow Eocene cooling through ~ 245–90 °C, which most likely reflected erosion of the overlying cover nappes and the Gosau Group sediments. Cooling reached up to 60 °C till the Oligocene (AFT ages of ~ 37–22 Ma) in association with erosion of cover nappes. The efficient Eocene erosion led to the formation of the first Cenozoic planation surface with supergene kaolinization in many places. (4) The early Miocene erosion coincided with surface lowering and resulted in the second planation surface favourable for kaolinization. (5) In the middle Miocene, the study area was covered by the Poľana, Javorie, and Vepor stratovolcanoes. (6) The late Miocene stage was related to the erosion and formation of the third Cenozoic planation surface and the final shaping of the mountains was linked to a new accelerated uplift from the Pliocene.