Conference Agenda

Base of the Calpionella alpina Subzone, or Calpionella alpina Ecoevent is being applied for years as a provisional marker of the Jurassic/Cretaceous boundary. The event is characterized by a decline of large species of Calpionella (= C. grandalpina Nagy), the disappearance of C. elliptalpina Nagy, the last occurrence of Crassicollaria brevis Remane and Cr. massutiniana (Colom), and increase in abundance of small (or medium-sized) spherical forms of Calpionella alpina Lorenz. The problem is that multiple conditions mentioned above are not always met together within a single studied section, and decision must be made which one is crucial. Some calpionellid specialists put more weight to the bloom of small spherical C. alpina, while for other the LO events are decisive. Visual identification of C. alpina bloom is difficult using standard range-charts, since C. alpina is usually presented as a single taxon, therefore the base of C. alpina Subzone falls somewhere in the middle of its total range. Furthermore, the taxonomy of Calpionella is inconsistent: some of the numerous species distinguished by Nagy are used (C. grandalpina, C. elliptalpina), as well as informal subdivisions into small, spherical, medium, etc. forms. The range-charts are rarely accompanied by quantitative or semi-quantitative graphs, which would be helpful to reveal an internal structure and dynamics of the C. alpina Ecoevent. Additionally, a division of underlying Crassicollaria Zone is not standardized, and it seems that Cr. colomi Subzone sometimes overlaps with abundance increase of small spherical C. alpina, leading to confusing stratigraphical interpretations and biased long-distance correlations.

The VOICE is a negative carbon isotopic excursion initially identified in organic carbon at high latitudes (Hammer et al., 2012) and recently documented in the Neuquén Basin, western Argentina (Pellenard et al., 2022; Weger et al., 2023). The global correlations of the carbon isotope curves show discrepancies in the trends, making its record unreadable at global scale. We propose an integrated radio-astrochronology of the VOICE anchored on calcareous nannofossil and Andean ammonite biostratigraphy on the Las Alcantarillas and Las Loicas sections. Five new CA-ID-TIMS U-Pb ages are introduced together with 532 datapoints of δ¹³C_org. Palynofacies analyses demonstrate the organic matter is mainly marine with no apparent source changes. The δ¹³C_org values decrease from -25 ‰ PDB to -30 ‰ PDB from the P. zitteli to the C. alternans/S. koeneni Andean ammonite zones before returning to -27 ‰ PDB in the latest Tithonian. The U-Pb ages indicate that the VOICE started around 146.18 Ma. They also show a pacing of the δ¹³C_org by the 405-ka eccentricity cycle. Anchoring these cycles to the U-Pb ages, we determine that the VOICE ended 142.44 Ma and lasted for ~4Ma. This new integrated chronostratigraphic framework provides with a reference for further global correlations of the carbon isotopic curves.

References:

Hammer, Ø., et al., 2012. Norwegian Journal of Geology 92, 103–112.

Pellenard, P., et al., 2022. 11th International Congress on the Jurassic System, 29 August – 2 September 2022, Budapest, Hungary, p. 88. https://jurassic2022.hu/download/JURA2022_AbstractBook_web.pdf

Weger, R.J., et al., 2023. GSA Bulletin 135, 2107–2120. https://doi.org/10.1130/B36405.1.

This research presents the results of cyclostratigraphic investigations performed in the Tithonian–lower Berriasian carbonates of the Torre de’ Busi and Lókút sections. A precise bio- and magnetostratigraphic control provided a temporal framework for this research; it allowed also to take an account on increasing sedimentation rates calculated for the Tithonian of both successions. Although studied sections are characterized by decreasing lithogenic influx, MS (Torre de’ Busi, Lókút) and ARM (Lókút) series indicate relatively well expressed 100-kyr short eccentricity cycles. Their number within given magnetozones correlates between the studied sections and corresponds with their durations estimated from the geomagnetic polarity time scale (GPTS). Long eccentricity cycles are poorly expressed and only within the lower/upper Tithonian transition interval a reliable 405-kyr cycles can be interpreted; consequently, most of long eccentricity cycles were interpolated through successive counting of 100-kyr cycles. The reliability of provided interpretation is additionally strengthened by correlation with the Jebel Meloussi (Tunisia), which manifests a similar record of the latest Tithonian–earliest Berriasian orbital forcing. Ultimately, the results of this study point to diachronic character of the base of the Alpina calpionellid Subzone, which may be shifted for at least 300-kyr, either due to inconsistent definition or a diachronic nature of the ‘Alpina event’ itself. Diachronism can be inferred also in case of some calcareous nannofossil zones and subzones, such as NJT17 and NC0.

Magnetostratigraphy, calibrated to chemo- and biostratigraphy, offers a reliable tool for creating high-resolution stratigraphic frameworks and can therefore be employed in selecting the Jurassic/Cretaceous (J/K) boundary stratotype. The Bosso Valley section, co-proposed with Torre de Busi for the J/K stratotype, was studied alongside others by Houša et al. (2004), which included magnetostratigraphy. Houša et al. identified five normal and five reverse polarity zones, including the subzones M20n.1r (Kysuca) and M19n.1r (Brodno). Their data were, however, accompanied by rock-magnetic analyses of only two samples. Rock-magnetic analyses can provide essential information on the origin of the carriers of the remanent magnetization, deciphering the correct applicability of the paleomagnetic record for magnetostratigraphy. Ten selected samples (one from each individual polarity zone) from the original Houša et al. sample collection will be used for additional rock-magnetic analyses. These analyses will include stepwise acquisition and demagnetization of isothermal remanent magnetization and a three-axial Lowrie (1990) test, which will allow further verification of the previous polarity zone interpretation and thus support the stratotype proposal. Furthermore, the position of Kysuca and Brodno subzones is very well defined by the large number of samples. Our re-evaluation of the paleomagnetic data and subsequent correlations revealed the mean directions of the Brodno subzone (Declination = 100.5°; Inclination = −41.5°) and the Kysuca subzone (Declination = 116.6°; Inclination = −30.1°). These are in good agreement with Houša et al.'s Early Berriasian (Declination = 100.1°; Inclination = −39.0°) and Late Tithonian (Declination = 107.0°; Inclination = −32.3°) reverse polarity mean directions, respectively.

A Berriasian age (145–142 Ma) for the base of the lower Yellow Cat Mbr. (YC) of the Cedar Mountain Fm. (CM) in Utah is indicated by microfossils, chemostratigraphy, and U-Pb dating of paleosols, with the onset of deposition near the beginning of Cretaceous. Euroamerican Morrison “style” dinosaur faunas dominated by diverse sauropods (mostly diplodocids), stegosaurs, small to medium ornithopods, large theropods (ceratosaurs, megalosaurids, and allosaurids), and uncommon coelurosaurs persisted during last 10 myr of the Jurassic. By contrast, the first 25 myr of the Early Cretaceous had Wealden “style” dinosaur faunas dominated by a low diversity of turiasaur and titanosauriform sauropods, polacanthid ankylosaurs, large ornithopods, large megalosauroid spinosaurids (exclusive to Europe), allosauroid carcharodontosaurid theropods, and an increased abundance of larger coelurosaurs reflecting a profound J-K dinosaur faunal turnover. The paleosol sequence at the base of the YC, laterally equivalent to the fluvial Buckhorn Conglomerate of the CM, consists of basal ferruginous paleosols (gleysols) overlain by silicified peat (histosols), which are then overlain by calcareous paleosols (vertisols and aridosols). A kaolinite bed (oxisol) has been identified at the J-K unconformity locally. Based on these paleosols, Utah’s earliest Cretaceous is characterized by an interval of unusually wet paleoclimates bracketed by drier paleoclimates during the Late Jurassic and remainder of the Early Cretaceous. Potential drivers close to the J-K boundary for this climatic excursion and faunal turnover include a mega-shield volcano(s) at Shatsky Rise in the western Pacific, and less significantly South Africa’s Morokweng impact. Was the Cretaceous bookmarked by asteroid impacts?

The Berriasian Bückeberg Group accumulated in the Lower Saxony Basin and comprises fluvial,
lacustrine and marine deposits of a late regression to early transgression. The geothermal reservoir
potential of the nearshore and terrestrial sandstone deposits have recently drawn economic interest.
A comprehensive facies-based paleodepositional interpretation of potential reservoir rocks and
implications for sequence stratigraphic surfaces are presented based on core analysis.
Facies are identified based on sedimentological and ichnological expression, e.g., sediment texture,
sedimentary structures, lithological accessories, bioturbation index (BI) and trace fossil assemblage.
Facies are grouped into facies associations. Potential sequence stratigraphic surfaces are proposed
based on vertical juxtaposition of facies associations.
Six facies associations are identified: (1) basin deposits below fair-weather wave base, (2) lagoon
deposits, and (3) floodplain accumulations are predominantly mudstone dominated. Mudstone to
sandstone dominated deposits are found in (4) crevasse-splays and (5) marine wave- and storm-
dominated deltaic deposits. Sandstone-dominated intervals are associated with crevasse splay
channels, proximal crevasse splays and deltafront deposits.
Basal contacts of the Bückeberg Group are preserved in two cores and support the interpretation of
deposition on a sequence boundary, possibly with conformable transgressive surface. Juxtaposition
of basin mudstone on deltaic deposits in two cores across the Lower Saxony Basin imply a
transgressive surface. Several other flooding surfaces identified in core are interpreted as autogenic.
The study refines the depositional model of the Bückeberg Group and permits a review of previously
proposed sequence stratigraphic surfaces. Concise interpretations of paleodepositional
environments and their responses to base level assist prediction of potential geothermal reservoirs.