Late Barremian–early Aptian ammonite bioevents from the Urgonian-type series of Provence, southeast France: Regional stratigraphic correlations and implications for dating the peri-Vocontian carbonate platforms

Abstract

This work provides a new ammonite age-calibration of the rudistid limestones of the Urgonian-type Provence carbonate platform (Southeast France) based on sampling along three ~200 km-long platform-to-basin transects and re-examination of historical collections. Ammonite key findings indicate that the first rudistid platform stage (including the Agriopleura and requieniid-monopleurid beds) develops and spreads northward through the Toxancyloceras vandenheckii-Gerhardtia sartousiana zones interval (lower upper Barremian). This stage is interrupted by the tectonically-induced deepening of the southern Provence domain during the Imerites giraudi Zone while the northern regions records the massive deposition of Palorbitolina-Heteraster beds. Recovery of the rudistid carbonate system is illustrated by the development of caprinid-bearing rudistid limestones in the North Provence domain through the Martelites sarasini Subzone (lower Martelites sarasini Zone, uppermost Barremian), which shows a bidirectional progradation toward the South Provence and Vocontian basins. The 2 caprinid-bearing limestones terminate at a short-term exposure and are overlain by cherty-oobioclastic deposits spanning the Pseudocrioceras waagenoides Subzone (upper M. sarasini Zone) to the lower Deshayesites forbesi Zone. A regional-wide flooding of the study area is illustrated by the abrupt change to a marl-dominated regime occurring in the upper D. forbesi Zone. Compared to the previous datings, the Barremian/Aptian boundary should be relocated in the lower part of the post-caprinid, cherty-oobioclastic deposits although its precise level cannot be fixed due to the lack of a continuous ammonite record. Ammonite age-calibration of the surrounding Urgonian rudistid platform series is discussed and gives evidence of a comparable twofold demise of the peri-Vocontian rudistid biota during the uppermost Barremian. Accordingly, the link between the final demise of the peri-Vocontian rudistid biota and the onset and/or culmination of the mid-early Aptian Oceanic Anoxic Event (OAE) 1a should be reconsidered.

Record of a dense succession of drowning phases in the Alpstein mountains, north-eastern Switzerland: part I—the Lower Cretaceous Tierwis Formation (latest Hauterivian to latest Barremian)

“…This sequence boundary is contemporaneous with the deposition of slumps and other gravity flows in the Umbria-Marche basin (e.g., Cecca et al, 1995), and to hiatuses on the perivocontian carbonate platforms (Arnaud, 2005;Delanoy, 1992), or to highly condensed series (Arnaud, 2005;Delanoy et al, 2012;Vermeulen et al, 2013). All these field data point to an important sea-level drop during the N. pulchella Zone (Frau et al, 2018). In the Alpstein, an important hiatus occurred in inner slope environments, marked by a polyphased hardground recording two generations of borings (Fig.…”

Integrated astrochronology of the Barremian Stage (Early Cretaceous) and its biostratigraphic subdivisions

“…Recent biostratigraphic revisions suggest these organic-rich layers appear during the Giraudi Zone (Frau et al, 2016) and envelop the negative excursion of the δ 13 C carb values observed in the Sarasini Zone (Stein et al, 2012). We thus define the Taxy Event from the base of the Giraudi Zone (Frau et al, 2018b) to the increase in the δ 13 C carb values in the Barremian-Aptian transition (Fig. 3).…”

Aptian carbonate platform development in the Southern Iberian Palaeomargin (Prebetic of Alicante, SE Spain)

“…Further north, the distal platform-top facies of the "U2" Urgonian limestones in the North Provencal Platform likewise contains a rich and diverse caprinid fauna , while requieniids and monopleurids are distributed throughout the platform interior facies À though a recent revision of the ammonite biostratigraphy of that region re-assigns these U2 limestones to the Martelites sarasini Subzone of latest Barremian, rather than earliest Bedoulian age (Frau et al, 2018).…”

“…Nevertheless, hypotheses that seek to link biotic turnover with global environmental changes rely crucially upon both sound stratigraphical correlation and adequate geographical sampling . The recently revised dating by Frau et al (2018) of the classic "U2" rudist limestones in the North Provencal Platform, from a previously supposed early Bedoulian age to the latest Barremian, thus requires critical consideration. Even if this age re-assignment (based on the evidence of two ammonite specimens from the overlying "U3" limestones) is confirmed, together with rigorous verification of the total ranges of the two taxa concerned, Pseudocrioceras sp., and Martelites sp., there is no justification as yet for extrapolating this revised dating to the Iberian examples discussed in this paper.…”