Andrzej Pszczółkowski

An account of the bio- and magnetostratigraphy of the Upper Tithonian—Lower Berriasian interval at Le Chouet, Drôme (SE France)

Abstract This paper discusses the results of a study of the Le Chouet section, its lithologies, facies, magnetic properties and fossil record (ammonites, calcareous nannofossils, calpionellids and calcareous dinoflagellates). Data obtained have been applied to give a precise biostratigraphy for this carbonate sequence as well as a paleoenvironmental reconstruction. Its relationship to magnetostratigraphy, based on a modern study of a French site, is important. Investigation of the micro- and macrofossils shows that the site comprises a sedimentary sequence in the Microcanthum to Jacobi ammonite Zones, and the Chitinoidella, Crassicollaria and Calpionella Zones. Several calpionellid and nannofossil bioevents have been recorded on the basis of the distribution of stratigraphically important planktonic organisms. The site allows us to calibrate the levels of various biomarkers and biozonal boundaries, and correlate them with the magnetozones M20n, M19r and M19n.

Integrated Magnetic Susceptibility and Geochemical Record of δ13C Anomalies in the Berriasian and Valanginian Sections from the Tethyan Domain (Western Carpathians, Poland)

New magnetic susceptibility (MS), stable isotope, and geochemical (major and trace elements) data are presented from the three Berriasian–Valanginian pelagic sections from the Western Carpathians of Poland. MS correlates well with lithogenic influx and reflects exactly the short-term transgressive–regressive cycles in the interval below the δ13C event (the Weissert event) recorded in the upper Valanginian. The pattern of changes in MS recorded for the Weissert event is more complicated, most probably also reflecting significant climatic changes. Redox-sensitive indicators (Th/U, Ce/Ce*) account for significantly oxygen-depleted conditions combined with relatively low content of productivity indicators (Al-normalized P, Ba, and Cu).

Comment on “Calpionellid distribution and microfacies across the Jurassic/Cretaceous boundary in western Cuba (Sierra de los Órganos)” by López-Martínez et al. (2013)

The paper by Lopez-Martinez et al. (2013) is a new contribution to the microfossil stratigraphy of the Tithonian-Berriasian limestones in the Los Organos Succession (Pinar del Rio Province, western Cuba). This is the result of a detailed (“bedby-bed”) study of one section (San Vicente) located in the north-eastern part of the Sierra de los Organos belt (western Cuba). The description of the El Americano Member (Tithonian-Berriasian, pro parte) is extremely concise, being limited to two sentences, only (Lopez-Martinez et al. 2013), probably because this unit was previously characterized in various publications (Housa & Nuez 1972; Pszczolkowski 1978; Myczynski & Pszczolkowski 1990; Pszczolkowski 1999; Cobiella-Reguera & Oloriz 2009; Pszczolkowski & Myczynski 2010; Iturralde-Vinent & Pszczolkowski 2011). However, in this way the authors have omitted some important features of the El Americano Member. In the type section, the El Americano Member deposits were described as dark-grey to black limestones with ammonites (Housa & Nuez 1972). Unfortunately, Figure 3 (Lopez-Martinez et al. 2013) contains a serious error as the authors claim that it shows “Calpionellid and ammonite biostratigraphy of the Rancho San Vicente section according to Pszczolkowski & Myczynski (2010)”. In fact, such a figure does not exist in the cited paper. If Figure 3 of Lopez Martinez et al. (2013) was extracted from Figure 2 in Pszczolkowski & Myczynski (2010), it should not be restricted to the “Rancho San Vicente section”, as it presents the stratigraphic position of the Guaniguanico units in general, in the Los Organos and Rosario successions. The upper part of the San Vicente section is shown in Figure 10 (Pszczolkowski & Myczynski 2010), but it contains biostratigraphic data on the Upper Berriasian and Lower Valanginian limestones, only. The results of the study by Lopez-Martinez et al. (2013) include some claims and conclusions that are certainly acceptable and others which are not convincing. Only a few items can be considered here. The authors do not mention, that at San Vicente the age of the basal part of the bedded limestones named “the Artemisa Formation”, later included in the El Americano Member of the Guasasa Formation, was identified by Pop (1976, fig. 4) as Upper Tithonian (Crassicollaria Zone). Therefore, the Late Tithonian age of the boundary between the San Vicente and El Americano members in the San Vicente section was known after 1976. The new data of Lopez-Martinez et al. (2013) allow us to refine the stratigraphic position of the basal limestones of the El Americano Member in the San Vicente section as the Boneti Subzone of the Chitinoidella Zone (Upper Tithonian). However, it is not exactly true that “In previous works (Pszczolkowski 1978, 1999), the contact between the San Vicente and the El Americano Members was dated as Kimmeridgian—Tithonian” (Lopez-Martinez et al. 2013, Discussion). In Table 4 (Pszczolkowski 1978), this contact is clearly diachronous and reaches Lower Tithonian (in places); on page 63 there is a conclusion that “... the carbonate bank of Sierra de los Organos had drowned at the Middle Tithonian time which resulted in a considerable uniformity of facies all over the Cordillera de Guaniguanico (Fig. 27)”. Nevertheless, drowning of the carbonate bank had started at the Kimmeridgian-Tithonian boundary (Pszczolkowski 1999; Pszczolkowski & Myczynski 2010). Considering this, the statement of Lopez-Martinez et al. (2013), that “in more detailed work it is possible to find a diachronism in the appearance of pelagic conditions” (and so on) is true, but not new (please see Pop 1976 and Pszczolkowski 1978, 1981). The next claim on page 203 (Lopez-Martinez et al. 2013) concerns the presence of juvenile gastropods and the lack, or extreme scarcity, of adult specimens in the Tithonian limestones (Pszczolkowski & Myczynski 2010). The authors (Lopez-Martinez et al. 2013), interpret this phenomenon in the San Vicente section “as rather due to taphonomic processes, similar to the interpretations by Fernandez-Lopez & Melendez (1995), than as a consequence of low oxygenation levels”. However, it seems that gastropods are very rare in the El Americano Member of the San Vicente section (in beds No. 20 and 43, only?), or alternatively, the authors did not consider them to be important enough to illustrate at least a single specimen of these molluscs. Therefore, it is rather strange that the problem of juvenile gastropods was undertaken in the paper by Lopez-Martinez et al. (2013). Originally, the figured juvenile gastropods were found in other sections of DISCUSSION – COMMENT