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

Abstract

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