Calpionellid distribution and microfacies across the Jurassic/ Cretaceous boundary in western Cuba (Sierra de los Órganos)

Abstract

A detailed bed-by-bed sampled stratigraphic section of the Guasasa Formation in the Rancho San Vicente area of the "Sierra de los Órganos", western Cuba, provides well-supported evidence about facies and calpionellid distribution across the Jurassic/Cretaceous boundary. These new data allowed the definition of an updated and sound calpionellid biozonation scheme for the section. In this scheme, the drowning event of a carbonate platform displayed by the facies of the San Vicente Member, the lowermost unit of the section, is dated as Late Tithonian, Boneti Subzone. The Jurassic/Cretaceous boundary was recognized within the facies of the overlying El Americano Member on the basis of the acme of Calpionella alpina Lorenz. The boundary is placed nearly six meters above the contact between the San Vicente and the El Americano Members, in a facies linked to a sea-level drop. The recorded calpionellid bioevents should allow correlations of the Cuban biozonation scheme herein proposed, with other previously published schemes from distant areas of the Tethyan Domain.

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 authors (López-Martínez et al 2013), interpret this phenomenon in the San Vicente section "as rather due to taphonomic processes, similar to the interpretations by Fernández-López & Meléndez (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.…”

“…Nevertheless, drowning of the carbonate bank had started at the Kimmeridgian-Tithonian boundary (Pszczółkowski 1999;Pszczółkowski & Myczyński 2010). Considering this, the statement of López-Martínez 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 1976and Pszczółkowski 1978, 1981.…”

“…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 Ló-pez- Martínez 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 (Pszczółkowski 1978(Pszczółkowski , 1999, the contact between the San Vicente and the El Americano Members was dated as Kimmeridgian-Tithonian" (López-Martínez et al 2013, Discussion).…”

“…), 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 López-Martínez et al (2013 the Guaniguanico megaunit; their occurrence was interpreted in terms of moderate to poor oxygen levels at the sedimentwater interface (Pszczółkowski & Myczyński 2010). It does not necessarily means "a clear anoxic facies" expected by López-Martínez et al (2013).…”

“…Therefore, it is rather strange that the problem of juvenile gastropods was undertaken in the paper by López-Martínez et al (2013 the Guaniguanico megaunit; their occurrence was interpreted in terms of moderate to poor oxygen levels at the sedimentwater interface (Pszczółkowski & Myczyński 2010). It does not necessarily means "a clear anoxic facies" expected by López-Martínez et al (2013). According to Pszczółkowski et al (2005), dysaerobic conditions at the sediment/seawater interface could be widespread in the northwestern part of the proto-Caribbean seaway around the Jurassic/Cretaceous boundary.…”