Ricardo Barragán

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.

Decapod crustaceans from the Cretaceous (Aptian–Albian) San Gil Group in the Villa de Leyva section, central Colombia

Abundant concretions at two localities in central Colombia where the San Gil Inferior and San Gil Superior formations are exposed, have yielded numerous crustacean individuals, comprising one new genus Rathbunassa n. gen. (Callianassidae), two new species Joeranina colombiana n. sp., Planocarcinus johnjagti n. sp., and three further species. The following taxa are recorded: ?Paraxiopsis sp. (Axiidae), Rathbunassa aquilae (rAtHBun, 1935) n. comb. (Callianassidae), Joeranina kerri (Luque, FeLdmAnn, SCHweitzer, JArAmiLLo & CAmeron, 2012) n. comb., Joeranina colombiana n. sp. (Palaeocorystidae), Cenomanocarcinus vanstraeleni StenzeL, 1945 (Cenomanocarcinidae), and Planocarcinus johnjagti n. sp. (Necrocarcinidae). Based on ammonite evidence, the locality within the San Gil Inferior Formation is considered to be of late Aptian age, while the one exposing the San Gil Superior Formation is of middle Albian date. Joeranina kerri is found at both localities; in contrast Planocarcinus johnjagti n. sp. occurs exclusively in the upper Aptian, while the remainder of species are all from the middle Albian locality. The taxa reported herein add important data to the palaeobiodiversity and distribution of Cretaceous decapod crustaceans.

Aptian ammonites from Mazapil, Zacatecas State (north-central Mexico) studied by BURCKHARDT in 1906: A revision

Twelve specimens of Aptian ammonites reported and drawn by Burckhardt in 1906, from the Mazapil area (Zacatecas State, north-central Mexico), are reviewed for taxonomical purposes. The work by Burckhardt was the first report of Aptian ammonoids in Mexico. In addition, it represents the only record of Aptian ammonites known from Zacatecas State. The taxonomic review of the specimens allows for the recognition of Dufrenoyia sp., Colombiceras spathi Humphrey, Colombiceras mexicanus (Humphrey) n. comb., Colombiceras sp., Colombiceras spp., and Acanthohoplites aff. bigoureti (Seunes). This ammonite assemblage is indicative of a stratigraphic range that spans the uppermost lower Aptian to the upper Aptian interval.

A negative carbon isotope excursion within the Dufrenoyia furcata Zone: proposal for a new episode for chemostratigraphic correlation in the Aptian

In this work we discuss a proposed updated division of the C7 isotope segment of MENEGATTI et al. (1998). The new standard division of the segment C7 is based on a revision of published Barre- mian-Aptian carbon isotope curves from stratigraphic sections of the Prebetic Domain in Spain. It includes four distinct isotopic subunits labeled C7a to C7d, with a characteristic negative carbon isoto- pe excursion at the base of the segment and which correlates with the Dufrenoyia furcata ammonite Zone. The negative excursion is recognized on a regional extent, and the term Intra-Furcata Negative Excursion (IFNE) is proposed to identify it. We provide possible sites correlatable with the IFNE in both the Old and New worlds, which suggest its potential use as an even global chemostratigraphic marker for the Aptian record.

Palaeoecological significance of Barremian ammonite assemblages and facies variations from Southwest Mexico

Analyses of ammonite shell forms of two Barremian stratigraphic sections from Southwest Mexico consist of two well-defined morphotypes: (1) Small uncoiled, mostly leptoceratoid ancyloconic shells of the families Ancyloceratidae and Hamulinidae, and (2) middle-sized involute to moderately evolute oxycone to discocone shells of the family Pulchelliidae. Index taxa allow the recognition of standard ammonite biozones for the Barremian, which permit the relative dating of different processes that occurred through the water column in the environment of deposition. The vertical distribution of ammonite morphotypes and facies suggests changes of the palaeoceanographic and sedimentological conditions that prevailed in the area during Barremian time. Petrologic data, analyses of the organic carbon and carbonate contents of the rocks support the idea that oxygen-deficient bottom waters existed within a shallow marine, tectonically active area with little carbonate deposition during the early early Barremian (upper part of the Taveraidiscus hugii Zone through the base of the Nicklesia pulchella Zone). These conditions in the basin caused a proliferation of middle-water depth ammonites of Morphotype 1 but prevented the abundance of nektobenthic forms of Morphotype 2. Oxic conditions on a more calcareous and open normal marine environment seem to have been reestablished progressively during a transgressive episode from late early-early late Barremian (upper part of the Nicklesia pulchella Zone through the Gerhardtia sartousiana Zone). This environmental setting supported more facies dependent nektobenthic ammonites of Morphotype 2 to flourish within the basin.

Kukulkanus, a new genus of buxtoniin brachiopod from the Artinskian–Kungurian (Early Permian) of Mexico

Torres-Martínez, M.A., Sour-Tovar, F. & Barragán, R., November 2017. Kukulkanus, a new genus of buxtoniin brachiopod from the Artinskian–Kungurian (Early Permian) of Mexico. Alcheringa 42, 268–276. ISSN 0311–5518. Kukulkanus is the first genus of the tribe Buxtoniini recorded from rocks of the late Cisuralian (Artinskian–Kungurian). The Early Permian (Cisuralian) outcrops of the Santa Rosa Group, from southeastern Chiapas, are one of the most important marine Palaeozoic successions of Mexico. The Artinskian–Kungurian Paso Hondo Formation is the youngest unit in the succession and is dominated by massive limestone. Different marine invertebrates deposited in massive calcareous rocks characterize this formation. The buxtoniin Kukulkanus spinosus gen. et sp. nov. is reported from a single bed within the unit. The outcrops are located in southeastern Chiapas, very near the Guatemala–Mexico border. The lithological features and the preservation of fossils indicate that the fossil-bearing rocks were deposited in a low-energy open-waters paleoenvironment over the continental platform. Fusulinids, cephalopods and brachiopods previously described for the Paso Hondo Formation have been correlated with faunas of different coeval localities from Texas, New Mexico, Coahuila, Chiapas and Venezuela, regions that form part of the biotic Grandian Palaeo-Province. Miguel A. Torres-Martínez [miguelatm@geologia.unam.mx] Departamento de Paleontología, Instituto de Geología, Circuito de la Investigación Científica, Avenida Universidad No. 3000. Colonia Universidad Nacional Autónoma de México, Delegación Coyoacán, Cd. Mx. C.P. 04510, Mexico. Francisco Sour-Tovar [fcosour@ciencias.unam.mx] Museo de Paleontología, Facultad de Ciencias, Universidad Nacional Autónoma de México. Av. Universidad No. 3000, Colonia Universidad Nacional Autónoma de México, Delegación Coyoacán, Cd. Mx. C.P. 04510, Mexico. Ricardo Barragán [ricardor@geologia.unam.mx] Departamento de Paleontología, Instituto de Geología, Circuito de la Investigación Científica, Avenida Universidad No. 3000. Colonia Universidad Nacional Autónoma de México, Delegación Coyoacán, Cd. Mx. C.P. 04510, Mexico.

Morphological and mineralogical characterization of speleothems from the Chimalacatepec lava tube system, Central Mexico

*ralopezm@geologia.unam.mx Citation:

Reply to the Comment of A. Pszczółkowski on "Calpionellid distribution and microfacies across the Jurassic/Cretaceous boundary in western Cuba (Sierra de los Órganos)" by López-Martínez et al. (2013)

1Instituto de Geologia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Delegacion Coyoacan, C.P. 04510 Mexico D.F., Mexico; rafaelopez83@hotmail.com 2Comenius University, Faculty of Natural Sciences, Department of Geology and Paleontology, Mlynska dolina G, 842 15 Bratislava, Slovak Republic; rehakova@fns.uniba.sk 3Departamento de Geologia, Universidad de Pinar del Rio, Marti 270, Pinar del Rio, C.P. 20100, Cuba