Celestina González-Arreola

Major lithostratigraphic units in land-outcrops of north-central Mexico and the subsurface along the northern rim of Gulf of Mexico Basin (Upper Jurassic - lowermost Cretaceous): a proposal for correlation of tectono-eustatic sequences

The stratigraphic and geodynamic interpretation of Upper Jurassic lithostratigraphic units is revised in north-central Mexico and the northern rim of the Gulf of Mexico Basin through updated ammonite and calpionellid biochronostratigraphy. Significant events in the geodynamic evolution in these areas are evaluated and interpreted in terms of tectono-eustatic sequences (TES) of third and second orders. 3rd-TES-I and 2nd-TES-II/III in Mexico and 3rd-TES-I, 3rd-TES-II, and 3rd-TES-III at the northern rim of the Gulf of Mexico show the main traits of the Upper Jurassic Supercycle in these regions, allowing the identification of a combined ‘Atlantic-Tethyan cachet’ in the course of structuring/configuration of the Gulf of Mexico Basin during the Late Jurassic. The easy identification of 3rd-TES-I in north-central Mexico and at the northern rim of the Gulf of Mexico Basin shows no significant difference in geodynamic history during the Oxfordian, which contrasts with the increasing difference from the Kimmeridgian to the Early-Middle Berriasian. Shared trends in stratigraphic architecture with the European margin of the North Atlantic Basin, as well as with epicontinental shelves surrounding Iberia and other Tethyan areas, are interpreted to show phases of the geodynamic evolution in the central North Atlantic Basin, traces of which are recognizable also in western Africa.

Geographic control on phenotype expression. The case of Hybonoticeras mundulum (Oppel) from the Mexican Altiplano

Hybonoticeras mundulum (Oppel) (m) s.s. is reported from the Mexican Altiplano on the basis of material collected bed-by-bed in sections in the States of Durango and Zacatecas. The known range of this species in the Mexican Altiplano is interpreted to be uppermost Kimmeridgian (upper to uppermost Beckeri Zone) to lowermost Tithonian (basal to lower Hybonotum Zone). The Mexican specimens studied are the most complete and valuable collection of H. mundulum (Oppel) s.s. known from a given area, and reveal that Mexican populations show phenotypic features different from European ones. Vicariant events accord with data available about the areal and biostratigraphic distribution of this species, as well as with the combination of allocyclic and autocyclic factors influencing Mexican seas, the breaking of populations rather than colonization events, and the impoverished ammonite assemblages showing endemic traits within the stratigraphic interval studied.

‘Autochthonous’ bivalve assemblages and palaeoecologic interpretation in the Upper Jurassic–Lowermost Cretaceous La Caja Formation from the Cañón de San Matías (Zacatecas, México)

Abstract The present research approaches the precise palaeoecologic interpretation based on the recognition of 12 ‘autochthonous’ bivalve assemblages among 52 registered from the Upper Jurassic–Lowermost Cretaceous La Caja Formation in the Canon de San Matias section (Mexican Altiplano). Fine-grained deposits together with the near-exclusive record of suspension-feeders are considered the evidence for low-energy and nutrient-rich environments. The presence of oxygen-dependent bivalves, mainly Buchia and Lucina , supports the interpretation of oxygenation as a major factor controlling ecology and therefore the composition of the ‘autochthonous’ bivalve assemblages studied. Significant changes in the composition of bivalve assemblages show no relation between fluctuations in ecological factors and background depositional conditions.

Lower Aptian AmmonitinaPseudohaploceras liptoviense (Zeuschner) in the Cumburindio Formation (Southwestern Mexico)

Abstract The presence of Pseudohaploceras liptoviense ( Zeuschner ) associated to Palorbitolina lenticularis ( Blumenbach )permits to interpret an Early Aptian age for the middle part of the lower member of the Cumburindio Formation nearby Turitzio (Michoacan). It is proposed that Boses species “Desmoceras” aguilerae, “D.” alzatei, “D.” burckhardti, “D.” durangense, “D.” tenuicostatum and “D.” wielandi are younger synonymous of Pseudohaploceras liptoviense ( Zeuschner ). An alternative interpretation as Mexican colonizers very close to Pseudohaploceras liptoviense ( Zeuschner ) cannot be conclusively disregarded.

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.

Lower Tithonian Microconchiate Simoceratins from Eastern Mexico: Taxonomy, Biostratigraphy, and Palaeobiogeography

The precise record of simoceratins sampled bed-by-bed is first reported from Mexico (Mazatepec area in Puebla, central-eastern Mexico), as well as the existence of lappeted peristomes in these ammonites. Both Pseudovolanoceras aesinense and the subspecies Pseudovolanoceras aesinense chignahuapense are shown to occur among Mexican simoceratins. The European species and the Mexican subspecies share the same stratigraphic range in the studied sections, yet they differ in ephebic sculpture. Ecological adaptation to neritic seas corresponding to eastern Mexico areas is interpreted, forcing phenotypic deviation with geographic significance, i.e., subspeciation. The new subspecies would indicate stratigraphic horizons within the Semiformiceras semiforme/Haploceras verruciferum Chronozone in the Mediterranean Tethys. A revision of contemporaneous simoceratins in the Americas is founded on a comparative analysis with respect to the European species P. aesinense.

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.

First record of the genus Simocosmoceras Spath, 1925, Ammonitina, in Mexico. Biostratigraphic and palaeobiogeographic interpretation

Abstract The occurrence of Simocosmoceras in Mexico is first reported from the Mazatepec area (Puebla) in East-central Mexico. Simocosmoceras pszczolkowskii apulcoensis n. subsp. shows closest morphological resemblance with Simocosmoceras pszczolkowskii Myczynski registered in western Cuba (Myczynski 1989). Ecological adaptation to comparatively epeiric seas in eastern Mexico is interpreted to cause phenotypic deviation with respect to Simocosmoceras pszczolkowskii Myczynski reported from western Cuba. The lack of transient phenotypes between Mexican and Cuban Simocosmoceras is assumed to support the interpretation of Simocosmoceras pszczolkowskii apulcoensis n. subsp. as a geographic subspecies. The new subspecies is interpreted to indicate stratigraphic horizons within the Semiforme/Verruciferm Zone in the Mediterranean Tethys.