Paleocene benthonic foraminiferal biostratigraphy,paleobiogeography and paleoecology of Atlantic—Tethyan regions: Midway-type fauna

The stratigraphic, geographic and bathymetric distribution of some Paleocene benthonic foraminiferal assemblages have been studied in the Tethyan and circum-Atlantic regions within the framework of planktonic foraminiferal zones. Although some species appear to be restricted to either the Tethyan-European area or to the western Atlantic, the majority of species are amphi-Atlantic and Tethyan in distribution. The cosmopolitan distribution is attributed to more equitable climatic conditions (lower polar—equatorial thermal gradient) and warmer, more uniform thermal structure of the oceans and different paleogeographic and paleo-oceanographic conditions.Two main distinct depth-controlled benthonic foraminiferal assemblages (exclusive of the shallow-warm water Tethyan carbonate assemblage) have been recognized in the Paleocene. The continental shelf fauna, termed here the “Midway-type fauna” (MF) is characterized by species of Cibicidoides alleni (Plummer) = propria Brotzen, howelli (Toulmin), succedens (Brotzen), Anomalinoides [acuta (Plummer), midwayensis (Plummer)], Gavelinella [danica (Brotzen), neelyi (Jennings)], and Osangularia plummerae Brotzen, as well as various lagenids (nodosariids, lenticulinids, vaginulinids), polymorphinids and textulariids. A lower continental slope and abyssal plain fauna, termed here the “Velasco-type fauna” (VF), is characterized by, amongst others, Gavalinella [beccariiformis (White), rubiginosa (Cushman), velascoensis (Cushman)], Nuttallides truempy (Nuttall), Nuttallinella florealis (Cushman), velascoensisZ (Cushman)], (Cushman), Aragonia velascoensis (Cushman), nodosariids (N. velascoensis Cushman, Dentalina limbata d'Orbigny), various agglutinated forms [Gaudryina pyramidata Cushman, Tritaxia aspera (Cushman), Dorothia ex. gr. oxycona trinitatensis (Cushman and Renz)], and various gyroidinids and buliminids. Pleuriostomellids and stilostomellids are quantitatively rare and unimportant until the Middle—Late Eocene.This paper discusses the biostratigraphy and biogeography of the “Midway-type fauna”.     

Microfacies,sedimentary environment and paleoecology of Paleocene–Eocene deposits in the Zagros Basin,north of Shiraz,southwest Iran

The Jahrum Formation act as reservoir rocks in the Zagros Mountains west of Iran. For the study of this formation, a stratigraphic section of Lapoee which is situated north of Shiraz has been examined. Petrographic and stratigraphic results along with field observations show that the Jahrum Formation consists of cream-grey thin-to-medium-bedded limestone so that at the top of the formation, they are locally changed to dolomite. The Jahrum Formation overlies the Sachun Formation. We also found Nubecularids as paleoecology indicators in middle parts of the Jahrum Formation. The presence of Nubecularids in the Lapoee stratigraphic section (i.e. the Jahrum Formation) indicates a lagoon depositional environment.     

Quantitative paleoecology of Cambrian (Series 2–Miaolingian) communities from central Sonora,Mexico

This work presents a paleoecological approach to study benthic communities preserved in Cambrian strata exposed at the Sahuaral locality in central Sonora, northwestern Mexico. Based on species richness and abundance, this work analyzed 627 individuals corresponding to 33 species from five distinctive Cambrian formations: the lowermost Proveedora Formation characterized by bioturbation horizons that record the occurrence of a benthic-infaunal biota from coastal shallow seas, followed by the Buelna Formation which contains reef deposits dominated by autotrophic epibenthic communities. The Cerro Prieto Formation was deposited in a high-energy shallow marine environment, dominated by primary consumers-epifaunal and suspensions feeders. The uppermost unit, the El Gavilán Formation, is an intercalation of shale and fossiliferous limestone characterized by the fossil remains of suspension feeders, detritus feeders and nektobenthic organisms of low energy deep water environments. The paleobiota consist of ichnofossils, microbial oncolites, chancellorids, brachiopods, hyolithids, and trilobites in a sequence of increasing diversity and complexity. Paleoecological indices (Simpson Dominance, Shannon-Weaver Index, Evenness Index, and Total Richness) were determined and compared in the study area. In addition, the effective number of species and the true diversities were obtained, which are similar between each station distributed in each formation. However, it is possible that the high degree of dominance is a factor to indicate an inequality between the true diversity and the species richness identified. These results provide new analytical and paleoecological criteria for better understanding depositional environments and fossil associations where the spatial distribution of benthic organisms, richness and abundance provide a valued window to Cambrian biotas. The structure of the marine community of the El Sahuaral area has a great affinity with other Cambrian communities, such as those from the Stephen Formation (Burgess Shale, British Columbia) and the Chengjiang biota of the Yangtze Shelf deposits in South China.