Study of ammonites and bivalves along selected sections on the Andean margin of northern Peru and Ecuador has made it possible to recognize correlatable marine transgressions and to propose a refined stratigraphic framework for the Upper Cretaceous of the region. Six maximum flooding events are recognized: latest Turonian-early Coniacian (major event), late Coniacian-early Santonian, late Santonian-early Campanian, mid Campanian-early late Campanian (major event), early Maastrichtian (major event), and terminal early Maastrichtian. Most of these events can be correlated with global eustatic sea-level rises, but their relative manifestations indicate that the Andean margin was already being deformed by the late Cretaceous "Peruvian" tectonic events. The onset of fine-grained clastic sedimentation in the Oriente and East-Peruvian basins in the mid Turonian-earliest Coniacian is taken as the first event of the "Peruvian" phase. The Campanian regional transgression in the Peruvian-Ecuadorian forearc zones concealed the "Peruvian" deformational event. The latter caused a palaeogeographic upheaval, indicated by the subsequent development of a NNE-trending forearc basin, which extended from Paita in northwestern Peru to northern Ecuador. In the forearc zones only short-lived transgressions are recorded in the late Campanian and early Maastrichtian as a result of nearly continuous tectonic activity. This culminated with a significant tectonic event in the late Maastrichtian, causing a widespread hiatus.
Various fossils (invertebrates, vertebrates, plants) and radiometric data have been obtained from the uppermost part of the marine Celendin Fm. and the lowermost part of the overlying Bagua Fm. (redbeds). After description of the stratigraphy and sampled localities, the fossils are discussed in terms of systematics, Ftratigraphy, paleoecology and biogeography. On the basis of ammonites, the uppermost Celendin Fmb. is dated as mid-Campanian. On the basis 0f.a charophyte assemblage and other evidence,
Large-scale biogeographic provinces of Cretaceous ammonoids, as currently defined in the literature, were delimited using qualitative assessments of taxonomic inventories. Using aggregated species occurrences in the Paleobiology Database, we generated a geographic network to quantify connectivity of Albian epicontinental basins and used the flow-based Infomap algorithm to delineate bioprovinces. Despite taxonomic, stratigraphic, and geographic limitations of the data, the Infomap bioprovinces are largely concordant with the traditional, qualitatively derived biogeographic model, including the Boreal-Pacific Subrealm, Arctic Subrealm, Tethyan Realm, and Austral Realm. An agglomerative hierarchical cluster analysis applied to the same occurrence data failed to replicate the Infomap bioprovinces or reproduce the traditional qualitative model. The observed asymmetrical distribution of the Infomap bioprovinces is consistent with the known hemispheric differences in paleogeographic and oceanographic features of the Albian Earth. The geographic network derived from ammonoid data is twice as dense as the one derived for Albian benthic marine invertebrates and thus more effective in delineating global biogeographic units. The network-based approach establishes a reproducible quantitative framework for delineating geographic boundaries of marine bioprovinces, tracking biogeographic changes over evolutionary time scales, and identifying biotic and abiotic factors that influence global partitioning of marine biodiversity.
The late Aptian (Early Cretaceous) is a crucial time interval for understanding the paleoceanographic changes in the Southern Hemisphere. Oceanographic changes in the emerging South Atlantic Ocean during this interval are reflected in the stratigraphic distribution of dinoflagellate communities recorded in the Muribeca and Riachuelo formations of the Sergipe Basin in northeastern Brazil. The Subtilisphaera community, in the lower and middle parts of the section, appears to be related to the Subtilisphaera Ecozone and suggests the onset of Tethyan influence in the central South Atlantic, in a restricted to inner-neritic environment. The succeeding Spiniferites community, in the middle part of the section, represents the first significant transgression, probably of eustatic origin. The Cyclonephelium-Exochosphaeridium community, in the upper part of the section, appears to be related to an oceanic event characterized by intermittent dysoxic-anoxic conditions. The uppermost part of the section is dominated by the Spiniferites community, related to a progressive regional transgression and culminating in an open-marine, fully Tethyan environment in the central part of the widening South Atlantic.
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