Aragonian stratigraphy reconsidered, and a re-evaluation of the middle Miocene mammal biochronology in Europe

The recently collected fauna of Armantes 1A in Chron C5Br of the Armantes section necessitates reinterpretation of the previous bio- and magnetostratigraphical correlations between the Armantes and Vargas sections (Calatayud-Daroca Basin, Central Spain) [W. Krijgsman, M. Garcés, C.G. Langereis, R. Daams, J. van Dam, A.J. van der Meulen, J. Agustí, L. Cabrera, A new chronology for the Middle to Late Miocene continental record in Spain, Earth Planet. Sci. Lett. 142 (1996) 367-380]. The long reversal in the Vargas section is now correlated to C5Br, instead of to C5Cr, on the basis of the biostratigraphical correlation of Armantes 1A to the faunas of Fuente Sierra 2 and 3 (in the Vargas section), which are situated in the basal part of the Middle Aragonian (MN5). This leads to the revised age of 16.0 Ma for the Early-Middle Aragonian (MN 4=5) boundary. Our age estimate of the MN5=6 boundary is maintained at ca. 13.75 Ma. The Vargas section is now considered to start in Chron C5Cn.2r and to end in C5Bn.1n. As a result of the revised correlation the duration of the time gap between the fossiliferous parts of Vargas and the younger Aragón section, previously estimated as ca. 1.5 Myr, is now reduced to less than 200,000 years. The tie points of the European mammal units (MN4-MN6) to the geomagnetic polarity time scale [F.F. Steininger, W.A. Berggren, D.V. Kent, R.L. Bernor, S. Sen, J. Agustí, Circum-Mediterranean Neogene (Miocene and Pliocene) marine-continental chronologic correlations of European mammal units, in: R.L Bernor, V. Fahlbusch, H.-W. Mittmann (Eds.), The Evolution of Western Eurasian Neogene Mammal Faunas, Columbia Univ. Press, New York, 1996, pp. 7-46] are evaluated. Our age estimates of the MN4=5 and MN5=6 boundaries are compatible with the new magnetostratigraphic calibration of middle Miocene mammal zones in the Swiss Molasse basin [O. Kempf, T. Bolliger, D. Kälin, B. Engesser, A. Matter, New magnetostratigraphic calibration of Early to Middle Miocene mammal biozones of the North Alpine foreland basin, in: J.-P. Aguilar, S. Legendre, J. Michaux (Eds.), Actes du Congrès BiochroM '97, Mém. Trav. E.P.H.E. 21 (1997) 547-562]. Ó 1999 Elsevier Science B.V. All rights reserved

Estudio paleontológico en las cuencas terciarias de Galicia

Se ha realizado una prospección paleontológica en nueve cuencas terciarias gnllegas, con el fin dc prccisar su edad y condiciones pnleoombiclltales. Presentamos los resultados obtenidos en base a hallazgos de micromamíferos, grandes mamíferos, peces, macrorestos vegetales y moluscos en las cuencas de As Pontes (A Coruila) y Roupar (Lugo). Las arci llas de los niveles inferiores de As Pontes contienen roedores, cuya edad corresponde al principio del Oligoceno superior (MP 25-26). Los lignitos inferiores han proporcionado un Antracotérido que probablemente corresponde también al Oligoceno. Las plantas de los niveles superiores pueden ser del Oligoceno o del Mioceno inferior. Las condiciones climáticas, siempre tropicales, debieron variar de cálidas a húmedas. En las arcillas inferiores hay peces y moluscos tanto dulceacuícolas como eurihalinos, y moluscos marinos litorales. Se apoyan con estos datos las hipótesis de contemporaneidad entre las cuencas de As Pontes y Roupar, y su carácter parálic

Eomyids: happy old age or premature death? Reconstructing the life history of Ligerimys (Eomyidae, Rodentia, Mammalia)

Animal sciencesNaturali

Updated Aragonian biostratigraphy: Small Mammal distribution and its implications for the Miocene European Chronology

This paper contains formal definitions of the Early to Middle Aragonian (late Early–Middle Miocene) smallmammal biozones from the Aragonian type area in North Central Spain. The stratigraphical schemes of two of the best studied areas for the Lower and Middle Miocene, the Aragonian type area in Spain and the Upper Freshwater Molasse from the North Alpine Foreland Basin in Switzerland, have been compared. This comparison allows the analysis of the order of shared mammal events in the two countries, and the quantification of the resulting asynchronies based on their temporal correlations. The order of the events is very similar in Spain and Switzerland. In order to estimate the diachrony, two age-model options are used for the Swiss record. Our preferred option yields no discrepancies with SW European paleomagnetic and radiometric calibrations of the Ramblian and Early Aragonian bioevents. All Swiss first taxa occurrences precede those in the Aragonian type area by 0.74Myr on average. The asynchronies (1-2Myr) of the species arriving in the late Middle to early Late Aragonian may be higher than in the Early Aragonian (0-1Myr). The implications for the biochronological mammal Neogene system are discussed. Evidence is given confirming the unfeasibility of a formal European biozonation, since it is realised, that 1) most indicator species and many genera of rodents yielding the most detailed zonations have limited geographical ranges hampering recognition of the mammal Neogene zones; and 2) first and last taxon occurrences are diachronical. Therefore, the mammal Neogene system based on a sequence of time-ordered reference localities is preferred to the one based on selected bioevents “developed in widespread geographic areas”

Presence of Karydomys (Rodentia, Cricetidae) in the Miocene of Chios.

International audienc

Unidades estratigráficas en el registro sedimentario neógeno del sector occidental de la Cuenca de Madrid

El sector occidental de la Cuenca de Madrid está constituido por depósitos siliciclásticos, en general areniscas arcósicas y lutitas, fundamentalmente de edad neógena. A partir de la cartografía y del estudio estratigráfico detallado de los materiales terciarios presentes en varias hojas geológicas a escala 1:50.000 de la zona SO de la cuenca, se han reconocido cinco unidades estratigráficas cuya denominación alude a las áreas donde aparecen mejor representadas. De base a techo, son: 1) Unidad de arcosas y lutitas de El Carpio, 2) Unidad de arcosas con cantos y conglomerados del Embalse de Castrejón, 3) Unidad de arcosas y lutitas de Los Vergales, 4) Unidad de arcosas gruesas con cantos de Batres, y 5) Unidad de arcosas blancas de Carranque-Griñón. Los límites entre ellas quedan definidos por cambios en la evolución en la vertical de los depósitos siliciclásticos, sobre todo relativos a su granulometría. Los materiales reconocibles en cada una de estas unidades se depositaron en su mayor parte en sistemas de abanicos aluviales, con variaciones en el carácter permanente o efímero de los sistemas distributarios y, en menor medida, en ambientes lacustres someros y palustres. La edad del conjunto estratigráfico analizado abarca esencialmente el Mioceno inferior y medio, no descartándose que la base de la Unidad de arcosas y lutitas de El Carpio sea Paleógeno y que la parte superior de la Unidad de arcosas blancas de Carranque-Griñón alcance el Mioceno superior (Vallesiense)

New species of Hispanomys (Rodentia, Cricetodontinae) from the Upper Miocene of Batallones (Madrid, Spain)

International audienc

Geology of the system of Miocene mammal sites of the Cerro de los Batallones, Madrid Basin

The Cerro de los Batallones (Los Batallones Butte) is located in the central-northern area of the Madrid Basin, central Spain. Six vertebrate localities containing a large variety of mammals together with amphibians, fishes and plant remains of Upper Vallesian Age (Late Miocene) have been found associated with the sediments forming the butte. From bottom to top, these sediments consist of magnesian lutite beds (Unit I), palaeosols formed of sepiolite and opal (Unit II), and siliclclastic, marlstone and carbonate beds (Unit III). Both the patch-like geometry and the composition of the deposits bearing the Upper Vallesian fauna indicate that their accumulation took place in cavities which acted as traps for both carnivores and herbivores. Although there is not conclusive evidence for the precise mechanism of formation of the holes, a combined effect of vertisol development followed by subsurface erosion processes ("pseudokarst") can be suggested as most reliable. Moreover, formation of the vertebrate localities of Cerro de los Batallones could provide some clues on the geological evolution of the Madrid Basin during the Upper Miocen