: A new skull belonging to the species Eurhinodelphis cocheteuxi (Cetacea, Odontoceti, Eurhinodelphinidae), found in the upper Lower–Middle Miocene of Antwerp (Belgium, southern margin of the North ...Sea Basin) associated with its ear bones (periotic, tympanic bullae, malleus and incus), is the basis of a redescription and systematic revision of the species. This species is then used as an isolated taxon in a phylogenetic study of extinct and extant odontocetes. The main results of the cladistic analyses are: a sister‐group relationship between E. cocheteuxi and the extant family Ziphiidae (beaked whales), and a more basal position of the superfamily Physeteroidea (sperm whales) in the tree. The possible paraphyly of the family Eurhinodelphinidae needs further investigation. The results are compared with the most recent morphological and molecular analyses. The species E. bossi, described in the Miocene of Maryland (east coast of the USA, Calvert Formation) is recognized in the Miocene of Belgium for the first time.
Este trabajo presenta los resultados del estudio paleontológico de la sección de Peña Adrián (Miranda de Ebro, Burgos), formada por facies aluviales y palustre-lacustres del Mioceno Superior. Se han ...muestreado dos niveles margosos, PAF15 y PAF24 (A y B) donde se han identificado diferentes géneros y especies de gasterópodos, carofitas, y ostrácodos. A partir del estudio estratigráfico y paleontológico ha sido posible conocer las condiciones ambientales del sistema lacustre y su variación a lo largo de la sucesión, mostrando fases de mayor y menor energía hasta la colmatación y retracción final del sistema.
Se describe Palaeodiplothrombidium microscutum gen, et sp. nov. a partir de un adulto y una deutoninfa preservados en ámbar del Mioceno inferior de Chiapas, México. Este taxón nuevo de ácaro es el ...primer registro de la Cohorte Parasitengona (Acari: Trombidiformes: Prostigmata) para un yacimiento de ámbar dentro de México y también el primer registro fósil de la familia Johnstonianidae a nivel mundial.
Resumen El estudio del ámbar del Mioceno temprano de Simojovel de Allende, Chiapas, ha tomado gran auge, ya que se ha visualizado que su estudio nos permite evidenciar el ambiente durante su ...depósito. En este trabajo se realizó la identificación de 34 especímenes presentes en una pieza de ámbar perteneciente al Museo del Ámbar Lilia Mijangos, con una edad aproximada de 20 millones de años. Los organismos fueron asignados a Martesia mazanticus sp. nov., considerada como nuevo taxón por las diferencias presentadas con las especies más afines M. fragilis y M. sanctipauli. Este es el primer registro del género Martesia en el ámbar de Simojovel. El presente hallazgo refuerza la teoría planteada de la presencia de una laguna estuarina rodeada de un manglar de Rhizophora como ambiente de depósito.
As formações argilosas do Miocénico de Lisboa foram alvo de um estudo extensivo de caracterização, com vista a estabelecer um conjunto de intervalos de valores para os principais índices físicos, ...parâmetros de compressibilidade e de resistência, que poderão ser úteis para o projeto geotécnico. O presente artigo descreve as características físicas e os parâmetros de compressibilidade para as principais formações miocénicas de cariz argiloso: Argilas dos Prazeres e Argilas do Forno do Tijolo. Apresenta-se os resultados dos elementos recolhidos de relatórios existentes e resultados obtidos de ensaios realizados sobre amostras recolhidas num campo experimental. Estabelece-se um conjunto de parâmetros que podem ser considerados representativos para as formações em estudo.
Partial melting is thought to profoundly impact the rheology and deformation behavior of the middle crust. Consequently, investigations of the pressure-temperature conditions of metamorphism, rates ...of heating, and durations of anatexis can provide unique constraints on tectonic processes. The Greater Himalayan Sequence (GHS), in the metamorphic core of the Himalayan orogen, is commonly considered to represent exhumed, anatectic, mid-crust. Here, we present detailed petrological and geochronological analysis of anatectic pelitic schist and felsic paragneiss from the uppermost structural level of the GHS to understand the timing and conditions of Himalayan anatexis. Petrologic analysis indicates that these rocks experienced high-grade metamorphism and partial melting up to peak conditions of ca. 720–745°C and ca. 9.6–10 kbar. Melt volumes of ca. 3% increased slightly during exhumation with nearly constant or slightly decreasing temperature, then decreased as rocks cooled, ultimate crossing the solidus at ca. 5.5 kbar and 700°C. Well-correlated U–Th–Pb ages and trace element data (HREE, Y, and Eu/Eu*) for monazite and zircon require prograde metamorphism and initial partial melting of GHS rocks at ca. 50 and 42–40 Ma, respectively, and crystallization of melts at ca. 24–18 Ma. These data indicate a long-lived (ca. 22–24 Myr) partially molten mid-crust in the eastern Himalayan orogen that formed as much as 10 Myr earlier and lasted 10 Myr longer than numerical models of viscous flow have predicted. Thermal buffering and melt stagnation may reflect feedbacks between thermal structure and shear stress. The change from thermal and mechanical stasis to rapid exhumation and cooling at ca. 24 Ma corresponds with an orogen-wide shift in deformation patterns, and may reflect arrival of mainland India.
•The upper GHS in the eastern Himalaya retained anatectic melts for ca. 22–24 Myr.•Partial melting initiated at 42–40 Ma and melts crystallized by 18 Ma.•Melt stagnation may reflect feedbacks between thermal structure and shear stress.•Rapid exhumation starting ca. 24 Ma may reflect arrival of mainland India.
Fossil plants provide evidence of biological evolution
and indicate changes in climate, sedimentation, hydrology, and sediment
burial. The study of fossil woods where there is optimal preservation of
...anatomic characteristics enables us to identify the genus and even the species
of plant communities of the past. This paper presents a site with silicified
wood fragments found in Middle Miocene deposits of the Ebro Basin. Their
occurrence in marly, muddy, and sandy beds suggests their deposition in
palustrine zones and floodplains during flooding periods. The anatomical
characteristics of the studied pieces suggest their assignment as cf. Salix (willow
tree). Typically, it would represent riparian forest vegetation, consistent with
the presence of a distal fluvial system. The age of the wood-bearing deposits
is 14.3 ± 0.14 million years, when an increase in humidity is reported by previous studies in the area, approximately 200,000 years after the Miocene
Climatic Optimum.
Las plantas fósiles son testimonio de la evolución biológica
y ayudan a reconocer cambios en el clima, la sedimentación, la hidrología y el
enterramiento de los sedimentos. Los estudios de maderas fósiles permiten,
en óptimas condiciones de preservación de caracteres anatómicos, diagnosis
a nivel genérico e incluso específico de la composición de las comunidades
vegetales. Se presenta el hallazgo de un yacimiento de maderas silicificadas
del Mioceno Medio en la cuenca del Ebro. Su localización en niveles de
margas, lutitas y areniscas finas sugiere el depósito en zonas palustres y
llanuras de inundación durante avenidas. Los caracteres anatómicos
observados aconsejan su adscripción como cf. Salix (sauce). Se trataría de vegetación de bosques de ribera en un sistema fluvial distal. La edad de los
depósitos es de 14,3 ± 0,14 millones de años, cuando comienza un incremento de humedad según estudios previos, aproximadamente 200 000 años
después del Óptimo climático del Mioceno.
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•We studied magmatic rocks from the Urumeih-Dokhtar magmatic belt, Iran.•All granitoids from BBMC have calc-alkaline geochemical affinities.•U–Pb zircon analyses suggest emplacement ...at 29–22 Ma.•Barren granitoids formed from a juvenile lower crustal source.•Productive adakites formed by partial melting of overthickened lower crust.
The Bezenjan-Bardsir magmatic complex (BBMC), situated at the southeastern part of the Urumieh-Dokhtar magmatic belt, includes a thick pile of volcanic rocks intruded by younger granitoids. The granitoids have granodioritic to quartz-monzonitic composition, while volcanic rocks are petrologically classified as basaltic andesite, andesite, dacite, rhyodacite, and rhyolite. In this study, U–Pb zircon geochronology, whole-rock geochemistry, and Sr–Nd isotopic analyses were performed on a wide range of granitoids exposed within the BBMC. This geochronology indicates that barren magmatism occurred during the Middle to Late Oligocene (29–23 Ma), followed by large-scale Cu mineralization during the Late Miocene. These BBMC rocks have strong depletions in Nb (2.5–17.3 ppm) and enrichments in light rare earth elements and large ion lithophile elements compared to N-MORB. Their normal calc-alkaline arc geochemical signature (low Sr/Y ratio of almost <55), negative Eu anomalies (Eu/Eu∗ = 0.6–1), enrichment in HFSE and the negative to positive εNd (t) values of −1.23 to +3.17, the Nd model ages (0.43–0.72 Ga) and radiogenic Sr isotope signatures (87Sr/86Sr = 0.7048–0.7063) suggest generation in a subduction zone setting; however, productive rocks elsewhere within the UDMB exhibit adakite-like calc-alkaline magmatic characteristics (high Sr and Sr/Y, but low Y). The BBMC igneous rocks show low Sr/Y (14.6–45.2), zircon Ce(IV)/Ce(III) (12–703), and Eu/Eu∗ (0.08–0.64) ratios, negative to slightly positive Eu anomalies, and enrichment in HFSE and 87Sr/86Sr, in agreement with other barren-type magmas through the UDMB. An integrated geochemical, petrological, and tectonic model suggests that barren magmatism in the BBMC was likely associated with partial melting of juvenile lower crust (amphibolite) due to northwestward subduction of the Neo-Tethys oceanic lithosphere, whereas productive adakitic rocks within the UDMB formed by partial melting of thickened lower crust (garnet-amphibolite).
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