The Cenozoic palaeoceanographical history of the South Atlantic and the Southern Ocean is summarised on the basis of changes in the ostracod faunas of DSDP/ODP Sites 329, 513, 689, 699, 1087 and ...1088. The results are mainly compared with the global palaeoceanographical history of Benson. The present study failed to find strong evidence for a sudden psychrospheric event (Sites 689 and 699) in the late Eocene, but there is, however, a decrease in abundance and diversity of ostracods from the mid-/late Eocene to the Oligocene at Sites 689 and 699. This suggests a more gradual palaeoceanographical change over a relatively long time interval. Mid-Miocene faunal changes occur at Site 1087 and coincide with the 16-14 Ma event of Benson. However, the faunal changes are, in contrast to Benson, here marked by a decline in abundance, diversity and faunal turnover. The local differences in faunal changes in mid-Miocene deep-sea ostracod faunas may be related to the initiation of NADW and/or a major expansion of the Antarctic ice sheet. We found little or no evidence for the 6.3-4.9 Ma event, which Benson recorded and related to the effects of a series of events such as the Messinian Salinity Crisis and increased glaciation on Antarctica. Similar to Benson's global data, we have also found a major faunal turnover at Sites 1087 and 1088 at 3.5 Ma. This is possibly related to the effects of a closure of the Straits of Panama, increased production of NADW, AAIW and AABW, and/or a major deglaciation of the Antarctica in the mid-Pliocene.
Dosadašnja istraživanja i shvaćanja, kako o starosti, tako i karakteru slijeda sedimenata fliša Pazinskoga bazena u Istri, upućivala su na ukupnu starost fliša od kasnoga lutecija do starijega ...priabonija. Međutim, nedavno su prikazani podaci, prema kojima jedan dio tih sedimenata odgovara kasnom oligocenu, što je bitna novost za razmatranje razvitka toga bazena, kao i orogena Dinarida. Ovaj rad odgovara na potrebu dodatne provjere starosti tih sedimenata zbog važnosti odnosnoga datiranja. Prikazani rezultati temelje se na usporedbi karaktera i slijeda sedimenata iz predjela odakle potječu nedavni podaci o oligocenu sa sedimentima drugih dijelova Pazinskoga bazena, te na biostratigrafskom datiranju pomoću planktonskih foraminifera i nanoplanktona. Ustanovljene biozone odgovaraju gornjem luteciju i donjem bartoniju, dakle, donjemu dijelu ukupnoga raspona starosti Pazinskoga fliša.
The dating of the flysch sediments of the coastal Dinarides is critical for considering the evolution of the Dinaric chain. The flysch of the Pazin Basin, Istria has been considered to be Late Lutetian to Late Eocene in age by many workers. The recently reported Late Oligocene age of a part of this flysch (ŠPARICA et al., 2005) is highly relevant when considering the sedimentary and tectonic evolution of the area, as well as the western Dinarides in general. The importance of the Late Oligocene dating, and the character of the succession of the area in question, which shows similarities with Middle Eocene sediments in other parts of the basin, provoked the need for a reevaluation of the dating of these specific sediments. The results presented here support the Middle Eocene age of these sediments, which is consistent with the dating proposed by previous workers, and agrees with the character of the relevant sedimentary succession.
Dosadašnja istraživanja i shvaćanja, kako o starosti, tako i karakteru slijeda sedimenata fliša Pazinskoga bazena u Istri, upućivala su na ukupnu starost fliša od kasnoga lutecija do starijega ...priabonija. Međutim, nedavno su prikazani podaci, prema kojima jedan dio tih sedimenata odgovara kasnom oligocenu, što je bitna novost za razmatranje razvitka toga bazena, kao i orogena Dinarida. Ovaj rad odgovara na potrebu dodatne provjere starosti tih sedimenata zbog važnosti odnosnoga datiranja. Prikazani rezultati temelje se na usporedbi karaktera i slijeda sedimenata iz predjela odakle potječu nedavni podaci o oligocenu sa sedimentima drugih dijelova Pazinskoga bazena, te na biostratigrafskom datiranju pomoću planktonskih foraminifera i nanoplanktona. Ustanovljene biozone odgovaraju gornjem luteciju i donjem bartoniju, dakle, donjemu dijelu ukupnoga raspona starosti Pazinskoga fliša.
El yacimiento de Fondota (Abiego, Huesca) es uno los yacimientos con más fósiles de icnitas de vertebrados de la Cuenca del Ebro. Éstas presentan una gran variedad de grados de preservación ...morfológica (MP) por lo que resulta fundamental conocer las condiciones sedimentológicas bajo las que se desarrolló. El yacimiento, localizado en la parte inferior de la Formación Peraltilla (Oligoceno inferior), se sitúa en la superficie de un nivel de calizas grises masivas que presenta indicadores de escasa profundidad y desecación (nodulización, laminación estromatolítica…). El nivel calcáreo correspondió a un área encharcada desarrollada sobre depósitos de un relleno de canal en una zona aluvial distal. En dicha situación, las icnitas se originaron bajo diferentes condiciones con variaciones en la humedad y el contenido de agua del substrato. Estas condiciones tuvieron una influencia directa en los valores altos o bajos de MP, y, por tanto, en la presencia/ausencia de detalles anatómicos.
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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).
The revision of holotypes and paratypes of Lithophyllum contii Mastrorilli, 1967 and Lithophyllum giammarinoi Mastrorilli, 1 968, coming from the Rupelian calcarenitic limestone of the "Molare ...Formation" (Tertiary Piedmont Basin), demonstrates that there are not enough elements to permit the distinction of two different species. So, according to priority, Lp. giammarinoi must be consider junior synonym of Lp. contii, that is here redescribed as Lithophyllum contii Mastrorilli sensu amplo.
La stratigraphie de l'Oligocène d'Aquitaine occidentale est revue en synthétisant les données bibliographiques et en réexaminant 93 sondages, dont 60 sont datés à l'aide de foraminifères ou ...nannofossiles calcaires. La révision de ces sondages a permis de reconstituer l'évolution sédimentaire de l'Aquitaine occidentale en relation avec les évènements tectoniques correspondants. Les petits foraminifères benthiques ont permis d'estimer les variations de la tranche d'eau dans les coupes, qui s'étendent du domaine épibathyal jusqu'au domaine saumâtre. Environ 60 % des foraminifères présents au Priabonien disparaissent au cours de cet étage et à la limite Éocène/Oligocène. L'apparition et la disparition des espèces est progressive dans l'Oligocène, ce qui permet d'en utiliser certaines comme marqueurs pour la stratigraphie du Bassin d'Aquitaine. Les foraminifères du Bassin d'Aquitaine montrent de nombreuses affinités avec ceux de la Paratéthys centrale, indiquant que ces deux régions étaient interconnectées à cette époque par le détroit de Gibraltar et la zone bétique. Sept formations sont retenues dans l'Oligocène marin du Bassin de l'Adour, dont une nouvellement introduite (Formation de Capcosle d'âge Rupélien-Aquitanien) et deux redéfinies (Formation de Biarritz d'âge Rupélien inférieur et Formation d'Escornebéou d'âge Chattien supérieur) ; trois sont distinguées dans le domaine continental (les Formations de Jurançon et de Campagne puis celle de l'Agenais). L'Oligocène de la plate-forme nord-aquitaine comprend deux formations marines (la Formation de Bel-Air et la Formation du Calcaire à Astéries avec le Membre à Crassostrea longirostris à la base) et trois formations continentales (du bas vers le haut : les Formations du Fronsadais, de Castillon et de l'Agenais). Trois grandes aires sédimentaires se différencient au cours de l'Oligocène dans la région aquitaine. La première, entre Labenne et Arcachon, se caractérise par les dépôts à dominance argileuse, bathyaux, épais (jusqu'à 1700 m). La deuxième aire forme un arc de cercle autour de la première et représente la plate-forme avec des sédiments plus variés : calcaires bioclastiques, argiles et sables coquilliers de 400–500 m d'épaisseur. La troisième comprend les sédiments continentaux à l'est et au sud du bassin. Les événements tectoniques pyrénéens influencent la sédimentation, comme le montrent, en premier lieu, la transgression du Rupélien moyen, qui est plus importante au nord qu'au sud, tandis que le phénomène inverse s'observe au Rupélien supérieur, et, deuxièmement, les transgressions du Chattien inférieur et supérieur, qui sont conditionnées par la subsidence locale et la réactivation d'anciennes structures.
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.
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