Miocene semidiurnal tidal rhythmites in Madre de Dios, Peru: Reply

Hoorn et al. commented on the following aspects of our 2005 Geology article: 1) the age of the sediments, 2) the interpreted brackish water affi nity of the studied deposits, and 3) the possible connection between Paraná and western Amazonia depositional systems during the late Miocene

Middle Miocene vertebrates from the Amazonian Madre de Dios Subandean Zone, Perú

A new middle Miocene vertebrate fauna from Peruvian Amazonia is described. It yields the marsupials Sipalocyon sp. (Hathliacynidae) and Marmosa (Micoureus) cf. laventica (Didelphidae), as well as an unidentified glyptodontine xenarthran and the rodents Guiomys sp. (Caviidae), “Scleromys” sp., cf. quadrangulatus-schurmanni-colombianus (Dinomyidae), an unidentified acaremyid, and cf. Microsteiromys sp. (Erethizontidae). Apatite Fission Track provides a detrital age (17.1 +- 2.4 Ma) for the locality, slightly older than its inferred biochronological age (Colloncuran-early Laventan South American Land Mammal Ages: ~15.6e13.0 Ma). Put together, both the mammalian assemblage and lithology of the fossil-bearing level point to a mixture of tropical rainforest environment and more open habitats under a monsoonal-like tropical climate. The fully fluvial origin of the concerned sedimentary sequence suggests that the Amazonian Madre de Dios Subandean Zone was not part of the Pebas mega-wetland System by middle Miocene times. This new assemblage seems to reveal a previously undocumented “spatiotemporal transition” between the late early Miocene assemblages from high latitudes (Patagonia and Southern Chile) and the late middle Miocene faunas of low latitudes (Colombia, Perú, Venezuela, and ?Brazil)

Provenance of the middle Jurassic-Cretaceous sedimentary rocks of the Arequipas basin (South Peru) and implication for the geodynamic evolution of the Central Andes

The southern Peruvian margin is considered a type locality for long-lived, active continental margin and has been the site of almost continuous subduction since at least the Cambrian. Following Triassic rifting, the southern Peruvian margin is supposed to have experimented extensional backarc setting but definitive evidences are scarce. Unlike other margin, the southern Peruvian margin has not been modified by terrane accretion since the onset of subduction and hence the sedimentary rocks of its adjacent basin may have the potential to record the geodynamic history of the margin between the Mitu Triassic rifting episode and the late Cretaceous onset of compression. In this study, we investigate the provenance of middle Jurassic–Santonian sedimentary rocks deposited in the Southern Peruvian Arequipa basin based on the measurement of 42 Sr-Nd isotopic composition, 993 U-Pb zircons ages and 232 Lu-Hf isotopes. The middle Jurassic formation (Puente and Cachios formations) have mean ÎμNd (0) values between from -8.5 (standard deviation (STD): 0.76) and -9.6 (STD:3.05) and are dominated by Brazilian/Pampean (0.5-0.7 Ga) Greenville/Sunsas (0.9–1.3 Ga) zircon U-Pb peak age which suggest an Eastern Cordillera provenance. An eastern provenance is also confirmed by the presence of juvenile to evolved nature of Hf isotopic Permian zircons that may be sourced by the the Eastern Cordillera. The Labra formation is marked by the first appearance of Triassic-Jurassic zircons from the Chocolate formation and by a strong increase in Famatinian zircon contribution but has similar other zircon age population contributions and Æ•Nd(t=0) values to those of the middle Jurassic formations thus suggesting a mixed provenance between Eastern Cordilera and/or Altiplano and Coastal Cordillera sources. The Titonian Gramadal Formation show similar Æ•Nd(t=0) values but distinct U-Pb zircon age pattern with almost similar contribution from all Precambrian sources of the Amazon craton and Eastern Cordillera which suggest a main source located in the Eastern Cordillera or in the Amazon craton. The presence of Jurassic zircons and dominance of Greenville/Sunsas and Brazilian/Pampean zircons population suggest a mixed provenance with sources located both in Coastal and Eastern cordilleras for the Hualhuani formation (Berrasian). Finally, the Santonian Chilcane Formation has the highest Æ•Nd(t=0) value (-5.5) and is characterized by strong contribution of Andean volcanic arc zircon, Jurassic, Permian, and Famatinian zircons which suggest a that these sedimentary rocks are mainly alimented by the Coastal Cordillera. Our multidisciplinary provenance dataset suggests that the middle Jurassic to early Cretaceous sedimentary rocks of the Arequipa basin are predominantly sourced by the Eastern Cordillera and to a lesser extent by the Coastal Cordillera. These associated with recent reevaluation of the depositional setting of the Jurassic to early cretaceous formation and the cumulative proportion curves of zircon age distribution suggest that the Arequipa basin tectonic setting is not that of backarc setting but rather reflect a rift like setting

Provenance sedimentary from Arequipa – Tarapacá Basin, based on U-Pb detrital zircons, and Sm-Nd isotopes: implications for southwestern of Gondwana

The beginning of the subduction processes began approximately ~ 530 Ma (Cawood et al., 2005), where an intense magmatism was manifested in the Ordovician that ends at the end of the Devonian (Chew et al., 2007), followed by a process of quiescence magmatic during the Pennsylvanian. The Permico is an assembly of Gondwana where heat accumulation in the Triassic led to a distensive period on a continental scale, which produced the generation of rift processes (i.e. Rift Mitu, Spikings et al., 2016). The closing of the Mitu rift is the reflection of the beginning of an oblique subduction, produced by the subduction of the Farallón oceanic plate under the South American continental plate, this subduction process is known as the beginning of the "Andean Cycle" (Romeuf et al., 1995, Boekhout et al., 2013, Haschke et al., 2006, Ramos & Aleman, 2000, Oliveros et al., 2006). This period is mainly marked by important processes of distention that gave rise to synchronous Mesozoic basins that developed in Western Gondwana. These distension processes were generated by negative roll-back processes (Ramos & Mpodozis., 1989). The Arequipa - Tarapacá basin (Vicente et al., 2006), is an extensive basin developed between 10 ° - 22 ° Lat. South. Where the present work is based on the establishment of sedimentary provenience, for the classic stratotype described by (Jenks, 1945; Vicente et al., 1981) in the valley of the Yura river where approximately ~ 5km of Mesozoic sediments emerge. The present work is based on the presentation of unpublished data of U-Pb in detrital zircons as, Sm-Nd geochemistry in total rock for said sediments. Based on this methodology, we will establish provenance of sediments of the Yura group, as well as the paleogeography of Mesozoic sediments in this portion of the Central Andes

A 60-million-year Cenozoic history of western Amazonian ecosystems in Contamana, eastern Peru

Weprovide a synopsis of ~60million years of life history in Neotropical lowlands, based on a comprehensive survey of the Cenozoic deposits along the Quebrada Cachiyacu near Contamana in PeruvianAmazonia. The 34 fossilbearing localities identified have yielded a diversity of fossil remains, including vertebrates,mollusks, arthropods, plant fossils, and microorganisms, ranging from the early Paleocene to the lateMiocene–?Pliocene (N20 successive levels). This Cenozoic series includes the base of the Huchpayacu Formation (Fm.; early Paleocene; lacustrine/ fluvial environments; charophyte-dominated assemblage), the Pozo Fm. (middle + ?late Eocene; marine then freshwater environments; most diversified biomes), and complete sections for the Chambira Fm. (late Oligocene–late early Miocene; freshwater environments; vertebrate-dominated faunas), the Pebas Fm. (late early to early late Miocene; freshwater environments with an increasing marine influence; excellent fossil record), and Ipururo Fm. (late Miocene–?Pliocene; fully fluvial environments; virtually no fossils preserved). At least 485 fossil species are recognized in the Contamana area (~250 ‘plants’, ~212 animals, and 23 foraminifera). Based on taxonomic lists from each stratigraphic interval, high-level taxonomic diversity remained fairly constant throughout themiddle Eocene–Miocene interval (8-12 classes), ordinal diversity fluctuated to a greater degree, and family/species diversity generally declined, with a drastic drop in the early Miocene. The Paleocene–?Pliocene fossil assemblages from Contamana attest at least to four biogeographic histories inherited from (i) Mesozoic Gondwanan times, (ii) the Panamerican realm prior to (iii) the time of South America’s Cenozoic “splendid isolation”, and (iv) Neotropical ecosystems in the Americas. No direct evidence of any North American terrestrial immigrant has yet been recognized in the Miocene record at Contamana.Facultad de Ciencias Naturales y Muse

Сверхлегкие генераторные модули для КВЧ-терапии

Разработаны миниатюрные генераторные модули для КВЧ-терапии, лег-ко фиксируемые в любом месте тела пациента. Могут быть использованы не только в медицине

Geochemistry of Upper Birimian sediments (major and trace elements and Nd-Sr isotopes) and implications for weathering and tectonic setting of the Late Paleoproterozoic crust

International audienceThe Upper Birimian (Paleoproterozoic) formations consist mainly of a detrital sedimentary pile intercalated with calc-alkaline volcanites that were accreted during the Eburnean orogeny (similar to 2.1 Ga). The sediments of the Upper Birimian group were analyzed for their major and trace elements concentrations and their Nd-Sr isotopic compositions. The shales are enriched in Al2O3 and K2O relative to PAAS and depleted in the other mobile major elements and LILE whereas the fe-shales show enrichments in CaO and MnO and depletions in Al2O3 and K2O relative to PAAS but have similar depletion in LILE. Together with the subarkose samples, the shales have undergone significant post-depositional K metasomatism as indicated in the A-CN-K diagram. The calculated pre-metasomatism CIA values (83-92) indicates a high degree of source weathering compatible with steady-state weathering under tropical to subtropical conditions. The fe-shales have lower CIA values (46-57) reflecting less intense weathering conditions. Low Eu anomalies and Th/Sc ratios combined with high Cr/Th ratios for certain samples indicate a significant input of basic detritus for the analyzed sediments. Provenance modeling indicates that the shales are best modeled with a mixture having 75% basalt (75B) and 25% granite (25G). The fe-shales have a similar provenance with their compositions being modeled with a 80B 20G mixture. The epsilon(Nd) values of selected shales, calculated at 2.1 Ga, the age of the deposition, vary from -2.8 to -8.6, which indicate that the sediment received 60-100% of its detritus from a juvenile Birimian volcanic arc. Therefore, the Birimian sediments deposited within an active continental margin setting mostly supplied by the adjacent volcanic are

Transition des stades alimentés à suralimentés dans les systèmes de rétro-bassin d'avant-pays (du bassin amazonien)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Miocene tidal-influenced sedimentation to continental Pliocene sedimentation in the forebulge backbulge depozones of the Beni Mamore foreland Basin (northern Bolivia)

International audienceMio-Pliocene deposits of the forebulge backbulge depozones of the Beni-Mamore foreland Basin indicate tidally to fluvially dominated sedimentation. Seven facies assemblages have been recognized: FAA FAG. FAA represents a distal bottom lake assemblage, FAB and FAD are interpreted as tidal flat deposits, FAC and FAG are interpreted as fluvial systems, FAE sediments are deposited in a subtidal/shoreface setting, and FAG represents a meandering fluvial system. The identification of stratigraphic surfaces (SU, MFS, and MRS) and the relationship among the facies assemblages permit the characterization of several systems tracts: a falling-stage systems tract (FSST) followed by a lowstand systems tract (LST), a transgressive systems tract (TST), and a highstand systems tract (HST). The FSST and LST may have been controlled by the uplift of the Beni-Mamore forebulge, whereas TST may result from a quiescent stage in the forebulge. Subaerial unconformity two (SU2) records the passage from a tide-influenced depositional system to a fully continental depositional system. The Miocene tidal-influenced deposits in the Beni Mamore Basin suggest that it experienced a connection, either with the South Atlantic Ocean or the Caribbean Sea or both