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

Evidences for a Paleocene marine incursion in southern Amazonia (Madre de Dios Sub-Andean Zone, Peru)

This article presents new biostratigraphic dating, facies analysis, organic geochemical data and Nd–Sr isotopic provenance from five outcrops of southern Amazonia (MD-85, MD-177 MD-184, MD-255 and MD-256) to document for the first time the presence of a shallow marine ingression in the Paleocene of southern Amazonia basin. The co-occurrence of a selachian assemblage encompassing Potobatis sp., Ouledia sp., and Pristidae indet. with the ostracod Protobuntonia sp. and the charophytes Peckichara cf. varians meridionalis, Platychara perlata, and Feistiella cf. gildemeisteri suggests a Paleocene age for the studied deposits (most likely Thanetian but potentially Danian). Fifteen facies have been recognized and have been grouped into three facies assemblages. Facies association A corresponds to the sedimentary filling of a tide-influenced meandering channel formed in the fluvial–tidal transition zone. Facies association B is related to more distal tidal-flats, little channelized tidal inlets and saltmarsh deposits. Facies association C corresponds to a stressed shallow marine environment such as a bay or a lagoon. The d13CTOC value (- 23.4‰) of MD-184 is enriched in 13C compared to the other samples suggesting the presence of substantial amounts of marine organic matter in MD-184. The d13CTOC values of samples from other outcrops (- 27.3 to - 29.8‰) indicate a mixed organic matter origin, from terrestrial to brackish environments. The analyzed sediments have similar Nd–Sr isotopic compositions as those of the Cenozoic sediments of the Altiplano (eNd(0) values from - 6.2 to - 10.7 and 87Sr/86Sr compositions from 0.712024 to 0.719026) indicating a similar volcanic source. This multidisciplinary dataset documents the presence of a tide-dominated estuary sourced by the proto-Western Cordillera debouching into a shallow marine bay during Paleocene times. This transgression might be explained by subsidence created in response to the proto-Western Cordillera loading. Similar to Miocene marine incursions affecting the Pebas megawetland, Paleogene marine incursions in the Amazonian foreland basin associated with Andean uplift may have played a role in the Neotropical biodiversity dynamics in favoring biogeographical isolation and promoting allopatric speciation for terrestrial organisms

1. Control geológico y climático del sistema Andino-Amazónico y de su biodiversidad

Los excepcionales recursos naturales de la Amazonia son el fruto de una larga historia geológica y climática en la que los Andes juegan un papel determinante. Desde su creación hasta la actualidad, el Impacto de esta cadena montañosa sobre el ambiente de la reglón ha dado forma a las faunas y floras sucesivas y sus distribuciones. Regulador de las precipitaciones y de la fantástica biodiversidad animal y vegetal de la región, el sistema geoclimático andino-amazónico debe ser considerado como un elemento fundamental a la hora de estudiar el impacto del cambio climático en la región.Les ressources naturelles exceptionnelles de l’Amazonie sont le fruit d’une longue histoire géologique et climatique où les Andes jouent un rôle déterminant. Depuis son apparition jusqu’á nos jours, l’impact de cette chaîne de montagne sur l’environnement de la région a donné forme aux faunes et flores successives et leurs distributions. Régulateur des précipitations et de la fantastique biodiversité de la région, le système géo-climatique andino-amazonien doit être considéré comme un élément fondamental si l’on souhaite étudier l’impact du changement climatique dans la région.The extraordinary natural resources of the Amazon region are the result of a long geological and climatic history, where the Andes play a decisive role. This mountain range has impacted on the environment of the region, arraying Flora and Fauna, and its successive distribution since its origin to the present. As a regulator of rainfalls and of the fantastic animal and vegetal biodiversity of the region, the Andean-Amazon geo-climate system must be considered as an essential element to study the Climate Change impact in the region