Reynaldo Charrier

The Tinguiririca Fauna, Chile: Biochronology, paleoecology, biogeography, and a new earliest Oligocene South American Land Mammal 'Age'

Abstract A new South American Land Mammal ‘Age’ (SALMA), the Tinguirirican, is formally established, based on an assemblage of at least 25 taxa from the Chilean Andes (and smaller correlative faunas from Argentine Patagonia) that lies near the Eocene–Oligocene transition. Tinguirirican faunas occur within a previously poorly sampled temporal interval, a significant gap in the SALMA succession, accounting for the very high percentage of taxa that are new. The Tinguirirican includes a suite of taxa not documented to co-occur elsewhere. It is defined by the first stratigraphic occurrences of taxa known elsewhere only from younger beds: caviomorph rodents; interatheriine interatheriids; an otherwise Deseadan and younger clade of notohippids, diagnosed by hypsodont lower incisors; the clade of archaeohyracids including those taxa more closely related to Archaeohyrax than to Pseudhyrax; leontiniids; and the clade of groeberiid marsupials stemming from the most recent common ancestor of Klohnia and Patagonia. Among its numerous noteworthy occurrences, the Tinguiririca Fauna includes the earliest rodents known from South America (documenting that caviomorphs had reached the continent near or before the Eocene/Oligocene boundary, with an African origin for the clade – based on preliminary phylogenetic analysis), an unusual diversity of therian species possessing a ‘gnawing’ dentition, and the world’s oldest mammalian herbivore assemblage dominated by species with hypsodont cheek teeth. The Tinguirirican assemblages indicate that Simpson’s ‘Second Faunal Stratum’ began considerably earlier (prior to the Deseadan) than previously thought. The stratotype sequence for the Tinguirirican SALMA assemblage in Chile has yielded high-precision 40Ar/39Ar radioisotopic dates, as have underlying non-fossiliferous beds. These indicate that the fauna is at least ∼31.5 Ma in age. While it potentially spans a range as large as 31–37.5 Ma or more, various lines of evidence hint that this SALMA is probably of short duration (possibly less than 2 m.y.). Body size distributions (cenograms), dental hypsodonty levels, and macroniche categories are employed to infer paleoenvironmental conditions for the Tinguiririca Fauna. Collectively, these analyses reveal some non-analog aspects of middle Cenozoic South American localities relative to modern systems; that an open, relatively dry habitat (with a mean annual rainfall of 1100 mm or less) was present at Tinguiririca, and that the most dramatic shift in Cenozoic South American paleoecology and paleoenvironment occurred between the Mustersan and Tinguirirican SALMAs. Additionally, the Tinguiririca Fauna is the first Cenozoic mammal assemblage dominated by hypsodont taxa (at levels dramatically higher than those of preceding times). The proportion of hypsodont taxa in modern assemblages correlates positively with the amount of open habitat, indicating that open habitat grassland/woodland environments flourished 15–20 million years earlier in South America than on other continents. Indeed, the Tinguiririca Fauna exhibits a proportion of hypsodont taxa exceeding even that seen in modern open habitats. Such faunas and habitats thus occur in very close proximity to the Eocene/Oligocene boundary and earliest Oligocene climatic ‘deterioration’, and their associated paleoclimatic and paleoenvironmental events. The mid-latitude Tinguiririca Fauna suggests complex biogeographic patterns during the early–middle Cenozoic – while it is decidedly ‘Patagonian’ in taxonomic composition, several members of the fauna hint at close affinities with lower latitude assemblages.

Uplift of the western border of the Altiplano on a west-vergent thrust system, Northern Chile

An air terminal building consisting of an arrival hall and a departure hall and one waiting hall possibly commonly used by both departing and arriving passengers. These halls are situated on separate above each other located levels and with the waiting hall on the top of the other levels and extending principally along the whole periphery of the building. The arrival and departure halls are located in the central portion of the building. The central portion also contains a baggage hall located between the arrival and the departure halls and commonly used for arriving and departing baggage and with direct access to the platform for the airplanes. The halls located in the center of the building are surrounded by wall elements which include therein or therebetween, all principal shafts necessary for the provision of and communication between the separated levels of the building, i.e. shafts for the installation of heating, water, sanitation, electricity and ventilation, lifts, escalators and others. On the same level as the baggage hall are also localities available for provision and service activities, catering a.s.o.

A geomorphological approach to determining the Neogene to Recent tectonic deformation in the Coastal Cordillera of northern Chile (Atacama)

The large (≈10000 km2) and local-scale ( 300 m) sedimentary succession was deposited east of the AFS. The succession fills previously deep paleovalleys. And it consists of gravel, so-called “Atacama Gravels”, which passes laterally into fine-grained playa related deposits near the AFS. We interpret the deposition of this succession as a result of a blocking closure of the valley flowing from the Precordillera due to the activity on AFS. A pedimentation episode followed sediment deposition and is locally strongly re-incised by the main modern-day river valleys draining the Precordillera. Incision may result from either regional uplift of the forearc, and/or from more localized activity on the AFS. Furthermore, Recent (Quaternary?) tectonic activity on the AFS has been observed which is consistent with a localized relative uplift of the crustal block west of the AFS.

Slope and climate variability control of erosion in the Andes of central Chile

Climate and topography control millennial-scale mountain erosion, but their relative impacts remain matters of debate. Confl icting results may be explained by the infl uence of the erosion threshold and daily variability of runoff on long-term erosion. However, there is a lack of data documenting these erosion factors. Here we report suspended-load measurements, derived decennial erosion rates, and 10 Be-derived millennial erosion rates along an exceptional climatic gradient in the Andes of central Chile. Both erosion rates (decennial and millenial) follow the same latitudinal trend, and peak where the climate is temperate (mean runoff ~500 mm yr ‐1 ). Both decennial and millennial erosion rates increase nonlinearly with slope toward a threshold of ~0.55 m/m. The comparison of these erosion rates shows that the contribution of rare and strong erosive events to millennial erosion increases from 0% in the humid zone to more than 90% in the arid zone. Our data confi rm the primary role of slope as erosion control even under contrasting climates and support the view that the infl uence of runoff variability on millennial erosion rates increases with aridity.

New evidence for late mesozoic-early Cenozoic evolution of the Chilean Andes in the upper Tinguiririca valley (35 °S), central Chile

Abstract New geologic, paleontologic and isotopic geochronometric results from the Termas del Flaco region in the upper Tinguiririca River valley in central Chile demand considerable revision of the accepted geotectonic history of the Andean Main Range in this region. A diverse, transitional Eocene-Oligocene aged, land-mammal fauna was recovered from several sites in volcaniclastic sediments of the Coya-Machali (=Abanico) Formation. Major results of our study include: 1) The 1000 + m thick studied deposits, previously attributed to the Cretaceous Colimapu Formation, belong to the Coya-Machali (=Abanico) Formation. Radioisotopic data from levels immediately above (31.5 Ma) and below (37.S Ma) the fossiliferous horizon indicate a latest Eocene to early Oligocene age for the basal part of the formation and the fauna contained in it. 2) The fossiliferous unit rests with slight angular offset on different Mesozoic units: “Brownish-red Clastic Unit” (BRCU) and Banos del Flaco Formation; in a limited area it also overlies a white tuff dated at 104 Ma. 3) The contacts just discussed (none of which is attributable to faulting), demonstrate the existence of two, or possibly three, unconformities in the region. 4) Sedimentological criteria argue against reference of the BRCU to the Colimapu Formation, and imply correlation of the former unit to basal levels with in the late Cretaceous Neuquen Group of western Argentina. 5) The Coya-Machali Formation, previously viewed as representing the western volcanic equivalent of Riogrdndico Supercycle deposits of western Argentino, is likely coeval to much younger units in that region such as the Agua de la Piedra Formation. 6) Paleomagnetic results from the fossil producing horizon indicate about 20 ° of post-early Oligocene, counterclockwise rotation. 7) Fossil mammals from the Coya-Machali Formation near Termas del Flaco represent a distinct biochronologic interval not heretofore clearly recognized from elsewhere on the continent. This new fauna helps fill the long recognized post-?middle Eocene, pre-late Oligocene faunal hiatus between the Mustersan and Deseadan South American Land Mammal Ages (SALMA). In addition, it records the earliest known presence of rodents in South America and otherwise differs strongly from the enigmatic Divisaderan SALMA.

Sedimentación sintectónica asociada a las estructuras neógenas en la Precordillera de la zona de Moquella, Tarapaca (19°15'S, norte de Chile).

En el norte de Chile (18-20°S), el borde occidental del alto Plateau andino (Altiplano) fue alzado por un sistema de fallas inversas de alto angulo y pliegues asociados. Este se desarrollo a lo largo de la Precordillera, que corresponde a la unidad morfoestructural que conecta al Altiplano, al este, y la Depresion Central, al oeste. En la zona de Moquella (19,3°S), ese sistema estructural esta representado por una flexura (Flexura Moquella) y depositos sintectonicos asociados. Esta flexura fue causada por una falla inversa, ciega y con vergencia al oeste, que estuvo activa, al menos, entre los 21 Ma y 16 Ma. Acomodo un total aproximado de 700 m del alzamiento del borde occidental del Plateau andino, contribuyendo de esta manera a casi un 20% de su alzamiento. Los depositos sintectonicos, de 300-400 m de espesor, corresponden a una sucesion sedimentaria y volcanica neogena, denominada Formacion Latagualla, expuesta en la Depresion Central hasta el borde occidental de la Precordillera. Esta formacion registro parte de la deformacion y la erosion neogena del borde occidental del Plateau andino a esta latitud. Las evidencias de su caracter sintectonico corresponden a su geometria en estratos de crecimiento asociados a la flexura. Ademas, sobre el eje de la Flexura Moquella se produjeron deslizamientos de grandes dimensiones que tambien han sido reconocidos mas al norte, en Arica, indicando ser un fenomeno caracteristico de este borde de los Andes.

K-Ar ages of basalt flows of the Meseta Buenos Aires in southern Chile and their relation to the southeast Pacific triple junction

The Meseta Buenos Aires faces the triple junction between the Nazca, Antarctic, and South American plates and consists of two olivine basaltic units separated by two sedimentary units. Seventeen whole-rock K-Ar age determinations gave a minimum age of 57 m.y. (late Paleocene) for the lower unit and ages ranging from 16 to 4.4 m.y. (early Miocene to Pliocene) for the upper unit. The Friasian Land-Mammal Stage sedimentary unit underlying the upper basaltic unit is assigned to the late Oligocene-early Miocene interval, and the marine sedimentary unit underlying the Friasian deposits and overlying the lower basaltic unit is assigned to the Eocene–early Oligocene interval. The lower basaltic unit rests unconformably on a marine fossiliferous sedimentary unit of probable Late Cretaceous to early Paleocene age. The basalts of the Meseta Buenos Aires are alkaline and are associated with andesite flows of tholeiitic character. The lower unit formed while the Farallon plate was being subducted under the South American plate, and any relation between this unit and the triple junction is excluded. The origin of the upper unit could be related to perturbations in the subcrustal mantle caused by the subduction of segments of the Chile Rise. Geochemical considerations, in addition to the fact that both basaltic units formed under different tectonic settings, are consistent with the hypothesis that the origin of the alkali basalts is independent of the environment in which they are found.

Miocene volcanism in the central Chilean Andes (31°30′S–34°35′S)

Abstract The name Farellones Formation is currently used to designate continental Miocene volcanic and volcaniclastic deposits that form a 400 km long and 26–65 km wide, N/S-oriented belt of outcrops located along the central Chilean Andes. These deposits are mainly located east of an Oligocene-Miocene volcanic belt and west of the present volcanic arc. The lava flows and pyroclastics of the Farellones Formation vary in composition from andesitic to rhyolitic and, in lesser proportion, from dacitic to basaltic. Major element geochemistry and some trace elements confirm a typical calc-alkaline nature of the continental margin. The Miocene volcanic activity that formed the Farellones Formation occurred between 19.3 and 7.4 Ma, according to available K/Ar data, but this activity was not totally synchronous along the belt. It is estimated that 15.000 km 3 of effusive material was extruded during this volcanic episode. The main Miocene volcanic activity can be related to an increase in the normal convergence rate between the Nazca and South American plates, which occurred between 26 and 9.6 Ma. The Farellones volcanic belt is not related to the present segmentation of the Nazca plate and thus represents an older Andean segment with a continuous and compositionally homogeneous volcanism possibly related to segmentation of the paleo-subduction zone.

THE FIRST CENOZOIC MAMMAL FAUNA FROM THE CHILEAN ALTIPLANO

Despite its richness, South Americas Cenozoic mammal record is strongly biased geographically towards a small portion of the continent, mainly Patagonia. The rapidly growing list of major Cenozoic localities at lower latitudes thus marks a significant advance in our understanding of mammalian evolution in South America (see summaries in Flynn and Swisher, 1995; Flynn and Wyss, 1998). This paper reports the discovery of the first Cenozoic mammal fauna known from the Chilean Altiplano. It is part of an ongoing collaborative effort to sample faunas of a variety of ages across a large latitudinal transect of western South America, the goal of which is to elucidate temporal patterns of provincialism within the continent, as well as the tectonic and uplift history of the Andes Mountains and associated paleoenvi

Late Miocene–Holocene canyon incision in the western Altiplano, northern Chile: tectonic or climatic forcing?

Abstract: Major fluvial incision (600–1000 m) affecting the Coastal Cordillera and Central Depression of northern Chile is analysed to evaluate supposed coeval uplift of the Altiplano and/or climatic changes in the Atacama Desert. The timing of the beginning of incision is constrained by the age of deposition of the Central Depression top. In the north (18–19°S), this top corresponds to fluvial gravels accumulated between 11.9 ± 0.6 Ma and 8.3 ± 0.5 Ma, which are genetically related to semiarid climate and to an eastward poorly dissected parallel drainage network that developed between 15.0 ± 0.6 and 11.2 ± 0.6 Ma; thus, gravel deposition ended at 11.9–11.2 Ma. To the south (19–20°S), the Central Depression top corresponds to c. 6 Ma alluvial deposits. Stratigraphically determined canyon ages and knickzone locations indicate that southward dissection began later and/or developed under a regime of lower erosion capacity owing to drier climate. Vertical incision rate evolution is compatible with eastward knickzone migration. Dissection required a considerable altitude difference between ancient and present-day river base levels, which was achieved predominantly by basin infill on an already partially elevated bedrock. Therefore subsequent incision would have been triggered by local semiarid climatic periods rather than by contemporaneous surface uplift. Exoreic canyons occur when climatic conditions in the catchments are arid–semiarid whereas endoreism is developed when these conditions in catchments are hyperarid.