Facies interpretation and geochronology of diverse Eocene floras and faunas, northwest Chubut Province, Patagonia, Argentina

2020 ◽  
Vol 133 (3-4) ◽  
pp. 740-752
Author(s):  
Justin Gosses ◽  
Alan R. Carroll ◽  
Benjamin T. Bruck ◽  
Brad S. Singer ◽  
Brian R. Jicha ◽  
...  

Abstract The Eocene Huitrera Formation of northwestern Patagonia, Argentina, is renowned for its diverse, informative, and outstandingly preserved fossil biotas. In northwest Chubut Province, at the Laguna del Hunco locality, this unit includes one of the most diverse fossil floras known from the Eocene, as well as significant fossil insects and vertebrates. It also includes rich fossil vertebrate faunas at the Laguna Fría and La Barda localities. Previous studies of these important occurrences have provided relatively little sedimentological detail, and radioisotopic age constraints are relatively sparse and in some cases obsolete. Here, we describe five fossiliferous lithofacies deposited in four terrestrial depositional environments: lacustrine basin floor, subaerial pyroclastic plain, vegetated, waterlogged pyroclastic lake margin, and extracaldera incised valley. We also report several new 40Ar/39Ar age determinations. Among these, the uppermost unit of the caldera-forming Ignimbrita Barda Colorada yielded a 40Ar/39Ar age of 52.54 ± 0.17 Ma, ∼6 m.y. younger than previous estimates, which demonstrates that deposition of overlying fossiliferous lacustrine strata (previously constrained to older than 52.22 ± 0.22 Ma) must have begun almost immediately on the subsiding ignimbrite surface. A minimum age for Laguna del Hunco fossils is established by an overlying ignimbrite with an age of 49.19 ± 0.24 Ma, confirming that deposition took place during the early Eocene climatic optimum. The Laguna Fría mammalian fauna is younger, constrained between a valley-filling ignimbrite and a capping basalt with 40Ar/39Ar ages of 49.26 ± 0.30 Ma and 43.50 ± 1.14 Ma, respectively. The latter age is ∼4 m.y. younger than previously reported. These new ages more precisely define the age range of the Laguna Fría and La Barda faunas, allowing greatly improved understanding of their positions with respect to South American mammal evolution, climate change, and geographic isolation.

1873 ◽  
Vol 163 ◽  
pp. 19-94 ◽  

The paper which I lay before the Society is an attempt to treat with sufficient osteological detail an extinct family of Ungulates which had an immense range of distribution and a great variety of forms in the two periods of the earth’s history which preceded our own. The fate this family has met with at the hands of palæontologists is a somewhat sad one, presenting a warning example of the unscientific method that was paramount in the palæontology of the Mammalia after the time of Cuvier. With the exception of England, where here the study of fossil Mammalia was founded on a sound basis, and some glorious exceptions on the continent, we have very few good palæontological memoirs in which the osteology of extinct mammals has been treated with sufficient detail and discrimination; and things have come to such a pass, that we know far better the osteology of South American, Australian, and Asiatic genera of fossil mammals than of those found in Europe. Nearly all fossil Mammalia which have been described in detail belong to genera that still exist on our globe, or whose differences from fossil forms are trifling. After the splendid osteological investigations of Cuvier had revealed to science a glimpse of a new mammalian world of wonderful richness, his successors have been bent rather on multiplying the diversity of this extinct creation, than on diligently studying the organization of the fossil forms that successively turned up under the zeal of amateurs and collectors. From the year 1828, and even before, when Laizer, Pomel, Croiset, and others began to give short notices on the Mammalia of Auvergne, mammalian genera and species from this locality have been multiplied at a prodigious rate, every private collector giving his own generic and specific names, with no better description than stating the real or supposed number of teeth, and some phrases as to the general resemblances of the fossil in question. Others substituted in their short notices other names, while the scientific work of description did not proceed further than the mere counting of the number of teeth. This process has given rise to such an utter confusion in the palæontology of the extinct Paridigitata, that even now (forty years after the date of the earliest notices) we are utterly ignorant of the true extent and organization of the Miocene mammalian fauna of Auvergne, for instance—though materials for a detailed study of the subject abound in all great public, and many private, collections, the fossils being very common. No palæontologist, even of the highest standing, could boast of knowing, in our own time what Dremotherium, Dorcatherium, Elaphotherium, Gelocus , and so on really are, what are the bones belonging to each set of teeth (as the names were mostly given to these last), whether they had horns or were hornless like the Tragulidæ , and so on. If we add that German authors described the genera of Paridigitates which were found and named in France under different names (as Palæomeryx , Microtherium , Hyotherium , and so on), when they came from German localities, the confusion may be guessed. Having no good descriptions and no figures of the genera noticed in France, the German authors almost necessarily fell into the mistake of renaming what was already named. Once named, the genus was allowed to go forth with the short and wholly insufficient characteristics given to it by the first describer, the impossibility of adding one’s name after the generic or specific designation seeming to take all interest from it. And this, moreover, is the best case; for frequently the same form was described by an other palæontologist under a different generic name, or, if this was Utterly impossible, a new species was made of it, founded on some difference in size or other trifling character. Happily, however, a reaction began to set in, one of the first to head it on the Continent being Rütimeyer, who did not confine his study merely to the teeth of fossil Mammalia, but aimed with brilliant success at a complete investigation of the osteology of the extinct genera and of their affinities with the living ones. Gaudry’s work on the fossils of Pikermi (the best palæontological work that has appeared in France since Cuvier’s 'Ossemens Fossiles’), Fraas’s 'Fauna von Steinheim,’ Alphonse Milne-Edwards’s 'Oiseaux Fossiles,’ and many others may be cited as examples to prove that the new tendency has fairly set in and will bear good fruit. The wide acceptance by thinking naturalists of Darwin’s theory has given a new life to palæontological research; the investigation of fossil forms has been elevated from a merely inquisitive study of what were deemed to be arbitrary acts of creation to a deep scientific investigation of forms allied naturally and in direct connexion with those now peopling the globe, and the knowledge of which will remain imperfect and incomplete without a thorough knowledge of all the forms that have preceded them in the past history of our globe.


2019 ◽  
Vol 157 (4) ◽  
pp. 539-550
Author(s):  
Gabriela Torre ◽  
Guillermo L. Albanesi

AbstractThe presence of a carbonate platform that interfingers towards the west with slope facies allows for the identification of an ancient lower Palaeozoic continental margin in the Western Precordillera of Argentina. The Los Sombreros Formation is essential for the interpretation of the continental slope of the Precordillera, which accreted to Gondwana as part of the Cuyania Terrane in the early Palaeozoic. The age of these slope deposits is controversial; therefore, a precise biostratigraphic scheme is critical to reveal the evolution of the South American continental margin of Gondwana. The study of lithic deposits of two sections of the Los Sombreros Formation, the El Salto and Los Túneles sections, provides important information for further understanding the depositional history of the slope. At El Salto section, the conodonts recovered from an allochthonous block refer to the Cordylodus proavus Zone (upper Furongian). The conodonts recovered from the matrix of a calclithite bed of the Los Sombreros Formation in the Los Túneles section are assigned to the Lenodus variabilis Zone (early Darriwilian), providing a minimum age for this stratigraphic unit. In addition, clasts from this sample yielded conodonts from the Paltodus deltifer − Macerodus dianae zones (upper Tremadocian). The contrasting conodont colour alterations and preservation states from the elements of two latter records, coming from the same sample, argue the reworked clasts originated in the carbonate platform and later transported to the slope during the accretion process of the Precordilleran Terrane to the South American Gondwanan margin during the Middle–Late Ordovician.


Radiocarbon ◽  
2012 ◽  
Vol 54 (01) ◽  
pp. 123-136 ◽  
Author(s):  
T Kuc ◽  
K Różański ◽  
M J Kotarba ◽  
T Goslar ◽  
H Kubiak

New attempts arc presented to determine the age of large Pleistocene mammals excavated at Starunia, ∼130 km southeast of Lviv, Ukraine. This remarkable discovery made at the beginning of the 20th century included a complete carcass of woolly rhinoceros (No. 2), fragments of 3 woolly rhinoceroses (Nos. 1, 3, and 4) and remnants of numerous specimens of other fossil fauna and flora. Although attempts to date paleontological findings from Starunia site go back to the early 1970s, the results obtained before 2006 arc somewhat misleading, mostly due to unresolved contamination problems. Comprehensive cleaning of the samples adopted in the framework of this study was aimed at removal of 2 potential sources of contamination: (i) radiocarbon-free hydrocarbons abundant at the burial site; and (ii) allochthonous organic materials containing contemporary carbon that were used in the past during preservation of the dated specimens. Two types of samples have been analyzed for their14C content in the framework of the present study: (i) fragments of bones and teeth collected from specimens stored or exposed in the Natural History museums in Lviv and Kraków; and (ii) samples of terrestrial macrofossils retrieved from sediment cores obtained during the 2007–2008 field campaigns in the Starunia area.14C analyses of collagen were supplemented by measurements of its elemental C/N ratio and13C/12C and15N/14N isotope ratios. Three14C dates obtained for rhinoceros No. 2 span the age range from 35.3 to 40.0 ka BP, in agreement with the minimum age estimated from macrofossils. The mean value of 37.7 ± 1.7 ka BP falls in the range of ages reported for big Pleistocene mammals from other locations in Europe. The bones of rhinoceros No. 3, which were found in close vicinity to those of rhinoceros No. 2, reveal a14C age of 36.7 ± 0.6 ka BP. The δ15N and δ13C values obtained for collagen extracted from bones and teeth belonging to rhinoceroses Nos. 1, 2, and 3 are in a broad agreement with analogous literature data for large Pleistocene mammals found in other sites in Europe, North America, and Siberia.


2020 ◽  
Author(s):  
Sumiko Tsukamoto ◽  
David Tanner ◽  
Christian Brandes ◽  
Christoph von Hagke

<p>For a better understanding of the recent exhumation history of the Alps and the distribution of palaeo- and recent earthquakes within the orogen, it is important to elucidate the Quaternary activity of major faults. In this study, we test the applicability of luminescence and electron spin resonance (ESR) dating, which have ultralow closure temperatures, to directly date fault gouge of the Simplon Fault. A dark grey to black, fine-grained fault gouge was sampled near Visp, Switzerland, from an outcrop that exposes rocks that formed at ductile/brittle conditions. Quartz and feldspar grains were extracted from the sample; quartz grains were used for ESR dating, whereas feldspar grains were used for infrared stimulated luminescence (IRSL) dating.</p><p>The IRSL measurements reveal that the natural post-IR IRSL signal, stimulated at 225°C (pIRIR<sub>225</sub>) was in saturation. The pIRIR<sub>225</sub> signal had an extremely low saturation dose, with a characteristic saturation dose (D<sub>0</sub>) of ~90 Gy. The natural IRSL signal at 50°C (IR<sub>50</sub>) is about 80 % of the laboratory saturation, so that this signal is presumably in the field saturation. The IR<sub>50 </sub>also showed a small D<sub>0</sub> of ~250 Gy. Although these D<sub>0</sub> values are unexpectedly small, the IRSL signals can be used to calculate the minimum age of the last seismic movement of the fault.</p><p>Both natural and laboratory-irradiated ESR spectra did not contain detectable Ti centre. Therefore, only the Al centre was used for ESR dating. The natural Al centre from the fault was not in saturation, with a preliminary equivalent dose value of ~1500 Gy. Since the last seismogenic movement most likely only partially reset the Al centre, the ESR age can be regarded as the maximum age of the last event.  We show that by combining luminescence and ESR dating, it is possible to narrow down the age range of the last seismic activity on the fault.</p>


2017 ◽  
Vol 54 (5) ◽  
pp. 512-528 ◽  
Author(s):  
John A. Percival ◽  
William J. Davis ◽  
Michael A. Hamilton

Paleoproterozoic metasedimentary successions of the northwestern Canadian Shield provide records of tectonic events, but the definition of depositional ages has proved elusive. Although previously poorly understood, the Montresor belt of western Nunavut yields new insight into the 2.2–1.8 Ga time window. On the basis of U–Pb analyses of detrital zircon in sedimentary rocks and igneous zircon in sills, we conclude that arenite of the lower Montresor group was deposited between 2.194 and 2.045 Ga, and arkose of the upper Montresor group after 1.924 Ga, adding constraints on the Rae cover sequence. The lower Montresor arenite yielded an older group (3.05–2.58 Ga) and a younger, more tightly constrained group (2.194 ± 0.014 Ga). Four of six zircon grains analyzed from a gabbro sill within the lower Montresor have discordant 207Pb/206Pb ages (2.71, 2.66, 2.53, and 2.39 Ga) and are considered to be inherited, whereas two grains provide an age of 2045 ± 13 Ma, interpreted to date crystallization and providing a minimum age for the lower Montresor package. Upper Montresor arkose contains detrital zircon with probability density peaks at 2.55–2.25 and 2.1–1.92 Ga, together with scattered older grains (3.8–2.65 Ga). The youngest grain yields an age of 1924 ± 6 Ma, establishing a maximum age for sandstone deposition. Provenance is inferred to have been from the west, where igneous sources of 2.5–2.3 Ga (Queen Maud block) and 2.03–1.89 Ga (Thelon orogen) are known. Collectively, the new ages suggest a minimum 120 million year gap between deposition of the pre-2045 ± 13 Ma lower and post-1924 ± 6 Ma upper parts of the Montresor group. Similar age constraints may apply to other parts of the Rae cover sequence.


2006 ◽  
Vol 43 (5) ◽  
pp. 571-591 ◽  
Author(s):  
Daniela A Vallini ◽  
William F Cannon ◽  
Klaus J Schulz

A geochronological study of the Chocolay Group at the base of the Paleoproterozoic Marquette Range Supergroup in Michigan, Lake Superior Region, is attempted for the first time. Age data from detrital zircon grains and hydrothermal xenotime from the basal glaciogenic formation, the Enchantment Lake Formation, and the stratigraphically higher Sturgeon Quartzite and its equivalent, the Sunday Quartzite, provide maximum and minimum age constraints for the Chocolay Group. The youngest detrital zircon population in the Enchantment Lake Formation is 2317 ± 6 Ma; in the Sturgeon Quartzite, it is 2306 ± 9 Ma, and in the Sunday Quartzite, it is 2647 ± 5 Ma. The oldest hydrothermal xenotime age in the Enchantment Lake Formation is 2133 ± 11 Ma; in the Sturgeon Quartzite, it is 2115 ± 5 Ma, and in the Sunday Quartzite, it is 2207 ± 5 Ma. The radiometric age data in this study implies the depositional age of the Chocolay Group is constrained to ~2.3–2.2 Ga, which proves its correlation with part of the Huronian Supergroup in the Lake Huron Region, Ontario, and reveals the unconformity that separates the Chocolay Group from the overlying Menominee Group is up to 325 million years in duration. The source(s) of the ~ 2.3 Ga detrital zircon populations in the Enchantment Lake Formation and Sturgeon Quartzite remains an enigma because no known rock units of this age are known in the Michigan area. It is speculated that once widespread volcano-sedimentary cover sequences in Michigan were removed or concealed prior to Chocolay Group deposition. The hydrothermal xenotime ages probably reflect basinal hydrothermal fluid flow associated with the period of extension, involving rifting and major dyke formation, that affected the North American provinces between 2.2 and 2.1 Ga.


2021 ◽  
Author(s):  
A.V. Anderson ◽  
K.E. Meisling

<div>Describes the organization, sedimentology, and depositional environments of the Ulungarat Basin succession including description of type sections of the Ulungarat and Mangaqtaaq formations. Table S1 documents published fossil and radiometric age constraints used to construct the mid-Paleozoic tectonostratigraphic chart (Fig. 12), including basis for age assignment and list of source references. A reference list of all sources cited in Table S1 is included.<br></div>


2021 ◽  
Author(s):  
A.V. Anderson ◽  
K.E. Meisling

<div>Describes the organization, sedimentology, and depositional environments of the Ulungarat Basin succession including description of type sections of the Ulungarat and Mangaqtaaq formations. Table S1 documents published fossil and radiometric age constraints used to construct the mid-Paleozoic tectonostratigraphic chart (Fig. 12), including basis for age assignment and list of source references. A reference list of all sources cited in Table S1 is included.<br></div>


2019 ◽  
Vol 46 (2) ◽  
pp. 383
Author(s):  
José I. Cuitiño ◽  
Sergio F. Vizcaíno ◽  
M. Susana Bargo ◽  
Inés Aramendía

Lago Posadas is located at the foot of the Southern Patagonian Andes, in southwestern Argentina, where the early Miocene Santa Cruz Formation (SCF) shows thick and laterally continuous exposures. This region has been scarcely explored for fossil vertebrates since the first efforts by J.B. Hatcher in 1898-99. In this contribution, we performed sedimentologic and paleontological studies in order to reconstruct depositional environments and the associated fossil vertebrate fauna. Sedimentologic data suggest that the sedimentary record begins with restricted marine-estuarine deposits grading upward to fluvial floodplains and fluvial channels. Extensive floodplains, occasionally interrupted by low-sinuosity, sand-dominated channels, show dominant reddish coloration, moderate to low paleosol development, abundant crevasse splay sandstones and lack of vegetal remains, suggesting deposition in a low gradient, oxygenated setting under elevated sedimentation rates. Vertical stratigraphic trends are subtle, suggesting little paleoenvironmental changes during deposition of the whole SCF in this region. Paleocurrent directions, sandstone composition and paleogeographic reconstructions all indicate that deposition of the SCF was strongly associated to the contemporaneous uplift of the Andes. Fossil vertebrates analyzed are the result of our collecting effort and revision of museum collections. The faunal assemblage includes 31 taxa: 28 mammals and three birds. Mammals belong to the main groups recorded in other areas of the SCF (metatherians, xenarthrans, notoungulates, litopterns, astrapotheres and rodents). The assemblage allows a Santacrucian Age sensu lato assignment for the fauna at Lago Posadas. Taxonomic revisions of several taxa are necessary to further adjust the biostratigraphic significance of this association. The combined record of arboreal, browser and frugivores, on one side, and grazer mammals and rheas, on the other, suggest the presence of both trees and open environments. Frugivores, among primary consumers, and the secondary consumers guild are under-represented due to sample and fossil remain size biases. The sedimentologic and paleontological record of the SCF in Lago Posadas suggests that the uplift of the Southern Patagonian Andes acted as a primary control on basin subsidence and sediment supply, providing a special signature for sub-andean localities. However, previously registered climatic changes are poorly recorded in this study.


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