No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Reconstruction of a fossil forest reveals details of the palaeoecology, palaeoenvironments and climatic conditions in the late Oligocene of South America
Abstract
This research focuses on the three-dimensional reconstruction of an in situ forest based on fossil
wood assemblages recovered in the Rancahué Formation (Upper Oligocene), Neuquén, Argentina.
Atherospermataceae, Lauraceae, Nothofagaceae, Eucryphiaceae, Cunoniaceae and Myrtaceae
specimens are described. The mapping of a forest floor section and in situ tree diameters enabled
the estimation of the following palaeoecological quantitative data: tree density, dominance, basal
area, biomass, diametric classes, canopy height, and age classes. Palaeoclimatical data was
determined on the basis of physiognomic anatomical features using multivariate anatomical
analyses. These results were compared with other proxies including Carlquist’s index, Coexistence
Approach (CA), Nearest Living Relatives (NLRs), and growth-rings analyses. The structural data
from the Aluminé forest inferred from these analyses includes: tree density of 463–701 tree/ha,
mean height of 15.22 m, dominance of the genus Nothofagoxylon ( 89.66 m2/ha), total basal area of
158.20 m2/ha, biomass between 43 and 712 tn/ha and mean age of 223 years (specimens between 31
and 700 years old). These results are comparable to those of mature low-to-middle altitude extant
forests dominated by Nothofagus and developed under humid-temperate conditions. Based on the
NLRs method, the Aluminé forest has a floristic composition similar to the present-day Valdivian
forest. The persistence of Nothofagus as the dominant element in temperate rainforests correlates
with regimes where large-scale disturbances, such as volcanism and earthquakes are prevalent. The
fossil taxa are closely related to the extant Laurelia, Persea, Eucryphia, Nothofagus, Weinmannia,
Myrceugenia and Luma. The forest shows intermixed deciduous and evergreen elements, and taxa
with shade-intolerance and intermediate shade tolerance. Also, the majority of these taxa need soils
with available water. The integrated analysis of multiple sets of proxy data suggests that the late
Oligocene forest grew under temperate and humid climate, while the eco-anatomical features and
sedimentary data provide information about the environmental stress conditions of its development
and the violent causes of burial.
... Myrceugenellites has four species: Two are from the Oligocene-Miocene of Patagonia, M. maytenoides and M. oligocenum Pujana (Nishida et al. 1988;Pujana 2009a;Brea et al. 2015) and are very similar between them; they mainly differ in the ray cell width. The third, M. grandiporosum Ruiz et al., is from the Paleocene of Patagonia and has poorly marked growth ring boundaries and vessels wider and in much lesser density than M. maytenoides (Ruiz et al. 2020). ...
... Nishida et al. (1981bNishida et al. ( , 1984b Perforation plates simple and some scalariform; idioblasts with crystals Mallotoxylon Lakhanpal & Dayal Lakhanpal & Dayal (1964) Axial parenchyma diffuse-in-aggregates and abundant Maloidoxylon Grambast-Fessard Grambast-Fessard (1966) the alternate intervessel pitting and mainly uniseriate rays observed in the specimen from Corcovado, it was placed in Nothofagoxylon ruei following Poole (2002). This fossil species (including its synonyms) was previously found in several Eocene-Miocene localities of Patagonia (Cozzo 1950;Salard 1961;Ancibor 1990;Pujana 2009b;Brea et al. 2015;Pujana et al. 2023). Pujana et al. (2023) discussed this fossil species' affinity to any concrete living species and concluded that it is not clear up to now but shares many characteristics with Nothofagus subgenera Nothofagus and Fuscospora. ...
... From the middle Eocene up to today the genera of fossil wood types found in Patagonia remain more or less constant (Pujana 2022). Podocarpaceae usually dominates among conifers, and Nothofagaceae, Myrtaceae, and Cunoniaceae appear to be the most common families in the wood assemblages (Pujana 2009a, b;Brea et al. 2015;Pujana & Ruiz 2019;Pujana et al. 2023). All the fossil genera of angiosperms found in Corcovado were previously found in other Patagonian studies. ...
Angiosperm fossil woods of putative Eocene age from Corcovado, Chubut Province are described. They are placed in four taxonomic units: Weinmannioxylon trichospermoides and cf. Caldcluvioxylon of the Cunoniaceae, Myrceugenellites maytenoides of the Myrtaceae, and Nothofagoxylon ruei of the Nothofagaceae. The taxa in the assemblage are in accordance with similar fossil wood assemblages previously described from the Eocene and Oligocene of Patagonia. All the taxa are anatomically similar to trees that live today in Patagonia. Some of the woods show decay patterns by different saproxylic organisms. These include arthropod borings with coprolites and fungal remains in fungi-decayed tissues that are consistent with an active saproxylic community involved in the recycling of wood in the depositional paleoenvironment.
... (11) W. multiperforatum (Petriella, 1972; Cerro Bororo, Chubut, Argentina; Paleocene). (12) W. multiperforatum (Brea et al., 2015;Rancahue Formation, Neuquen, Argentina;Oligocene). (13,14) Racemofructus fasciculatus gen. et sp. ...
... (Poole et al., 2000), while Pujana et al. (2018) considered Weinmannioxylon trichospermoides similar to wood of several species in Weinmannia s.l. Weinmannioxylon multiperforatum (the type species) and Weinmannioxylon pluriradiatum, also considered similar to wood of Weinmannia s.l. and Cunonia (Petriella, 1972;Brea et al., 2015), EOCENE CUNONIACEAE INFRUCTESCENCES FROM PATAGONIA | 997 have been found at several Paleogene localities in Chubut and Neuquén provinces in Argentina (Petriella, 1972;Raigemborn et al., 2009;Brea et al., 2015;Jud and Gandolfo, 2021). One Neogene occurrence of wood from the Falkland (Malvinas) Islands has been assigned to cf. ...
... (Poole et al., 2000), while Pujana et al. (2018) considered Weinmannioxylon trichospermoides similar to wood of several species in Weinmannia s.l. Weinmannioxylon multiperforatum (the type species) and Weinmannioxylon pluriradiatum, also considered similar to wood of Weinmannia s.l. and Cunonia (Petriella, 1972;Brea et al., 2015), EOCENE CUNONIACEAE INFRUCTESCENCES FROM PATAGONIA | 997 have been found at several Paleogene localities in Chubut and Neuquén provinces in Argentina (Petriella, 1972;Raigemborn et al., 2009;Brea et al., 2015;Jud and Gandolfo, 2021). One Neogene occurrence of wood from the Falkland (Malvinas) Islands has been assigned to cf. ...
Premise:
Two distinct types of fossil infructescences from the early Eocene Laguna del Hunco flora, Chubut Province, Patagonia, Argentina, preserve features of the family Cunoniaceae. The goal of the study is to assess their affinities within Cunoniaceae and to interpret their evolutionary and biogeographical significance.
Methods:
Specimens were collected from the Tufolitas Laguna del Hunco, Huitrera Formation. They were prepared, photographed, and compared morphologically with similar extant and fossil fruits and infructescences using published literature and herbarium material.
Results:
The fruit and infructescence morphology place the fossil taxa within Cunoniaceae. They do not conform to any extant genus, supporting the erection of two new fossil genera. Racemofructus gen. nov. shares diagnostic features of the tribe Cunonieae, especially Weinmannia s.l., and exhibits two tribal morphological synapomorphies: a racemose inflorescence and a replum composed of a single column. Cunoniocarpa gen. nov. specimens are paniculate inflorescences with basipetally dehiscent, bicarpellate capsules that have persistent styles and calyces. Its replum morphology suggests possible affinity to the tribe Caldcluvieae, particularly to the genus Ackama.
Conclusions:
The new Patagonian fossils described herein constitute the oldest record of cunoniaceous capsules globally, supplementing a significant body of fossil evidence from pollen, wood, and reproductive structures from southern South America and Antarctica that suggests that the Cunoniaceae were diversified and widely distributed in the Southern Hemisphere by the early Eocene. Racemofructus and Cunoniocarpa are, respectively, the first fossil records from South America of reproductive structures with affinity to tribes Cunonieae and Caldcluvieae. This article is protected by copyright. All rights reserved.
... Statistical characteristics of the growth rings have been used to determine the average annual radial growth and aspects of the paleoenvironment when the tree was growing, especially the mean ring width (e.g. Creber, 1977;Creber and Chaloner, 1985;Ammons, 1987;Morgans, 1999;Morgans and Hesselbo, 1999;Brison et al., 2001;Falcon-Lang et al, 2004;Taylor and Ryberg, 2007;Brea et al., 2015) and mean sensitivity, a measure of the relationship between tree growth and climate (Ammons, 1987;Morgans, 1999;Morgans and Hesselbo, 1999;Falcon-Lang, 2003;Falcon-Lang et al., 2004;Taylor and Ryberg, 2007;Davies-Vollum et al., 2011;Brea et al., 2015). ...
... Statistical characteristics of the growth rings have been used to determine the average annual radial growth and aspects of the paleoenvironment when the tree was growing, especially the mean ring width (e.g. Creber, 1977;Creber and Chaloner, 1985;Ammons, 1987;Morgans, 1999;Morgans and Hesselbo, 1999;Brison et al., 2001;Falcon-Lang et al, 2004;Taylor and Ryberg, 2007;Brea et al., 2015) and mean sensitivity, a measure of the relationship between tree growth and climate (Ammons, 1987;Morgans, 1999;Morgans and Hesselbo, 1999;Falcon-Lang, 2003;Falcon-Lang et al., 2004;Taylor and Ryberg, 2007;Davies-Vollum et al., 2011;Brea et al., 2015). ...
... Detrending and prewhitening are necessary prerequisites to cross-correlation of tree-ring width time series, because low frequency trends of biological origin are present in most tree-ring time series (Fritts, 1976), often resulting in spurious significance in the correlation coefficients. In an excellent recent study, Brea et al. (2015) used what they termed dendrochronological techniques, but their techniques did not include statistical crossmatching, the guiding principle of dendrochronology. In this case crossmatching would not have been possible, because the average number of measured rings per specimen was less than 20. ...
... This decrease in temperature is reflected in the paleofloras of Patagonia, where the tropical to subtropical Gondwanan elements found in the Eocene (e.g., Akania, Eucalyptus, Gymnostoma) were gradually replaced by typically cool-temperate taxa (e.g., some Proteaceae, temperate subgenera of the Nothofagaceae, etc.) (Barreda et al., 2021). In addition, according to paleobotanical micro-and macrofossil records, the most abundant plants in the Oligocene forests of Patagonia were members of the Nothofagaceae (e.g., Barreda, 1997;Brea et al., 2015). The trees of this family became more common after the Eocene and have dominated most of the Patagonian arboreal component of the paleofloras since then . ...
... Only a few fossil woods have been described from the Oligocene of Patagonia. At parallel 39°, Brea et al. (2015) described 20 fossil woods from the late Oligocene, which included Nothofagaceae, Myrtaceae, Laurales, and Cunoniaceae and a remarkable absence of conifers. This latter assemblage diverges in the general composition from the one described herein but coincides in some taxa like the Nothofagaceae and Cunoniaceae. ...
Eleven well-preserved fossil woods were collected from sediments of the San José Formation in the Pato Raro Heights, Chilean Patagonia. Based on their wood anatomy, the specimens were placed in six fossil species: Two conifers of the Podocarpaceae (Phyllocladoxylon antarcticum and a new species of Podocarpoxylon with abundant resin content), one species of the Nothofagaceae (Nothofagoxylon ruei) and one of the Cunoniaceae (Weinmannioxylon trichospermoides), both previously described from Patagonia, a new species of Myrtineoxylon, with the typical anatomy of the family Myrtaceae, and a new taxon with unknown affinity, which was placed in a new fossil genus and species. The assemblage studied provides insights into the Oligocene forests of Patagonia and helps to fill a gap in the knowledge of the Oligocene paleofloras of the region.
... In Patagonia, there are a few isolated fossil wood descriptions from the Eocene-Oligocene (e. g. Romero 1970;Brea 1995;Martínez & Pujana 2010;Terada et al. 2006a, b), but the only wood collections with a significant sample size are from Eocene strata of Mocha Island (Nishida 1984b) and the upper Oligocene Rancahué Formation (Brea et al. 2015), both from northern Patagonia. Their relatively large sample sizes allow comparing them with the Río Turbio woods. ...
... Although Nishida's (1984b) Eocene wood collection includes a Podocarpaceae, most of the woods are Cupressaceae, Myrtaceae, Laurales and Leguminosae, differing from the Río Turbio assemblage and seemingly more similar to extant floras from Central Chile. Brea et al. (2015) described a fossil forest from northern Patagonia with 40% of the stumps being Nothofagaceae and with a notable absence of gymnosperm woods. This assemblage from the upper Oligocene was deposited after the vegetation change when the Nothofagaceae became canopy dominants and the conifers became subordinate. ...
Over 80 samples of fossil woods were collected from numerous outcrops of the Río Turbio Formation, southwestern Patagonia. Preservation of the woods is variable and only about half of these samples could be identified to genus level. The assemblage consists of six types of conifers and four types of dicotyledons, one of them a new species of Caldcluvioxylon (Cunoniaceae). We provide an emended diagnosis of Caldcluvioxylon . A previously described fossil wood from this stratigraphic unit, thought to have affinity with Proteaceae, was re-examined and is described herein as Scalarixylon romeroi sp.nov. Other families recognized in the Río Turbio Formation wood assemblage are Araucariaceae, Podocarpaceae, and Nothofagaceae. Differences in the taxonomic composition of the upper and lower members of the Río Turbio Formation are consistent with the age difference between them according to recent isotopic dating. The diversity of fossil wood is also consistent with the fossil leaves and pollen from each stratigraphic level and most of the taxa are shared with coeval Antarctic fossil wood floras.
... In Patagonia, there are six reported fossil Lauraceae woods: Laurinoxylon atlanticum (Romero, 1970) Nishida, 1990 from a locality of uncertain age in Chilean Patagonia. All of these taxa have simple perforation plates that differ from L. patagonicum (Romero 1970, Brea 1995, Brea et al. 2012, 2015, Ruiz et al. 2020. Laurinoxylon atlanticum further differs because it has more abundant axial parenchyma and its idioblasts are unclear (Romero 1970). ...
Two silicified fossil woods are identified as a new species of Laurinoxylon from the Huitrera Formation at Laguna del Hunco in the Chubut Province of Argentina. Supporting characters include the absence of growth ring boundaries, vessels solitary or in short radial multiples, simple and scalariform perforation plates, alternate intervessel pitting, scalariform vessel-ray pits, scarce axial parenchyma, septate fibres, rays usually one to four cells wide, and idioblasts commonly associated with rays and rarely with the axial parenchyma. The fossil woods resemble members of the Perseae-Cinnamomeae-Laureae clade but do not closely match any extant genus; they therefore probably represent an extinct lineage. Although lauraceous woods are known from other Palaeocene and Eocene floras in Patagonia, the presence of the family at Laguna del Hunco was previously based only on leaf compressions without preserved cuticular details. Our new record confirms the occurrence of Lauraceae in the diverse Laguna del Hunco flora, which contains many genera associated with extant rainforest floras.
... Similar studies were carried out in the late Oligocene of northwestern Patagonia (Brea et al., 2015), early Miocene of southeastern Patagonia (Brea et al., 2012(Brea et al., , 2017, and in the Cretaceous and lower Cenozoic of Antarctica (Francis and Poole, 2002;Poole et al., 2005). The Río Leona Formation yielded a large amount of very well-preserved fossil woods, making it appropriate for these kinds of studies and allowing to apply a variety of methods to infer past climatic conditions. ...
Patagonia has a rich record of fossil woods that are a unique data store of paleoclimatic information. We studied the wood flora recovered from the Río Leona Formation (early Miocene) of southern Patagonia near El Calafate and Río Turbio localities, Santa Cruz Province, Argentina. The fossil wood assemblage was analyzed using various methodologies (anatomy analysis, Vulnerability and Mesomorphic indices, and the Coexistence Approach) to determine paleoclimate variables including mean annual temperature (MAT) and mean annual precipitation (MAP). The anatomy analysis developed by Wiemann et al. (1998, 1999) is based mostly on woods from the Northern Hemisphere. We applied those equations to extant woods from the southernmost region of South America to test their functionality and to compare them with the results obtained from the fossils. These equations gave limited results. Climate signals from fossil woods suggest a microthermal climate for the region with MAT of 8–12 °C and MAP of 80–170 cm/year. In addition, part of the results points towards an environment with water in abundance (i.e., Coexistence Approach and some wood characters influenced by the environment) and other results suggest wood tolerance to hydric stress (i.e., Vulnerability Index, Mesomorphy Index, and wood characters influenced by the environment). These suggest an environment with rainy and dry seasons, which is also supported by the presence of well-marked growth ring boundaries and false rings. These conditions can be found today in central Chile, a region that shares some vegetation elements with the Río Leona Formation and has a Mediterranean climate.
... Chichinales Fm., Río Negro Province (Ragonese, 1977). Rancahué Fm., Neuquén Province (Brea et al., 2015). Carmen Silva locality, Tierra del Fuego Province (Caviglia, 2017); Cullen Fm., Tierra del Fuego Province (Caviglia, 2019). ...
The breakup of Gondwana and the associated climatic changes led to the fragmentation of floras that were once connected across the Southern lands. The diversity of the Gondwanan remnants has long been assumed to have fluctuated in Patagonia across the Cenozoic, although it has never been quantified so far. Here we address when the major floristic members of the Gondwanan legacy (e.g., southern beeches, proteas, podocarps, gumtrees) expanded, contracted, or became extinct during the Patagonian biogeographic isolation (Eocene–Miocene) on the basis of the re-assessment of the fossil record (i.e., woods, leaves, and spore-pollen grains). We found that the Patagonian floras experienced moderate to severe shifts in the diversity of the Gondwanan component —relative to the total flora— with the highest estimates in the late Eocene–early Oligocene (∼50%) and the lowest estimates in the late Miocene (∼20%) according to the fossil pollen record. The most important floristic changes include two major replacements: 1) tropical Gondwanan taxa (e.g., Akania, Eucalyptus, Gymnostoma) by typically cool-temperate taxa (e.g., Nothofagaceae) in the Eocene, and 2) humid taxa (e.g., Podocarpaceae) by arid-adapted floras, mostly of non-Gondwanan affinity, across the Miocene. The variation in diversity of the Gondwanan component from Patagonia shows a striking resemblance to that from Australia for the same period, probably indicating a global-scale driver of floristic turnover (e.g., global cooling conditions). Today, the Patagonian subantarctic forests harbor only about ∼15% of the Gondwanan diversity, representing a three-fold decrease from its climax in the late Eocene–early Oligocene.
... Moreover, the middle Eocene-early Oligocene interval was characterized by the invasion of Nothofagus forests in Patagonia in close agreement with a marked cooling trend (Barreda & Palazzesi, 2007). Fossil woods of Nothofagaceae were recorded from several regions in Antarctica (Poole, 2002 and references therein) and in Patagonia (Poole, 2002;Pujana, 2009;Brea et al., 2015;Pujana et al., 2015;Egerton et al., 2016;Terada et al., 2006). Records of Nothofagacean leaves from the Paleogene of Patagonia are fairly abundant (eg. ...
... Colombia's Cerrejón Formation, older than the Piedra Chamana fossils at ~58 Ma (late Middle Paleocene, paleolatitude of 5°N), are floristically similar to modern tropical forests at the familial level (with prevalent legumes) and are considered the earliest record of Neotropical rainforest based on leaf morphology and floristics (Wing et al. 2009). At higher southern latitudes of the continent, the rich fossil record from Patagonia includes early to middle Eocene (48-52 Ma) leaf floras from central Patagonia showing the presence of diverse (temperate /subtropical) rainforest with megatherm dicots, palms, and gymnosperms during the Paleocene-Eocene thermal Maximum (Wilf et al. 2005;Wilf et al. 2013) and an in situ late-Oligocene (25)(26) fossil forest in northern Patagonia dominated by Nothofagoxylon (Brea et al. 2015). Apart from numerous records from the Paleogene of Patagonia (Herbst et al. 2007;Brea et al. 2008;raigemborn et al. 2009), the majority of fossil woods described from South America (and also Mexico and Central America) are Cretaceous or Neogene in age. ...
the fossil woods and leaves of the Fossil Forest Piedra Chamana represent a diverse assemblage of plants dating to 39 Ma (late Middle Eocene). the fossils are preserved in an ashfall and overlying lahar deposits near the small village of Sexi in the northern Peruvian Andes (central Cajamarca). the assemblage includes dicot wood types and leaf morphotypes, as well as a diversity of mono- cot material. the ~30 dicot wood types are referred to the families Acanthaceae, Anacardiaceae, Apocynaceae, Combretaceae, Cordiaceae, Dipterocarpaceae, Euphorbiaceae, Fabaceae, Lechythidaceae, Lythraceae, Malvaceae, Melasto- mataceae, Muntingiaceae, rubiaceae, rutaceae, and Sapindaceae. Described herein are descriptions of the rst 17 wood types that have been assigned to the families Acanthaceae through Lythraceae; descriptions of the additional wood types will appear in a later paper. the paleovegetation can be characterized as lowland tropical forest with a dry aspect based on preliminary analysis of oristic af nities and wood anatomical characteristics of the fossils.
... Several species based on wood specimens have been described from the Cenomanian to early Campanian of King George Island (Isla 25 de Mayo) and Livingston Island, South Shetland Islands, Antarctica (Torres, 1985;Poole et al., 2000Poole et al., , 2001. Additional reports come from the Paleogene to Miocene of Chilean and Argentinean Patagonia (Petriella, 1972;Brea et al., 2004Brea et al., , 2012Brea et al., , 2015Terada et al., 2006). Fossil pollen grains with affinities for Cunoniaceae are known from the Late Cretaceous to late Paleocene of the Antarctic Peninsula (Cranwell, 1959;Askin, 1992) and the late Paleocene to mid-Miocene of Patagonia (Petriella and Archangelsky, 1975;Romero and Castro, 1986;Barreda et al., 2007). ...
Background and aims:
Radially symmetrical, five-winged fossil fruits from the highly diverse early Eocene Laguna del Hunco flora of Chubut Province, Patagonia, Argentina, are named, described and illustrated. The main goals are to assess the affinities of the fossils and to place them in an evolutionary, palaeoecological and biogeographic context.
Methods:
Specimens of fossil fruits were collected from the Tufolitas Laguna del Hunco. They were prepared, photographed and compared with similar extant and fossil fruits using published literature. Their structure was also evaluated by comparing them with that of modern Ceratopetalum (Cunoniaceae) fruits through examination of herbarium specimens.
Key results:
The Laguna del Hunco fossil fruits share the diagnostic features that characterize modern and fossil Ceratopetalum (symmetry, number of fruit wings, presence of a conspicuous floral nectary and overall venation pattern). The pattern of the minor wing (sepal) veins observed in the Patagonian fossil fruits is different from that of modern and previously described fossil Ceratopetalum fruits; therefore, a new fossil species is recognized. An apomorphy (absence of petals) suggests that the fossils belong within crown-group Ceratopetalum CONCLUSIONS: The Patagonian fossil fruits are the oldest known record for Ceratopetalum Because the affinities, provenance and age of the fossils are so well established, this new Ceratopetalum fossil species is an excellent candidate for use as a calibration point in divergence dating studies of the family Cunoniaceae. It represents the only record of Ceratopetalum outside Australasia, and further corroborates the biogeographic connection between the Laguna del Hunco flora and ancient and modern floras of the Australasian region.
... In Argentina, a fossil wood, Laurinoxylon atlanticum (Romero) Dup eron-Laudoueneix and Dup eron 2005, with closest affinities with the genus Persea, specially P. lingue (Miers ex Bertero) Nees is reported from the Eocene of Patagonia (Romero, 1970) and upper Oligocene of Neuqu en, Argentina (Brea et al., 2015). The material described by Romero (1970) is characterized by diffuse porous wood; solitary vessels, in radial multiples; simple perforation plates; short vessel members with narrow diameters and with mostly alternate intervessel pits; vasicentric parenchyma, sometimes aliform and locally confluent; low rays, 1e2 seriate, heterocellular; narrow fibers with thin walls and few cells with contents, only present in ray cells. ...
The late Eocene to earliest Miocene volcanic arc of the Southern Central Andes (33-40°S) and North Patagonian Andes (40-44°S) exhibits distinctive features that shed light on the dynamics of subduction-related volcanic activity in extensional tectonic settings. This period is particularly significant in the Andes, as it records the opening of forearc, intra-arc, and retroarc extensional basins, accompanied by high-volume volcanism, preceding the middle-late Miocene final major uplift phase of the Andes. This extensional event occurred in two phases, associated with changes in the geometry and dynamics of the subduction system: from oblique convergence at low rates during the late Eocene-early Oligocene to an orthogonal convergence at high rates during the late Oligocene-early Miocene. This study presents a compilation of field, petrographic, geochemical, and isotopic data from volcanic sequences in the North Patagonian Andes and the Southern Central Andes, aiming to analyze petrogenetic processes at different stages of arc evolution.
During the late Eocene to early Oligocene, subduction-related volcanism occurred in a wide area from 100 to 300 km from the trench. In this period, magmatic arc rocks exhibit intermediate composition and a relatively homogeneous geochemical signature, transitional between tholeiitic and calc-alkaline series, with a marked subduction-related signature. These magmas originated from depleted mantle sources with high slab-derived fluid and sediment contributions and limited crustal interactions. In contrast, the late Oligocene to earliest Miocene volcanic activity, at the peak of the extensional regime, displays significant geochemical differences along the Andes. In the Southern Central Andes (33-40°S), volcanism displays compositions similar to those of the previous stage with varying influence from the subducting slab. In some sectors, magmas register the climax of the extensional conditions, whereas the youngest volcanic rocks towards the north (33-34°S) present evidence of the onset of contractional tectonics, demonstrated by the increased interaction of the magmas with a progressively thickened crust. In the North Patagonian Andes (40-44°S), subaerial and subaqueous arc-related lava flows are interbedded with marine deposits, indicating a rapid subsidence regime. These rocks exhibit geochemical features transitional from arc to E-MORB and even OIB compositions, which suggest a genesis primarily dominated by decompression melting of a heterogeneous mantle source. Above all, the contrasting nature of late Eocene-early Miocene arc products in the Southern Central and Patagonian Andes highlights that no single process can explain the changes in composition, distribution, and evolution of arc magmatism; rather, it is a combination of factors, including variations in subduction zone configuration and mantle dynamics and composition.
We compiled the numerous fossil records (486) assigned to Nothofagaceae including pollen grains (from surface sediments and continental and oceanic borehole cores), leaves, woods and reproductive structures from South America. All the records are revised and the latest systematic treatments and ages of the bearing strata of each record are followed. When possible, we proposed a subgeneric affinity to each record based on updated bibliography. Fossils of three (Nothofagus, Fuscospora and Lophozonia) of the four subgenera are found in similar proportions through time since the Late Cretaceous. Fossils with reliable affinity with subgenus Brassospora were not found in South America. Most of the records are concentrated in the southern tip of South America (Patagonia Region) and nearby areas. After a significant presence of Nothofagaceae in the Cretaceous, the family declined in diversity and abundance in the Palaeocene and then increased from the Eocene to the Miocene. In the Miocene, the records reach their maximum diversity and abundance, and Nothofagaceae usually dominate the assemblages of pollen, leaves and woods from Patagonia. Pliocene Nothofagaceae records are virtually absent, probably because sedimentary rocks of that age are rare in Patagonia. The fossil record for Nothofagaceae varies according to environmental turnover; when tropical/subtropical floras were present in Patagonia in the Palaeocene–early Eocene, Nothofagaceae contracted southwards and when open steppes developed in the Miocene of east Patagonia, Nothofagaceae contracted westward.
It is widely recognized that fossil leaves are good proxies for paleoclimate estimates, and leaf physiognomy analysis is a traditional technique used to make climate estimates. There are only a few paleoclimate reconstructions for the southern part of South America based on this technique. Here we report climate parameters using fossil leaves from the Río Turbio (Eocene-Oligocene) and Río Guillermo (Oligocene-early Miocene?) formations in southern South America, Cuenca Austral, Argentina. We used univariate (leaf margin and leaf foliar area analysis) and multivariate methods (CLAMP, DiLP) on two datasets from South America, in the Southern Hemisphere. Lower and upper members of the Río Turbio Formation show a mixed paleoflora represented by paratropical as well as cool-temperate taxa such as Nothofagus, with a similar percentage of untoothed fossil leaves. Climate estimates indicate warm and humid conditions for both Río Turbio Formation members. The Río Guillermo Formation is represented by mostly cool-temperate elements, mainly Nothofagus, and most with toothed margins. The paleoclimate analysis indicates a decrease in temperature and precipitation when comparing the two studied formations. Today, temperate forests in southern Argentina have a plant composition and climate more similar to the estimates made for the Río Guillermo Formation.
The structure of the living Patagonian flora, dominated by the steppe, is a direct consequence of past climatic and tectonic events. These arid-adapted communities were widespread during the Late Neogene, but their origin in Patagonia can be traced back to the Paleogene. Vegetational trends throughout Paleocene-Miocene time are based on available paleobotanical and palynological information. Four major supported stages in vegetation turnovers are recognized: (1) Paleocene and Early Eocene floras were rainforest-dominated, including many angiosperms with warm-temperate affinities (e.g., palms, Juglandaceae, Casuarinaceae). However, mainly in the Early Eocene, some geographic areas influenced by warm but drier conditions are suggested by the occurrence of certain taxa (e.g., Anacardiaceae). These areas containing arid-adapted floras would have arisen in Patagonian inland regions, in a generally wet continent. (2) The Middle Eocene-Early Oligocene interval was distinguished by the invasion ofNothofagus forests. Progressive replacements of megathermal communities by meso- and microthermal rainforest are documented.Nothofagus forest expansion suggests a marked cooling trend at this time, although some megathermal elements (AquifoliaceaeIlex, Tiliaceae-Bombacaceae, Sapindaceae) were still present at the beginning of this period. Arid-loving taxa have not been recorded in abundance. (3) Late Oligocene-Early Miocene floras were characterized by the occurrence of shrubby-herbaceous elements belonging to Asteraceae, Chenopodiaceae, Ephedraceae, Convolvulaceae, Fabaceae, and Poaceae. They began to give a modern appearance to plant communities. Xerophytic formations would have occupied coastal salt marshes and pockets in inland areas. Megathermal angiosperms of the Rubiaceae, Combretaceae, Sapindaceae, Chloranthaceae, and Arecaceae occurred mainly during the Late Oligocene. Forests of Nothofagaceae, Podocarpaceae, and Araucariaceae are still documented in extra-Andean Patagonia; however, a contrast between coastal and inland environments may have developed, particularly in the Miocene. (4) Middle-Late Miocene records show an increasing diversity and abundance of xerophytic-adapted taxa, including Asteraceae, Chenopodiaceae, and ConvolvulaceaeCressa/Wilsonia. Expansion of these xerophytic taxa, coupled with extinctions of megathermal/nonseasonal elements, would have been associated with both tectonic and climatic forcing factors, led to the development of aridity and extreme seasonality. These arid-adapted Late Miocene floras are closely related to modern communities, with steppe widespread across extra-Andean Patagonia and forest restricted to the western humid upland regions.
There are distinct relationships among the anatomy of wood, the morphology of leaves, and the climate in which woody plants are growing. The relationships between leaf morphological characters and climate have been known for many years, but wood characters as climate indicators are less well studied. In this article, we use measurements of wood anatomy and leaf morphology from woody dicotyledonous plants, growing in Florida and Connecticut, to determine the accuracy to which statistical models can predict climate. The strength of the relationship between climate and physiognomy is important because it allows us to evaluate the phenotypic plasticity that woody plants express under various climates. In this study we use canonical correspondence and regress ion models to examine how precisely wood anatomical and leaf morphological characters are related to climate. For leaves, canonical correspondence analysis (CCA) using 31 characters gave the closest estimate of mean annual temperature (MAT) in Connecticut, whereas a regression equation using only a single leaf character (leaf margins with no teeth) as predictor gave the closest estimate in Florida. For wood, CCA using 13 wood characters gave the closest estimate in Florida, whereas a regression equation using only a single wood character (the occurrence of vessels smaller than 100 mum) gave the closest estimate in Connecticut. CCA showed that, although MAT has a smooth and continuous relationship with leaf physiognomy, this is not the case for wood. Temperate woods form a different physiognomic population than subtropical and tropical woods, in which the physiognomy of temperate woods is more strongly influenced by MAT than is the physiognomy of subtropical and tropical woods.
Inside Wood is an Internet-accessible wood anatomy reference, research, and teaching tool. The Inside Wood database has coded wood anatomical descriptions based on the IAWA List of Microscopic Features for Hardwood Identification and is accompanied by a collection of photomicrographs. As of November 2010 there were over 5,800 descriptions and 36,000 images of modern woods, and over 1,600 descriptions and 2,000 images of fossil woods. CITES-listed timber species and other endangered woody plants are included in this digital collection hosted by North Carolina State University's library. This web site has value in helping with wood identification because it has a multiple entry key that allows searching by presence or absence of IAWA features and it serves as a virtual reference collection whereby descriptions and images can be retrieved by searching by scientific or common name or other keywords.
Composition and diversity of the understory of ñire (Nothofagus antarctica) forests in relation to forest structure: We describe the species composition and diversity of the understory of Nothofagus antarctica (ñire) forest depending on the forest structure. The study was conducted in the northwest of Chubut, where the forest was classified into 10 forest types, taking into account the forest height and the canopy cover. On the basis of vegetation inventory, we studied the differences among forest types in terms of species richness, diversity, dominance and understory cover (total and by origin and life form). We recorded 105 species (73% native and 27% exotic) distributed in 43 families. In all the structures analyzed high coverage of herbaceous species was recorded. In the forest type with the highest tree-height the highest coverage were recorded, composed of native species typical of the forest under dense canopies, and of exotic species, typical of disturbed environments, in open forests. In the forest type with the lowest tree-height, where species of the forest, of disturbed environments, and of the steppe coexist, there was greater diversity and species richness.
The incidences of selected features of dicotyledonous wood that are believed to be of ecologic and/or phylogenetic significance (distinct growth rings, narrow and wide vessel diameter, high and low vessel frequencies, scalariform perforations, tangential vessel arrangement, ring porosity, and helical wall thickenings) were plotted through time (Cretaceous–Recent). There are marked differences between the Cretaceous and Tertiary in the frequency of all wood anatomical features. Incidences of features that are associated with markedly seasonal climates in extant floras do not approach modern levels until the Neogene. Correlations of wood anatomical features with ecology do not appear to have been constant through time, because in the Cretaceous different features provide conflicting information about the climate. Throughout the Tertiary the southern hemisphere/tropical and the northern hemisphere/temperate regions differed in the incidences of ecologically significant features and these differences are similar to those in the Recent flora. Possibilities for reliably using dicotyledonous wood for climatic reconstructions appear restricted to the Tertiary and Quaternary. However, at present the fossil wood record for most epochs and regions is too limited to permit detailed reconstructions of their past climate.
Stand tables from forest inventories representing >22 × 106 ha of forests in tropical Asia were used to estimate aboveground biomass. The mean inventory-based for moist forests (225 Mg/ha) was lower than that reported by direct measurements for mature forests in the same region (350 Mg/ha), whereas the mean inventory-based biomass for dry forests (82 Mg/ha) was higher than estimates based on direct measurements (55 Mg/ha). Human use of the forests in tropical Asia is leading to degradation. Between 2 national forest inventories of Peninsular Malaysia in 1972 and 1981, the total area and biomass of forests declined by 18 and 28% respectively. (See also 91L/08507 and 08812). -from Authors
The fossil history of plant life in Antarctica is central to our understanding of the evolution of vegetation through geological time and also plays a key role in reconstructing past configurations of the continents and associated climatic conditions. This book provides the only detailed overview of the development of Antarctic vegetation from the Devonian period to the present day, presenting Earth scientists with valuable insights into the break up of the ancient supercontinent of Gondwana. Details of specific floras and ecosystems are provided within the context of changing geological, geographical and environmental conditions, alongside comparisons with contemporaneous and modern ecosystems. The authors demonstrate how palaeobotany contributes to our understanding of the palaeoenvironmental changes in the southern hemisphere during this period of Earth history. The book is a complete and up-to-date reference for researchers and students in Antarctic palaeobotany and terrestrial palaeoecology.
Coastal exposures of the Santa Cruz Formation in southern Patagonia have been a fertile ground for recovery of Early Miocene vertebrates for more than 100 years. This volume presents a comprehensive compilation of important mammalian groups which continue to thrive today. It includes the most recent fossil finds as well as important new interpretations based on 10 years of fieldwork by the authors. A key focus is placed on the paleoclimate and paleoenvironment during the time of deposition in the Middle Miocene Climatic Optimum (MMCO) between 20 and 15 million years ago. The authors present the first reconstruction of what climatic conditions were like and present important new evidence of the geochronological age, habits and community structures of fossil bird and mammal species. Academic researchers and graduate students in paleontology, paleobiology, paleoecology, stratigraphy, climatology and geochronology will find this a valuable source of information about this fascinating geological formation.
The Aluminé Basin is a volcano-sedimentary depocentre located in the Andean retroarc at 39°S. It is the southern part of a major depositional system: the Bío Bío-Aluminé Basin. Stratigraphical, geochronological, sedimentological and structural analysis allow us to conclude that the basin evolved through two stages: an Oligocene extensional stage filled with basalts and reworked volcaniclastic and pyroclastic deposits (Rancahue Formation) and a Miocene contractional stage, filled with alluvial and pyroclastic deposits covered by basaltic lavas (Chimehuín and Tipilihuque formations). The volcanic-rich (basaltic) infill of the extensional stage has a western provenance and was derived from widespread magmatic activity that took place during the Oligocene in the adjacent cordilleran axis. The contractional stage basin is an intramontane depocentre limited by uplifted blocks generated mainly by the inversion of Mesozoic extensional faults. It is strongly asymmetric and shows eastern provenance. Structural and geomorphological evidence indicate the existence of a non-depositional hiatus between the two stages.
The nearest-living-relative method exists in numerous taxon-and assemblage-based variations and is still one of the most powerful approaches to obtain qualitative and quantitative paleoclimate (or paleoenvironment) information. Taxon-based approaches relying only on the presence-absence of taxa are less sensitive to taphonomy than assemblage-based approaches, which typically also rely on the relative abundance of taxa. Stratigraphically, taxon-based methods are limited to periods after the time when the major evolutionary radiation of the respective taxon group occurred; typically, they cannot be applied to pre-Cenozoic times. In contrast, assemblage-based techniques are mostly restricted in their application to Quaternary sequences.