Preliminary palynological data on floristic and climatic changes during the Middle Eocene-Early Oligocene of the eastern Ebro Basin, northeast Spain

1996 ◽  
Vol 92 (3-4) ◽  
pp. 281-305 ◽  
Author(s):  
Carla Cavagnetto ◽  
Pere Anadón
Keyword(s):  
Middle Eocene ◽  
Climatic Changes ◽  
Ebro Basin ◽  
Palynological Data ◽  
Early Oligocene

scholarly journals Climate Change in the Southern Ocean During the Middle Eocene to Early Oligocene: A Palynological Perspective

2021 ◽  
Author(s):  
◽  
Claire Andrea Storkey
Keyword(s):  
Southern Ocean ◽  
Middle Eocene ◽  
Climatic Changes ◽  
Weddell Sea ◽  
Sea Surface ◽  
Total Abundance ◽  
Dinoflagellate Cysts ◽  
Early Oligocene ◽  
Cooling Effects ◽  
Terrestrial Material

<p>The Antarctic and Southern Ocean is an area that was greatly affected by climatic changes during the Middle Eocene to Early Oligocene (E/O). This study aims to document climate-induced changes of the marine palynomorphs (mostly dinoflagellate cysts) by developing a Circum-Antarctic biozonation, and establishing the distribution and effects of cooling on the palynomorph assemblages and the palaeoenvironment. Samples were obtained from four sites by the Ocean Drilling Program (ODP) and Deep Sea Drilling Project (DSDP) and the palynological content was analyzed. These sites were selected as they may record effects of circulation changes and cooling trends, reflecting climate changes. ODP site 696B, was inner neritic and located in the South Orkney microcontinent, Weddell Sea. The other three sites were pelagic with ODP 699A located on the Northeast Georgia Rise, Falklands, ODP 748B located in the Western part of the Raggart Basin, Kerguelen Plateau and DSDP 277 located in Cathedral Depression on the Southern Campbell Plateau. From this analysis a comprehensive record of the local climatic transitions was ascertained, utilising assemblages of fossil organic-walled dinoflagellate cysts (dinocysts), acritarchs, prasinophyte algae, microforaminiferal linings, scoledonts and terrestrial material. The establishment of a standard nannofossil biostratigraphy provided a temporal framework of the marine palynomorphs in each site. Key dinocyst datums recognised as first or last occurrences that correlated reliably between sites, were compared with the nannofossil zones of each site. The purpose was to provide a Middle Eocene/Early Oligocene dinocyst biostratigraphy that temporally constrains the assemblages. Six primary datums and two secondary datums resulted, which lead to the recognition of four biozones and established a new biozonation in the Southern Ocean. The zones identified various dinocyst events, giving an indication of their probable palaeoenvironments. The Circum-Antarctic distribution pattern of palynomorph assemblages was documented in each site as a total abundance of grains per gram. The ranges and composition of palynomorph assemblages of each site were displayed as a percentage of total abundance. To document any cooling effects the dinocysts were separated into Gonyaulacoid or Peridinioid assemblages to best illustrate their preferred palaeoenvironment. Key findings showed that the pelagic and inner neritic sites differed greatly. Site 696B was the most climatically stable site and dominated by Peridinioid dinocysts which are predominantly heterotrophic. They are most common in an inner neritic palaeoenvironment, but are also present in nutrient upwellings and eutrophic surface waters with lower sea surface temperatures. Terrestrial material dominates all marine palynomorphs in this site which was shallow and warm with few changes up to the E/O boundary ~33.7 Ma, but became more variable in the Early Oligocene. In comparison, the pelagic sites (699, 748B, 277) were unstable, with missing or condensed sediments and no palynomorphs present at differing times. They were mostly dominated by Gonyaulacoid dinocysts, which are autotrophs and generally located in outer neritic to open ocean palaeoenvironments. The non dinocysts of Prasinophyte algae and Leiosphaeridia palynomorphs appeared in higher abundances in the pelagic sites than in the inner neritic sites. Specific dinocyst markers identified temperature changes within the pelagic sites, subsequently highlighting the climatic changes that occurred during the Middle Eocene/Early Oligocene. From ~46 Ma the pelagic sites recorded conditions that were oceanic and cooler. Between ~44 - ~41.5 Ma, a warming in site 748B indicated enhanced stratification and elevated nutrient availability. This was not the case in site 696B and may be due to warm temperatures already present. From ~41.4 Ma the pelagic sites showed that the palaeoenvironment continued to cool, indicated by the presence of Leiosphaeridia and Prasinophyte algae. The palaeoenvironment was oceanic with upwelling and offshore sea surface productivity, illustrated by the Gonyaulacoid and Peridinioid dinocysts present. During the Late Eocene from ~37 Ma a transitional and changeable palaeoenvironment was shown by the high numbers of Operculodinium spp present in sites 696B and 277. From ~33.7 Ma (E/O boundary) in the pelagic sites, most Peridinioid dinocysts had disappeared and very few Gonyaulacoid dinocysts were present. In contrast the inner neritic site (696B) Peridinioid dinocysts were still dominant, and a more gradual disappearance of all the marine palynomorphs was evident.</p>

scholarly journals Climate Change in the Southern Ocean During the Middle Eocene to Early Oligocene: A Palynological Perspective

2021 ◽  
Author(s):  
◽  
Claire Andrea Storkey
Keyword(s):  
Southern Ocean ◽  
Middle Eocene ◽  
Climatic Changes ◽  
Weddell Sea ◽  
Sea Surface ◽  
Total Abundance ◽  
Dinoflagellate Cysts ◽  
Early Oligocene ◽  
Cooling Effects ◽  
Terrestrial Material

<p>The Antarctic and Southern Ocean is an area that was greatly affected by climatic changes during the Middle Eocene to Early Oligocene (E/O). This study aims to document climate-induced changes of the marine palynomorphs (mostly dinoflagellate cysts) by developing a Circum-Antarctic biozonation, and establishing the distribution and effects of cooling on the palynomorph assemblages and the palaeoenvironment. Samples were obtained from four sites by the Ocean Drilling Program (ODP) and Deep Sea Drilling Project (DSDP) and the palynological content was analyzed. These sites were selected as they may record effects of circulation changes and cooling trends, reflecting climate changes. ODP site 696B, was inner neritic and located in the South Orkney microcontinent, Weddell Sea. The other three sites were pelagic with ODP 699A located on the Northeast Georgia Rise, Falklands, ODP 748B located in the Western part of the Raggart Basin, Kerguelen Plateau and DSDP 277 located in Cathedral Depression on the Southern Campbell Plateau. From this analysis a comprehensive record of the local climatic transitions was ascertained, utilising assemblages of fossil organic-walled dinoflagellate cysts (dinocysts), acritarchs, prasinophyte algae, microforaminiferal linings, scoledonts and terrestrial material. The establishment of a standard nannofossil biostratigraphy provided a temporal framework of the marine palynomorphs in each site. Key dinocyst datums recognised as first or last occurrences that correlated reliably between sites, were compared with the nannofossil zones of each site. The purpose was to provide a Middle Eocene/Early Oligocene dinocyst biostratigraphy that temporally constrains the assemblages. Six primary datums and two secondary datums resulted, which lead to the recognition of four biozones and established a new biozonation in the Southern Ocean. The zones identified various dinocyst events, giving an indication of their probable palaeoenvironments. The Circum-Antarctic distribution pattern of palynomorph assemblages was documented in each site as a total abundance of grains per gram. The ranges and composition of palynomorph assemblages of each site were displayed as a percentage of total abundance. To document any cooling effects the dinocysts were separated into Gonyaulacoid or Peridinioid assemblages to best illustrate their preferred palaeoenvironment. Key findings showed that the pelagic and inner neritic sites differed greatly. Site 696B was the most climatically stable site and dominated by Peridinioid dinocysts which are predominantly heterotrophic. They are most common in an inner neritic palaeoenvironment, but are also present in nutrient upwellings and eutrophic surface waters with lower sea surface temperatures. Terrestrial material dominates all marine palynomorphs in this site which was shallow and warm with few changes up to the E/O boundary ~33.7 Ma, but became more variable in the Early Oligocene. In comparison, the pelagic sites (699, 748B, 277) were unstable, with missing or condensed sediments and no palynomorphs present at differing times. They were mostly dominated by Gonyaulacoid dinocysts, which are autotrophs and generally located in outer neritic to open ocean palaeoenvironments. The non dinocysts of Prasinophyte algae and Leiosphaeridia palynomorphs appeared in higher abundances in the pelagic sites than in the inner neritic sites. Specific dinocyst markers identified temperature changes within the pelagic sites, subsequently highlighting the climatic changes that occurred during the Middle Eocene/Early Oligocene. From ~46 Ma the pelagic sites recorded conditions that were oceanic and cooler. Between ~44 - ~41.5 Ma, a warming in site 748B indicated enhanced stratification and elevated nutrient availability. This was not the case in site 696B and may be due to warm temperatures already present. From ~41.4 Ma the pelagic sites showed that the palaeoenvironment continued to cool, indicated by the presence of Leiosphaeridia and Prasinophyte algae. The palaeoenvironment was oceanic with upwelling and offshore sea surface productivity, illustrated by the Gonyaulacoid and Peridinioid dinocysts present. During the Late Eocene from ~37 Ma a transitional and changeable palaeoenvironment was shown by the high numbers of Operculodinium spp present in sites 696B and 277. From ~33.7 Ma (E/O boundary) in the pelagic sites, most Peridinioid dinocysts had disappeared and very few Gonyaulacoid dinocysts were present. In contrast the inner neritic site (696B) Peridinioid dinocysts were still dominant, and a more gradual disappearance of all the marine palynomorphs was evident.</p>

scholarly journals The Cenozoic Malaguide Basin from Sierra Espuña (Murcia, S Spain): An Example of Geological Heritage

Geosciences ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 34
Author(s):  
Santiago Moliner-Aznar ◽  
Manuel Martín-Martín ◽  
Tomás Rodríguez-Estrella ◽  
Gregorio Romero-Sánchez
Keyword(s):  
Middle Eocene ◽  
Geological Heritage ◽  
Passive Margin ◽  
Early Miocene ◽  
Late Oligocene ◽  
Deep Basin ◽  
Sedimentary Evolution ◽  
Early Oligocene ◽  
Upper Oligocene ◽  
Very High

The Cenozoic Malaguide Basin from Sierra Espuña (Internal Betic Zone, S Spain) due to the quality of outcropping, areal representation, and continuity in the sedimentation can be considered a key-basin. In the last 30 years, a large number of studies with very different methodological approaches have been done in the area. Models indicate an evolution from passive margin to wedge-top basin from Late Cretaceous to Early Miocene. Sedimentation changes from limestone platforms with scarce terrigenous inputs, during the Paleocene to Early Oligocene, to the deep basin with huge supplies of turbidite sandstones and conglomerates during the Late Oligocene to Early Miocene. The area now appears structured as an antiformal stack with evidence of synsedimentary tectonics. The Cenozoic tectono-sedimentary basin evolution is related to three phases: (1) flexural tectonics during most of the Paleogene times to create the basin; (2) fault and fold compartmentation of the basin with the creation of structural highs and subsiding areas related to blind-fault-propagation folds, deforming the basin from south to north during Late Oligocene to Early Aquitanian times; (3) thin-skin thrusting tectonics when the basin began to be eroded during the Late Aquitanian-Burdigalian. In recent times some works on the geological heritage of the area have been performed trying to diffuse different geological aspects of the sector to the general public. A review of the studies performed and the revisiting of the area allow proposing different key-outcrops to follow the tectono-sedimentary evolution of the Cenozoic basin from this area. Eight sites of geological interest have been selected (Cretaceous-Cenozoic boundary, Paleocene Mula Fm, Lower Eocene Espuña-Valdelaparra Fms, Middle Eocene Malvariche-Cánovas Fms, Lowermost Oligocene As Fm, Upper Oligocene-Lower Aquitanian Bosque Fm, Upper Oligocene-Aquitanian Río Pliego Fm, Burdigalian El Niño Fm) and an evaluation has been performed to obtain four parameters: the scientific value, the educational and touristic potential, and the degradation risk. The firsts three parameters obtained values above 50 being considered of “high” or “very high” interest (“very high” in most of the cases). The last parameter shows always values below 50 indicating a “moderate” or “low” risk of degradation. The obtained values allow us considering the tectono-sedimentary evolution of this basin worthy of being proposed as a geological heritage.

scholarly journals Late oligocene–early miocene shortening in the Thrace Basin, northern Aegean

2021 ◽  
Author(s):  
Ümitcan Erbil ◽  
Aral I. Okay ◽  
Aynur Hakyemez
Keyword(s):  
Large Scale ◽  
Middle Eocene ◽  
Early Miocene ◽  
Fold Axis ◽  
Late Oligocene ◽  
The Balkans ◽  
Sedimentary Sequences ◽  
The North ◽  
Early Oligocene ◽  
Thrace Basin

AbstractLate Cenozoic was a period of large-scale extension in the Aegean. The extension is mainly recorded in the metamorphic core complexes with little data from the sedimentary sequences. The exception is the Thrace Basin in the northern Aegean, which has a continuous record of Middle Eocene to Oligocene marine sedimentation. In the Thrace Basin, the Late Oligocene–Early Miocene was characterized by north-northwest (N25°W) shortening leading to the termination of sedimentation and formation of large-scale folds. We studied the stratigraphy and structure of one of these folds, the Korudağ anticline. The Korudağ anticline has formed in the uppermost Eocene–Lower Oligocene siliciclastic turbidites with Early Oligocene (31.6 Ma zircon U–Pb age) acidic tuff beds. The turbidites are underlain by a thin sequence of Upper Eocene pelagic limestone. The Korudağ anticline is an east-northeast (N65°E) trending fault-propagation fold, 9 km wide and 22 km long and with a subhorizontal fold axis. It is asymmetric with shallowly-dipping northern and steeply-dipping southern limbs. Its geometry indicates about 1 km of shortening in a N25°W direction. The folded strata are unconformably overlain by Middle Miocene continental sandstones, which constrain the age of folding. The Korudağ anticline and other large folds in the Thrace Basin predate the inception of the North Anatolian Fault (NAF) by at least 12 myr. The Late Oligocene–Early Miocene (28–17 Ma) shortening in the Thrace Basin and elsewhere in the Balkans forms an interlude between two extensional periods, and is probably linked to changes in the subduction dynamics along the Hellenic trench.

Falcatifolium (Podocarpaceae) macrofossils from paleogene sediments in south-eastern Australia: a reassessment

1998 ◽  
Vol 11 (6) ◽  
pp. 711 ◽  
Author(s):  
Robert S. Hill ◽  
Leonie J. Scriven
Keyword(s):  
Leaf Morphology ◽  
Middle Eocene ◽  
Late Eocene ◽  
South Eastern ◽  
Early Oligocene ◽  
Extant Species ◽  
Eastern Australia ◽  
South Eastern Australia

A re-investigation of macrofossils previously referred to the extantpodocarpaceous genus Falcatifolium Laubenfels shows thatno records can be sustained. Falcatifolium australisD.R.Greenwood from Middle Eocene sediments in Victoria bears littleresemblance to extant species in the genus and is transferred to the newfossil genus Sigmaphyllum R.S.Hill & L.J.Scriven.Specimens from Early Oligocene sediments in Tasmania previously assigned toFalcatifolium are described as a second species ofSigmaphyllum, S. tasmanensisR.S.Hill & L.J.Scriven, and specimens from mid to late Eocene sediments inTasmania previously assigned to Falcatifolium do notbelong to that genus, although their true generic affinities are uncertain.Dispersed cuticle specimens from Late Eocene–Oligocene sediments inSouth Australia referred to Falcatifolium are notreliable records of the genus and require further investigation. However,Dacrycarpus eocenica D.R.Greenwood, from Middle Eocenesediments in Victoria is transferred to Falcatifolium,and is similar to the extant species F. angustumLaubenfels, which has a leaf morphology unusual for the genus.Falcatifolium eocenica (D.R.Greenwood) R.S.Hill & L.J.Scriven is the only reliable record of the genus in the Australian fossilrecord to date.

Paleogeographic evolution of the United States Pacific Northwest during Paleogene time

1987 ◽  
Vol 24 (8) ◽  
pp. 1652-1667 ◽  
Author(s):  
Paul L. Heller ◽  
Rowland W. Tabor ◽  
Christopher A. Suczek
Keyword(s):  
United States ◽  
Pacific Northwest ◽  
Middle Eocene ◽  
The United States ◽  
Oceanic Islands ◽  
Local Source ◽  
Second Phase ◽  
Early Oligocene ◽  
Basin Development ◽  
Major Transition

Paleogeographic reconstructions for Oregon and Washington during Paleogene time illustrate a major transition from a dominantly compressional (prior to middle Eocene time) to an extensional tectonic regime. This transition resulted in the development of three phases of Paleogene basin evolution in the United States Pacific Northwest. During the initial phase, basins formed along the continental margin during collision of oceanic islands. Sediments in these basins were derived from nearby orogenic highlands. The second phase of basin development began in middle Eocene time and consisted of rapid subsidence of individual basins that formed within a broad forearc region. Nonmarine basins that formed during this phase were caused by extension possibly associated with transcurrent faulting. Rapid sedimentation in both marine and nonmarine basins during this time consisted dominantly of sandstone derived from Cretaceous plutonic sources far to the east. The final stage of basin development was the modification of previous basin configurations by the growth of the Cascade volcanic arc, which was initiated in early Oligocene time. The rising Cascade Range diverted streams carrying eastern-derived material, thereby reducing overall sedimentation rates in the coastal basins and providing a local source of volcanic detritus.

Paleolake salinity evolution in the Qaidam Basin (NE Tibetan Plateau) between ~42 and 29 Ma: Links to global cooling and Paratethys sea incursions

2021 ◽  
Author(s):  
Chengcheng Ye ◽  
Yibo Yang ◽  
Xiaomin Fang ◽  
Weilin Zhang ◽  
Chunhui Song ◽  
...  
Keyword(s):  
Climate Change ◽  
Tibetan Plateau ◽  
Middle Eocene ◽  
Qaidam Basin ◽  
Regional Climate ◽  
Regional Climate Change ◽  
Driving Mechanism ◽  
The Tibetan Plateau ◽  
Early Oligocene ◽  
Global Cooling

&lt;p&gt;Global cooling, the early uplift of the Tibetan Plateau, and the retreat of the Paratethys are three main factors that regulate long-term climate change in the Asian interior during the Cenozoic. However, the debated elevation history of the Tibetan Plateau and the overlapping climate effects of the Tibetan Plateau uplift and Paratethys retreat makes it difficult to assess the driving mechanism on regional climate change in a particular period. Some recent progress suggests that precisely dated Paratethys transgression/regression cycles appear to have fluctuated over broad regions with low relief in the northern Tibetan Plateau in the middle Eocene&amp;#8211;early Oligocene, when the global climate was characterized by generally continuous cooling followed by the rapid Eocene&amp;#8211;Oligocene climate transition (EOT). Therefore, a middle Eocene&amp;#8211;early Oligocene record from the Asian interior with unambiguous paleoclimatic implications offers an opportunity to distinguish between the climatic effects of the Paratethys retreat and those of global cooling.&lt;/p&gt;&lt;p&gt;Here, we present a complete paleolake salinity record from middle Eocene to early Miocene (~42-29 Ma) in the Qaidam Basin using detailed clay boron content and clay mineralogical investigations. Two independent paleosalimeters, equivalent boron and Couch&amp;#8217;s salinity, collectively present a three-staged salinity evolution, from an oligohaline&amp;#8211;mesohaline environment in the middle Eocene (42-~34 Ma) to a mesosaline environment in late Eocene-early Oligocene (~34-~29 Ma). This clay boron-derived salinity evolution is further supported by the published chloride-based and ostracod-based paleosalinity estimates in the Qaidam Basin. Our quantitative paleolake reconstruction between ~42 and 29 Ma in the Qaidam Basin resembles the hydroclimate change in the neighboring Xining Basin, of which both present good agreement with changes of marine benthic oxygen isotope compositions. We thus speculated that the secular trend of clay boron-derived paleolake salinity in ~42-29 Ma is primarily controlled by global cooling, which regulates regional climate change by influencing the evaporation capacity in the moisture source of Qaidam Basin. Superimposed on this trend, the Paratethys transgression/regression cycles served as an important factor regulating wet/dry fluctuations in the Asian interior between ~42 and ~34 Ma.&lt;/p&gt;

scholarly journals Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the Southwest Pacific

2015 ◽  
Vol 11 (4) ◽  
pp. 2977-3018 ◽  
Author(s):  
K. M. Pascher ◽  
C. J. Hollis ◽  
S. M. Bohaty ◽  
G. Cortese ◽  
R. M. McKay
Keyword(s):  
Oxygen Isotope ◽  
High Latitude ◽  
Large Scale ◽  
Middle Eocene ◽  
Late Eocene ◽  
Climate History ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Radiolarian Assemblages

Abstract. The Eocene was characterised by "greenhouse" climate conditions that were gradually terminated by a long-term cooling trend through the middle and late Eocene. This long-term trend was determined by several large-scale climate perturbations that culminated in a shift to "ice-house" climates at the Eocene–Oligocene Transition. Geochemical and micropaleontological proxies suggest that tropical-to-subtropical sea-surface temperatures persisted into the late Eocene in the high-latitude Southwest Pacific Ocean. Here, we present radiolarian microfossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP) Sites 277, 280, 281 and 283 from the middle Eocene to early Oligocene (~ 40–33 Ma) to identify oceanographic changes in the Southwest Pacific across this major transition in Earth's climate history. The Middle Eocene Climatic Optimum at ~ 40 Ma is characterised by a negative shift in foraminiferal oxygen isotope values and a radiolarian assemblage consisting of about 5 % of low latitude taxa Amphicraspedum prolixum group and Amphymenium murrayanum. In the early late Eocene at ~ 37 Ma, a positive oxygen isotope shift can be correlated to the Priabonian Oxygen Isotope Maximum (PrOM) event – a short-lived cooling event recognized throughout the Southern Ocean. Radiolarian abundance, diversity, and preservation increase during the middle of this event at Site 277 at the same time as diatoms. The PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. These high-latitude taxa also increase in abundance during the late Eocene and early Oligocene at DSDP Sites 280, 281 and 283 and are associated with very high diatom abundance. We therefore infer a~northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau towards the end of the late Eocene. In the early Oligocene (~ 33 Ma) there is an overall decrease in radiolarian abundance and diversity at Site 277, and diatoms are absent. These data indicate that, once the Tasman Gateway was fully open in the early Oligocene, a frontal system similar to the present day was established, with nutrient-depleted subantarctic waters bathing the area around DSDP Site 277, resulting in a more oligotrophic siliceous plankton assemblage.

An Early Oligocene age for the oldest known monkeys and rodents of South America

2021 ◽  
Vol 118 (37) ◽  
pp. e2105956118
Author(s):  
Kenneth E. Campbell ◽  
Paul B. O’Sullivan ◽  
John G. Fleagle ◽  
Dorien de Vries ◽  
Erik R. Seiffert
Keyword(s):  
South America ◽  
Amazon Basin ◽  
Middle Eocene ◽  
Detrital Zircons ◽  
Age Difference ◽  
Early Oligocene ◽  
Lower Oligocene ◽  
Upper Oligocene ◽  
Caviomorph Rodents ◽  
Age Estimates

The Santa Rosa fossil locality in eastern Perú produced the first Paleogene vertebrate fauna from the Amazon Basin, including the oldest known monkeys from South America. This diverse paleofauna was originally assigned an Eocene age based largely on the stage of evolution of the site’s caviomorph rodents and marsupials. Here, we present detrital zircon dates that indicate that the maximum composite age of Santa Rosa is 29.6 ± 0.08 Ma (Lower Oligocene), although several zircons from Santa Rosa date to the Upper Oligocene. The first appearance datum for Caviomorpha in South America is purported to be the CTA-27 site in the Contamana region of Perú, which is hypothesized to be ∼41 Ma (Middle Eocene) in age. However, the presence of the same caviomorph species and/or genera at both CTA-27 and at Santa Rosa is now difficult to reconcile with a >11-My age difference. To further test the Middle Eocene age estimate for CTA-27, we ran multiple Bayesian tip-dating analyses of Caviomorpha, treating the ages of all Paleogene species from Perú as unknown. These analyses produced mean age estimates for Santa Rosa that closely approximate the maximum 29.6 ± 0.08 Ma composite date provided by detrital zircons, but predict that CTA-27 is much younger than currently thought (∼30 Ma). We conclude that the ∼41 Ma age proposed for CTA-27 is incorrect, and that there are currently no compelling Eocene records of either rodents or primates in the known fossil record of South America.

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