Reducing Disparity in Radio‐Isotopic and Astrochronology‐Based Time Scales of the Late Eocene and Oligocene

Sahy, Diana; Condon, Daniel J.; Hilgen, F.J.; Kuiper, Klaudia F.

doi:10.1002/2017pa003197

Cited by 24 publications

(37 citation statements)

References 96 publications

(291 reference statements)

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“…Although these data are not from the Karaburun section, instead coming from localities to the south and northwest, they provide further useful age constraints on the formation. Zircon U-Pb ages of 33.9 (±0.4) Ma (Kıyıköy locality; Okay et al, 2020), 32.5 Ma, 31.7 Ma, and 31.04 Ma (localities to the south of Karaburun; Okay et al, 2019) have been recorded, all of which are compatible with the age determination of the Karaburun section (age calibration model of Sahy et al, 2017).…”

Section: Integrated Conclusionsupporting

confidence: 71%

Biostratigraphy and paleoenvironments of the Oligocene succession(İhsaniye Formation) at Karaburun (NW Turkey)

Simmons¹,

Bidgood²,

Connell³

et al. 2020

Turkish J Earth Sci

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The biostratigraphy and paleoenvironments of the İhsaniye Formation exposed at Karaburun in northwest Turkey is described based upon the study of abundant and well-preserved foraminifera, calcareous nannofossils and palynomorphs. The studied succession is Early Oligocene in age, with calcareous nannofossil zones upper NP21 (Subzone CNO1) to lower NP23 (Subzone CNO3) and planktonic foraminifera zones O1 (~P18) and O2 (~P19) represented, and palynological assemblages suggestive of zones D13 to D14a. Based on these new data, a revised interpretation of the stratigraphic succession is presented. Deposition was controlled by a now inverted normal fault, with deposition of older stratigraphy (upper NP21 to NP22) restricted to the original hanging wall. During NP23, deposition commenced on the footwall, resulting in progressive onlap of an exposed Eocene reefal limestone (Soğucak Formation). Three primary sedimentary facies are present: marls with thin calcareous siltstones, marls with synsedimentary slumps and debris flows, and coarse pebbly sandstones. The coarse pebbly sandstones were deposited in a fan-delta/shoreface paleoenvironment and represent the initial phase of onlap during biozone NP23 onto a rocky shoreline on the footwall side of the fault. The marl-dominated facies represent deposition in outer shelf-upper bathyal environments. The succession demonstrates evidence for a near-end Eocene relative sea-level fall. Changes in the abundance of planktonic foraminifera and the onlap onto the footwall demonstrate maximum subsequent transgression within NP23. This reflects eustasy rather than Paratethyan relative sea-level. No interpretation of sea-water salinity reduction can be made for the sediments deposited during biozone NP23 in the studied sections, although this is noted in coeval sediments in parts of Paratethys (the "Solenovian Event"). Together with the open marine nature of the diverse and abundant fossil assemblages, it is suggested that deposition of the Karaburun section was strongly influenced by a connection to the global ocean, via the Çatalca Gap, as suggested in a recent study.

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Section: Integrated Conclusionsupporting

confidence: 71%

Biostratigraphy and paleoenvironments of the Oligocene succession(İhsaniye Formation) at Karaburun (NW Turkey)

Simmons¹,

Bidgood²,

Connell³

et al. 2020

Turkish J Earth Sci

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“…The Eocene-Oligocene boundary lies close to the Chadronian-Orellan boundary (Zanazzi et al, 2009). As such, both the Eocene-Oligocene boundary and Chadronian-Orellan Boundary were placed at 33.84 ±0.10 Ma (Ogg and Smith, 2004) but are now placed at 34.09 ± 0.08 Ma (Sahy et al, 2017). Mesohippus…”

Section: Appendix A: Biostratigraphymentioning

confidence: 96%

“…Thus, the new ash dates from the Toadstool Geologic Park sequence should provide a stronger geochronologic framework for calibrating the section than dates from the polarity reversals from the marine record. The Orellan-Chadronian boundary is placed at 33.9 Ma which is synchronous with the UPW at 33.939 ±0.033 Ma (Sahy et al, 2015), and near the Eocene-Oligocene boundary at 34.09 ± 0.08 Ma (Sahy et al, 2017). The accuracy of these dates is vital to correlating the terrestrial and marine climate records.…”

Section: Uncertainty In Magnetic Polarity Zonesmentioning

confidence: 99%

Changes in Mammalian Abundance Through the Eocene-Oligocene Climate Transition in the White River Group of Nebraska, Usa

Gillham¹,

Secord²

2019

Geological Society of America Abstracts With Programs

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Marine records show major cooling during the Eocene-Oligocene Climate Transition (EOCT). Most proxy studies in the White River Group suggest drying across the EOCT, and some suggest cooling. The lower resolution continental record has hindered a direct correlation of the marine climate record to Nebraska. I explore various correlation schemes and what they imply for faunal changes. This study compiles and analyzes data from 4,875 specimens in the University of Nebraska State Museum (UNSM) collection to test the hypothesis that climate change across the Eocene-Oligocene (E-O) boundary caused significant abundance changes in mammals. A series of binning schemes was created. One binning scheme followed previously established lithological zones, two schemes were based on average sediment accumulation rates, and three more were created by applying a cubic spline curve to published 206 Pb/ 238 U zircon ash dates. For the purpose of correlating the marine and Toadstool sections, I constructed a high-resolution (±0.5 m) carbon isotope stratigraphy across the E-O boundary using fossil enamel from the oreodont Merycoidodon. Results show that turnover in taxonomic abundance occurs throughout the study interval and is not concentrated across the EOCT. The largest pulse of faunal change and largest abundance changes for the most common taxa, Merycoidodon and the horse Mesohippus, slightly predate the EOCT. This raises the possibility that climate change began earlier in the continental interior than indicated by the marine benthic oxygen isotope record. Chord distance analyses reveal that the faunal composition of Orellan zones are more similar to one another than they are to the faunas of Chadron zones. This similarity is likely caused by the extinction, or near extinction, of Chadron taxa like Megacerops around the EOCT. Despite the lack of significant change in evenness, numerous taxa underwent extended changes in relative abundance through time. Archaeotherium, a water-dependent artiodactyl, decreased in relative abundance through time just as Poebrotherium, a water-independent camelid, increased in abundance through time. Changes in the relative abundances of Poebrotherium and Archaeotherium are consistent with a drier environment beginning in EOCT. The level of waterdependence in other taxa is less clear, and their changes in abundance cannot be confidently explained through diet, dentition, body mass, or locomotion.

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“…An obvious requirement is that geologic records are complete and that composite records from deep-sea cores are properly constructed in addition to adequate full recognition of cycles and their modulations. Uncertainties in radioisotopic dating, mostly linked to issues regarding the age calibration of standards, are pivotal to astronomical tuning as they are used as a first order constraint (see Sahy et al, 2017;Westerhold et al, 2012, for discussion). A final essential limitation is the accuracy of the orbital solution target curves which is known to worsen beyond some age back in the past (Laskar et al, 2004(Laskar et al, , 2011a(Laskar et al, , 2011b.…”

Section: Orbital Tuning Of the Middle Eocene Interval And Assessment mentioning

confidence: 99%

High‐Resolution Integrated Cyclostratigraphy From the Oyambre Section (Cantabria, N Iberian Peninsula): Constraints for Orbital Tuning and Correlation of Middle Eocene Atlantic Deep‐Sea Records

Dinarès-Turell

Martínez‐Braceras

Payros

2018

Geochem Geophys Geosyst

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The astronomical timescale accuracy generally exceeds other dating methods. Precise age models are pivotal for paleoclimatic research. The middle Eocene astronomical timescale has been poorly constrained due to scarcity of suitable records leading to the so call “Eocene astronomical timescale gap.” We present magnetic susceptibility and color proxy records from an expanded 60 m long cyclic hemipelagic succession from the Oyambre Cape in northern Spain (∼1.3 My long stratigraphic section tuned to the ∼43.1–44.4 Ma interval in the Lutetian stage). We use the strong eccentricity amplitude modulation of precession in the sedimentary record for orbital tuning. The tuned record is correlated at precession level with previously tuned Ocean Drilling Program (ODP) Site 1260 from the equatorial Atlantic (the only oceanic record that registers geochemical variations in the precession band) and to other lower resolution deep‐sea records at eccentricity level from the Southern Atlantic. Our data is consistent with a very long eccentricity minimum (driven by a ∼2.4 My periodicity) at 43.15 Ma in the orbital solutions and an age for the C20n/C20r reversal boundary at ∼43.45 Ma. However, we challenge previous correlations between these Atlantic sites (shifts of one 100 ky eccentricity cycle). Data allows to rule out correlation to either younger or older 405 ky eccentricity cycles, which constrains chronologies for the middle Eocene, emphasizing the need for consistent astrochronological frameworks involving expanded outcrops. This should aid to overcome oceanic drilling shortcomings and sedimentary complexities. Our study highlights this integration need to achieve accuracy and stability of orbital timescales underpinning Eocene paleoclimatic records.

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Reducing Disparity in Radio‐Isotopic and Astrochronology‐Based Time Scales of the Late Eocene and Oligocene

Cited by 24 publications

References 96 publications

Biostratigraphy and paleoenvironments of the Oligocene succession(İhsaniye Formation) at Karaburun (NW Turkey)

Biostratigraphy and paleoenvironments of the Oligocene succession(İhsaniye Formation) at Karaburun (NW Turkey)

Changes in Mammalian Abundance Through the Eocene-Oligocene Climate Transition in the White River Group of Nebraska, Usa

High‐Resolution Integrated Cyclostratigraphy From the Oyambre Section (Cantabria, N Iberian Peninsula): Constraints for Orbital Tuning and Correlation of Middle Eocene Atlantic Deep‐Sea Records

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