scholarly journals The record of the Eocene-Oligocene Transition and the “Grande Coupure”. Magnetostratigraphic constraints from the Ebro Basin revisited.

2021 ◽  
Author(s):  
Miguel Garcés ◽  
Elisabet Beamud ◽  
Miguel López-Blanco ◽  
Manuel Gómez ◽  
Elisenda Costa ◽  
...  
Keyword(s):  
Time Scale ◽  
Lacustrine Sediments ◽  
Magnetic Polarity ◽  
Added Value ◽  
Time Lags ◽  
Geological Time ◽  
Ebro Basin ◽  
Geological Time Scale ◽  
Geological Processes ◽  
Age Constraints

<p>Magnetostratigraphy is the key to put disparate chronological pieces together in a consistent chronostratigraphic framework. Provided that a long continuous record of reversals can be obtained from the sedimentary record, a correlation with the GPTS may be established. Magnetostratigraphy provides added value to the chronology as long as it keeps certain independence from external age constraints, such as bioevents calibrated elsewhere or radiochronologic data.</p><p>An independent correlation is meant to not be anchored to a given chron on the basis of an external age constrain. Our experience recommends that external age constraints are best taken with flexibility, allowing for the searching of a best fit between the magnetic polarity sequence (in meters) and the GPTS (in million-years). This rationale relies on the fact that the Geological Time Scale is the tool that allows earth-scientist of many varied disciplines to understand and discuss about the dimension of time. But the time scale calibration is a task in continuous refinement. As the accuracy and precision of the dating tools increases, our ability to unravel lag times in geological processes increases too. As more refined data is produced, the calibration of the time scale reveals as an ongoing task rather than a final product.</p><p>Here we present the case of the Eocene-Oligocene Transition (EOT) as recorded in alluvial-lacustrine sediments of the eastern Ebro Basin. An earlier work provided a magnetostratigraphic correlation that was in agreement with small-mammals biostratigraphic data. A key constraint to this study was the Santpedor locality, which yielded a characteristic post-Grand Coupure small mammal assemblage, then attributed to the lowest Oligocene.</p><p>An extended record of the magnetostratigraphy has challenged the earlier correlation and puts forward an alternate scenario that reveals a misfit with earlier and recent biochronological interpretations of the fossil mammal record. The significance of this discrepancy in terms of heterochrony of biostratigraphic events, the punctuated character of faunal replacement across the EOT, and time lags between the marine and continental realms may need to be addressed.</p>

scholarly journals Dating the late Proterozoic stratigraphic record

2018 ◽  
Vol 2 (2) ◽  
pp. 137-147 ◽  
Author(s):  
Galen P. Halverson ◽  
Susannah M. Porter ◽  
Timothy M. Gibson
Keyword(s):  
Time Scale ◽  
Snowball Earth ◽  
Geological Time ◽  
Geological Time Scale ◽  
Testing Hypotheses ◽  
Stratigraphic Record ◽  
Composite Section ◽  
Age Model ◽  
Age Constraints ◽  
Age Estimates

The Tonian and Cryogenian periods (ca. 1000–635.5 Ma) witnessed important biological and climatic events, including diversification of eukaryotes, the rise of algae as primary producers, the origin of Metazoa, and a pair of Snowball Earth glaciations. The Tonian and Cryogenian will also be the next periods in the geological time scale to be formally defined. Time-calibrating this interval is essential for properly ordering and interpreting these events and establishing and testing hypotheses for paleoenvironmental change. Here, we briefly review the methods by which the Proterozoic time scale is dated and provide an up-to-date compilation of age constraints on key fossil first and last appearances, geological events, and horizons during the Tonian and Cryogenian periods. We also develop a new age model for a ca. 819–740 Ma composite section in Svalbard, which is unusually complete and contains a rich Tonian fossil archive. This model provides useful preliminary age estimates for the Tonian succession in Svalbard and distinct carbon isotope anomalies that can be globally correlated and used as an indirect dating tool.

Neogene and Quaternary coexisting in the geological time scale: The inclusive compromise

2009 ◽  
Vol 96 (4) ◽  
pp. 249-262 ◽  
Author(s):  
Brian McGowran ◽  
Bill Berggren ◽  
Frits Hilgen ◽  
Fritz Steininger ◽  
Marie-Pierre Aubry ◽  
...  
Keyword(s):  
Time Scale ◽  
Geological Time ◽  
Geological Time Scale

Biostratigraphy of Paleocene-Eocene deposits of the Ukrainian Carpathians based on planktonic foraminifera

2021 ◽  
Vol 3-4 (185-186) ◽  
pp. 56-64
Author(s):  
Svitlana Hnylko
Keyword(s):  
Benthic Foraminifera ◽  
Time Scale ◽  
Planktonic Foraminifera ◽  
Complete Sequence ◽  
Geological Time ◽  
Geological Time Scale ◽  
The Carpathians ◽  
Geological Maps ◽  
Sponge Spicules

Paleogene deposits are the main reservoir of hydrocarbon resources in the Carpathians and creation of the modern stratigraphic scheme of these deposits is the basis for improving the efficiency of geological search works. The reliable stratification is a necessary precondition for the preparation of geological maps. Stratification of the Paleocene–Eocene sediments is provided by foraminifera, nannoplankton, dinocysts, radiolarians, sponge spicules, palynoflora. Planktonic foraminifera is the main stratigraphic group of the Paleogene fauna. In the predominantly non-calcareous flysch of the Paleocene–Eocene of the Carpathians, mainly agglutinated benthic foraminifera of siliceous composition are developed. Planktonic foraminifera are distributed locally – in calcareous facies. The most complete sequence of Paleocene–Eocene planktonic foraminifera is represented in the Metova Formation (the Vezhany nappe of the Inner Carpathians). The results of own researches of natural sections of sediments distributed within the Magursky, Monastyretsky and Vezhany nappes of the Ukrainian Carpathians together with the analysis of literature sources are used. The article presents a generalized biozonal division of the Paleocene–Eocene of the Ukrainian Carpathians by planktonic foraminifera. On the basis of certain correlation levels, a comparison with the Geological Time Scale was made. The Parvularugoglobigerina eugubina Zone (lowermost Danian), Globoconusa daubjergensis Zone (middle Danian), Praemurica inconstans Zone (upper Danian); Morozovella angulata Zone (lower Selandian); Globanomalina pseudomenardii Zone fnd Acarinina acarinata Zone (upper Selandian–Thanetian); Morozovella subbotinae Zone (lower Ypresian), Morozovella aragonensis Zone (upper Ypresian); Acarinina bullbrooki Zone (lower Lutetian), Acarinina rotundimarginata Zone (upper Lutetian); Hantkenina alabamensis Zone (Bartonian); Globigerinatheka tropicalis Zone (lower Priabonian) and Subbotina corpulenta Zone (upper Priabonian) based on planktonic foraminifera are characterized in studied deposits.

Experimental fluid-mediated alteration of zircon under lower greenschist facies conditions

2020 ◽  
Vol 58 (2) ◽  
pp. 247-265
Author(s):  
Colter J. Kelly ◽  
Daniel E. Harlov ◽  
David A. Schneider ◽  
Simon E. Jackson ◽  
Renelle Dubosq
Keyword(s):  
Ion Exchange ◽  
Inductively Coupled Plasma ◽  
Earth Science ◽  
Science Research ◽  
Aqueous Fluid ◽  
Mapping Technique ◽  
Geological Time ◽  
Geological Time Scale ◽  
Chemically Modified ◽  
Geological Processes

ABSTRACT The use of zircon in the dating of geological processes and tectonic events has become a standard approach in many aspects of Earth science research. As a result, understanding how zircon interacts with aqueous fluids during metasomatism has become increasingly important. The alteration of natural zircon is driven primarily by coupled dissolution–reprecipitation or by ion-exchange with an aqueous fluid. In this study, whole and intact, euhedral light-brown zircon crystals (100–250 μm in length; 2 mg) from the Oligocene Fish Canyon Tuff (FCT) were experimentally reacted with an alkali-bearing reactive fluid and a REE + P source (0.5 mg CePO4 or 0.5 mg YPO4). Experiments were conducted in sealed Au metal capsules at 350 °C and 100 MPa for 182 days. During the experiment, the zircon became colorless, indicating annealing of the radiation damage in the crystal. Two-dimensional element maps of the outermost 3 μm of unpolished zircon crystal surfaces were produced using a grind of contiguous 7 μm analytical spots via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The chemical maps indicate that the surface of the zircon crystals from each experiment heterogeneously reacted with the fluid, such that the Ce and Y concentration of chemically modified areas increased (by an order of magnitude) in the CePO4-bearing and YPO4-bearing experiments, respectively, when compared with the chemical maps of unaltered zircon grain surfaces. Helium ion microscopy of polished crystals revealed discontinuous micron-scale altered domains at the crystal margin, consistent with the findings of the unpolished mapping technique. Interestingly, the Th and U concentration of the altered zircon grain surfaces were consistent with the unaltered zircon regardless of the experiment. Incorporation of REEs on the zircon grain surface likely occurred via the coupled substitution REE3+ + P5+ ↔ Zr4+ + Si4+. The results from these experiments imply that the surfaces of minimally metamict zircon can be chemically modified by alkali-bearing fluids via ion exchange under lower greenschist pressures and temperatures over relatively short time periods with respect to the geological time scale.

Sign in / Sign up

Export Citation Format

Share Document