Recalibrating the Devonian time scale: A new method for integrating radioisotopic and astrochronologic ages in a Bayesian framework

The numerous biotic, climatic, and tectonic events of the Devonian cannot be correlated and investigated without a well-calibrated time scale. Here, we updated the calibration of the Devonian time scale using a Bayesian age-depth model that incorporates radioisotopic ages and astrochronology durations. We used existing radioisotopic ages collected and harmonized in the last two geologic time scale compilations, as well as new U-Pb zircon ages from Emsian {Hercules I K-bentonite, Wetteldorf, Germany: 394.290 ± 0.097(0.21)[0.47] Ma} and Eifelian K-bentonites {Tioga B and Tioga F K-bentonites, Fayette, New York, USA: 390.82 ± 0.18(0.26)[0.48] Ma and 390.14 ± 0.14(0.23)[0.47] Ma, respectively}. We anchored floating astrochronology stage durations on radioisotopic ages and chained astrochronologic constraints and uncertainty together to extrapolate conditioning age likelihoods up or down the geologic time scale, which is a new method for integrating astrochronology into age-depth modeling. The modeling results in similar ages and durations for Devonian stages regardless of starting biostratigraphic scaling assumptions. We produced a set of rescaled biostratigraphic zonations, and a new numerical calibration of Devonian stage boundary ages with robust uncertainty estimates, which allow us to evaluate future targets for Devonian time scale research. These methods are broadly applicable for time scale work and provide a template for an integrated stratigraphic approach to time scale modeling.

Redwood National and State Parks: Geologic resources inventory report

Comprehensive park management to fulfill the NPS mission requires an accurate inventory of the geologic features of a park unit, but Comprehensive park management to fulfill the NPS mission requires an accurate inventory of the geologic features of a park unit, but park managers may not have the needed information, geologic expertise, or means to complete such an undertaking; therefore, the Geologic Resources Inventory (GRI) provides information and resources to help park managers make decisions for visitor safety, planning and protection of infrastructure, and preservation of natural and cultural resources. Information in the GRI report may also be useful for interpretation. park managers may not have the needed information, geologic expertise, or means to complete such an undertaking; therefore, the Geologic Resources Inventory (GRI) provides information and resources to help park managers make decisions for visitor safety, planning and protection of infrastructure, and preservation of natural and cultural resources. Information in the GRI report may also be useful for interpretation. This report synthesizes discussions from a scoping meeting for Redwood National and State Parks (referred to as the “parks” throughout this report) held in 2004 and a follow-up conference call in 2019. Two GRI–compiled GIS data sets of the geology and geohazards of the parks are the principal deliverables of the GRI. The GRI GIS data are available on the GRI publications website http://go.nps.gov/gripubs and through the NPS Integrated Resource Management Applications (IRMA) portal https://irma.nps.gov/App/Portal/Home. Enter “GRI” as the search text and select a park from the unit list. Writing of this report was based on those data and the interpretations of the source map authors (see “GRI Products” and “Acknowledgements”). A geologic map poster illustrates the geology GRI GIS data set and serves as a primary figure for this GRI report. No poster was prepared for the geohazards GRI GIS data set. Additionally, figure 7 of this report illustrates the locations of the major geologic features in the parks. Unlike the poster, which is divided into a northern and southern portion to show detail while accommodating the parks’ length, figure 7 is a single-page, simplified map. The features labeled on figure 7 are discussed in the “Geologic History, Features, and Processes” chapter. To provide a context of geologic time, this report includes a geologic time scale (see "Geologic History, Features, and Processes"). The parks’ geologic story encompasses 200 million years, starting in the Jurassic Period. Following geologic practice, the time scale is set up like a stratigraphic column, with the oldest units at the bottom and the youngest units at the top. Organized in this manner, the geologic time scale table shows the relative ages of the rock units that underlie the parks and the unconsolidated deposits that lie at the surface. Reading the “Geologic Event” column in the table, from bottom to top, will provide a chronologic order of the parks’ geologic history. The time scale includes only the map units within the parks that also appear on the geologic map poster; that is, map units of the geohazards data are not included. Geology is a complex science with many specialized terms. This report provides definitions of geologic terms at first mention, typically in parentheses following the term. Geologic units in the GRI GIS data are referenced in this report using map unit symbols; for example, map unit KJfrc stands for the Cretaceous (K) and Jurassic (J) Franciscan Complex (f), Redwood Creek schist (rc), which underlies a portion of the Redwood Creek watershed (see “GRI Products”).

Machine Learning Applied to K-Bentonite Geochemistry for Identification and Correlation: The Ordovician Hagan K-Bentonite Complex Case Study

Altered tephras (K-bentonites) are of great importance for calibration of the geologic time scale, for local, regional, and global correlations, and paleoenvironmental reconstructions. Thus, definitive identification of individual tephras is critical. Single crystal geochemistry has been used to differentiate tephra layers, and apatite is one of the phenocrysts commonly occurring in tephras that has been widely used. Here, we use existing and newly acquired analytical datasets (electron probe micro-analyzer [EPMA] data and laser ablation ICP-MS [LA-ICP-MS] data, respectively) of apatite in several Ordovician K-bentonites that were collected from localities about 1200 km apart (Minnesota/Iowa/Wisconsin and Alabama, United States) to test the use of machine-learning (ML) techniques to identify with confidence individual tephra layers. Our results show that the decision tree based on EPMA data uses the elemental concentration patterns of Mg, Mn, and Cl, consistent with previous studies that emphasizes the utility of these elements for distinguishing Ordovician K-bentonites. Differences in the experimental setups of the analyses, however, can lead to offsets in absolute elemental concentrations that can have a significant impact on the correct identification and correlation of individual K-bentonite beds. The ML model using LA-ICP-MS data was able to identify several K-bentonites in the southern Appalachians and establish links to K-bentonites samples from the Upper Mississippi Valley. Furthermore, the ML model identified individual layers of multiphase eruptions, thus illustrating very well the great potential of applying ML techniques to tephrochronology.

Plate Tectonics

This chapter illustrates the most significant revolution in the understanding of the Earth discovered in the last 75 years, plate tectonics. The theory of plate tectonics is the second overarching precept of the field of geology (after the geologic time scale). Plate tectonics and its history as a theory are traced in this chapter. Early explorers and others had noticed the apparent fit in the shapes of the continents, but these ideas were not explicitly stated until Alfred Wegener detailed his evidence for the drift of the continents, though he had no viable mechanism on how the drift would have occurred. World War II technology, including sonar and radar, allowed scientists to understand the ocean floor. Rather than a flat, featureless plain, they found a vast undersea mountain range known as the mid-oceanic ridge that wraps around the world like seams on a baseball. Harry Hess proposed a new mechanism for continental drift through mantle convection cells, causing seafloor spreading. These ideas were confirmed by magnetic surveys and subsequent research, leading to the theory of plate tectonics. A final section looks at the maturation of the theory as geologists continue to learn more details about the movement and intricacies of the tectonic plates.

Geologic Time

Geologists first unraveled the geologic time scale by relative age-dating, discussed in the last chapter. Once geologists sorted out the order of rock units, subsequent advances in methodologies, detailed in this chapter, by chronometric and numerical means based on radioisotopes, other atomic measures, and quantitative techniques, were employed to measure time. Many minerals and rocks have “clocks” within them that can be used to pin down the actual age of the particular geologic sample or the age of boundaries between formal units of the geologic time scale. This chapter explains how geologists decipher those clocks and determine the ages of rocks by numerical age-dating. The history of radioisotopes is tracked, starting with Ernest Rutherford and Pierre and Marie Curie. The modern geologic time scale is depicted and expanded upon, along with why it is essential for geologic maps and how the time scale can help with people-sized problems and challenges faced on the Earth.

Large Igneous Provinces of the Amazonian Craton and their Metallogenic Potential in Proterozoic Times

This paper overviews the Proterozoic Large Igneous Provinces of the Amazonian Craton, characterized by large volumes of extrusive and intrusive magmatic rocks. We reassess the geologic, geochronologic and geochemical information to stablish three intracontinental felsic volcanic-plutonic igneous belts (i.e., SLIPs), namely: Orocaima (1.98-1.96 Ga), Uatumã (1.88-1.87 Ga) and Alta Floresta (1.80-1.79 Ga). The Avanavero LIP (1.79-1.78 Ga), as well as the Rincón del Tigre-Huanchaca LIP (1.11 Ga) are also revisited. The relationships of these events with intraplate settings through time and space are apparent. We examine the main characteristics of each magmatic event in light of the U-Pb zircon and baddeleyite ages and coupled isotopic-geochemical constraints, the geodynamic significance, and metallogenetic potential. The Uatumã and Alta Floresta SLIPs host the most important mineral resources within the Amazonian Craton. Global barcode matches of the Proterozoic SLIPS/LIP events of Amazonia are also addressed, as well as their possible links with geologic time-scale periods: the Orosirian, Statherian and Stenian boundaries. We also evaluate the available paleomagnetic data to address issues related to the barcode match of such SLIP/LIP events in the context of supercontinent cycles.

Systematics of Lutetian Larger Foraminifera and magneto-biostratigraphy from the South Pyrenean Basin (Sierras Exteriores, Spain)

An extense systematic description of the Eocene larger foraminiferal faunas recorded in the South Pyrenean Basin (Sierras Exteriores) is presented herein. The large dataset provided in this work includes both Nummulites and Alveolina species, along with a variety of other porcellaneous and hyaline taxa with lesser biostratigraphic relevance, are represented. The larger foraminifera described in this work correspond mainly to the Lutetian (SBZ13 to SBZ16 biozones) interval, but late Ypresian (SBZ11, Cuisian) and Bartonian (SBZ17) shallow benthic zones have also been identified.As one of the most relevant results of this systematic analysis, a new species, Idalina osquetaensis, is described. The systematic revision of middle to late Lutetian alveolines led to a reassessment of A. fusiformis and the finding of two new precursor forms, described as affinis of their corresponding species, A. aff. fragilis and A. aff. elongata. The new forms A. aff. elongata and A. aff. fragilis fill the gap in the middle to late Lutetian alveolinid biostratigraphy. Despite not being exclusive to SBZ16, these new forms provide realiable biostratigraphic information where Nummulites are not present. This realibility lies on the correlation of Nummulites and Alveolina biomarkers in the same sections and their calibration to the global time scale through magnetostratigraphy. In fact, magnetostratigraphic calibration of all described taxa is also provided, along with an update of the SBZ calibration to the current Geologic Time Scale (Gradstein et al., 2012).

Magnetostratigraphy of U-Pb–dated boreholes in Svalbard, Norway, implies that magnetochron M0r (a proposed Barremian-Aptian boundary marker) begins at 121.2 ± 0.4 Ma

The age of the beginning of magnetic polarity Chron M0r, a proposed marker for the base of the Aptian Stage, is disputed due to a divergence of published radioisotopic dates and ambiguities in stratigraphic correlation of sections. Our magnetostratigraphy of core DH1 from Svalbard, Norway, calibrates a bentonite bed, dated by U-Pb methods to 123.1 ± 0.3 Ma, to the uppermost part of magnetozone M1r, which is ~1.9 m.y. before the beginning of Chron M0r. This is the first direct calibration of any high-precision radioisotopic date to a polarity chron of the M sequence. The interpolated age of 121.2 ± 0.4 Ma for the beginning of Chron M0r is younger by ~5 m.y. than its estimated age used in the Geologic Time Scale 2012, which had been extrapolated from radioisotopic dates on oceanic basalts and from Aptian cyclostratigraphy. The adjusted age model implies a commensurate faster average global oceanic spreading rate of ~12% during the Aptian–Santonian interval. Future radioisotopic dating and high-resolution cyclostratigraphy are needed to investigate where to expand the mid-Jurassic to earliest Cretaceous interval by the required ~4 m.y.

Astronomical calibration of the OAE1b, Col de Pré Guittard, Vocontian Basin, France

<p>The Cretaceous period was punctuated by several episodes of widespread deoxygenation of the sea floor referred to as Oceanic Anoxic Events. The OAE1b around the Aptian - Albian boundary is characterized by a series of black shales deposits, namely Jacob, Kilian, Paquier and Leenhardt levels. They are well documented in the Vocontian Basin, and their equivalent have been observed in different basins across the globe. Disagreement of more than a million of years exist about the timing of these events, leaving vast uncertainties about the causes of these recurring environmental changes. In order to better understand the relation between the climate perturbation and anoxic events during the Aptian-Albian period, we have focused on high-resolution investigations of magnetic susceptibility of Col de Pré-Guittard section, Drôme, France (GSSP of the Albian Stage; Kennedy et al., 2017). This section in the Blue Marls Formation consists of monotonous dark-grey marlstones interrupted by limestone beds and organic-rich layers. Spectral analyses were conducted on a magnetic susceptibility signal sampled every 5 cm. From this, we detected the record of the eccentricity, obliquity and precession cycles. We used the 100-kyr eccentricity cycles to construct an orbital time scale and shows that the interval starting above the Jacob level and ending above the Leenhardt level contains 21 repetitions of the 100-kyr eccentricity in the magnetic susceptibility data, leading to a duration of ca. 2.1 Myr. This duration is significantly shorter than the duration of 4 Myr provided by the current geologic time scale (Gale et al., 2020) but agrees with the U-Pb ages anchored to a δ<sup>13</sup>C<sub>org</sub> curve from the High Arctic (Herrle et al., 2015).</p><p>References:</p><p>Gale, A.S., Mutterlose, J., Batenburg, S., 2020. Chapter 27: The Cretaceous Period, in: Gradstein, F.M., Ogg, J.G., Schmitz, M.D., Ogg, G.M. (Eds.) Geologic Time Scale 2020. Elsevier BV, Amsterdam, The Netherlands, pp. 1023–1086.</p><p>Herrle, J., Schröder-Adams, C.J., Davis, W., Pugh, A.T., Galloway, J.M., Fath, J., 2015. Mid-Cretaceous High Arctic stratigraphy, climate, and Oceanic Anoxic Events. Geology 43, 403–406.</p><p>Kennedy, J.W., Gale, A.S., Huber, B.T., Petrizzo, M.R., Bown, P., Jenkyns, H.C., 2017. The Global Boundary Stratotype Section and Point (GSSP) for the base of the Albian Stage, of the Cretaceous, the Col de Pré-Guittard section, Arnayon, Drôme, France. Episodes 40, 177–188.</p>