Richard J. Howarth

Bio: Richard J. Howarth is an academic researcher from University College London. The author has contributed to research in topics: Geologist & Control chart. The author has an hindex of 28, co-authored 88 publications receiving 5402 citations. Previous affiliations of Richard J. Howarth include University of Bristol & University of Cambridge.

Strontium Isotope Stratigraphy: LOWESS Version 3: Best Fit to the Marine Sr‐Isotope Curve for 0–509 Ma and Accompanying Look‐up Table for Deriving Numerical Age

Abstract: An improved and updated version of the statistical LOWESS fit to the marine 87Sr/86Sr record and a revised look-up table (V3:10/99; available from j.mcarthur@ucl.ac.uk) based upon it enables straightforward conversion of 87Sr/86Sr to numerical age, and vice versa, for use in strontium isotope stratigraphy (SIS). The table includes 95% confidence intervals on predictions of numerical age from 87Sr/86Sr. This version includes the Triassic and Paleozoic record (0509 Ma) omitted from previous versions because of the paucity of adequate data at the time of preparation. We highlight differences between the previous versions of the table and the current version and discuss some aspects of the 87Sr/86Sr record that may have geological significance. We give examples of how the table can be used and where it has proven useful.

Statistics For Strontium Isotope Stratigraphy: A Robust Lowess Fit to the Marine Sr‐Isotope Curve For 0 to 206 Ma, With Look‐Up Table For Derivation of Numeric Age

Abstract: We provide a best‐fit curve to 1849 strontium isotope data for the period 0 to 206 Ma using the LOcally‐WEighted regression Scatterplot Smoother (LOWESS) method. This is a robust, nonparametric modern regression technique. Since it does not yield an explicit mathematical equation relating 87Sr/86Sr to time, a look‐up table to determine numeric age has been generated in steps of 1 × 10−6 in 87Sr/86Sr. The calibration uses the timescales of Shackleton and coworkers for 0‐7 Ma; Cande and Kent for 7‐72 Ma; Obradovich for 72‐95 Ma and Gradstein and coworkers for >95 Ma. The look‐up table includes 95% confidence intervals on the predictions of numeric age. When using this table, the uncertainty on the 87Sr/86Sr of the sample whose age is sought must be added to that inherent in the LOWESS regression. We show how to determine the uncertainty in 87Sr/86, i.e., how best to obtain the 95% confidence bounds on a single measurement of 87Sr/86 for a sample, and on the mean 87Sr/86 value for 2 or more replicate measure...

Strontium isotope stratigraphy

Abstract: © F. M. Gradstein, J. G. Ogg, and A. G. Smith 2004. The 87Sr/86Sr value of Sr dissolved in the world's oceans has varied though time, which allows one to date and correlate sediments. This variation and its stratigraphic resolution is discussed and graphically displayed. INTRODUCTION The ability to date and correlate sediments using Sr isotopes relies on the fact that the 87Sr/86Sr value of Sr dissolved in the world's oceans has varied though time. In Fig. 7.1, we show this variation, plotted according to the time scale presented in this volume. More detail is given in Fig. 7.2, on which we plot both the curve of 87Sr/86Sr through time and the data used to derive it. Comparison of the measured 87Sr/86Sr of Sr in a marine mineral with a detailed curve of 87Sr/86Sr through time can yield a numerical age for the mineral. Alternatively, 87Sr/86Sr can be used to correlate between stratigraphic sections and sequences by comparison of the 87Sr/86Sr values in minerals from each (Fig. 7.3). Such correlation does not require a detailed knowledge of the trend through time of 87Sr/86Sr, but it is useful to know the general trend in order to avoid possible confusion in correlation near turning points on the Sr curve. Strontium isotope stratigraphy (SIS) can be used to estimate the duration of stratigraphic gaps (Miller et al., 1988), estimate the duration of biozones (McArthur et al., 1993, 2000, 2004) and stages (Weedon and Jenkyns, 1999), and to distinguish marine from non-marine environments (Schmitz et al., 1991; Poyato-Ariza et al., 1998).

Basinal restriction, black shales, Re‐Os dating, and the Early Toarcian (Jurassic) oceanic anoxic event

Abstract: [1] Profiles of Mo/total organic carbon (TOC) through the Lower Toarcian black shales of the Cleveland Basin, Yorkshire, United Kingdom, and the Posidonia shale of Germany and Switzerland reveal water mass restriction during the interval from late tenuicostatum Zone times to early bifrons Zone times, times which include that of the putative Early Toarcian oceanic anoxic event. The degree of restriction is revealed by crossplots of Mo and TOC concentrations for the Cleveland Basin, which define two linear arrays with regression slopes (ppm/%) of 0.5 and 17. The slope of 0.5 applies to sediment from the upper semicelatum and exaratum Subzones. This value, which is one tenth of that for modern sediments from the Black Sea (Mo/TOC regression slope 4.5), reveals that water mass restriction during this interval was around 10 times more severe than in the modern Black Sea; the renewal frequency of the water mass was between 4 and 40 ka. The Mo/TOC regression slope of 17 applies to the overlying falciferum and commune subzones: the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years. The more restricted of the two intervals has been termed the Early Toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to NW Europe. Crossplots of Re, Os, and Mo against TOC show similar trends of increasing element concentration with increase in TOC but with differing slopes. Together with modeling of 187 Os/ 188 Os and d 98 Mo, the element/TOC trends show that drawdown of Re, Os, and Mo was essentially complete during upper semicelatum and exaratum Subzone times (Mo/TOC regression slope of 0.5). Drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of Re, Os, and Mo, via a low-salinity surface layer, created isotopic excursions of up to 1.3% in d 98 Mo and up to 0.6% for 187 Os/ 188 Os. Restriction thereby compromises attempts to date Toarcian black shales, and possibly all black shales, using Re-Os chronology and introduces a confounding influence in the attempts to use d 98 Mo and initial 187 Os/ 188 Os for palaeo-oceanographic interpretation.

Regression Diagnostics: Identifying Influential Data and Sources of Collinearity

Abstract: 1. Introduction and Overview. 2. Detecting Influential Observations and Outliers. 3. Detecting and Assessing Collinearity. 4. Applications and Remedies. 5. Research Issues and Directions for Extensions. Bibliography. Author Index. Subject Index.

Trace Elements in Soils and Plants

Abstract: Fifteen or more elements present in rocks and soils normally in very small amounts are essential for plant and/or animal nutrition. By the nature of their low abundance in natural uncontaminated earth materials or plants, they are known as trace elements, minor elements or micro-nutrients. Boron, copper, iron, manganese, molybdenum, silicon, vanadium and zinc are required by plants; copper, cobalt, iodine, iron, manganese, molybdenum, selenium and zinc by animals. In addition essential roles of arsenic, fluorine, nickel, silicon, tin and vanadium have in recent years been established in animal nutrition.