Dynamic ecophenotypy in the Silurian Monograptidae (Graptolithina)

2021 ◽  
pp. 1-10
Author(s):  
Misha WHITTINGHAM ◽  
Andrej SPIRIDONOV ◽  
Sigitas RADZEVIČIUS
Keyword(s):  
Primary Productivity ◽  
Initial Phase ◽  
Gamma Ray ◽  
Storm Events ◽  
Baltic Basin ◽  
Sea Level Fluctuations ◽  
Extinction Event ◽  
Ring Structures ◽  
Thickened Ring ◽  
Fifth Order

ABSTRACT The monograptids from the Wenlock and Ludlow (mid- to late Silurian) of the palaeotropical Baltic Basin exhibit thickened ring structures (sicular annuli) over their initial phase of growth. Appearing before the lundgreni extinction event, they persisted throughout the remainder of the Silurian, fluctuating in number over that period. To better understand the mechanisms controlling their development and variation, counts of sicular annuli were taken from three well cores in Lithuania, compared between species in each sample and compared with contemporaneous gamma ray data, accompanied by the stable isotope (δ13C), and acritarch diversity data. Mean counts of annuli fluctuated greatly over the studied interval, but showed negligible variation between species, indicating that the trait is ecophenotypic. The fluctuation in annulus presence aligned with variations in fourth- and fifth-order cycles derived from the gamma ray trends, which represent significant sea level fluctuations, δ13C ratios, and primary productivity, suggesting that annuli were more plentiful in high-stand states which are associated with the wetter climate and more productive conditions, whereas dryer, less productive conditions were not conducive to annulus development. In light of this evidence, we hypothesise that the action of upwelling as a result of intensified storm events during wetter periods would have encouraged phytoplankton blooms, increasing construction of annuli. These results show the potential utility of sicular annuli in the study of Silurian climate change and give new insights into graptolite palaeoecology.

High-resolution assessment of the Valgu event: conodont diversity and δ18Ophos during the early Telychian (Silurian) in the Baltic Basin

2020 ◽  
Author(s):  
Monica Alejandra Gomez Correa ◽  
Emilia Jarochowska ◽  
Peep Männik ◽  
Axel Munnecke ◽  
Michael Joachimski
Keyword(s):  
Carbon Cycle ◽  
Sea Level ◽  
Global Climate ◽  
Baltic Basin ◽  
Sea Level Fluctuations ◽  
Core Section ◽  
Storm Wave ◽  
The Baltic ◽  
A Minor ◽  
The Impact

<p>The influence of global climate and oceanographic system dynamics over biological patterns throughout Earth’s history is one of the main concerns in paleobiology. Periods that record changes in biodiversity of various magnitude are of particular interest in this field. Previous studies of major Silurian bioevents (e.g. Ireviken, Mulde and Lau) suggest that these events affected different faunas and have been correlated with positive carbon isotope (δ<sup>13</sup>C<sub>carb</sub>) excursions and positive shifts in oxygen isotopes (δ<sup>18</sup>O<sub>phos</sub>) ratios, suggesting there was a disturbance in the carbon cycle, a drop in temperature, and potential glaciations. However, the impact of the biological events has not been fully assessed, and the influence of climate change remains unclear.</p><p>Here, we focus on the Valgu event, a minor episode of proposed environmental and faunistic changes in the early Telychian, which has been recognized in Baltica and Laurentia paleocontinents by changes in conodont succession and a positive excursion in δ<sup>13</sup>C<sub>carb</sub>. In this study, we assess a limestone-marl alternation core section in Estonia deposited below the storm wave base during the Valgu event. We test for a substantial decrease in the biodiversity of conodont communities, for extent perturbation in the carbon cycle, manifest in a positive δ<sup>13</sup>C<sub>carb</sub> excursion, and an abrupt positive δ<sup>18</sup>O<sub>phos</sub> shift, which might be indicative of rapid cooling and a rapid sea-level fall typical for glacio-eustatic cycles. To this aim, we measured bulk-rock δ<sup>13</sup>C<sub>carb</sub> as well as δ<sup>18</sup>O<sub>phos</sub> in monogeneric conodont samples and analyzed the conodont diversity from the event interval.</p><p>The lower part of the investigated section is characterized by shallow-water bioclastic limestones containing green algae. On top of this facies, a pronounced hardground indicates a gap in deposition and marks the boundary between the bioclastic limestones and the overlying sediments composed of nodular limestones and marls, which were deposited below the storm wave base. They show a positive carbon shift of ca. 1.4 ‰ during the Valgu interval, but no indication of an extreme change in the conodont biodiversity is evident. Likewise, the δ<sup>18</sup>O<sub>phos</sub> in conodonts remains constant in the section, arguing against cooling or glacially-driven sea-level fluctuations as drivers for the observed changes.</p>

A high-resolution, multiproxy stratigraphic analysis of the Devonian–Carboniferous boundary sections in the Moravian Karst (Czech Republic) and a correlation with the Carnic Alps (Austria)

2013 ◽  
Vol 151 (2) ◽  
pp. 201-215 ◽  
Author(s):  
TOMÁŠ KUMPAN ◽  
ONDŘEJ BÁBEK ◽  
JIŘÍ KALVODA ◽  
JIŘÍ FRÝDA ◽  
TOMÁŠ MATYS GRYGAR
Keyword(s):  
Czech Republic ◽  
Gamma Ray ◽  
Sensu Stricto ◽  
Black Shales ◽  
Element Geochemistry ◽  
Carnic Alps ◽  
Sea Level Fluctuations ◽  
Stratigraphic Analysis ◽  
Carbon Isotope Excursion ◽  
Moravian Karst

AbstractA multidisciplinary correlation of the Devonian–Carboniferous (D–C) boundary sections from the Moravian Karst (Czech Republic) and the Carnic Alps (Austria), based on conodont and foraminifer biostratigraphy, microfacies analysis, field gamma-ray spectroscopy (GRS), carbon isotopes and element geochemistry, is presented in this paper. The study is focused on the interval from the MiddlePalmatolepis gracilis expansaZone (Late Famennian) to theSiphonodella sandbergiZone (Early Tournaisian). In Lesní lom (Moravian Karst), a positive δ13C excursion in theBisphatodus costatus–Protognathodus kockeliInterregnum from a distinct laminated carbonate horizon is correlated with a carbon isotope excursion from the Grüne Schneid section of the Carnic Alps and is interpreted as the equivalent of the Hangenberg black shales and a local expression of the global Hangenberg Eventsensu stricto. Higher up at both sections, a significant increase in the terrigenous input, which is inferred from the GRS signal and elevated concentrations of terrigenous elements (Si, Ti, Zr, Rb, Al, etc.), provides another correlation tieline and is interpreted as the equivalent of the Hangenberg sandstone. Both horizons are discussed in terms of relative sea-level fluctuations and palaeoceanographic changes. Recent studies show that conodont biostratigraphy is facing serious problems associated with the taxonomy of the first siphonodellids, their dependence on facies and discontinuous occurrences of protognathodids at the D–C boundary. Therefore, the correlative potential of geochemical and petrophysical signatures is high and offers an alternative for the refining of the problematic biostratigraphic division of the D–C boundary.

scholarly journals Linking the progressive expansion of reducing conditions to a stepwise mass extinction event in the late Silurian oceans

Geology ◽  
2019 ◽  
Vol 47 (10) ◽  
pp. 968-972 ◽  
Author(s):  
Chelsie N. Bowman ◽  
Seth A. Young ◽  
Dimitri Kaljo ◽  
Mats E. Eriksson ◽  
Theodore R. Them ◽  
...  
Keyword(s):  
Mass Extinctions ◽  
Turnover Rates ◽  
Baltic Basin ◽  
Faunal Turnover ◽  
Isotope Data ◽  
Reducing Conditions ◽  
Carbon Isotope Excursion ◽  
Extinction Event ◽  
Mass Extinction Event ◽  
The Baltic

Abstract The late Ludlow Lau Event was a severe biotic crisis in the Silurian, characterized by resurgent microbial facies and faunal turnover rates otherwise only documented during the “big five” mass extinctions. This asynchronous late Silurian marine extinction event preceded an associated positive carbon isotope excursion (CIE), the Lau CIE, although a mechanism for this temporal offset remains poorly constrained. Here, we report thallium isotope data from locally reducing late Ludlow strata within the Baltic Basin to document the earliest onset of global marine deoxygenation. The initial expansion of anoxia coincided with the onset of the extinction and therefore preceded the Lau CIE. Additionally, sulfur isotope data record a large positive excursion parallel to the Lau CIE, interpreted to indicate an increase in pyrite burial associated with the widely documented CIE. This suggests a possible global expansion of euxinia (anoxic and sulfidic water column) following deoxygenation. These data are the most direct proxy evidence of paleoredox conditions linking the known extinction to the Lau CIE through the progressive expansion of anoxia, and most likely euxinia, across portions of the late Silurian oceans.

scholarly journals Upper Homerian (Silurian) high-resolution correlation using cyclostratigraphy: an example from western Lithuania

2017 ◽  
Vol 67 (2) ◽  
pp. 307-322 ◽  
Author(s):  
Sigitas Radzevičius ◽  
Brigita Tumakovaitė ◽  
Andrej Spiridonov
Keyword(s):  
Wavelet Transform ◽  
Comparative Analysis ◽  
Gamma Ray ◽  
Spectral Estimation ◽  
Time Interval ◽  
Continuous Wavelet ◽  
Baltic Basin ◽  
Regional Stage ◽  
Carbon Isotopic ◽  
Water Facies

AbstractThe Gėluva regional stage stratigraphically corresponds to the late Wenlock. This time interval witnessed significant graptolite extinctions and turnovers of conodont faunas, as well as a large positive Mulde carbon isotopic excursion. Thus, the development of a detailed stratigraphy is a necessary step in understanding the complex patterns of regional and global variations in the sediments accumulating during the time interval studied. Therefore, in this contribution we present a cyclostratigraphic analysis of gamma ray (GR) logs from four wells, which are located in the deep water facies belt of the Lithuanian part of the Silurian Baltic Basin of the Gėluva regional stage. The analysis was performed using REDFIT spectral estimation, continuous wavelet transform and signal filtering techniques. As a result two 4thorder and five 5thorder cycles were distinguished and named in all sections. The correlation of cycles between sections was calibrated with the graptolite biozones. The comparative analysis revealed that intra-basinal cyclostratigraphic correlation could achieve resolution of the order of several tens of thousands of years.

scholarly journals Sequence Stratigraphy of the Arab A to C Members and Hith Formation, Offshore Abu Dhabi

GeoArabia ◽  
1998 ◽  
Vol 3 (2) ◽  
pp. 251-268 ◽  
Author(s):  
Samir R. Azer ◽  
Ross G. Peebles
Keyword(s):  
Upper Jurassic ◽  
Abu Dhabi ◽  
Petroleum Reservoir ◽  
Sequence Stratigraphic ◽  
Sea Level Fluctuations ◽  
Layer Cake ◽  
Geochemical Analyses ◽  
System Tracts ◽  
Maximum Flooding Surface ◽  
Fifth Order

ABSTRACT The Upper Jurassic Hith Formation and Arab members A, B and C, in central and western offshore Abu Dhabi, consist of 450 to over 600 feet of massive to interbedded anhydrites with varying proportions of limestones and dolomites. A high resolution sequence stratigraphic framework for this important petroleum reservoir interval was developed from core and well log data, and various inorganic geochemical analyses. This data was acquired from wells located at 3 locations spread over 100 kilometers. Nineteen shallowing-upward parasequences, corresponding to fourth and possibly fifth-order cycles, were recognized for the Arab members as follows: A (7 cycles), B (5 cycles), and C (7 cycles). Five parasequences were recognized for the Hith Anhydrite Formation. The Arab parasequences are arranged in a layer-cake stacking pattern and vary in thickness from 6 to 30 feet. These are interpreted to correspond to transgressive-regressive episodes which are driven by low-amplitude sea-level fluctuations (eustacy). The typical parasequence consists of shoal grainstones, representing transgressive system tracts, that pass upward into thin-bedded lagoonal burrowed mud/wackestones, representing the maximum flooding surface. These are overlain by coarse bioclastic grainstones capped by algal laminites and culminate into supratidal anhydrites, which pinchout eastwards. In the west offshore Abu Dhabi the parasequences are thicker and consist of intertidal pack/grainstones overlain by anhydrites.

On the possible gamma-ray source in Cygnus

1967 ◽  
Vol 31 ◽  
pp. 469-471
Author(s):  
J. G. Duthie ◽  
M. P. Savedoff ◽  
R. Cobb
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Right Ascension

A source of gamma rays has been found at right ascension 20h15m, declination +35°, with an uncertainty of 6° in each coordinate. Its flux is (1·5 ± 0·8) x 10-4photons cm-2sec-1at 100 MeV. Possible identifications are reviewed, but no conclusion is reached. The mechanism producing the radiation is also uncertain.

Solar Flare Energetic Neutral Emission Measurements in the Project Coronas-I

1994 ◽  
Vol 144 ◽  
pp. 635-639
Author(s):  
J. Baláž ◽  
A. V. Dmitriev ◽  
M. A. Kovalevskaya ◽  
K. Kudela ◽  
S. N. Kuznetsov ◽  
...  
Keyword(s):  
Solar Flare ◽  
Energy Range ◽  
Gamma Rays ◽  
Pulse Shape ◽  
Gamma Ray ◽  
Pulse Shape Discrimination ◽  
Shape Discrimination ◽  
Solar Neutron ◽  
Low Altitude

AbstractThe experiment SONG (SOlar Neutron and Gamma rays) for the low altitude satellite CORONAS-I is described. The instrument is capable to provide gamma-ray line and continuum detection in the energy range 0.1 – 100 MeV as well as detection of neutrons with energies above 30 MeV. As a by-product, the electrons in the range 11 – 108 MeV will be measured too. The pulse shape discrimination technique (PSD) is used.

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