Petrography of Late Cambrian to Middle Ordovician radiolarian chert in Kazakhstan with special reference to the emergence of benthic animals in the pelagic realm

Sedimentology ◽  
2020 ◽  
Vol 67 (5) ◽  
pp. 2764-2776
Author(s):  
Yoshitaka Kakuwa ◽  
Olga I. Nikitina
Keyword(s):  
Special Reference ◽  
Radiolarian Chert ◽  
Middle Ordovician ◽  
Late Cambrian ◽  
Benthic Animals

Trace fossils in Ordovician radiolarian chert successions in the Southern Uplands, Scotland

2016 ◽  
Vol 107 (1) ◽  
pp. 13-22 ◽  
Author(s):  
Yoshitaka Kakuwa ◽  
James D. Floyd
Keyword(s):  
Organic Matter ◽  
Trace Fossils ◽  
The Other ◽  
Ocean Bottom ◽  
Animal Life ◽  
Radiolarian Chert ◽  
Benthic Animal ◽  
Middle Ordovician ◽  
Firm Evidence ◽  
Benthic Animals

ABSTRACTRadiolarian chert and associated siliceous claystone in the Southern Uplands of Scotland are examined, in order to study the Great Ordovician Biodiversification Event of benthic animals on the pelagic ocean bottom. Trace fossils which are uncommon, but convincing, are found in the grey chert and siliceous claystone of Gripps Cleuch. These observations constitute firm evidence that large benthic animals which could leave visible trace fossils had colonised the Iapetan Ocean by the late Middle Ordovician, confirming previous studies from Australia for Panthalassa, the other huge ocean. Red chert is, however, a poor recorder of trace fossils, probably because the highly oxidising environment breaks down organic matter, both inhibiting high-density activity of large benthic animals and removing clear traces of benthic animal life.

K–Ar age determinations on the fine fractions of clay mineral ‘Crystallinity Index Standards’ from the Palaeozoic mudrocks of southwest England

Clay Minerals ◽  
2019 ◽  
Vol 54 (1) ◽  
pp. 15-26 ◽  
Author(s):  
Anna C. Schomberg ◽  
Klaus Wemmer ◽  
Laurence N. Warr ◽  
Georg H. Grathoff
Keyword(s):  
Clay Mineral ◽  
Crystallinity Index ◽  
White Mica ◽  
Early Jurassic ◽  
Late Triassic ◽  
X Ray Diffraction ◽  
Middle Ordovician ◽  
Late Cambrian ◽  
Isotopic Analyses ◽  
Mineral Crystallinity

AbstractClay mineral ‘Crystallinity Index Standards’ (CIS) composed of Palaeozoic mudrocks from southwest England were investigated systematically in five sub-fractions per sample for the first time. X-ray diffraction was used to determine mineral assemblages, calibrated 001 illite full-width-at-half-maximum (FWHM) values and illite polytype compositions, in addition to K–Ar isotopic analyses of all fine fractions. The FWHM results of the <2 µm fraction are consistent with previous studies and reflect the range of diagenetic to epizonal grades covered by the sample set SW1 to SW7 (~0.61–0.26°2θ). Diagenetic and lower anchizone samples also show significant broadening of 001 illite reflections in the finer fractions and contain mixtures of authigenic 1M + 1Md illite and detrital 2M1 white mica polytypes suitable for illite age analysis. The estimated end-member ages of the Bude (SW1-1992) and younger Crackington (SW3-2000) mudstones yield detrital ages of Late Cambrian to Middle Ordovician (493–457 Ma) and a broad range of 1M + 1Md illite ages between Middle Permian and Early Jurassic (271–190 Ma). The detrital age of the stratigraphically older Crackington Formation mudrock (SW2-1992) is Late Devonian (384–364 Ma) with 1M + 1Md illite ages between Late Triassic and Early Jurassic (219–176 Ma). The origin of Mesozoic 1M + 1Md illite ages may represent neocrystallized illite associated with Mesozoic hydrothermal events or similar events that thermally reset older authigenic illite with partial loss of radiogenic argon and no renewed crystal growth. In contrast, upper anchizonal and epizonal Devonian slates (SW3-2012, SW4-1992, SW6-1992 and SW7-2012) contain only the 2M1 polytype, with K–Ar ages younger than the stratigraphic age. The three finest fractions of SW4-1992 yield consistent Late Carboniferous ages (331–304 ± 7 Ma) that are considered to date the neocrystallized 2M1 mica. Most fractions of epizonal slate (SW6-1992, SW7-2012) yield Early Permian ages (293.6–273 Ma) corresponding to published cooling ages of the Tintagel High-Strain Zone and the intrusion of the Bodmin granite (291.4 ± 0.8 Ma). These first K–Ar age constraints for the fine fractions of the CIS should provide useful reference values for testing analytical procedures of illite age analysis.

Early radiation of echinoderms

1997 ◽  
Vol 3 ◽  
pp. 205-224 ◽  
Author(s):  
James Sprinkle ◽  
Thomas E. Guensburg
Keyword(s):  
Mass Extinction ◽  
Fossil Record ◽  
Early Paleozoic ◽  
Soft Substrate ◽  
Middle Cambrian ◽  
Middle Ordovician ◽  
Late Cambrian ◽  
Low Diversity ◽  
Early Radiation ◽  
Ways Of Life

Echinoderms underwent a major two-part radiation that produced all of the major groups found in the fossil record between the Early Cambrian and the Middle Ordovician. A small initial radiation in the Early and Middle Cambrian produced about nine classes containing low-diversity members of the Cambrian Evolutionary Fauna. These were characterized by primitive morphology, simple ambulacral feeding structures, and the early development of a multiplated stalk or stem for attachment to skeletal fragments on a soft substrate. Several groups became extinct at the end of the Middle Cambrian, leaving the Late Cambrian as a gap of very low diversity in the fossil record of echinoderms with only four classes preserved and very few occurrences of complete specimens, mostly associated with early hardgrounds. The survivors from this interval re-expanded in the Early Ordovician and were joined by many newly evolved groups to produce a much larger radiation of more advanced, diverse, and successful echinoderms representing the Paleozoic Evolutionary Fauna on both hard and soft substrates. At least 17 classes were present by the Middle Ordovician, the all-time high point for echinoderm class diversity, and nearly all of the major ways-of-life (except for deep infaunal burrowing) had been developed. With the rise to dominance of crinoids, many less successful or archaic groups did not survive the Middle Ordovician, and echinoderm class diversity dropped further because of the mass extinction at the end of the Ordovician. This weeding-out process of other less-successful echinoderm groups continued throughout the rest of the Paleozoic, and only five classes of echinoderms have survived to the Recent from this early Paleozoic radiation.

Palynology of the Ordovician Kanosh Shale at Fossil Mountain, Utah

2015 ◽  
Vol 89 (3) ◽  
pp. 424-447 ◽  
Author(s):  
Marco Vecoli ◽  
John H. Beck ◽  
Paul K. Strother
Keyword(s):  
North America ◽  
Shallow Water ◽  
New Taxa ◽  
Middle Ordovician ◽  
Incomplete Knowledge ◽  
Late Cambrian ◽  
Freshwater Influence ◽  
Depositional Setting ◽  
Biological Differences

AbstractPalynomorph assemblages recovered from the Kanosh Shale at Fossil Mountain, Utah, are dominated by operculate acritarchs and cryptospores with minor smaller acritarchs. The present findings add new data to the largely incomplete knowledge of Ordovician acritarch assemblages from Laurentia, up to now known only from very few localities in North America. These populations contain some species in common with acritarchs from the Canning and Georgina basins in Australia and with assemblages from China; they indicate a Middle Ordovician (Dapingian-Darriwilian) age. The assemblage is lacking many typical marine acritarchs of this age, which, in combination with some cryptospores, is probably reflecting the likelihood of freshwater influence in the Kanosh Basin. This observation is congruent with previous interpretations of the depositional setting of the Kanosh Shale as a shallow water lagoon that supported the deposition of carbonate hardgrounds.Four new taxa are described: Busphaeridium vermiculatum n. gen., n. sp.; Digitoglomus minutum n. gen., n. sp.; Turpisphaera heteromorpha n. gen., n. sp.; and Vermimarginata barbata n. gen., n. sp. In addition, the abundance of operculate forms has enabled the revision and a new emendation of the genus Dicommopalla and clarification of the “opalla” complex. We also propose new and revised suprageneric taxa that emphasize inferred biological differences among acritarch genera. The Sphaeromorphitae subgroup is emended to include forms lacking sculptural elements. Two new informal subgroups are proposed: the Superornamenti and the Operculate Acritarchs. Cryptospores are abundant throughout the sections studied and they appear to be more closely related to the late Cambrian Agamachates Taylor and Strother than to Darriwilian and younger Ordovician cryptospores from Gondwana.

Lichidae (Trilobita): Morphology and classification

2002 ◽  
Vol 76 (2) ◽  
pp. 306-320 ◽  
Author(s):  
H. B. Whittington
Keyword(s):  
Special Reference ◽  
External Surface ◽  
Surface Form ◽  
Type Specimens ◽  
Middle Ordovician ◽  
Strongly Convex ◽  
Early Diversification

Morphology is reviewed with special reference to the doublure and thoracic characters; a reconstruction of Richterarges aquilonius is used to suggest possible lichid anatomy. The relatively large hypostome and wide doublure, and the thorax with, or without, the strongly convex posterior pleural bands characterize lichids, in addition to the distinctive glabellar morphology. Relatively shallow furrows on the external surface form strong ridges on the visceral surface of the exoskeleton; apodemes are absent. Type specimens of species described by Schmidt, recently traced in Russian museums, are figured. Lichids differ from odontopleurids in morphology and anatomy, and are unlike Scutelluinae; accepted subfamilial divisions of Lichidae are reinforced by thoracic characters. A single lichid species is known in the early Tremadoc, in the early Middle Ordovician the main four subfamilies are recognised and are widespread; their ancestry and early diversification remain unknown.

Latest Middle Cambrian metazoan reef from northern Iran

1995 ◽  
Vol 132 (4) ◽  
pp. 367-373 ◽  
Author(s):  
B. Hamdi ◽  
A. Yu. Rozanov ◽  
A. Yu. Zhuravle
Keyword(s):  
Northern Iran ◽  
Middle Cambrian ◽  
Middle Ordovician ◽  
Late Cambrian ◽  
The Family ◽  
Middle And Late Cambrian

AbstractMiddle and Late Cambrian reefs were built mainly by cyanobacterial communities. A few reefs with a metazoan as well as an algal component, however, are known from this interval. A Middle Cambrian reef formed primarily by spicular demosponges is described here from the Mila Formation in the Elburz Mountains, northern Iran. The reef is enclosed within calcareous grainstones which contain terminal Middle Cambrian (late Mayan) trilobites. The Mila Formation reef was constructed by sponges of the family Anthaspidellidae and bacterial (algal?) sheaths, and is the earliest metazoan reef to be documented from the interval after the demise of archaeocyath sponges. The reefal community is typical of subsequent reefal communities of Early–Middle Ordovician age. The Ordovician examples differ only by the incorporation of additional metazoan elements.

U–Pb age determinations on Proterozoic to Devonian rocks from northern Ellesmere Island, Arctic Canada

1987 ◽  
Vol 24 (2) ◽  
pp. 246-256 ◽  
Author(s):  
H. P. Trettin ◽  
R. Parrish ◽  
W. D. Loveridge
Keyword(s):  
Deep Water ◽  
Lower Cambrian ◽  
Crystalline Basement ◽  
Significant Component ◽  
Zircon Age ◽  
Water Basin ◽  
Middle Ordovician ◽  
Late Cambrian ◽  
Deep Water Basin ◽  
Age Determinations

This paper presents age determinations on six units of the Franklinian deep-water basin and the Pearya Terrane of northern Ellmere Island and discusses their tectonic implications.Four different fractions of detrital zircon from the Lower Cambrian Grant Land Formation of the deep-water basin all have average 207Pb/206Pb ages of 2.2–2.4 Ga, suggesting that the sediments were derived mainly from Aphebian–Archean parts of the Canadian Shield rather than from the Neohelikian crystalline basement of Pearya, as assumed earlier. The first evidence for Ordovician arc-type volcanism in the northern part of the deep-water basin is provided by a Llandeilo(?) zircon age of [Formula: see text] but the fault-bounded volcanic unit could be exotic.Four major stratigraphic successions are recognized in Pearya. Present zircon studies confirm that succession I has been affected by a 1.0–1.1 Ga orogeny, as inferred earlier by Sinha and Frisch from a Rb–Sr isochron. A zircon age of [Formula: see text] on a rhyolite demonstrates that succession II extended into the Late Cambrian or Early Ordovician.Granitic intrusions in the Pearya Terrane, at Cape Richards and Cape Woods, are, respectively, Middle Ordovician (463 ± 5 Ma) and Devonian (382 ± 18 Ma or, more likely, 390 ± 10 Ma) in age on the basis of combined zircon and sphene determinations. They are post-tectonic with regard to major deformations in the Middle Ordovician and Late Silurian. Both have a significant component of xenocrystic zircon, which appears to have been derived from succession I of Pearya on the basis of upper intercept ages.

A revision of the stratigraphic nomenclature of the Cambrian–Ordovician strata of the Philipsburg tectonic slice, southern Quebec

2007 ◽  
Vol 44 (12) ◽  
pp. 1775-1790 ◽  
Author(s):  
O Salad Hersi ◽  
G S Nowlan ◽  
D Lavoie
Keyword(s):  
Middle Ordovician ◽  
Upper Cambrian ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Lower Ordovician ◽  
Stratigraphic Position ◽  
Stratigraphic Nomenclature ◽  
Unconformable Contact ◽  
Tectonic Slice ◽  
Upper Boundary

The Philipsburg tectonic slice is bounded to the west by a northeast–southwest-trending thrust fault (Logan’s Line) and preserves 10 formations of Middle (?) to Late Cambrian (Milton, Rock River, and Strites Pond formations), Early Ordovician (Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations), and early Middle Ordovician (Luke Hill, Solomons Corner, and Corey formations) age. The strata were previously assigned to the Philipsburg Group. Early correlations between the Philipsburg succession and coeval strata of the St. Lawrence Platform were mainly based on sparse macrofauna and inferred stratigraphic position. Unconformities at the Cambrian–Ordovician and Early Ordovician – Middle Ordovician boundaries occurring in autochthonous St. Lawrence Platform and the allochthonous Philipsburg succession (Philipsburg tectonic slice) highlight new stratigraphic interpretations between the inner-shelf (St. Lawrence Platform) and the outer-shelf (Philipsburg) successions. The succession in the Philipsburg tectonic slice is divided into three new groups. The Middle (?) to Upper Cambrian Missisquoi Group (new) includes the Milton, Rock River, and Strites Pond formations. The upper boundary of the Missisquoi Group is defined by the upper unconformable contact between the Upper Cambrian Strites Pond Formation and overlying Lower Ordovician Wallace Creek Formation. The Missisquoi Group correlates with the Potsdam Group of the St. Lawrence Platform. The Lower Ordovician School House Hill Group (new) includes the Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations. The upper boundary of this group is marked by a regionally extensive unconformity at the top of the Naylor Ledge Formation and correlates with the younger Beekmantown-topping unconformity. The School House Hill Group is correlative with the lower to upper part of the Beekmantown Group (Theresa Formation and the Ogdensburg Member of the Beauharnois Formation) of the St. Lawrence Platform. The Middle Ordovician Fox Hill Group (new) consists of the Luke Hill, Solomons Corner, and Corey formations. This group correlates with the uppermost part of the Beekmantown Group (Huntingdon Member of the Beauharnois Formation and the Carillon Formation).

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