The Global Stratotype Section and Point (GSSP) for the base of the Katian Stage of the Upper Ordovician Series at Black Knob Ridge, Southeastern Oklahoma, USA

AbstractThree available graphic-correlation analyses are used to calibrate mid-Palaeozoic conodont zonations: Sweet's scheme for the mid- to Upper Ordovician; Kleffner's for the mid- to Upper Silurian; and Murphy & Berry's for the lower and middle Lower Devonian. The scheme of Sweet is scaled by applying the high-precision U-Pb zircon date of Tucker and others for the Rocklandian and linked with that of Kleffner by scaling the graptolite sequence of the Ordovician-Silurian global stratotype section to fit two similarly derived dates from this sequence. The top of Kleffner's scheme, all of Murphy & Berry's, as well as standard zones to the Frasnian are calibrated by using tie-points of the latest Cambridge-BP time-scale (GTS 89). However, the recent microbeam zircon date by Claoué-Long and others for the Hasselbachtal Devonian-Carboniferous auxiliary stratotype is used to calibrate the standard Famennian zones. Also the similarly derived but preliminary determination reported by Roberts and others from the Isismurra Formation of New South Wales is tentatively taken as the top of the Tournaisian and so used to calibrate Tournaisian zones. Despite the considerable extrapolation required to compile these schemes and their inherent errors, the resultant time-scale closely agrees with other dates of Tucker and others from the Llanvirn as well as the GTS 89 Homerian-Gorstian tie-point. This suggests that stratigraphic methods can be usefully applied to geochronometry. The Llandovery appears to have lasted longer (16 m. y.) than usually envisaged and the Ordovician-Silurian boundary may need to be lowered to approximately 443.5 Ma. Certainly, chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high-resolution dating for their calibration will be crucial to more accurate biochronometries.

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Acritarch assemblages from the Middle–Upper Ordovician in the Aksu area, northwestern margin of the Tarim Basin, Xinjiang, China

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen ◽

10.1127/njgpa/2020/0882 ◽

2020 ◽

Vol 295 (2) ◽

pp. 169-183 ◽

Cited By ~ 2

Author(s):

Kui Yan ◽

Thomas Servais ◽

Longlong Shan ◽

Jun Li

Keyword(s):

Tarim Basin ◽

Late Ordovician ◽

Northwestern Part ◽

Upper Ordovician ◽

The World ◽

Northwestern Margin ◽

Stratotype Section ◽

Compositional Changes

Upper Darriwilian to middle Katian (Ordovician) outcrops are well exposed in the Kalpin (Aksu) area, in the northwestern margin of the Tarim Basin, Xinjiang, China. The Dawanxigou and Sishichang sections in the Kalpin area, near the Dawangou Auxiliary Stratotype Section and Point (ASSP), were palynologically investigated. Both sections provide well-preserved acritarch assemblages dominated by acanthomorph, sphaeromorph and netromorph morphotypes, attributed to 36 species and 20 genera. A comparison of the acritarch assemblages with coeval microfloras from other parts of the world confirms a wide cosmopolitism distribution, indicative of a breakdown of acritarch provincialism during the Late Ordovician. Several acritarchs from the Tarim Basin are restricted to the Late Ordovician, and as they are distributed worldwide, they present a potential for global bio-stratigraphical correlations. The acritarch assemblages from the different sections of the northwestern part of the Tarim Basin show slightly variable compositions, probably caused by different palaeo-ecological settings. The diversity and compositional changes of the acritarch assemblages, combined with the sedimentological evidence, suggest a transgressive sequence from the Sargan Formation to the Qilang Formation.

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New data on Hirnantian (latest Ordovician) postglacial carbonate rocks and fossils in northern Guizhou, Southwest China

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2015-0197 ◽

2016 ◽

Vol 53 (7) ◽

pp. 660-665 ◽

Cited By ~ 6

Author(s):

Guang-Xu Wang ◽

Ren-Bin Zhan ◽

Ian G. Percival

Keyword(s):

Warm Water ◽

Guizhou Province ◽

Upper Ordovician ◽

Cool Water ◽

Coral Fauna ◽

Rugose Coral ◽

Stratotype Section ◽

New Interpretation ◽

Brachiopod Fauna ◽

Hirnantia Fauna

The Kuanyinchiao Formation (Hirnantian, Upper Ordovician), yielding the typical Hirnantia fauna, has commonly been accepted as representing cool-water sediments deposited during the glacial interval in the Hirnantian Global Boundary Stratotype Section and Point (GSSP) region of South China. Recent investigation reveals that the uppermost carbonate-dominated part of this formation yields a warm-water rugose coral fauna with Silurian affinities at many localities of northern Guizhou Province, which substantially differs from the underlying cool-water fauna. This suggests that these carbonates were probably postglacial warm-water sediments, rather than having formed during the Hirnantian glacial interval as previously thought. Such a conclusion is consistent with the evidence from the associated brachiopod fauna, i.e., the Dalmanella testudinaria – Dorytreta longicrura community, which is similarly distinct from the underlying typical Hirnantia fauna. The sedimentological data show warm-water features at the same level (e.g., the presence of oolitic grains), also supporting this new interpretation.

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