First record of the Hirnantian (Upper Ordovician) δ¹³C excursion in the North American Midcontinent and its regional implications

Abstract

The most prominent of the two major global δ13C excursions in the Ordovician, the Hirnantian δ13C excursion (HICE), which is previously recorded from the uppermost Ordovician in a few sections in Nevada, Quebec, Arctic Canada, Baltoscandia, Scotland and China, is documented for the first time from the North American Midcontinent. Samples through the Girardeau Limestone and Leemon Formation in Missouri and Illinois show elevated δ13C values of +4‰ to +5‰. Although not determined precisely, the beginning of the HICE is likely to be in the upper part of the Orchard Creek Shale, and it ends in the upper Leemon Formation. Being extraordinarily useful chronostratigraphically, the presence of the HICE makes it possible to provide a firm dating of the study interval, whose age has long been controversial. Comparison between the study sections and coeval HICE sequences in North America and Europe show striking similarities, especially in sea-level history, indicating that major local lowstands reflect eustatic sea-level changes. A comparison with Hirnantian diamictite successions in North and South Africa and Argentina suggests that these lowstands correspond to two major Gondwanan glacial episodes.

Hirnantian (latest Ordovician) glaciations and their consequences for the Oslo Region, Norway, with a revised lithostratigraphy for the Langøyene Formation in the inner Oslofjorden area

“…At the close of deposition in the Høyerholmen Member, there appear to have been subaerial exposure of larger areas indicated by angular unconformities. This emergence is regarded as an expression of maximum HICE and a draw-down of sea level during the glaciation (Bergström et al, 2006). There are several phases of channel fill, and an early phase of incised valley formation is likely at this time.…”

“…sea-level fluctuations on many continents at different palaeolatitudinal positions (Kaljo et al, 2001;Bergström et al, 2006;Brenchley et al, 2006;Štorch, 2006;Johnson & Baarli, 2007;Davies et al, 2009;Ghienne et al, 2014;Demski et al, 2015;Kröger et al, 2015). The Oslo Region was situated in a subtropical position during the Ordovician (Torsvik & Cocks, 2013), and the effects of sea-level changes are also recorded there.…”

“…Testing chemostratigraphy in the Oslo Region, Bergström et al (2006) accepted Brenchley & Newall's stratigraphy (with the Hovedøya tidal channel). Based on the δ 13 C curve, they proposed that the upper parts of the Husbergøya Formation ought to be placed within the Hirnantian.…”

The New Ordovician Stage Standard as Applied to the Stratigraphic Units of the Western Altai-Sayan Folded Area

“…Хирнантский ярус делится на два «временных отрезка» [Bergstrom et al, 2009], при этом нижняя граница верхнего «неформального» подъяруса маркируется не видом-индексом какой-либо граптолито-вой или конодонтовой зоны, а концом «Хирнантского углеродного изотопного сдвига» («Hirnantian isotopic carbon excursion» -HICE), зафиксированного в многочисленных регионах мира [Underwood et al, 1997;Bergstrom et al, 2006Bergstrom et al, , 2009Chen et al, 2006;Kaljo, Martma, 2011;Mitchell et al, 2011].…”

Mass concentration of Hirnantian cephalopods from the Siljan District, Sweden; taxonomy, palaeoecology and palaeobiogeographic relationships

“…2). The section spans the Hirnantian (Normalograptus extraordinarius -N. persculptus graptolite biozones) albeit with the first Hirnantian lowstand unconformity (named HA by Bergstraem et al 2006) between the two units. A hiatus at the top of the Glisstjårn Formation (HB sensu Bergstraem et al 2006) reflects a period of non-deposition/ and or erosion before the Silurian (Aeronian) shale of the Kallholn Formation commences.…”