0381216 - GLÚ 2013 RIV GB eng J - Journal Article
Štorch, Petr - Frýda, J.
The late Aeronian graptolite sedgwickii Event. Associated positive carbon isotope excursion and facies changes in the Prague Synform (Barrandian area, Bohemia).
Geological Magazine. Roč. 149, č. 6 (2012), s. 1089-1106. ISSN 0016-7568. E-ISSN 1469-5081
R&D Projects: GA ČR GA205/09/0619
Institutional research plan: CEZ:AV0Z30130516
Keywords : carbon isotope record * community evenness * extinction * graptolites * Silurian * species richness
Subject RIV: DB - Geology ; Mineralogy
Impact factor: 2.270, year: 2012

Lower Silurian black-shale succession of the Prague Synform provided detailed insight into graptolite faunal dynamics and diversity trends from middle Aeronian diversity maximum through late Aeronian crisis. Graptolite diversity decreased from 33 taxa in the Lituigraptus convolutus Biozone to 17 taxa in the upper part of the Stimulograptus sedgwickii Biozone and newly erected Lituigraptus rastrum Biozone. The graptolite assemblages of the latter biozones exhibit low species richness along with high dominance. Many graptolite species that became extinct in the early part of the sedgwickii Zone were promptly replaced by new forms. In the later part of the sedgwickii Zone, however, replacement of extinct species by new forms considerably decelerated. The increased rate of graptolite extinction in the convolutus-sedgwickii zone boundary beds coincided with subtle changes in black shale lithologies and a positive shift in δ¹³C_org (for 2.2 >) compared to baseline values. Sea-level drawdown can be inferred from silt sedimentation and/or temporary nondeposition in the middle of the sedgwickii Zone. Middle part of the sedgwickii Zone sees also TOC fluctuations and strong positive δ¹³C_org excursion with peak shift at least 7 >. Still elevated values of δ¹³C_org returned to baseline values in the course of the rastrum Zone. The sedgwickii Event exhibits substantial reorganization of the graptolite fauna, its taxonomical impoverishment and concomitant increase in species dominance rather than sudden collapse of the pre-extinction assemblage. Associated changes in lithology, TOC and strong δ¹³C_org excursion suggest a relatively extended and probably multi-phase period of stress conditions which affected the pelagic realm inhabited by graptolites in the course of the late Aeronian interval. Aeronian-Telychian boundary is drawn in pale-coloured barren mudstone which separated black shales of L. rastrum and Rastrites linnaei biozones.
Permanent Link: http://hdl.handle.net/11104/0215975