On the lower boundary of the Floian Stage in Estonia/Flo lademe alumine piir Eestis

The lower boundary of the Second Stage of the Lower Ordovician Series, the Floian Stage, is defined by the first appearance of the graptolite Tetragraptus approximatus. In the stratotype section of Diabasbrottet at Hunneberg, southern Sweden, the boundary falls within the Megistaspis planilimbata tr...

Full description

Saved in:
Bibliographic Details
Published in:Estonian journal of earth sciences 2012-12, Vol.61 (4), p.205
Main Authors: Parnaste, Helje, Viira, Viive
Format: Article
Language:English
Subjects:
Geomorphology
Graptolites
Natural history
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The lower boundary of the Second Stage of the Lower Ordovician Series, the Floian Stage, is defined by the first appearance of the graptolite Tetragraptus approximatus. In the stratotype section of Diabasbrottet at Hunneberg, southern Sweden, the boundary falls within the Megistaspis planilimbata trilobite Zone and within the Oelandodus elongatus-Acodus deltatus deltatus conodont Subzone of the Paroistodus proteus Zone, and within the Hunneberg Regional Stage. Graptolites, including the index species T. approximatus, are missing in the terrigenous sediment of Estonia. The earliest trilobites are poorly preserved in this terrigenous succession. They represent an interval older than the Megalaspides dalecarlicus Zone but probably younger than the M. planilimbata Zone, and are correlative to the Prioniodus elegans conodont Zone. Thus the lower boundary of the Second Stage can be detected using mainly conodonts. In accordance with conodont occurrence, the base of the Floian (i.e. somewhat higher than the base of the O. elongatus-A. d. deltatus Subzone) falls within the Joa Member of the Leetse Formation. Probable levels have been suggested in some localities. Thus the lower part of the Leetse Formation belongs to the Tremadoc Stage, and to the Hunneberg Regional Stage. Key words: Hunneberg, Billingen, Floian, graptolites, conodonts, trilobites, Baltoscandia. On diskuteeritud Alam-Ordoviitsiumi Flo lademe alumise piiri ule Baltoskandias, naidates erinevate faunagruppide levikut ja tsonaalsust. Kuna erinevate faunagruppide uurijate poolt on seda piiri Eesti geoloogilises labiloikes naidatud erineval tasemel, siis on siin ara toodud korrelatsioon Rootsis asuva tuuplabiloikega ja tapsustatud piiri asukoht Eesti labiloigetes. Lahtuvalt konodontide levikust eelviidatud Rootsi labiloikes langeb Flo lademe alumine piir Eestis Leetse kihistu Joa kihistikku. Seega on Leetse kihistu alumine osa Tremadoci-ealine, kuuludes samas Hunnebergi regionaalsesse lademesse.
ISSN:1736-4728
DOI:10.3176/earth.2012.4.02