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Porkuni, Siuge Member (Ordovician of Estonia)

Also known as Borkholm

Where: Lääne-Viru, Estonia (59.2° N, 26.2° E: paleocoordinates 26.2° S, 0.3° W)

• coordinate stated in text

• small collection-level geographic resolution

When: Normalograptus extraordinarius graptolite zone, Siuge Member (Ärina Formation), Porkuni (445.6 - 443.7 Ma)

• The Porkuni Regional Stage is formerly known as the "Borkholm'sche Schicht" (Raukas & Teedumäe [eds.] 1997, Geology and Mineral Resources of Estonia, html version, Spinachitina taugourdeaui chitinozoan zone.

• member-level stratigraphic resolution

Environment/lithology: perireef or subreef; lithified, shelly/skeletal lime mudstone and nodular, shelly/skeletal chert

• "North Estonian Confacies Belt at the northern flank of the Livonian Tongue" (Kröger & Isakar, 2006);

•"inter-reef facies" (Raukas & Teedumäe [eds.] 1997, Geology and Mineral Resources of Estonia, html version,;

•A more datailed description of environment and setting is given in Kröger (2007).

• "The Siuge Member consists of a succession of roughly 1.5 m slightly dolomitised biomicritic wackestones to micritic bioclastic packstones. The skeletal grains include fragments of crinoids, ostracods, and brachiopods. Grains of quartz only account for less than 10% of the total sediment (Oraspõld 1975). A relatively high content of bitumen is characteristic of the sediments of the Siuge Member. The limestones consist of cross-bedded channel fillings with thin argillaceous interlayers (Fig. 3). Locally, layers or nodules of chert occur at the bottom of the channel structures. The layers with chert nodules have a thickness of less than five centimetres and contain numerous small but macroscopic remains of predominantly bryozoan zooaria, ostracod tests, and echinoderm ossicles. Gastropods, bivalves, graptolites, and cephalopods are less common, but occur in considerable numbers." (Kröger, 2007)

Size class: macrofossils

Preservation: cast, recrystallized, replaced with silica

Collected by M. Isakar, B. Kröger, among others in 2000, 2004, and earlier; reposited in the MfN

• TUG = Tartu Ülikool Geoloogiamuuseum, Tartu, Estonia

•NMB = Museum für Naturkunde Berlin

•The materials "have been collected since the nineteenth century by Wilhelm Dames, Walther Rosenberg (at reposition of NMB), Arwed von Wahl (in collection of GIT), Karl Orviku, and Ülle Sirk. However, the bulk of the material was collected by Mare Isakar (Tartu) and Björn Kröger (stored in the collection of TUG) during two field trips in 2002 and 2004." (Kröger, 2007)

Primary reference: B. Kröger and M. Isakar. 2006. Revision of annulated orthoceridan cephalopods of the Baltoscandic Ordovician. Fossil Record 9(1):137-163 [B. Kröger/B. Kröger/B. Kröger] more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 87313: authorized by Björn Kröger, entered by Torsten Liebrecht on 14.03.2009, edited by Pete Wagner and Björn Kröger

Creative Commons license: CC BY (attribution)