Integrated biostratigraphy of the lower Silurian of the Aizpute-41 core, Latvia

Abstract

Integrated graptolite, conodont and chitinozoan biostratigraphical data is presented from the Rhuddanian through to lower Sheinwoodian of the Aizpute-41 core, Latvia. Correlation of the biozonation schemes based upon the three groups is achieved from the cyphus through to lowermost riccartonensis graptolite biozones, except for the upper Aeronian and lower Telychian, which lack both chitinozoans and graptolites, and upper lapworthi through to approximately base murchisoni graptolite Biozone, where there is interpreted to be an unconformity. Datum 2 of the Ireviken Event is correlated with a level at the base of or within the murchisoni Biozone. It is possible that the changes in conodont assemblages at Datum 2 on Gotland are the result of an unconformity here. Streptograptus? kaljoi sp. nov., from the lower spiralis graptolite Biozone, is described.

Graptolite assemblages and stratigraphy of the lower Silurian Mrákotín Formation, Hlinsko Zone, NE interior of the Bohemian Massif (Czech Republic)

“…8F) (Figs 6A, 9D) -a species with robust, dorsally arcuate rhabdosome and long genicular spines -has not been found in the Barrandian area and resemble also Pribylograptus sp. of Loydell et al (2003).…”

“…Pribylograptus sp. recorded by Loydell et al (2003) from the lower Demirastrites triangulatus Biozone of Aizpute-41 core in Latvia exhibits dorsally curved rhabdosome and thecae with long spinose genicular hoods. Latvian rhabdosome is apparently more robust than Chinese specimens.…”

The Aeronian/Telychian (Llandovery, Silurian) boundary, with particular reference to sections around the El Pintado reservoir, Seville Province, Spain

“…Three graptolitic bands with a total thickness of 50 mm occur 5 m above the sedgwickii The Ohesaare core, Saaremaa, Estonia exhibits a substantial unconformity comprising most of the Aeronian and the lowermost Telychian (Loydell et al 1998), with the lowest Telychian strata yielding Spirograptus turriculatus Biozone graptolites, again including Torquigraptus proteus. An unconformity, encompassing fewer graptolite biozones than in Ohesaare, but including the uppermost Aeronian and lowermost Telychian has also been interpreted from the Kolka-54 core, Latvia record (Loydell et al 2010).…”

“…An unconformity, encompassing fewer graptolite biozones than in Ohesaare, but including the uppermost Aeronian and lowermost Telychian has also been interpreted from the Kolka-54 core, Latvia record (Loydell et al 2010).…”

“…Three graptolitic bands with a total thickness of 50 mm occur 5 m above the sedgwickii The Ohesaare core, Saaremaa, Estonia exhibits a substantial unconformity comprising most of the Aeronian and the lowermost Telychian (Loydell et al 1998), with the lowest Telychian strata yielding Spirograptus turriculatus Biozone graptolites, again including Torquigraptus proteus. An unconformity, encompassing fewer graptolite biozones than in Ohesaare, but including the uppermost Aeronian and lowermost Telychian has also been interpreted from the Kolka-54 core, Latvia record (Loydell et al 2010).Graptolitic sections through the Aeronian/Telychian boundary appear to be present in the subsurface of western Lithuania: range charts and descriptions of the graptolites are provided by Paškevičius (1979). Sections appear to be condensed with the thickness from base sedgwickii Biozone to base crispus Biozone ranging between 4.5 m and 7.5 m. High resolution sampling through the interval will be needed should the cores be restudied.…”