Correlation of upper Llandovery–lower Wenlock bentonites in the När (Gotland, Sweden) and Ventspils (Latvia) drill cores: role of volcanic ash clouds and shelf sea currents in determining areal distribution of bentonite

Abstract

Study of volcanic ash beds using biostratigraphy, sanidine composition and immobile elements within bentonites has manifested several well-established and some provisional correlations between Gotland and East Baltic sections. Energy dispersive X-ray fluorescence microanalysis of phenocrysts has revealed bentonites containing Mg-rich or Fe-rich biotite. Sanidine phenocrysts contain, in addition to a major Na and K component, often a few per cent of Ca and Ba. On the basis of new correlations the mapping of the distribution areas of bentonites has been extended from the East Baltic to Gotland. The bentonite distribution can be separated into two parts in North Latvia–South Estonia, indicating the existence of shelf sea currents in the Baltic Silurian Basin

Silurian bentonites in Lithuania: correlations based on sanidine phenocryst composition and graptolite biozonation – interpretation of volcanic source regions

“…Central European sources from the collision zone of Avalonia and Baltica can be supposed. This result confirms that Telychian volcanic ashes, forming a number of the Estonian-Latvian bentonites which are not found in Lithuania, reached the East Baltic area from the northwestern direction (present-day orientation) -from the margins of the Iapetus Ocean (Kiipli et al 2008b(Kiipli et al , 2008c(Kiipli et al , 2010b(Kiipli et al , 2012a(Kiipli et al , 2013a. Scarcity of bentonites in the upper Homerian and Lower Ludlow of Lithuania and their frequent occurrence in Latvian and Estonian sections indicate a source from the northwest in terms of presentday orientation.…”

“…The occurrence of bentonites in the Silurian of Lithuania is also described in Lapinskas (1965Lapinskas ( , 2000 and Motuza et al (2002). The areal distribution schemes of ca 20 bentonites from Estonia, Latvia and Scandinavia indicate volcanic sources from the Iapetus Palaeo-Ocean in the Telychian and Lower Sheinwoodian (Kiipli et al 2008b(Kiipli et al , 2008d(Kiipli et al , 2010b(Kiipli et al , 2012a(Kiipli et al , 2013a. Several other researchers discuss a possible Central European source for ash beds (Batchelor & Jeppsson 1999;Böhnke & Katzung 2001;Hetherington et al 2011).…”

“…To avoid these shortcomings, researchers have used the composition of apatite phenocrysts (Batchelor 2009;Carey et al 2009;Ray et al 2011) or trace elements for proving correlations (Huff et al 1998;Kiipli et al 2008bKiipli et al , 2013a; Inanli et al 2009;Hetherington et al 2011. Up to now we have studied mostly Estonian and Latvian sections Kiipli et al 2010aKiipli et al , 2011Kiipli et al , 2012a. Some Silurian bentonites of Lithuania have been studied by Kiipli et al (2008c) using the same methods.…”

“…Volcanic ashes occurring in palaeontologically wellcharacterized sedimentary sections offer a unique possibility of detailed correlations between different environments (Kiipli & Kallaste 2002;Kiipli et al , 2008aKiipli et al , 2009Kiipli et al , 2010bKiipli et al , 2011Kiipli et al , 2012aKiipli et al , 2012b. The mentioned studies used magmatic sanidine composition of bentonites (altered volcanic ashes) analysed by X-ray diffractometry as a correlation criterion.…”

The Llandovery–Wenlock boundary interval in west-central continental Estonia: an example from the Suigu (S-3) core section

“…Only the topmost part of the M. margaritana CtZ (represented by a single sample just above the gap) might be preserved in the Suigu (S-3) core section. A gap in this section is also supported by the absence of the Ohesaare (ID 210), Lusklint (ID 150) and Ireviken (ID 127) K-bentonites known in several other sections in Baltoscandia (Kiipli et al 2010(Kiipli et al , 2012. As the first two of them occur in the upper part of the Upper Pt.…”