Tarmo Kiipli

ALTERED VOLCANIC ASH AS AN INDICATOR OF MARINE ENVIRONMENT, REFLECTING pH AND SEDIMENTATION RATE – EXAMPLE FROM THE ORDOVICIAN KINNEKULLE BED OF BALTOSCANDIA

The composition of altered volcanic ash of the Late Ordovician Kinnekulle bed was studied in geological sections of the Baltic Paleobasin. The composition of altered ash varies with paleosea depth from northern Estonia to Lithuania. The ash bed in shallow shelf limestones contains an association of illite-smectite (I-S) and K-feldspar, with the K2O content ranging from 7.5 to 15.3%. The limestone in the transition zone between shallow- and deep-shelf environments contains I-S-dominated ash with K2O content from 6.0 to 7.5%. In the deep-shelf marlstone and shale, the volcanic ash bed consists of I-S and kaolinite with a K2O content ranging from 4.1 to 6.0%. This shows that authigenic silicates from volcanic ash were formed during the early sedimentary-diagenetic processes. The composition of the altered volcanic ash can be used as a paleoenvironmental indicator showing the pH of the seawater or porewater in sediments as well as the sedimentation rate.

Identification of the O-bentonite in the deep shelf sections with implication on stratigraphy and lithofacies, East Baltic Silurian

Abstract Pyroclastic sanidine composition is used for correlation of the Osmundsberg bentonite (O-bentonite) bed from Estonia to Latvia. Chemical changes during conversion of volcanic ash to authigenic silicates in shallow and deep shelf sediments differ, leading to the formation of kaolinite-rich bentonite in deep shelf and feldspar-rich bentonite in shallow shelf environments. The Rumba Formation in Estonia is proved to be of Lower Telychian age. Firmly based correlation between shallow and deep shelf sediments allows tracing of facies variations that occurred during environmental changes in the Late Llandovery times.

Wenlock bentonites in Lithuania and correlation with bentonites from sections in Estonia, Sweden and Norway

Abstract Seven Wenlock bentonite beds from four drill cores in Lithuania with sufficient thickness for sampling were analysed by XRD and XRF. The sanidine composition of bentonites combined with graptolite biozonation of the host rock were used for correlations. Two of the studied bentonite samples at the antennulariuslflexilis biozone boundary can be confidently correlated between two Lithuanian sections. Four of the studied bentonites can be correlated with lower or higher probability with earlier studied bentonites in Estonia and Sweden. Identification of the Grötlingbo Bentonite in the Viduklė-61 drill core, and descriptions of other east Baltic sections enables composition of a thickness map of the Grötlingbo Bentonite. The thickness pattern with two axes, and the layered composition of the Grötlingbo Bentonite, indicate a change of the wind direction during a long lasting eruption. Hypothetical location of the volcanic source in the Silurian was within the zone of the Baltica-Laurentia collision.

Reconstruction of currents in the Mid-Ordovician–Early Silurian central Baltic Basin using geochemical and mineralogical indicators

In the central part of the Mid-Ordovician–Early Silurian Baltic Basin, two different transport pathways of terrigenous material can be recognized. Kaolinite indicates the south-to-north sediment influx, and Cr the western and northern sources. A pathway from the Ukrainian Shield in the South was active in the Floian–Darriwilian (Ordovician) and in the Llandovery (Silurian). The influx from the western source was active in the Sandbyan, and influx from the northern side occurred in the Katyan. The sediment transport was carried out by water flows, which turned into rapid currents from time to time. These currents, coming from the ocean surface waters, were oxygenated facilitating red facies formation in the central Baltic Basin. Currents on the shelf were linked to the adjacent oceanic currents, which changed in course with the drift of Baltica from temperate to subtropical latitudes.

Composition and correlation of volcanic ash beds of Silurian age from the eastern Baltic

Sanidine composition and bulk geochemistry of volcanic ash beds from the East Baltic indicate the subalkaline nature of the volcanism near the margins of the Baltica plate during the Silurian. Several bentonites in the Wenlock include a previously unknown sanidine with 48 to 58 mol % of the Na+Ca component. In contrast to the earlier Telychian volcanism, sodium-rich sanidine occurs in ash beds which originate from relatively moderately evolved dacitic magma. The studied material from two drill cores integrated with previous research enables production of a more complete list of 49 volcanic eruption layers for the lower to middle Wenlock in the East Baltic. This updated list of bentonites characterized by their sanidine compositions forms a good basis for future integrated bio- and chemostratigraphic correlations in northern Europe.

Geochemical evolution of Caledonian volcanism recorded in the sedimentary rocks of the eastern Baltic region

Abstract This article describes the occurrence, bulk geochemistry and phenocryst compositions of Caledonian volcanic ash beds (bentonites) in the sedimentary sections of the Palaeozoic Baltic sedimentary basin. Four periods of volcanism are recognized in the eastern Baltic region: (a) Late Sandbian with sources derived from the convergent margin between Avalonia and Baltica; (b) Late Katian with sources from the margin of the Iapetus Ocean (Norwegian Caledonides); (c) Aeronian (with extension into Telychian and Sheinwoodian) with sources in the Central European Caledonides; and (d) Telychian to Early Ludlow with sources derived from the convergent margin between Laurentia and Baltica (Norwegian Caledonides). Trace element compositions in bentonites indicate mostly evolved source magmas of rhyolitic and dacitic composition. The volcanism in the Aeronian is characterized by less evolved basaltic and trachyandesitic compositions. Sanidine compositions indicate the existence of potassium-dominated (over sodium) source magmas in Late Sandbian and from the late Homerian to Early Ludlow. During other periods both potassium- and sodium-dominated source magmas occur. The presence of sodium-rich sanidine in many bentonites combined with the scarcity of biotite suggests that the source magmas were water-undersaturated. Biotite phenocrysts are mostly Mg-rich, but Fe-rich varieties occur in the Late Sandbian and Early Telychian.

Correlation of Silurian bentonites based on the immobile elements in the East Baltic and Scandinavia

This article presents a dataset of geochemical analyses from Silurian altered volcanic ash beds (bentonites) characterising 132 eruptions and preserved in sedimentary sections of the East Baltic area. TiO2, Nb, Zr, Th, Y, Ce, Cr and V ratios with Al2O3 are used for identifying correlations between ash beds from Scandinavian sections. Some correlated ash beds are illustrated by schematic maps of areal distribution indicating volcanic sources from directions of both Iapetus and Rheic palaeo-ocean margins.

Hematite and goethite in Telychian marine red beds of the East Baltic

Abstract Hematite and goethite were determined by X-ray diffractometry using natural goethite and hematite for calibration. The subtraction of diffractograms before and after ignition at 500[ddot]C was applied for goethite identification and quantification, and ZnO was used as internal standard for the matrix correction. Red terrigenous claystones from deep shelf facies revealed co-occurrences of hematite and goethite, on average 1.7% hematite and 0.6% goethite. Grey claystones from the onshore facies of deep shelf contained yellow goethitic layers with the goethite content from 1.6 to 12.5%. Red metabentonites, layers of altered volcanic ash, contained only hematite, on average 2.7%, and did not reveal goethite above the detection limit. The occurrence of red metabentonites points to the early diagenetic origin of hematite in volcanic ash beds as well as in red terrigenous host rock. Several pathways of hematite and goethite formation are considered for different rock types.

Upper Katian (Ordovician) bentonites in the East Baltic, Scandinavia and Scotland: geochemical correlation and volcanic source interpretation

Altered volcanic ash interbeds (bentonites) in the upper Katian of Baltoscandia indicate significant volcanic activity in neighbouring tectonically active areas. Katian bentonites in the East Baltic can be reliably correlated using sanidine phenocryst composition. Ratios of immobile trace elements TiO 2 , Nb, Zr and Th to Al 2 O 3 enable extension of the correlations to Scandinavia, where late diagenetic alterations could have caused recrystallization of sanidine phenocrysts. At least seven volcanic eruptions were recognized in Baltoscandian sections. Several bentonites found in deep-sea sediments are absent in shallow-sea sediments, indicating extensive breaks in sedimentation and erosion during late Katian and Hirnantian times. The areal distribution pattern of Katian bentonites in Baltoscandia indicates a volcanic source from the north or northwest (present-day orientation) from the margins of the Iapetus Palaeo-Ocean. Signatures of ultra-high-pressure metamorphism in the Seve Nappe (Central Sweden) and intrusions in the Helgeland Nappe Complex in Central Norway have been proposed as potential sources of the magmas that generated the volcanic ashes deposited in the East Baltic in Katian times. Geochemical similarities between Baltoscandian and Dob9s Linn bentonites from southern Scotland suggest a common volcanic source in Katian times.

Upper Silurian stratigraphy of Podolia revisited: carbon isotopes, bentonites and biostratigraphy

Nowadays carbon isotopes and bentonites have become new authorities in stratigraphy besides traditional biostratigraphy. Three positive carbon isotope excursions have been identified in the Upper Silurian of Podolia: the mid-Ludfordian excursion, the late Přídolí excursion at the Trubchyn/Dzvenygorod junction and the SIDE at the Silurian–Devonian boundary. Fourteen bentonite beds are known from this upper Ludlow–Přídolí interval. Some of these are better studied and are helpful for correlation of sections. Using the stage slices as a framework, we show that the Přídolí can be subdivided into “natural” stage rank units based on the integrated bio-, litho- and chemostratigraphy.