Enli 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.

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.

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.

Carbonate distribution in the East Baltic deep shelf in the late Ordovician—early Silurian

Abstract Calcite and dolomite diminished and disappeared offshore in the East Baltic shelf in the Ordovician—Silurian. The distribution was influenced by transgressions—regressions, transportation processes, and dissolution effects. Calcite dissolved due to the relatively low pH of deep seawater and pore waters. Only small amounts of dolomite were present in the deep shelf. Low pH was also evidenced by clay minerals of the Llandovery bentonite layers. The bentonite matrix varied in composition from illite—smectite to kaolinite-containing. Kaolinite formation was promoted by the decrease of seawater pH with depth. Three time intervals can be distinguished when different prevailing factors governed the carbonate distribution in the East Baltic shelf: the late Ordovician global regression, the Aeronian increased primary productivity, and the Telychian high atmospheric CO2.