Baltoscandic conodont life environments in the Ordovician: Sedimentologic and paleogeographic evidence

Abstract

Modern ecologic models for conodonts were extrapolated principally from experience with North American shallow-water subequatorial faunas. Further evidence can be derived from the calcareous lower part of the Swedish Ordovician. This succession among other things offers uniformity of facies, as well as long-ranging conodont genera. Paleomagnetic data indicate deposition at 60°S, i.e., relatively cool climate and fluctuations in air and shallow-water temperatures. The succession might represent a subantarctic shallow-water carbonate platform. Another interpretation favors depth of 100 to 500 m. The relative frequencies of long-ranging conodont genera were plotted against facies data. All data indicate complexity of interaction of depth, temperature, and current dependent factors that influenced the distribution of conodont genera, in particular during a regressive phase about the Arenigian-Llanvirnian transition. Microzarkodina, Periodon, and Protopanderodus had extended frequency minima during the regression. Paroistodus was abundant before the regression, then apparently disappeared from Europe. In a section at Skovde, formed perhaps in particularly deep water, Baltoniodus has a minimum and Drepanoistodus a maximum that might correspond to the peak of regression, but elsewhere the conditions are either ambiguous or reversed. At least Protopanderodus and Periodon probably were not epibenthic, since they occur with shelly fauna in carbonates as well as with graptolites in dark mudstones and with radiolarians in ophiolite-associated cherts (in Scotland). The importance of sorting by differential transport is stressed throughout the study.

Sedimentological analysis of resurge deposits at the Lockne and Tvären craters: Clues to flow dynamics

“…The sediments of the target seabed belonged to a hemipelagic carbonate facies that was deposited extremely slowly with monotony of fauna and sediment. This facies prevailed on the Baltic Shield throughout much of the Ordovician (Lindström 1971(Lindström , 1984. Although photosynthesizing algae temporarily lived in parts of the sea that were not deeper than 50 m to 100 m (Nordlund 1986), these algal remains were transported and there is no evidence that the sediments in which they occur were deposited at particularly shallow depths.…”

“…Although photosynthesizing algae temporarily lived in parts of the sea that were not deeper than 50 m to 100 m (Nordlund 1986), these algal remains were transported and there is no evidence that the sediments in which they occur were deposited at particularly shallow depths. There is structural and stratigraphic evidence that deposition took place below hurricane wave base (Lindström 1963(Lindström , 1971(Lindström , 1984, which suggests a depth below 100 m. 2. For resurge to have generated a single massive deposit that settled out of suspension, the water depth should have been greater than the order of tens of meters (Ormö and Lindström 2000).…”

“…Only much later (Lindström 1984;Ormö and Lindström 2000) did it become evident that the sea was more likely at least as deep as the deepest reasonable in the case of deposition on a continental shelf of modern type, that is, about 200 m. However, 200 m was taken as a minimum, not as the established depth. The target water depth for Lockne can now be assessed through best-fit numerical models constrained by the geomorphology of the crater Shuvalov et al 2005;Lindström et al 2005a).…”

Conodont biozonation in the upper Arenig of Sweden

“…In the Hällekis quarry (Kinnekulle, Västergötland) the B. norrlandicus Zone is c. 3 m thick (calculation based on undescribed sample series, Löfgren collection). The zone is probably thinner than that in the Gullhögen/Skövde section in Västergötland (see Lindström, 1984 for particulars of the sequence) and the sections at Kårgärde, Rävanäs and Leskusänget in Dalarna. See Figure 2 for locations of all of these sections.…”

“…This quarry section (see also Lindström, 1984) is the topic of a separate publication and will not be described in detail here, but pertinent parts of the sequence will be compared with the corresponding parts of other sections in northern Öland.…”