Palaeokarst formation in the early Palaeozoic of Baltoscandia – evidence for significant sea-level changesin a shallow epicontinental sea
2013 (English)In: Proceedings of the 3rd IGCP591 Annual MeetingLund, Sweden, 9–19 June 2013 / [ed] Lindskog, A. & Mehlqvist, K, Lund: Lund University , 2013, 169-170 p.Conference paper, Abstract (Other academic)
In the Lower Palaeozoic sedimentary succession of Sweden palaeokarsts have been reportedfrom different stratigraphic levels in the Silurian strata of Gotland by Calner(2008; see references therein). Until last year there were no records of Cambrian karstsand in the Ordovician only the basin-wide Katian palaeokarst horizon in the UpperOrdovician Slandrom Limestone has been described in detail (Calner et al. 2010a). Theunconformities and disconformities on top of the slightly older Kullsberg mounds inquarries located in the Siljan impact structure (Dalarna) presumably represent an earlierregression and karstic development (Calner et al. 2010b). Beside these reports, there isonly the statement by Nielsen (1995) that karst may have formed at the top of theDarriwilian Komstad Limestone. During the last two years, however, several new andsignificant palaeokarst surfaces have been detected in the Cambrian–Ordovician successionsof Sweden (Lehnert et al. 2012).At Kakeled Quarry (Västergötland), a palaeokarst cave with a breccia fill (large, angularOrsten clasts in a dark limestone matrix) is exposed beneath a ‘Middle Cambrian’palaeokarst surface (Jiangshanian Stage) located close to the top of the Kakeled LimestoneBed of the Alum Shale Formation (Lehnert et al., 2012). In the karstic pockets,a mass occurrence of Orusia lenticularis occurs. These shallow-water brachiopods originallysettled on hard substrates after a major regression exposing, regionally, the seafloors of the alum shale basin. Their reworking and concentration in the conglomeraticbed overlying the irregular palaeokarst surface reflects deposition during transgressionin extremely shallow marine environments.A younger karst surface is exposed in Tomten Quarry at Torbjörntorp (Västergötland).In two dimensions in the quarry wall it resembles the “Schrattenkalk”, but rockslabs cut vertically and parallel to bedding planes display a karren system that resembles“Napfkarren” or cockling features. Trilobites of the Furongian Ctenopyge bisulcata andC. linnarssoni zones occur in the 1–2 cm thick, glauconitic packstone bed that overliesthe palaeokarst surface and which represents the upper Tremadocian BjørkåsholmenFormation. The associated stratigraphic gap comprises the six uppermost trilobite zonesof the Furongian plus most of the Tremadocian. Darriwilian conodonts with reworked170older material within a limestone bed slightly above the glauconitic packstone bed indicateyet another substantial gap in the succession.In the new Tingskullen core from northeastern Öland, another palaeokarst surfacewith grikes and evidence of repeated exposure marks the top of the upper TremadocianObolus conglomerate (?) or a lower limestone part of the Djupvik Formation (“CeratopygeShale”). This palaeokarst surface is overlain by glauconitic limestone of the KöpingsklintFormation and inferably reflects the global Ceratopyge Regressive Event(CRE).At the base of the Lanna Limestone in the Siljan area, palaeokarst is associated withthe Dapingian Blommiga Bladet (‘flowery sheet’) hardground complex, which can becorrelated across most of Baltoscandia.The basin-wide palaeokarst in the Katian Slandrom Limestone (Calner et al. 2010a)no longer marks the youngest Ordovician karst record. Recently, Hirnantian karst cavesand solution cavities filled with greenish marls of the Glisstjärn Formation have beenrecognized in sections of the Boda Limestone in the Siljan Ring structure (Dalarna).Solution and karst cave formation reflects an interval of the regression during theHirnantian glaciation and the youngest period of subaerial exposure during the Ordovician.Some earlier sedimentary models suggesting that Baltoscandia was flooded by a deepepicontinental sea are challenged by the discovery of multiple palaeokarst developmenttogether with other shallow-water features. Instead, palaeokarst formation impliessubaerial exposure during a number of major regressions.
Place, publisher, year, edition, pages
Lund: Lund University , 2013. 169-170 p.
Limestone, Ordovician, Silurian, karst, Baltoscandia
Research subject Earth Science with specialization in Historical Geology and Palaeontology
IdentifiersURN: urn:nbn:se:uu:diva-213234OAI: oai:DiVA.org:uu-213234DiVA: diva2:681383
3rd IGCP 591 Annual Meeting