A Palynological Study from Sweden Reveals Stable Terrestrial
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Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 105, 149–158, 2015 (for 2014) A palynological study from Sweden reveals stable terrestrial environments during Late Silurian extreme marine conditions Kristina Mehlqvist, Jane Wigforss-Lange and Vivi Vajda Department of Geology, Lund University, So¨lvegatan 12, SE-223 62 Lund, Sweden. Email: [email protected] ABSTRACT: A palynological study of the upper Silurian O¨ ved–Ramsa˚sa Group in Ska˚ne, Sweden yields a well preserved spore assemblage with low relative abundances of marine micro- fossils. In total, 26 spore taxa represented by 15 genera were identified. The spore assemblage is dominated by long-ranging cryptospore taxa, and the trilete spore Ambitisporites avitus-dilutus. However, key-species identified include Artemopyra radiata, Hispanaediscus lamontii, H. major, H. verrucatus, Scylaspora scripta and Synorisporites cf. libycus. Importantly, Scylaspora klintaensis was identified, allowing correlation with the Klinta 1 drillcore (Ska˚ne). A Ludlow age is inferred for the exposed succession, which agrees well with previous conodont stratigraphy. The organic residue is dominated by phytodebris and spores, but with high relative abundances of acritarchs at two levels, possibly related to flooding surfaces. Based on the palynofacies analysis, a near-shore marine environment is proposed. The close prox- imity to land is inferred by the high proportions of spores, and the dispersed assemblage most likely represents the local flora growing on delta plains. The palynological signal also infers a stable terrestrial environment and vegetation, in contrast to unstable conditions in the marine environment characterised by ooid formation in an evaporitic environment. Comparisons with coeval spore as- semblages from Gotland, Avalonia and Laurentia show relatively close similarities in taxonomic composition at the generic level. KEY WORDS: cryptospores, early land plants, Klinta, Ludfordian, sea level, stratigraphy Records of early land plants from Baltica have previously comprise research on conodonts (Jeppsson 1975; Jeppsson & been described from Ro¨sta˚nga, Ska˚ne (Sweden). These Late Laufeld 1986), tentaculitids (Larsson 1979), chitinozoans (Grahn Ordovician (Katian) spores represent the oldest record of land 1996) and d13C composition (Wigforss-Lange 1999; Jeppsson plants from Baltica (Badawy et al. 2014). Other records of cryp- et al. 2012). However, all these studies focus on the marine tospores are from Ordovician (latest Katian–Hirnantian) de- microfossils or sedimentological/geochemical aspects and no posits from the Valga-10 core in southern Estonia (Vecoli et contributions concern terrestrial microfossils. Our study focuses al. 2011). Studies concerning terrestrial palynomorphs from on upper Silurian successions from southern Sweden, with the the top Ordovician to the Wenlock successions of Baltica are aim of describing the dispersed spore assemblages and other scarce, but middle Llandovery to late Ludlow spore assemb- organic debris recovered from exposures at Klinta, providing lages were described by Hagstro¨m (1997) from the Na¨rborrnin- the first record of terrestrial palynology in these strata. We gen 1 and Burgsvikborrningen 1 cores and from outcrops on correlate our results with zonation schemes based on marine Gotland. A rich and well-preserved palynoflora of crypto- microfossils and compare our terrestrial palynological signal spores, vascular plant spores, fungal spores and hyphae was to the environmental changes within the marine realm. recovered especially from the Ludfordian Burgsvik Beds by Hagstro¨m (1997). Sherwood-Pike & Gray (1985) also reported fungal spores and hyphae from these beds. Silurian spores have 1. Geological setting also been studied from Ska˚ne and Gotland by Gray et al. By the time of the Silurian, Baltica was located south of the (1974). Hagstro¨m & Mehlqvist (2012) described further early Equator in the tropical climate zone (Fig. 1a; Moore et al. (Ludlow) land plant remains from Gotland. Upper Silurian 1994). The platform was partly covered by an epicontinental outcrop sections and bore cores from Ska˚ne have also yielded sea and remnants of Silurian deposits are found in Norway, spore assemblages (Mehlqvist et al. 2012, 2014). mid and south Sweden, the Baltic Sea, the East Baltic States, ¨ The upper Silurian Oved-Ramsa˚sa Group in Ska˚ne, Sweden Denmark and Poland. The Baltoscandian Platform was, during has been subjected to numerous investigations over the two the Palaeozoic, strongly affected by the Caledonian orogenic last centuries. The strata representing the youngest Palaeozoic cycle that resulted in the collision of the continents Laurentia, are mainly exposed in limestone and sandstone quarries, and Baltica and Avalonia (Fig 1a). The Iapetus and Rheic Oceans along the shore of Lake Ringsjo¨n, the so-called Klinta expo- were closing up and the active fold belts on the western and sure. The first publication, from 1725, is a documentation of southeastern margins of the Baltic platform formed the Arctic– the fossil content (Bromell 1725–1729). Succeeding compre- North Atlantic Caledonides and the North German–Polish hensive publications concerning the exposed successions at Caledonides (Frost et al. 1981; Ziegler 1984; Zeh & Gerdes Klinta include, for example, Eichsta¨dt (1888), Gro¨nwall (1897), 2010). The former, wide shelf areas transformed to marginal Hadding (1927, 1933), Regne´ll (1960); and detailed studies basins where clastics, derived from the mountain ranges, were Downloaded6 2015 from Thehttps://www.cambridge.org/core Royal Society of Edinburgh.. IP address: doi:10.1017/S1755691015000043 170.106.202.8, on 27 Sep 2021 at 09:04:40, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1755691015000043 150 KRISTINA MEHLQVIST ET AL. FD0D (a) (b) 3UHFDPEULDQ%DVHPHQW 6LEHULD bQJHOKROP 0D 0D 6NnQH 3DOHR]RLF (TXDWRU 0HVR]RLF .ULVWLDQVWDG +HOVLQJERUJ %DOWLFD 5LQJVM|Q .OLQWD /XQG /DXUHQWLD %MlUVM|ODJnUG $YDORQLD 0DOP| &HQR]RLF 0D 6NDOD *RQGZDQD NP Figure 1 (a) Palaeogeographic map showing the position of Baltica, during the late Silurian to Early Devonian. Red circle marks the study site in Ska˚ne, Sweden. Numbers show the location of other study sites, compared with Klinta: 1 ¼ Gotland; 2 ¼ Wales; 3 ¼ Scotland; 4 ¼ Nova Scotia. (Map modified after Scotese et al. 1985). (b) The principal exposures of the O¨ ved Ramsa˚sa Group are found in Klinta and Bja¨rsjo¨laga˚rd, Sweden (Locality map modified after Wikman & Bergstro¨m 1987). deposited (Zeh & Gerdes 2010). The sedimentary strata reflect In sedimentological and petrographic studies, these deposits a gradual shallowing-up from deep-water graptolitic shales to have been shown to contain cerebroid ooids and evaporite shallow marine limestones and sandstones. Following the pro- tracers, which are linked to changes in faunas (Wigforss-Lange grading, shoreline marine deposition ceased, as indicated by 2007; Jeppsson et al. 2012). The depositional setting has been the onset of early Devonian ‘‘Old Red Sandstone’’ deposition interpreted as a near-shore tidally-influenced environment grad- (Bassett 1985). ing from open marine shallow subtidal to lagoonal intertidal The youngest Palaeozoic stratum in southern Sweden is conditions (Wigforss-Lange 2007). the O¨ ved–Ramsa˚sa Group, which is sub-divided into the Klinta The present stratigraphical scheme and nomenclature for Formation (Jeppsson & Laufeld 1986) and the overlying O¨ veds the O¨ ved-Ramsa˚sa Group is primarily based on conodont Sandstone Formation (Hadding 1927). These sediments are stratigraphy established by Jeppsson (1975) and Jeppsson & dominated by mudstones, inter-layered with shallow marine Laufeld (1986), and on spores from land plants studied from carbonates, grading into sandstones in the younger part of the the drillcores Klinta 1 and Bja¨rsjo¨laga˚rd 2 (Mehlqvist et al. succession. The majority of the outcrops representing the 2012). O¨ ved-Ramsa˚sa Group are found in central Ska˚ne at Klinta The section at Klinta investigated herein comprises the and Bja¨rsjo¨laga˚rd (Fig. 1b). The Klinta exposures are located Bja¨r and Bja¨rsjo¨ members containing the conodont faunas along the shoreline of the eastern lake Ringsjo¨n (Figs 1b, 2). Ozarkodina excavata (former Hindeodella excavata), older Figure 2 One of the studied exposures at Klinta, located by the shore of the eastern Lake Ringsjo¨n, Sweden. Downloaded from https://www.cambridge.org/core. IP address: 170.106.202.8, on 27 Sep 2021 at 09:04:40, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1755691015000043 LUDFORDIAN TERRESTRIAL SPORE ASSEMBLAGES FROM SWEDEN 151 Table I Raw data, % of spore taxa identified in each sample. Taxa highlighted in yellow are trilete spore species; the rest are cryptospores. $ " ! % % % ! % # # !! " " " !! ! ! " ! ! ! !! ! ! " " ! ! ! ! "