Significance of a Halysitid-Heliolitid Mud-Facies Autobiostrome from the Middle Silurian of Gotland, Sweden

Calner, Mikael; Sandström, Olof; Mõtus, Mari-Ann

doi:10.2307/3515615

Cited by 8 publications

(25 citation statements)

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“…P. unicostatus is the most frequent coniform taxon in the Djupvik 1 sample but rare in that from Blåhäll 1. Neither species were found in the similarsized collection just below, from the uppermost bed of the biostrome (top of the 'upper limestone-dominated unit' of Calner, Sandström & Mõtus (2000). Probably, the reappearance of P. unicostatus can be used as an ancillary indicator in the same way as in the midSheinwoodian.…”

Section: B the Kockelella Ortus Absidata Zonementioning

confidence: 85%

“…Since K. o. absidata is the only robust Kockelella known from this interval on Gotland, these are herein accepted as evidence for inclusion in either of these zones. The lowermost find of K. o. absidata in such a frequency is from Djupvik 1 at -1.05/-0.95 m. In both the very large collection G94-8LJ from -1.52/-1.47 m from Djupvik and in G94-77LJ from the 'top marker bed' (Calner, Sandström & Mõtus, 2000) at Blåhäll 1, just above the biostrome, there is a juvenile sp (Pa) element of K. ortus cf. absidata.…”

Section: B the Kockelella Ortus Absidata Zonementioning

confidence: 99%

“…3b) at Värsendeojk 5 and Svarvare 3; Subzone 1 at Gannarveskär 2, 4 (up to −0.04 m), Robbjänskvarn 1 and 2; Subzone 2 at Gannarveskär 4, 2, Klintebys 1, Bara 1 (through the oolite), and in the När-1 drillcore at 230.30-230.25 m; Subzone 3 at Sandhamn 1, Mulde Tegelbruk 1 and in the När-1 drillcore at 210.23-210.09 m, and Subzone 4 at Blåhäll 1 up to just above the biostrome (see Fig. 5 in Calner, Sandström & Mõtus, 2000). The correlation of these with the graptolite zonation is shown in Fig.…”

Section: A the Ozarkodina Bohemica Longa Zonementioning

confidence: 99%

“…These strata reflect deposition of both carbonate and fine siliciclastics, the latter mainly detrital clay and silt together with small amounts of sand. Below, facies changes are described across the palaeo-platform margin as depicted by Calner, Sandström & Mõtus (2000). Transects A-A' and E-E' include the best successions of exposures and show the largest proximality differences, and are for this reason highlighted (Fig.…”

Section: Facies Descriptionsmentioning

confidence: 99%

“…2a,b;Calner, 2002). Bioherms and biostromes occur in several facies associations throughout the interval (Manten, 1971;Riding, 1981;Kano, 1994), notably also in the distal slope to basin environment (Stel, 1978;Nield, 1982;Calner, Sandström & Mõtus, 2000).…”

Section: A Geological Settingmentioning

confidence: 99%

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Carbonate platform evolution and conodont stratigraphy during the middle Silurian Mulde Event, Gotland, Sweden

2003

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-Evidence from sedimentology and conodont biostratigraphy is used to reinterpret the mid-Homerian (Late Wenlock) succession on Gotland, Sweden. A new conodont zonation includes from below: the Ozarkodina bohemica longa Zone (including five subzones), the Kockelella ortus absidata Zone and the Ctenognathodus murchisoni Zone (two taxa are named, Ozarkodina bohemica longa and Pseudooneotodus linguicornis). These new zones are integrated with facies in order to correlate strata and infer the major depositional environments and the controls on deposition during the mid-Homerian Mulde Event. Reef-associated and skeletal carbonate deposition predominated before and after the event, i.e. during the uppermost O. s. sagitta Zone and, again, in the C. murchisoni Zone. These periods are characterized by the expansion of reefs and shoal facies across marls in the topmost Slite Group on eastern Gotland and in the lower parts of the Klinteberg Formation on western Gotland, respectively. The intervening O. b. longa and K. o. absidata zones are initially characterized by rapid facies changes, including siliciclastic deposition, and later stabilisation of a carbonate depositional system. The composition of sediments and depositional rates are closely related to the creation and destruction of accommodation space and reflects a classical case of depositional bias of the carbonate and siliciclastic depositional systems. Based on coastline migration, stratal boundaries, and the stratigraphic position of major reef belts, several facies associations can be fitted into a sequence stratigraphic model for platform evolution. A highstand systems tract (HST) situation prevailed prior to, and during the early part of the event; the upper Slite Group including the lower Fröjel Formation. This HST was characterized by prolific skeletal production and regional reef development except for during the latest stage when carbonate production declined at the onset of the Mulde Event. Platform growth was inhibited during a following regressive systems tract (RST) when regional siliciclastic deposition predominated; the Gannarve Member. The subsequent lowstand resulted in regional emersion and karstification, i.e. a complete termination of the platform. The postextinction transgressive systems tract (TST) is exclusively composed of non-skeletal carbonates; the Bara Member of the Halla Formation. Re-occurrence of reefs and a prolific skeletal production marks platform recovery during a second HST; the remaining Halla and the lower Klinteberg formations. Integration of high-resolution biostratigraphy and sequence stratigraphy reveals that the major physical control on platform evolution was a 5th order eustatic sea-level change during an early part of the Mulde Event, and that the bulk of the strata accumulated when the platform aggraded and prograded during the highstand systems tracts. Thus, Silurian oceanic events and associated sea-level changes had profound impact on the neritic carbonate system. The Gotland-based middle and late Homerian...

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Section: B the Kockelella Ortus Absidata Zonementioning

confidence: 85%

Section: B the Kockelella Ortus Absidata Zonementioning

confidence: 99%

Section: A the Ozarkodina Bohemica Longa Zonementioning

confidence: 99%

Section: Facies Descriptionsmentioning

confidence: 99%

Section: A Geological Settingmentioning

confidence: 99%

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Carbonate platform evolution and conodont stratigraphy during the middle Silurian Mulde Event, Gotland, Sweden

2003

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The Silurian Mulde Event and a scenario for secundo–secundo events

Jeppsson¹,

Calner²

2002

Transactions of the Royal Society of Edinburgh: Earth Sciences

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Graphic correlation using graptolites and conodonts provides a high-resolution timescale for correlating from coastal to deep oceanic sections and, thereby, also a detailed record of the sequence of changes during the Mulde Secundo-Secundo Event. That interval includes sedimentary facies otherwise unknown in older Wenlock to early Ludlow strata on Gotland. The identified sequence of changes includes a detailed record of, in order: two extinctions (Datum points 1 and 1·5); widespread deposition of carbon-rich sediments extensive enough to cause a δ13C increase of c. 4.8‰, the onset, maximum and end of a sea-level fall and rise of at least 16 m during 30 kyr; a third extinction (Datum 2); a disaster fauna; and a slow faunal recovery. Thus, a secondary result of the event was a weakened greenhouse effect triggering a glaciation: the Gannarve Glaciation (new term). The order of changes proves that regression did not cause the extinctions. Faunal and sea-level changes, as well as the sedimentary succession, fit well with predictions based on an oceanic model. Extinctions were primarily caused by a severe drop in primary planktonic productivity, causing starvation among planktonic larvae in non-coastal settings. The Grötlingbo Bentonite (new term), the thickest in the Wenlock of Gotland, was deposited across the basin shortly after Datum 2. Temporal resolution is high enough to permit some comparison with Quaternary glaciations.

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Ludlow (Silurian) stromatoporoid biostromes from Gotland, Sweden: facies, depositional models and modern analogues

Sandström¹,

Kershaw²

2002

Sedimentology

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Stacked stromatoporoid-dominated biostromes of the Ludlow-age Hemse Group (Silurian) in eastern Gotland, Sweden, are 0AE5-5 m thick and a few tens of metres to >1 km in lateral extent. They form one of the world's richest Palaeozoic stromatoporoid deposits. This study compiles published and new data to provide an overall facies model for these biostromes, which is assessed in relation to possible modern analogues. Some biostromes have predominantly in-place fossils and are regarded as reefs, but lack rigid frameworks because of abundant low-profile non-framebuilding stromatoporoids; other biostromes consist of stromatoporoid-rich rudstones interpreted here as storm deposits. Variation between these two 'end-members' occurs both between interlayered biostromes and also vertically and laterally within individual biostromes. Such variation produces problems of applying established reef classification terms and demonstrates the need for the development of terminology that recognizes taphonomic destruction of reef fabrics. An approach to such terminology is found in all four categories of a recent biostrome classification scheme that are easily recognized in the Hemse biostrome facies: autobiostromes (>60% in place); autoparabiostromes (a mixture of in-place and overturned reef-building organisms, 20-60% in place); parabiostromes (builders are overturned and damaged, <20% in place); and allobiostromes (transported and detrital reef material, nothing in place). These categories provide a broad taphofacies scheme for the Hemse biostromes, which are mostly autoparabiostrome to allobiostrome. The biostromes developed on crinoidal grainstone sheets and expanded laterally across relatively flat substrates in a marine setting of low siliciclastic input. Planar erosion surfaces commonly terminate biostrome tops. Three broadly similar modern analogues are identified, each of which has elements in common with the Hemse biostromes, but none of which is an exact equivalent: (a) laterally expanded and coalesced back-barrier patch reefs behind the Belize barrier, an area influenced by limited accommodation space; (b) a hurricaneinfluenced shelf, interpreted for Grand Cayman, where reef cores consist of rubble and lack substantial framework; the wide distribution of rounded pebbles and cobbles of stromatoporoids in the Hemse biostromes most probably resulted from hurricanes; (c) coral carpets in 5-15 m water depth of the northern Red Sea, where lateral expansion of low-diversity frames dominated by Porites coral has produced low-profile biostromes up to 8 m thick and several km long. Such carpets accumulated large amounts of carbonate, with little export, as in the Hemse biostromes, although the latter did not build frameworks because of the nature of growth of the stromatoporoids. The notable lack of algae in the Hemse biostrome facies is also a feature of Red Sea (2002) 49, 379-395 Ó 2002 International Association of Sedimentologists 379 coral carpets; nevertheless, coral carpets are ecologically different. Hemse biostromes lac...

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Significance of a Halysitid-Heliolitid Mud-Facies Autobiostrome from the Middle Silurian of Gotland, Sweden

Cited by 8 publications

References 0 publications

Carbonate platform evolution and conodont stratigraphy during the middle Silurian Mulde Event, Gotland, Sweden

Carbonate platform evolution and conodont stratigraphy during the middle Silurian Mulde Event, Gotland, Sweden

The Silurian Mulde Event and a scenario for secundo–secundo events

Ludlow (Silurian) stromatoporoid biostromes from Gotland, Sweden: facies, depositional models and modern analogues

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