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Laufield 1974[1]

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  • Succession of Limestones and Shales
  • Shallow shelf above thin (75-125m) Ord. succession
  • 500-200m thick, thickest in south. Oldest @ NW.
  • Shallow epicontinental sea
  • Near equator (Creer 1973)
  • Water depth never > 175-200m (Gray, Laufield & boucot, 1974)
  • Dominated by reefs, starting to grow in Llandovery (sea then 50-100m deep.
  • NW shelf becomes shallower, from bioherm detritus and terriginous infilling. Migration of reef zone to SW, but complicated by sea level change.


  • Burgsvik group:
  • Thin → v thick beds, light grey, fine grained, slightly calcareous, argillaceous sst - intercalated w/ v. thin bedded blue-grey claystone.
  • The sst in places overlain by the "Upper Burgsvik Beds": thin-bedded, light-to-bluish grey, oolitic lst with, in places, alternating sandy beds. These are the ones containing problematic structures (Manten 1966).
  • Strong lateral variation - correltation difficult.

Manten 1966[2]

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Re. the Upper Burgsvic Beds. Age is probably lowermost Devonian (Downtonian)

  • Formed close to the shoreline on a beach "faintly sloping towards the open sea" affected by tides.
Evidence
Cross-bedding
Ripple marks
Offshore bars
oolites
rounded oolite pebbles in ssts and oolites
slightly rounded fossils, sorted by size, between sst and uppermost oolite
lamellibranch (molluscs?) with thick shells
Rare burrows
clay lenses (deposited behind low barriers?)
erosion channels
Pothole-like escavations
mud cracks
"dendritic patterns of rill marks" - suggest form on beach/unvegetated ground which periodically ran dry.

Manten 1971

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Divides Burgsvic beds into 3 members, based on bore-hole. Upper bed varies a little along strike but can be recognised across whole outcrop belt, with distinctive lower contact. Lower beds are exposed at Kullunde 1 & Glasskär 1-3

Long 1993[3]

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Thorough sedimentological analysis. Surmises and challenges sedimentary descriptions:

  • Near-shore sands: Munthe 1910, Manten 1966
  • Locally emergent, offshore bars: Agterberg 1958, Manten 1971
  • beach deposits: Stel & de Coo 1977, Laufield & Bassett
Intertidal exposure: Grey et al 1974, Laufield & Martinsson 1981
tidal influence: Manten 1966, Stel & de Coo 1977

Contains logs of cores

Microbial origin of unusual wrinkle structures described by Manten 1966.

Lithofacies

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→ zst-s/mst
Poor exposure. Interbeds in middle, thick seq. in lower.
→ f-vf. ssf
→ biofacies - oo, onco, bioclastic

Problematic structures

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  • wrinkles are kinneyia ripples (Martinsson 1965) or Runzel-marken (Reineck 1969, or wrinkle marks (Reineck & Sing 1973, Allen 1984).
  • Wind stress on freshly deposited seds? Not nec.. soft sed failure of sand beds over mud.

Interpretation

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Shoaling sequence - migration of storm dominated sandbanks, or sand-wave complexes.

Formation: detatched offshore bars (Swift & Field 1981, Brenner et al 1985)? Isolated bars in mid-shelf (La Fon 1981)?
Cross stratification abundant. so can't be tide-dominated.
Storm beds abundant. So Storms probably created bars.
Prod & scour marks etc irregularly aligned - waves influenced sea floor.

Stel & de Coo[4]

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Detailed Petrographic and paleæoecological analysis of top few metres. sst at top of middle member, and in upper member, deposited @ beach to lower foreshore. Oolites & oncolites in upper strate form, in "agitated shallow marine setting" - minor tidal influence

Calner 2005

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[5]

  • Anachronistic facies found near Lau event in Late Silurian.
  • Basal Eke Fm. contiains flat-pebble conglomerates

Cherns 1983

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In a SGU we don't have.

Jux & Stauber

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Bassett et al 1989[6]

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Assign a Mid-Ludfordian (Upper Ludlow) age to the Burgsvik. Positive δ13Corg excursion during Eke and Burgsvik beds. Could be interpreted as climate (arid vs. wet) controling facies distribution, sea level shifts less important; high δ13C observed in arid deposits.

Sherwood-Pike and Grey[7]

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Key text.




See

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Agterberg 1958:254-256 ==1958, Agterberg, F.P.: An undulation of the rate of sedimentation in southern Gotland: Geologie en Mijnbouw, New Series Vol. 20, pp. 253-260.

Reflist

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  1. ^ Laufeld, S. (1974). Silurian Chitinozoa from Gotland. Fossils and Strata. Universitetsforlaget.
  2. ^ Manten, A.A. (1966). "Some problematic shallow-marine structures". Marine Geol. 4 (3): 227–232. doi:10.1016/0025-3227(66)90023-5. Retrieved 2007-06-18.
  3. ^ Long, D.G.F. (1993). "The Burgsvik beds, an Upper Silurian storm generated sand ridge complex in southern Gotland". Geologiska Föreningens i Stockholms Förhandlingar (Now GFF). 115 (4): 299–309. doi:10.1080/11035899309453917. ISSN 0016-786X.
  4. ^ Stel, J.H. (1977). The Silurian Upper Burgsvik and Lower Hamra-Sundre Beds, Gotland. Rijksmuseum van Geologie en Mineralogie. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Calner, M. (2005-04-01). "A Late Silurian extinction event and anachronistic period". Geology. 33 (4): 305–308. doi:10.1130/G21185.1. {{cite journal}}: Check date values in: |date= (help)CS1 maint: date and year (link)
  6. ^ Bassett; et al. (1989). "The Wenlock-Ludlow carbon isotope trend in the Vidukle core, Lithuania, and its relations with oceanic events" (PDF). {{cite journal}}: Cite journal requires |journal= (help); Explicit use of et al. in: |author= (help)
  7. ^ Sherwood-pike, M.A. (1985). "Silurian fungal remains: probable records of the class Ascomycetes". Lethaia. 18: 1–20. doi:10.1111/j.1502-3931.1985.tb00680.x. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)