Algae as depth indicators in the Silurian of the Oslo region

Lauritzen, Ørnulf; Worsley, David

doi:10.1111/j.1502-3931.1974.tb00891.x

Cited by 17 publications

(7 citation statements)

References 4 publications

(2 reference statements)

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“…Several researchers have used algal fossils to argue for absolute depths in the Silurian. Lauritzen & Worsley (1974) first noted the occurrence of the supposed cyanophyte Girvanellu in association with in situ assemblages of the brachiopod Stricklundia in Norway and suggested, on this basis, that these BA 4 assemblages accumulated in less than 60 m of water. This figure was based on comparisons with modern oscillatoriacean cyanobacteria.…”

Section: Paleontological Evidence For Absolute Depth: Photic-zone Indmentioning

confidence: 99%

Absolute depths of Silurian benthic assemblages

Brett

Boucot

Jones

1993

LET

156

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A variety of evidence can be used to estimate the absolute depth of the well‐established depth gradient of Silurian onshore‐to‐offshore benthic assemblages (BA 1–5); this evidence is reviewed herein. There is a fair degree of consistency between fossil benthic assemblages and the occurrence of certain primary sedimentary structures, particularly those involved in storm deposition. A second, probably stronger, line of evidence for absolute depth of Silurian benthic assemblages involves the distribution of fossils of light‐sensitive organisms and of reefs. Among these, the most important are the calcified dasycladacean algae, to which the cyclocrinitids of the Middle Ordovician ‐ Early Silurian may belong. The modem dasycladaceans have a narrowly restricted bathymetric range. Maximum depth for modern calcified dasycladaceans is about 90 m, but the vast majority occur at 30 m or less. Some Silurian occurrences of these algae are abundant, particularly in BA 3 and 4; rarely, small specimens of cyclocrinitids and receptaculitids are found in the lower, outer portions of BA 4 and even into 5. This evidence constrains much of the spectrum (BA 1–5) of Silurian fossil communities to a rather narrow depth range, within the photic zone. Based on taxonomic uniformitarianism, we would place the depth of Silurian BA 1 through 4 between 0 and about 40–60 m. The common coincidence of the lower end of storm wave base and the lower end of the photic zone near the BA 4–5 boundary also suggests that this position may represent water depths on the order of 50 m. Several other lines of evidence ‐including algal borings, widths of facies belts, separation of communities by basalt flows whose thicknesses are known ‐ also support a relatively shallow depth range for BA 14. The absence of storm‐disturbed beds over large parts of several major platforms below about the BA 3–4 boundary region suggests that major storms of the Silurian may have been far weaker than those of the present, possibly owing to a different climatic regime. □Absolute depth, Silurian, photic zone, calcareous algae, Benthic Assemblage, storms.

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Section: Paleontological Evidence For Absolute Depth: Photic-zone Indmentioning

confidence: 99%

Absolute depths of Silurian benthic assemblages

Brett

Boucot

Jones

1993

LET

156

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“…ISSN 0024-1164. Lauritzen & Worsley (1974) claim that the in situ occurrence of Girvanella is a reliable indication of water depth. Their reasoning is that Girvanella is a blue-green alga related to the Oscillatoriaceae and that as such it would not inhabit depths exceeding 60 m. This leads them to state (p. 161) that: 'the association of Stricklandia and Girvanella places an upper depth limit of less than 60 metres for the Stricklandia community.…”

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confidence: 99%

Girvanella and other algae as depth indicators

Riding

1975

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Girvarzella is interpreted to be the calcified sheath of a variety of filamentous blue‐green algae. At present there are no clear limits which can be set on its depth of occurrence. The usefulness of benthic calcareous algae as depth indicators in palaeoenvironmental studies is dependent upon the level of identification. At high taxonomic levels it is very limited. Algae are not restricted to the euphotic zone (ka. 150 m). Calcareous green algae are restricted to shallower water (0‐ca. 100 m) than are calcareous red algae (0‐ca. 400 m) but they are prone to fragmentation and subsequent transportation. Narrower depth limits for lower taxonomic levels have been demonstrated in Recent green and red algae, but have yet to be recognized in ancient environments. In the Palaeozoic, problems of correctly identifying calcareous algae further restrict their use as depth indicators.

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“…The Ringerike succession was apparently deposited in progressively deeper water conditions from Eocoelia-equivalent communities in Stage 6, through Pentamerus-(7a and 7b), Stricklandia-(7c), to Clorinda-equivalent communities in 8a (the 'zone' fossil for 8a in Ringerike is Cyrtia exporrecta, a typical constituent of the British Clorinda communities). The rocks of Stages 8b to 8d appear )to have been deposited in much more shallow water, Pentamerus-equivalent communities being associated with reef structures and algae suggestive of shallow water conditions (Lauritzen & Worsley 1974). Thus, with the significant exceptions of Stages 6c and 7a in Ringerike, large mean shell size in these atrypid assemblages appears to be associated with both low faunal diversity and shallow water environments.…”

Section: Variation In Atrypid Communitiesmentioning

confidence: 94%

An environmental study of Silurian atrypid communities from southern Norway

Worsley

Broadhurst

1975

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Atrypid communities are described from the Silurian succession of southern Norway. These atrypids show striking variation in their mode of occurrence, several features of which are described quantitatively. Mature, well‐developed communities occur in calcareous rocks which were apparently deposited in a well‐aerated shallow environment. Stunted communities (identified by small shell size despite maturity) occur in carbonate‐poor sediments deposited in deeper and less turbulent environments. Other communities are composed of immature shells which were apparently killed by a catastrophic event. Communities are also seen in which catastrophe was not total, and survivors can be recognised. The atrypid niche was taken over by other animal communities when major environmental changes took place.

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Algae as depth indicators in the Silurian of the Oslo region

Cited by 17 publications

References 4 publications

Absolute depths of Silurian benthic assemblages

Absolute depths of Silurian benthic assemblages

Girvanella and other algae as depth indicators

An environmental study of Silurian atrypid communities from southern Norway

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