Facies and paleoecology of the late Ordovician (Caradoc-Ashgill) stromatoporoid bioherms of Tasmania, Australia

Akihiro Kano, Noriko Fujishiro

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Stromatoporoids, together with other sedentary organisms, form bioherms in the Ordovician Gordon Group which were deposited on a carbonate platform of the Western Tasmanian Terrane. The shallow marine carbonates of the older formations show monotonous lithofacies and biota. The variety of the lithofacies and the diversity of sedentary organisms increases in the younger formations which exhibit evidence of subaerial exposure (fissure fillings and mud-cracks). These phenomena partly reflect the tectonic history of the Western Tasmania Terrane, and probably indicate a general increase in amplitude of sea-level change during the late Ordovician (Caradoc-Ashgill). The biohenns are most frequent in the uppermost horizons (the Den Formation - late Caradoc to early Ashgill?), where the outcrops exhibit floatstone and bindstone fabrics. Stromatoporoids and corals construct generally small-scale (less than several meters in width and less than 1 m in height) binding structure. Based on growth forms, stromatoporoid genera are assigned to two morphotypes. Morphotype A generally shows laminar to low domical forms (low height/width ratio) exhibiting ragged margins and sediment inclusions within skeletons. In contrast, morphotype B consists of high domical growth forms (high height/width ratio) and lacks sediment inclusions. These differences in growth forms are interpreted to reflect different modes of biomineralization, together with environmental preferences of the individual organisms. Results of this study and previous publications, overall suggest a progressive development and diversification of biohermal biota in the middle to upper Ordovician of Tasmania. The scale and diversity of the Tasmanian bioherms are probably much smaller than the bioherms and reefs of the younger ages (Silurian and Devonian), and for stromatoporoids, the tendency of diversification is consistent with those of the other Ordovician sections. The Gordon Group provides useful information regarding the early evolutionary history of the Ordovician - Devonian reef-forming communities.

Original languageEnglish
Pages (from-to)65-84
Number of pages20
JournalFacies
Issue number37
Publication statusPublished - Dec 1 1997

Fingerprint

bioherm
Caradocian
paleoecology
Ordovician
growth form
morphotype
lithofacies
biota
terrane
reef
biomineralization
subaerial exposure
history
carbonate platform
den
fissure
sea level change
Silurian
skeleton
sediment

All Science Journal Classification (ASJC) codes

  • Geology
  • Stratigraphy
  • Palaeontology

Cite this

Facies and paleoecology of the late Ordovician (Caradoc-Ashgill) stromatoporoid bioherms of Tasmania, Australia. / Kano, Akihiro; Fujishiro, Noriko.

In: Facies, No. 37, 01.12.1997, p. 65-84.

Research output: Contribution to journalArticle

@article{5381b5ae0f2a46dd89e90b18736db479,
title = "Facies and paleoecology of the late Ordovician (Caradoc-Ashgill) stromatoporoid bioherms of Tasmania, Australia",
abstract = "Stromatoporoids, together with other sedentary organisms, form bioherms in the Ordovician Gordon Group which were deposited on a carbonate platform of the Western Tasmanian Terrane. The shallow marine carbonates of the older formations show monotonous lithofacies and biota. The variety of the lithofacies and the diversity of sedentary organisms increases in the younger formations which exhibit evidence of subaerial exposure (fissure fillings and mud-cracks). These phenomena partly reflect the tectonic history of the Western Tasmania Terrane, and probably indicate a general increase in amplitude of sea-level change during the late Ordovician (Caradoc-Ashgill). The biohenns are most frequent in the uppermost horizons (the Den Formation - late Caradoc to early Ashgill?), where the outcrops exhibit floatstone and bindstone fabrics. Stromatoporoids and corals construct generally small-scale (less than several meters in width and less than 1 m in height) binding structure. Based on growth forms, stromatoporoid genera are assigned to two morphotypes. Morphotype A generally shows laminar to low domical forms (low height/width ratio) exhibiting ragged margins and sediment inclusions within skeletons. In contrast, morphotype B consists of high domical growth forms (high height/width ratio) and lacks sediment inclusions. These differences in growth forms are interpreted to reflect different modes of biomineralization, together with environmental preferences of the individual organisms. Results of this study and previous publications, overall suggest a progressive development and diversification of biohermal biota in the middle to upper Ordovician of Tasmania. The scale and diversity of the Tasmanian bioherms are probably much smaller than the bioherms and reefs of the younger ages (Silurian and Devonian), and for stromatoporoids, the tendency of diversification is consistent with those of the other Ordovician sections. The Gordon Group provides useful information regarding the early evolutionary history of the Ordovician - Devonian reef-forming communities.",
author = "Akihiro Kano and Noriko Fujishiro",
year = "1997",
month = "12",
day = "1",
language = "English",
pages = "65--84",
journal = "Facies",
issn = "0172-9179",
publisher = "Springer Verlag",
number = "37",

}

TY - JOUR

T1 - Facies and paleoecology of the late Ordovician (Caradoc-Ashgill) stromatoporoid bioherms of Tasmania, Australia

AU - Kano, Akihiro

AU - Fujishiro, Noriko

PY - 1997/12/1

Y1 - 1997/12/1

N2 - Stromatoporoids, together with other sedentary organisms, form bioherms in the Ordovician Gordon Group which were deposited on a carbonate platform of the Western Tasmanian Terrane. The shallow marine carbonates of the older formations show monotonous lithofacies and biota. The variety of the lithofacies and the diversity of sedentary organisms increases in the younger formations which exhibit evidence of subaerial exposure (fissure fillings and mud-cracks). These phenomena partly reflect the tectonic history of the Western Tasmania Terrane, and probably indicate a general increase in amplitude of sea-level change during the late Ordovician (Caradoc-Ashgill). The biohenns are most frequent in the uppermost horizons (the Den Formation - late Caradoc to early Ashgill?), where the outcrops exhibit floatstone and bindstone fabrics. Stromatoporoids and corals construct generally small-scale (less than several meters in width and less than 1 m in height) binding structure. Based on growth forms, stromatoporoid genera are assigned to two morphotypes. Morphotype A generally shows laminar to low domical forms (low height/width ratio) exhibiting ragged margins and sediment inclusions within skeletons. In contrast, morphotype B consists of high domical growth forms (high height/width ratio) and lacks sediment inclusions. These differences in growth forms are interpreted to reflect different modes of biomineralization, together with environmental preferences of the individual organisms. Results of this study and previous publications, overall suggest a progressive development and diversification of biohermal biota in the middle to upper Ordovician of Tasmania. The scale and diversity of the Tasmanian bioherms are probably much smaller than the bioherms and reefs of the younger ages (Silurian and Devonian), and for stromatoporoids, the tendency of diversification is consistent with those of the other Ordovician sections. The Gordon Group provides useful information regarding the early evolutionary history of the Ordovician - Devonian reef-forming communities.

AB - Stromatoporoids, together with other sedentary organisms, form bioherms in the Ordovician Gordon Group which were deposited on a carbonate platform of the Western Tasmanian Terrane. The shallow marine carbonates of the older formations show monotonous lithofacies and biota. The variety of the lithofacies and the diversity of sedentary organisms increases in the younger formations which exhibit evidence of subaerial exposure (fissure fillings and mud-cracks). These phenomena partly reflect the tectonic history of the Western Tasmania Terrane, and probably indicate a general increase in amplitude of sea-level change during the late Ordovician (Caradoc-Ashgill). The biohenns are most frequent in the uppermost horizons (the Den Formation - late Caradoc to early Ashgill?), where the outcrops exhibit floatstone and bindstone fabrics. Stromatoporoids and corals construct generally small-scale (less than several meters in width and less than 1 m in height) binding structure. Based on growth forms, stromatoporoid genera are assigned to two morphotypes. Morphotype A generally shows laminar to low domical forms (low height/width ratio) exhibiting ragged margins and sediment inclusions within skeletons. In contrast, morphotype B consists of high domical growth forms (high height/width ratio) and lacks sediment inclusions. These differences in growth forms are interpreted to reflect different modes of biomineralization, together with environmental preferences of the individual organisms. Results of this study and previous publications, overall suggest a progressive development and diversification of biohermal biota in the middle to upper Ordovician of Tasmania. The scale and diversity of the Tasmanian bioherms are probably much smaller than the bioherms and reefs of the younger ages (Silurian and Devonian), and for stromatoporoids, the tendency of diversification is consistent with those of the other Ordovician sections. The Gordon Group provides useful information regarding the early evolutionary history of the Ordovician - Devonian reef-forming communities.

UR - http://www.scopus.com/inward/record.url?scp=5844287777&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=5844287777&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:5844287777

SP - 65

EP - 84

JO - Facies

JF - Facies

SN - 0172-9179

IS - 37

ER -