Biogenic and physical sedimentary structures in latest Cambrian-earliest Ordovician mudrock facies (Famatina Range, Northwestern Argentina)
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Universitat de Barcelona
2003
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| author | S. B. Esteban |
| author_facet | S. B. Esteban |
| contents | Biogenic and physical sedimentary structures in latest Cambrian-earliest Ordovician mudrock facies (Famatina Range, Northwestern Argentina) S. B. Esteban Ciencias de la Tierra Mudrocks NW Argentina Late Cambrian Famatina Range Early Ordovician Lamination is a common feature in shales and other mud-dominated rocks. When combined with other geologicalevidence, the diverse lamination types can provide important information about sedimentary processes anddepositional environments. Petrographic and Scanning Electron Microscope studies performed in the latest Cambrian-earliest Ordovician lower Member of the Volcancito Formation (Famatina Range) have revealed three distincttypes of lamination in mudrocks. Thick horizontal lamination (> 0.5 mm thick) is characterized by dark claylaminae alternating with calcite and quartz-rich light colored silt laminae. Silty laminae show micro-scours at thebase, and unidirectional micro-ripple cross-lamination. This type of lamination is dominant in the lower part ofthe succession, and it is interpreted as formed by bottom flowing currents, probably induced by storms. Wavylamination shows clear undulation surfaces at megascopic scale. In thin section, wavy lamination is composedby alternating black organic-rich laminae less than 0.2 mm thick, and lighter colored carbonate-rich clay and finesilt laminae (0.1-0.2 mm thick). This second type of lamination is observed at the lower and middle parts of thesequence and it is interpreted as produced by benthic microbial mat development (probably cyanobacteria). Thinhorizontal lamination (< 0.5 mm thick) is characterized by dark organic and clay-rich laminae alternating withlighter colored quartz-rich silty laminae. This lamination may be associated with suspension settling from dilutesuspended fine-grained sediment flows. Thin horizontal lamination is predominant at the upper part of the succession.Changes in lamination and sedimentary processes observed from base to top of the studied successionrecord a major deepening event in the basin during the latest Cambrian - earliest Ordovician, which finally triggeredthe deposition of a thick lower Tremadoc black shale package. This event was also responsible of a significantfaunal change through the sequence. The representing fauna of the Parabolina frequens argentina Biozonechanges upwards from predominant benthic trilobites (e.g. Parabolinella, Angelina hyeronimi (KAYSER),Shumardia erquensis KOBAYASHI, Onyclopyge, etc.) to pelagic trilobites (exclusively Jujuyaspis), which occurassociated with planktonic graptolites (Rhabdinopora). Changes in facies pattern and faunal components recorda relative sea level rise, which resulted in a major transgression at the base of the Ordovician. 2003 artículo científico 1695-6133 https://www.redalyc.org/articulo.oa?id=50510108 en http://www.redalyc.org/revista.oa?id=505 Geologica Acta: an international earth science journal application/pdf Universitat de Barcelona Geologica Acta: an international earth science journal (España) Num.1 Vol.1 |
| format | Artículo científico |
| id | redalyc_50510108 |
| institution | Redalyc |
| language | en |
| publishDate | 2003 |
| publisher | Universitat de Barcelona |
| spellingShingle | Biogenic and physical sedimentary structures in latest Cambrian-earliest Ordovician mudrock facies (Famatina Range, Northwestern Argentina) S. B. Esteban Ciencias de la Tierra Mudrocks NW Argentina Late Cambrian Famatina Range Early Ordovician Biogenic and physical sedimentary structures in latest Cambrian-earliest Ordovician mudrock facies (Famatina Range, Northwestern Argentina) S. B. Esteban Ciencias de la Tierra Mudrocks NW Argentina Late Cambrian Famatina Range Early Ordovician Lamination is a common feature in shales and other mud-dominated rocks. When combined with other geologicalevidence, the diverse lamination types can provide important information about sedimentary processes anddepositional environments. Petrographic and Scanning Electron Microscope studies performed in the latest Cambrian-earliest Ordovician lower Member of the Volcancito Formation (Famatina Range) have revealed three distincttypes of lamination in mudrocks. Thick horizontal lamination (> 0.5 mm thick) is characterized by dark claylaminae alternating with calcite and quartz-rich light colored silt laminae. Silty laminae show micro-scours at thebase, and unidirectional micro-ripple cross-lamination. This type of lamination is dominant in the lower part ofthe succession, and it is interpreted as formed by bottom flowing currents, probably induced by storms. Wavylamination shows clear undulation surfaces at megascopic scale. In thin section, wavy lamination is composedby alternating black organic-rich laminae less than 0.2 mm thick, and lighter colored carbonate-rich clay and finesilt laminae (0.1-0.2 mm thick). This second type of lamination is observed at the lower and middle parts of thesequence and it is interpreted as produced by benthic microbial mat development (probably cyanobacteria). Thinhorizontal lamination (< 0.5 mm thick) is characterized by dark organic and clay-rich laminae alternating withlighter colored quartz-rich silty laminae. This lamination may be associated with suspension settling from dilutesuspended fine-grained sediment flows. Thin horizontal lamination is predominant at the upper part of the succession.Changes in lamination and sedimentary processes observed from base to top of the studied successionrecord a major deepening event in the basin during the latest Cambrian - earliest Ordovician, which finally triggeredthe deposition of a thick lower Tremadoc black shale package. This event was also responsible of a significantfaunal change through the sequence. The representing fauna of the Parabolina frequens argentina Biozonechanges upwards from predominant benthic trilobites (e.g. Parabolinella, Angelina hyeronimi (KAYSER),Shumardia erquensis KOBAYASHI, Onyclopyge, etc.) to pelagic trilobites (exclusively Jujuyaspis), which occurassociated with planktonic graptolites (Rhabdinopora). Changes in facies pattern and faunal components recorda relative sea level rise, which resulted in a major transgression at the base of the Ordovician. 2003 artículo científico 1695-6133 https://www.redalyc.org/articulo.oa?id=50510108 en http://www.redalyc.org/revista.oa?id=505 Geologica Acta: an international earth science journal application/pdf Universitat de Barcelona Geologica Acta: an international earth science journal (España) Num.1 Vol.1 |
| title | Biogenic and physical sedimentary structures in latest Cambrian-earliest Ordovician mudrock facies (Famatina Range, Northwestern Argentina) |
| topic | Ciencias de la Tierra Mudrocks NW Argentina Late Cambrian Famatina Range Early Ordovician |
| url | https://www.redalyc.org/articulo.oa?id=50510108 |