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A Late Ordovician ice sheet in South America; evidence from the Cancaniri tillites, southern Bolivia

Frank Schoenian and Sven O. Egenhoff
A Late Ordovician ice sheet in South America; evidence from the Cancaniri tillites, southern Bolivia (in The evolution of the Rheic Ocean; from Avalonian-Cadomian active margin to Alleghenian-Variscan collision, Ulf Linnemann (editor), R. Damian Nance (editor), Petr Kraft (editor) and Gernold Zulauf (editor))
Special Paper - Geological Society of America (2007) 423: 525-548

Abstract

Detailed mapping and facies analysis of a thick succession of diamictites of the Upper Ordovician Cancaniri Formation in southern Bolivia has revealed a glacioterrestrial origin for these sediments. The Cancaniri diamictites were deposited during three advances of a temperate, grounded ice sheet. They contain subglacial, englacial, and proglacial outwash sediments that increase in abundance from southeast to northwest. Clast fabrics and deformation features indicate SSE to NNW motion of the ice masses. Components of the diamictites usually display abrasion features such as facets and glacial striae. Provenance studies indicate that the pebbles comprise approximately 35% of siliciclastic sediments, mainly from the underlying shallow marine Ordovician rocks, 27% of slightly metamorphosed sediments that in part can be attributed to the Precambrian-Cambrian Puncoviscana Formation of northwestern Argentina, and a crystalline basement suite of metamorphic rocks (18%) and magmatic (mainly plutonic) rocks (20%). Due to the absence of typical lithologies, the Brazilian Shield, the Paraguay belt, and the southern Arequipa-Antofalla block could be excluded as possible source areas. The crystalline and metasedimentary clasts display strong affinities with the Pampean basement in central Argentina. All data consistently suggest that the Cancaniri tillites of southern Bolivia were deposited by a regional, low-latitude ice sheet that was independent of the main inland ice mass of Gondwana and centered SSE of the study area, in a Neoproterozoic to Cambrian orogenic belt in the area of the present Argentinean Chaco.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 423
Title: A Late Ordovician ice sheet in South America; evidence from the Cancaniri tillites, southern Bolivia
Title: The evolution of the Rheic Ocean; from Avalonian-Cadomian active margin to Alleghenian-Variscan collision
Author(s): Schoenian, FrankEgenhoff, Sven O.
Author(s): Linnemann, Ulfeditor
Author(s): Nance, R. Damianeditor
Author(s): Kraft, Petreditor
Author(s): Zulauf, Gernoldeditor
Affiliation: Humboldt University, Museum of Natural History, Berlin, Federal Republic of Germany
Affiliation: Staatliche Naturhistorische Sammlungen Dresden, Museum fuer Mineralogie und Geologie, Dresden, Federal Republic of Germany
Pages: 525-548
Published: 2007
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 120
Accession Number: 2008-044796
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. cols., 3 plates, geol. sketch maps
S21°45'00" - S21°10'00", W64°49'60" - W64°25'00"
Secondary Affiliation: Ohio University, USA, United StatesCharles University Prague, CZE, Czech RepublicUniversitaet Frankfurt am Main, DEU, Federal Republic of GermanyColorado State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200813
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