Document Detail


Probable calcified metaphytes in the latest Proterozoic Nama Group, Namibia: origin, diagenesis, and implications.
MedLine Citation:
PMID:  11538648     Owner:  NASA     Status:  MEDLINE    
Abstract/OtherAbstract:
Samples from the Huns Limestone Member, Urusis Formation, Nama Group, at two adjacent localities in southern Namibia contain thin foliose to arched, sheet-like carbonate crusts that are 100-500 micrometers thick and up to 5 cm in lateral dimension. Morphologic, petrographic, and geochemical evidence supports the interpretation of these delicate crusts as biogenic, most likely the remains of calcified encrusting metaphytes. The original sediments of the fossiliferous samples contained aragonitic encrusting algae, botryoidal aragonite cements, and an aragonite mud groundmass. Spherulites within the precursor mud could represent bacterially induced mineral growths or the concretions of marine rivularian cyanobacteria. Original textures were severely disrupted during the diagenetic transition of aragonite to low-magnesian calcite, but some primary structures remain discernible as ghosts in the neomorphic mosaic. Gross morphology, original aragonite mineralogy, and hypobasal calcification indicate that the crusts are similar to late Paleozoic phylloid algae and extant peyssonnelid red algae. Structures interpreted as possible conceptacles also suggest possible affinities with the Corallinaceae. Two species of Cloudina, interpreted as the remains of a shelly metazoan, are also known from limestones in the Nama Group. It is possible, therefore, that skeletalization in metaphytes and animals arose nearly simultaneously near the end of the Proterozoic Eon.
Authors:
S W Grant; A H Knoll; G J Germs
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of paleontology     Volume:  65     ISSN:  0022-3360     ISO Abbreviation:  J Paleontol     Publication Date:  1991  
Date Detail:
Created Date:  1996-07-23     Completed Date:  1996-07-23     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  100971397     Medline TA:  J Paleontol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1-18     Citation Subset:  S    
Affiliation:
Botanical Museum, Harvard University, Cambridge, Massachusetts 02138, USA.
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MeSH Terms
Descriptor/Qualifier:
Algae, Red
Animals
Calcium Carbonate / analysis*
Carbonates / analysis
Crystallization
Cyanobacteria
Evolution*
Fossils*
Geologic Sediments / chemistry*
Geological Phenomena
Geology
Minerals / analysis
Namibia
Paleontology
Seaweed
Chemical
Reg. No./Substance:
0/Carbonates; 0/Minerals; 471-34-1/Calcium Carbonate
Investigator
Investigator/Affiliation:
A H Knoll / Harvard U, Cambridge, MA, Botanical Museum

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