Early Silica Diagenesis in Volcanic and Sedimentary Rocks: Devitrification and Replacement Phenomena

1973 ◽  
Vol 31 ◽  
pp. 206-207
Author(s):  
S. W. Wise ◽  
F. M. Weaver ◽  
N. Guven
Keyword(s):  
Coastal Plain ◽  
Deep Sea ◽  
Carbonate Rocks ◽  
Sedimentary Rocks ◽  
Primary Component ◽  
Early Diagenesis ◽  
Gulf Coastal Plain ◽  
Fine Grained ◽  
Silica Diagenesis ◽  
Volcanic Glasses

Although silica is a primary component of flints, cherts, volcanic glasses, and siliceous deep sea oozes, mobilization pathways and modes of reprecipitation of this element during early diagenesis of volcanic and sedimentary rocks remains an elusive geologic problem. As a result, the source and mode of deposition of vast Tertiary silica deposits of the Atlantic and Gulf Coastal Plain and offshore deep sea deposits is currently a topic of sharp debate. Both volcanic and biogenous sources of silica have been variously postulated as ultimate or immediate silica sources for a broad range of fine-grained silica-rich rocks including claystones, “opal claystones,” “buhrstones,” “pseudobuhrstones,” cristobalitic cherts, and silicified chalks and limestones. Current scanning electron microscope/electron microprobe investigations of incipient stages of diagenesis in geologically young biogenous sediments, volcanic glasses, and silica-replaced carbonate rocks, however, do allow silica pathways to be traced and silica sources to be ascertained.

Allometry and Paleoecology of Medial Miocene Dwarf Rhinoceroses from the Texas Gulf Coastal Plain

Paleobiology ◽  
1982 ◽  
Vol 8 (1) ◽  
pp. 16-30 ◽  
Author(s):  
Donald R. Prothero ◽  
Paul C. Sereno
Keyword(s):  
Body Size ◽  
Coastal Plain ◽  
Sympatric Species ◽  
High Plains ◽  
Gulf Coastal Plain ◽  
Canine Tooth ◽  
Positive Allometry ◽  
Mammalian Faunas ◽  
The Common ◽  
Limb Proportions

Barstovian (medial Miocene) mammalian faunas from the Texas Gulf Coastal Plain contained four apparently sympatric species of rhinoceroses: the common forms Aphelops megalodus and Teleoceras medicornutus, a dwarf Teleoceras, and a dwarf Peraceras. Previous work has suggested positive allometry in tooth area with respect to body size in several groups of mammals, i.e., larger mammals have relatively more tooth area. However, dwarfing lineages were shown to have relatively more tooth area for their body size. Our data show no significant allometry in post-canine tooth area of either artiodactyls or ceratomorphs. Similarly, dwarf rhinoceroses and hippopotami show no more tooth area than would be predicted for their size. Limbs are proportionately longer and more robust in larger living ceratomorphs (rhinos and tapirs) than predicted by previous authors. Limb proportions of both dwarf rhinoceroses and dwarf hippopotami are even more robust than in their living relatives.The high rhinoceros diversity reflects the overall high diversity of Barstovian faunas from the Texas Gulf Coastal Plain. The first appearance of several High Plains mammals in these faunas indicates “ecotone”-like conditions as faunal composition changed. Study of living continental dwarfs shows that there is commonly an ecological separation between browsing forest dwarfs and their larger forebears, which are frequently savannah grazers. This suggests that the dwarf rhinoceroses might have been forest browsers which were sympatric with the larger grazing rhinos of the High Plains during the Barstovian invasion. The continental dwarf model also suggests that insular dwarfism may be explained by the browsing food resources that predominate on islands.

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