Diatoms in coal: Miocene Venado Formation, Limon Basin, Costa Rica, Central America
Diatoms occur in coal in the Venado Formation on the southwest flank of the Limon Basin in Provincia Alajuela, northern Costa Rica. The Venado Formation contains more than 300 m of mudstones, siltstones, sandstones, limestones, and coal beds that crop out on the northeast flank of the Cordillera de Tilaran. Coal beds of unknown extent and correlation occur mainly in the middle part of the formation. The coal deposit here named informally the Pataste coal bed. Coal samples were examined with a scanning electron microscope and an x-ray analyzer attachment. Part A contains abundant diatoms and macerated diatom material and rare spicules of freshwater sponges. Diatoms identified are Melosira ambigua, Pinularia, Eunotia spp. and Achnathes exigua. Parts B and C of the coal bed contain fewer diatom remains and more sponge spicules than part A. The common presence of Melosira ambigua in A implies the proximity of open-water lacustrine environments. The other diatom species are benthic or bottom-dwelling forms that lived in slightly acidic, humic-rich paludal environments. Presumably, the swamp in which the coal was formed was most extensive during the deposition of A, and became progressively restricted thereafter. The increase of sponge spicules relative to diatoms in B and C suggests progressively, shallower lacustrine or restricted swamp conditions. The comparatively great abundance of biogenic opaline material in the coal is due to the influx of silica form a volcanic source represented by the tonstein layers.
- Research Organization:
- Geological Survey, Denver, CO (USA)
- OSTI ID:
- 6196823
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COAL DEPOSITS
PALEONTOLOGY
PETROGRAPHY
COSTA RICA
COAL
DEPOSITION
DIATOMS
GEOLOGIC FORMATIONS
LITHOLOGY
PETROLOGY
SCANNING ELECTRON MICROSCOPY
SEDIMENTARY BASINS
X-RAY DIFFRACTION
ALGAE
CARBONACEOUS MATERIALS
CENTRAL AMERICA
CHROMOPHYCOTA
COHERENT SCATTERING
DEVELOPING COUNTRIES
DIFFRACTION
ELECTRON MICROSCOPY
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGY
LATIN AMERICA
MATERIALS
MICROSCOPY
MINERAL RESOURCES
PLANTS
RESOURCES
SCATTERING
011000* - Coal
Lignite
& Peat- Reserves
Geology
& Exploration