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GEOL 3213 MICROPALEONTOLOGY
Introduction & Classification Of Diatoms Diatoms Biology &
Ecology
Unicellular & eukaryotic; lack flagella; asexual and sexual
reproduction May be single celled or in chains Photosynthetic,
productive even in cold nutrient-rich water (Antarctic, etc.) Base
of the food chain = Grass of the sea Planktic and benthic forms
Diatoms Biology & Ecology
Can move on & within the sediment with mucus streamers
associated with a groove called the raphe Can live
heterotrophically in the dark Freshwater (lacustrine, swamp, marsh,
riverine, even terrestrial) & marine; also found in hot
springs, hypersaline lakes, & melt-water pools on icebergs
Diversity of benthic forms is high worldwide Diatom
Classification
Diatoms are golden brown algae Some classify them in the Phylum
Bacillariophyta Other workers put them, with the coccolithophores,
in the Phylum Chrysophyta Frustrule shapes vary greatly, so there
is no simple summary of morphology Two major subdivisions are
recognized: Centrales (centric) = circular, oblong, hemicircular,
triangular, or quadrangular, with surface features arranged around
a central point Pennales (pennate) = elongate with major features
at right angles to the median line (long axis).(These are further
subdivided into 7 subgroups.) Diatom Skeletons Range: Skeleton
called a frustrule
Jurassic(?) marine, Mid-Cretaceous to Recent Oldest nonmarine forms
are Eocene Skeleton called a frustrule Overlapping bivalves Box =
hypotheca Lid = epitheca Overlapping sides = girdle Porous (called
punctae);striae & costae Raphe = groove Opalline Marine
dominantly centric forms (Cretaceous to Recent) Nonmarine
dominantly pennate forms (Paleocene to Recent) As small as 5 um and
up to 500 or more um Account for 70-90% siliceous particles
suspended in oceanic water Siliceous skeleton resistant to solution
Their solution and reprecipitation leads to chert formation
Sediments: oozes, diatomaceous earth, diatomite HOW DIATOMS
REPRODUCE Alternation of sexual and asexual reproduction
Girdle views of diatom valves through several reproductive
phases.Note the progressive decrease in soze of some forms. Diatom
Morphology Striae = line of punctae
Costae = raised ridge parallel to striae Centrales Examples of
Centrales Pennales Examples of Pennales Diatom Diversity Through
Time
Centric forms Cretaceous to Recent Dominate the plankton Pennate
forms Paleocene to Recent Dominate the benthos Diatoms Uses
Applications of diatom studies Age-dating and correlation
Especially for the Tertiary Many short-ranged species
Paleoenvironmental studies Used a lot by Quaternary geologists
O18/O16 ratios used for paleotemperature studies Used to detect
polluted water because of environmental sensitivity, e. g., to
nitrate and phosphate nutrient enrichments Diatom Lab Exercise
Name: ______________
Examine the slides with marine diatoms Examine the slides with
freshwater diatoms Determine which of the unknowns is from a
freshwater deposit and which is from a marine deposit.State your
reasons: UnknownMarine? Nonmarine?Reason(s) 1 2 End of File Which
are pennate and which are centric diatoms?