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: Unknown Marine? Nonmarine? Reason(s) 1 2

End of File Which are pennate and which are centric diatoms?