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.) • Range: Diatom Skeletons – 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: ______________ 1. Examine the slides with marine diatoms 2. Examine the slides with freshwater diatoms 3. Determine which of the unknowns is from a freshwater deposit and which is from a marine deposit. State your reasons: Unknown Marine? Nonmarine? 1 2 Reason(s) End of File • Which are pennate and which are centric diatoms?