Day 9 geology
Evaporites Rock Gypsum -- Castile Formation Rhythmic layering maybe seasonal - during the summer, streams are carrying in stuff, then it freezes over in the winter. Salt domes - rock salt Sedimentary rock -- 1 shale, 2 sandstone, 3 siltstone Biochemical rock -- Most, but not all limestone -- shells and precipitates (warm, shallow marine) Phosphorites - Apatite CaPO4, bones, teeth, scales, bug carapace, some shells (varied marine) Diatomite Grades of coal -- Coal is formed from swamp deposits, buried and dehydrated Peat -- wet muck, mostly decayed plant matter Lignite -- low grade, soft, brown coal Bituminous -- dull black coal Anthracite -- high grade, black, shiny coal Diagenises -- changes that occur after sediment deposition Solution (material removed) Compaction (pore space reduced) Reprecipitation Recrystallization (grains grow larger) Lithification Recrystallization -- individual grains undergo solution and redeposition within the rock; some grains grow larger and interlock Cementation -- secondary mineral fills pores to hold grains together Compaction -- sediment is decreased as a result of its mineral grains being squeezed together by the weight of overlying sediment or by mechanical means. Color of sedimentary rocks Major rock mineral -Sandstone Quartz White
Limestone Calcite White Shale Ilite White Minor mineral coloring component Yellow, brown and red Iron oxide
Greens and blacks
Fe hydroxides
White
Quartz, calcite
Black
Carbon (biogenic)
Black
Pyrite (fine-grained)
Graded bedding -- Larger grains on the bottom and smaller on the top Ripple marks -- mini sand dunes created by water flowing over. Current that goes the same direction has asymmetric ripples
Current that goes back and forth has symmetrical ripples
Flute cast -- Trenches in the bottom of a stream dug into soft, fine sediment which typically get filled by an overlying bed Scour and fill -- concave-upwards erosion surface cut into the underlying bed by a high-velocity flow of water, and filled by a sediment Concretion -- formed by the local accumulation of matter, especially within the body or within a mass of sediment. Depositional Environments -- Glacial -- ice Colluvial -- slope wash Fluvial -- River Channel Flood plain Lacustrine -- lake Paludal -- Swamp Eolian - Wind Depositional Environments Mixed -- Deltaic Estuarine Salt marsh Beach Marine - Littoral Shallow shelf Deep marine Fossils -- any evidence of ancient life Unaltered ramiains Soft parts Hard parts Altered remains Permineralization fl petrifaction Replacement Carbonization Why are fossils important? Environmental indicators Marine vs. terrestrial etc Shallow vs deep marine Lake vs. flood plain, jungle, desert, etc Correlation of rock units over distance Age indicators Index fossils (those with limited age range) Economic products Crushed stone/gravel Limestone -- cement/concrete Clay/shale -- concrete, brick, ceramics Coal -- Fuel Gypsum -- Plaster of Paris; sheet rock
Reservoir rock for water, oil and gas Salt domes; salt, petrol, gypsum, sulfur, limestone (New York is made of Triassic sandstone (brown stone)) Typical hill country home -- cretaceous limestone (austin chalk) Verde antique (serpentine) Portland Cement -- Fired mixture of limestone, clay, and fly ash Ground to