GEL 1 Lecture Notes - Lecture 22: Geothermal Gradient, Salt Dome, Foraminifera
Shells/Fossils/Petroleum
Calcium carbonate producers
●Foraminifera a group of organisms that secrete a CaCO3 shell (carbonate)
● calcium carbonate is easy to analyze because it dissolves in acid
Siliceous sediment producers
● Diatoms - SiO2 shells (glass)
○ photosynthetic
○ glass is harder to analyze
looking at chemistry of shells can tell us temperature, circulation changes, nutrient
concentrations etc about the ocean
Modern coral reef
● shallow, tropical depositional environments
● coral: a reef-building organism
● limestone: composed of skeletal remains of silicate …….
○ composed entirely of broken fossil marine organisms
○ biochemical sedimentary rock
○ fossiliferous limestone
Stratigraphy
● stacked rock units give us a bigger picture about change over time
● sedimentary layers are like a 'strip chart' of changing environments, sea level, and
climate through time
● sed rocks contain the fossil record of evolution
● all fossil fuels are found in sedimentary rocks
Organic matter in sediments: oil/gas reservoir
● require burial of organics (algae, not animals or plants) in anoxic environments
○ post burial, temperature increases
■ geothermal gradient
○ generates petroleum
■ petroleum can moves through fractures and/or porous sedimentary rock
○ trapped and extracted
■ accumulates somewhere, a trap
■ some impermeable layer
● salt deposits in the Gulf of Mexico help trap petroleum because salt is impermeable
○ salt dome
○ shale
■ clay and mudstones are impermeable too
● natural gas overlies petroleum
Document Summary
Foraminifera a group of organisms that secrete a caco3 shell (carbonate) Calcium carbonate is easy to analyze because it dissolves in acid. Glass is harder to analyze looking at chemistry of shells can tell us temperature, circulation changes, nutrient concentrations etc about the ocean. Limestone: composed of skeletal remains of silicate . Composed entirely of broken fossil marine organisms. Stacked rock units give us a bigger picture about change over time. Sedimentary layers are like a "strip chart" of changing environments, sea level, and climate through time. Sed rocks contain the fossil record of evolution. All fossil fuels are found in sedimentary rocks. Require burial of organics ( algae , not animals or plants) in anoxic environments. Petroleum can moves through fractures and/or porous sedimentary rock. Salt deposits in the gulf of mexico help trap petroleum because salt is impermeable. Natural gas overlies petroleum the (cid:258)eolo(cid:258)ic ti(cid:295)e scale: key eve(cid:296)ts. Concentrations of o2 and co2 in atmosphere change.
