http://apps.usd.edu/escistudy/geoltime.pl This is from Tim Heaton’s Webpage. Go to the above URL to test your knowledge of the Geologic Time Scale. Quiz on Thursday.
Devonian black shale I-64 roadcut, eastern Kentucky
Bioturbation Laminated mud, Fissile rock from Tucker (1991) p. 104
Sulfate Reduction SO4-- + C (organic) + H20H2S + 2HCO3- Hydrogen sulfide then combines with available iron oxide to make pyrite.
Major Ions in: SeawaterRiver water (ppm) (ppm) Chloride Cl- 18,000 7.8 Sodium Na+ 10,770 6.3 Sulfate SO4-- 2715 11.2 Magnesium Mg++ 1290 4.1 Calcium Ca++ 412 15.0 Potassium K+ 380 2.3 Bicarbonate HCO3- 140 58.4
Pyrite is abundant in marine mudstones, but, because the sulfate concentration in most streams and groundwater is low, it is absent from most non-marine mudstones.
Idealized Midcontinent Cyclothem (Pennsylvanian Age)
This is where petroleum originates:organic matter in black shale (photosynthesis by marine algae). This organic material is commonly called kerogen. After burial and heating, the hydrocarbons migrate upward, and are (possibly) trapped before they reach the surface.
Battlement Mesa, Colorado-- where Exxon had a go at production from oil shale in the middle 1970’s, but went bust in the early 1980’s. Oilshale--mudrock rich in kerogen (a potential source rock for petroleum) that has not been buried deeply enough to generate oil. Optimum temperatures for formation of hydrocarbons from kerogen-- about 20º-90º C (burial to between about 600 and 6000 meters)
Traps-- places where upward-migrating hydrocarbons accumulate to make an oil reservoir. (oil and gas are buoyant-- less dense than water) Tar sand-- oil reservoir has been exposed at the surface or degraded by bacteria; volatiles have been lost, only heavy molecules remain (tar, asphalt; Athabaska Tar Sands near Ft. McMurray, no. Alberta)
Wackes-- sandstone with a muddy “matrix”. Are they sandstone / mudrock hybrids?? NO! Textbook p. 110 doesn’t explain origin of “matrix” of wackes
Costa Rica from P.E. Potter
Beach sand with abundant volcanic rock fragments, Pacific coast of Costa Rica. With burial, what will happen to the porosity?
Trace fossils are structures produced in sediments and rocks by the life processes of organisms. 23
From: R.H. Dott, J.Sed.Petrology, v. 53, p.21 Bioturbation = sediment mixing by organisms to the extent that individual traces are difficult to see. Most trace fossils have high preservation potential. 24
Amalgamate-- “to mix so as to make a unified whole; blend; unite; combine” 25 From: R.H. Dott, J.Sed.Petrology, v. 53, p.15