Presentation on theme: "In the news today: A gold nugget weighing more than 6 lbs. (3 kg.) that was found earlier this year in one of California's historic gold- mining districts."— Presentation transcript:
In the news today: A gold nugget weighing more than 6 lbs. (3 kg.) that was found earlier this year in one of California's historic gold- mining districts went on the auction block yesterday. It was expected to fetch over $350,000. The IPCC (Intergovernmental Panel on Climate Change) has concluded that "it is 'effectively certain' that: higher greenhouse gas concentrations will warm the climate system relative to lower concentrations, changes in climate will change weather patterns, a warmer climate will cause heat waves to become more frequent and/or intense, average sea-level and storm-surge heights will increase with warming, and climate changes will cause shifts in the distributions and characteristics of biological systems (among other impacts)." [ In this context, "effectively certain" means >95% statistical likelihood. ]
Light refreshments beforehand!
Archidiskodon meridionalis, the giant Siberian mammoth of the middle Pleistocene Below, microtine rodent teeth. Everything big and small has a chance to become a fossil. Which do you think is more likely to make it?
Sediments & sedimentary rocks - Part II
2. Biogenic rocks a. limestones b. chert c. coal 3. Chemical and evaporite sedimentary rocks 1. Clastic sedimentary rocks
Forams are part of the PLANKTON in the world's oceans, the basis for the marine food chain. Away from the continental margins (where the clastics are dominant), the remains of forams, called tests, are one of the principal components of marine sediments - called calcareous ooze. Most forams are in the sand size category: to 2.0 mm across. a. LIMESTONES CALCITE (CaCO 3 ) is the dominant mineral in limestones.
Foram ooze covering basalts of the Mid-Atlantic Ridge.
Some, however, gets subducted with the slab, being converted into CO 2 gas that helps to power the explosive volcanism of island arc systems.
Coccoliths are also calcareous - making structures from calcium carbonate. They are SO SMALL that forams are giant by comparison. Their remains (as at right) are smaller than pollen grains. Imagine, then, how MANY of them it took to create THESE: Chalk in the White Cliffs of Dover, United Kingdom
LITHOGRAPHIC limestone is particularly fine- grained, and is derived from algal muds in quiet lagoons.
A rather famous fossil from the Solnhofen Limestone of Bavaria
Fossiliferous limestone is merely any limestone with visible fossils, like this. Much limestone is made up of remains of shells of brachiopods or other molluscs. Coquina is entirely composed of loosely cemented shell fragments. The calcium carbonate in these fossils can also dissolve and be recrystallized as calcite cement in the clastic sedimentary rocks, like sandstones and conglomerates.
Distribution of limestones in the contiguous United States.
A slab of Kaibab Limestone in a quarry in northern Arizona. The clear stratification (layering) makes it obvious that this piece is standing on end.
ALL of Bermuda, Puerto Rico, and the Bahamas consist of limestone.
A coralline limestone. Since corals can only live in clean, warm salt water, finding this rock tells you those conditions existed when it was formed, even if this is in northern Alaska today!
b. Chert -Chert is made up of crypto-crystalline quartz (SiO 2 ) - This can form as a chemical precipitate directly from sea water around the MORRS, or, more commonly, by recrystallization of remains of diatoms and radiolaria.
~ 4 km Radiolaria and marine diatoms are throughout the oceans, BUT commonly masked by the overwhelming dominance of the forams. Only in waters below the carbonate compensation depth (CCD), about 4 km deep, do they become of major importance - as the carbonates dissolve! Decreasing input of land-derived silicates
Cherts & graywackes from the Golden Gate north into Oregon provide evidence for a Jurassic trench.
Distribution of modern marine sediments.
c. coal PeatLigniteBituminous (soft) coal Drag line mining
Just to put a little perspective on the size of that bucket....
3. Evaporites & Chemical Sedimentary Rocks - created by either chemical changes in water OR the evaporation of waters that leave dissolved minerals behind Tufa towers (freshwater limestone) at Mono Lake, California. The limestone precipitates as cold, saturated groundwater from the Sierra Nevada enters the warm water of the lake.
SALTS are left behind as water evaporates. In enclosed basins, this can yield large quantities of salts (halite and other water- soluble minerals). Above, Owens Lake, eastern California. Above right, salt pillars on the shore of the Dead Sea, Israel. At right, the Devils Golf Course in Death Valley, California.
Salts of the Bonneville Salt Flats in Utah are familiar for the countless dozens of car commercials filmed here. And if you've seen the film "Independence Day," you may remember the finale...
The Bonneville Salt Flats are also where the world land speed record has been set - in excess of 700 mph. Many salt flat areas, however, are not quite as accommodating of high-speed wheeled traffic.
A large gypsum mine in New Mexico, extracting the minerals left behind by evaporation of an ancient arm of the sea. Another gypsum mine in Colorado.
BORAX provided early mining in eastern California, and is today extracted in vast amounts for detergents and glassmaking.