TEST YOUR KNOWLEDGE Answers on Page 42
Robert G. Font, CPG-03953
robertfontphd@gmail.com
1. Pleurocoelus describes a fossil: a) Pelecypod. b) Sauropod. c) Cephalopod.
d) Who dreams up these weird names for fossils, dude? Why not something simple and descriptive, such as Clotilda the toothless clam, or Desmond the squashed-face dinosaur, or Mortimer the arm-weary mollusk…
2. “Hanging” lobes, knobs, bulges or lumps may form along bedding planes separating distinct sedimentary layers, where material from the overlying layer descends into the underlying bed. What term below describes these features?
a) Load cast. b) Boudinage. c) Concretion. d) Not sure, man, but these “hanging bulges” sound as something ugly to run into…
3. Of the choices below, which one should NOT be expected to apply to clay-rich soils or argillaceous sediments as values of Atterberg limits and indices increase?
a) Strength decreases. b) Permeability decreases. c) Potential volume change decreases.
d) Hey hombre, who cares about the increasing limit of Atterberg’s index… just give me another tequila shot…
4. Which of these is a source of lithium? a) Cinnabar. b) Spodumene. c) Wolframite. d) Dude, do you know my pharmacist?
5. As geoscientists, it is sometimes helpful for us to comprehend the order of magnitude of the time frame involving various geological processes. Say that in our field work we encounter a horizontal, 100-meter thick basaltic sill with an olivine layer at its base. Think of an olivine crystal that solidifies at the top of the cooling sill. How long would it take for it to settle to the bottom? Is it a matter of minutes, hours, days, years? For simplicity, let us assume that the olivine crystal
is nearly spherical with a density (Do) of 3.8 gcm-3 and a diameter (do) of 0.25 cm. Assume a Newtonian viscosity for the basaltic magma (Um) at around 1200°C of ≅ 50 kgm-1sec-1 and a density (Dm) of ≅ 2,700 kgm-3. Recall that the acceleration of gravity is 9.8 msec-2. Ignore any turbulence or convection in the melt, or any crystal-crystal or bubble-bubble interac-
tion, etc. Thus, to a first approximation, what is the time that it takes for our olivine crystal to settle to the bottom of the sill?
a) A few hours. b) A few minutes. c) A few days. d) A few years.
e) Dude, the day that I start thinking of little olivine spheres floating and sinking in magma, I’d say it is time to go PARTY!
40 TPG •
Oct.Nov.Dec 2020
www.aipg.org
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