I. Question (1-25) Flashcards
Determining „texture‟ in calcareous rocks commonly includes which of the following observations?
i. biologically produced textures
ii. grain type
iii. presence/absence of micrite
iv. presence/absence of sparite
a. i, ii
b. i, iii, iv
c. i, ii, iii, iv
d. iii, iv
c. i, ii, iii, iv
Biologically produced textures (i) - These include features like fossil fragments, bioclasts, and structures formed by organisms (e.g., stromatolites).
Grain type (ii) - Identifying whether the grains are skeletal (bioclastic), non-skeletal (like ooids or peloids), or intraclasts.
Presence/absence of micrite (iii) - Micrite (microcrystalline calcite) is the fine-grained carbonate mud that may fill spaces between grains or form the rock matrix.
Presence/absence of sparite (iv) - Sparite (sparry calcite) is a coarser crystalline calcite that may fill pore spaces or replace micrite.
How does the ocean water depth influence the production and/or preservation of carbonate sediment?
i. Algae can produce carbonate at any depth in the water column.
ii. Calcite and aragonite are only undersaturated in water depths greater than 4500m.
iii. Shallow water carbonate production can be diluted in the sedimentary deposits by abundant siliciclastic material from the continents.
iv. Warm surface (<100m) water can be supersaturated with respect to calcium carbonate.
a. i, ii
b. i, iii, iv
c. i, ii, iii, iv
d. iii, iv
d. iii, iv
Statement i (False) - Algae that produce carbonate, such as coral and calcareous algae, typically thrive in shallow, sunlit waters (generally less than 100 meters deep). They do not produce carbonate at any depth since they rely on photosynthesis.
Statement ii (False) - Calcite and aragonite are not only undersaturated at depths greater than 4500 meters. The depth at which calcium carbonate dissolves (the Carbonate Compensation Depth, or CCD) typically occurs around 4000–4500 meters, but undersaturation can start at shallower depths, depending on local ocean chemistry.
Statement iii (True) - In shallow marine environments, carbonate sediment production can indeed be diluted by the influx of siliciclastic sediments from continental sources, such as rivers and coastal erosion.
Statement iv (True) - Warm, shallow surface waters (generally less than 100 meters) are often supersaturated with respect to calcium carbonate, promoting the precipitation of carbonate minerals like aragonite and calcite.
The phi units for cobble
a. -2 to 4
b. -2 to -6
c. -6 to -8
d. < -8
c. -6 to -8
In figure 2, where is the oldest volcano produced by hot spot?
a. 1
c. 3
b. 2
d. 5
a. 1
In figure 2, where is the youngest volcano?
a. 1
c. 3
b. 4
d. 5
d. 5
The two most abundant elements in the Earth’s continental crust are (in order of their abundance!)
# 1 is
# 2 is
- Oxygen (O) - Approximately 46% by weight
- Silicon (Si) - Approximately 28% by weight
A sandstone is gradually dragged down in a subduction zone. It is heated more and more as it descends into the Earth, and eventually it melts. The molten material hardens into rock. This solid material is now
a. a metamorphic rock
b. an igneous rock
c. magma
d. a mantle plume
b. an igneous rock
An elevation roughly circular or elliptical in plan, the top of which is a comparatively smooth platform and deeper than 100 fathoms.
a. ridge
b. plateau
c. seamount
d. guyot
d. guyot
A guyot, also known as a tablemount, is an underwater volcanic mountain (seamount) with a flat top. It is typically more than 100 fathoms (600 feet or 183 meters) deep. The flat top is a result of erosion when the guyot was above sea level, before subsiding to its current depth.
Ridge (a): A long, narrow elevation of the seafloor.
Plateau (b): A broad, flat region, usually shallower than a guyot.
Seamount (c): A submerged volcanic peak, typically with a pointed or rounded top, not flat like a guyot.
The lowering of the water table near the well is called a(n) __________.
a. Aquiclude
b. cone of depression
c. influent zone
d. sinkhole
b. cone of depression
Given the geometry of the surface and water table depicted in the cross section above, which of the following statements is true?
a. The stream is gaining water from the groundwater
b. The stream is losing water to the groundwater.
c. The stream is gaining water from the groundwater on the west side and losing water to the ground water on the east side.
d. The stream and the groundwater are not connected.
a. The stream is gaining water from the groundwater.
While walking along a beach, you saw this obvious break in the rocks exposed in the cliffs. This break is actually a
a. a normal fault
b. a thrust fault
c. a strike-slip fault
d. nobody’s fault
a. a normal fault
A vein outcrops at three points, A, B and C. B is 300 feet N20E of A, While C is 400 feet N80E of A. B is 200 feet higher than A and C is 100 feet lower than A. Determine the strike and dip of the vein using analytical methods.
Strike: Approximately 334.7° (measured clockwise from North)
Dip: Approximately 46.5°
A dipping surface which crops out in a valley or on a ridge will give rise to a V-shaped outcrop. Given this, which of the given figure depicts a rock unit: (write the corresponding letter)
- dipping steeply (i.e., dip > gradient of valley) downstream?
- dipping gently (i.e, dip< gradient of valley) downstream?
- dipping upstream?
- C
- B
- B
Given the following mineral assemblage and Paragenetic sequence, identify the deposit type and describe the probable history and controls of mineralization of this deposit. (15 points)
The given mineral assemblage and paragenetic sequence suggest that the deposit type is an epithermal vein-type deposit, likely of the intermediate-sulfidation subtype. Here’s the reasoning and interpretation:
Deposit Type:
Epithermal intermediate-sulfidation deposits are characterized by:
Fluidized breccias and quartz-rich veins.
Base metal sulfides (sphalerite, galena, chalcopyrite) associated with precious metals (gold/electrum).
Carbonate minerals often forming late-stage gangue.
Probable History and Controls of Mineralization:
Stage I (Fluidized Breccias):
This stage indicates early hydrothermal brecciation, likely caused by the rapid release of fluid pressure, forming fluidized breccias.
The absence of significant mineral deposition suggests that this stage is primarily mechanical rather than mineralizing.
Stage II (Quartz):
Quartz deposition occurs as a primary gangue mineral, suggesting the introduction of silica-rich hydrothermal fluids.
This stage could represent an early pulse of boiling or mixing of hydrothermal fluids, forming quartz veins.
The presence of adularia and sericite indicates potassic alteration and intermediate sulfidation conditions.
Stage III (Base Metal):
Deposition of sphalerite, galena, chalcopyrite, pyrite, marcasite, and tennantite.
The introduction of base metals indicates an increase in sulfur activity and metal-rich fluids, often associated with boiling and cooling events.
Gold/electrum deposition alongside base metals indicates favorable conditions for precious metal precipitation, likely driven by boiling or rapid cooling.
This stage is critical for the main ore formation.
Stage IV (Carbonate):
Late-stage carbonate deposition indicates cooling and neutralization of fluids.
Carbonate gangue minerals often overprint sulfide mineralization, suggesting a waning hydrothermal system.
Mineralization Controls:
The primary control on mineralization is likely structural, such as faulting and fracturing that created fluid pathways.
Fluid boiling and mixing played significant roles in ore deposition, especially in the transition from quartz to base metal stages.
Temperature and pressure changes influenced the precipitation of base metals and precious metals, while carbonate deposition marked the cooling and waning stage.
What is the strike of the geologic contact on the given
figure
o 295
o 270
o 330
o 125
330°
The is the highest point on a fold.
a. top b. hinge point c. crest d. hat e. aota
c. crest
It is possible to determine the sense of fault motion through Riedel shears alone.
a. False b. True c. Not True d. Can’t say e. nota
b. True
Riedel shears (R-shears and R’-shears) are small-scale shear fractures that develop in fault zones and can indicate the sense of fault motion. The orientation and geometry of Riedel shears help geologists determine whether the fault motion is dextral (right-lateral) or sinistral (left-lateral).
The formula for shear strain exy, is .
a. cos b. sin c. cotan d. a/b e. b/a
b. sin
The mantle is thought to be fluidous since _waves can not travel through it.
a. Body b. Rayleigh c. surface d. sea e. S
e. S
In a stream bed, the base of a coal bed is exposed at an elevation of 1845 feet and the top of the coal bed at 1632 feet. The horizontal distance between exposure is 2100 feet in the direction of N 33 E. The dip of the coal bed is 42 degrees to the N 5 E. Find the thickness of the coal bed.
142.52 feet
Given the following data:
Drillhole 1 has a collar elevation of 1000 meters
Drillhole 2 has a collar elevation of 1200 meters
Drillhole 3 has a collar elevation of 900 meters
Drillhole 2 is 500 meters N35°W of drillhole 1 and drillhole 3 is 400 meters N75°W of drillhole 1.
The top of the gold-bearing quartz vein was intersected at depths of 400 meters in drillholes 1, 2, and 3.
Find the strike and dip of the vein using analytical methods.
Strike: 239.8° (approximately 240°), which can also be expressed as N60W.
Dip: 46.4°
Pull-apart basins form in a/an tectonic regime.
a. compressional b. transtensional c. extensional d. nota
b. transtensional
A vein strikes N90°E and dips 35 ° to the south. What is its apparent dip in a N 90°E section. In what direction would its apparent dip be at 20 °.
The apparent dip in the N90°E section is 0°, and the apparent dip at 20° from the strike is approximately 13.5°.
A vein strikes N-S and clips 35 degrees North. Using analytical and graphical methods, determine the apparent Dip in a N 45° E section. In what direction would its apparent dip be at 25 degrees.
- Apparent Dip in N45°E section: 26°
- Apparent Dip at 25° from strike: 16.5°
