Mixed Deck — All ASBOG Topics Flashcards

Which map symbol correctly represents a vertical contact?

Answer: A straight line without any dip tick

A vertical contact or vertical fault is shown as a straight line with no dip tick because the feature is perpendicular to the map surface.

Which index property is most directly used to assess the liquefaction potential of a sandy soil?

Answer: Relative density

Relative density (Dr) controls how loosely or densely sand is packed, which directly governs its susceptibility to liquefaction under cyclic loading.

What does a river's longitudinal profile describe, and what is a knickpoint?

Answer: The elevation change along the river from headwaters to mouth; a steep reach or waterfall where the graded profile is interrupted

A river's longitudinal profile plots elevation against distance downstream; a knickpoint is an abrupt steepening or waterfall that disrupts the smooth concave-up graded profile, typically due to base level change or resistant rock.

What is the significance of a prominent V-shaped outcrop pattern of a rock formation on a topographic map?

Answer: It shows that a dipping formation crosses a valley, with the V pointing in the dip direction if dipping upstream

The Rule of V's states that a dipping formation crossing a valley forms a V-shaped pattern pointing in the updip direction if dipping downstream, or pointing upstream if dipping in the same direction as stream flow but at a dip angle less than the stream gradient.

What is the term for the angle between a fault plane and the horizontal?

Answer: Dip

Dip is the angle measured downward from horizontal to the fault or bedding plane.

The Mohorovičić discontinuity (Moho) is a major seismic boundary within the Earth. What does it represent?

Answer: The boundary between the crust and the mantle.

The Mohorovičić discontinuity, or Moho, is defined by a sharp increase in the velocity of seismic waves (both P-waves and S-waves). This velocity change marks the transition from the lower-density crustal rocks to the higher-density mantle rocks (peridotite).

The cone of depression created by a pumping well will be steeper (greater drawdown per unit distance) in an aquifer with:

Answer: Low transmissivity and low storativity

Low transmissivity means greater head loss is needed to convey water to the well, and low storativity means little water is released per unit head decline, both steepening the cone.

Which depositional model best explains thick, laterally extensive beds of clean quartz sandstone interbedded with shale on a continental shelf?

Answer: Storm-dominated shelf (hummocky cross-stratification)

Storm-dominated shelves produce hummocky cross-stratified (HCS) sands interbedded with fair-weather muds, creating thick laterally continuous sheet-sand bodies.

In marine geochemistry, the 'residence time' of an element in the ocean is defined as:

Answer: The total oceanic inventory of the element divided by its input or removal rate

Residence time reflects how long an element remains dissolved in seawater before removal; elements with long residence times (e.g., Na) are well-mixed, while those with short times (e.g., Al) are highly reactive.

In the Strahler stream ordering system, how is the order of a stream reach determined?

Answer: All streams are assigned order 1 at the headwaters, and order increases by 1 each time two streams of equal order join; the junction of unequal orders retains the higher order

In the Strahler system, unbranched headwater streams are order 1; when two order-1 streams join, they form order 2; when two streams of the same order n join, they form order n+1; junction of streams of different orders retains the higher order.

Which property of a rock unit makes it most useful as a regional stratigraphic marker bed?

Answer: Lateral continuity and distinctive character

Marker beds are useful precisely because they can be traced over a wide area and are lithologically or biologically distinctive.

What is 'induced seismicity,' and which industrial activity has been most widely linked to significant induced earthquake sequences in the United States?

Answer: Induced seismicity is earthquakes triggered by human activities; wastewater disposal (injection of produced water from oil and gas operations into deep disposal wells) has caused the most significant induced earthquake sequences in the central US since 2008

Induced seismicity refers to earthquakes triggered by human activities; deep-well injection of wastewater (primarily produced water from oil and gas operations) into crystalline basement aquifers in the central US has been responsible for a dramatic increase in earthquake rates, including M5+ events in Oklahoma, Kansas, and Ohio.

Bowen's Reaction Series describes which process?

Answer: The sequential crystallization of minerals from a cooling basaltic magma

Bowen's Reaction Series outlines the continuous and discontinuous branches of mineral crystallization as basaltic magma cools, predicting which minerals form first.

Which classification scheme is most commonly used to categorize mineral resources and ore reserves in US practice?

Answer: SEC Regulation S-K 1300

In US practice, the SEC's Regulation S-K 1300 (effective 2021) is the standard for reporting mineral resources and reserves for publicly listed companies, replacing the former Industry Guide 7.

A highway cut slope in weak shale is designed at a ratio of 2H:1V (Horizontal:Vertical). What does this ratio mean?

Answer: For every 1 foot of vertical drop, the slope extends 2 feet horizontally

A 2H:1V slope means that for every 1 foot of vertical height, the slope extends 2 feet horizontally, resulting in a slope angle of about 26.6 degrees from horizontal.

When correlated globally, the base of the Cambrian System is defined by the first appearance of which fossil?

Answer: Treptichnus pedum (ichnofossil)

The base of the Cambrian (GSSP at Fortune Head, Newfoundland) is defined by the first appearance of the trace fossil Treptichnus pedum.

Which Quaternary dating method relies on the accumulation of cosmogenic nuclides in surface rocks exposed to cosmic radiation?

Answer: Surface exposure dating

Surface exposure dating measures cosmogenic nuclides like ¹⁰Be and ²⁶Al that accumulate in rock surfaces exposed to cosmic rays.

On a standard geologic map, what does a strike and dip symbol that looks like a 'T' with the number '35' next to the shorter line represent?

Answer: A planar feature striking parallel to the long line and dipping 35 degrees in the direction of the short line.

The standard symbol for strike and dip on a geologic map uses a long line to represent the strike direction of a planar feature (like a sedimentary bed or fault). The shorter, perpendicular line points in the direction of the dip. The accompanying number indicates the angle of the dip in degrees from the horizontal.

A geologist recognizes a set of parallel joints in an outcrop. To determine if the joints are systematic (tectonic), which observation is MOST diagnostic?

Answer: Joints cut through multiple lithologies and maintain consistent orientation

Systematic joints are planar, parallel, and persistent across multiple rock types, reflecting a regional stress field rather than local effects.

What is a perched stream, and under what geologic conditions does it form?

Answer: A perched stream flows above the regional water table due to an impermeable layer (clay, bedrock) beneath its channel that prevents infiltration, making it a losing stream perched above the local aquifer

A perched stream occurs when an impermeable layer beneath the channel prevents water from percolating to the main water table, so the stream loses water but remains above the regional groundwater level, essentially perched on a local perched water table.