TOPOGRAPHIC MAP
a two-dimensional (flat) representation (model) of a three-dimensional land surface (landscape).
relief
on a topographic map; the difference in elevation between landforms, specific points, or other features on a landscape or map.
contour lines
used on a topographic map to represent the elevations of hills and valleys; the distinguishing features of a topographic map; specifically, the lines of equal elevation (the coastline and 300ft-line). Each one of these connects all points on the map that
quadrangle
a section of Earth's surface that is bounded by lines of latitude at the top (north) and bottom (south) and by lines of longitude on the left (west) and right (east)
declination
at the bottom margin of a topographic map; shows the difference in degrees between the compass north (MN) and true north (a star symbol)
index contours
on a topographic map - heavy brown contour lines, they have elevations printed on them. These are your starting point when reading elevations on a topographic maps.
contour interval
on a topographic map, when the map has five contours for every 400 ft of elevation, or a ____ of 80 ft. All contour lines are multiples of the ____ above a specific surface (usually sea level)
gradient
on a topographic map, a measure of steepness of a slope.
benchmark
the notation 'BM' denotes this, is a permanent marker (usually a metal plate) placed by the US Geological Survey or Bureau of Land Management at the point indicated on the topographic map.
ratio scale
on a map, the proportion by which you will reduce the real object to the model size.
fractional scale
topographic maps often model large portions of Earth's surface, so the ratio scale must be greater than normal - like 1:24,000; indicating that the portion of Earth represented has been reduced to the fraction of 1/24,000th of its actual size.
verbal scales
on a map, "1 in. on the map = 6, 2/3 football fields", scales that are expressed in words.
graphic bar scales
all topographic have these printed in their lower margin, essentially rulers for measuring distances on a map.
principal meridians
on a topographic map, north-south lines.
base lines
on a topographic map, east-west lines.
townships
on a map, the north-south lines of the grid are called ____ and are numbered relative to the baseline.
ranges
on a map, the east-west squares of the grid are ____ and are numbered relative to the principal meridian.
bearing
the compass direction along a line from one point to another. If expressed in degrees east or west of true north or south, it's quadrant bearing. Expressed in degrees between 0-360, it's called azimuth bearing.
topographic profile
a cross section that shows the elevations and slopes along a given line; cross sectional representation of the rise and fall fo a landscape along a line of interest drawn on the map
GPS (Global Positioning System)
a constellation of 28 navigational communication satellites in 12-hour orbits approximately 12,000 miles above Earth. Each system satellite communicates simultaneously with fixed ground-based Earth stations and other satellites, so it knows exactly where
Universal Transverse Mercator System (UTM)
the US National Imagery and Mapping Agency (NIMA) developed this global military navigation grid and coordinate system in 1947. Unlike the latitude-longitude grid that is spherical and measured in degrees, seconds, and nautical miles, this grid is rectang
STRUCTURAL GEOLOGY
the study of how geologic units (bodies of rock or sediment) are arranged when first formed and how they are deformed afterwards.
stress and strain
When a body of rock or sediment is subjected to severe ____ (directed pressure) or _____ (undergo deformation, such a change in shape). Much of the study of structural geology involves deciphering these relationships.
geologic maps
generally, geologists can see how bodies of rock or sediment are positioned where they crop out (stick out of the ground at an outcrop) at Earth's surface. Geologists record this data on flat (two-dimensional) ____ using different colors and symbols to re
formations
The rocks are commonly divided into mappable rock units that can be recognized and traced across the map area. This division is made based on color, texture, or composition. Can also be divided into 'members' comprised of 'beds'.
beds
individual layers of rock or sediment. Composed from 'members'
contacts
the boundaries between geologic units; form the lines on geologic maps. A geologic map also shows the topography of the land surface with contour lines, so it is both a geologic and topographic map.
geologic cross section
a drawing of a vertical slice through Earth, with the material in front of it removed: a cutaway view. It shows the arrangement of formations and their contacts. Also shows the topography of the land surface, like a topographic profile.
block diagram
a combination of the geologic map and cross section. It looks like a solid block, with a geologic map on top and a geologic cross section on each of its visible sides. Each block diagram is a small three-dimensional model of a portion of Earth's crust.
strike
the 'compass bearing' (direction) of a line formed by the intersection of a horizontal plane (such as the surface) of an inclined (tilted) layer (like a bed, stratum) of rock, fault, fracture, or other surface.
dip
the maximum angle of inclination (tilting) of the rock layer (stratum, fault, or fracture); 'dip direction' is always measured perpendicular to the line of strike and in the direction that the rock layer tilts down into the ground (the 'dip angle').
attitude
the orientation of a rock unit or surface. Geologists devised a system for measuring and describing this to understand three-dimensional relationships of formations and geologic structures. Strike and dip serve this purpose.
quadrant bearing
if a strike is expressed in degrees east or west of true north or true south.
azimuth bearing
if a strike is expressed as a three-digit in degrees between 000 and 360. In this form, north is 000 degrees (or 360 deg), east is 090 deg, south is 180 deg, and west is 270 deg.
unconformities
a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time. May be a very irregular surface, because it is usually a surface where erosion has occurred.
disconformity
unconformity between relatively parallel strata.
angular unconformity
unconformity between nonparallel strata, they are angled in some fashion.
nonconformity
unconformity between sedimentary rock/sediment and igneous or metamorphic rock.
faults
in rock units are breaks along which movement has occurred. These form when brittle rocks experience three kinds of severe stress: tension, compression, and shear.
normal faults (as well as reverse and thrust faults)
these faults involve the vertical motion of rocks. Named by noting the sense of motion on the top surface of the fault (top block) relative to the bottom surface (bottom block), regardless of which one has actually moved.
hanging wall
the top surface of the fault; is the base of the hanging wall block of rock.
footwall
the bottom surface of the fault; forms the top of the footwall block. The headwall block sits on top of the footwall block.
normal faults
caused by tension (rock lengthening). As tensional stress pulls the rock apart, gravity pulls down the hanging wall block relative to the location of the footwall block. Named due to its 'normal' response to gravity.
reverse faults
caused by compression (rock shortening). As compressional stress pushed the rock together, one block of rock gets pushed atop another. The hanging wall block moves upward in relation to the footwall block, 'reverses'. Generally place older strata on top o
thrust faults
these are reverse faults that develop at a very low angle and may be very difficult to recognize. Generally place older strata on top of younger strata.
strike slip faults (lateral faults)
caused by shear and involved horizontal motion of rocks. The rocks on opposite sides of this fault have moved to the right or left of the other.
antiforms
an 'upfold' or convex fold. If the oldest rocks are in the middle, then they are called 'anticlines'.
synforms
'downfolds' or concave folds. If the youngest rocks are in the middle, then they are called 'synclines'.
fold axis (or hinge line)
in a fold, each stratum is bent around an imaginary axis, like the crease in a piece of folded paper. For all strata in a fold, the fold axes lie within the axial plane of the fold.
plunging fold
as opposed to a horizontal fold, this is a fold which is plunging into the ground; 'plunge' is the angle between the fold axis and horizontality. And the 'trend' of the plunge is the bearing (compass direction), measured in the direction that the axis is
limbs
the two sides of a fold, one on each side of the axial plane.
overturned fold
if a fold is tilted so that one limb is upside down, then the entire fold is called an ____.
monoclines
folds with two axial planes that separate two nearly horizontal limbs from a single, more steeply inclined limb.
domes
large, circular structures formed when strata are warped upward, like an upside-down bowl. Strata are oldest at the center of this structure.
basins
large, circular structures formed when strata are warped downward, like a bowl. Strata are youngest at the center of this structure.
WATER TABLE
the upper surface of underground water below which the ground is wholly saturated with water; the upper boundary of the zone of saturation.
groundwater
water within the saturated zone which can be withdrawn from the ground through a well.
flow lines
an imaginary line that traces the path that a particle of ground water would follow as it flows through an aquifer; they run perpendicular to contour lines, converge or diverge, but never cross.
cone of depression
The zone around a well in an unconfined aquifer that is normally saturated, but becomes unsaturated as a well is pumped, leaving an area where the water table dips down to form a cone shape. The shape of the cone is influenced by porosity and the water yi
aquifers
Subterranean, porous, water-holding rocks that provide millions of wells with steady flows of water.
confining beds
a geologic unit which is relatively impermeable and does not yield usable quantities of water. Groundwater occurs in two types of aquifers: confined and unconfined. A confined aquifer is overlain by an impermeable layer such as rock or clay.
hydraulic gradient
The slope of the water table. It is determined by finding the height difference between two points on the water table and dividing by the horizontal distance between the two points.
water table contours
identifies flow lines- paths traveled by droplets of water from the points where they enter the water table to the points where they enter a lake or stream
karst
An area of irregular limestone in which erosion has produced fissures, sinkholes, underground streams, and caverns.
sinkholes
a large surface crater caused by the collapse of an underground channel or cavern; often triggered by groundwater withdrawal.
solution valleys
valley-like depressions formed by a linear series of sinkholes or collapse of the roof of a linear cave.
springs
places where water flows naturally from the ground (from spaces in the bedrock).
disappearing streams
streams that terminate abruptly by seeping into the ground.
artesian wells
wells in which water flows naturally from the top of the well.
recharging
process of precipitation infiltrating the ground and adding to the underground water supply.
water table contour maps
Map like a topographic contour map except that it shows the elevation of top of water table (subsurface region saturated with water); used in study of depth of water table and changes in water table over time. Useful in determining: paths of water flow al
RELATIVE AGE DATING
the process of determining when something formed or happened in relation to other things.
absolute age dating
the process of determining when something formed or happened in exact units of time such as days, months, or years.
Law of Original Horizontality
sedimentary layers (strata) and lava flows were originally deposited as relatively horizontal sheets, like a layer cake. If they are no longer horizontal or flat, it is because they have been displaced my subsequent movements of the Earth's crust.
Law of Lateral Continuity
lava flows and strata extend laterally in all directions until they thin to nothing (pinch out) or reach the edge of their basin of deposition.
Law of Superposition
in an undisturbed sequence of strata or lava flows, the oldest layer is at the bottom of the sequence and the youngest is at the top.
Law of Inclusions
any piece of rock (clast) that has become included in another rock or body of sediment must be older than the rock or sediment into which it has been incorporated. Such a clast (usually a rock fragment, crystal, or fossil) is called an inclusion. The surr
Law of Cross-Cutting
any feature that cuts across a rock or body of sediment must be younger than the rock or sediment that it cuts across. Such crosscutting features include fractures (cracks in rock), faults (fractures along which movement has occurred), or masses of magma
Law of Unconformities
surfaces called unconformities represent gaps in the geologic record that formed wherever layers were not deposited for a time or else layers were removed by erosion. Most contacts between adjacent strata or formations are conformities, meaning that rocks
disconformity
an unconformity between parallel strata or lava flows. Most of these are very irregular surfaces, and pieces of the underlying rock are often included in the strata above them.
angular unconformity
an unconformity between two sets of strata that are not parallel to one another. If forms when new horizontal layers cover up older layers folded by mountain-building processes and eroded down to nearly level surface.
nonconformity
an unconformity between younger sedimentary rocks and subjacent metamorphic or igneous rocks. It forms when stratified sedimentary rocks or lava flows are deposited on eroded igneous or metamorphic rocks.
Principle of Fossil Succession
geologists have also determined that fossil organisms originate, co-exist, or disappear from the geologic record in a definite sequential order recognized throughout the world, so any rock layer containing a group of fossils can be identified and dated in
range zone
the sequence of strata in which fossils of a particular organism are found is called a ___ ___, which represents a chron of time.
index zone
organisms whose range zones have been used to represent named divisions of the geologic time scale are called ___ ___.
eras (oldest to youngest)
Precambrian, Paleozoic, Mesozoic, Cenozoic
periods of Paleozoic Era (oldest to youngest)
Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian
periods of Mesozoic Era (oldest to youngest)
Triassic, Jurassic, Cretaceous
periods of Cenozoic Era (oldest to youngest)
Paleogene, Neogene
isotopes
atoms of an element that have the same number of protons and electrons but different numbers of neutrons. This means that the different ____ of an element vary in atomic weight (mass number) but not in atomic number (number of protons).
parent isotope
when a mass of atoms of a radioactive isotope is incorporated into the structure of a newly formed crystal or seashell, it is referred to as a ____ ____.
daughter isotope
when atoms of the parent isotope decay to a stable form, they have become a ____ ____. A parent isotope and its corresponding daughter are called a decay pair.
half-life
atoms of a parent isotope always decay to atoms of their stable daughter isotope at an exponential rate that does not change. The rate of decay can be expressed in terms of __-__ - the time it takes for half of the parent atoms in a sample to decay to sta
EPICENTER
the point of an earthquake on Earth's surface (location on a map) directly above the 'focus' (underground origin of the earthquake, in bedrock).
seismic waves
the episodic releases of energy that occur along fault lines strain the bedrock like a person jumping on a diving board. This strain produces elastic waves of vibration and shaking called ___ ___ (or earthquake waves). These originate at the earthquake's
seismographs
earthquake-detecting instrument. Although most damage from an earthquake usually occurs close to is epicenter, these can detect the earthquake's waves of energy even when they travel through Earth's rocky body or along Earth's surface to locations thousan
fault motions
movements of Earth's crust along breaks in the rocks; these are the most common source of earthquakes felt by people. These motions can occur along faults that do not break the Earth's surface or along faults that do break the Earth's surface. These motio
P-waves
primary, these waves travel fastest and arrive at seismographs first. Compressional, or "push-pull" waves.
S-waves
secondary, these waves travel more slowly and arrive at seismographs second. Perpendicular, shear, or "side-to-side" waves.
L-waves
surface seismic waves; travel along Earth's surface and thus are recorded after the S-waves and P-waves arrive at the seismograph.
arrival time
The time at which a seismic wave arrives at a seismometer, usually noted on a seismogram.
S-minus-P time interval
subtract the arrival of the first P wave from the first S wave to get time interval.
first motion
the relative motions of blocks of rock on either side of a fault zone can be determined by mapping the way the pen on a seismograph moved (up or down on the seismogram) when P-waves first arrived at various seismic stations adjacent to the fault. This pen
blind faults
faults such as the New Madrid System that are not visible on satellite images and photographs, because they are ___ ___ (faults that do not break Earth's surface). These faults occur in the Paleozoic and Precambrian rocks that are buried beneath approxima
SOURCE ROCK
a rock rich in organic matter which, if heated sufficiently, will generate oil or gas. Typically these are fine-grained rocks such as shales or limestones and contain about 1.0% organic matter. Rocks of marine origin tend to be oil-prone, whereas terrestr
reservoir rock
a porous and permeable body of rock that contains economical amounts of hydrocarbon, they are able to store and transmit fluids. Sedimentary rocks are the most common because they have more porosity than most igneous and metamorphic rocks and form under t
seal rock
a relatively impermeable rock, commonly shale, anhydrite, or salt, that forms a barrier or cap above and around reservoir rock such that fluids cannot migrate beyond the reservoir. Chalk and coal could also possibly act like a seal if they are not fractur
formation of oil and gas
flooded forests: plants are buried and decay in stagnant muds, compaction and chemical alteration take place, deep burial generates oil and gas. Lake/sea with abundant nutrients: plankton die, dead plankton sink into a stagnant sea-bed, organic-rich mud f
formation of hydrocarbon
favorable preservation conditions for this formation: high organic production, anaerobic depositional systems, moderate to low rate of sedimentation. Common environments: lake and ocean strat (thermal stratification), barred basin (salinity contrast), con
types of hydrocarbon
Algae and Bacteria form oil in shallow burial and gas in deep burial. Plants form coal in shallow burial and gas in deep burial.
kerogen formation
forms from fats, waxes, and oils. Under increasing heat and pressure creates heavy oil and subsequently gas and light oil.
woody kerogen formation
forms from cellulose and wood. under increasing heat and pressure creates coal and gas.
migration
movement of hydrocarbons from the source rock; the movement of newly generated hydrocarbons out of the source rock is primary migration, also called expulsion. The further movement of the hydrocarbons into reservoir rock in a hydrocarbon trap or other are
porosity
the percentage of pore volume or void space, or that volume within that can contain fluids.
permeability
the ability, or measurement of a rock's ability, to transmit fluids, typically measured in darcies or millidarcies. Formations that transmit fluids readily, such as sandstones, are described as permeable and tend to have many large, well-connected pores.
effects of cement
reduces porosity and permeability. Adding it is bad for reservoirs but good for seals (a tightly cemented sandstone can act as a seal while a poorly cemented sandstone can be a great reservoir)
trap
a geologic structure or a stratigraphic feature that allows the accumulation of hydrocarbons.
stratigraphic trap
type of trap; result from changes in rock type or pinch-outs, unconformities, or other sedimentary features such as reefs or build-ups.
structural trap
type of trap; hydrocarbon traps that form in geologic structures such as folds and faults, namely anticlines.
combination trap
type of trap; have aspects of both structural and stratigraphic traps.
Darcy's Law
water removal is a function of hydraulic gradient and conductivity - a function of viscosity.
subsidence
withdraw faster than it recharges (cm per day).
aquitard
impermeable bed under an aquifer.