Geology Midterm Flashcards
What is Environmental Geology?
focuses on the relationships between humans and earth -drinking water -soils -resources -disaster prevention Includes all branches of Geology
What is Geology?
The study of the Earth
What branches are included in the study of Geology?
- minerology and economic geology (mineral resources)
- petrology (rock)
- sedimentology (sedimentary rocks, weathering and erosion)
- structural geology (rocks deformed, bending/breaking)
- hydrology (study of H2O)
What is Hydrology?
The study of the earth’s water systems.
- surface water
- ground (subsurface) water
What is Hydrogeology?
the science that applies geologic methods to understanding hydrologic problems.
What are the methods of Hydrogeology?
- Contour Mapping
- Cross Sections (vertical profiles and side views)
3 categories required for hydrogeological reports
- stratigraphic
- structural
- geomorphic
What is Stratigraphic Information?
deals with the physical characteristics of the rock units and their relationships to other rock units in the area.
What information does stratigraphic information include?
- nomenclature (name, group, formation member)
- age (0-4.5 byr)
- bed unit/thickness
- areal extent
- lithology (rock type: sand-sediment, sandstone-rock)
- texture(grain size, sorting, porosity, permeability)
- composition (minerals)
- erosion surfaces (unconformities)
What does Structural Information deal with?
deformatin of rock units (bending and breaking) and their resulting shapes and interrelationships.
3 categories of rock deformation/structural information
- folding (bending)
- fracturing (breaking rx)
- faulting (breaking rx)
What is Geomorphologic Information?
deals with the physical featured present on the earth’s surface (landforms)
Geomorphologic information includes info on the topics?
- erosional features (valley - river, sinkholes; sinkholes)
- depositional features (sand dunes, morraines
- petrogenic features (landscapes resulting from rx forming process that are mainly igneous in origin. lava flow, caldera)
Definition of Rock?
Condolidated or partly consolidated aggregate of 1 or more minerals, glass, or solidified organic matter.
Definition of Sediment?
loose grains or particles resulting from erosion of any pre-existing rocks.
Definition of Soil?
Allows plant growth
weathered rocks and mineral grains (sediments) that are capable of supporting plant life.
What are the rock processes?
- weathering
- lithification
- metamorphism
- melting
- crystallization
Def. of weathering?
process acting at/near the surface of the earth, which causes physical changes in and/or chemical decomposition of rock.
2 major categories of weathering?
physical and chemical weathering
What is Physical Weathering?
creates small pebbles from alrger rocks without changing their chemical composition
causes of physical weathering?
- frost wedging (freezing/thawing of h2o in rock fractures)
- abrasion (friction and impact)
- pressure release (exfoliation)
- burrowing organisms
- plant roots
What is chemical weathering?
alteration of a rock through chemical reactions between rock and atmospheric chemicals. results in formation of new minerals and dissolution of existing ones.
specific rnxs involved in chemical weathering?
- solution
- oxidation
- hydration
- hydrolosis
Solution rxn for chemical weathering?
dissolving pre-existing rx.
main acid causing solution is CO2
Oxidation Chemical Weathering?
Oxygen is added to a mineral
Fe + O = hematite (iron oxide)
Hydration Chemical Weathering?
H2O added to mineral
Hydrolosis Chemical Weathering?
Breaking apart by WIR
5 factors determining the rate of weathering
- climate
- composition of the parent rock
- surface area
- biological activity
- time
What is Lithification?
process of changing a sediment to a sedimentary rock. happens through COMPACTION and CEMENTATION.
What is Cementation?
the precipitation of chemicals in the spaces between the sediment grains. temperature drops as fluids move to the surface, so ions precipitate out as solids and cement the sediments together.
What is Compaction?
Loss of space (pores) between the rock grains through a change in the packing arrangement of the grains as an overburden pressure is applied.
Categories if Igneous Rocks?
Extrusive and Intrusive
What is Extrusive Ign Rx?
- originate from lava flows
- cooling of pyroclastic material (ash fall, ash flow)
- cools quickly
- has very small crystals
- Aphantic
What is Intrusive Ign Rx?
-form from the crystallization of magma deep in the earth’s crust
-cools slowly
has large crystals
-Phaneritic
Aphanitic Magma?
Fine crystals
extrusive
Phaneritic Magma?
Coarse Crystals
Intrusive
Extrusive Igneous Structures
lava flows (vesicles, amygdaloidal, fragmental, porphyritic, columnar jointing, fissures, plateau basalts, volcanoes)
- lava tubes (crust forms on top. when lava done flowing, leaves a tube).
- calderas (blows top due to pressure)
Intrusive Igneous Structures?
-made of country rock: older rock which magma intrudes
Tabulate Structures:
-Dike: tabulate body which cuts across surrounding country rock layers
-Sill: “” runs parallel to country rock layers
-Laccolith: sill with a mushroom shape.
Deep Structures:
-Pluton: rock crystallized deep in earth with no particular shape -> Stock: areally small (100km2)
Metamorphic Rocks?
Changin of form of a pre-existing rock in the subsurface due to T, P,and t exposed.
Factors influencing chemical composition of parent rock?
Chemical composition: compositon same as parent rock, no new elements added.
Subsurface Pressure:
-Lithostatic Pressure (pressure applied equally on all sides of buries rock.
-Differential Stress (pressure not applied equally)
What is groundwater?
water stored in the pores within the underground rocks and unconsolidated material.
Subsurface Zonations based on water saturation?
Zone of Aeration: pores are filled with air and water
Zone of Saturation: pores completely filled with groundwater
Capillary Fringe: region where water moved upward based on surface tension
Water Table: subsurface separating the zones of aeration and saturation
What is an aquifer?
“water bearing”
refers to rock or unconsolidated material which stores waster and transmits water in significant quantities
What is an aquitard?
rocks through which groundwater moves very slowly, and considered to not flow through at all.
prevents pollutants from getting into subsurface aquifers and moving between aquifers
What is primary pososity?
formed at the time a sediment was deposited.
what is secondary porosity?
formed after rock has been lithified (solution, fracture, vesicular)
What is porosity?
the space available in a rock or sediment
what is permeability?
the ease with which a fluid will move through a rock.
factors of permeability
pore throat diameter
fractures
sorting
Types of sedimentary rocks
Clastic
Chemical
Organic
What are clastics?
sedimentary rocks formed from the lithification of sediments resulting from weather of pre existing rock.
Classification of clastics
based of grain size
>2mm: gravel: conglomerate (rounded grains), breccia (angular grains)
1/16mm: Sand: Sandstone
1/256: Mud: Siltstone, Shale
Describing clastic rocks categories
rock name (eg sandstone)
color
porosity
texture
clastic porosities
0-3% - tight 3-6% - poor 6-12% - fair 12-20% - good >20% - excellent
unconcolidated sediment - max 48.6% consolidated sediment (clastic rock) - max 30%
clastic textures
grain size of the majority of grains
2.0 - conglomerate/breccia - gravel
clastic sorting
poor - >4 - on/off energy (flash flood)
medium - 3-4
well 1-2 - constant energy (velocity)
Evaporite Categories
Carbonates and Evaporites
Types of Carbonates
Limestone and Dolomite
- Oolitic - precipitates around particles floating in the water. looks like sandstone. ringed sphere.
- Micritic - lime mud, looks like shale but reacts w/ acid
Types of Evaporites
Gypsum
Anhydrite
Halite
-no fossils, no rxns with acid.
Types of organic sedimentary rocks
Carbonates and Coal
Names of Organic Carbonates
(fossiliforous) Limestone and Dolomite
Three categories of Organic limestones?
the exoskeletons of marine organisms.
Reefs/corals
coquinas (shells)
crinoids (spines, spinal cords)
What is Dolomite
re-crystallization of limestone by magnesium rich briner migrating through subsurface. Does not react that much with acid
What are styolites?
jagged dark colored lines formed from dissolution of carbonate rock and concentration of the insoluble material.
what are vugs?
larger holes in rocks (larger than vescicles)
can be in basalt or dolomite
what is coal?
formed in swamps or bogs wehre there are very low concentrations of oxygen or where organic matter accumulates at a much faster rate than it decomposes.
what are rock units?
found in layers (sedimentary) in the subsurface called beds.
what is a rock bed?
the smallest division of a rock unit
is a sequence of sediments or sedimentary rock which is bound both on top and bottom by sharp contact.
what is lamination?
beds less than 1 cm thick
Rock Unit Nomenclature categories?
1 - Groups
2 - formations
3 - members
4 - beds
Describing formations?
main/basic unit of measuring
based of physical characteristics that are easily distinguished in the field (color, grain size, hardness)
Describing groups?
a combination of formations which have some feature or relationship in common
(all formations were deposited in a fluvial (river) environment.
Describing members?
subdivision of formations
Rocks range in age from
4.5 byr to present
how do older rocks end up on the surface?
erosion
faulting of the earth’s surface
non-deposition
what period are the oldest rocks from?
precambrian
Cenozoic Era
present - 70 myr ago
“New Life”
Age of the mammals
Mesozoic Era
70 myr - 220 myr
“Middle Life”
Age of the Dinosoars
Paleozoic Era
220 myr - 545 myr
“Old Life”
Age of Invertebrates
Cryptozoic/Precambrian Era
545 myr - 4.5 byr
soft jelly bodied creatures (jelly fish)
When did the extinctions happen? Why?
70 myr - end of mesozoic - meteorite impact
220 myr - end of paleozoic - harsh conditions due to basalt fissure eruptions
aquifer recharge and discharge regions?
recharge - water enters an aquifer
discharge - water leaves an aquifer
Aquifer recharge areas
rain, precipitation, snow flooding - overland flow losing streams/influent streams lakes/ponds artificial recharge basins wastewater treatment plants
aquifer discharge areas
anywhere where the water table intersects the surface of the earth gaining streams/effluent streams water wells springs lakes/ponds
unconfined aquifers
a formation that is exposed to atmospheric pressure changes
the water in the aquifer has a water table which if in direct contact with the atmosphere through pores in the overlying rock and soil.
has an aquitard btw of the aquifer and ground surface?
static watertable well
water well drilled into an unconfined aquifer
confined aquifer
formation that is bound both above and below by aquitards
one end is structurally higher than the other
pressurized groundwater system.
potentiometric surface (piezometric surface)
imaginary surface or P. level to which water will rise in a well at any given point.
What is an unconformity?
A surface contact which represents a period of non-deposition or erosion
surface that represents “missing time”
what do unconformities do?
place rocks of differnt hydraulic conductivity next to one another
affect the continuity of rock units
affect the direction of ground water flow
control potential sites for recharge and discharge in an aquifer
3 types of unconformities:
disconformities
angular conformities
non-conformities
what is a disconformity?
separates beds which are parallel to one another (between sedimentary beds)
rocks age from 100myr-400myr with no gap in between.
what is angular unconformity?
found between sedimentary rock layers
contact in which overlying beds are dipping at a different angle to that of the underlying beds.
what is non-conformity?
contact between a sedimentary rock layer and an igneous rock
represents deep erosion to the surface of the pluton, followed by the deposition of a significant sequence of sedimentary layers.
unconsolidated material
all aquifers except clay
n - 25-60%
k - good since not lithified
clastics
all aquifers except shale
sandstone most common and important aquifer on a global scale
n - 0-30%
organic (carbonates)
all aquifers, how good is dependent on the degree of dissolution of rx
dissolution (vugs) - n: 0-40%
Volcanic Ign. Rocks
-Basalt
n- type: vesicular
n: 3-35%
Basalts originated from fissure eruptions and can create massive aquifers.
Intruvive Igneous Rocks - Aquitard/Aquifer?
All Aquitards
Metamorphic Rocks - Aquitard/Aquifer?
All Aquitards
Perched Aquifer
layer of saturated soil/rx above the main (regional) aquifer
water will move laterally above the low k layer (clay) and eventually spill over it’s edge and down into the main aquifer.
Contact Spring
A bed bounded btw an overlying aquifer and underlying aquitard
Fault Spring
water moves along fault line
Fracture Spring
water moves through fractured rocks
solution spring
occurs in carbonates
carbonic acid dissolves LST to create vugs
what is a sinkhole?
water not coming out of a spring/hole
