Geology Midterm Review (Set 2)

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Holohyaline

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composed entirely of glass

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Hypocrystalline

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composed of crystals and glass ("both")

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Porphyritic

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rock composed of TWO DIFFERENT SIZE CRYSTALS

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Phenocryst

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the larger crystals in a porphyritic

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Groundmass

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the fine-grained crystals surrounding the larger crystals in a porphyritic rock

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Vesicle

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holes in igneous rock formed by escaping gases during solidification

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Felsic

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high in SiO2 (silicic) and low in ferromagnesian minerals (LIGHT IN COLOR)

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Mafic

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low in SiO2 and high in ferromagnesian minerals (DARK IN COLOR)
Note: Obsidian = black but felsic

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Granite

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Intrusive igneous rock composed of feldspars and quartz (>65% SiO2) [Felsic]

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Rhyolite

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Extrusive igneous rock composed of feldspars and quartz (>65% SiO2) [Felsic]

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Diorite

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Intrusive igneous rock composed of feldspars (55-65% SiO2) [intermediate]

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Andesite

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Extrusive igneous rock composed of feldspars (55-65% SiO2) [intermediate]

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Gabbro

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Intrusive igneous rock composed of pyroxene and olivine (<55% SiO2) [Mafic]

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Basalt

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Extrusive igneous rock composed of pyroxene and olivine (<55% SiO2) [Mafic]

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Continuous Series

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part of Bowen’s reaction series, change in plagioclase composition (calcium rich at top to sodium rich at bottom)

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Discontinuous Series

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part of Bowen’s reaction series, change to different
ferromagnesian minerals (from olivine to pyroxene, to amphibole, to biotite)

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Shield Volcanoes

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broad, dome-shaped volcano with gently sloping sides
• Form from – repeated eruption of fluid basaltic magmas (no explosive eruptions)
• Typically found – ocean islands (not on plate boundaries)

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Composite Volcanoes (Stratovolcanoes)

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large volcano with large slope angles
• Form from - Composed of alternating layers of lava (explosive eruptions)
• Typically found – subduction zone volcanic arcs

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Crater

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the depression near the vent area at the top of the cone (<1.6km in diameter)

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Caldera

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 removal of magma from the magma chamber after an eruption can cause the
roof to collapse (>1.6km in diameter)

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Dike

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tabular, parallel-sided sheet of igneous rock that cuts the layering of the rock it
intrudes

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Sill

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tabular, parallel-sided sheet of igneous rock that is parallel to the layering of the
rock it intrudes

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Batholith

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largest type of pluton; irregular shape and cuts across layering of the rock it
intrudes

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Laccolith

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variation of a sill where the layers of rock above the intrusion are bend
upwards into a dome

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Stock

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same def. As a batholith but less than 10km in maximum dimension

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Pluton

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body of intrusive igneous rock regardless of size or shape

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Volcanic Neck

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a vol. pipe (see below), but all the surrounding rock is eroded away

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Volcanic Pipe

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nearly cylindrical conduit that fed the volcanic vent

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Pahoehoe

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lava that forms smooth, ropy surfaces

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A’a

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crumbly lava that forms when the lava becomes more viscous due to cooling OR
an increase in shear

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Pyroclastic flow

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a type of pyroclastic density current; very dense b/c of high
proportion of pyroclastic debris, fast moving (450 mph), tend to follow pre
existing valleys

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Pyroclastic surge

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a type of pyroclastic density current; low density b/c of higher das content, not confined by topography,

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Lahar

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water saturated pyroclastic flow (always follow pre-existing pathways b/c of
high density)

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Nuee ardentes

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 “burning cloud” (in front of pryo. dens. currents)

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Clastic rock

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aggregates of individual grains of minerals or other rock fragments; made of “bits”

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Nonclastic rock

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interlocking network that makes a crystalline texture and is formed from chemical precipitation from aqueous solutions; can be inorganic (precipitation of limestone or gypsum) or organic (precipitation of shells by organisms)

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Clast

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individual fragments of clastic rocks

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Detrital

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when clastic rock fragments have been eroded from another rock and transported some distance, then the rock is called Detrital

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Roundness/Angularity

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measure of the sharpness of the clasts’ edges; well rounded clasts indicate a long transport distance (usually from wind/water) while angular clasts suggest short transport distance; transport by ice tends to result in irregular grains

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Sphericity

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measure of how closely a clast approached a spherical shape; increased sphericity suggests longer transport distance

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Claystone

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particles mostly clay sized (table above); also called mudstone

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Siltstone

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mostly silt sized

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Sandstone

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mostly sand sized

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Congolmerate

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greater than sand sized and particles are rounded

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Breccia

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greater than sand sized and particles are angular

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Shales

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if the rock is fine-grained (clay or siltstone) and has foliation (i.e.: rock forms planar fabric)

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Coquina

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if the rock is composed exclusively of cemented together shells

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Sorting

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measure of range in particle size; narrow range of sizes is well-sorted while wide range of sizes is poorly sorted

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Porosity

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measure of the pore space in a rock

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Permeability

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measure of the ability of the rock to pass a fluid

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Types of nonclastic sedimentary rocks

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classification based on type of grains and the surrounding matrix, but is great variability
o Grain types:
 Bioclastic debris (shells, exoskeletons, bones, usually CaCO(3))
 Oolites (small spherical grains of CaCO(3))
 Intraclasts (chemically precipitated CaCO(3))
 Pellets (ocean organism poop)
o Matrix types:
 Usually in oceanic nonclastic rocks matrix is CaCO(3)
 Continental sedimentary rocks have greater variability (groundwater can bind grains together with CaCO(3), SiO(2), other chemical cements)
o Evaporites:
 Salt beds, gypsum beds are sedimentary rocks created by evaporation of lake water or seawater
 Sodium carbonate (Na(2)CO(3)), sodium sulfate (Na(2)SO(4)) also common
o Banded Iron deposits
o Chert

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Oolitic limestone

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composed of accumulation of oolites (rocks with spherical grains of concentric layers)

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Lithification

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weathering processes break down rock into finer and finer material and such material is often transported and deposited as sediment. The processes of compaction and cementation of this sediment over a long period of time turn the sediment into rock. The formation of rock in this way is termed lithification

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Cementation

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sediments being pressed and “bonded” (glued in a way) together (by compaction) until they form rock (Silica compounds or Calcium compounds are common 'cements')

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Bedding

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most fundamental structure of sedimentary rocks; this is the layering that is characteristic of sedimentary rocks

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Laminae

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when beds are < 1 cm thick

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Parallel Bedding

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typically form in environments where the sediments are able to settle from a suspension to a point on the bottom without a significant current; example environments: lake deposits, slow moving rivers/streams, low velocity currents, some types of ashfalls or very fine grained wind deposits

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Cross Bedding

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result of deposition of sediment in a wave-like manner at the sediment-fluid interface; large scale cross-beds are typical of aeolian environments (sand dunes, desert landscapes), smaller cross-bedding (especially tabular) is more indicative of fluvial ripples and deposition; example environments: moderate flow rate streams/rivers, majority of wind deposits; 3 types: tabular, wedge-shaped, trough

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Trough Cross Bedding

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curved lower boundaries (formed by wind)

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Tabular Cross Bedding

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bounded by planar boundaries that are parallel (formed in streams)

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Wedge Cross Bedding

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bounded by planar boundaries that are non-parallel

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Ripples

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causes by cycle of erosion and deposition; distance from crest to crest is less than 0.3 m (Dunes/megaripples— > 0.3 m crest to crest

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Graded Bedding and Turbidity Currents

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similar to parallel bedding except grain size changes systematically from bottom to top; occurs when sediments are transported in suspension as well as along the bed; often formed by turbidity currents but other processes can form them too

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Varve

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seasonal, thin lake bedding

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o Alluvial (fluvial)

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stream/river

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o Lacustrine

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lake; landlocked body of water occupying a morphological (hole or lowpoint) basin; inflow exceeds outflow; areas near an inlet may have courser sediments, but majority of the lake bed is usually covered in fine-grained clay and siltstones; tend to be fine-grained and well-sorted

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o Paludal

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swamp; tend to be anoxic (without oxygen); plant and organic tend to be preserved; coal and other organic rich sediments are usually interpreted to be the remains of ancient swamps

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o Braided River

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variable but usually high flow rate and high carrying capacity; often form in areas where the flow is highly variable i.e. arid environments where the river may be dry most of the year except during periods of intense rain or in glacial environments; rapid flow rate can carry large clasts; deposition is usually poorly sorted conglomerates and sandstones

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Stratigraphy

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the science of rock strata; deals with the horizontal and vertical changes and relationships between sedimentary rock units

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Lithostratigraphy

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based on physical changes

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Biostratigraphy

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based on changes in fossil assemblage

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Chronostratigraphy

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based on changes in age

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Magnetostratigraphy

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based on changes in magnetism

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Allostratigraphy

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based on changes in position relative to unconformities

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Sequence Stratigraphy

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based on relationship to worldwide unconformities (6 worldwide unconformities are recognized)

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Cinder Cone

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volcano composed entirely of pyroclastic material—doesn't erupt any lava (extremely viscous magma, lots of gases, high in SiO2—Rhyolitic magma)

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Wedge cross-bedding

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bed planes are planar but not parallel (formed in fluvial environments, characteristic of pinchouts)

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o Law of Superposition

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“in a sequence of layered rocks, any layer is older than the layer next above it”

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o Principle of Original Horizontality

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-“layers of sediments are originally deposited horizontally”

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o Principle of Lateral Continuity

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“sediments initially extend laterally in all directions

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• Formation

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body of material which can be identified by its lithological characteristics and its stratigraphic position

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• Diachronous

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a formation has the sample lithological properties but it formed at different times in different places

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• Facies

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the aspect, appearance, and tcharacteristics of a rock unit, usually reflecting the conditions of its origins

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• Contact

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boundary between two different litholigic units

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• Angular unconformity

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an angle exists between beds below the unconformity and the beds above

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• Disconformity

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the angle of the bedding is the same between beds above and below it, but erosion occurs, making the surface non-flat

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• Paraconformity

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beds lie parallel to one another but there is a time gap (where erosion occurred) in between the laying of consecutive rock layers (can't detect without dating the rocks)

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• Nonconformity

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deposition of sediments on nonstratiform rocks (igneous or metamorphic rock)
• Principle of Cross-Cutting Relationships – any unit that has a boundary that cuts across other strata must be younger than the rock it cross-cuts

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• Included fragments

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clasts in a clastic rock are older than the rock strata in which they are found

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• Transgression/regression

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rising/receding of oceans that results in sediments from different depositional environments in the same cross section of rock (i.e.: facies changes)

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• Sedimentary basin

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a low-lying depression with no outlet; a low area of the earth’s crust, usually formed tectonically, where sediments accumulate or have accumulated

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• Petroleum reservoir

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rocks with high permeability and porosity that the oil and gas can flow through and accumulate

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• Petroleum trap

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anything that keeps the oil and gas from flowing and concentrates in one place

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• Weathering

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the mechanical and chemical breakdown of pre-existing rocks into smaller particles

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• Mechanical weathering

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physical breakdown of a rock into smaller fragments; force exerted on the rock is greater than the strength of the rock

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• Chemical weathering

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the occurrence of reactions between the rock and reactants such as oxygen, carbon dioxide, and water

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• Frost action

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propagation of microfractures due to the water/ice interface migration through the pore space in a rock

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• Talus slope

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large, angular fragments

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• Salt weathering

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crystallization of salt within a rock

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• Exfoliation and pressure release weathering

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a pluton buried within the earth is initially well below the surface, erosion causes the top of the pluton to be exposed and results in a pressure release, which leads to exfolitation (cracking in an onionlike pattern on the exposed portion of the rock)

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• Hydrolysis

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reaction between acidic solutions and silicate materials

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• Oxidation

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reaction of free ocygen with metallic elements  rust

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• Erosion

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the detachment and transportation of surface particles under the action of an erosional force

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• Raindrop erosion

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– the impact of falling drops of rain on soil particles  initiates the erosion process

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• Overland flow

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the first few inches of the surface become saturated and water flows downslope in a thin sheet – leads to sheet erosion

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• Sheet erosion

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the removal of a uniform layer of soil from the land surface as a result of rainsplash or runoff

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• Rill erosion

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the development of small grooves spaced fairly uniformly along the slope; caused when runoff is heavy and water concentrates in rivulets; water eventually collects into channels (rills) that eorde the bottom and sides of the rill and enlarge

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• Gully erosion

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when rills increase in size they become gullies (these enlarge upstream)

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• Differential erosion

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differences in erosion rates of different rock units or soil units

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• Contour farming

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creation of small ridges that slow runoff water

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• Strip cropping

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growing different crops on alternating strips of land, so as to create natural dams and slow runoff water

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• Terracing

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the creation of terraces, or a leveled section of a hill, so as to slow runoff water

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• Conservation tillage

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farming without plowing or tilling the land, allowing the plants to stay mostly on the surface  supposed to keep carbon in the soil better than regular farming

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James Hutton

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o Known as the founder of modern geology
o He was a great observer of the world around him. More importantly, he made carefully reasoned geological arguments. Hutton came to believe that the Earth was perpetually being formed; for example, molten material is forced up into mountains, eroded, and then eroded sediments are washed away. He recognized that the history of the Earth could be determined by understanding how processes such as erosion and sedimentation work in the present day. His ideas and approach to studying the Earth established geology as a proper science.
o Hutton perceived that sedimentation takes place so slowly that even the oldest rocks are made up of, in his words, “materials furnished from the ruins of former continents.” The reverse process occurs when rock exposed to the atmosphere erodes and decays. He called this coupling of destruction and renewal the “great geological cycle,” and realized that it had been completed innumerable times
o Theory of Uniformitarianism—this was the belief that geological forces at work in the present day—barely noticeable to the human eye, yet immense in their impact—are the same as those that operated in the past. This means that the rates at which processes such as erosion or sedimentation occur today are similar to past rates, making it possible to estimate the times it took to deposit a sandstone, for example, of a given thickness

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Charles Lyell

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o English geologist Sir Charles Lyell, who was born the year Hutton died and whose influential book Principles of Geology won wide acceptance for the Theory of Uniformitarianism
o Lawyer that began dabbling into geology, which turned into his passion. His first paper, "On a Recent Formation of Freshwater Limestone in Forfarshire", was presented in 1822. By 1827 he had abandoned the law and embarked on a long geological career that would result in the widespread acceptance of the ideas proposed by James Hutton a few decades before

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Alfred Wegener

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German Meteorologist
o Wegener’s Theory of Continental Drift (1912)
 Realized that the continents could fit together like a massive jigsaw puzzle
 Noted that some mountain belts, structural trends, and rock types would be continuous if the continents were joined
 Noted that fossil distribution could be explained if continents were joined- including some land plants and animals that would otherwise be unable to migrate
 Presence of rock types that form under specific climatic conditions in locations that do not have that climate
 Proposed that the less dense continents “drifted” through the oceanic crust and the mantle and were “crumpled” at the leading edges
• Ignored because of the mechanical impossibility of continents drifting through the solid oceanic crust and mantle

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Normann Bowen

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o experimented by melting powdered rock and then letting it cool to certain temperatures
o examined which minerals were present at each temperature
o devised an idealized sequence of mineral crystallization
o Bowen’s reaction series
 Two crystallization sequences: continuous (plagioclase) and discontinuous (ferromagnetism minerals)