lit host rat i graphy
TRANSCRIPT
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Lithostratigraphy
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Lithology
The study and description of the physical
character of rocks, particularly hand
samples and outcrops
Refers to the physical characteristics: rock
type, color, mineral composition, grain
size, lithological characteristics
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Historical Principles
Nicolaus Steno
Danish
Physician
1638 1687
Superposition
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Stenos Second Principle
Principle of
Original
Horizontality
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Stenos Third Principle Principle of Original Lateral Continuity
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Stenos Laws (Principles)
Foundation for Stratigraphy
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Lithostratigraphic units
Stratotype a designated type unit or type
section
Type section
Type locality
Lithosome mass of rock of essentially
uniform character and having
intertonguing relationships with adjacentmasses of different lithology. (lithology)
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Rock Units
Lithostratigraphic units
Formation
Group
Supergroups
Member
Beds
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Stratrigraphic relationships
Contacts
Conformity
Unconformity
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Contacts
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Conformable contacts
Abrupt contacts
Gradational contacts
Progressive gradual contacts
Intercalated contacts increased number of
thin interbeds.
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Contacts
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Contacts between laterally adjacent
lithosomes
Pinch-outs
Intertonguing
Progressive lateral gradation See Figure 12.1
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Contacts
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Unconformity
Diastem little hiatus, little or no erosion, minor
depositional break
Hiatus that part of a lacuna that is represented
by nondeposition Lacuna
Cavity, hole or gap
Unrecorded stratigraphic record at an erosion
surface, consisting of (a) the record destroyed by
erosion = erosional vacuity (b) the record never
represented by strata = hiatus
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Types of Unconformities
Angular unconformity
Nonconformity
Disconformity Paraconformity
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Nonconformity
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Angular unconformity
f
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Disconformity plus
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Vertical successions of Strata
Cyclic successions Cyclic sedimentation
Rhythmic sedimentation Rhythmites Varves
Cyclothems
Autocyclic sucessions controlled by processeswithin the basin
Storm beds, turbidites
Allocyclic sucessions caused by variations external
to the depositional basin Changes in climate eustatic sea level changes Tectonic movement
Larger area of influence
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Allocyclic Succession scales
First-order cycles Eustatic cycles, 200-
500 million years
Too large to see in normal outcrop, large sets
of data and outcrops or subsurface data
Major tectonic episodes, construction of
Pangea, major continental rifting.
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Second order cycles
Icehouse states cool periods
Greenhouse states warm periods,
greenhouse gases, CO2 were abundant.
Supercycles
Transgressive sequences cratonic
sequences. 10 to 100 of millions of years
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North
American
Cratonic
Sequences
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Third-order cycles
Episodicities on the order of 1 to 10 million
years
Regional scales
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Bed-scale cycles
Meter-scale cycles
Less than 1 million years, 0.2 to 0.5 millionyears, 200,000 to 500,000 years
Fourth-order scales
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Fifth-order scales
0.01 to .2 million years
10,000 years to 200,000 years
Orbital parameters
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Milankovitch cyclesEccentricity variation
in the shape of theorbital path
Obliquity changes
in the angle that the
axis makes with the
plane of orbit
Precession
wobbling of the
Earths axis
100,000 years
41,000 years,
21.5 to 24.5
degrees
26,000 years,
axis points to
different spots
in the sky.
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Orbital Forcing
Link between orbital cycles, climate, and
sea level
Quaternary deposits, back to Miocene
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Cyclostratigraphy
Relationship of strata to the various cyclic
sedimentation causes
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Facies
A stratigraphic body as differentappearance or composition, general
appearance or nature of one part of a rock
body as contrasted with other parts. Lithofacies ss, ls, cong, silt, sh
Biofacies fossil content no lithology
Subfacies subdivisions of facies Microfacies thin section facies
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Law of the correlation (or
succession) of facies
Walthers Law
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Walthers Principle
A conformable vertical sequence offacies was generated by a lateral
sequence of environments.
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Lateral Succession
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Lithofacies changes Onlap = Transgression
Fining upward sequence
Offlap = Regression
Coarsening upward
sequence
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Sea level changes
Eustatic Sea-level changes world wide
sea level changes
Relative sea-level eustatic to regional
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Mechanisms of sea-level change
Ocean steric (thermohaline) volume
changes on the order of 1 m.
Glacial accretion and wastage 1 to 10 m.
Liquid water on land generally less than
1 m.
Crustal deformation 1 to 100 m.
Glacial rebound
sedimentation
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Major types of stratigraphic units
Lithostratigraphic units
Biostratigraphic units
Magnetopolarity units Geochronologic units
Table 12.3 you can read and know these.
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Correlation
Demonstration of equivalency of stratigraphicunits
Physical correlation Physical characteristics to match equivalent beds or
units Lateral continuity trace bed or laminae from area to
area
Lithologic similarity unique kinds of rocks
Sequence of beds multiple units used by their
sequence. Geophysical characteristics seismic, electrical logs,
sonic, radioactive, magnetic properties
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Correlation
Lithocorrelation similar lithology,
stratigraphic position
Marker beds, key beds
Biocorrelation fossil content
Chronocorrelation - age
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Correlation
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Electric logs
Spontaneous Potential
Resistivity
Gamma Ray
Density log
Acoustic log
Neutron log
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Electric log