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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


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


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

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