Lithostratigraphy

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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 adjacent masses 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
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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 processes
  within 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 million
  years, 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 cycles
Eccentricity variation in the shape of the
orbital path
100,000 years
Obliquity changes in the angle that the axis
makes with the plane of orbit
41,000 years, 21.5 to 24.5 degrees
Precession wobbling of the Earths axis
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 different appearance 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 of facies 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 stratigraphic
  units
• 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