Transcript Lithostratigraphy - Cal State LA

Geologic Map of LA Area
Lithostratigraphy

Branch of
stratigraphy
dealing with the
study of units of
rock. Each unit is
composed of a
body of rock which
is dominated by a
certain lithology or
similar color,
mineralogic
composition, and
grain size.
Intro
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Stratigraphy
governed by code
Extensive
nomenclature
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View of the Lyell Land Group on
the southern shores of Lyell Land
and the snow-capped Berzelius
Bjerg seen from Scoresby Land.
The basal formation of the Lyell
Land Group (Kempe Fjord
Formation) is not exposed, and
most of the overlying Sandertop
Formation is covered by scree to
the left (west). The rest of the
group is well exposed and shows
the pale weathering Berzelius Bjerg
Formation, followed by the grey to
brownish red weathering Kap
Alfred Formation. The Vibeke Sø
Formation forms a conspicuous
pale unit in the centre of the
picture and is overlain by the
reddish Skjoldungebræ Formation.
The top of the group is formed by
the yellowish weathering
Teufelsschloss Formation. The Lyell
Land Group is overlain by grey, red
and pale weathering mainly
carbonate rocks of the Ymer Ø and
Andrée Land Groups. Mountain
summit is approximately 1900 m.
geus.dk/publications
Stratified rocks
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Categories of
classification
Physical properties/
content
Time
Physical Stratigraphic Units
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Lithostratigraphic
Lithodemic
• Intrusives, not layered
Magnetopolarity
stratigraphic
• Based on magnetic
properties
Pedostratigraphic
Based on soil
horizons
Allostratigraphic
• Defined by bounding
unconformities
• May have formal units
between
Allostratigraphic
unitst
IV Lithostratigraphic Units

Lithologically
defined e.g.
• Mineralogy,
texture, sed
structures (dep
environment)

Hierarchy
• Supergroup,
group, formation,
member, bed
Criteria for Formation

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Single or
combination of
lithologies
Definable boundaries
(sharp/gradational)
Mappable at scale of
map
Reference section
(stratotype)
Designate thickness,
characteristics,
geographic extent
Peer
review/published
West Ural. Geologic map. 1:500 000. 1979.
Formation=1 or more
lithologies
Jurassic, Blue Lias Fm.
England www.discoveringfossils.co.uk
Ordovician St. Peter
Sandstone , U.S.
Silica Quarry Pacific,
MO.
Fm Contacts = sharp/ gradational
Gradational transition from St. Peters
sandstone to overlying Joachim
Dolomite (thru dolomitic sandstone,
sandy dolomite)
Colorado National Monument, Gradational contact between the Wingate Sandstone and the
Kayenta Formation. Unconformity between Kayenta and overlying Entrada Sandstone. Wingate
Sandstone, Kayenta Formation, Entrada Sandstone, Morrison Formation, and Summerville
Formations. Circa 1950. U.S. Geological Survey Professional paper 451.
Fm Must Have Stratotype
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Stratotype=type
section
Independence
Formation
stratotype,
Atchison, Kansas
© by J.S. Aber
Fm Must Have Peer Review
Supergroup, Group
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Not usually
designated
(no need)
•
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Usually used
for regional
synthesis
Group = 2+
formations;
related
•
Name must
include
geographic
term and
word group.
Member
A. Subdivision of Formation
B. Lithologically distinct from formation
C. Formation may or may not have member
D. Member name must have geographic
term, word member, and may have
lithologic term e.g.. Los Angeles
Sandstone Member
E. Need not be mappable
Bed

Lithologically
distinct
• e.g.. coal
bed, fossil
beds,
dolomite
• Need not be
mappable
A coal seam in northwest Colorado.
(Reproduced by permission of JLM Visuals.)
Name of
Lithostratigraphic
Units

Named for area
where well
exposed,
thoroughly
described
• Towns, rivers,
other
geographic
features
• St Peter
Sandstone,
Green River
Shale, Monterey
Formation,
Sisquoc
Formation