Misson Choudhury, Budding Geologists ,graduated from utkal university odisha,now pursuing M.sc applied geology in Bangalore university ..love to geologic mapping,drawing ,climbing ,tracking..

1.  The purpose of lithostratigraphic classification is to
organize systematically rock strata of the earth into
named units that will represent the variations of
these rocks in lithologic character.
 All stratigraphic units are composed of rock and
thus have rock characters, but only
lithostratigraphic units are differentiated on the
basis of kind of rock (lithologic character);
limestone, sandstone, sand, tuff, claystone, basalt,
marble and so on.
 The recognition of such units is useful in
visualizing the physical picture of the Earth’s strata
In determining local and regional structure
 In investigating and developing mineral resources,
 In determining the origin of rock strata

2. Definitions
Lithostratigraphy
 The element of stratigraphy that deals with the
lithology of strata and with their organization into
units based on lithologic character.
Lithostratigraphic classification
 The organization of rock strata into units on the
basis of their lithologic character.
Lithostratigraphic units
 A body of rock strata that is unified by consisting
dominantly of certain lithologic type or
combination of lithologic types
 A lithostratigraphic unit may consist of
sedimentary or igneous, or metamorphic rocks or
of an association of two or more of these.

3.  Lithostratigraphic units are recognized and defined
by observable physical features and not by
inferrred geologic history or mode of genesis.
 Fossils may be important in the recognition of a
lithostratigraphic unit.
 Only major lithologic features readily recognizable
in the field should serve as the basis for lithologic
units.
Lithostratigraphic Zone (Lithozone)
 An informal lithostratigraphic unit used to indicate
a body of strata that is unified in a general way by
lithologic features

4. Lithostratigraphic horizon (lithohorizon)
 A surface of lithostratigraphic change or of
distinctive lithostratigraphic character.
Kinds of lithostratigraphic units
1. Hierarchy of Formal Lithostratigraphic units
 Formal lithostratigraphic units are those that are
defined and named in accordance with an
established or conventionally agreed scheme of
classification and nomenclature.
 The conventional hierarchy of formal
lithostrtigraphic terms is as follows.
Group – two or more formations
Formation – primary unit of lithostratigraphy
Member – named lithologic entity within a
formation
Bed – named distinctive layer in a member or
formation

5. 2. Formation
 The formation is the primary formal unit of
lithostratigraphic classification
 It is a body of rock strata of intermediate rank in
the hierarchy of lithostratigraphic units.
 Formations are the only formal lithostratigraphic
units into which the stratigraphic column
everywhere should be divided completely on the
basis of lithology.
 Formations may be composed of sedimentary
rocks, or extrusive or intrusive igneous rocks or
metamorphic rocks or under some circumstances
associations of two or more of these types of rock.

6. Member
 A member is the formal lithostratigraphic unit next in
rank below a formation and is always a part of a
formation.
 It is recognized as a named entity within the formation
because it possess lithologic characters distinguishing it
from adjacent parts of the formation.
 No fixed standard is required for the extend or
thickness of a member.
 A formation need not be divided into members unless
useful purpose is served.
 Some formations may be completely divided into
members, others may have only certain parts
designated as members; still others may have not
members.
 A member may extend from one formation to another.

7. Bed
 A bed is the smallest formal unit in the hierarchy
of lithostratigraphic units.
 It is a unit layer in a stratified sequence of rocks
which is lithologically distinguishable from other
layers above and below.
 The term “bed” is applied to layers a centimeter to
a few meters in thickness.
 Those of less thickness are called laminae
 A single named bed or named sequence of beds
may constitute a member or a formation, and in
such a case, the unit term bed is replaced by
member or formation, for example “Bracklesham
Beds” = Bracklesham Formation.

8. Group
 A group is the formal lithostratigraphic unit next in
rank above a formation.
 The term is applied most commonly to a sequence
of two or more associated formations with
significant unifying lithologic features in common.
 Formations need not be aggregated into groups,
but the term group is generally used for an
assemblage of formations
 The name of a group should preferably be derived
from an appropriate geographical features near the
type areas of its component formation. Eg.,Garwal
Group.
 A group may be extended laterally beyond the area
where it is divided into formations

9. Subgroup or Supergroup
 A group may on occasion be divided into subgroups.
 The term supergroup may be used for several associated
groups or for associated formations and groups with
significant features in common.
Complex
 A complex is lithostratigraphic unit composed of diverse
types of any class or classes of rock (Sedimentary, igneous,
metamorphic) and characterized by highly complicated
structure to the extend that the original sequence of the
component rocks may be obscured
 The term may be used as a part of formal name in the place
of a lithologic or rank term, for ex., Akkajaure complex,
Lewisian Complex.
 The rank of a complex may be equivalent to a group, a
formation, or a member.
 The term ‘basement complex’ is applied informally to rocks
of complicated structure (commonly igneous or metamorphic)
underlying a less deformed, dominantly sedimentary
sequence in any region.

10. Informal Lithostratigraphic Units
 The term “measures” has been used
informally for a sequence of coal beds( eg.
The Mora coal measures), but “The Coal
Measures” has also been used historically
for a series of the Carboniferous System.
 When informal units such as those
mentioned above are given geographic
names, the unit-term should not be
capitalized.
 Geographic names should be combined
with the terms “Formation” and “Group”
only in formal nomenclature.

11. Tongue and Lentil
 Tongue and lentil have been used frequently as
independent lithostratigraphic rank terms, but
more correctly they are only specially shaped forms
of members.
 A lentil is a lens-shaped body of rock of different
lithology than the unit
 A projecting part of a unit extending out beyong its
main body may be called a tongue.
 Lentil might be part of a narrow tongue.

12. Reef
 Reef is a term commonly applied to a mass of organic
carbonate built in place by corals, algae or other sedentary
organisms.
 Reefs are of variable size and shape and may occur as limited
isolated masses.
Great Barrier Reef
 The Great Barrier Reef is the world's largest coral reef
system composed of over
 2,900 individual reefs and
 900 islands stretching for over 2,300 kilometres (1,400 mi)
 over an area of approximately 344,400 square kilometres
(133,000 sq mi).
 The reef is located in the Coral Sea, off the coast of
Queensland, Australia.