emphasison tectonic effects on the stratigraphic record.
Stratigraphic record: The geologic record based on or derived from a study of the stratigraphic
sequence; the rocks arranged chronologically as in a geologic column.
Stratigraphy: 'Hie word stratigraphy comes from the Latin stratum and the Greek graphia, which means the descriptive science of layered rocks. It deals with the form, arrangement, distribution, chronologic succession, classification, and relationship of rock strata (and other associated rock bodies), in normal sequence with respect to and/or all the characters, properties and attributes, which rocks may possess. It thus involves origin, composition, environment, age, history, relationship to organic evolution and innumerable other features of rock strata.The stratigraphy is mainly exercised on sedimentary rocks, but it isalso applicable to igneous and metamorphicrocks as faras they pertain to stratigraphy and related to stratigraphic classification. Some non-Stratford rock bodies are considered under stratigraphy because of their association with or close relation to rock strata.
Research in stratigraphy is governed by a set of authoritative regulations, which arc usually
contained in a booklet, called stratigraphic code of a given country. Evidently, Pakistan has also prepared and printed its own stratigraphic code, Rahman (1962) that lays down the principles of stratigraphic classification as well as important and required terminology. Fundamental and most common item in the stratigraphic research is the lithostratigraphic description of the rock strata in which rock strata is divided into formations, member, bed, group and super group. All of these are defined in the Stratigraphic Code of Pakistan (1962).The items not given in thecode and used in this report are defined below. These are selected from “An International Guide to stratigraphic classification terminology and usage, (Int. Sub Comm, on Stratigraphic Classification Report-7, 1972).
Stratum: A geologic stratum is a layer (a generally tabular body) of rock characterized by certain unifying characters, properties or attributes, distinguishing it from adjacent layers. Adjacent strata may be separated by visible planes of bedding or parting, or by less perceptible boundariesof change in lithology, in mineralogy, in fossil contents, in chemical constitution, in physical properties, in age, or in any other property of rocks.
Stratigraphic unit:Astratigraphic unit isa stratum or assemblage of adjacentstrata, recognized as a unit (distinct entity) in the classification of the Earth's rock sequence, with respect to any of the many
characters, properties,or attributes which rocks may possess.Stratigraphic units of one category will not necessarily coincide with those of any other category and it is therefore, essential to keep their named units distinct. Clear definition of stratigraphic unit is of paramount importance.
Complex: A lithostratigraphic unit composed of diverse rock types of any class (sedimentary, igneous, metamorphic) or classes, and characterized by highly complicated structure may be calleda Complex, e.g. Kirana Complex, Bcsham Complex. The rank of a complex may be equivalent to a Group,Super group, Formation or Member.
Stratotypes: Many kinds of stratigraphic units are best defined by reference to a designated type in a
specific sequence of rocks strata a stratotype. The value of a stratotype is that it provides a clear, uniform, and unchanging definition, which should mean the same thing to everyone and to which everyone can return for reference. It is essential that a stratotype be carefully selected and clearly marked, and it is desirable that it to be officially approved by the highest-ranking pertinent organization of stratigraphers. In the case of Pakistan, Stratigraphic Committee of Pakistan formalizes the names and stratotype of stratigraphic units.
Some other stratotype related terms used in the literature are given below:
A unit-stratotype is the type section of strata serving as the standard for the definition and recognition of a stratigraphic unit. The upper and lower limits of a unit-stratotype are fixed by boundary-stratotypes.
A boundary-stratotype is a specific point in a specific sequence of rock strata, which serves as the standard for definition and recognition of a stratigraphic boundary.
A composite-stratotype is a unit stratotype formed by the combination of several specified component- stratotype.
A hypostratotype (reference section) is a secondary stratotype used to extend the knowledge of the unit or boundary established by a stratotype to other geographic areas or other fancies.
Type locality: The type locality of a stratigraphic feature (unit, boundary, or other feature) is the specific geographic area in which itsstratotype issituated,or, lacking a designated stratotype, the area where it was originally defined.
Formal versus Informal Stratigraphic Terminology: A formal unit is named representative of an
established or conventionally agreed scheme of classification. An informal unit is based only in the sense of a general noun without being necessarily named or without being part of a specific scheme of classification. The initial letter of a named formal unit-term is capitalized, e.g. Bara Formation that, of an informal unit except for the geographic ones, are not capitalized e.g. Khyber limestone, Pasuslate etc.
Formal Lithostratigraphic Unit: In other countries of the world, it requires publication, in a recognized scientific medium of a statement of intention to establish a new unit, together with a description whereas in Pakistan; formalization of the unit is the responsibility of stratigraphic committee of Pakistan. However, in both the cases the description of stratigraphic unit, which desirably includes the following, where applicable:
(a) Name; Definition;general geographic area Kind and rank of proposed unit General concept.
General lithology; historical background; synonymy; previous treatment; reasons for proposal
Stratotype (or specific type locality) Hypostratotype or reference sections
Regional aspects. Extent of unit, geomorphic expression, thickness variations, lateral changes in character, stratigraphic relations, relations to other units, dimensions and shape Age and correlation
Distinctive or identifying features. Criteria to be used in extending the unit away from its stratotype and particularly criteria to be used in extending its boundaries from the boundary-stratotypes
As already stated that in Pakistan the formalization of a stratigraphic unit is authorized to the Stratigraphic Committee of Pakistan. Thus, authority is composed of members/representatives from all the geoscientific organizations of Pakistan.
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