Chemostratigraphy is the study of chemical variations in sedimentary rocks to determine stratigraphic relationships. It uses inorganic geochemical data like carbon and oxygen isotopes to correlate rock layers. Oxygen isotopes fractionate with temperature changes and are measured in marine organism shells to create records for paleoclimate analysis. Carbon also has stable isotopes that provide information about past climate, evolution, and atmospheric CO2 levels. Chemostratigraphy has advantages over other correlation techniques as it can be used on any aged sediments regardless of lithology or environment. It has been applied successfully at major geologic boundaries and in unconventional reservoirs. Recent studies have also used sulfur and strontium isotopes to better understand changes around the Ordov

1. Chemostratigraphy
Mohd Farhan
5531
BSc(H) Geology 2nd
Year

2. Chemostratigraphy
 Chemostratigraphy, or chemical stratigraphy, is the study of the
chemical variations(correlation on the basis of oxygen and
carbon isotope) within sedimentary sequences to determine
stratigraphic relationships.
 Chemostratigraphy may be defined as a correlation technique
involving the application of inorganic geochemical data.
 sedimentary geochemistry has been in use to understand the
conditions of deposition, climatic variations, tectonic setting,
provenance, reservoir characteristics, etc.
However,characterization of depositional units for distinction
and correlation based on stratigraphic variation of geochemical
traits and usage of the term “chemostratigraphy.
 the basic idea of chemostratigraphy is nearly as old
as stratigraphy itself, distinct chemical signatures can be as
useful as distinct fossil assemblages or distinct lithographies in
establishing stratigraphic relationships between different rock
layers.
 Chemostratigraphy found its utility for comparing and
contrasting geochemical compositions of strata across major
geochronological boundaries, such as Precambrian–Cambrian,
Permian–Triassic, Triassic–Jurassic, Jurassic–Cretaceous,
Cretaceous–Tertiary, Palaeocene–Eocene, etc

3. Oxygen isotopes
 The two oxygen isotopes used in chemostratigraphy are
16
O and
18
O. 99.8% of all the oxygen is in the form of
16
O,
18
O makes up most of the remaining 0.2%.
 these two isotopes are present in the oceanin this ratio.
these two isotopes fractionated with changes in
temperature
Oxygen isotopes are measured with respect to an
arbitrary laboratory standard calledPDB(Pee Dee
Belemnite)
Oxygen isotopes are measured in the shells of marine
organisms, because the isotope record occurs primarily
in ocean water.
 The records of oxygen isotopes from deep-marine
carbonate sediments have become powerful tools for
Paleoclimaticanalyses

5. Carbon isotopes
 Like oxygen, carbon has more than one
stable isotope in the Earth's oceans and
atmosphere
 two stable carbon isotopes, the
abundance of 12C in nature is given as
98.89%, while 13C forms the
remaining 1.11%.
 The knowledge of the C isotope record is
very important not only in stratigraphic
correlation but also because of its potential
to help understand the development of
Earth’s climate, evolution of its biota, and
CO2 levels in the atmosphere.

7. APPLICATION OFCHEMOSTRATIGRAPHY
The obvious advantages of elemental
chemostratigraphy are that it can be utilized
in sediments of any lithology, any age, found
in any location and deposited in any
environment
A further advantage of the technique is that
it can be applied to field outcrop, core,
sidewall core and ditch cuttings samples.
Chemostratigraphy is also applicable in
Clastic, Carbonate and Unconventional
Reservoirs

8. Chemostartigraphy of Ordovician- Silurian Boundary
 During the past two decades, a very large amount of
chemostratigraphic research has been carried out in
lower Paleozoicsedimentary successions around the
world that has led to very significant improvements in
our understanding of stratigraphic relations at both
localand regional scales.
 Most of the investigations in the Ordovician‐Silurian
boundary interval have been based on ¹³C but recent
pioneer studies using ³⁴S and ⁸⁶Sr/⁸⁷Sr suggest that
also these isotopes have great potential as tools for both
correlationand understanding of paleoenvironmental
changes. Because very little has been published on the
use of the two latter isotopes in the Ordovician‐Silurian
boundary successions, the present review is focused on
¹³C chemostratigraphy.

9. Thank you
Reference:
Sedimentary Geology(D.R. Prothero)
Principle of Elemental Chemostratigraphy(Neil Craigie)