ASTM D7708-11

Standard Test Method for Microscopical Determination of the Reflectance of Vitrinite Dispersed in Sedimentary Rocks

SIGNIFICANCE AND USE
The mean reflectance of the vitrinite maceral in sedimentary rocks as determined by this test method is used as an indicator of thermal maturity, that is, the progressive geochemical alteration of dispersed organic material experienced during diagenesis, catagenesis, and metagenesis. In the case of hydrocarbon source rocks, three major categories of thermal maturity are defined by vitrinite reflectance: immature (Roran ≤ 0.5%), mature (Roran ≈ 0.5-1.35%), and overmature (Roran ≥ 1.35%) with respect to the generation of liquid hydrocarbons. Thermal maturity as determined by the reflectance of vitrinite dispersed in sedimentary rocks is similar to the rank classification of coals as presented in Classification D388 and measured similarly to the reflectance of vitrinite in coal as presented in Test Method D2798. The mean reflectance of the vitrinite maceral in sedimentary rocks correlates with geochemically determined parameters of thermal maturity and can be used to characterize thermal maturation history, to calibrate burial history models, and to better understand the processes of hydrocarbon generation, migration, and accumulation in conventional and unconventional petroleum systems.
SCOPE
1.1 This test method covers the microscopical determination of the reflectance measured in oil of polished surfaces of vitrinite dispersed in sedimentary rocks. This test method can also be used to determine the reflectance of macerals other than vitrinite dispersed in sedimentary rocks.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Mar-2011
• ICS: 91.100.15 - Mineral materials and products
• Technical Committee: D05 - Coal and Coke
• Drafting Committee: D05.28 - Petrographic Analysis of Coal and Coke

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D7708 −11
StandardTest Method for
Microscopical Determination of the Reflectance of Vitrinite
Dispersed in Sedimentary Rocks
This standard is issued under the fixed designation D7708; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.3.1 alginite, n—a liptinite maceral occurring in structured
morphologies, telalginite, and unstructured morphologies, la-
1.1 This test method covers the microscopical determination
malginite.
of the reflectance measured in oil of polished surfaces of
3.3.2 bituminite, n—an amorphous primary liptinite maceral
vitrinite dispersed in sedimentary rocks. This test method can
with low reflectance, occasionally characterized by colored
also be used to determine the reflectance of macerals other than
internal reflections and weak orange-brown fluorescence, de-
vitrinite dispersed in sedimentary rocks.
rived from bacterial biomass and the bacterial decomposition
1.2 The values stated in SI units are to be regarded as
of algal material and faunal plankton. Bituminite is equivalent
standard. No other units of measurement are included in this
to the amorphous organic matter recognized in strew slides of
standard.
concentrated kerogen (1).
1.3 This standard does not purport to address all of the
3.3.2.1 Discussion—Bituminite may be distinguished from
safety concerns, if any, associated with its use. It is the
vitrinite by lower reflectance, as well as higher fluorescence
responsibility of the user of this standard to establish appro-
intensity if fluorescence is present in vitrinite. Bituminite has
priate safety and health practices and determine the applica-
poorly-defined wispy boundaries and may be speckled or
bility of regulatory limitations prior to use.
unevenly colored whereas vitrinite has distinct boundaries and
is blockier and evenly colored. The occurrence of bituminite in
2. Referenced Documents
association with lamalginite and micrinite is common. Rock
2.1 ASTM Standards:
type, thermal maturity, and geologic occurrence can be used to
D121 Terminology of Coal and Coke
interpret the potential presence of bituminite; for example,
D388 Classification of Coals by Rank
bituminite may be expected to occur in lacustrine or marine
D2797 Practice for Preparing Coal Samples for Microscopi-
settings. It is less commonly present in fluvial or similar
cal Analysis by Reflected Light
proximal depositional environments, where vitrinite may be
D2798 Test Method for Microscopical Determination of the expected to occur in greater abundance.
Vitrinite Reflectance of Coal
3.3.3 chitinozoan, n—a group of flask-shaped, sometimes
ornamented marine microfossils of presumed metazoan origin
3. Terminology
which are composed of ’pseudochitin’ proteinic material and
3.1 Definitions—For definitions of terms, refer to Terminol-
which occur individually or in chains. Chitinozoan cell walls
ogy D121.
are thin, opaque to translucent, and range from dark gray to
white in reflected white light similar to vitrinite. Chitinozoans
3.2 Abbreviations:
are common in Ordovician to Devonian marine shales.
3.2.1 R ran—mean random reflectance measured in oil.
o
Other organizations may use other abbreviations for mean
3.3.4 conodont, n—the phosphatic, tooth-like remains of
random reflectance.
marine vertebrate worm-like animals present from the Cam-
brian through Triassic, composed predominantly of apatite
3.3 Definitions of Terms Specific to This Standard:
with subordinate amounts of organic matter. Conodont mor-
phology is variable, but often well-defined denticles and blades
This test method is under the jurisdiction of ASTM Committee D05 on Coal
are preserved. In reflected white light examination conodonts
and Coke and is the direct responsibility of Subcommittee D05.28 on Petrographic
range from pale yellow to light brown to dark brown and to
Analysis of Coal and Coke.
black.
Current edition approved April 1, 2011. Published April 2011. DOI: 10.1520/
D7708–11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to a list of references at the end of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7708−11
3.3.5 fusinite, n—an inertinite maceral distinguished princi- 3.3.13 maceral, n—an organic component occurring in sedi-
pally by the preservation of some feature(s) of the plant cell mentary rocks and coal that is distinguished on the basis of its
optical microscopic properties, primarily reflectance and mor-
wall structure, high relief, and reflectance substantially higher
phology.
than first cycle vitrinite in the same sample. When less than
50-µm in size this maceral is assigned to inertodetrinite. Other
3.3.14 maceral classification, n—the systematic division of
organizations may define macerals using different technical
the organic components (macerals) in sedimentary rocks and
specifications. coal based on their appearance in the optical microscope under
incident white and fluorescent light.
3.3.6 graptolite, n—colonial, chitinous animal which occurs
3.3.15 micrinite, n—an inertinite maceral, generally
as thin, elongate bodies sometimes showing complex skeletal
nonangular, exhibiting no relict plant cell wall structure,
morphology and with reflective dark gray to white color in
smaller than 10 µm and most commonly occurring as granular
reflected white light similar to vitrinite (2). Graptolites occur
particles around 1- to 5-µm diameter. Other organizations may
from the Cambrian through Carboniferous.
define macerals using different technical specifications.
3.3.7 huminite, n—maceral group present in lignite and
3.3.15.1 Discussion—Micrinite is a secondary maceral
immature sedimentary rocks with reflectances intermediate to
formed from liptinite macerals during maturation.
those of associated darker liptinites and brighter inertinites (3).
3.3.16 mineral matter, n—in sedimentary rocks and coal,
Huminite is equivalent to the vitrinite maceral group that
the non-organic fraction composed of physically discrete
occurs in subbituminous and higher rank coals with measured
particles of minerals such as clays, pyrite, quartz, carbonates,
reflectance values greater than 0.5% (4).
etc., and all elements other than carbon, hydrogen, oxygen,
3.3.8 inertinite, n—maceral group with macerals that exhibit
nitrogen and sulfur in the organic fraction.
higher reflectance than other organic components in the same
3.3.17 recycled vitrinite, n—vitrinite that has undergone at
sample; for example, semifusinite, fusinite, and inertodetrinite.
least one additional cycle of burial, exhumation, and erosion in
Inertinite macerals generally lack fluorescence and usually
contrast to first cycle vitrinite which has undergone only one
retain preserved plant cell wall structure(5).
burial cycle. The additional cycle may result in exposure to
thermal maturation, chemical or thermal oxidative processes,
3.3.9 inertodetrinite, n—an inertinite maceral occurring as
or both, and mechanical abrasion (sometimes resulting in
individual, angular, clastic fragments incorporated within the
increased particle rounding) that is not experienced by first
matrix of other macerals (commonly vitrinite) or minerals, and
cycle vitrinite contained in the same sample.
in the size range from 2- to 50-µm. Other organizations may
3.3.17.1 Discussion—Recycled vitrinite has higher reflec-
define macerals using different technical specifications.
tance than co-occurring first cycle vitrinite, and sometimes is
3.3.9.1 Discussion—Inertodetrinite is derived through the
less angular, due to the rounding of grain boundaries experi-
disintegration of other inertinite macerals, that is, fusinite and
enced during transportation. Recycled vitrinite may have bright
semifusinite, by mechanical abrasion during transport.
or dark halos, representing thermal oxidation and weathering
3.3.10 kerogen, n—dispersed or concentrated organic processes, respectively, which are not present in the co-
occurring first cycle vitrinite. Recycled vitrinite has a higher
matter, or both, occurring in sediments and sedimentary rocks
variance of reflectance values, representative of the many
that is insoluble in organic solvents.
possible sources and processes occurring during transportation,
3.3.11 lamalginite, n—an unstructured liptinite maceral
and may show greater relief than first cycle vitrinite in the same
with low reflectance distinguished primarily by the presence of
sample. Recycling of vitrinite may be inferred from the
bright fluorescence and lamellar character.
geologic context; for example, a higher proportion of recycled
vitrinite may be observed in a catchment collecting sediments
3.3.12 liptinite, n—maceral group with macerals that exhibit
derived from a growing orogenic belt.
lower reflectance than other organic components in the same
sample of sedimentary rocks and coal, appearing black to dark
3.3.18 scolecodont, n—the chitinous, variably mineralized
gray in reflected white light and that fluoresce under blue to
fossil remains of the jaw elements of polychaete annelid
ultraviolet light in coals ranked medium volatile bituminous
worms, which occur as lamellar to tooth-like structures with
and lower. Liptinite maceral fluorescence can be used as a
spongy, laminated, or granular texture, and with reflective dark
qualitative thermal maturity indicator as fluorescence changes
gray to white color similar to vitrinite. Scolecodonts occur
from green to yellow to orange before becoming extinguished
from the Ordovician to recent.
at advanced maturity.
3.3.19 semifusinite, n—an inertinite maceral with morphol-
3.3.12.1 Discussion—Liptinite macerals are observed only
ogy like fusinite sometimes with less distinct evidence of
in coals of maturity up to approximately the high volatile
cellular structure, and with reflectance ranging from slightly
bituminous to medium volatile bituminous transition, and in
greater than that of the associated vitrinite to that of the least
sedimentary rocks of equivalent thermal maturity. Liptinite
reflective fusinite. Semifusinite may show irregular mosaic
macerals undergo chemical changes during maturation which texture or satin anisotropy when viewed under polarized
render their optical distinction from vitrinite and inertinite reflected white light.
macerals difficult at maturities higher than medium volatile
3.3.19.1 Discussion—Low-reflecting semifusinite may be
bituminous. distinguished from vitrinite by higher reflectance and relief,
D7708−11
and the presence of more arcuate boundaries. The most reliable intensity diminishes and fluorescence color shifts toward red
distinguishing feature of low-reflecting semifusinite is the wavelengths with increasing thermal maturity.
frequent presence of well-preserved cellular structure or open
3.3.22 thermal maturity, n—the degree of thermal alteration
cell lumens, or both. However, it is not unusual for cell lumens
of the dispersed organic matter contained in sedimentary rocks,
to also remain open in vitrinite when deposited in clay-rich
synonymous with coal rank. Thermal maturity of sedimentary
sediments. Semifusinite usually has more distinct particle
rocks commonly is defined by vitrinite reflectance, spectral
boundaries, which distinguishes it from vitrinite which has a
fluorescence, X-ray diffraction crystallography, or by organic
more porous and textured surface. Geologic context is impor-
geochemical parameters.
tant; a greater proportion of semifusinite can be expected in
3.3.23 vitrinite, n—vitrinite dispersed in Upper Silurian and
sediments or coals associated with more arid locations,
younger age sedimentary rocks is the remains of coalified
climates, and time periods.
material from vascular land plants. Vitrinite dispersed in
3.3.20 solid bitumen, n—a secondary maceral associated
sedimentary rocks may be representative of a large variety of
with hydrocarbon generation from kerogen distinguished pri-
precursor plant materials with differing original chemistries
marily by its conformation to pores, voids and fractures in the
and structures. Vitrinite typically occurs as finely comminuted
rock matrix, embayment by authigenic mineral grains, and the
dark gray to white particles (in reflected white light) of sizes
absence of features such as cellular structure indicating deri-
less than 100 µm dispersed throughout the mineral matrix
vation from precursor plant material. Solid bitumens may show although particles of larger size can also be present. Vitrinite
homogenous or granular textures; irregular anisotropic mosaic dispersed in sedimentary rocks may occur as fragments of coal
textures also are common, particularly at advanced stages of which include other macerals, including inertinite and liptinite.
thermal maturity (6). Solid bitumens may exhibit fluorescence
3.3.23.1 Discussion—The identification of the primary vi-
at low thermal maturity.
trinite (first cycle vitrinite) population is essential for deter-
mining the peak thermal maturity experienced by a sedimen-
3.3.20.1 Discussion—For the purpose of reflectance mea-
tary rock. This can be complicated by: the chemical and
surement it is important to distinguish solid bitumen from
structural heterogeneity of dispersed vitrinite reflecting mul-
vitrinite since both macerals appear gray under reflected white
tiple sources; the presence of similar organic components
light and the reflectance of both advances with increasing
resembling vitrinite, including solid bitumen, bituminite, re-
maturity. Several populations of solid bitumen with distinct
cycled vitrinite, low-reflecting semifusinite, and zooclasts;
reflectance ranges can be present in a single whole-rock
vitrinite reflectance retardation or suppression, or both; altera-
sample. Solid bitumens are characterized by their pore-filling
tion by oxidation or weathering from sample handling or by
or anastamosing forms. Boundaries of solid bitumen can be
exposure to the atmosphere at outcrop; and the potential for
well-defined by textural embayment by authigenic minerals
contamination such as cavings and drilling mud additives in the
such as calcite and dolomite that commonly form contempo-
case of drill cuttings. The term vitrinite is currently used as
raneously with solid bitumen deposition. However, vitrinite
both a macera
...