U.S. Geological Survey Open-File Report 92-409, Version 1.1

                   VITRINITE REFLECTANCE AND
                CONODONT COLOR ALTERATION INDEX
                        DATA FROM ALASKA

The data in this directory represent an update of U.S.
Geological Survey (USGS) Open-File Report 92-409. These data,
now consisting of more than 10,000 vitrinite-reflectance and
conodont color-alteration-index determinations from samples
representing over 3,800 localities throughout the state, are
the data underlying the "Generalized Thermal Maturity Map
of Alaska" (Miscellaneous Investigations Map I-2494)
produced by the USGS in 1996, also available on this CD-ROM.

In addition to the data themselves, these files identify the 
original source of the data; complete references are found in  
"Sources of Data," below. Sample preparation and analytical 
techniques, vitrinite-reflectance histograms, and further 
sample information are commonly provided in the original 
sources. Vitrinite-reflectance determinations conducted by 
M.J. Pawlewicz in USGS laboratories compose many of these 
data; sample preparation and analytical techniques under 
which those data were collected are described in "Methods," 
below. Nearly all of the conodont color-alteration-index 
data were produced by A.G. Harris in USGS laboratories, and 
those techniques also are described in the "Methods" section.

VERSION HISTORY

Version History for:

Johnsson, M.J., Pawlewicz, M.J., Harris, A.G., and 
     Valin, Z.C., 1992, Vitrinite reflectance and conodont 
     color alteration index data from Alaska: Data to 
     accompany the thermal maturity map of Alaska: U.S. 
     Geological Survey Open-File Report 92-409, 3 diskettes.

Version 1.1 - July 21, 1999
     Added attitional data, published online and as part of 
     USGS DDS-54.

Version 1. - July 21, 1992
     First release


DATA STRUCTURES

This directory contains vitrinite-reflectance and conodont
color-alteration-index data from Alaska in three file
formats: a Microsoft Excel (version 5.0) workbook, a set of
four ASCII files; and a set of four files in Adobe's
"portable document format" (PDF). The Excel workbook
contains four spreadsheets: one each for vitrinite-
reflectance data from outcrops, vitrinite-reflectance data
from wells, conodont color-alteration-index data from
outcrops, and conodont color-alteration-index data from
wells. These spreadsheets are neatly formatted and will
generally be easier to work with than the ASCII or PDF files,
but they do require that the user own a copy of the Microsoft
Excel application. The ASCII files are tab-delineated, with
the first two records consisiting of title and field
labels, respectively. Manipulation of the ASCII files
requires a database manager, spreadsheet, or word-processing
program capable of reading ASCII files. The PDF files can be
viewed by the Adobe Acrobat Reader application, available on
this disk or at http://www.adobe.com.

The spreadsheet "Ro Outcrop Data" (and it's ASCII and PDF 
file equivalents) contains 3,943 mean vitrinite-reflectance 
values from 2,319 localities. Each record consists of 10 
fields. The first field is a record number beginning with the 
prefix "VO-" and ending with a four-digit number that is 
provided merely for cross-referencing purposes and is unique 
to each record; record numbers higher than VO-3716 are 
additions to the data reported in Open-File Report 92-409. 
The second field is the 1:250,000-scale quadrangle 
corresponding to the sample locality; samples collected 
offshore are from dredge hauls. The third and fourth fields 
are the latitude and longitude of the sample locality, 
expressed in decimal degrees north and west, respectively. 
Sample localities from USGS and PGS sources were taken from 
1:63,360- or 1:250,000-scale topographic maps by the 
geologist collecting the sample. Localities for data taken 
from the literature, if not tabulated by the authors, were 
determined from location maps or figures provided by the 
authors. Localities presented in section-township-range 
format were converted to decimal degrees, taking the center 
of the section as the sample locality; the resulting loss of 
precision is reflected in the data file by our reporting 
these data to only the nearest thousandth of a degree (three 
decimal places). Data provided by oil companies commonly were 
reported in section-township-range format. The fifth field is 
the sample elevation, if known, in meters above or below (-) 
sea level. The sixth field is the collectors' sample number. 
The seventh and eighth fields are the stratigraphic age and 
lithologic unit from which the sample was collected, if 
known. Note that ages are expressed in stratigraphic termsÑ 
Lower, Middle, and UpperÑand that these terms are abbreviated 
"L.," "M.," and "U." The ninth field is the mean vitrinite 
reflectance in oil (Ro), in percent. This is an interpretive 
value corresponding to the indigenous vitrinite population; 
most operators, after examining the histogram of individual 
vitrinite-reflectance values, exclude individual values from 
the calculation of the mean if they could reflect 
nonvitrinite or recycled material. Where more than one sample 
was available from a single locality, the mean value was used 
to represent the thermal maturity at that locality. Any value 
lying beyond two standard deviations of the mean was excluded 
from the calculation. The tenth field is the source of the 
data; see "sources of data," below for a key to sources. 
Samples for which the data source is followed by 
"[Pawlewicz]"  were analyzed by M.J. Pawlewicz in USGS 
laboratories, and the sample preparation and analytical 
techniques he adopted are described below.

The spreadsheet "CAI Outcrop Data" (and its ASCII and PDF 
file equivalents) contains 1,491 conodont color-alteration- 
index determinations from 1,323 localities in Alaska. Each 
record consists of 11 fields. The first field is a record 
number, beginning with the prefix "CO-" and ending with a 
four-digit number that is a record number for cross-reference 
purposes; numbers higher than CO-1500 represent additions to 
the data reported in Open-File Report 92-409. The second 
field is the 1:250,000-scale quadrangle corresponding to the 
sample locality. The third and fourth fields are the latitude 
and longitude of the sample locality, expressed in decimal 
degrees north and west, respectively. Sample locations 
generally were taken from 1:63,360-scale topographic maps by 
the geologist collecting the sample. The fifth field is the 
collectors' sample number. The sixth field is the 
stratigraphic age of the sample, as determined from conodont 
biostratigraphy. Note that ages are expressed in 
stratigraphic termsÑLower, Middle, and UpperÑand that these 
terms are abbreviated "L.," "M.," and "U." The seventh field 
is the rock unit from which the sample was collected, if 
known. Note that the age determination may not, in some 
cases, correspond to the known age of the supposed rock unit 
sampled. Many of the conodont samples were collected in the 
course of geologic mapping to help identify stratigraphic 
units, and if the conodont age does not match the known 
stratigraphic age then the rock unit reported in field seven 
is suspect. The eighth and ninth fields are the minimum and 
maximum conodont color alteration index, respectively, 
observed in conodonts from the sample. Where more than one 
sample was available from a single locality, the mean value 
was used to represent the thermal maturity at that locality. 
Any value lying beyond two standard deviations of the mean 
was excluded from the calculation. The tenth field is the 
individual or corporation that collected the sample, and the 
eleventh field is the individual who performed the CAI 
determination. Nearly all CAI determinations were made by 
A.G. Harris, and her sample preparation and analytical 
techniques are described below.

The spreadsheet "Ro Well Data" (and its ASCII and PDF file
equivalents) contains 4,990 mean vitrinite-reflectance values
from 224 wells. Each record consists of 10 fields. The first
field is a record number beginning with the prefix "VW-" and
ending with a four-digit number that is provided merely
for cross-referencing purposes and is unique to
each record. Record numbers higher than VW-4482 are additions
to the data presented in Open-File Report 92-409. The next
six fields (fields 2 through 7) are identical in all records
corresponding to a given well. The second field is the
1:250,000-scale quadrangle on which the well is located. The
third and fourth fields are the well name and its American
Petroleum Institute number, respectively. The fifth and sixth
fields are the latitude and longitude of the well top,
expressed in decimal degrees north and west, respectively.
The seventh field is the elevation of the Kelley bushing, in
meters above sea level. This value can be used in conjunction
with the sample depth (the eighth field) to obtain XYZ
coordinates for each sample. Latitude, longitude, and Kelley
bushing elevation are from the Petroleum Information
Corporation's Well History Control System (WHCS) file. For
some wells, the elevation datum was not the Kelley bushing
but the ground elevation. For those wells, ground elevation
is reported in field 7. The eighth field is the sample depth,
uncorrected for well deviation. For cutting samples, the
lower limit of the depth range corresponding to the cutting
samples is reported in field 8. The ninth field is the mean
vitrinite reflectance in oil (Ro), in percent. This is an
interpretive value corresponding to the indigenous vitrinite
population; most operators, after examining the histogram of
individual vitrinite-reflectance values, exclude individual
values from the calculation of the mean if they could reflect
non-vitrinite or recycled material. The tenth field is the
source of the data; see "sources of data," below for a key to
sources. Samples for which the data source is followed by
"[Pawlewicz]" were analyzed by M.J. Pawlewicz in USGS
laboratories, and the sample-preparation and analytical
techniques he adopted are described below.

The spreadsheet "CAI Well Data" (and its ASCII and PDF file 
equivalents) contains 18 conodont color-alteration-index 
determinations from 14 wells. Each record consists of 14 
fields. The first field is a record number, beginning with 
the prefix "CW-" and ending with a four-digit number that 
corresponds to the record number in the USGS database 
maintained by A.G. Harris from which the data were extracted. 
The next six fields (fields 2 through 7) are identical in all 
records corresponding to a given well. The second field is 
the 1:250,000-scale quadrangle on which the well is located. 
The third and fourth fields are the well name and its 
American Petroleum Institute number, respectively. The fifth 
and sixth fields are the latitude and longitude of the well 
top, expressed in decimal degrees north and west, 
respectively. The seventh field is the elevation of the 
Kelley bushing, in meters above sea level. This value can be 
used in conjunction with the sample depth (the eighth field) 
to obtain XYZ coordinates for each sample. Latitude, 
longitude, and Kelley bushing elevation are from the 
Petroleum Information Corporation's Well History Control 
System (WHCS) file. The eighth field is the sample depth, 
uncorrected for well deviation. Depth ranges correspond to 
the interval over which cuttings were collected. The ninth 
field is the stratigraphic age of the sample, as determined 
from conodont biostratigraphy. Note that ages are expressed 
in stratigraphic termsÑLower, Middle, and UpperÑand that 
these terms are abbreviated "L.," "M.," and "U." The tenth 
field is the rock unit from which the sample was collected, 
if known. The eleventh and twelfth fields are the minimum and 
maximum conodont color-alteration-index, respectively, 
observed in conodonts from the sample. The thirteenth field 
is the individual or corporation that collected the sample, 
and the fourteenth field is the individual who performed the 
CAI determination (A.G. Harris in all cases). Sample-
preparation and analytical techniques are described below.

SOURCES OF DATA

Conodont color-alteration-index (CAI) data were produced from
samples supplied by the individuals or corporations listed in
the "collector" field of the CAI data files. Actual CAI
determinations were made in USGS labs; the name of the person
responsible for the data is given in the "CAI determination"
field of each record. Nearly all CAI determinations were made
by A.G. Harris, and the procedures outlined in "Methods,"
below, apply to those data.  Vitrinite-reflectance data, in
contrast,  were assembled from diverse sources. The following
list explains the "source of data" cited in the last field of
each record:

GMC Ñ Alaska Division of Geological and Geophysical Surveys, 
Geologic Materials Center (GMC) data reports. Number of 
report indicated; if followed by "[Pawlewicz]" the data were 
generated by M.J. Pawlewicz at the USGS, and the procedures 
described in "Methods," below, apply. GMC reports may be 
ordered from Geologic Materials Center, P.O. Box 772116, 
Eagle River, AK  99577.

MMS Ñ U.S. Department of the Interior, Minerals Management
Service well files maintained at Minerals Management
Service, 949 E 36th Avenue, Anchorage, AK 99508-4302.

PGS Ñ Petroleum Geochemistry System Database maintained by
Petroleum Information Corporation. The number in
brackets following the reference is the extended American
Petroleum Institute (API) number, which serves as a record
number to locate the data within the database. This is a
commercial product available from Petroleum Information
Corporation, P.O. Box 2612, Denver, CO  80201-2612.

USGS Ñ Data produced in USGS labs from samples collected by
USGS scientists or donated to the USGS for use in this
study. Name in brackets is that of the person
responsible for the data; if "Pawlewicz" the procedures
described in "Methods" apply.

Oil Companies Ñ Four oil companies (ARCO, British Petroleum,
Chevron, and Shell) made generous donations of data from
their internal files.

Literature Ñ Literature citations refer to data collected
directly from published sources. Only actual tabulated
data were used; data were not interpolated from figures.
Cited sources are as follows:

   Belowich, M.A., 1986, Basinal trends in coal,
      petrographic, and elemental composition with
      applications toward seam correlation, Jarvis Creek
      Coal Field, Alaska, in Focus on Alaska's Coal '86,
      Proceedings of the conference held at Anchorage,
      Alaska, October 27Ð30, 1986: Fairbanks, Alaska,
      Mineral Industry Research Laboratory, p. 300Ð335.
   Bruns, T.R., von Huene, R., Curlotta, R.C., and
      Lewis, S.D., 1985, Summary geologic report for the
      Shumagin Outer Continental Shelf (OCS) planning
      area, Alaska: U.S. Geological Survey Open-File
      Report 85-32, 58 p.
   Fisher, M.A., 1980, Petroleum geology of Kodiak
      Shelf, Alaska: American Association of Petroleum
      Geologists Bulletin, v. 64, p. 1140Ð1157.
   Fisher, M.A., Patton, W.W., Jr., and Holmes, M.L.,
      1982, Geology of Norton Basin and continental shelf
      beneath northwestern Bering Sea, Alaska: American
      Association of Petroleum Geologists Bulletin, v.
      66, p. 255Ð285.
   Krumhardt, A.P., 1994, Conodont analyses from the
      Arctic National Wildlife Refuge, northeast Brooks
      Range, Alaska 1990-1993: Alaska Division of
      Geological and Geophysical Surveys Public-Data File
      94-25, p. 79.
   Merritt, R.D., 1985a, Coal atlas of the Matanuska
      Valley, Alaska: Alaska Division of Geological and
      Geophysical Surveys Public-Data File 85-45, 270 p.
   Merritt, R.D., 1985b, Coal atlas of the Nenana Basin,
      Alaska: Alaska Division of Geological and
      Geophysical Surveys Public-Data File 85-41, 197 p.
   Merritt, R.D., 1986a, Depositional environments and
      resource potential of Cretaceous coal-bearing
      strata at Chignik and Herendeen Bay, Alaska
      Peninsula: Alaska Division of Geological and
      Geophysical Surveys Public-Data File 86-72, 20 p.
   Merritt, R.D., 1986b, Geology and coal resources of
      the Wood River Field, Nenana Basin: Alaska Division
      of Geological and Geophysical Surveys Public-Data
      File 85-41, 11 p.
   Merritt, R.D., 1990, Coal resources of the Susitna
      Lowland, Alaska: Alaska Division of Geological and
      Geophysical Surveys Report of Investigations 90-1,
      181 p.
   Rao, P.D., 1980, Petrographic, mineralogical, and
      chemical characterization of certain Arctic Alaskan
      coals from the Cape Beaufort region: Alaska
      Division of Geological and Geophysical Surveys,
      Mineral Industry Research Laboratory Report 44, 66 p.
   Rao, P.D. and Smith, J.E., 1983, Petrology of
      Cretaceous coals from northern Alaska: Alaska
      Division of Geological and Geophysical Surveys.
      Mineral Industry Research Laboratory Report 64, 141 p.
   Reifenstuhl, R.R., in press, Gilead sandstone,
      northeastern Brooks Range, Alaska; an Albian to
      Cenomanian marine clastic succession, in Reger, R.,
      ed., Short notes on Alaskan geology: Alaska
      Division of Geological and Geophysical Surveys.
   Reifenstuhl, R.R., 1990, Vitrinite reflectance data
      for some early Tertiary through Jurassic outcrop
      samples, northeastern Alaska: Alaska Division of
      Geological and Geophysical Surveys Public Data File
      90-5a, 3 p.
   Robinson, M.S., 1989, Kerogen microscopy of coal and
      shales from the North Slope of Alaska: Alaska
      Division of Geological and Geophysical Surveys
      Public Data File 89-22, 19 p.
   Smith, J. and Rao, P.D., 1986, Geology and coal
      resources of the Bering River Coal Field, in Focus
      on Alaska's Coal '86, Proceedings of the conference
      held at Anchorage, Alaska October 27Ð30, 1986:
      Fairbanks, Alaska, Mineral Industry Research
      Laboratory, p. 266Ð299.
   Turner, R.F., Bolm, J.G., McCarthy, C.M., Steffy,
      D.A., Lowry, P., and Flett, T.O., 1983a,
      Geological and operational summary Norton Sound
      COST No. 1 well, Norton Sound, Alaska: U.S.
      Geological Survey Open-File Report 83-124, 164 p
   Turner, R.F., Bolm, J.G., McCarthy, C.M., Steffy,
      D.A., Lowry, P., Flett, T.O., and Blunt, D.,
      1983b, Geological and operational summary Norton
      Sound COST No. 2 well, Norton Sound, Alaska: U.S.
      Geological Survey Open-File Report 83-557, 154 p.
   Turner, R.F., Lynch, M.B., Conner, T.A., Hallin, P.J.,
      Hoose, P.J., Martin, G.C., Olson, D.L.,
      Larson, J.A., Flett, T.A., Sherwood, K.W., and
      Adams, A.J., 1987, Geologic and operational
      summary, Kodiak Shelf stratigraphic test wells,
      western Gulf of Alaska: U.S. Minerals Management
      Service OCS Report MMS 87-0109, 341 p.
   Turner, R.F., McCarthy, C.M., Comer, C.D., Larson,
      J.A., Bolm, J.G., Banet, A.C., Jr., and Adams,
      A.J., 1984a, Geological and operational summary
      St. George Basin COST No. 1 Well Bering Sea,
      Alaska: U.S. Minerals Management Service OCS Report
      MMS 84-0016, 105 p.
   Turner, R.F., McCarthy, C.M., Comer, C.D., Larson,
      J.A., Bolm, J.G., Flett, T.O., and Adams, A.J.,
      1984b, Geological and operational summary St.
      George Basin COST No. 2 Well Bering Sea, Alaska:
      U.S. Minerals Management Service OCS Report MMS 84-
      0018, 100 p.
   Turner, R.F., McCarthy, C.M., Steffy, D.A., Lynch,
      M.B., Martin, G.C., Sherwood, K.W., Flett, T.O.,
      and Adams, A.J., 1984c, Geological and
      operational summary Navarin Basin COST No. 1 Well
      Bering Sea, Alaska: U.S. Minerals Management
      Service OCS Report MMS 84-0031, 245 p.

METHODS

Vitrinite-Reflectance Procedures Followed by M.J. Pawlewicz

Sample-preparation procedures depend on the lithology and
organic-carbon content of the sample. Coals require no
special preparation other than crushing to ~0.1 mm and
casting in epoxy. Shales and siltstones similarly require no
special processing, but their kerogen must be concentrated by
the crush-and-float technique described below. Sandstones
and carbonates require acid digestion before kerogen
concentration. Sandstones are digested successively in
hydrochloric and hydrofluoric acids; carbonate samples
generally require only a hydrochloric-acid treatment. For
shales, about 20-40 g of material are required, depending on
organic content. Sandstones and siltstones require about 40 g
of material, and carbonate samples should consist of 60-70 g
of material.

The crush-and-float technique (see Barker, 1982; Barker and 
Pawlewicz, 1986b) begins with crushing of shales and 
siltstones or acid digestion of sandstones and carbonates. 
Before milling in a micropulverizer, large (>10 cm) pieces of 
rock are reduced to 2Ð4 cm in diameter by hand, then crushed 
by a jaw crusher to yield a uniform particle size of 2-5 mm. 
The sample is then milled in a micropulverizer, yielding 
particles ~150 µm in diameter (100 mesh). The crushed sample 
(shales and siltstones) or residue after acid digestion 
(sandstones and carbonates) is then placed into a 50-mL 
polycarbonate test tube for kerogen concentration. Enough 
ZnBr2 (specific gravity 2.1 g/cm3) is added to each tube to 
just wet the sample. Each tube in turn is then stirred with a 
stirring motor and paddle turning at about 700 RPM. 
Additional ZnBr2 is then added to yield a thin slurry, and 
the volume of material in each tube is kept approximately 
equal for all samples to facilitate balancing the tubes 
before centrifugation.

The ZnBr2-sample slurries are centrifuged for 12 minutes at 
about 2,800 RPM, which separates organic material (which 
floats in ZnBr2) from inorganic material (which settles to 
the bottom of the tube). The supernatant is decanted, saved, 
and labeled; the inorganic material is discarded. The 
supernatant is then returned to the centrifuge tubes, diluted 
with water, and centrifuged for 5 minutes to wash the sample 
of ZnBr2. The supernatant is discarded, and the washing is 
repeated two more times. The washed organic material is then 
set on a hot plate at ~28 ¡C to dry overnight.  The kerogen 
concentrate (or crushed coal) is then cast in epoxy on 
standard petrographic slides, using the method described by 
Baskin (1979). A surface parallel to the slide is cut in the 
epoxy by use of a thin-section machine. The saw marks caused 
by this procedure are removed by using a 600-grit sandpaper 
and water. Slides are polished in two steps (see Pawlewicz, 
1987). The first step is a 90-second treatment, using 0.5-µm 
grit (alpha alumina) on a nap-free cloth with the lap turning 
at 60 RPM. The slide is removed and thoroughly cleaned of all 
polishing compound, then polished for an additional minute, 
using CeO2 on a napped cloth also revolving  at 60 RPM. After 
rinsing with water, the slides are cleaned in an ultrasonic 
cleaner and blown dry with a stream of air. The slides are 
then placed in a desiccator until ready for use.

Several assumptions are made when making vitrinite-
reflectance measurements. The first assumption is that the 
organic matter in the sample is representative of that 
incorporated into the sediment during deposition. Separating 
material recycled from older rock units from indigenous 
material (derived from vegetation coeval with sediment 
deposition) is an important consideration. Availability of 
the organic material and factors controlling local 
sedimentation determine the distribution of the organic 
material in the depositional environment, as well as the type 
of organic material preserved. The net result is that many 
distinct populations of organic material may be found in any 
lithologic unit. Homogenous vitrinite populations do occur, 
but infrequently.

The second assumption is that organic material is distributed 
evenly throughout the slide and that measurements taken at 
any point on the polished section will yield the same mean 
value (to within ~5 percent).  The presence of recycled 
material, or material other than terrestrial organic matter, 
is noted but not quantified during analysis. In samples in 
which organic material is sparse, it is even more difficult 
to select the indigenous population while rejecting recycled 
or non-indigenous material.

Vitrinite-reflectance determinations were made on a Zeiss
Universal microscope, fitted with an MPC-65 microscope
controller and interfaced with an IBM OS-2 Model 60 computer
running the Zeiss reflectance program PHOTAN. This program
allows for the immediate compilation of reflectance data,
storage on disk in several formats, and printing of the data
and histogram.  

Our usual procedure is to perform one scan per sample, 
measuring the reflectance of all the pertinent material as 
defined above. The mean of the individual values is usually 
taken as representing the thermal maturity of the sample, but 
rare values that are significantly different from the modal 
population may be discounted. Extensive editing of data or 
repeat analyses of any sample are not allowed.

Bimodal samples, where there is a distinct break in the
reflectance values in the histograms, present special
problems in interpretation. If the sample is from outcrop, or
core from a borehole, the lowest reflectance values from
terrestrial organic material must be the correct thermal
maturity indicator. Higher values are probably recycled
material. When the separation of reflectance values is vague
or the values range widely, then the decision usually
is to use the mean of all readings. Operator experience
obviously is beneficial in the evaluation of complex
vitrinite-reflectance populations.

Conodont Color-Alteration-Index Procedures Followed by
A.G. Harris

Detailed descriptions of techniques for concentrating
conodonts from rock, sediment, and residue matrix were given
by Collinson (1963), Stone (1987), and Harris and Sweet
(1989). The sample-preparation techniques used in this study,
with some exceptions, followed those of Harris and Sweet 
(1989).  Most of the samples reported here are from carbonate 
rocks. Samples from outcrops usually consisted of 3-8 kg of
material, but well samples (generally cuttings) were much
smaller (0.1Ð1 kg). Samples were crushed to fragments ~2 cm
in diameter in a standard rock crusher that was scrubbed
with a wire brush and thoroughly cleaned with compressed air
between samples. Well cuttings did not require crushing but
were wet-sieved and cleaned of contaminants (including metal
shavings, which were removed with a hand-held magnet).
Crushed samples or well cuttings were placed in plastic pans
and covered with 6Ð7% glacial acetic acid (limestones) or 
4Ð5% formic acid (dolostones). After 1Ð3 days, or when all 
CO2 generation ceased, the insoluble reside was washed 
through nested 20- and 200-mesh sieves. The >20-mesh fraction 
was reacidified and washed repeatedly until <100 g of >20-
mesh rock remained.  Samples containing abundant noncarbonate 
minerals were crushed to particles <1 cm diameter before re-
acidification. The 20-200 mesh (75Ð850 µm) fraction was oven-
dried at <50¡C.  Conodonts were concentrated from chert 
following the general recommendations in Orchard (1987). 
Samples weighing 20Ð200 g were crushed to <2-cm diameter and 
placed in a 1-L polypropylene beaker in a fume hood and 
immersed in 4Ð5 % hydrofluoric acid. After 24 hours, sodium 
carbonate was added to the solution to neutralize the 
remaining acid. The insoluble residue was then washed gently 
through stainless-steel sieves and dried as above.

Because conodonts generally have a specific gravity of 2.87 
to 3.0 g/cm3, heavy-liquid separation techniques were used to 
concentrate them from the 75Ð850 µm acid-insoluble residue. 
In a fume hood, the residue was poured into a transparent, 2-
L separatory funnel containing tetrabromoethane adjusted to a 
density of 2.865 g/cm3 for limestone samples or 2.88 g/cm3  
for dolostones, and stirred at 15-minute to 1-hour intervals 
about 5Ð10 times. The heavy-mineral concentrate was drawn off 
onto filter papers, thoroughly washed with acetone, and air-
dried in a hood. If concentrates contained >20% iron- bearing 
minerals (exclusive of unweathered pyrite) they were 
subjected to magnetic separation, using a Frantz-type 
electromagnetic separator and the procedures outlined by Dow 
(1965) and Stone (1987), to separate phosphatic minerals from 
nonphosphatic, predominantly iron-bearing, minerals. If the 
heavy-mineral concentrate contained significant amounts of 
nonmagnetic minerals (pyrite, barite, fluorite, etc.), 
additional heavy-liquid separation was performed, using 
methylene iodide adjusted to a specific gravity of 3.1 g/cm3, 
in which the relatively less dense conodonts float.

The final concentrate was then picked for conodonts by 
sprinkling the residue onto a picking tray with a numbered 
grid and white background to form a loose layer one grain 
thick. The conodonts were picked under a binocular zoom 
microscope at 20Ð50x magnification, using a fine wetted 
brush. The conodonts were transferred to a microfossil slide 
very lightly coated with water-soluble glue.  Conodont color- 
alteration-index (CAI) values were determined, following the 
procedures given in Epstein and others (1977) and Rejebian 
and others (1987). A set of CAI standards was used for 
indexing: each CAI value is represented by 10Ð30 naturally 
and experimentally altered, morphologically diverse 
specimens. The standard used for this study includes clusters 
of conodonts with CAI values of 1, 1.5, 2, 3, 4, 4.5, 5, 5.5, 
6, 6.5, 7, 7.5, and 8. The set of CAI standards, mounted on 
transparent glass set on white paper, was placed under a 
binocular zoom microscope. The field was illuminated with 
white light from a Tiyoda microscope light, using an 8V, 5A 
bulb. Relatively thin, unornamented specimens containing as 
little white matter as possible were selected for indexing. 
These specimens were placed next to the CAI standards under 
the microscope, and a best match was determined. When 
possible, at least five specimens representing different 
morphotypes were indexed for CAI values of 1 through 5. Some 
samples contained conodonts representing two CAI values 
(e.g., 4 and 4.5, indexed as 4Ð4.5) whereas some others, 
commonly from hydrothermal or contact-metamorphic regimes, 
yielded conodonts having a discontinuous range of CAI values 
(e.g., 2, 3, and 6). The latter were indexed as having the 
full range of values (e.g., 2Ð6). For samples containing 
conodonts with CAI values above 5, similar procedures were 
followed, except when a continuous range of CAI values was 
present (e.g., 5.5, 6, 6.5, and 7). For these samples, every 
specimen was indexed, and the sample was assigned the mean 
CAI value.

Some conodonts extracted from chert using hydrofluoric acid 
could not be used for CAI analysis because of chemical 
alteration. This sample-preparation technique produces 
conodonts with a wide range of preservation quality so that a 
sample may yield some specimens that are brittle, corroded, 
and bleached and others that are unaffected to only slightly 
affected by the acid treatment; some conodonts must dissolve 
completely. The unaffected conodonts probably have had the 
shortest exposure to the hydrofluoric acid. Only chemically 
unaltered specimens were used for CAI analysis.

Conodonts exposed on surfaces of indurated siliciclastic
rocks could not be freed from their matrix. Nevertheless,
these samples were indexed under the microscope by placing
morphologically similar CAI standards on the rock next to the
exposed specimens and determining a best match. Such
determinations are less accurate than those made on matrix-
free specimens, particularly for CAI values less than 5.

References Cited

Barker, C.E., 1982, A rapid method for concentrating
   sedimentary organic matter for vitrinite reflectance
   analysis: Journal of Sedimentary Petrology, v. 52, p.
   663Ð664.
Barker, C.E. and Pawlewicz, M.J., 1986b, Concentration of
   dispersed sedimentary organic matter for vitrinite
   reflectance analysis using a simple crush and float
   method: Society for Organic Petrology Newsletter, v. 3,
   p. 3.
Baskin, D.K., 1979, A method of preparing phytoclasts for
   vitrinite reflectance analysis: Journal of Sedimentary
   Petrology, v. 49, p. 633Ð635.
Collinson, C.W., 1963, Collection and preparation of
   conodonts through mass production techniques: Illinois
   Geological Survey Circular  343, 16 p.
Dow, V. E., 1965, Magnetic separation of conodonts, in
   Kummel, B. and Raup, D., eds., Handbook of
   Paleontological Techniques: San Francisco, W. H.
   Freeman, p. 263Ð267.
Epstein, A.G., Epstein, J.B., and Harris, L.D., 1977,
   Conodont color alteration--an index to organic
   metamorphism: U.S. Geological Survey Professional Paper
   995, 27 p.
Harris, A.G., and Sweet, W.C., 1989, Mechanical and chemical
   techniques for separating microfossils from sediment and
   residue matrix, in Feldmann, R. M., Chapman, R. E., and
   Hannibal, J. T., eds., Paleotechniques: Paleontological
   Society Special Publication 4, p. 70Ð86.
Orchard, M.J., 1987, Conodonts from western Canadian chert;
   Their nature, distribution and stratigraphic
   application, in Austin, R. L., eds., Conodonts;
   Investigative techniques and applications: Chichester,
   U.K., Ellis Horwood Ltd. and British
   Micropalaeontological Society, p. 94Ð119.
Pawlewicz, M.J., 1987, Polishing method for dispersed
   vitrinite and coal slides: The Society for Organic
   Petrology Newsletter, v. 4, p. 1.
Rejebian, V.A., Harris, A.G., and Huebner, J.S., 1987,
   Conodont color and textural alteration; an index to
   regional metamorphism, contact metamorphism, and
   hydrothermal alteration: Geological Society of America
   Bulletin, v. 99, p. 471Ð479.
Stone, J., 1987, Review of investigative techniques used in
   the study of conodonts, in Austin, R.L., ed.,
   Conodonts; Investigative techniques and applications:
   Chichester, U.K., Ellis Horwood Ltd. and
   British Micropalaeontological Society, p. 17Ð34.