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Published by

STATE OF ALASKA

DEPARTMENT OF NATURAL RESOURCES

DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYS

2006

Report of Investigations 2006-1

YUKON FLATS BASIN, ALASKA: RESERVOIRCHARACTERIZATION STUDY

byR.R. Reifenstuhl

Reifenstuhl—

YU

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ASIN

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GG

S Report of Investigations 2006-1

Report of Investigations 2006-1


by

R.R. Reifenstuhl

2006

This DGGS Report of Investigations is a final report of scientific research.It has received technical review and may be cited as an agency publication.

Division of Geological & Geophysical Surveys publications can be inspected at thefollowing locations. Address mail orders to the Fairbanks office.

Alaska Division of Geological University of Alaska Anchorage Library& Geophysical Surveys 3211 Providence Drive3354 College Road Anchorage, Alaska 99508Fairbanks, Alaska 99709-3707

Elmer E. Rasmuson Library Alaska Resource LibraryUniversity of Alaska Fairbanks and Information Services (ARLIS)Fairbanks, Alaska 99775-1005 3150 C Street, Suite 100

Anchorage, Alaska 99503

Alaska State LibraryState Office Building, 8th Floor333 Willoughby AvenueJuneau, Alaska 99811-0571

STATE OF ALASKAFrank Murkowski, Governor

DEPARTMENT OF NATURAL RESOURCESMike Menge, Commissioner

DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYSRobert F. Swenson, Acting State Geologist and Acting Director

This publication released by the Division of Geological & Geophysical Surveys wasproduced and printed in Fairbanks, Alaska at a cost of $3 per copy. Publication is requiredby Alaska Statute 41, “to determine the potential of Alaskan land for production ofmetals, minerals, fuels, and geothermal resources; the location and supplies of groundwaterand construction materials; the potential geologic hazards to buildings, roads, bridges,and other installations and structures; and shall conduct such other surveys andinvestigations as will advance knowledge of the geology of Alaska.”

ii

iii

CONTENTS

Abstract ................................................................................................................................................................... 1Introduction ............................................................................................................................................................. 1Background ............................................................................................................................................................. 2Porosity and Permeability Methodology ................................................................................................................. 3Petroleum geology framework ................................................................................................................................. 4Porosity, permeability, and petrographic overview of drill core and outcrop samples ............................................ 4Conclusions ............................................................................................................................................................. 11Acknowledgments ................................................................................................................................................... 11References cited ...................................................................................................................................................... 11

TABLES

Table 1. Porosity, permeability, location, age (if known), lithology, and vitrinite reflectance (Ro)for 26 Exxon drill core samples from the Yukon Flats basin and basin perimeter .................................. 5

2. Summary of petrographic analyses of framework grain size mean, maximum, andminimum for the Exxon drill core samples from Yukon Flats basin and basin perimeter .................. 7

3. Porosity, permeability, location, and stratigraphic information for 11 outcrop samplesfrom the Yukon Flats basin .................................................................................................................... 7

FIGURES

Figure 1. Location map with color Digital Elevation Model (DEM) base showing east-central Alaskaand Yukon Flats basin ........................................................................................................................... 2

2. General geologic map of the Yukon Flats basin and basin margin ........................................................ 33. Graph showing porosity versus permeability for Yukon Flats basin drill core samples ....................... 44. Graph showing porosity versus permeability for Yukon Flats basin-fill sandstone;

typically Tertiary age ............................................................................................................................. 65. Quartz–Feldspar–Lithic Folk sandstone classification diagram, Yukon Flats basin core

hole samples .......................................................................................................................................... 86. Tectonic setting plot [quartz–feldspar–lithic (includes chert)] of Yukon Flats basin core

hole samples .......................................................................................................................................... 97. Tectonic setting plot [quartz (total)–feldspar–lithic] of Yukon Flats basin core hole samples ............. 10

APPENDICES

Appx 1. Summary of petrography ....................................................................................................................... 132. Yukon Flat basin and basin perimeter drill core photomicrographs ...................................................... 20

AbstractThe Yukon Flats basin is located in east-central Interior Alaska. To characterize the potential siliciclastic

reservoirs of selected Tertiary outcrop samples and selected Exxon core material, 26 Exxon drill coresamples were analyzed for porosity and permeability (P&P), and petrographic composition. The Exxondrill hole locations were on the basin margins. In addition to the core samples, 40 outcrop samples werecollected from Tertiary basin fill. Gravity and seismic geophysical information suggest 4,575-m-thickdepocenters locally. Potential energy resources include coalbed methane, shalebed methane, and conven-tional gas and oil. A summary of the P&P data from the basin margin cores includes porosities of 1.1 to11.7 percent (average about 4 percent) and permeabilities of 0.001 to 171.3 millidarcies (average 0.4 md).A summary of the P&P data from the 11 Yukon Flats basin outcrop samples includes porosities of 2.7 to38.7 percent (average about 13 percent) and permeabilities of 0.006 to 203 md (average about 20 md). P&Preduction is common in the vast majority of the drill core sandstones, in which ductile grains (shale,mudstone, argillite, and phyllite) total from 2 to 27 percent. Potential reservoir sandstones crop out north-east of Rampart, along the Yukon River, where a more-than-1-km-thick stratigraphy of probable Eoceneunits includes thick, meandering stream deposits of sandstone, conglomerate, and lignite coal beds up to10 cm thick. At Schieffelin Creek, on the Yukon River, several hundred meters of Eocene to Oligocenefluvial sandstone, pebbly sandstone with lesser conglomerate, and minor coal are well exposed and yieldgood petrophysical characteristics (8.8 md permeability and 15.8 percent porosity). Petrographically, drillcore samples from the Yukon Flats basin perimeter wells range from litharenite sandstone (10 samples), tosublitharenite sandstone (1 sample), to quartzarenite sandstone (1 sample), and are erosional products of aprovenance dominated by quartz-rich and chert-rich rocks, with lesser contributions from quartz-poorrocks such as shale, mafic and intermediate igneous rocks, and metamorphic rocks. Seven of the 12 point-counted drill core sandstones are volcaniclastic-rich and Paleogene to Eocene age.

1Alaska Division of Geological & Geophysical Surveys, 3354 College Rd., Fairbanks, Alaska 99709-3707Email: [email protected]


byRocky R. Reifenstuhl1

INTRODUCTIONThe Yukon Flats basin is located in east-central Inte-

rior Alaska (fig. 1). The goal of this study is tocharacterize the potential siliciclastic reservoirs of se-lected Tertiary outcrop samples and selectedbasin-perimeter, drill hole core material. This reservoircharacterization study is an element of the federally-funded Yukon Flats basin project, a collaborative effortby the U.S. Geological Survey (USGS) and DGGS toevaluate the basin’s petroleum potential. Integration ofthis study with the USGS work will result in a more ac-curate evaluation of the principal target reservoirs andenergy potential of the Yukon Flats basin. More infor-mation regarding the USGS oil and gas assessment ofthe Yukon Flats can be found at: http://pubs.usgs.gov/fs/2004/3121/ and http://energy.cr.usgs.gov/oilgas/noga/

Twenty-six Exxon drill core samples were analyzedfor porosity and permeability; 12 of these were analyzedpetrographically and point counted during 2002. TheExxon drill hole locations were sited on the basin mar-gins. In addition to the core samples, about 40 outcropsamples were collected during July and September 2002fieldwork. Ten of the outcrop samples were analyzed

for porosity and permeability, and 15 were examinedpetrographically.

To summarize and place into perspective, Yukon Flatsbasin porosity and permeability data are described us-ing the classification framework of North (1985):Porosity (in percent), 0–5 negligible, 5–10 poor, 10–15fair, 15–20 good, >20 very good; Permeability (inmillidarcies), <1.0–15 poor to fair, 15–50 moderate, 50–250 good, 250–1,000 very good, >1,000 excellent.Porosity values of Yukon Flats basin core samples (withnumber of samples falling into each range shown in pa-rentheses) are: negligible (15), poor (6) and fair (2), andpermeability is poor to fair (23). Porosity values of YukonFlats basin outcrop samples are: negligible (2), poor(3) fair (1) and good (3), and permeability is poor to fair(7), and moderate (3).

The core material is from shallow core holes drilledby Exxon from 1985 through 1987 primarily to deter-mine source rock potential around the Yukon Flats basinmargin (fig. 2). Although the main objective of the Exxondrilling was to evaluate source rock potential near theYukon Flats basin margin, reservoir potential was a sub-

2 Report of Investigations 2006-1

ordinate consideration. As a consequence, most non Ter-tiary-age sandstones yield poor reservoir characteristics.Doyon Native Corporation currently holds the core ma-terial and provided access. Thousands of meters of corematerial were examined; 26 potential reservoir sand-stones were selected. These 26 siliciclastic sandstonespecimens were selected based on visual attributes sug-gesting potential reservoir characteristics.

BACKGROUNDReservoirs are key components of petroleum sys-

tems—they provide the storage for hydrocarbons intowhich companies drill to extract oil and gas. Petroleumreservoir characterization is the complex process of iden-tifying and quantifying properties that influence thedistribution and migration of oil or gas within a reser-voir. Studying the geologic details of known and potentialreservoirs allows for simulation of different economicscenarios essential to reservoir development and pro-duction management. Reservoir characterization studies

can be done from well core, down-hole geophysical in-formation, surface geophysical information, or surfacebedrock exposures. The ultimate goal of this reconnais-sance-level study is to develop reasonable physicaldescriptions of potential reservoirs that will minimizeexploration, development, and production costs as wellas financial risks while maximizing hydrocarbon recov-ery potential.

In this report, potential reservoirs are being charac-terized and quantified using petrophysics (porosity andpermeability) and detailed thinsection petrography. Pet-rographic study includes counting sandstone grain types,measuring grain size, determining what kind of cementbinds the sandstone, and when, during the geologic his-tory of the sandstone, that cement formed. Additionally,the details and distribution of the sandstone reservoirrock types are considered within a reconnaissance geo-logic framework. Reconnaissance geologic mappingindicates that sandstone bedrock exposures are relativelyuncommon within the basin.

!

!

!

!

FAIRBANKS

RAMPART LIVENGOOD

FORT YUKON

Ruby-Rampart Trough

Preacher Creek Fault

Tintina Fault ZoneHot Springs Fault

Yukon R ive r

EAGLE

CIRCLE

TANANA

COLEEN

CHRISTIAN

LIVENGOOD

FORT YUKON

BIG DELTA

BLACK RIVER

CHARLEY RIVER

FAIRBANKS

KANTISHNA RIVER

150°W 147°W 144°W 141°W

65°N

65°N

66°N

66°N

67°N

67°N

68°N

Porcupine River

Fish Hook Bend

Deacons Rock

"No Name" Creek

The Mudbank onHodzana River

North ForkPreacher Creek

Little WashingonCreek

Crooked Creek

Bryant CreekSchieffelin Creek

MooseHide Bluffs

Maypole HillDrew Mine

Kaltag Fault Zone

Yukon Flats Basinand map location

50 km ¯

Sample locations

Quadrangle

Rivers/streams

Faults

Towns

200 km

Figure 1. Location map with color Digital Elevation Model (DEM) base showing east-central Alaska and YukonFlats basin. Figure shows major geologic units, field sample locations, quadrangle index, major fault zones,and reported localities of tasmanite (organic shale containing a significant percentage of palynomorphs of thegenus Tasmanites).

Yukon Flats Basin, Alaska: Reservoir characterization study 3

POROSITY AND PERMEABILITYMETHODOLOGY

Porosity and permeability (P&P) data obtained fromcore and surface outcrops can serve as a useful screen-ing tool in the search for potential petroleum reservoirs.P&P data are useful in evaluating reservoir potentialwhen they are integrated with petrographic details, rockbody geometry, and depositional environment. Porosityis the percent volume of pore space of the rock that isavailable to store oil or gas. Permeability (reported asmillidarcies, or md) is a measure of how well connectedthese pore spaces are. If permeability is reasonably high,hydrocarbons in the pore space of a reservoir can flowthrough the rock and reach the wellhead for successfuleconomic oil and gas recovery. However, it is possibleto have oil trapped in a reservoir with little or no per-meability, making hydrocarbon mobility and extractiondifficult. Low porosity and permeability of reservoirsare significant technical problems that limit produc-tion in petroleum basins worldwide. P&P data havebeen obtained from producing reservoirs and potentialreservoirs for decades by petroleum companies operat-ing throughout Alaska, but very little of this informationis publicly available. Likewise, although state, federal,and university geologists may have collected potential

reservoir data from the Yukon Flats basin, no public orpublished source exists for this information.

From the Yukon Flats basin and basin perimeter, 26drill hole core sandstones and 10 outcrop sandstoneswere selected for P&P analyses. Fifteen outcrop-derivedsandstone thinsections were petrographically examined.Twelve of the drill core samples were selected for addi-tional detailed petrographic point counting analysis. Forthe porosity and permeability analyses, each sample isdrilled, resulting in a 2.5-cm-diameter core plug. Nextthe plug is tested with nitrogen gas for its flow capacity.The sandstones are measured for grain volume, bulkvolume, and sample weight. These quantitative data arenecessary to calculate porosity, permeability, and graindensity. Details of individual sandstone grain boundaries,sandstone cement type, geologic timing of cementation,and visible porosity are evaluated using thinsections anda petrographic microscope.

Petrographic point counting involves selecting rep-resentative fine-grained sandstones from rock units ofinterest and systematically identifying and tabulating themineral composition of 400 framework grains. Resultsare plotted on diagrams that yield a sandstone classifi-cation and an inferred tectonic environment of deposi-tion for the sandstone. These are useful for comparison

Figure 2. General geologic map of the Yukon Flats basin and basin margin. General airborne magnetic trends are shown,along with localities of reported tasmanite (an organic-rich shale with abundant palynomorphs of the genus Tasmanites).From Scott and others (1998) based on Kirschner (1994).


of sandstones within the Yukon Flats basin and for com-parison of sandstone reservoirs globally. The composi-tion of potential reservoir sandstones is fundamental tounderstanding its viability as a reservoir rock.

PETROLEUM GEOLOGYFRAMEWORK

The Yukon Flats basin is located in east-centralAlaska, between the Trans-Alaska pipeline and the Ca-nadian border, and contains known coal-bearing strataon the western, southwestern, and southeastern margins.The Yukon Flats basin is considered to be a latest Creta-ceous and Cenozoic sedimentary basin that formed dueto extensional forces. These pull-apart forces are asso-ciated with movement along the well known and welldocumented Tintina and Kaltag fault systems (Kirschner,1994; fig. 1). The Tintina fault system extends south-eastward into Yukon Territory, Canada, where it formsthe southwest boundary of the Whitehorse trough. TheTintina and Kaltag faults are similar in nature to the wellknown San Andreas fault system in southern California.

Gravity and seismic geophysical information suggestthat this Yukon Flats basin is locally filled with at least5,000 m of nonmarine sediments consisting of three thickrock packages, each including different proportions of

lake and river sediments (Kirschner, 1994). The lakesediments in the Yukon Flats basin may include oil-proneor gas-prone organic material. Oil and gas plays includereservoir sandstones that might trap hydrocarbons in ei-ther a fault-related structure or in a structure that isformed by a non-permeable layer (topseal) overlying aporous and permeable sandstone layer (reservoir). Lakesediments can act as both topseals and as source rock.Petroleum generation is estimated to be possible belowthe 2,130 to 3,050 m region based on a typical increaseof temperature with depth gradient that is reasonable foran interior basin (Kirschner, 1994; R.G. Stanley, USGS,personal commun., 2002). Potential energy resourcesinclude coalbed gas, shalebed methane, conventional gas,and oil.

POROSITY, PERMEABILITY, ANDPETROGRAPHIC OVERVIEW OFDRILL CORE AND OUTCROPSAMPLES

A summary of the porosity and permeability datafrom the 24 Yukon Flats basin margin drill cores includesporosity of 1.1 to 11.7 percent (average about 4 percent)and permeability of 0.001 to 171.3 md (average about0.4 md; fig. 3; table 1). A summary of the porosity and

Figure 3. Porosity versus permeability for Yukon Flats basin drill core samples. These samples are fromthe Exxon shallow drill core material from their sites around the perimeter of the Yukon Flats basin.Core plugs (2.5-cm diameter) are cut from the Exxon core. The plug is then measured for its capac-ity for flow to nitrogen gas as well as grain volume, bulk volume, and weight. Porosity, permeability,and grain density are derived from these data and are critical information related to oil and gasreservoirs.


Table 1. Porosity, permeability, location, age (if known), lithology, and vitrinite reflectance (Ro) for 26 Exxon drillcore samples from the Yukon Flats basin and basin perimeter. Analyses by Core Laboratories, Denver, Colo-rado. See text for explanation of porosity and permeability methodology. See table 2 for framework grainsummary statistics; see appendix for photomicrographs.

Sample Permeability Helium GrainIdentification Air Klink Porosity Density

Number (md) (md) (%) (g/cc) Rock Unit

85-23-23 0.6975 0.5171 10.12 2.65 Bryant Creek, early to middle Eocene, conglomerate,Ro=0.60-0.76

85-23-66 0.5128 0.3666 8.56 2.59 Bryant Creek, early to middle Eocene, sandstone?,Ro=0.60-0.76

85-23-136 0.0006 0.0001 3.65 2.72 Bryant Creek, early to middle Eocene, sandstone,Ro=0.60-0.76

85-26-68.5 0.0016 0.0003 2.27 2.68 Eagle trough, middle to late Albian, sandstone,Ro=0.53-0.61

85-26-106.5 0.0033 0.0008 1.87 2.67 Eagle trough, middle to late Albian sandstone,Ro=0.53-0.61

85-26-110.5 0.0243 0.0103 1.96 2.67 Eagle trough, middle to late Albian sandstone,Ro=0.53-0.61

85-27-22 0.0127 0.0046 7.50 2.65 Step Mountain, Late Triassic to Jurassic shale,Ro=3.03

85-30-121 172.31766 153.56833 7.57 2.76 Drew Mine, early Eocene sandstone, Ro=0.37-0.4585-31-18 0.2045 0.1287 11.71 2.69 Maypole Hill, early Eocene sandstone, Ro=0.52-0.5986-3-8 0.0108 0.0037 3.90 3.04 Coal Creek, Oligocene, lithology not on core record,

Ro=0.3586-5-38 0.1712 0.1051 7.86 2.59 Preacher Creek, Paleogene, conglomerate, Ro=0.90-

1.0286-5-67 0.0026 0.0006 2.54 2.72 Preacher Creek, Paleogene, claystone, Ro=0.90-1.0286-6-17 0.0015 0.0003 1.68 2.64 No Name Creek No. 1, Paleocene or Eocene,

lithology?, Ro=.96-1.086-6-41 0.0012 0.0002 1.54 2.67 No Name Creek No. 1, Paleocene or Eocene, silty

shale, Ro=.96-1.086-7-37 0.0019 0.0004 1.55 2.67 No Name Creek No. 2, Paleocene or Eocene

sandstone86-7-66 0.0020 0.0004 1.31 2.66 No Name Creek No. 2, Paleocene or Eocene

sandstone86-7-96 0.0004 0.0001 1.18 2.67 No Name Creek No. 2, Paleocene or Eocene siltstone86-7-120 0.0099 0.0033 5.86 2.71 No Name Creek No. 2, Paleocene or Eocene

sandstone86-8-54 0.0004 0.0001 0.58 2.73 No Name Creek No. 2, late Paleocene-Eocene

siltstone, Ro=-.70—.8786-9-35 0.7107 0.5281 1.05 2.72 No Name Creek No. 1, probable Paleogene siltstone,

Ro=1.1986-9-39 0.0145 0.0054 4.16 2.67 No Name Creek No. 1, probable Paleogene

sandstone, Ro=1.1987-8-95 0.0044 0.0011 5.66 2.65 Hodzana River No. 2, age?, lithology not recorded,

Ro=3.41=3.9787-10-92 0.0220 0.0091 2.66 2.67 Grayling Fork Jurassic-Cretaceous, lithology?,

Ro=4.26-4.9286-9-59.5 Sample Failed No Name Creek No. 1, probable Paleogene

conglomerate, Ro=1.1985-30-100 Sample Unsuitable 2.58 Drew Mine, early Eocene sandstone, Ro=0.37-0.4586-8-60 Sample Unsuitable 2.62 No Name Creek No. 2, late Paleocene- Eocene

siltstone, Ro=.70-.87


permeability data from the 11 Yukon Flats basin out-crop samples includes porosity of 2.7 to 38.7 percent(average about 13 percent) and permeability of 0.006 to203 md (average about 20 md; fig. 4; table 3). Summa-rizing all Yukon Flats basin petrophysical data foroutcrop samples using the qualitative terminology ofNorth (1985) (with numbers of samples in parentheses)yields: porosity that is negligible (2), poor (3), fair (1),good (3); permeability results that are poor to fair (7),and moderate (3); and core sample porosity that is neg-ligible (15), poor (6) and fair (2); and permeability thatis poor to fair (23).

Distinguishing between analytical data from theExxon basin-margin drill core samples and the DGGS-collected, basin-fill, outcrop samples is important, asoutcrop samples consistently yield higher petrophysicalvalues relative to core samples

Exxon’s shallow drilling program focused primarilyon the source rock potential of the basin-margin rocks.These potential hydrocarbon source rocks would, pre-sumably, extend beneath the Yukon Flats basin, charginghydrocarbon plays within the basin. Reservoir rock wasa secondary objective for the Exxon basin and basin-margin shallow drilling project. Porosity andpermeability of the sandstone samples from the shallowdrilling program are relatively low, as a consequence ofExxon’s focus on source rock. In summary, this smallsample number (24) of basin and basin-margin sand-

stones indicates generally poor petrophysical character-istics for hydrocarbon reservoirs (fig. 3; tables 1 and 2).In contrast, DGGS-collected outcrop samples from theTertiary-age Yukon Flats basin fill suggest locally goodreservoir potential with encouraging porosity and per-meability characteristics (fig. 4; table 3).

Petrography of Yukon Flats basin-perimeter drill coresamples ranges from litharenite sandstone (10 samples),sublitharenite sandstone (1 sample) to quartzarenite sand-stone (1 sample; fig. 5). The petrographic protocol isthat of Decker (1985), Van der Plas and Tobi (1965),and Dickinson (1970); 300 framework grains werecounted on each of 12 drill core thinsections. Only onedrill core sandstone (SA86-27-22) is composed of morethan 95 percent quartz; it plots as a compositionally purequartzarenite. This basin-margin sandstone from the StepMountain area east of the Yukon Flats basin is Late Tri-assic to Jurassic age, with less than 0.01 md permeability,and about eight percent porosity. Compositionally, thequartzarenite is anomalous quartz rich relative to the re-maining 11 drill core samples.

Porosity and permeability reduction is common inthe vast majority of the drill core sandstones. Ductilegrains, such as shale, mudstone, argillite, and phyllite,total from 2 to 27 percent, averaging about 13 percent inthe drill core sandstone samples. Abundance of ductilerock fragments in most of the drill core sandstones de-creases their viability as potential reservoirs due to the

Figure 4. Porosity (percent) on vertical axis versus permeability (millidarcies[md]) on horizontal axis for Yukon Flats basin-fill sandstone; typically Ter-tiary age. Core plugs (2.5-cm diameter) are cut from the outcrop sample,which is then measured for its capacity for flow to nitrogen gas as well asfor grain volume, bulk volume, and weight. Porosity, permeability, and graindensity are derived from these data and are critical information related tooil and gas reservoirs.


Tabl

e 2.

Sum

mar

y of

pet

rogr

aphi

c an

alys

es o

f fra

mew

ork

grai

n si

ze m

ean,

max

imum

, and

min

imum

for

the

Exxo

n dr

ill c

ore

sam

ples

from

Yuk

on F

lats

bas

in a

ndba

sin

peri

met

er (p

etro

grap

hic

anal

yses

by

Mic

hael

D. W

ilson

, Col

orad

o).

Petr

ogra

phic

Sum

mar

y St

atis

tics,

Yuko

n Fl

ats B

asin

Cor

e H

ole

Dat

a

Cor

e ho

le S

A#-

dept

h (f

t)85

-23-

136

85-2

6-68

86-3

-15

85-2

3-83

85-2

7-22

85-3

1-18

86-5

-67

86-7

-79

86-7

-120

86-9

-39

87-1

0-92

87-8

-95

Mea

n gr

ain

size

(mm

)0.

079

0.30

80.

111

0.10

90.

216

0.24

30.

232

0.15

20.

326

0.25

30.

057

0.14

3St

anda

rd d

evia

tion

(mm

)0.

149

0.63

80.

158

0.11

90.

074

0.23

40.

309

0.05

60.

154

0.09

0.25

30.

199

Mea

n fr

amew

ork

frac

tion

0.11

70.

429

0.14

10.

128

0.21

60.

275

0.28

90.

152

0.32

60.

253

0.15

50.

186

(>30μm

)(m

m)

Stan

dard

dev

iatio

n of

0.03

40.

211

0.05

0.04

90.

073

0.09

60.

110.

056

0.15

30.

090.

071

0.06

1fr

amew

ork

grai

ns(>

30μm

)(m

m)

Min

ium

size

val

ue (m

m)

0.00

020.

0004

0.00

020.

0004

0.08

480.

0007

0.00

070.

0664

0.12

020.

1021

0.00

020.

0004

Max

imum

size

val

ue (m

m)

0.27

71.

308

0.34

10.

346

0.67

0.77

40.

801

0.43

72.

055

0.62

30.

929

0.53

4

Tabl

e 3.

Por

osity

, per

mea

bilit

y, lo

catio

n, a

nd st

ratig

raph

ic in

form

atio

n fo

r 11

outc

rop

sam

ples

from

the

Yuko

n Fl

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asin

. See

text

for p

oros

ity a

nd p

erm

eabi

lity

met

hodo

logy

. See

figu

re 4

for g

raph

ical

pre

sent

atio

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Sam

ple

Per

mea

bilit

yH

eliu

mG

rain

Iden

tific

atio

nA

irK

link

Poro

sity

Den

sity

Num

ber

(md)

(md)

(%)

(g/c

c)R

ock

unit,

com

men

ts, l

atitu

de-lo

ngitu

de

02R

R37

E0.

552

0.39

838

.72.

6466

.686

04, 1

48.3

5004

, Hod

zana

Riv

er (R

.), ‘M

udba

nk’,

ss/c

oal

02R

R38

B22

520

326

.52.

6965

.541

33, 1

50.1

1760

, Yuk

on R

iver

, 10

km E

Ram

part,

1 k

m s

ectio

n02

RR

38C

32.5

27.1

24.0

2.69

65.5

4133

, 150

.117

60, Y

ukon

Riv

er, 1

0 km

E R

ampa

rt, 1

km

sec

tion

02R

R38

H10

.68.

149.

32.

6865

.541

33, 1

50.1

1760

, Yuk

on R

iver

, 10

km E

Ram

part,

1 k

m s

ectio

n02

RR

39B

0.33

30.

223

8.1

2.71

65.6

6865

, 149

.823

46, Y

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Figure 5. Quartz–Feldspar–Lithic Folk sandstone classification diagram, Yukon

resulting high degree of intergranular porosity reduction.In these sandstones with abundant ductile frameworkgrains, intergranular porosity is reduced primarily byplastic grain deformation. Other means of porosity re-duction in these sandstones include quartz and chertsuturing, and siderite cementation. Photomicrographs inthe appendix show some of these textural, grain size,and grain-boundary relationships.

Drew Mine drill core sandstone yields anomalouslyhigh permeability (154 md) and good porosity (7.7 per-cent; fig. 3, table 1). This sandstone was not selected forthinsectioning and petrographic examination. This wasbecause most, though not all, core samples that wereanalyzed for petrophysics were cut for thinsection. None-theless, Drew Mine core yields high porosity andpermeability and merits further investigation.

Maypole Hill drill core sandstone yields anomalouslyhigh porosity (11.7 percent) yet the permeability remains<1 millidarcy (0.13 md) due to occlusion of pore throats.The mechanism of pore connectivity reduction in theMaypole Hill sandstone is most likely due to the alter-ation of mafic volcanic rock fragments that are commonin the sandstone.

The vast majority of sandstone bodies visited duringthe field program yielded petrophysical analyses indi-cating fair to good potential reservoir quality. Similarly,these samples were reasonably quartz and chert rich (figs.5–7). Therefore, the extrapolated reservoir characteris-tics for the Tertiary section of the Yukon Flats basin ishere interpreted to be generally fair, with locally goodreservoir quality. Based on the small number of pre-Ter-tiary age drill core sandstones analyzed for this study,hydrocarbon reservoir quality in the Yukon Flats basinmargin is considered poor.

Sandstone reservoir viability is affected by grain sizeand grain-size distribution. Consequently these data werecollected for drill core samples (table 2). One hundredframework grain size measurements were recorded fromeach drill core sandstone thinsection. Individual sand-stone samples range from a framework grain size meanof 0.079 mm (very fine sand) to a grain size mean of0.33 mm (medium sand). Eight of the 12 point-countedsandstone core samples are fine grained (0.125 to 0.25mm). Sandstone grain measurements and standard de-viation are shown in table 2.


Figure 6. Tectonic setting plot [quartz–feldspar–lithic (includes chert)] of Yukon Flatsbasin core hole samples. Eleven of 12 sandstones plot in one of the ‘Recycled’ fieldsand one sandstone plots in the ‘Craton Interior’ field. This plot includes chert grainswith the lithic components. The consequence is a significant shift toward the lithicpole of any chert-rich sandstone. When compared with figure 5 it graphically con-veys the influence of the chert component relative to other lithic grains.

Chert is an abundant framework grain in severalsamples. The Jurassic- to Cretaceous-age Grayling Forksandstone core contains 67 percent chert. The middle tolate Albian age Eagle Trough sandstone includes 36 per-cent chert. The Paleocene age Preacher Creek sandstoneincludes 33 percent chert. The Bryant Creek sandstoneincludes 31 percent chert. The Early Eocene age May-pole Hill sandstone core includes 20 percent chert. TheOligocene(?) age Coal Creek sandstone includes 16 per-cent chert. Abundant chert in these samples suggestserosion of a recycled orogenic provenance or a transi-tional recycled provenance of the Dickinson and others(1983) classification (figs. 6 and 7).

Outcrop samples—Outcrops of the fluvial sandstoneof the early Tertiary age basin fill were sampled during

the several-day helicopter-supported field program. Thelocalities where outcrop sandstones were collected areshown in figure 1. Ten outcrop sandstones were ana-lyzed for porosity and permeability, and 15 thinsectionswere examined petrographically.

Promising potential reservoir sandstones crop out justnortheast of the town of Rampart. Here, along the YukonRiver, a more than 1-km-thick stratigraphic section ofprobable Eocene age (Reifenstuhl and others, 1997b)includes thick, meandering stream deposits of sandstone,conglomerate, and coal. In outcrop, sandstone rangesfrom very light gray to nearly white, and from light brownto orange-brown. Sandstone is typically poorly sortedand contains up to 10 percent finely disseminated or-ganic material. Polymictic conglomerate is up to 10 m


thick, locally cuts into sandstone and silty mudstone,contains less than 10 percent organic debris, with rarelogs up to 1.5 m long and 20 cm in diameter. Coal bedsare up to 10 cm thick and are a minor stratigraphic com-ponent. Coal grade appears to be lignite.

At Schieffelin Creek, on the Yukon River, severalhundred meters of Eocene to Oligocene age fluvial sand-stone, pebbly sandstone with lesser conglomerate, andminor coal are well exposed. These bedload-dominatedbraided stream deposits suggest good reservoir poten-tial in outcrop, are stratigraphically similar to the Rampartlocality, and yield good petrophysical characteristics (8.8md and 15.8 porosity; fig. 4; table 3).

Sandstones from the Rampart and Schieffelin Creeklocalities are promising potential reservoirs due to rela-tively low ductile grain percentages and relatively highmeasured porosity and permeability (fig. 4; table 3).Ductile lithic grains constitute a significantly lower per-centage at these outcrop localities relative to the Tertiaryage drill core sandstones, and relative to sandstone at

the Drew Mine, Maypole Hill, Bryant Creek, andPreacher Creek localities.

The sandstone at the ‘mudbank’ locality on theHodzana River has impressive petrophysical results (fig.4; table 3), but these clastic deposits are poorly lithified,poorly indurated, and of unknown age. Based on out-crop relationships, nature of organic material, andlocation within the basin, ‘mudbank’ sandstone, siltyshale, and organic-bearing deposits are interpreted to bevery young, and high in the stratigraphic section. Con-sequently ‘mudbank’-equivalent stratigraphy is unlikelyto be buried deep enough and in a position within a po-tential Yukon Flats basin petroleum system.

Geologic setting and source area of sandstoneunits—The tectonic provenance of the Yukon Flats ba-sin sandstones is determined using models developedby Dickinson and Suczek (1979) and Dickinson and oth-ers (1983; figs. 6 and 7). These models have been appliedto sandstones worldwide and to sandstone from otherAlaska basins (Reifenstuhl and Reifenstuhl, 2003;

Figure 7. Tectonic setting plot [quartz (total)–feldspar–lithic] of Yukon Flats basin core holesamples. Eleven of 12 sandstones plot in the ‘Recycled Orogen’ field and two plot in the‘Craton Interior’ field


Reifenstuhl and others, 1997a; Wartes and Reifenstuhl,1997; Reifenstuhl, 1995; Reifenstuhl, 1991). The 12point-counted drill hole samples from the Yukon Flatsbasin are erosional products of a provenance dominatedby quartz-rich and chert-rich rocks, with lesser contri-butions from rocks that are quartz poor, such as shale,mafic and intermediate igneous rocks, and metamorphicrocks. One sample (from the Step Mountain area) indi-cates a strictly quartz-rich source (fig. 5). This quartz-richsample is the Triassic- to Jurassic-age sandstone thatcrops out east of the Yukon Flats basin. This sandstonewas derived from a craton interior (figs. 6 and 7).

Seven of the 12 point-counted drill core sandstonesare volcaniclastic-rich (figs. 6 and 7) and Paleogene toEocene age (table 1). These seven volcaniclasticlitharenite sandstones were deposited during and after atime of documented, locally important continental rift-ing and bimodal volcanism in the Rampart area(Reifenstuhl and others, 1997b). This volcanism wasprobably related to crustal thinning and tectonism alongthe Tintina Fault system. Consequently, these mafic vol-canic-rich sandstones of Paleogene to Eocene age recorderosion of basalt and rhyolite uplands and are corre-spondingly rich in volcanic lithic fragments.

CONCLUSIONSSummarizing all Yukon Flats basin petrophysical data

using the qualitative terminology of North (1985), out-crop samples yield porosity that is negligible (2 samples),poor (3), fair (1), good (3) and permeability that is poorto fair (7), moderate (3); core sample porosity is negli-gible (15), poor (6) fair (2), and permeability is poor tofair (23).

To summarize the outcrop petrographic data: twodistinct groups are evident and supported by thepetrophysical results. Sandstones cropping out atSchieffelin Creek and northeast of Rampart aresubarenite sandstone rich in quartz and chert, and rela-tively poor in ductile grains. These sandstones have alow percentage of volcanic rock fragments and their pore-clogging alteration products. Sandstones at these YukonRiver sections yield good reservoir characteristics asdefined by porosity, permeability, and petrology. Con-versely, sandstone outcrops at Maypole Hill and NoName Creek are litharenite sandstones with either abun-dant volcanic rock fragments or ductile lithic grains.Consequently, outcrop sandstones from Maypole Hill andNo Name Creek yield poor reservoir characteristics.

Drew Mine drill core sandstone yields very high per-meability (154 md) and good porosity (7.6%). Nooutcrop samples were analyzed for petrophysics fromthis locality. Petrographically Drew Mine sandstone isvery poorly sorted, greenish dark gray litharenite sand-stone, containing abundant volcanic rock fragment.

These characteristics suggest that it is unlikely to havegood porosity or clear pore throats.

Viable reservoir characteristics are documented insandstones from outcrops at Schieffelin Creek and north-east of the town of Rampart. Drew Mine drill coresandstone is not well constrained by the current recon-naissance data set. Additional sampling is required tounderstand the reservoir characteristics of sandstones atDrew Mine.

Drill core sandstones are from both basin fill, andbasin margin stratigraphy. Generally the basin marginsandstones yield poor reservoir characteristics: low po-rosity, low permeability, high percentage of ductile,pore-filling framework grains, and quartz overgrowths.Siderite cementation commonly reduces pore space. Ofthe 23 drill core sandstones, only one has greater than 1md permeability. Eighteen of the 23 drill core sandstonesare of Tertiary age and, in any basin model or petroleumplay model, must be considered to be Yukon Flats basinfill. The remaining five drill core sandstones are consid-ered to be basin margin stratigraphy. Porosity values ofthe Tertiary age sandstone are generally better than thatof basin margin sandstones (fig. 3; table 1). For example,six of the 18 Tertiary-age sandstones have more than 6percent porosity. However, 22 of 23 drill core sandstoneshave less than 1 md permeability.

ACKNOWLEDGMENTSI thank Rick Stanley (U.S. Geological Survey) for

reviewing an earlier version of this report. I also thank asecond reviewer who requested anonymity.

REFERENCESDecker, John, 1985, Sandstone modal analysis proce-

dure: Alaska Division of Geological & GeophysicalSurveys Public-data File 85-3 p. 1–35.

Dickinson, W.R., 1970, Interpreting detrital modes ofgraywacke and arkose: Journal of Sedimentary Pe-trology, v. 40, p. 695–707.

Dickinson, W.R., and Suczek, C.A., 1979, Plate tecton-ics and sandstone compositions: The American As-sociation of Petroleum Geologists, v. 63, no. 12, p.2164–2182.

Dickinson, W.R., Beard, L.S., Brakenridge, G.R.,Erjavec, J.L., Ferguson, R.C., Inman, K.F., Knepp,R.A., Lindberg, F.A., and Ryberg, P.T., 1983, Prov-enance of North American Phanerozoic sandstonesin relation to tectonic setting: Geological Society ofAmerica Bulletin, v. 94, no. 2, p. 222–235.

Folk, R.L., 1974, Petrology of sedimentary rocks: Aus-tin, Texas, Hemphill Publishing Company, 182 p

Kirschner, C.E., 1994, Interior basins of Alaska, inPlafker, G., and Berg, H.C., eds., The Geology of


Alaska: Boulder, Colorado, Geological Society ofAmerica, The Geology of North America, v. G-1,p.469–493.

North, F.K., 1985, Petroleum geology: Unwin HymanInc, Winchester, Mass., 631 p.

Reifenstuhl, R.R., 1991, Gilead sandstone, northeasternBrooks Range, Alaska; an Albian to Cenomanianmarine clastic succession, in Reger, R.D., ed., Shortnotes on Alaskan geology 1991: Alaska Division ofGeological & Geophysical Surveys ProfessionalReport 111, p.69–76.

Reifenstuhl, R.R., 1995, Lithofacies, petrology, andpetrophysics of the Kemik Sandstone (Lower Creta-ceous), eastern Arctic Slope, Alaska, in Combellick,R.A., and Tannian, Fran, eds., Short notes on Alaskageology 1995: Alaska Division of Geological &Geophysical Surveys Professional Report 117,p. 53–67.

Reifenstuhl, R.R., and Reifenstuhl, A.E., 2003, Prelimi-nary petrographic study of 11 Mississippian to Ter-tiary age sandstones, Sagavanirktok Quadrangle,Brooks Range foothills and North Slope, Alaska, inClautice, K.H., and Davis, P.K., eds., Short Noteson Alaska Geology 2003: Alaska Division of Geo-logical & Geophysical Surveys Professional Report120, p. 71–81.

Reifenstuhl, R.R., Wilson, M.D., and Mull, C.G., 1997a,Petrography of the Tingmerkpuk Sandstone(Neocomian), northwestern Brooks Range, Alaska;

A preliminary study, in Clough, J.G., and Larson,Frank, eds., Short notes on Alaska Geology 1997,Recent research on Alaska geology: Alaska Divisionof Geological & Geophysical Surveys ProfessionalReport 118, p. 111–124.

Reifenstuhl, R.R., Dover, J.H., Pinney, D.S., Newberry,R.J., Clautice, K.H., Liss, S.A., Blodgett, R.B.,Bundtzen, T.K., and Weber, F.R., 1997b, Geologicmap of the Tanana B-1 Quadrangle, central Alaska:Alaska Division of Geological & Geophysical Sur-veys Report of Investigations 97-15a, 17 p., 1 sheet,scale 1:63,360.

Scott, A.R., Tyler, Roger, and Clough, J.G., 1998, Ex-ploration for coalbed methane in frontier regionsusing limited data: American Association of Petro-leum Geologists 1998 annual meeting, ExpandedAbstracts. (Illustration from accompanying presen-tation made at AAPG 1998 annual meeting, Salt LakeCity, UT, May 17-20, 1998.)

Van der Plas, L., and Tobi, A.C., 1965, A chart for judg-ing the reliability of point counting results: Ameri-can Journal of Science, v.263, no. 1, p. 87–90.

Wartes, M.A., and Reifenstuhl, R.R., 1997, Preliminarypetrography on the provenance of six Neocomian toAlbian sandstones, northwestern Brooks Range,Alaska, in Clough, J.G., ed., Short Notes on AlaskaGeology 1996: Alaska Division of Geological &Geophysical Surveys Professional Report 118,p.131–140.


APP

RE

ND

IX 1

Sum

mar

y of

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rogr

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ount

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Anat

ase

11

1Py

rite

11

Cla

y an

d M

ud M

atrix

1223

1410

26

151

18C

lay

Lam

inae

12

17

158

Com

men

tsD

iffic

ult

diffe

rent

iatin

g be

twee

n ar

gilla

ceou

s ch

ert a

nd

shal

e/

mud

ston

e;

poss

ible

co

ntin

uum

be

twee

n pu

re c

hert

and

pure

sh

ale.

Seve

ral

styl

oliti

c th

in

clay

lam

inae

ar

e pr

esen

t.

Der

ived

fro

m lo

w-

grad

e qu

artz

ose

met

a-se

dim

ents

(m

icac

eous

qu

artz

ites/

ar

gilli

te/

phyl

lite)

and

ch

ert

terra

ne;

cher

t pr

obab

ly

from

qu

artz

ites.

Sutu

ring

occu

rs a

long

w

hat a

re

prob

ably

pa

rtial

illit

ic

inhe

rited

cl

ay ri

ms.

Man

y gr

ains

ar

e pa

rtial

ly

alte

red

to

gree

nish

sm

ectit

ic

clay

s (c

orre

nsite

?).

Der

ived

fro

m te

rrane

co

nsis

ting

of

low

-gra

de

quar

tzos

e m

eta-

sedi

men

ts

(mic

aceo

us

quar

tzite

s/

argi

llite

/ ph

yllit

e) a

nd

cher

t. C

hert

from

qu

artz

ites?

Der

ived

fro

m te

rrane

co

nsis

ting

of

low

-gra

de

quar

tzos

e m

eta-

sedi

men

ts

(mic

aceo

us

quar

tzite

s/

argi

llite

/ ph

yllit

e) a

nd

cher

t. C

hert

from

qu

artz

ites?

Der

ived

fro

m te

rrane

co

nsis

ting

of

low

-gra

de

quar

tzos

e m

eta-

sedi

men

ts

(mic

aceo

us

quar

tzite

s/

argi

llite/

ph

yllit

e) a

nd

cher

t. C

hert

from

qu

artz

ites?

Der

ived

fro

m te

rrane

co

nsis

ting

of

low

-gra

de

quar

tzos

e m

eta-

sedi

men

ts

(mic

aceo

us

quar

tzite

s/

argi

llite/

ph

yllit

e) a

nd

cher

t. C

hert

from

qu

artz

ites?

All o

f the

la

min

ar

mat

rix

coun

ts

repr

esen

t w

hat m

ay b

e a

silt/

mud

/ cl

ay c

last

th

at o

ccur

s at

the

edge

of

the

thin

se

ctio

n.

Der

ived

fro

m te

rrane

co

nsis

ting

of

low

-gra

de

quar

tzos

e m

eta-

sedi

men

ts

(mic

aceo

us

quar

tzite

s/

argi

llite/

ph

yllit

e) a

nd

cher

t. C

hert

from

qu

artz

ites?

POR

ES

POR

E-FI

LLIN

G C

OM

PON

ENTS


Sam

ple

SA85

-26-

68.5

SA85

-23-

136

No

Num

ber

SA85

-23-

83SA

85-2

7-22

SA85

-31-

18SA

86-5

-67

SA86

-7-7

9SA

86-7

-120

SA86

-9-3

9SA

87-1

0-92

SA87

-8-9

5

Com

men

tsTr

aces

of

diss

olut

ion

pore

s oc

cur

in th

e si

derit

e ce

men

t.

The

alte

red

duct

ile

grai

ns a

nd

mat

rix a

nd

corre

n-si

te

(?) c

lays

pr

obab

ly

cont

ain

sign

ifica

nt

amou

nts

of

mic

ro-

poro

sity

.

Qua

rtzos

e sa

ndst

one

fragm

ents

: ill

itic

quar

tz-

aren

ites,

gr

ain

sutu

ring;

lo

cal

abun

dant

ch

ert.

B

orde

rline

m

eta-

quar

tzite

s.

Trac

es o

f di

ssol

utio

n po

res

occu

r in

the

side

rite

cem

ent.

Trac

es o

f di

ssol

utio

n po

res

occu

r in

the

side

rite

cem

ent.

Trac

es o

f di

ssol

utio

n po

res

occu

r in

the

side

rite

cem

ent.

Sev

en o

f the

qu

artz

ce

men

t co

unts

re

pres

ent

coar

sely

cr

ysta

lline

qu

artz

that

pa

rtial

ly fi

lls

fract

ures

.

Bord

erlin

e m

eta-

quar

tzite

(p

ossi

bly

argi

llite

gr

ade)

; w

eldi

ng o

f gr

ains

and

re

-cr

ysta

llize

d m

atrix

yie

ld

enig

mat

ic

grai

n bo

unda

ries.

Com

men

tsTh

e qu

artz

ose

sand

ston

e fra

gmen

ts

are

slig

htly

ill

itic

sand

ston

e an

d si

ltsto

ne

quar

tz-

aren

ites

cem

ente

d by

sut

urin

g an

d qu

artz

ov

ergr

owth

s.

The

kaol

inite

is

pro

babl

y a

repl

acem

ent

of a

mic

a (p

roba

bly

a m

usco

vite

).

Mos

t pel

lets

ar

e pr

obab

ly

alte

red

volc

anic

cla

y vu

g fil

ls

(cel

adon

ite?

). T

houg

h gr

een,

they

do

not

hav

e th

e in

tern

al

fabr

ic ty

pica

l of

gl

auco

nite

.

Trac

es o

f pl

agio

clas

e ar

e pr

esen

t.

The

side

rite

cem

ent

appe

ars

to

be a

ffect

ed

by s

urfa

ce

wea

ther

ing

and

is

stai

ned

by

limon

ite

and/

or

hem

atite

.

The

quar

tzos

e sa

ndst

one

fragm

ents

ar

e illi

tic

quar

tz-

aren

ites

cem

ente

d by

sut

urin

g an

d m

ay b

e bo

rder

line

met

a-qu

artz

ites.

The

quar

tzos

e sa

ndst

one

fragm

ents

ar

e sl

ight

ly

illitic

sa

ndst

one

and

silts

tone

qu

artz

-ar

enite

s ce

men

ted

by s

utur

ing

and

quar

tz

over

grow

ths

.

The

quar

tzos

e sa

ndst

one

fragm

ents

ar

e ill

itic

quar

tz-

aren

ites

cem

ente

d by

sut

urin

g an

d m

ay b

e bo

rder

line

met

a-qu

artz

ites.

The

pore

s in

an

kerit

e ce

men

t all

occu

r in

anke

rite

that

fil

ls

fract

ures

. S

ome

of

thes

e po

res

are

quite

la

rge

(up

to

0.5m

m in

lo

ng

dim

ensi

on).

The

quar

tzos

e sa

ndst

one

fragm

ents

ar

e ill

itic

quar

tz-

aren

ites

cem

ente

d by

sut

urin

g an

d m

ay b

e bo

rder

line

met

a-qu

artz

ites.

Com

men

tsTh

e m

icac

eous

sc

hist

fra

gmen

t is

ques

tiona

ble

.

Sid

erite

ce

men

t co

ntai

ns

mat

rix

mat

eria

l; m

atrix

m

ater

ial

cont

ains

ab

unda

nt

side

rite.

The

kaol

inite

co

unt

repr

esen

ts a

re

plac

emen

t of

an

unkn

own

fram

ewor

k gr

ain.

Two

of th

e ka

olin

ite

coun

ts a

nd

six

of th

e si

derit

e co

unts

oc

cur a

s fra

ctur

e fil

ls.

Kao

linite

bo

ok c

lust

er

in m

ass

of

anke

rite:

m

iner

al

repl

acem

ent

or p

ore

fill.

All

of th

e ca

rbon

ate

fragm

ents

ar

e do

lom

ite.

Beig

e cl

ay

pelle

t=

mic

rocr

ysta

llin

e cl

ay

grai

n=

recr

ysta

llize

d cl

ay

pelle

t?

16 Report of Investigations 2006-1—Appendix 1

Sam

ple

SA85

-26-

68.5

SA85

-23-

136

No

Num

ber

SA85

-23-

83SA

85-2

7-22

SA85

-31-

18SA

86-5

-67

SA86

-7-7

9SA

86-7

-120

SA86

-9-3

9SA

87-1

0-92

SA87

-8-9

5

Mon

ocry

stal

line

Qua

rtz

240

5724

893

1625

1019

2133

Poly

crys

talli

ne Q

uart

z2

913

74

48

1113

203

14D

ense

Che

rt22

1514

261

1223

3335

1363

20Po

rous

Che

rt (

>33%

vis

ible

por

osity

)2

Argi

llace

ous

Che

rt13

31

78

66

66

31

Exte

nsiv

ely

Frac

ture

d C

hert

0.3

1.0

Mic

aceo

us Q

uart

zite

(5-1

5%

mic

as/c

hlor

ite)

0.3

1.3

2.7

4.0

2.7

8.3

10.0

6.3

11.0

5.0

Hig

hly

Qua

rtzo

se A

rgill

ite0.

31.

70.

71.

03.

71.

01.

71.

31.

31.

3St

able

Hea

vy M

iner

als

(Zirc

on e

tc.)

0.3

0.3

0.3

Qua

rtzo

se S

ands

tone

Fra

gmen

t4.

30.

30.

31.

71.

33.

30.

70.

7Pl

agio

clas

e (<

33%

dis

solu

tion)

1.7

2.0

1.0

4.7

Pota

ssiu

m F

elds

par

(<33

% d

isso

lutio

n)0.

30.

70.

3G

rani

tic F

ragm

ent

(>40

% F

elds

pars

)1.

00.

32.

3G

neis

sic

Frag

men

t (>

40%

Fel

dspa

rs)

Feld

spat

hic

Silts

tone

/Mud

ston

e9.

31.

7Fe

ldsp

athi

c Sa

ndst

one

Frag

men

t4.

3Si

licic

Vol

cani

c Fr

agm

ent

1.7

0.3

4.7

0.3

0.3

Mic

ropo

rous

Sili

cic

Volc

anic

Fra

gmen

t0.

71.

1B

asic

Vol

cani

c Fr

agm

ent

1.7

8.0

Plas

tical

ly D

efor

med

Bas

ic V

olca

nic

Frag

men

t0.

71.

7

Dev

itrifi

ed T

uff F

ragm

ents

8.7

3.3

Uns

tabl

e H

eavy

Min

eral

s (E

pido

te e

tc.)

0.3

2.3

0.3

Dio

rite/

Gab

bro

Frag

men

ts0.

7C

alci

te F

ragm

ents

(inc

ludi

ng fo

ssil

frag

men

ts)

2.3

1.0

Org

anic

Fra

gmen

t0.

65.

64.

00.

34.

30.

62.

01.

0U

ndef

orm

ed S

hale

/Mud

ston

e Fr

agm

ents

17.3

3.0

0.6

6.3

4.7

6.7

2.9

8.0

10.0

0.6

Inde

term

inat

e D

uctil

e0.

33.

00.

712

.00.

60.

70.

3C

lay

Pelo

id0.

31.

34.

30.

3Ph

yllit

e Fr

agm

ent

0.3

6.7

6.7

6.3

3.3

5.3

4.7

4.3

3.7

0.3

13.7

Mus

covi

te1.

70.

32.

00.

71.

00.

60.

9B

iotit

e0.

3C

hlor

ite0.

71.

3M

etas

iltst

one/

Met

amud

ston

e1.

31.

31.

01.

72.

03.

64.

32.

4M

ica/

Chl

orite

Sch

ist

2.0

1.7

1.0

3.3

0.3

0.7

0.7

0.3

Unk

now

n Fr

amew

ork

Com

pone

nt2.

01.

71.

03.

30.

30.

70.

70.

3M

acro

pore

in A

nker

ite C

emen

t0.

7In

terg

ranu

lar P

ore

(2–2

0um

)1.

3In

terg

ranu

lar P

ore

(>20

um)

0.7

Kao

linite

0.3

1.3

0.3

FRAM

EWO

RK

CO

MPO

NEN

T (%

of r

ock)


Sam

ple

SA85

-26-

68.5

SA85

-23-

136

No

Num

ber

SA85

-23-

83SA

85-2

7-22

SA85

-31-

18SA

86-5

-67

SA86

-7-7

9SA

86-7

-120

SA86

-9-3

9SA

87-1

0-92

SA87

-8-9

5

Chl

orite

0.7

1.0

Cor

rens

ite2.

7Si

derit

e5.

75.

70.

712

.01.

711

.74.

30.

7An

kerit

e1.

70.

32.

71.

35.

01.

0Q

uart

z O

verg

row

ths

0.3

5.0

0.3

14.7

0.7

0.3

0.7

2.3

3.7

3.7

Pyrit

e0.

30.

3C

lay

and

Mud

Mat

rix4.

07.

74.

73.

30.

72.

05.

00.

36.

0C

lay

Lam

inae

0.3

0.7

0.3

2.3

0.3

19.3

Q Q

uart

zose

Com

pone

nts

(% F

ram

e-w

ork)

4775

9171

9836

7389

8076

9378

F F

elds

path

ic C

ompo

nent

s (%

Fra

me-

wor

k)17

.62.

81.

510

.50.

4

L L

ithic

Com

pone

nts

(% F

ram

ewor

k)35

.522

.38.

927

.42.

453

.926

.210

.919

.524

.16.

821

.7To

tal Q

uart

z (%

Fra

mew

ork

Frac

tion)

4.6

50.8

71.4

31.2

95.2

7.2

26.6

36.4

25.6

42.3

25.1

48.9

Tota

l Che

rt (%

Fra

mew

ork

Frac

tion)

36.1

18.7

15.6

33.1

2.4

20.2

32.5

38.8

41.5

19.3

67.2

21.3

C/Q

Pol

yqua

rtz/

Tota

l Qua

rtzo

se (%

Q

uart

zose

Fra

ctio

n)1.

00.

40.

40.

70.

10.

90.

80.

70.

90.

70.

80.

6

Tota

l Fel

dspa

rs (%

Fra

mew

ork

Frac

tion)

1.8

2.4

1.5

5.8

0.4

Tota

l Pla

gioc

lase

(% F

ram

ewor

k Fr

actio

n)1.

82.

41.

15.

1

Tota

l Pot

assi

um F

elds

par

(%

Fram

ewor

k Fr

actio

n)0.

40.

70.

4

P/F

Plag

iocl

ase/

Tota

l Fel

dspa

r (%

Fel

d-sp

ar F

ract

ion)

1.0

1.0

0.8

0.9

Tota

l Bas

ic V

olca

nics

(% F

ram

ewor

k Fr

actio

n)11

.614

.1

Tota

l Sili

cic

Volc

anic

s (%

Fra

mew

ork

Frac

tion)

1.8

0.4

5.1

0.8

0.4

0.5

Tota

l Vol

cani

cs (%

Fra

mew

ork

Frac

tion)

13.3

0.4

19.1

0.8

0.4

0.5

B/V

Bas

ic V

olca

nics

/Tot

al V

olca

nics

(%

Tota

l Vol

cani

cs)

0.9

0.7

V/L

Tota

l Vol

cani

cs/T

otal

Lith

ic (%

Tot

al

Lith

ic)

0.4

0.0

0.4

0.0

0.0

0.1

Tota

l Duc

tile

(% F

ram

ewor

k Fr

actio

n)22

.121

.88.

626

.72.

431

.424

.910

.919

.423

.72.

920

.5To

tal S

light

ly D

efor

med

Duc

tile

(%

Fram

ewor

k Fr

actio

n)10

.513

.55.

918

.01.

215

.58.

42.

79.

79.

91.

414

.2

Tota

l Ext

ensi

vely

Def

orm

ed D

uctil

e (%

Fr

amew

ork

Frac

tion)

9.1

6.0

1.9

6.4

1.2

11.6

11.4

6.8

6.6

10.6

1.4

1.9

Tota

l Ext

ensi

vely

Def

orm

ed (%

Duc

tile

Frac

tion)

4127

2224

5037

4663

3445

509.

1

Tota

l Cou

nts:

Q

uart

z+C

hert

+Fel

dspa

rs+A

mph

ibol

e12

118

123

417

524

292

141

221

173

169

191

188.

0

Tota

l Ext

ende

d Fr

actio

n (%

Tot

al

Qua

rtz+

Che

rt+F

elds

par+

Amph

ibol

e)2

14

01

2


Sam

ple

SA85

-26-

68.5

SA85

-23-

136

No

Num

ber

SA85

-23-

83SA

85-2

7-22

SA85

-31-

18SA

86-5

-67

SA86

-7-7

9SA

86-7

-120

SA86

-9-3

9SA

87-1

0-92

SA87

-8-9

5

Tota

l Sed

imen

tary

+ V

olca

nic

+ M

etam

orph

osed

(% T

otal

Cou

nts)

259

103

9415

417

179

168

198

208

179

152

153.

0

M M

etam

orph

ic C

ompo

nent

s (%

Tot

al

Sedi

men

tary

+Met

amor

phic

+Vol

cani

c)4

4552

2939

2138

3632

523

57.5

V V

olca

nic

Com

pone

nts

(% T

otal

Se

dim

enta

ry+M

etam

orph

ic+V

olca

nic)

14.7

0.6

29.6

1.2

0.6

0.7

S S

edim

enta

ry C

ompo

nent

s (%

Tot

al

Sedi

men

tary

+Met

amor

phic

+Vol

cani

c)81

5548

7061

4961

6468

4896

42

Met

amor

phic

& S

edim

enta

ry D

uctil

es (%

Li

thic

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ctio

n)62

100

9699

100

5795

100

100

9843

95

Labi

le C

ompo

nent

s (V

olca

nic/

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ous/

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licic

) (%

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ic F

ract

ion)

384

143

52

7

Car

bona

te C

ompo

nent

s (%

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ic

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tion)

505

Poly

crys

talli

ne Q

uart

z (%

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al

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ewor

k Fr

actio

n)2

1014

85

410

1115

224

16

Tota

l San

dsto

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one

(% T

otal

Fr

amew

ork

Frac

tion)

20.4

2.0

0.4

2.9

5.5

3.4

8.1

5.5

3.4

Gra

nitic

Fra

gmen

ts (%

Tot

al F

ram

ewor

k Fr

actio

n)1.

10.

42.

5

Tota

l Pyr

oxen

e+Am

phib

ole

(% T

otal

Fr

amew

ork

Frac

tion)

Tota

l Mic

as+C

hlor

ite (

% T

otal

Fr

amew

ork

Frac

tion)

2.0

0.4

3.8

1.8

0.8

1.0

0.7

1.1

Tota

l Phy

llite

+Sch

ist (

% T

otal

Fr

amew

ork

Frac

tion)

18

78

47

55

40

15

Tota

l Vol

cani

c/Pl

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us +

Se

dim

enta

ry (T

otal

Cou

nts)

263

118

106

162

2319

315

818

720

817

715

616

2

Volc

anic

/Plu

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urce

(% T

otal

Vo

lcan

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+ In

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+

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men

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165

17

363

22

12

Indi

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ourc

e (%

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al

Volc

anic

/Plu

toni

c +

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us +

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dim

enta

ry S

ourc

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208

212

1714

135

1217

44

Sedi

men

tary

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ow G

rade

Met

(% T

otal

Vo

lcan

ic/P

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+ In

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+

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men

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6587

9780

8350

8494

8881

9594

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l Cou

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nd L

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299

298

299

300

300

293

299

300

300

300

242

300

Tota

l Pla

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mph

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(Tot

al C

ount

s)38

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03.

053

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Tota

l Pla

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(% T

otal

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+ B

asic

13

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0.0

100.

026

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Tota

l Am

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Sam

ple

SA85

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68.5

SA85

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136

No

Num

ber

SA85

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83SA

85-2

7-22

SA85

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18SA

86-5

-67

SA86

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9SA

86-7

-120

SA86

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9SA

87-1

0-92

SA87

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5

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(% T

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Pl

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86.8

73.6

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l Int

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ent

(% A

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7.4

0.3

5.7

0.7

14.7

1.7

11.7

5.7

7.0

1.0

Tota

l Int

ergr

anul

ar Z

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e C

emen

t (%

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just

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otal

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Tota

l Int

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anul

ar A

uth.

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t (%

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ount

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70.

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ts (%

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otal

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nts)

0.7

7.7

5.4

6.7

14.7

3.4

15.7

2.0

14.0

8.7

13.2

4.7

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l Det

rital

Mat

rix (%

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d To

tal

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nts)

4.0

7.7

4.7

3.3

0.7

2.0

5.0

0.4

6.0

Tota

l Dis

solv

edFr

amew

ork

(% T

otal

Fr

amew

ork

Frac

tion)

0.6

0.1

0.2

0.2

Tota

l Int

ergr

anul

ar P

oros

ity (%

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uste

d To

tal C

ount

s)2.

00.

8

Tota

l Sec

onda

ry P

oros

ity (%

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uste

d To

tal C

ount

s)0.

50.

10.

11.

0

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l Vis

ible

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osity

(% A

djus

ted

Tota

l C

ount

s)2.

50.

10.

11.

0

Seco

ndar

y Po

rosi

ty (%

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al V

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le

Poro

sity

)21

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0.0

100.

010

0.0

Tota

l Car

bona

te+Z

eolit

e+C

lay

Cem

ents

(T

otal

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nts)

222

118

1044

539

1820

3

Car

bona

te C

emen

ts (%

Tot

al

Car

bona

te+Z

eolit

e+C

lay

Cem

ents

)10

010

094

2010

010

090

9485

100

Cla

y Po

re F

illin

gs (%

Tot

al

Car

bona

te+Z

eolit

e+C

lay

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ents

)10

06

8010

615

Tota

l Int

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anul

ar V

olum

e (%

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d To

tal C

ount

s) P

rese

nt C

ompo

sitio

n5

1510

1017

521

214

914

11

Com

pact

ion

Loss

(% A

djus

ted

Tota

l C

ount

s) P

rese

nt C

ompo

sitio

n32

2328

2821

3317

3623

2922

27

Bul

k Vo

lum

e C

orre

cted

Com

pact

ion

Loss

: Rec

onst

ruct

ed C

ompo

sitio

n34

2731

3125

3421

3727

3226

30

Cal

cula

ted

Initi

al P

oros

ity:

Rec

onst

ruct

ed c

ompo

sitio

n37

3838

3838

3838

3837

3837

38


No Name Creek #2, SA Corehole 7, 1986-120,Paleocene or Eocene, PL, 40X. Medium-grained, wellsorted chert- and ductile-rich lithic sandstone cementedby suturing and plastic deformation. A shear zonecontaining some finely crystalline siderite occurs at theleft edge of the view. Point-counted visible porosity is0 percent; chert is abundant (42 percent) as are ductilegrains (19 percent).

APPENDIX 2Yukon Flat basin and basin perimeter drill core photomicrographs

Photomicrographs of Yukon Flats basin sandstone thinsections from the Exxon shallow drill hole program arebasin fill and basin-perimeter bedrock.

Abbreviations used and photomicrograph caption format:Locality information, creek or physiographic drill core site name;Number of core hole (#2, for example, if two core holes were drilled at a particular location);Number of core hole (sequentially in the Exxon Yukon Flats basin drilling program; includes the prefix SA);Year core drilling took place (for example, 1986);Depth of core sample in feet;Age, where known;PL (plane light);XP (crossed polarizers);Magnification (40X or 100X for example, for a 4 inch by 6 inch image)

Bluish-gray or blue area in photomicrographs is porosity, which has been filled with epoxy during samplepreparation. Porosity has been reduced during the rock’s burial and compaction by deformation of the ductileshale, phyllite, and metamorphic grains. Also, dissolution of silica from quartz and chert has decreased porositylocally.

A summary of the porosity and permeability data from the 24 Yukon Flats basin margin drill cores includesporosity of 1.1 to 11.7 percent (average about 4 percent) and permeability of 0.001 to 171.3 md (average about 0.4md; fig. 3; table 1). In summary, this small sample number (24) of basin and basin-margin sandstones analyzed forporosity and permeability indicates generally poor petrophysical characteristics for hydrocarbon reservoirs (seetext for details).

Compositionally, Yukon Flats basin perimeter drill core samples range from litharenite sandstone (10 samples),sublitharenite sandstone (1 sample) to quartzarenite sandstone (1 sample; fig. 5).

Sandstone reservoir viability is affected by grain size and grain-size variability, consequently these data werecollected for drill core samples. One hundred framework grain-size measurements were recorded from each drillcore sandstone thinsection. Individual sandstone samples range from a framework grain size mean of 0.079 mm(very-fine sand) to a grain size mean of 0.33 mm (medium sand). Eight of the 12 point-counted sandstone coresamples are fine grained (0.125 to 0.25 mm). Sandstone grain measurements and standard deviation are shown intable 2.

No Name Creek #2, SA Corehole 7, 1986-79, Paleoceneor Eocene, PL, 100X. The major agents of porositydestruction in this sandstone are suturing and plasticdeformation of ductile grains. A trace of visible porosityoccurs in a cluster of kaolinite at the upper left and acrystal of siderite is present within this mass ofauthigenic clay.


No Name Creek #2, SA Corehole 7, 1986-120,Paleocene or Eocene, PL, 100X. All visible porosityhas been eliminated by a combination of plasticdeformation, suturing of chert, and siderite infill. Ahighly deformed phyllite is at center of view; a veryfinely crystallized siderite mass occurs just above. Thesiderite may infill or mask an argillaceous grain or amass of matrix material.

Grayling Fork, SA Corehole 10, 1987-92, Jurassic–Cretaceous, PL, 40X. This sample is a fine-grained,well sorted, chert-rich, quartzose sandstone cementedprimarily by suturing. A trace of point-count measuredporosity (1 percent) occurs in this sample. Chert is veryabundant in this sandstone (67 percent).

No Name Creek #2, SA Corehole 7, 1986-79, Paleoceneor Eocene, PL, 40X. Fine-grained, well sorted chert-and ductile-rich lithic sandstone cemented by suturingand plastic deformation. Point-count measured visibleporosity is 0 percent. Quartz (36 percent), chert (38percent), and ductile grains (11 percent) are the dominantcomponents.

Grayling Fork, SA Corehole 10, 1987-92, Jurassic–Cretaceous, PL, 100X. Visible porosity in this chert-rich sandstone is virtually nil due to a combination ofsuturing, quartz overgrowths (4 percent), and ankeritecement (5 percent)(stained pale blue).


Bryant Creek, Corehole 23, 1985-83, age?, PL, 100X.The lack of visible porosity in this sandstone is primarilyattributable to plastic deformation of ductile grains,suturing, and siderite cement (6 percent). The latter hasbeen partially altered to hematite (dark reddish-brownto black).

Maypole Hill, Corehole 31, 1985-18, Early Eocene, PL,40X. Medium-grained, well sorted, slightlyargillaceous, chert-rich lithic sandstone cemented bysuturing and plastic deformation and smectitic clay(corrensite?). Traces of visible intergranular what? Issomething missing?. Abundant framework grains arechert (20 percent), basic volcanics (14 percent), andductile grains (12 percent).

Bryant Creek, Corehole 23, 1985-83, age?, PL, 40X.Fine-grained, well sorted chert- and ductile-rich lithicsandstone cemented by suturing and plastic deformationand siderite. Point-count measured porosity in thissandstone is 0 percent. Quartz (31 percent), chert (33percent), and ductile grains (26 percent; primarily shale,mudstone, argillite, and phyllite fragments) are majorframework components.

Step Mountain, Corehole 27, 1985-22, Late Triassic toJurassic, PL, 100X. Quartz overgrowths (15 percent)and compaction loss by suturing and minor plasticdeformation (21 percent uncorrected for changes in bulkvolume) are the major agents of porosity loss. The palegreen grain at the center-bottom of view may be analtered glauconite pellet.


Step Mountain, Corehole 27, 1985-22, Late Triassic toJurassic, PL, 40X. Fine-grained, well sorted, highlyquartzose sandstone cemented by quartz overgrowthsand suturing. Point-count measured porosity in thissample is 2 percent. Quartz forms 95 percent of theframework fraction.

Maypole Hill, Corehole 31, 1985-18, Early Eocene, PL,100X. Plastic deformation of ductile grains (includingaltered basic volcanic rock fragments) is the majormechanism of porosity loss in this highly lithicsandstone. Minor agents of porosity loss are matrixinfill (4 percent), authigenic clay (3 percent; corrensite?),and suturing.

Preacher Creek, Corehole 5, 1986-67, Paleogene, PL,40X. Medium-grained, well sorted, argillaceous chert-and ductile-rich lithic sandstone cemented by suturing,plastic deformation, and siderite. Point-count measuredporosity is 0 percent. The major framework componentsare quartz (27 percent), chert (33 percent), and ductilegrains (25 percent; shale, mudstone, argillite, andphyllite).

Hodzana River #2, Corehole 8, 1987-95, Age unknown,PL, 100X. Suturing and plastic deformation are themajor mechanisms of porosity destruction. Minor agentsof porosity loss are quartz overgrowths (4 percent) andmatrix infill (6 percent).


Preacher Creek, Corehole 5, 1986-67, Paleogene, PL,100X. The lack of visible porosity is attributable to acombination of siderite and ankerite cements, plasticdeformation of ductile grains, and suturing of chert. Ahighly deformed phyllite is at the upper left.

Eagle Trough, Corehole 26, 1985-68.5, Middle to lateAlbian, PL, 100X. Visible porosity destroyed by plasticdeformation and chert suturing. Mudstone frameworkgrains are extensively deformed and are dark brown andmottled in this image.

Hodzana River #2, Corehole 8, 1987-95, Age unknown,PL, 40X. Fine-grained, well-sorted, slightly argillaceouschert- and ductile-rich lithic sandstone cemented bysuturing and plastic deformation. Point-count measuredporosity is 0 percent. Quartz (48.9 percent), chert (21.3percent), and phyllite (15.3 percent) are the majorframework components. Matrix content is 6 percent.

Eagle Trough, Corehole 26, 1985-68.5, Middle to lateAlbian, PL, 200X. Visible porosity destroyed by plasticdeformation and chert suturing. Grain at center is afeldspathic–lithic sandstone cemented by chlorite orsmectitic clay. Mudstone extensively deformed.


Coal Creek, Corehole 3, 1986-15, Oligocene, PL, 40X.Porphyroblasts of quartz and epidote containingabundant fine inclusions float in a mass of pale greenchlorite and colorless muscovite or pyrophyllite.Sphene, zoisite, and plagioclase are present in minoramounts.

Coal Creek, Corehole 3, 1986-15, Oligocene, XP, 40X.View similar to previous view but in crossed polarizers.The grains with the highest birefringence are epidote.

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