Geochemistry and Organic Petrology of the Anna Shale (Pennsylvanian) and Pyrite “Suns” - PowerPoint Presentation

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Geochemistry and Organic Petrology of the Anna Shale (Pennsylvanian) and Pyrite “Suns” in Southwestern Illinois

Jacob Dyson

1

, Susan Rimmer

1

, Scott Erick

2

Southern Illinois University Carbondale

1

Illinois Geological Survey

2

Pyrite suns

Disk-shaped pyrite concretions

Occur at the contact between the Herrin

(No. 6) Coal and the Anna ShaleRange in size from 1cm to 15cm

(Redrafted from: Krause, 1979 after

Allgaier

, 1974)

Objectives

Assess the source-rock quality of the Anna Shale

Determine sources of OM using organic petrography

Evaluate the paleo-redox conditions during Anna Shale depositionInvestigate trace element enrichments of pyrite suns

Area of study

C6848

Washington County

Perry County

C7005

C7003

C7009

Lively Grove Mine

Prairie Eagle Mine

N

20 km

10 mi

Core Location

Herrin (No. 6) Coal Sample

Pyrite Sun and Roof Shale Samples

Source rock quality and maturity

*random vitrinite reflectance of Herrin (No. 6) Coal

TYPE I

KEROGEN

TYPE II

KEROGEN

TYPE

III

KEROGEN

TYPE

IV

KEROGEN

C6848

C7003

C7005

C7009

Roof Samples

Average

Range

TOC

15.9

wt

%2.2-37.0 wt %HI225 mg HC/g TOC 54-438 mg HC/g TOC

S11.32 mg HC/g0.05-4.76 mg HC/gS245.9 mg HC/g1.2-159 mg HC/g Tmax422°C 411-432°C*Ro0.43%

Lower Anna Shale and TOC intervals >20%

Upper Anna Shale and low TOC intervals

Organic petrography

6848 103-108

7003 30-35

Maceral

Average percent

from visual estimates

Micrinite

60.1%

Other Inertinites

7.9%

Bituminite

10.9%

Other Liptinites

2.0%

Solid Bitumen

17.8%Vitrinite1.3%disseminated micrinitelayered micrinitesolid bitumen40 um40 um

7005 65-70

7005 65-70

7005 30-35

7005 30-35

v

itrinite

solid bitumen

c

utinite

bituminite

bituminite

c

utinite

40 um

40 um40 um40 um

C-S relationships

N

ormal marine conditions line goes through the origin

Data show positive intercept on the S axisSuggests an anoxic depositional environment

DOP

≥

0.42 =

dysoxic

DOP

≥

0.75 = anoxic/euxinicTwo trends of constant S/Fe ratio

Estimated DOP suggests dysoxic and anoxic conditions

C6848

C7003

C7005

C7009

Roof Samples

C-S-Fe relationships

DOP 0.42DOP 0.75DOP 0.51

DOP 0.73

Paleo-redox conditions

Core C7009

Cyclic

paleo-redox conditions

Large amounts of OM deposited in anoxic intervals

0

40

20

TOC (

wt

%)

Anoxic

Dysoxic

O

xic

Ni/Co1050EuxinicAnoxicDysoxicOxic5V/Cr1000.40.9V/(V+Ni)AnoxicDysoxic

O

xic109.2Depth (m)

109.4109.6109.8

X-ray diffraction of pyrite suns

EPMA for pyrite sun trace elements

Vertical and horizontal point

traverses

Analyzed for Mo, Cu, Zn, As, Pb, and CdAny concentration is below microprobe detection limits ~0.05

wt%Next step LA-ICP-MS

Paleo-redox conditions of roof samples

V/Cr

Ni/Co

Dysoxic

Oxic

Dysoxic

Oxic

V/(

V+Ni

)

Dysoxic

Oxic

Anoxic

Euxinic

Roof 2

Roof 4 Roof 1 Roof 5Roof 6Roof 7Roof 2Roof 4 Roof 1 Roof 5

Roof 6

Roof 7Roof 2Roof 4 Roof 1

Roof 5Roof 6Roof 7

Pyrite suns occurPyrite suns do not occur

Summary

Source-rock quality

Type II

kerogen; Average 15.9% TOCImmature - average Tmax 422°C

Sources of OMDominantly micrinite, solid bitumen, and bituminitePaleo-redox conditionsCyclic between dysoxic and anoxic conditions

Trace elements in pyrite suns

Not detectable to 0.05 wt% using a microprobePaleo-redox conditions of roof shale samples

Unclear relationships with pyrite sun occurrence

Thank you!

Special thanks to:

Dr. Dave

Moecher – University of KentuckyPrairie State Generating CompanyBarry Sargeant – Knight Hawk Coal LLC

Zain Abdi – Southern Illinois University CarbondaleJoe Devera – Illinois State Geologic Survey