From: Nizich, Sharon [mailto:Nizich.Sharon@epa.gov]

Sent: Thursday, September 3, 2015 12:16 PM

To: Szabo, Aaron <Aaron_L_Szabo@omb.eop.gov>

Cc: Fairchild, Susan <Fairchild.Susan@epa.gov>

Subject: FW: CORRECTED file

Hello Aaron- Susan our geologist, realized the previous version of this document had a problem 

with one of the maps. This draft should be clearer for you.

Thanks!

Sharon Nizich

Environmental Engineer

U.S. EPA/OAR/OAQPS

Sector Policies and Programs Division (SPPD)

109 TW Alexander Dr. (D243-04)

RTP, NC 27711

(919) 541-2825 

<<OKLAHOMA and OHIO v3.pdf>>

From: Fairchild, Susan

Sent: Thursday, September 03, 2015 11:32 AM

To: Nizich, Sharon; Morales, Mariel; Barnett, Keith

Subject: CORRECTED file

The maps, their captions, and the points got messed up in the transition from Word to adobe. So 

I’ve edited it and I think this one is captured correctly. I didn’t change the text.

Susan Fairchild

Senior Environmental Scientist

(919) 541-5167

USPS Address:

OAQPS/SPPD/MMG

Mail Code D 243-04

Research Triangle Park, NC 27711
Mercury Content of Oklahoma and Ohio Shale Deposits

Supplying the Brick Industry

Report to the Brick MACT Project File

Prepared by: Susan Fairchild

July 29, 2015
- 1 -

EXECUTIVE SUMMARY

This report supports development of the emission limits for mercury under the maximum achievable 

control technology (MACT) standard for the Brick Manufacturing source category.

Ten shale and clay deposits in Ohio and Oklahoma are currently used by U.S. brick manufacturing 

companies as a source of raw material. Available information was reviewed to understand the source(s) 

of mercury in the clays. The Oklahoma Geological Survey provided detailed historical and stratigraphic 

maps of rock sequences across the state. The Ohio Geological Survey materials were less detailed, but 

provided similar information.

All clays used in these states are formed by the weathering of shale, a sedimentary rock. Clay deposits 

are formed by the weathering of host rock, and are deposited through erosional processes to a local 

area, usually a geologic basin. While clays can be formed from the weathering of all types of rock, the 

clays used by the brick industry in Ohio and Oklahoma originate from shale sequences formed during 

the Devonian, Pennsylvanian, and Permian periods. Note that all Ohio and Oklahoma clay deposits are 

extracted at or near the surface in ‘pits’.

Variability of mercury content is expected due to the geological events which occurred over the course 

of shale sequence formation and the concentration of mercury by the weathering process. The severity 

of that variability is dependent on several factors, including volcanic activity during shale formation, 

availability of associated minerals with which to form stable bonds, the shales’ carbon content, and 

irregular rates of organic deposition. 

Given the above factors, we conclude a correlation is apparent between the clay’s organic content, 

general color of the clay, and the relative mercury content. 

METHOD

Existing information was obtained to locate, identify, and characterize the geological history of the clay 

deposits in this report. Analyses of the mercury content of each clay deposit used by brick 

manufacturers in Oklahoma and Ohio were supplied from existing company data collected in rock and 

soil assays. No new testing was required. Companies identified each sample of the deposits by location 

(latitude, longitude), age, rock type, and sample description. 

Geologic maps from the State Geologic survey offices and reviews of the geological history were next 

located online for both Ohio and Oklahoma. The geologic time scale was also reproduced for reference 

from the Geological Society of America (see Appendix 1).

Google Earth © was used to locate deposits by latitude and longitude. Once the deposit was located and 

a pit was identified, the clay deposit coordinates were transferred to the respective geologic map. The 

historical geology of each area was reviewed and noted. State Geological Survey maps, geologic history 

reports, cross-sectional maps and related materials were used to determine the age of surface deposits 

and near-surface deposits, and to ascertain potential origins and explanations of the variation of 

mercury content for the clay deposits, if possible. Other sources of information were also retrieved and 

reviewed for relevancy to this study.
- 2 -

OHIO 

Brick companies extract clays from five locations in Ohio, as shown on page 6 in the geologic map 

(Figure 1.) These are the Belden-Sugarcreek fire clay/shale, site 1; Whitacre Greer-Lower Kittaning clay, 

site 2; Whitacre Greer-Brookville clay, site 3; Whitacre Greer-Red clay Pit, site 4; and Glen-Gery, 

Caledonia and Iberia-Green shale and clay, site 5. While we did not obtain complete assays of all clays 

sampled, we note, in general, the red color of clays indicates an oxidizing environment with a high-iron 

content, and the green and gray colors of clays indicates a reducing environment. These distinctions play

a significant role in the geochemistry of the rock from which clays are derived.

Geological Overview:

Overall, the bedrock geology of Ohio consists of late-Precambrian age igneous and metamorphic rock at 

depth overlaid by flat lying to gently dipping sedimentary rocks including carbonates, evaporite

minerals, and shales that are alternatingly high in silica and organic content. The shales were formed 

from sediments deposited beginning 450 million years ago and continuing for another 150 million years 

thereafter (i.e., from Upper Ordovician to Lower Permian). Surface-layer Quaternary sediments 

irregularly overlie shale deposits north and west of the glacial margin. Clays are found in two geologic 

basins: Appalachian (younger) basin and the Michigan (older) basin, and the clays used by brick 

companies are located in Pennsylvanian and Devonian age shale deposits in these basins. The Devonian 

period in Ohio was preceded by a period of widespread erosion, followed by accumulation of sediments 

of marine and sub-marine origin in the Michigan basin. Lithification of these sediments formed 

sandstone, shale, and limestone. Another period of widespread erosion preceded the early and midPennsylvanian period, characterized by a 16 million year accumulation of deltaic and marine sandstone, 

siltstone, and shales in the Appalachian basin. High carbon content is a characteristic of all clays formed 

during the Pennsylvanian system, as implied by the name of the period “Carboniferous Period”, 

particularly the shales, which are deltaic in origin. Site 5 clays are of Devonian age1, which predates the 

Carboniferous Period, and as such would not have a high carbon content. The Cincinnati and Findlay 

arches rise between the two basins and several high-angle normal faults, located north and central in 

the state, dislocate strata.

The cross sectional map at the base of Figure 1 depicts the underlying rock layers along the bent line 

from A to A’. All five Ohio clay deposits are located in the Greenville Province, shown from the angle 

apex in the cross section to A’. Due to regional uplift, rock units exposed at the surface increase in age 

from the east border of Ohio going west to the center of the state, and then decrease in age mid-state 

going west. 

One brick company reported a clay deposit (site 2 in Figure 1) of Precambrian age. However, this is an 

apparent error. According to the information available from the Ohio Geological Survey, rocks of this 

age are not exposed at or near the surface. Site 2 was located using its latitude and longitude 

coordinates with Google Maps© aerial photography. The site 2 location then was transferred to the 

Ohio geologic map, and found to be in the Northeastern quadrant of Ohio. This site is not near known 

faulting that could explain Precambrian rocks at the surface. The oldest exposed rocks in the state, 

consisting mainly of alternating shale and limestone sequences, occur in strata of the Ordovician system

 

1

Late Devonian age clastic rocks and clays from these deposits are found in both the Appalachian and the 

Michigan (older) basins. However the Michigan basin is located in the Northwest quadrant of Ohio, and although 

clay deposits are available in this area, brick companies are not currently using clay deposits from the Michigan 

basin. 
- 3 -

located in the southwest corner of Ohio.2 We therefore conclude that the site 2 clay deposit is most 

likely of Pennsylvanian age (potentially the clay from which this shale was initially formed was 

Precambrian.) The remaining companies reported clay deposits of Devonian and Pennsylvanian ages. 

Mercury Content of Ohio Clays

Ohio clay mercury content showed the concentration of mercury in clays varied widely between sites 

and even within the same clay deposit. Sites 1, 3, and 5 were sampled multiple times, and one sample 

each was obtained from sites 2 and 4. Three samples were obtained from site 1, ranging from 15.6 to 

56.9 parts per billion (ppb) mercury (Hg). Five samples were obtained from site 3, ranging from 32.8 to 

132 ppb Hg. Site 3 has the overall highest average mercury content, highest single measurement, and 

the widest range of mercury sample results. Four samples were obtained from site 5, ranging from 12.9 

to 18.2 ppb Hg. Only one mercury measurement for Site 4 was provided, and is the lowest single 

measurement of mercury of any site of Ohio brick clay deposits. Site 2 mercury content is comparable to 

that for site 1, a result that is not apparent from a review of the geological map alone.

We note that pre-anthropogenic mercury is deposited geologically through volcanic, igneous intrusive, 

hydrogeologic, and other geothermal processes. While faulting in Ohio is noted, the fault zones are not 

located proximate to, or within the Ohio clay deposits. Orogenous processes west (Rocky Mountain 

range) and east (Appalachian Mountain range) of the Ohio sediment deposition basins are the likeliest 

sources of mercury during the Pennsylvanian period. 

Mercury is readily absorbed by organic matter, and is also known to bond readily with minerals 

containing manganese, sulfur, and iron. Chemical assays of the sample were not obtained, but as noted 

earlier, the Ohio geological survey reports interspersing of high-organic content shale with other 

sedimentary deposits. 

Neither igneous intrusives nor active geothermal vents are noted locally, but volcanic activity, which is 

known to be a source of mercury, may be responsible for deposition during this period. Remote volcanic 

activity during the Pennsylvanian period could be a potentially significant source of mercury deposition 

to the deltaic muds, especially those high in organic matter, a characteristic of the thick deltaic shale 

sequences of the Pennsylvanian system. Proximity to the area of volcanic activity is not necessary for 

this mechanism to occur. Mercury, emitted to the atmosphere from volcanic activity outside the area, 

may remain airborne, carried by air currents, and be deposited locally. Erosional processes would also 

be expected to contribute to migration and accumulation of mercury in the Appalachian basin 

sediments, and mercury would be expected to become concentrated manganese, sulfur, and ironbearing minerals, and in areas with accumulated organic matter. Figure 2 is an aerial photograph of site 

3, with dark piles indicating high carbon content at the same site with clays of lighter color indicating 

lower carbon content. The formation of high carbon content sediments during a time of active 

volcanism indicates the conditions are right for concentration of mercury in the sediment.

 

2 The youngest Precambrian rocks are located at depth, and the Ohio Geological Survey reports that rocks of these 

ages are igneous and metamorphic rocks over 900 million year old, and include granite, gneiss, schist, amphibolite,

and marble. From the Ohio Geological Survey stratigraphic map, we found that rocks of Precambrian age could 

only be reached by drilling through 11 layers of rock accumulated in the Appalachian basin formation in eastern 

Ohio, which we believe would be cost-prohibitive.
- 4 -

Figure 1. Geologic Map of Ohio showing the locations of active clay pits used by the US Brick Industry (Ohio GS, 2015.)

5

1

3

4

2
- 5 -

The diagenesis3 of the rocks could account for a wide range of mercury content of samples within the 

same deposit and age. Studies4 of regional geochemistry, particularly of mercury deposition to 

sedimentary rocks, explain this process. “The main factors controlling the concentrations of mercury in 

sedimentary and metasedimentary rocks are: the presence or absence of volcanism in the source areas 

and areas of deposition; the amount of manganese oxides in oxidizing environments or the amount of 

organic material and sulfur in reducing environments; the thermal history of the rock; the intensity of 

regional hydrothermal activity; and the effect of diagenesis.”

McNeal also suggests a mechanism of mercury enrichment of soils during the weathering process. 

Mercury compounds which are stable in the environment may be concentrated by the weathering of a 

large thickness of shale into a smaller volume of clays.

A significant variability of mercury in the clays would be expected as a result of the diagenesis of the 

shale sequences and the concentration of mercury by weathering as each layer of shale is exposed and 

weathered, forming the clay deposit.

Moreover, because the shale that is a 

source of the clay was also previously 

formed from clay deposits, the 

accumulation of mercury from volcanic 

origin likely includes earlier geologic 

periods potentially in the Cambrian 

and Precambrian series. Mercury 

content in the clay is not evenly 

distributed or invariable across a single 

clay layer because deposition of 

organic matter, to which mercury 

forms a stable bond, is not evenly 

distributed. Minerals associated with 

mercury in the oxidizing environment 

such as manganese are typically 

heterogenous in the host rock, and as a 

result the mercury accumulation in the 

clay from this source is likely to be 

variable across the clay deposit. 

 

3 Diagenesis in this context refers to processes including alteration by deposition of mercury of volcanic origins, 

erosional processes and transmittal of mercury through water borne movement, and geochemical processes in 

both reducing and oxidizing environments.

4

“The Geochemistry of Mercury in Sedimentary Rocks and Soils in Pennsylvania”. McNeal, James M. and Rose, 

Arthur W. Geochimica et. Coamochimica. Acta. Issue 12, Vol.38, pp.1759 To 1784. December 1974. Pergamon 

Press.

Figure 2. Light and dark-colored piles are indicative of a range of organic 

content, and of associated mercury content of the clays. Courtesy Google 

Earth©, 2015.
- 6 -

Table 1. Ohio Clay Deposit Mercury Analysis

Hg 

Content 

[ppb]

Name

Site #

Average 

Hg content 

for deposit

Geologic Description Age

31.7 Belden- Plants 2, 3, 

4, 6, 8 & 9 

Sugarcreek

1 34.7

Lower Kittanning (#5 

Fireclay)

Pennsylvanian 

System (300-

325 million 

years old)

56.9

50% Clarion (#4 Shale) & 

50% Brookville (#4 Fireclay)

15.6 Clarion (#4 Shale)

39

Whitacre Greer 2 74.3

Lower Kittanning #5

114

Brookville

32.8

67.7

132

60.2

5.43 Whitacre Greer 3 5.4 Buffalo Shale #7

18.2 Glen-Gery 

CorporationCaledonia4 15.55

Shale

Devonian

(350-420 

million years 

old)

12.9

17 Glen-Gery 

Corporation - Iberia 5 15.05 13.1
- 7 -

OKLAHOMA 

Brick companies extract clays from five locations in Oklahoma, as shown in the geologic map below 

(Figure 3.) Three clay deposits accessed by the brick industry (Boral-Muskogee, site 1; Acme-Fort Smith, 

site 2; and Acme-Tulsa, site 3) are from Pennsylvanian-age shales. Two deposits (Acme-Oklahoma, site 4; 

and Boral–Union City, site 5) are from younger Permian-age shales. As with the clays in Ohio, complete 

metals assays of the Oklahoma clay deposits were not obtained. 

Figure 3. Geologic Map of Oklahoma. (Oklahoma GS, 2015.)

Geological Overview:

The Pennsylvanian Period (300-324 million years ago) in Oklahoma was characterized by crustal activity 

marked by both mountain building and subsidence across the area. Uplifts to areas west and northwest 

established the Ancestral Rockies mountain chain. Previously deposited sediments in the Wichita, 

Arbuckle, and Ouachita Uplifts became lithified5, deformed and raised, forming significant mountains, 

while rapid nearby subsidence created the Arkoma basin, which received sediments as they eroded from 

the highlands. 6

The cross-sectional diagrams (Figure 4) along B to B’, and (Figure 5) along E to E’, show the age and 

configuration of the strata.

 

5 The term lithified refers to the process by which sediments -- in this case clay, calcareous deposits, sand, and 

organic matter-- become rock, i.e., shale, limestone, sandstone, and coal, respectively.

6 Kenneth S. Johnson, Oklahoma Geological Survey, Educational Publication 9, 2008. 

5

4

3

1

2
- 8 -

The Arkoma basin, in which sites 1-3 (Figure 4) are located, is on the outer rim of the Ozark Uplift. These 

clay deposits originate from marine shale of mid-Pennsylvanian age, and the deposits are up to 18,000 

feet thick. The shale occurs with interbedded sandstone, limestone, conglomerate, and coal. Sites 1 and 

2 are bordering quaternary sand, silt, clay and gravel flood plain. Site 3 does not border this gravel 

deposit. Sites 1 and 3 are both located in a structure known as the Claremore Cuesta Plains, and Site 2 is 

capped by Pennsylvanian age sandstone. While we generally group sites 1-3 together geologically, we 

note that variations within the sediment sources (mountains) would be expected to yield similar 

variations in the accumulated sediment. We also note site 2 is not in Oklahoma. While the brick 

company may operate out of Oklahoma, the latitude and longitude coordinates of the clay pit is about 

two miles across the border into Arkansas.7

A shallow inland sea covered most of Western Oklahoma during the Permian period. Layers of shallowmarine limestones and gray shales in this area intersperse and gradually give way to high iron content 

deposits of red shales and limestones. Evaporite minerals such as salts and gypsum are also common in 

the area marked by the last vestiges of the ancient sea. Sites 4 and 5 are located in this area, known as 

the Anadarko Basin. 

Figure 4. This cross-section of the Anadarko basin is the location of sites 4 and 5. (Oklahoma GS.)

Mercury content of Oklahoma Shale and Clay Deposits

Thus the clays and shale deposits found in the Arkoma Basin (sites 1-3) and those found in the Anadarko 

Basin (sites 4 and 5) are of different ages, formed under different conditions, and of different origins. It 

is therefore not surprising to find that the associated mineral assemblages vary widely between these 

deposits, and may also be expected to vary within each deposit due to the sediment source and alluvial 

contribution.

 

7 This political boundary does not affect the geology.

Sites 4 and 5
- 9 -

Figure 5. The Arkoma Basin6 is the location of sites 1, 2, and 3, as shown in this cross section E to E’. (Oklahoma GS)

Mercury samples were fairly consistent within each site, but varied across the Arkoma Basin deposits. 

Sites 2 and 3 were each sampled and analyzed for mercury twice and site 1 was sampled and analyzed 

once. Mercury content of the deposits in the Pennsylvanian shales runs from 14.7 to 34.4 parts per 

billion, and are generally in the same range. Sites 1 and 4 are each characterized by one mercury 

analysis result. Site 5, Permian age shale used by the Union City Boral pit measured the lowest mercury 

content and the Fort Smith Acme pit averaged the highest. 

As with the Ohio clay deposits, contribution to the concentration of mercury in the clays is largely 

attributed to distant volcanic activity (in this case, areas to the east and northwest) and to accumulation 

of stable mercury compounds in organic material and minerals in the clays as a result of weathering 

processes. Figure 5 illustrates visual differences in clays as an indicator of mercury content. 

Table 2. Oklahoma Clay Deposit Mercury Analysis

Hg 

Content 

[ppb]

Name

Site #

Average Hg 

content for 

deposit

Geologic 

Description Age

21.7

Boral-Muskogee Plant 1 21.7 Shale Mix

Pennsylvanian

34.4 Acme-Fort Smith Plant 2 33.9

Shale 33.4

14.7 Acme-Tulsa Plant 3 16.7

18.7

Acme- Oklahoma City Plant 4

Clay

Permian

1

Boral- Union City Plant 5 1

Shale Mix

Sites 1, 2, and 3
- 10 -

Figure 6 below shows aerial photographs of two different clay deposits in Oklahoma. The Boral plant in 

Union City uses a clay/ shale mix that is weathered from Permian age shales high in iron, but lower in 

organic content, as evidenced by the red color. The Union City clay averaged 1 parts per billion (ppb) 

mercury. The clay pit used by Acme in Fort Smith, Oklahoma is probably higher in organic content 

(indicated by the dark gray color), and has a higher mercury content. The Fort Smith deposit averaged 

about 34 ppb mercury.

Figure 6. Two clay deposits used by the Brick industry in Oklahoma illustrate how color can be an indicator of geochemistry, 

organic content, and mercury content. (Google Earth, 2015.)

References:

1. Oklahoma Geological Survey. “Geologic Map of Oklahoma”. Kenneth S. Johnson, Educational 

Publication 9:2008.

2. Oklahoma Geological Survey. “Geomorphic Provinces of Oklahoma” Kenneth S. Johnson, Neville 

M. Curtis, Jr., William E. Ham. Educational Publication 9:2008.

3. Ohio Geological Survey. “Geologic Map of Ohio”. Slucher and others. Ohio Department of 

Natural Resources, Geologic Records Center, Division of Geological Survey.

4. Google Earth, 2015.

5. “The Geochemistry of Mercury in Sedimentary Rocks and Soils in Pennsylvania”. McNeal, James 

M. and Rose, Arthur W. Geochimica et. Coamochimica. Acta. Issue 12, Vol.38, pp.1759 To 1784.

December 1974. Pergamon Press. 
- 11 -

Appendix 1. Geologic Time Chart