Stop 1Central Maryland Research and Education Facility at Upper Marlboro

Maryland Agricultural Experiment Station Farm

Prince Georges County, MD

Background

The surficial geology of an extensive portion of the Southern Maryland Coastal Plain

consists of sediments that have significant amounts of a sulfide mineral, pyrite, in the unoxidized

or unweathered part of the regolith. These sediments are mainly of Tertiary (Nanjemoy,

Marlboro Clay, Aquia Fms) and Late Cretaceous (Magothy, Matawan/Monmouth Fms) ages and

occur at the surface throughout most of Anne Arundel County and to a lesser extent in Prince

Georges County (Fig. 1-2). Only the Nanjemoy, Aquia, & Matawan/Monmouth Fms are

glauconitic

This stop is situated within the outcrop area of the glauconitic Aquia Formation of

Paleocene age. The soil to be examined is identified as the Annapolis (previously Collington)

series, which is the most extensive glauconitic soil in Maryland. Glauconitic soils occur in six of

Maryland's Coastal Plain counties and occupy over 47,000 hectares.

Acid sulfate problems associated with the exposure of sulfide-bearing soil materials in

the inner Maryland Coastal Plain have been documented for many years. The microbially

mediated processes of sulfide and iron oxidation and hydrolysis are essentially the same as those

which occur in coal mining areas in the Appalachian provinces of Western Maryland, which lead

to problems of extremely acid soils and acid mine drainage. On the Coastal Plain, similar

problems arise when construction activities expose sulfide-bearing horizons deep within the

regolith.

.

Figure 1-1.

56

Coastal Plain Geology – Stop 1

Kp: Potomac Group

Kmo: Monmouth Formation

Kma: Matawan Formation

Ta: Aquia Formation (Paleocene)

Tn: Nanjemoy Formation (Eocene)

Tc: Calvert Formation (Miocene)

QTu: Upland Deposits (Quaternary)

QTl: Lowland Deposits (Quaternary)

Cre

tace

ou

sTe

rtia

ryQ

uat

.

DC

Figure 1-2

57

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

0 0.1 0.2 0.3 0.4

De

pth

(cm

)%S

Ap1

Ap2

BE

Bt

BCj

Cj1

Cj2

Figure 1-3 (Data from D. P. Wagner dissertation) shows

the distribution of sulfur in the soil profile (near pit 1A).

Nearly all of the sulfur in the subsoil of this profile is

present as jarosite, and because only small amounts of

sulfur were present in surface horizons (upper 50 cm), no

attempt was made to fractionate sulfur in the surface

horizons. It is interesting to note that even though the

highest jarosite concentrations were measured (Phil

Snow PhD dissertation – differential extraction and XRF

techniques) in the argillic horizon (0.22% S), field

observations failed to detect jarosite, This is in contrast

to other profiles described in which field observations

were able to detect jarosite concentrations later

determined in the laboratory to be as low as 0.02 %

jarosite-S. Perhaps masking action by pedogenic

processes leading to argillic horizon formation tend to

destroy or cover over discrete jarosite mottles. Partial

hydrolysis of jarosite to iron oxide could also mask the

conspicuous yellow color of the mineral.

Pyrite Associated with Glauconitic Materials

Glauconite is A 2:1 phyllosilicate of the mica group that

has ferrous and ferric Fe in the octahedral position

(Fanning et al., 1989a). Typically, glauconite occurs as Figure 1-3

fine sand size pellets that are green to black in color. In Maryland, glauconite is found in Tertiary sediments of the Piney Point, Nanjemoy, and Aquia Formations and in Cretaceous sediments of the Monmouth and Matawan Formations. These sediments dip to the southeast and occur at or near surface along the western part of the Coastal Plain in a band approximately 30 km wide. This band begins about 15 km east of the fall line and extends along a NE to SW direction. In Maryland, approximately 50 000 hectares (120 000 acres) have been mapped in soil series developed in glauconitic sediments exposed at the surface. These soils are mainly in fine-loamy and clayey families of Typic and Aquic Hapludults and Typic Endoaquults. Many of these soils have >20% glauconite by weight in the <2 mm fraction (some >40%) and thus are in glauconitic mineralogical families, although some contain <20% and would be in mixed, rather than glauconitic, families.

The soil/geologic column in glauconitic sediments can be divided into an upper oxidized zone,

which contains oxidized forms of Fe such as goethite and jarosite, and a lower unoxidized zone

which contains pyrite (Wagner, 1982; Wagner et al., 1982; Valladares, 1998). While pyrite has

also been found in some lignitic layers in Cretaceous sediments in Maryland, it is generally not

present except in the glauconitic materials. The boundary between the oxidized and unoxidized

zones is usually quite abrupt, and occurs at depths ranging from between approximately 2 and 8

m under most natural land surfaces.

58

A

B

Micrographs of thin sections from samples collected from the oxidized zone (A) and from the unoxidizedzone (B) of the Nanjemoy formation in Charles County, MD. Note the presence of black pyrite around and within some of the glauconite grains (green) in the unoxidized zone. Plane polarized light. Frame length approximately 1.2 mm.

Micrograph of thin section from a sample collected from unoxidized zone of the Nanjemoy formation in Charles County, MD. Note the presence of (light) pyrite around and within some of the glauconite grains (green). Combined reflected and plane polarized light. Frame length approximately 1.2 mm.

Light Microscopy

Observations of thin sections using plane

polarized light show that the glauconite

in the oxidized zone appears yellowish

green (5Y-2.5GY 6/6-6/8) in color, while

in the unoxized zone the glauconite

appeared to be more bluish green (5GY

5/8-6/8) in color. This difference in color

has been attributed to a difference in the

ratio of ferrous to ferric Fe in the mineral

structure (Fanning et al., 1989b; Stucki

and Roth, 1977). Furthermore, pyrite can

be clearly seen in the unoxidized zone as

opaque grains under transmitted light and

as yellowish colored grains under

reflected light (Fig. 1-4). While some of

the pyrite occurred distinctly apart from

the glauconite, a portion of the pyrite was

intimately associated with glauconite.

This pyrite occurred both as embedded

grains within the matrix of glauconite

and also within fissures and other voids

in the glauconite. Pyrite is absent from

samples of the oxidized zone. However,

there were within the oxidized materials,

zones of Fe oxide or oxyhydroxide

concentrations visible as coatings and

soft masses.

Electron Microscopy Figure 1-4 Figures 1-5A and 1-5B show the

accumulation of pyrite on one face of a fracture through a glauconite grain. The backscattered

image of the minerals in this figure illustrates the compositional difference between the pyrite

(more electron dense) as the light colored phase, and the glauconite (less electron dense).

Essentially all of the pyrite associated with the glauconite demonstrates a euhedral habit,

suggesting that this portion of the pyrite was authigenic (formed post-depositionally).

Pyrite also occurs in the sediment in phases not associated with glauconite. Clusters of euhedral

pyrite having an octahedral habit have been observed, with some crystal and clusters ranging up

to >20 /un in size (Fig. 1-6A). The delicate euhedral structures showed no evidence of abrasion

or rounding which indicates that the grains also formed post-depositionally, as forms of this

nature would not tolerate the forces of sedimentary transport.

59

SEM of pyrite from the unoxidized zone of the Nanjemoyformation which were separated from the nonmagnetic (non-glauconitic) fraction using heavy liquids. Pyrite occurred both as clusters of euhedral crystals (A) and also with a framboidalhabit (individual microcrystals show pyrithohedral habit) (B).

A

B

Scanning electron micrograph of euhedral pyrite (light area) on an exposed fissure in a glauconite grain (A) from the unoxidized zone in the Nanjemoy formation. B is a higher magnification of the inset area grain shown in A (backscatter electron emission). Rabenhorst, M. C. and D. S. Fanning. 1989. Soil Sci. Soc. Am. J. 53:1791-1797.

A

B

Framboidal pyrite was also observed in the heavy fraction (Fig. 1-6B). Pyrite framboids have

been reported in materials formed under a variety of environments including tidal marsh and

estuarine sediments and in coal. While other habits have been reported, the individual

microcrystals within the framboid shown in Fig. 1-6B appear to be pyritohedral in shape. Pyrite

framboids have been clearly shown to occur in sediments as both allogenic grains having formed

in one environment and being transported to another, and as authigenic grains forming in place.

The framboidal nature of this portion of the pyrite is not therefore indicative of its origin in these

sediments.

Figure 1-5 Figure 1-6

60

There are two soil pits open for examination (Stop 1A and Stop 1B) (Fig 1-1). Due to the great

depth to sulfides, the sulfide bearing zone is not exposed in the pits. At Stop 1B we will try to make an

auger boring deep enough to reach the sulfides demonstrating the presence of sulfidic materials at depth

in these landscapes (at Stop 1A, the depth to sulfide is estimated to be approximately 8 m below the

surface).

The exposed Annapolis profile (1A) is an example of a post-active acid sulfate soil. Unlike the

soil to be observed at Stop 1B, this soil occurs in a well drained upland position and is much more typical

of the majority of post-active acid sulfate soils in the Coastal Plain. As indicated in the following

description made of a profile located near to the pit exposed for this tour (but note that this is not the same pit/pedon), Jarosite mottles occur within 1 m of the land surface.

Table 1A- Pedon description of Pedon S79MD16-1 (S79 MD 033-1 by FIPS) Annapolis (formerly Collington) loamy fine sand (taxadjunct) - Nearby to where the pit for Stop 1A is located - but not the same pit/pedon.Inceptic Hapludult, fine-loamy, mixed, mesic

Horizon Depth (cm) Description

Ap 0-30 Dark brown (10YR 3/3) moist, pale brown (10YR 6/3) dry, loamy fine sand; weak medium granular structure in upper 5 cm, massive below 5 cm; friable; pH 4.8; abrupt smooth boundary.

E 30-37 Yellowish brown (10YR 5/4) to dark yellowish brown (10YR 4/4) loamy fine sand; massive; friable; pH 4.8; clear smooth boundary.

BE 37-54 Yellowish brown (10YR 5/4) to dark yellowish brown (10YR 4/4) fine sandy loam; weak medium subangular blocky structure; friable; pH 4.6; clear smooth boundary.

Bt 54-68 Dark yellowish brown (10YR 4/4) and olive (5Y 5/4) where indurated, sandy clay loam; weak coarse prismatic breaking to moderate medium subangular blocky structure; friable to firm and very firm where indurated; thin nearly continuous brown (7.5YR 4/4) clay films on ped faces and fossil casts; pH 4.6; clear smooth boundary.

BCj 68-100 Olive (5Y 4/3) fine sandy loam; common medium yellow (5Y 7/6) jarosite concentrations, and common medium strong brown (7.5YR 5/6) iron oxide concentrations where slightly indurated; weak coarse subangular block structure; friable; pH 4.5; gradual smooth boundary.

Cj1 100-130 Olive (5Y 4/3) fine sandy loam; common medium yellow (5Y 7/6) jarosite concentrations; massive; friable; pH 4.4; gradual smooth boundary.

Cj2 130-190+ Olive (5Y 4/3) fine sandy loam; common to many medium yellow (5Y 7/6) jarosite concentrations; massive; friable to firm where partially indurated; pH 4.2.

Location Prince Georges County, Maryland; University of Maryland Tobacco Research Farm near westernmost buildings, east side of farm lane, 35 meters east of tobacco drying barn. Approximately 38.858031, -76.779382

Vegetation Grass

Parent Material Glauconitic, sulfidic sediments of the Aquia Formation of Paleocene age

Physiography Coastal Plain Upland

Elevation 30 m

Slope 2% northern aspect

Drainage Well drained

Permeability Moderately slow

Moisture Moist

Groundwater 7 meters

Described by D. P Wagner and D. S. Fanning 8/29/78

Remarks An auger boring at this site did not encounter sulfidic strata within a depth of 8 m. Caving of the hole prevented deeper observation. This soil is a taxadjunct of the Collington series, which is classified as a Typic Hapludult

61

Pedogeomorphic modeling of the depth to sulfide-bearing materials - Aquia Formation

Based on the M.S. Thesis of Terry M. Valladares

While the approximate geographic extent of sulfide-bearing sediments is known, the

depth at which sulfides occur is highly variable, ranging from 2 m to over 15 m. Because

geomorphic factors control the depth to sulfidic “unoxidized zone” materials, soil-geomorphic

landscape models were developed to estimate the depths at which these potentially hazardous

materials occur in various portions of a landscape. Information regarding the depths at which

sulfides occur in various landscapes would prove useful to those who engage in land

development and highway construction activities. This would allow earth-moving activities to

be better managed to avoid disturbance of sulfidic materials and thereby minimize the potential

hazard of developing acid sulfate conditions.

Materials in the unoxidized zone generally have moist Munsell chromas of 1 or less and values

of 4 or less, that is, they are usually black or dark grey in color. The boundary between the

oxidized and unoxidized zone is almost always very sharp or abrupt and is therefore easily

distinguished in the field. The depth at which this boundary occurs in the natural landscape or

the depth at which the sulfide-bearing materials is encountered is primarily a function of

topographic variables which control the depth of geologic oxidation and weathering. As shown

in Fig. 1-7, sulfide-bearing materials have pHs in the range of 4.5 to 7.5.

There are sharp increases in chromium-reducible sulfur (CRS) contents across the abrupt

morphological boundary determined from field observations (based on differences in color),

indicating that accurate determinations of the boundary between oxidized and sulfide-bearing

strata could be made in the field (Fig. 1-8). CRS contents for both Upper Cretaceous and

Tertiary sulfide-bearing materials vary between 0.3 and 2.1% (0.6 to 4.0% pyrite). As shown in

Fig. 1-9, moist incubation of fine sandy loam Aquia, Nanjemoy sulfide-bearing materials

-200

-150

-100

-50

0

50

3 4 5 6 7Dis

tan

ce f

rom

bo

un

dar

y (

cm)

pH

Aquia (Paleocene)Nanjemoy (Eocene)

Changes in pH across the morphological boundary (zero line) between the oxidized and unoxidizedzones in the aquia and Nanjemoy formations. Borings sampled had depths to sulfides ranging from 2.6 to 11.1 m (Aquia) and 4.1 to 8.1 m (Nanjemoy).

Figure 1-7

62

-200

-150

-100

-50

0

50

0 0.5 1

Dis

tan

ce f

rom

bo

un

dar

y (

cm)

% CRS

Aquia (Paleocene)Nanjemoy (Eocene)

Chromium reducible sulfur (CRS) contents across the morphological boundary (zero line) between the oxidized and unoxidized zones in the Aquia and Nanjeoy formations.

2

3

4

5

6

7

0 10 20 30 40 50 60

pH

Time (days)

Aquia (Paleocene)Nanjemoy (Eocene)

Graphs of moist, aerobic incubation pH vs time for samples from the Nanjemoy and Aquia sulfide-bearing samples. Samples were collected between 5 and 150 cm below the boundary between the oxidized and unoxidized zones, and samples contained between 0.4% and 1.1% chromium-reducible sulfur (CRS).

demonstrate that they are also sulfidic or potentially acid (pHs dropped to values between 2.3

and 3.0 by the end of the incubation).

Figure 1-8

Figure 1-9

63

Highly significant regression models indicate that point relief (the difference in elevation between the point of interest and the lowest point or hydrologic base point in the landscape unit) could explain at least 75% of the variability in depth to sulfides (Fig. 1-10). These models result in a reasonably good agreement between observed and predicted depths to sulfides on model validation data sets. Fig. 1-11 shows spatial patterns of the depth to sulfides (estimated using the quantitative model) for the Aquia geomorphological setting.

The Upper Marlboro site is a very broad interfluve with undulating topography and

several small hills rising to an elevation of about 36 m (Fig. 1-11). On the western edge of the

Upper Marlboro landscape, the area slopes steeply downwards to the Western Branch of the

Patuxent River. This site is almost entirely covered by the Aquia Fm except for erosional

remnants of Pleistocene terrace deposits at the surface along transects 2, 3, and 4 (Figs 1-12, 1-

13, 1-14).

y = 2.71e0.06x

R² = 0.75

y = 0.89x - 14.65R² = 0.96

y = 0.75x + 2.72R² = 0.83

0

2

4

6

8

10

12

14

16

18

0 10 20 30

Dep

th t

o s

ulf

ides

(m

)

Point relief (m)

Matawan/Monmouth Fms Nanjemoy & Marlboro Clay Fms

Aquia Fm

Talbot Fm

Figure 1-10

64

Figure 1-11

65

Transect 2

Transect 3

As shown in the cross-sections of transects 2, 3, and 4 (Figs 1-12, 1-13, 1-14

respectively), the boundary between oxidized and sulfide-bearing strata occurs at a relatively

constant elevation (about 26.5 m) in the portion of the landscape furthest from the Western

Branch of the Patuxent River. This section of the landscape also has thin remnants of

Pleistocene terrace deposits at the surface. These terrace deposits are of fluvial origin and are

probably of Late Pleistocene age (Glaser, 1981). Both pH and chromium reducible sulfide

(CRS) data (generally equivalent to pyrite in these landscapes and systems) are provided in Figs

1-7 and 1-8.

Figure 1-12

Figure 1-13

66

Transect 4

Transect 5

Along transect 5, there is a gradual sloping downwards (≈1.5% slope) of the sulfide surface

toward the highly dissected backslope areas of Western Branch (Fig. 1-15). Therefore, sulfides

occur at shallower depths in areas further away from the highly dissected Western Branch

channel. Sulfides are not found even at depths of 12.0 to 12.5 m at UM 1-1 (summit) and UM 1-

2 (shoulder) (Fig. 1-11). The entire UM 1-2 profile is highly oxidized and indicates the edge

weathering effect typical of steep valley backslopes (Richardson and Daniels, 1993). Depth to

sulfides is more strongly affected by the Western Branch channel at distances of up to 0.6 km

from the channel. Sulfides occur at greater depths with decreasing distance from the channel and

is related to the highly oxidized nature of profiles (“red edge effect”) that occur close to steep

valley backslopes in otherwise nearly level landscapes. Thus, at the Upper Marlboro site,

proximity to the Western Branch channel has more effect on the depth to sulfides than local

variations in topography.

Figure 1-14

Figure 1-15

67

Figure 1-16. Left – A zone of silica-cemented shell-casts in a Bqm horizon beneath a Bt horizon in a monolith (from the

collection of soil monoliths in H. J. Patterson Hall of the University of Maryland in College Park, MD) of the Annapolis

soil series variant (Typic Hapludult; fine-loamy, glauconitic, mesic), a post-active acid sulfate soil collected near to Stop

1A. Based on other XRD work in similar settings, the silicified/indurated material is thought to be cemented by opal-CT.

This zone shown is for the 40 cm to 75 cm depth.

Right – A large piece (35 cm by 22 cm) of the silica-cemented shell casts material from the same soil near Stop 1A. This

material had a pH of about 4.0 (in water). It likely had a pH of about 8 when the shells were present, when the silica may

have been deposited after being released into solution by active acid sulfate weathering higher in the soil-geologic column

and when pyrite was still present in these soil materials. The past presence of pyrite is inferred by the presence of

jarosite concentrations on some of the shell casts.

68

Stop 1B

Figure 1-17. Location of Stop 1B which occurs along transect 2 (Valladares) roughly midway between points 2-1 and 2-2.

Transect 2

Approximate Location of Stop 1B

69

Tab

le 1

-2 P

edo

n d

escr

ipti

on

of

Ad

elp

hia

pit

sto

p 1

B. (

Ori

gin

al d

escr

ipti

on

19

98 w

as in

th

e ge

ner

al v

icin

ity;

up

dat

ed

fro

m a

uge

r b

ori

ng

on

Ju

ne

13,

201

6 b

y M

. Rab

enh

ors

t an

d D

. Sm

ith

.)

Ho

rizo

n

Dep

th

(cm

)

pH

Ju

ne

201

6

Text

M

atri

x C

olo

r

Red

ox

Feat

ure

s St

ruct

ure

C

on

sist

. B

ou

nd

. O

ther

Co

mm

ents

D

epl.

Co

nc.

A

0-6

fsl

10

YR3/

3

1-2

gr

vfr

cs

Ap

8

-24

fsl

10

YR3/

4

1 s

bk

fr

cs

BE

24

-50

fsl

10

YR4/

4

Bt

50

-75

cl

10

YR4/

4

cmf

2.5

Y5/3

cm

d

7.5

YR3/

4,4

/6

2m

sbk

fr

cs

10%

wea

ther

ed (

kao

linit

ized

) fe

ldsp

ar 7

.5YR

6/4

BC

7

5-1

00

sl

10

YR4/

4

cmf

2.5

Y4/2

cm

f 7

.5YR

4/4

, 4

/6

1co

pl /

1

msb

bk

vfr

cs

30%

wea

ther

ed (

kao

linit

ized

) fe

ldsp

ar 7

.5YR

6/4

;

BC

g1

100

-14

0lf

s 5

Y4/2

m

m&

co d

1

0YR

4/6

1

cop

l/

1m

sbk

fr

cs

35%

wea

ther

ed (

kao

linit

ized

) fe

ldsp

ar 7

.5YR

6/4

; so

me

we

ath

ered

fra

gmen

ts a

re

wh

ite

2.5

Y7/2

BC

g2

140

-17

5lf

s 5

Y4/2

M

(45

%)m

d

7.5

YR3

/4

1m

&co

sbk

vfr

BC

g3

175

-24

0lf

s 5

Y4/2

cf

p 7

.5YR

4/6

m

ost

ly in

u

pp

er p

art

BC

gj

240

-30

0lf

s 5

Y4/2

M

(20

%)

md

5Y6

/4

Co

nce

ntr

atio

ns

are

jaro

site

BC’

300

-32

24

.11

lfs

7.5

YR

3/4

, 4/6

m

m&

co d

5

Y4/2

Cgs

e 3

22-3

40

4.9

8

lfs

10

Y2.5

/1

c(20

%)m

d

7.5

YR3

/3

Sulf

ide

Bea

rin

g

Co

nsi

sten

ce: v

fr –

ver

y fr

iab

le; f

r –

fria

ble

; St

ruct

ure

: gr –

gran

ula

r; s

bk –

sub

angu

lar

blo

cky;

pl –

pla

ty; m

a –

mas

sive

; co

– c

oar

se; m

– m

ediu

m;

Red

ox

Feat

ure

s: A

BU

ND

AN

CE

f –

few

; c –

co

mm

on

; m –

man

y; S

IZE

f –

fin

e; m

– m

ediu

m; c

o –

co

arse

; CO

NTR

AST

f –

fai

nt;

d –

dis

tin

ct; p

– p

rom

inen

t;

Text

ure

: fsl

– f

ine

san

dy

loam

; cl –

cla

y lo

am; s

l – s

and

y lo

am; l

fs –

loam

y fi

ne

san

d;

70

Figure 1-18. June 13, 2016 boring at Stop 1B showing contact with unoxidized zone (BC’ over Cgse) at 322 cm.

71

0.00

0.20

0.40

0.60

0.80

1.00

1.20

3

3.5 4

4.5 5

5.5 6

6.5 7

050

100150

200250

300350

400450

pH - Sept 1995

pH - O

ct. 1998

pH June 2016

CRS

pH

%CRS

Depth (cm)

Figure 1-19. Percent CRS and pH measured above and below the boundary between

the oxidized and unoxidized zones in a boring near to Stop 1B. The pH measurements

were made in the Fall of 1995, in the Fall of 1998 and on June 13, 2016. The 3 borings

were probably made within 30 m of each other.

72

References - Mid-Conference Tour

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Balduff, D. M. 2007. Pedogenesis, inventory, and utilization of subaqueous soils in Chincoteague Bay, Maryland. In: Environmental Science and Technology. University of Maryland, College Park, MD.

Bradley, M. P. & Stolt, M. H. 2002. Evaluating methods to create a base map for a subaqueous soil inventory. Soil Science, 167, 222-228.

Bradley, M. P. & Stolt, M. H. 2003. Subaqueous soil-landscape relationships in a Rhode Island estuary. Soil Science Society of America Journal, 67, 1487-1495.

Castenson, K. L. & Rabenhorst, M. C. 2006. Indicator of reduction in soil (IRIS): Evaluation of a new approach for assessing reduced conditions in soil. Soil Science Society of America Journal, 70, 1222-1226.

Coppock, C. & Rabenhorst, M. C. 2003. Subaqueous soils of Rehoboth Bay, DE: Soil mapping in a coastal lagoon. In: Annual Meeting Soil Science Society of America. Denver, CO.

Demas, G. P. 1998. Subaqueous soil of Sinepuxent Bay, Maryland. Ph.D. Dissertation. In: Natural Resource Sciences and Landscape Architecture. University of Maryland, College Park.

Demas, G. P. & Rabenhorst, M. C. 1998. Subaqueous soils: a resource inventory protocol. In: Proceedings of the 16th World Congress on Soil Science. Montpellier, France. August 20-26,1998.

Demas, G. P. & Rabenhorst, M. C. 1999. Subaqueous soils: Pedogenesis in a submersed environment. Soil Science Society of America Journal, 63, 1250-1257.

Demas, G. P. & Rabenhorst, M. C. 2001. Factors of subaqueous soil formation: a system of quantitative pedology for submersed environments. Geoderma, 102, 189-204.

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Fiola, J. C. , B. M. Wessel, and M. C. Rabenhorst. 2016. Constructing and Evaluating a Monolith of an Active Acid Sulfate Soil with a Duripan. 8th International Acid Sulfate Soils Conference, College Park, MD, USA. July 17-23, 2016. Abstracts.

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