GEOLOGICAL SURVEY PROFESSIONAL PAPER

I./

"**'
Sand Dunes on the

Central Delmarva Peninsula,

Maryland and Delaware

By CHARLES S. DENNY and JAMES P. OWENS

SURFACE AND SHALLOW SUBSURFACE GEOLOGIC STUDIES IN THE 

EMERGED COASTAL PLAIN OF THE MIDDLE ATLANTIC STATES

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1067-C

During the maximum advance of the 

late Wisconsin ice sheets, an 

environment cooler and drier than 

the present one permitted dune 

building on the Delmarva Peninsula

UNITED STATES GOVERNMENT PRINTING OFFICE : WASHINGTON 1979
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Denny, Charles Storrow, 1911-

Sand dunes of the central Delmarva Peninsula, Maryland and Delaware.

(Surface and shallow subsurface geologic studies in the emerged Coastal Plain uf the Middle Atlantic States)(Geological Survey

professional paper); 1067-C) 

Bibliography: p.

Supt. of Doc. no.: I 19116:1067-0 

1. Sand-dunes Delmarva Peninsula. I. Owens, James Patrick, 1924- joint author. II. Title. III. Series. IV. Series: United

States. Geological Survey. Professional paper ; 1067-C. 

GB636.D44D46 551.4'5 77-608322

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, B.C. 20402 

Stock Number 020-001-03193-1
CONTENTS

Page

Abstract ————————- 

Introduction ——————-

Acknowledgments - 

Lithology————————-

Sand composition - 

Internal structure ——- 

Weathering——————- 

River dunes ——————- 

Upland dunes—————• 

Age and origin————- 

References cited ———•

Cl 

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ILLUSTRATIONS

FIGURE 1. Map showing distribution of Parsonsburg Sand, central Delmarva Peninsula———————

2. Sketch showing parabolic dunes, central Delmarva Peninsula ————————————————

3. Frequency curves showing grain size of dune sand——————————————————————

4. Ternary diagram showing quartz-feldspar ratios in dune sand————————————————

5. Ternary diagram showing heavy-mineral assemblages in dune sand ————————————

6. Cross section of bedded sand containing animal burrows———————————————————

7. Cross section of weathering profile in Parsonsburg Sand———————————————————

8. Diagrams showing clay-sized mineral assemblages in weathering profiles of four dunes—

9. Soil map of sand dune near Snow Hill, Md———————————————————————————

10. Cross section of weathering profile in parabolic dune near Pittsville, Md —————————

11. Cross section of dune near Wango, Md —————————————————————————————

12. Map of sand dunes along Nanticoke River ———————————————————————————

13. Map of sand dunes near Snow Hill, Mcl —————————————————————————————

14. Cross section of isolated dunes southeast of Pocomoke River————————————————

15. Rose diagram showing orientation of river dunes———————————————————————

16. Asymmetric profiles of parabolic dunes —————————————————————————————

17. Map of sand dunes near Parsonsburg, Md ———————————————————————————

18. Cumulative curve showing spacing between upland dunes——————————————————

19. Map showing orientation of parabolic dunes on uplands east and south of Salisbury, Md

20. Rose diagram showing orientation of upland dunes east and south of Salisbury, Md ——

C2

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7

8

9

10

10

11

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12

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TABLES

TABLE 1. Weathering profile in sand dune southeast of Pocomoke River near Snow Hill, Md •

2. Soils developed on parabolic dune near Snow Hill, Md—————————————————-

3. Dimensions of dunes along the Nanticoke and Pocomoke Rivers———————————-

4. Dimensions of dunes on uplands east of Salisbury, Md—————————————————-

C6 

8

11

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in
SURFACE AND SHALLOW SUBSURFACE GEOLOGIC STUDIES IN THE EMERGED COASTAL PLAIN OF

THE MIDDLE ATLANTIC STATES

SAND DUNES ON THE

CENTRAL DELMARVA PENINSULA,

MARYLAND AND DELAWARE

By CHARLES S. DENNY and JAMES P. OWENS

ABSTRACT

Inconspicuous ancient sand dunes are present in parts of the central 

Delmarva Peninsula, Maryland and Delaware. Many dunes are roughly 

U-shaped, built by northwest winds, especially on the east sides of 

some of the large rivers. On the uplands, the form and spacing of the 

dunes are variable. A surficial blanket composed mainly of mediumand fine-grained sand—the Parsonsburg Sand—forms both the ancient 

dunes and the broad plains between the dunes. The sand that forms 

the dunes is massive and intensely burrowed in the upper part; traces 

of horizontal or slightly inclined bedding appear near the base. Quartz 

is the dominant mineral constituent of the sand. Microline is abundant 

in the very fine to fine sand fraction. The heavy-mineral assemblages 

(high zircon, tourmaline, rutile) are more mature than in most of the 

possible source rocks. The most abundant minerals in the clay-sized 

fraction are dioctahedral vermiculite, kaolinite, illite, montmorillonite, 

and gibbsite. The first four minerals are common in deposits of late 

Wisconsin and Holocene age. The gibbsite may be detrital, coming 

from weathered rocks of Tertiary age. The soil profile in the dune sand 

is weakly to moderately developed. At or near the base of the Parsonsburg Sand are peaty beds that range in age from about 30,000 to 

about 13,000 radiocarbon years B.P. Microfloral assemblages in the 

peaty beds suggest that the dunes on the uplands formed in a spruce 

parkland during the late Wisconsin glacial maximum. The river dunes 

may also be of late Wisconsin age, but could be Holocene.

INTRODUCTION

Ancient sand dunes are common morphologic features 

in parts of the central Delmarva Peninsula, Maryland 

and Delaware. Many of the dunes are parabolic forms 

built by northwest winds. U-shaped forms are best developed on the east sides of some of the larger rivers. On 

the uplands, the dunes assume a variety of forms. Some 

are U-shaped, others are irregular mounds, still others 

are long narrow ridges having only a slight curvature in 

plan to suggest dune-building by northwest winds.

The dunes are inconspicuous. Their relief is low, especially on the uplands. Most parabolic dunes have gentle 

side slopes; rarely is the slope to windward gentler than 

that to leeward. The spacing between the dunes is irregular; some are in groups, others are more or less isolated. 

In short, the dunes on the central Delmarva Peninsula

are not well developed either in form or in abundance 

compared with those in other parts of the Atlantic Coastal 

Plain (Thorn, 1967).

A surficial blanket of sand, the Parsonsburg Sand 

(Rasmussen and Slaughter, 1955; Denny and others, 

1978), covers many areas in the central Delmarva Peninsula (fig. 1) and is the material that forms the dunes. 

However, in some places, the surface of the Parsonsburg 

Sand is a gently undulating plain without any dune forms. 

In the uplands east and south of Salisbury, Md., the Parsonsburg Sand commonly consists of an upper light-colored sand and a lower dark-colored sand or silt-clay rich 

in organic matter. Peaty sediment is also found in the 

upper sand in some places. The organic matter ranges in 

radiocarbon age from about 30,000 to about 13,000 years 

B.P. and contains microfloral assemblages suggesting 

that when the sand was deposited the climate was cooler 

and drier than it is at present. The region may have been 

a pine-birch barrens in which were shrubs, small ponds, 

and swamps containing spruce and alder. Presumably, 

this is the environment in which the dunes on the uplands 

were formed (Sirkin and others, 1977).

Along the rivers where the best developed parabolic 

dunes occur, the Parsonsburg Sand mantles terraces 

east of the rivers. The terraces are underlain either by 

sandy beds of Tertiary age (Beaverdam Sand and Pensauken Formation) or of Sangamon age (Kent Island 

Formation; Owens and Denny, 1978). At one locality, 

the Parsonsburg Sand is underlain by peaty sediment 

and may be contemporaneous with some of the Parsonsburg Sand on the uplands. Elsewhere along the rivers, 

the sand might range in age from late Sangamon to early 

Holocene.

The uplands east and south of Salisbury include a large 

area of what Rasmussen called the "Maryland basins," 

groups of more or less circular poorly drained swales bordered by low sandy ridges (Rasmussen, 1953, 1958). 

Comparison of a map of the "Maryland basins" east of

Cl
C2 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES 

75°45' 75°30'

38°30' —

38°15' —

EXPLANATION

Parsonsburg Sand

10 KILOMETERS

5 MILES

FIGURE 1.—Distribution of the Parsonsburg Sand (Denny and others, 1978) on the central Delmarva Peninsula between 

the Nanticoke and Pocomoke Rivers. In many areas, the Parsonsburg Sand forms parabolic or irregularly shaped 

dunes. Areas outlined are locations of detailed maps of the dunes reproduced in this paper.

Salisbury (Rasmussen and Andreasen, 1959, pi. 4) with 

our map of the sand dunes in the same area shows wide 

discrepancies between the position and form of the sand 

dunes and the rims of the "Maryland basins."

The U-shaped or parabolic dunes are a type "*** in 

which the middle part has moved forward with respect 

to the sides or arms" (McKee, 1966, p. 9-10; see also

Hack, 1941, p. 242; Cooke and Warren, 1973, fig. 4.27). 

When the dunes were active, the "arms [were] *** anchored by vegetation and the entire dune [was] *** relatively stable" (McKee, 1966, p. 10). Figure 2 illustrates 

the terms used to describe the dunes.

The individual dunes range from small knolls about 1 

m (3-4 ft) high and about 30-90 m (100-300 ft) in di-
SAND DUNES ON THE CENTRAL DELMARVA PENINSULA C3

500 1000 METERS

_LJ_

1000 2000 3000 FEET

Direction of dune-building wind 

Crest

PROFILE OF DUNE

FIGURE 2.—Parabolic dunes in the Laurel quadrangle, Delaware, 

central Delmarva Peninsula.

ameter, to long narrow ridges as much as 4.6 m (15 ft) 

high and more than 4 km (2.5 mi) in length. In plan, some 

ridges are long, gently curving bands; others turn as

much as 180°. The long, gently curving ridge in figure 

2. is interpreted to be three parabolic dunes whose arms 

are connected. The dune was built by northwest winds; 

it has a gentle windward or back slope to the northwest 

and a steeper slip face to the southeast.

ACKNOWLEDGMENTS

On behalf of the Delmarva project, it is a pleasure to 

acknowledge the assistance of the Maryland Geological 

Survey, K. N. Weaver, Director, and of the Delaware 

Geological Survey, R. R. Jordan, Director, and the staffs 

of the Surveys. Grace Brush, C. B. Hunt, and L. C. Peltier visited the area and offered helpful suggestions. 

Various members of the U.S. Department of Agriculture 

aided the study in various ways, especially Klaus Flack, 

R. L. Hall, Ray Daniels, and Paul Siegrist.

Finally, our thanks to our colleagues in the U.S. Geological Survey—to Melodie Hess and the late Karl Stefansson for many mineralogical determinations, and to 

M. J. Grolier, J. T. Hack, W. S. Kirk, R. B. Mixon, William Raspet, and R. S. Sigafoos for discussions and for 

assistance in the field.

LITHOLOGY

The Parsonsburg Sand that forms the dunes is composed largely of medium- and fine-grained sand. Roughly 

45 percent of the grains range in diameter from 0.25 to 

0.50 mm and about 40 percent, from 0.125 to 0.25 mm 

(fig. 3). Small amounts of coarser and finer grains include 

small pebbles, granules, very fine sand, and silt. The size 

distribution is common for dune sand. A binocular examination of several samples of sand reveals large percentages of rounded to well-rounded grains in the medium and coarse sand fractions. In addition, many of the 

sand grain surfaces are frosted and pitted.

SAND COMPOSITION

The mineral composition of the Parsonsburg Sand and 

of its possible source rocks is discussed in detail elsewhere (Denny and others, 1978; Owens and Denny, 

1978). The dune sands are mostly quartz, although the 

mineralogy varies from place to place. Microcline, the 

next most abundant constituent, makes up 10-20 percent of the very fine to fine sand fraction (0.149-0.074 

mm) but declines rapidly in the medium to coarse sand 

fractions, where it is estimated to occur in amounts less 

than 5 percent. The compositional variation of the light 

minerals in the dune sand in the size range cited above is 

shown in figure 4 together with the quartz-feldspar ratios in the various possible source rocks. Except for the 

sand of the Walston Silt and those from the modern barrier at Assateague Island, the Parsonsburg Sand has a 

lower feldspar content than do most of the possible 

source formations. The heavy-mineral assemblages in
C4 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

EXPLANATION

70 -

60-

b 

D 60

I

LU

40 -

30 -

20 -

10 

QUARTZ

PLAGIOCUASE

EXPLANATION

Holocene barrier 

Parsonsburg Sand

 Upland east and south of Salisbury, Md.

* Along Nanticoke River

A Along Pocomoke River 

Sinepuxent Formation 

Ironshire Formation 

Omar Formation

O Walston Silt (Samples from weathered zone)

+ Beaverdam Sand

 Pensauken Formation

FIGURE 4.—Ternary diagram showing quartz-feldspar ratios for the 

Parsonsburg Sand and possible source rocks in the very fine to fine 

sand-size fraction (0.149-0.074 mm).

the Parsonsburg Sand are more mature (higher zircontourmaline-rutile concentrations) than they are in most 

adjacent formations except the Walston (fig. 5).

The more mature composition of the Parsonsburg Sand 

as compared with that of most of the adjacent source 

rocks suggests several possible interpretations. The first 

explanation is that the Parsonsburg Sand is well drained, 

and the compositional maturity is the result of intrastratal weathering of the more labile minerals such as amphiboles, pyroxenes, and to a lesser degree the feldspars. This explanation does not seem likely because the 

older Ironshire Formation of Sangamon age composed of 

relatively well-sorted clean sand is compositionally less

1 2 3 

DIAMETER, IN PHI UNITS 

B

FIGURE 3.—Frequency curves showing grain size of dune sand. 

A, Dunes on the central Delmarva Peninsula. PS is a curve 

representing an average of 25 samples. Field numbers S3, 

Nil, P2, SH1, and W17 designate curves for individual samples. B, Comparison of Delmarva dunes with those of other 

regions: PS, Delmarva dunes; K, Kelso dunes, Mojave Desert, California (Sharp, 1967, fig. 17, sample 13); WS, dunes 

at White Sands National Monument, New Mexico (McKee, 

1966, table 1, dome-shaped and parabolic dunes): WSn, near 

source, WSf, 16 km (10 mi) from source.
SAND DUNES ON THE CENTRAL DELMARVA PENINSULA C5

HORNBLENDE 

EMDOTE 

GARNET 

ACTINOLm EXPLANATION 

TREMOLFTE

STAUROLFTE 

SILUMANFTE 

KYANFTE 

OTHERS

Holocene barrier 

Parsonsburg Sand

 Upland east and south of Salisbury, Md.

® Along Nantkoke River

A Along Pocomoke River 

Sinepuxent Formation 

Ironshke Formation 

Omar Formation

Wateton Silt (Samples from weathered zone) 

Beaverdam Sand 

Pensauken Formation

FIGURE 5.—Ternary diagram showing heavy-mineral assemblages (> 

2.80 sp gr; 0.149-0.074 mm in diameter) in Parsonsburg Sand and 

in possible source rocks.

mature than the Parsonsburg Sand (figs. 4 and 5). A second explanation is that the Parsonsburg Sand acquired 

its maturity through mechanical abrasion. The rounded 

and pitted nature of many of the quartz sand grains in 

the Parsonsburg lends support to this explanation. A 

third explanation is that the Parsonsburg Sand was derived from deeply weathered beds near the surface of 

adjacent formations. The mineralogy of the Walston Silt 

(figs. 4 and 5) supports this explanation. On the basis of 

existing information, the sands of the Parsonsburg were 

probably derived from adjacent older rocks in two steps. 

First, the parent rock was deeply oxidized under subaerial conditions, and second, the weathered debris was 

reworked by wind and water to form the Parsonsburg 

Sand.

INTERNAL STRUCTURE

The sand that forms the dunes is massive in the upper 

part; toward the base, however, traces of bedding appear. Many fresh exposures show no bedding; it is only 

when the outcrop has dried out and has been etched by

wind-driven sand that the face may show a faint stratification caused by slight changes in grain size. The beds 

are 1-2 cm thick. The attitude is horizontal or slightly 

inclined, rarely more than 10°. High-angle cross-bedding 

was nowhere observed. The sand below the dunes is 

commonly well stratified in horizontal layers and is described elsewhere (Denny and others, 1978).

The typical cross section through a dune and into the 

underlying sand shows a gradual transition from massive 

sand above to well-bedded sand below, the result of the 

disturbance or alteration of the sand during and after 

deposition. Some of the disturbance is due to the growth 

and decay of roots. Large tubes 0.3-0.6 m (1-2 ft) in 

diameter at the top and tapering downward to depths of 

2 m (6 ft) or more are clearly root casts; in some of them 

the root is still preserved. Some of the alteration is the 

result of weathering and will be discussed shortly.

The most distinctive feature of the gradual transition 

downward from massive to well-bedded sand is what appears to be ancient animal burrows, tube-shaped bodies 

of sand differing slightly from the enclosing sand in texture or color (fig. 6). In cross section, some of these tubes

15 CENTIMETERS

I

5 INCHES

FIGURE 6.—Cross section of bedded sand cut by irregular bodies of 

massive sand. The massive sand fills tubes and cavities believed to 

be animal burrows. The larger cavities appear to have formed 

where many tubes intersect. The animal is unknown. Sketched from 

a photograph. Exposure in borrow pit north of Parsonsburg, Md. 

(Pittsville 17, fig. 16).
C6 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

resemble the outline of fingerprints and thumbprints. Individual tubes are about 1-3 cm (0.4-1.0 in.) in diameter, range from perhaps 5-15 cm (2-6 in.) in length, 

and have long axes more or less vertical. In places, many 

such filled burrows intersect to form large bodies of massive sand. The burrows are especially conspicuous where 

filled with black sand. When the burrows were open to 

the sky, water or wind moved black sand across the 

ground surface and into the open end of the tube. The 

animal that formed the tubes is unknown.

WEATHERING

A dune of Parsonsburg Sand is typically weathered to 

depths ranging from about 0.3 to 1.2 m (1 to 4 ft). A surface horizon (fig. 7, horizons 1 and 2) of loose, very pale 

brown loamy sand overlies an intermediate horizon of 

slightly sticky brown sandy loam (horizon 3). The underlying material (horizon 4) is a loose, very pale brown 

loamy sand or sand that contains thin discontinuous yellowish-brown wavy bands or lamellae (U.S. Soil Conservation Service, 1975, p. 25) of material similar to that in 

the intermediate horizon (table 1). The intermediate horizon is discontinuous, and in places the upper horizon 

overlies the basal horizon, as shown in the right-hand 

part of figure 7.

In the weathering profiles at only two localities (the 

uplands east of Pittsville, Md.), the zircon, tourmaline, 

and rutile percentages decline with depth, suggesting local postdepositional chemical weathering.

The clay-sized fraction (<2 microns) of samples from 

several weathering profiles in the dune sand were Xrayed; the results are shown in figure 8. In the weath1 METER

1 2 3 FEET

FIGURE 7.—Cross section of weathering profile in Parsonsburg 

Sand forming a parabolic dune. Numbers designate weathering horizons. 1, gray, loamy sand (plow layer); 2, pale-yellowish-brown loamy sand; 3, brown sandy loam, discontinuous; 4, very pale brown sand and loamy sand containing 

wavy brown bands (lamellae) of sandy loam. Dune is near 

Snow Hill, Md., southeast of the Pocomoke River (locality 

G5, fig. 13). For descriptions of horizons, see table 1. Sketched 

from a photograph.

TABLE 1.—Weathering profile in sand dune southeast of Pocomoke 

River near Snow Hill, Md. (loc. G5, fig. 13)

[Color designations are based on the "Munsell Soil Color Chart" (Munsell Color Co., 1954). 

See also table 2]

Horizon Description Average depth in 

m(ft)

1. Loamy sand, gray (2.5Y 7/2),

structureless (Ap horizon) —————— 0.0-0.3 (0.0-0.9)

2. Loamy sand, pale yellowish brown 

(10YR 6/4, dry) becomes paler 

upward; structureless or faint paperthin wavy bands parallel to ground 

surface; few fine roots (A(?) horizon); 

transitional downward into horizon 3- 0.3-0.6 (0.9-1.9)

3. Sandy loam, brown (7.5YR 5/4, moist), 

slightly sticky; weak fine subangular 

blocky structure, unstratified; few 

fine roots; many burrows (B horizon); 

transitional downward into horizon 4. 

In places horizon 2 directly over lies 

horizon 4 ——-————-——-——— 0.6-0.9 (1.9-3.0)

4. Sand and loamy sand, very pale brown 

(10YR 7/4-8/1, moist) mottled with 

light yellowish brown (10YR 6/4), 

single grain, loose, many burrows, 

unstratified; contains yellowishbrown wavy bands (lamellae) of sandy 

loam similar to those of horizon 3, 

bands 0.25-2.5 cm (0.1-1.0 in.) 

thick, 5.0-60.0 cm (2.0-24.0 in.) 

long; in a vertical plane the 

undulations range from 5.0-10.0 cm 

(2.0-4.0 in.) high; bands become 

sandier with depth (C horizon) ———— 0.9-1.5 (3-6)

ering profile in the dune near Snow Hill (G5, fig. 8 ), the 

most common minerals are dioctahedral vermiculite, kaolinite, illite, montmorillonite, and gibbsite. Not shown 

in this figure but also present in the samples are halloysite and goethite. Vermiculite (containing chloritized layers) is the most common mineral throughout all the 

weathering horizons in this profile; kaolinite (+halloysite) is the next most common mineral. Illite, montmorillonite, and gibbsite are minor constituents. This particular profile shows little variation in mineral concentrations 

from top to bottom.

Samples from weathering profiles at three other localities in dune sand (D3d, P12d, SH20) and at one locality 

in sand of presumed Sangamon age (S5) have in general 

the same clay mineralogy. There is, however, some variation in the mineral concentration through the weathering profiles. In the D3d profile, kaolinite is the major 

mineral in the lower part of the profile but declines toward the surface, where it is replaced by vermiculite as 

the major mineral. Gibbsite also increases toward the 

surface. The same pattern is followed to varying degrees 

in the other profiles.

The mineral assemblages in the weathered zone of the
SAND DUNES ON THE CENTRAL DELMARVA PENINSULA C7

GROUND SURFACE2.0

2.2 —

EXPLANATION 

Montmorillonite

Vermiculite

Gibbsite

B Horizon of soil profile

FIGURE 8.—Clay-sized (< 2 microns) mineral assemblages in the weathering profiles of four dunes composed of Parsonsburg Sand

and in a weathering profile in the Ironshire Formation.

dune sand in the central Delmarva Peninsula appear 

anomalous in some respects. Vermiculite (soil chlorite in 

part), kaolinite, illite, and montmorillonite are common 

in deposits of Wisconsin and Holocene age (Owens and 

others, 1974). The presence of gibbsite is particularly interesting. To some, the presence of this mineral in a soilmineral assemblage suggests intermediate to intense 

weathering if the deposit is well drained and is Quaternary in age (Jackson, 1965). On the other hand, the upward increase in chloritized Vermiculite, particularly into 

the A soil horizon, suggests mild weathering in welldrained Quaternary deposits (Jackson, 1965). As most 

dunes are of late Wisconsin age and as the climate was 

probably cool temperate, the gibbsite in the soil profile is 

probably detrital. A study of the clay-silt fraction in the 

possible source rocks (Owens and Denny, 1978; Denny 

and others, 1978) shows that the Tertiary units, particularly the Beaverdam Sand, have large concentrations of

gibbsite locally in the weathered zone. This unit and perhaps also the Walston Silt may have supplied silt-sized 

aggregates of gibbsite to westerly winds. If so, the gibbsite could have been carried across the peninsula and deposited during deposition of the Parsonsburg Sand. 

Thereafter, the gibbsite could have been redistributed in 

the dune sand. Gibbsite was removed from the surface 

horizon (2) and deposited in the intermediate horizon (3) 

and along bedding planes in the underlying material (horizon 4) to form the wavy brown bands or lamellae.

Most samples of peaty clay at the base of many of the 

dunes contain gibbsite. Its presence in these unweatherecl peaty sediments suggests that in these beds the 

mineral is indeed detrital rather than a product of postdepositional subaerial oxidation. The presence of gibbsite in the basal clays supports the interpretation that 

most if not all of the gibbsite in the overlying sands is 

also detrital.
C8 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

The soils developed on the parabolic dune near Snow 

Hill, Md. (G5), are largely Entisols (Regosols) (fig. 9) or 

soils without pedogenic horizons (Lakeland series, no B 

horizon. For explanation of soil terminology see Hall, 

1973; Birkeland, 1974). Adjacent to the dunes are areas 

of Ultisols or soils containing a horizon of clay accumulation (Fort Mott and Sassafras series, B horizon). These 

three series are described in table 2. The dune near Snow 

Hill is mapped as a complex of the Lakeland and Fort 

Mott soil series. This relation is shown in figure 7, which 

has a Fort Mott profile on the left and a Lakeland profile 

on the right.

The discontinuous yellowish-brown wavy bands (lamellae) in the basal or C horizon appear to be associated 

in the lower part of the profile with traces of the original 

bedding of the deposit. This relationship is illustrated in 

a section through a low parabolic dune at Glass Hill, 

about 3 km west of Pittsville, Md. (fig. 10). Massive sand 

about 1.75 m (70 in.) thick containing wavy brown bands 

(lamellae) in the lower part grades downward into horizontally bedded sand at a depth of about 2.5 m (95 in.). 

The sand containing wavy brown bands is intensely burrowed. Near the base, discontinuous masses of unburrowed sand show faint horizontal stratification, in part 

due to dark-mineral laminae. The wavy brown bands (lamellae) may be the result of the deposition of silt- and 

clay-sized particles by water moving down through the 

sand, as previously mentioned.

The arrangement of the weathering horizons in some 

exposures suggests the destruction of weathering products by erosion and deposition. For example, in figure 7, 

horizon 3 is shown to be discontinuous; it appears to have 

been partially removed and subsequently buried by 

younger sand (horizons 1 and 2).

75°27'30"

38°07' —

1 MILE

EXPLANATION

Lake land soil series

Sassafras soil series 

Fort Mott soi series

771— Complex of Lakeland and 

Fort Mott soi series

Borrow pit (figure 13) 

FIGURE 9.—Soils developed on parabolic dune near Snow Hill, Md. 

Outline of dune shown by hachured line. Dune is composed of Parsonsburg Sand; the adjacent areas are underlain by the Kent Island Formation of late Sangamon age. Lakeland, Sassafras, and 

Fort Mott are well drained to excessively drained soils. Remainder of area is underlain by moderately well to poorly drained soils. 

Map generalized from Hall (1973). For description of soil units see 

table 2.

TABLE 2.—Soils developed on parabolic dune (G5) near Snow Hill, Md.

[Modified from Hall, 1973. Horizon thickness in cm (in.)]

Lakeland loamy sand Lakeland loamy sand, clayey 

substratum Fort Mott loamy sand Sassafras sandy loam

0-25 (0-10), grayishbrown (2.5Y 5/2) loamy 

sand.

25-100 (10-40), lightyellowish-brown (2.5Y 6/ 

4) and yellowish-brown 

(10YR 5/6) loamy sand.

100-183 (40-72), paleolive (5Y 6/3) to lightgray (5Y 7/1) sand.

Similar to Lakeland loamy Al

sand, except that A 

horizon is sandier and C 

horizon contains more 

clay at depth of about 

152-213 (60-84).

A2

B22t

0-8 (0-3), grayish-brown Al

(10YR 5/2) loamy sand.

8-61 (3-24), lightyellowish-brown (2.5Y 6/ A2 

4) loamy sand.

B21t 61-76 (24-30), yellowishbrown (10YR 5/6) sandy 

loam.

76-94 (30-37), strong 

brown (7. SYR 5/6) heavy 

sandy loam.

94-127 (37-50), lightyellowish-brown (2.5Y 6/ 

4), very light loamy sand; B22t 

irregular inclusions of 

material similar to that in 

B22t horizon in upper C 

part.

Bl

B21t

0-3 (0-1), very dark

grayish-brown (10YR 3/2) 

sandy loam.

3-20 (1-8), olive-brown 

(2.5Y 4/4) to grayishbrown (10YR 5/2) sandy 

loam.

20-33 (8-13), lightyellowish-brown (10YR 6/ 

4) heavy sandy loam.

33-53 (13-21), lightyellowjsh-brown (10YR 6/ 

4) light sandy clay loam.

53-84 (21-33), strongbrown (7.5YR 5/6) sandy 

clay loam.

84-127 (33-50),

yellowish-brown (10YR 5/ 

8) loamy sand.
SAND DUNES ON THE CENTRAL DELMARVA PENINSULA C9

^Ground surface

0 10 20 30 40 CENTIMETERS

I III I

I n i r

0 5 10 15 INCHES 

EXPLANATION

Yellowish-brown wavy bands 

(lamellae)

- Bedded sand

FIGURE 10.—Cross section of weathering profile in parabolic 

dune near Pittsville, Md. The dune is mapped as Evesboro loamy sand, 5-15 percent slopes (Hall, 1970). Numbers designate weathering horizons. Sketched from photograph.

In some dunes, an older weathering profile appears to 

be truncated by a younger sand layer (fig. 11). A discontinuous horizon (3) of brown silty sand separates a surface horizon (1 and 2) of a very pale brown sand from a

basal horizon (4) of pale-yellow to white sand containing 

discontinuous wavy bands of brown silty sand, the whole 

probably constituting a single weathering profile. However, the intermediate and the basal horizons (3, 4) may 

constitute an ancient weathering profile, truncated at 

the top and overlain by a younger deposit of sand (1 and 

2). This dune near Wango, Md., was perhaps first built, 

then weathered, eroded, and finally covered by younger 

sand. If this is a two-cycle dune, when did the episodes 

of weathering, erosion, and deposition take place? If the 

older dune (3, 4) is late Wisconsin in age, the early episode of weathering may have been early Holocene, the 

"comparatively warm Hypsithermal interval" (Flint, 

1971, p. 524), the surface sand (1 and 2) being younger. 

The climate of the Eastern United States during the interval 10,000-6,000 years ago may have been slightly 

drier than it is at present (Wright, 1971, p. 452). Perhaps 

the surface sand is no more than a few hundred years 

old, the result of deforestation and cultivation in colonial 

times.

RIVER DUNES

Dunes of Parsonsburg Sand are found along the Chicamacomico, Nanticoke, Wicomico, and Pocomoke Rivers (fig. 1). Only those along the Nanticoke and the Pocomoke are described here. The dunes are on the 

southeast sides of the valleys (figs. 12 and 13) and near 

the rivers are at altitudes of about 3 m (10 ft); away from 

the rivers, they are at altitudes of about 12 m (40 ft). 

Near the rivers, the valley sides are underlain (fig. 14) 

by sand, gravel, and, locally, clay-silt of the Kent Island 

Formation (upper Sangamon); farther from the rivers, 

the valley sides are underlain by either the Omar Formation (lower Sangamon) or the Beaverdam Sand (Pliocene).

The river dunes vary greatly in size. Mean values for 

the dimensions of the Nanticoke River dunes are: diameter 1,130 m (3,700 ft); length of arm about 760 m (2,500 

ft); and height about 3 m (10 ft). For the Pocomoke River 

dunes, dimensions are: diameter about 1,070 m (3,500 ft); 

height about 2.2 m (7.3 ft); and length about 580 m (1,900 

ft). The data are summarized in table 3. The axial trend 

of more than 90 percent of the river dunes is northwest 

(fig. 15).

The largest and most spectacular of the river dunes 

are long isolated sand ridges such as Easter Hill near 

Seaford, Del. (fig. 12). Easter Hill stands on an essentially featureless plain about 3.2 km (2 mi) south of the 

river and is about 5 km (3 mi) long. The plain is underlain 

largely by the Beaverdam Sand. A second long sand 

ridge is found about 1 km (0.6 mi) to the south. Bedding 

was not observed in the few exposures available in the 

dunes. The form of these long sand ridges in plan and in 

profile (fig. 16) suggests that each one is made up of several nearly straight parabolic dunes whose arms touch
CIO GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

SW

30 40 FEET

38°37'3tT —

38°30'

FIGURE 11.—Cross section through sand dune, suggesting two successive episodes of dune building. The dune is on Beech Island near 

Wango, Md. For approximate description of weathering horizons 1, 2, 3, and 4, see table 1.

tation ridges on the northwest coast mark the landward 

edge of great dune fields.

Isolated ridges like Easter Hill might form where the 

supply of sand is available only from time to time. Suppose, for example, that sand from a bare Nanticoke flood 

plain formed a dune ridge on the edge of a terrace southeast of the river. If, in time, the surface of the flood plain 

became more or less stabilized by vegetation so that the 

supply of sand to the westerly winds was greatly reduced, it would seem likely that the dune on the terrace 

edge would move southeastward as sand was eroded 

from its gentle windward slope and deposited on its 

steeper slip face. If, after a time, the vegetation on the 

flood plain were disrupted, sand would again be available 

for eolian transport, and a second dune ridge would form 

on the edge of the terrace southeast of the river. Perhaps 

some such mechanism operated to produce the isolated 

ridges south of the Nanticoke River near Seaford (fig. 

12).

SantoiDcvnmaD 012345 KILOMETERS 

' , I I I I I I

EXPLANATION

£1?$: :£S Dunes at Rasonsbupg Sand

FIGURE 12.—Dunes of Parsonsburg Sand along Nanticoke River near 

Sharptown, Md., and Seaforcl, Del. Easter Hill is a dune nearly 5 km 

in diameter. Several large U-shaped dunes near Santo Domingo are 

also shown. For location see figure 1.

one another. Deposition was by winds from the northwest. The ridges resemble the "complex transverse 

dune" of David (1972, chap. 7, fig. 15).

The environment in which such long isolated sand 

ridges are formed is not known. Jordan (oral commun., 

1973) has suggested that Easter Hill might be a "precipitation ridge" or "a ridge due to precipitation of sand at 

a forest edge," as described by Cooper (1958, p. 55). 

This suggestion is reasonable. However, the features described by Cooper on the Oregon-Washington coast are 

much larger than Easter Hill, and between them and the 

sand source at the beach is a sheet of sand. The precipiUPLAND DUNES

The dunes on the upland east and south of Salisbury 

(fig. 1) are long narrow ridges that range in diameter 

from about 600 to 6,000 m (2,000-19,500 ft; table 4). 

Many of the dunes are symmetrical in cross profile, and 

the side slopes are very low, commonly only 2° or 3°. 

Some of the ridges are asymmetric in cross profile, the 

steeper slopes being on the southeast sides of the ridges. 

The steepest slopes are not more than about 10°. The 

dunes curve and recurve and have no consistent alinement overall, nor are they arranged in as orderly a fashion as are parabolic dunes in other regions (Cooper, 1967, 

pi. 6; Thorn, 1967, figs. 9 and 11).

Upland dunes northwest of the Pocomoke River near 

Snow Hill (fig. 13) tend to be elongated in an easterly or 

a northeasterly direction. Between the upper reach of 

Dividing Creek and Nassawango Creek, the ridge pattern suggests the southeast advance of a tongue-shaped 

mass of dunes onto the plain northwest of the river un-
SAND DUNES ON THE CENTRAL DELMARVA PENINSULA 

75°30'

Cll

75°22'30"

38°07'30" — 1000 2000 3000 4000 5000 METERS

EXPLANATION

Dunes of Parsonsburg Sand

X Borrow pit 

G5 fidd number

FIGURE 13.—Dunes of Parsonsburg Sand near Snow Hill, Md. Upland dunes northwest of Pocomoke River and river dunes southeast of

the river are shown. For location see figure 1.

TABLE 3.—Dimensions of dunes along the Nanticoke and Pocomoke

0 1000 2000 3000 FEET

EXPLANATION 

Marsh deposits (Holocene)

Parsonsburg Sand (Wisconsin)

Kent Island Formation (upper Sangamon)

Omar Formation (lower Sangamon)

FIGURE 14.—Cross section of isolated parabolic dunes on southeast 

side of Pocomoke River, near Snow Hill, Md. The slip face on the 

southeast side of the dunes is steeper than the back slope on the 

northwest side.

I In meters; feet in parentheses]

Minimum Maximum Mean 1

Nanticoke River

Height———— 

Width—————

Length of arm —

760 (2,500) 4,720 (15,500) 

1.5 (5) 5 (15) 

46 (150) 400 (1,300) 

150 (500) 2,590 (8,500)

1,130(3,700) 

3 (9.5) 

200 (660) 

760 (2,500)

Pocomoke River

TV

Height-———— 

Width—————

Length of arm —

1 Of maximum width

600 (2,000) 2,200 (7,200) 

1 (3) 5 (15) 

60 (200) 64 (210) 

90 (300) 1,580 (5,200)

or height or of longer arm.

1,070 (3,500) 

2.2 (7.3) 

290 (950) 

580 (1,900)
C12 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

TABLE 4.—Dimensions of dunes on uplands east of Salisbury. Md. N

FIGURE 15.—Rose diagram showing that the long axes of most river 

dunes trend northwest, suggesting formation by northwest winds. 

Diagram based on 47 measurements of axis of parabolic dunes measured on l:24,000-scale topographic maps. 4, number of dunes.

NNW 

METERS 

10-,

5— 

SEA LEVEL

SSE

NNW

METERS

10

SSE

SEA LEVEL

50 100 150 METERS

0 100 200 300 400 F£!ET

FIGURE 16.—Asymmetric profiles of parabolic dunes formed by winds 

from the northwest. Easter Hill (A) and adjacent dune (B) near 

Seaford, Del. (Laurel quadrangle, Delaware). Vertical exaggeration x 5.

derlain by the Omar Formation of early Sangamon age 

(Owens and Denny, 1978).

Dunes on the Wicomico-Pocomoke River divide north 

of Parsonsburg, Md. (fig. 17), are long narrow gently 

curving low ridges that have a tendency to run in an east-

|In meters; feet in parentheses]

Minimum Maximum Mean 1

Diameter——— 600(2,000) 6,000(19,500) 1,220(4,000)

Height-———— 1 (3) 6 (20) 1.8 (5.8)

Width——-—— 60 (200) 640 (2,100) 19 (61 )

Length of arm— 210 (700) 1,980 (6,500) 540 (1.800)

1 Of maximum width or height or of longer arm. 

75°27'30"

38°25'

o .5 1 KILOMETER

0 1/2 1 MILE 

___EXPLANATION

:-;:;'':i ;.:\\v Dunes of Parsonsburg Sand

X Borrow pit 

P17 Field number 

—-•—— Intermittent stream

FIGURE 17.—Sand dunes on uplands near Parsonsburg, Md. Most of 

the basins between the dunes are poorly drained. Based on soil 

drainage as shown on soil maps of Wicomico County, Md. (Hall, 

1970, sheets 11, 12, 19, 20, 27, 28, 36, and 37, scale 1:15,840). For 

location see figure 1.

erly or northerly direction. Many of the narrow bands 

are connected to form a pattern resembling parabolic 

dunes formed by northwest winds. The prominent northtrending sandy ridge near Parsonsburg is the crest of the
SAND DUNES ON THE CENTRAL DELMARVA PENINSULA C13

Wicomico River-Pocomoke River divide at an altitude 

of about 25 m (80 ft). Attached to the ridge on both sides 

are many curving arms suggesting that the divide is a 

line of parabolic dunes. The soil in the basins between 

the ridges is very poorly drained; the surface layer (0.3 

m; 1 ft) is a black muck. The swales commonly have 

standing water in the spring and dry out in the summer. 

The modern streams have bisected some of these ancient 

dunes even in this headwater area.

The spacing of the dunes on the uplands is irregular 

(fig. 18). Groups of individual knolls or ridges do not 

closely resemble well-recognized dune patterns, which 

are commonly characterized by a regularity of the spacing of the individual elements (Cooke and Warren, 1973, 

p. 280).

The shape of the upland dunes suggests that the dunebuilding winds were dominantly from the northwest (fig. 

19). Nearly 80 percent of the dune axes are in the northwest quadrant (fig. 20).

On the uplands west and south of Salisbury (fig. 1), a 

belt of Parsonsburg Sand, ranging from about 2-7 km 

(1.0^.5 mi) in width, extends from the Nanticoke River 

south-southeast for about 55 km (44 mi), almost to the 

Pocomoke River. In this belt, the surface expression of 

the Parsonsburg Sand is not uniform. In places there are 

parabolic dunes similar to those elsewhere. Also present 

are ridges as much as 4.5 km (2.8 mi) long and 0.5 km 

(0.3 mi) wide and irregularly shaped areas as much as 2 

km (1.2 mi) in diameter. The belt of Parsonsburg Sand 

follows the landward edge of the Kent Island Formation 

that marks a shoreline of the Sangamon Sea on this part 

of the peninsula. Some of the topographic features, such 

as the west-facing scarp southwest of Hebron, which has 

a toe at about 10.5 m (35 ft), and some of the larger

110

100

90

80

70

60

50

40

30

20

10

0 200 400 600 800 1000 1200 1400 1600 

SPACING BETWEEN DUNES, IN METERS

FIGURE 18.—Cumulative curve showing spacing between upland 

dunes. Distance between the dunes ranges from less than 100 m 

(328 ft) to more than 1,500 m (4,920 ft). The estimated mean spacing is 317.5 m (1,048 ft). Curve is based on 191 measurements 

along lines trending N. 45° W. across the uplands east of Salisbury, Md., and spaced 1 km (0.62 mi) apart.

75°30' 75°22'30"~

38°30'—

22'30" —

38°15'

FIGURE 19.—Orientation of parabolic dunes on uplands east and 

south of Salisbury, Md. Axes of parabolic dunes were measured 

on l:24,000-scale topographic maps. Arrows show inferred direction of dune-building wind.

ridges, may be shore features of Sangamon age. Others 

are probably sand dunes of either Sangamon or Parsonsburg age. Without radiometric dates or knowledge of the 

microflora, one can only guess.

AGE AND ORIGIN

Near the base of the Parsonsburg Sand that forms the 

dunes of the central Delmarva Peninsula are peaty beds 

dated by radiocarbon as about 30,000 to about 13,000 

years B.P. (Denny and others, 1978). The microflora in 

the peaty beds (Sirkin and others, 1977) suggests that in 

early Parsonsburg time the area was a pine-birch barrens and later, a boreal forest. During the Wisconsin glacial maximum, about 18,000 years B.P., the area supported a spruce parkland and local bog tundra. Spruce
C14 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

FIGURE 20.—Rose diagram showing the orientation of dunes on uplands east and south of Salisbury, Md. Diagram based on 179 

measurements of axes of parabolic dunes measured on 1:24,000- 

scale topographic maps. 10, number of dunes.

remained an important element in the flora until about 

13,000 years B.P.

Areas of bare ground, which are not available at present, are probably the prime requirement for dune formation. We assume that during the glacial maximum, the 

upland dunes were formed in the spruce parkland where 

such areas of bare ground existed, perhaps the shores of 

interdune ponds or the banks of streams.

We postulate that the source of the sand was older 

sands of early Sangamon (Omar) age (Denny and others, 

1978). The sands were beach and nearshore deposits 

ranging in altitude from about 10 to 14 m (35 to 45 ft) 

above sea level. To account for Parsonsburg Sand on the 

high divide near Parsonsburg, we further postulate a 

Sangamon island capped by sand dunes as the local 

source of the Parsonsburg Sand at altitudes ranging from 

about 20 to 24 m (65 to 80 ft) above sea level.

Mineralogically, the dune sand has a lower feldspar 

and a higher stable heavy-mineral content than do most 

of the other formations of the central Delmarva Peninsula. The only exception is the deeply weathered Walston Silt which caps the higher parts of the uplands. The 

dune sand is thought to have been derived from the Walston and the upper weathered horizons in other adjacent 

formations. The clay-silt fraction in the dune sand and in 

the unweathered peaty sediment beneath the dunes contains small but consistent concentrations of gibbsite. 

These facts suggest to us that the sand was indeed derived from weathered beds in the source areas and that 

the gibbsite is mostly detrital and not an indicator of 

postdeposition weathering. The data indicate that any 

evaluation of the clay-mineral assemblages in the soil horizons must take into account the weathering history of 

the parent rock.

The absence of high-angle crossbedding so characteristic of parabolic dunes elsewhere (McKee, 1966) requires an explanation. Perhaps the parabolic shape of the 

sand ridges is related more to the presence of adjacent 

swales than to the forward movement of a slip face on 

the leeward edge of a blowout. If the dunes formed in a 

spruce parkland, perhaps the sand was blown out of a 

swale and accumulated on its rim, where the vegetation, 

such as grass and small shrubs, held the sand, inhibiting 

the formation of a slip face and the migration of the dune 

(Goldsmith, 1973, p. 1128; 1975, p. 17).

The dunes are low and inconspicuous features of the 

landscape. Their distribution is spotty and irregular. The 

field relations can be explained if we assume that there 

were local sources of dune-building sand and a means of 

stabilizing the windblown sand before it had moved very 

far. We suggest that on the uplands in late Wisconsin 

(Parsonsburg) time, the poorly drained basins between 

the dunes (fig. 17) were small ponds. Perhaps during the 

winter and early spring the ponds were dry or frozen, 

leaving areas of bare sandy ground. Westerly winds 

picked up sand and deposited it on the edge of the basin, 

where it was held by plants and small shrubs.

The dunes along the rivers differ from those on the 

uplands; the differences suggest that the age and depositional environment of the river dunes may not be the 

same as for the upland dunes. The river dunes are largely 

confined to the southeast or east sides of the river valleys, and parabolic forms are better developed than on 

the uplands. The Parsonsburg Sand that forms the river 

dunes does not contain peaty sediment, in marked contrast to the upland dunes that commonly have peaty beds 

at or near the base of the formation. The only exceptions 

are a dune along the Nanticoke River (near Mardela 

Springs, Md.) and one near Federalsburg, Md., on Marshyhope Creek just north of the area shown in figure 1. 

The river dunes may be of late Wisconsin age. On the 

other hand, they may be Holocene, formed prior to the 

development of the adjacent marsh and swamp coincident with the postglacial rise in sea level.

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___ 1967, Coastal dunes of California: Geol. Soc. America Mem. 104,

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SAND DUNES ON THE CENTRAL DELMARVA PENINSULA C15

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•fr U.S. Government Printing Office: 197*—281-359/61