Postdepositional Alteration of 

Surface and Near-Surface

£E0I,QGICAJ> SURVEY PROFESSIONAL PAPIER 1 0 6 7>-F
Postdepositional Alteration of 

Surface and Near-Surface 

Minerals in Selected Coastal 

Plain Formations of the Middle 

Atlantic States

By JAMES P. OWENS, MELODIE M. HESS, CHARLES S. DENNY, 

and EDWARD J. DWORNIK

SURFACE AND SHALLOW SUBSURFACE GEOLOGIC STUDIES IN THE 

EMERGED COASTAL PLAIN OF THE MIDDLE ATLANTIC STATES

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1067-F

Methods for studying the effects of weathering 

are outlined formations range from late 

Miocene to middle Wisconsinan

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1983
UNITED STATES DEPARTMENT OF THE INTERIOR 

JAMES G. WATT, Secretary

GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Main entry under title:

Postdepositional alteration of surface and near-surface minerals in selected Coastal Plain formations of the Middle Atlantic 

States.

(Surface and shallow subsurface geologic studies in the emerged coastal plain of the Middle Atlantic States)

(Geological Survey professional paper ; 1067-F) 

Bibliography: p. 45 

1. Weathering-Middle Atlantic States. 2. Geology, Stratigraphic-Tertiary. I. Owens, James P., 1924- . II. Title. III.

Series: Geological Survey professional paper ; 1067-F. 

QE570.P67 551.3'02'0975 82-600119

For sale by the Distribution Branch, U.S. Geological Survey, 

604 South Pickett Street, Alexandria, VA 22304
CONTENTS

Abstract _________

Introduction ______

Method of study ___

Page

Fl

1

2

2

3

3

3

3

7

7

7

7

Previous investigations ________________________________

Regional geology and sample localities ____________________

Localities studied _____________________________________

West of Chesapeake Bay ____________________________

Hayfield, Va _____________________________

Sand mineralogy ____________________________

Clay-silt mineralogy _________________________

Interpretation ______________________________

Bowling Green, Va ______________________________

Sand mineralogy __________________ 12 

Clay-silt mineralogy ________________ 12 

Interpretation ___________________ 13

Round Bay, Md _____________________ 13 

Sand mineralogy __________________ 14 

Clay-silt mineralogy ________________ 14 

Interpretation ____________________ 14

Summary of weathering effects west of Chesapeake

Bay ________________________ 15 

Between Chesapeake and Delaware Bays __________ 16

Betterton, Md _______________________ 16 

Sand mineralogy __________________ 16 

Clay-silt mineralogy ________________ 18 

Interpretation _____________________ 18

Houston, Del ______________________ 18 

Sand mineralogy ___________________ 18 

Clay-silt mineralogy ________________ 19 

Interpretation _____________________ 19

Whaleysville, Md _____________________ 21 

Sand mineralogy __________________ 22 

Clay-silt mineralogy ________________ 22 

Interpretation ____________________ 22

Localities studied-Continued

Between Chesapeake and Delaware Bays-Continued

Germantown,1 Md _____——————————————— F24

Sand mineralogy _____———————————— 24

Clay-silt mineralogy ___________————— 24

Interpretation ______—————————————— 25

Worton Point, Md ______________————— 26

Sand mineralogy _____————————————— 26

Clay-silt mineralogy __——————————————— 27

Interpretation ___________————————— 28

Pittsville, Md ______________________ 29

Sand mineralogy ___________—————— 30

Clay-silt mineralogy ______————————— 31

Interpretation _________——————————— 31

Summary of weathering effects between Chesapeake

and Delaware Bays _________—————— 32

Northeast of Delaware Bay _________——————— 33

Hammonton, N.J _________——————————— 33

Sand mineralogy ___________——————— 33

Clay-silt mineralogy ___________————— 34

Interpretation _______________————— 35

Bernardsville, N.J ____________———————— 35

Sand mineralogy ________————————— 35

Clay-silt mineralogy _________—————— 37

Interpretation _______________————— 37

"Van Sciver Lake beds" ___________—————— 38

Sand mineralogy ___________——————— 39

Clay-silt mineralogy _____________——— 39

Interpretation ___________————————— 40

Summary of weathering effects northeast of

Delaware Bay ____________—————— 40

Conclusions _____________—————————————— 41

Appendix ___________——————————————————— 44

References _____________———————————————— 45

ILLUSTRATIONS

Page

F4

5

6

8

9

10

FIGURE 1. Map showing generalized geology in the Coastal Plain of New Jersey, Pennsylvania, Delaware, Maryland, and Virginia _

2. Chart showing formations and informally named Coastal Plain units ____________________ _______

3. Columnar section showing stratigraphy in pit and adjacent gully at Hayfield, Va _______________________ 

4-5. Diagrams showing distributions of:

4. Light minerals in formations in the study area ________________________________________

5. Heavy minerals in formations in the study area _______________________________________

6. Graph showing calculated clay mineral concentrations in some formations in the study area _________________

7. X-ray traces of the < 2-/t fraction in sands of the Potomac Formation at Hayfield, Va ____________________ 12

8. Columnar section showing geology at Bowling Green, Va ___________________________________ 13

9. X-ray traces of clay minerals in the Yorktown Formation at Bowling Green, Va ________________________ 14

10. Columnar section showing geology at Round Bay, Md _____________________________________ 15

11. X-ray traces of untreated, unoriented specimens in samples of the Calvert and Aquia Formations at Round Bay, Md ____ 16

12. Columnar section showing geology as exposed in a bluff west of Betterton, Md _______________________ 17

13. X-ray traces showing clay minerals in sand of the Pensauken Formation at Betterton, Md __________________ 19 

14. Transmission electron microscope photomicrographs of < 2-/t fraction in sand of the Pensauken Formation at Betterton,

Md ______________________________________________________________ 20

in
IV ILLUSTRATIONS

	Page

15. Columnar section showing geology in a pit northeast of Houston, Del _____________________________ F21

16. X-ray traces of clay minerals in the Beaverdam Sand and the Pensayken Formation northeast of Houston, Del ______ 22

17. Columnar section in an auger hole west of Whaleysville, Md _________________________________ 23

18. X-ray diffractograms of untreated < 2-/t fraction in sand of the Omar Formation and the Beaverdam Sand at

	Whaleysville, Md _______________________________________________________ 24

19. Columnar section showing geology in a pit east of Germantown, Md _____________________________ 25

20. X-ray traces of clay minerals in the Ironshire Formation at Germantown, Md ________________________ 26

21. Micrographs of gibbsite from < 2-/t fraction in sand of the Ironshire Formation _______________________ 27

22. Columnar section showing the Kent Island Formation at Worton Point, Md __________________________ 28

23. X-ray traces of clay fraction in sand of the Kent Island Formation at Worton Point, Md ___________________ 29

24. Electron micrographs of clay fractions from the Kent Island Formation at Worton Point, Md., showing vermiculite flakes

	and hexagonal kaolinite aggregates ____________________________________—_—_—_— 30

25. Columnar section of the Parsonsburg Sand near Pittsville, Md _______________________________— 31

26. X-ray traces of clay-silt fraction in the Parsonsburg Sand near Pittsville, Md _____________________—_— 32

27. Columnar section showing geology in a borrow pit at Hammonton, N. J _____________________—_—_— 34

28. X-ray traces of clay-silt fraction in the Bridgeton Formation at Hammonton, N.J _______________—_—_— 35

29. Transmission electron microscope micrographs of clay fraction of sand of the Bridgeton Formation and the Cohansey Sand

	at Hammonton, N.J., showing morphology of minerals __________________________________ 36

30. Scanning electron microscope micrographs of clay fraction of the Bridgeton sand at Hammonton, N.J ___________ 37

31. Columnar section showing geology in a roadcut near Bernardsville, N.J _______________________—_— 38

32. X-ray traces of three samples collected from a roadcut near Bernardsville, N.J _________________—_———— 39

33. Transmission electron microscope micrograph of clay-silt fraction in sand of the "older drift" at Bernardsville, N.J ____ 39

34. Columnar section showing geology in pits at Van Sciver Lake, Pa ________________________—_———— 40

35. X-ray traces of untreated samples in the "Van Sciver Lake beds" in Pennsylvania _______________—_—_— 41

36. Transmission electron microscope micrograph of clay fraction in sand of the "Van Sciver Lake beds" in Pennsylvania _— 41
SURFACE AND SHALLOW SUBSURFACE GEOLOGIC STUDIES 

IN THE EMERGED COASTAL PLAIN OF THE MIDDLE ATLANTIC STATES

POSTDEPOSITIONAL ALTERATION OF SURFACE AND NEAR-SURFACE

MINERALS IN SELECTED COASTAL PLAIN FORMATIONS OF

THE MIDDLE ATLANTIC STATES

By JAMES P. OWENS, MELODIE M. HESS, CHARLES S. DENNY, and

EDWARD J. DWORNIK

ABSTRACT

The depth and intensity of postdepositional subaerial weathering 

were examined in several Coastal Plain formations from New Jersey to 

Virginia. This region was divided into three study areas: (1) west of 

Chesapeake Bay, (2) between Chesapeake and Delaware Bays (Delmarva Peninsula), and (3) northeast of Delaware Bay. The mineralogy 

of well-drained sandy beds from 12 sites in these three areas was compared to ascertain compositional maturity (defined, for example, for 

clay-sized material as the presence of iron and aluminum oxides or 

hydrated silicates) in relation to the age of the formation containing 

the sand.

Three categories of weathering profiles were recognized. In the 

first, the clay-mineral type and the degree of intrastratal solution of 

sand minerals seemed reasonable relative to the age of the formation 

on which the weathering profile was developed. In the second, the 

mineralogy appeared too young relative to the age of the formation on 

which the weathering profile had developed. This type of unit is most 

common west of Chesapeake Bay. The relationship is interpreted as 

resulting from local tectonics. In the third, the weathering mineralogy 

appeared too old relative to the age of the unit. The overmature 

minerals in these units were either reworked into these units during a 

marine transgression or introduced into a sandy unit as loess and 

subsequently distributed throughout the dominantly sandy units by illuviation.

In summary, most of the weathering-age relationships followed a 

predictable pattern. The use of this technique to determine relative 

ages and uplift patterns in this region is in its initial stage but holds 

much promise. The existence of some anomalies, however, points to 

the need to obtain a detailed geologic history of a given deposit before 

this weathering-age technique can be applied.

INTRODUCTION

Studies of subaerial alteration in unconsolidated 

sediments as a method of establishing the age of these 

sediments has been attempted in many regions. Such a 

technique has been widely utilized, for example, in the 

midcontinent glacial deposits, where the depth of 

leaching of calcium carbonate or the degree of development and thickness of soil zones have been used as 

methods of establishing the relative ages of these 

deposits.

As an adjunct to the mapping of surficial sediments in 

the Coastal Plains of the Middle Atlantic States (New 

Jersey to Virginia), 12 sites were sampled to determine 

whether the degree and depth of weathering, as compared with the stratigraphic age of a deposit, could be 

used as an age indicator in this terrane. The method was 

tested by determining the weathering effects developed 

on deposits of a variety of ages (Early Cretaceous to late 

Pleistocene) and lithologies. The weathering mineral 

model proposed by Jackson (1965) was used initially as a 

standard to determine the sequence of weathering products (minerals) relative to time.

Like some glacial drift, the Coastal Plain formations 

are suitable for studying weathering because, in addition to their high porosity, they contain an abundance of 

easily weatherable minerals-mostly feldspar, calcareous materials, and, to a lesser degree, glauconite, 

micas, and ferromagnesian minerals. The formations 

selected for study are all well-drained sands or gravelly 

sands, locally containing thin to thick beds of compact 

clay or clay-silt. Because a major objective of this study 

was to assess the effects of mineral alteration during 

leaching, only the interstitial clay-silt fractions in the 

sands were analyzed. The much higher porosity of the 

sands in comparison with the less permeable beds of clay 

or clay-silt was the principal reason for this sampling 

procedure. It was reasoned that any alteration effects 

would be accelerated and therefore more readily detectable in the fine-grained fraction of the sands. Assessing 

the effects of leaching or weathering over a broad 

region on a variety of formations resulted in a study of

Fl
F2 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

many lithologies. Most of the Coastal Plain sample sites 

were in units mapped by us or by coworkers. The ages of 

these units have been determined by biostratigraphic 

and radiometric methods.

One complicating factor in our study was postdepositional stripping, which, in places, has interrupted or 

destroyed the upper leached or weathered zone. Although we made an effort to collect samples from areas 

where this effect had been minimal, we were forced to 

collect some of our samples from dug pits on remnant 

knobs high in the landscape. Therefore, a degree of 

uncertainty exists as to the results obtained from these 

sites.

As the study progressed, it became apparent that a 

knowledge of the depositional history of each deposit 

was essential to a proper evaluation of the laboratory 

results. Simply stated, the effect of inherited (detrital) 

clay minerals from source lands or reworked (multicycle) clay minerals from underlying units had to be determined before any analysis of postdepositional weathering effects could be made.

Additionally, because of the very large area encompassed in our investigation and the relatively small 

number of sites examined in detail, our results can be 

considered only as a prelude to a more detailed study.

METHOD OF STUDY

Most of the samples were collected from freshly dug 

pits. Some of the sites were natural exposures that had 

recently eroded or slumped, and exposed fresh 

sediments. Within the stratigraphic framework worked 

out in the study areas (Owens and Minard, 1975, 1979; 

Owens and Denny, 1979; Minard, 1980; Force and Moncure, 1977; present field studies in southeastern 

Virginia; Wayne Newell, written commun., 1978), the 

formations sampled included a wide variety of lithologies; thus, many mineral combinations (lithofacies) 

were analyzed.

The sand minerals were separated into two classes: 

those having a specific gravity of greater than 2.85 (the 

"heavy" minerals) and those having a specific gravity of 

less than 2.85 (the "light" minerals). These minerals 

were then examined under the petrographic microscope 

to determine provenance, the degree of reworking from 

other units (first-cycle as opposed to multicycle 

sediments), and, perhaps more important, the effects of 

intrastratal solution. Only light minerals in the 0.077- to 

0.177-mm size range were identified under the 

petrographic microscope. The ratios of these light 

minerals (largely quartz and feldspar), therefore, are not 

representative of the entire sand fraction but tend to be 

biased in favor of feldspar, which, because of its good 

cleavage, tends to be concentrated in the finer size fractions during transport.

The clay minerals were identified by standard X-ray 

techniques. Only the minerals having well-ordered 

crystal structures were detected. Other amorphous 

forms such as allophanes were not recognized and are 

disregarded in our discussion. Supplemental studies of 

some samples by transmission electron microscopy and 

scanning electron microscopy were made because the 

X-ray analyses indicated the presence of minerals (such 

as halloysite) that have excellent crystal morphology. 

The scanning electron microscope was equipped with an 

energy-dispersive X-ray analyzer, which gave qualitative elemental analyses. This capability helped in 

distinguishing the anhedral forms of aluminum oxides 

(gibbsite) from aluminum silicates (vermiculite, illite, 

and feldspars).

Individual clay minerals were identified and classified 

by the technique described by Reynolds and Hower 

(1970). Their terminology differs from that used by 

other mineralogists, particularly in the classification of 

clays having large unit-cell dimensions (for example, 

montmorillonites of other workers are classified here as 

mixed-layer illite-smectite). Only the untreated patterns 

are illustrated in our report. The specific determinations 

listed were based on samples treated by standard clayidentification techniques (chemical or heating).

PREVIOUS INVESTIGATIONS

Within the area of our investigation, all the early 

studies of mineral alteration in surficial sediments were 

made by soil scientists. These investigations for the 

most part examined the mineralogy of the upper 1.5 m 

of the surficial beds. Many of these studies were conducted by the Agronomy Department of Rutgers University in New Jersey (Tedrow, 1954; Krebs and 

Tedrow, 1957; Novak and others, 1971). These investigations were usually site specific and did not represent a comprehensive study of a soil or a group of soils 

over a large area.

Weathering studies based in part on these agronomic 

studies were conducted by Lodding (1961, 1972) and 

Bowman (1966) on the Pensauken Formation, as shown 

on the geologic map of New Jersey (Johnson, 1950). 

Bowman's studies were the most detailed, concentrating 

on the Coastal Plain between Camden and Jamesburg, 

N.J. Generally, he found that gibbsite and locally 

metahalloysite were most abundant at depth and that 

clay mica (illite-muscovite mixed layering) and chlorite 

increased toward the top of the profile. Perhaps 

Bowman's greatest contribution was recognizing the 

widespread distribution of gibbsite in the Pensauken 

Formation and the depths at which it was present. 

Because he adopted the age assigned to this unit on the 

New Jersey geologic map, he thought that the mineral 

assemblages that he reported were Pleistocene.
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F3

Outside New Jersey, particularly in Alabama and 

Georgia, Clarke (1971) described several weathering 

profiles in the Coastal Plain sediments. He concluded 

that the gibbsite-bearing rocks in this region were prePleistocene in age, developed on sediments derived from 

the feldspar-rich metamorphic and igneous rocks of the 

Appalachian Mountain system.

In the field of agronomy, weathering sequences 

related to environment, intensity, and time were outlined by Jackson (1965). This oft-cited paper is used as a 

model to define weathering sequences in a variety of terranes. Jackson proposed three major weathering 

categories: mild, intermediate, and intensive. We are 

concerned in our study only with those minerals discussed in each of these categories in well-drained 

topographic positions. The mild category is characterized by chloritized vermiculite, allophane, and quartz. 

The intermediate category contains kaolinite, halloysite, 

chloritized vermiculite, and montmorillonite. The intensive mineral assemblage (referred to as laterization) includes hematite, goethite, anatase, gibbsite, boehmite, 

kaolinite, and allophane. We will elaborate on the model 

in the conclusions to this paper.

REGIONAL GEOLOGY AND SAMPLE LOCALITIES

Figure 1, a generalized geologic map of the Coastal 

Plain sediments, shows the localities from which 

samples were collected in the Middle Atlantic States.

As this figure shows, the Coastal Plain lies between 

the Atlantic Ocean on the east and the Piedmont physiographic province on the west. The rocks of the Piedmont province are largely metamorphic and crystalline 

and were the source of large quantities of weatherable 

(labile) minerals in the Coastal Plain sediments (that is, 

feldspar, chlorite, biotite, and muscovite) in addition to 

contributing the readily alterable clay mineral, illitesmectite.

The formations comprising the Coastal Plain of the 

Middle Atlantic States are shown in figure 2. The sampling program did not follow a prescribed sequential 

stratigraphic plan but was dictated in large part by the 

availability of fresh cutbanks or slump blocks. The 

typically unconsolidated nature of the Coastal Plain 

sediments and the ephemeral nature of natural outcrops 

forced us to follow such a sampling procedure.

The Coastal Plain formations in the study area are 

comprised of unconsolidated sediments and were 

deposited in a wide variety of paleoenvironments: (1) 

fluviatile (channel fill and overbank principally), (2) 

estuarine-barrier-back barrier, and (3) marine (inner 

shelf and perhaps middle shelf). Therefore, the weathering effects on a large number of lithofacies and 

lithologies (feldspathic, glauconitic, and micaceous 

sands) were studied. Some of the sands were first cycle

(notably, the most feldspathic sands), whereas others 

were multicycle and contained fewer weatherable 

minerals.

Twelve sites were studied in detail; their general locations are shown in figure 1. Particulars for each are 

given in the appendix. The data given in the main body 

of the report typically refer to a single formation only. 

The conclusions drawn from each formation were 

checked at other localities within the formation to see if 

the data thus obtained had regional continuity. (They 

did.)

LOCALITIES STUDIED

The sample sites in this paper will be discussed by 

geographic area (fig. 1) rather than in stratigraphic 

order. The three main areas are (1) west of the 

Chesapeake Bay, (2) between Chesapeake Bay and 

Delaware Bay, and (3) northeast of Delaware Bay. The 

stratigraphic position of a formation can be determined 

by referring to figures 1 and 2.

WEST OF CHESAPEAKE BAY

West of Chesapeake Bay, three localities were 

selected for detailed study: the Hayfield site (beds of 

Early Cretaceous age), the Bowling Green site (beds of 

early to middle Pliocene age), and the Round Bay site 

(beds of middle Miocene and late Paleocene age).

HAYFIELD, VA.

"UPLAND GRAVELS" AND POTOMAC FORMATION, 

LOCALITY NO. ANNA 1

A columnar section showing the geology at the 

Hayfield, Va., site is illustrated in figure 3. Two formations are exposed: the "upland gravels" of probable 

Pliocene age and the Potomac Formation of early 

Cretaceous (Barremian Stage) age. A large time gap is 

represented by the unconformity between the two units.

The "upland gravels" at this site have been removed 

for aggregate and were not sampled. The mineralogy of 

probable equivalent upland beds will be discussed in the 

Bowling Green site description.

Approximately 12 m of the Potomac Formation is well 

exposed at this locality. The formation consists of interstratified thick beds of sand and clay-silt. The sand is 

loose, extensively cross stratified, typically medium 

grained, and moderately well sorted and has subangular 

to angular grain shapes. The angularity of the grains 

suggests that this deposit is probably a first-cycle sediment. Two sand beds are present, separated by a claysilt bed (fig. 3). The upper sandy bed is typically a light 

gray but is stained a dark yellowish orange (10 YR 6/6) 

in the upper 1.5 m. There is no pronounced clay accumulation in this sand; specifically, it does not have a welldeveloped B horizon. In fact, the soil-forming processes
F4

78°

GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES 

77° 76° 75° 74°

PENNSYLVANIA Approximate 

southern limit of 

Wisconsin glaciation

EXPLANATION

Approximate Sinepuxent Formation inn 

of Coastal Plain

Quaternary deposits, undifferentiated 

Ironshire Formation

Omar Formation (including beds or Accomae trough near Accomac, Va. )

•Tut o Upper Tertiary deposits, undifferentiated

walston Silt (including Windsor Formation 

of Coch, 1968)

Beaverdam Sand

Pensauken Formation

Bridgeton Formation

Cohansey Sand and Kirkwood Formation,

undivided

Tertiary and Upper Cretaceous deposits, 

undifferentiated

Potomac Formation

Contact

Sample site, approximately located—See

appendix for specific locality of numbered

site

Approximate inner edge of Coastal Plain 

Approximate southern limit of Wisconsin 

glaciation

SCALE 1:2500000 25 50 75 100 KILOMETERS

25 50 MILES

FIGURE 1.—Generalized geology in the Coastal Plain of New Jersey, Pennsylvania, Delaware, Maryland, and Virginia. Formation boundaries 

are only approximate, and some units have been deleted to emphasize others. Sample sites are shown by number but are only approximately located. Specific sample localities are given in the appendix. The locality numbers shown in the figure are 1, Bowling Green 1, 

Bowling Green, Va.; 2, Anna 1, Hayfield, Va.; 3, R.B. 51, Round Bay, Md.; 4, Hanesville 1, Worton Point, Md.; 5, Bet. 3, Betterton, 

Md.; 6, Harr. 5, Houston, Del; 7, Pitt. 8, Pittsville, Md.; 8, Wh. 1A, Whaleysville, Md.; 9, Ber. 2, Germantown, Md.; 10, Newtonsville 

1, Hammonton, N.J.; 11, TWA 15A, Van Stiver Lake, Pa.; 12, Bern. 1, Bemardsville, N.J.
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F5

AGE VIRGINIA MARYLAND DELAWARE NEW JERSEY PENNSYLVANIA ?

cc 

< 

z 

cc LU

§0

o>

c

0>

o 

^

o

I

Unnamed beds of marsh - swamp - river fill

Sinepuxent >

Parsonsburg ^

Ironshire — — — — — — —

Omar (including deposits in — 

Accomac trough)

— "Van Sciver Lake beds' 

—"Spring Lake beds"

o

O N 

O

Z 

LU 

O

Windsor(?)— — — Walston 

of Coch (1968)

Bacons Castle(?)—Beaverdam 

of Coch (1965) /

Yorktown

Upland gravels" (undifferentiated)

cc

cc

LU

"St. Marys 

of Virginia"

"St. Marys 

of Maryland

Choptank 

Calvert

'Pocomoke-Manokin beds'

Choptank 

Calvert

Pensauken

Bridgeton

Cohansey 

Kirkwood

Nanjemoy 

Aquia

— — — — — — — Manasquan

— Vincentown >

—— Hornerstown >

Brightseat Brightseat

o 

O

N

O

D 

O

UJ

O

CC

o

CO 

LU

Marshalltown 

Englishtown

*

Tinton

- Red Bank 

Navesink 

Mount Laurel 

Wenonah 

Marshalltown 

Englishtown 

Woodbury 

Merchantville

Magothy 

Raritan

Potomac Formation

FIGURE 2.-Formations and informally named units cropping out or occurring in shallow subsurface in the Coastal Plain of Virginia, 

Maryland, Delaware, and New Jersey (Pennsylvania?). Diagonal lines indicate absence of a unit.
F6 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

DEPTH BELOW 

SURFACE, 

IN FEET

(METERS) 

0

T (0)

10- 

(3.0)

20- 

(6.1)

30- 

(9.1)

40- 

(12.2)

"Upland gravels" (gravel to 3 inches)

Sand, cross-stratified, medium to coarse 

grained dark yellowish orange (10 YR 

6/6) in upper part, very pale orange (10 

YR 6/2) below

Pale-olive (10 Y 6/2) massive clay-silt 

weathered dark yellowish orange (10 YR 

6/6) at top. Iron oxides commonly developed in sandy beds intercalated with 

clay-silt

Sand, medium grained in upper part, grading to coarse grained in lower part. Thin 

gravel layers (all quartz) interbedded in 

lower part. Most very pale orange (10 YR 

8/6). Very feldspathic throughout. Clay 

breccia common

EXPLANATION

Gravel

Pale gray clay-silt

Sand 

Silt

Clay

Crossbedded 

sand

FIGURE 3. - Columnar section showing the stratigraphy in a pit and an adjacent gully at Hayfield, Va., 5 km (3.1 

mi) south of Alexandria in the Annandale 7.5-minute quadrangle. Locality no. Anna 1. Arrows indicate 

sample locations in profile. Surface elevation is 64 m (210 ft) above sea level.

have not destroyed the cross-stratification in the upper 

zones of iron oxide staining.

The underlying, generally massive clay-silt is pale 

gray to pale olive and approximately 4.6 m thick. Thin 

beds or laminae of fine-grained to very fine grained sand 

are interbedded with the clay-silt. Iron oxide staining is 

common along the sandy laminae.

Another sand bed approximately 4.6 to 6.0 m thick 

underlies the clay-silt. The sand in this bed is unconsolidated, moderately sorted, and extensively crossstratified, like that in the near-surface sand bed. The 

trough style of crossbedding is essentially the same as 

that in the upper sand. In general, the sand is coarse 

grained and gravelly in the lower part of this bed and
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F7

becomes finer upward to the clay-silt boundary. Taken 

in conjunction with the clay-silt, the sand forms an 

upward-fining cycle. For the most part, the sand is a 

pale orange locally stained by thin layers of iron oxide. 

The overall sedimentary structures and upward-fining 

sequences of the deposit indicate this formation to be 

fluvial in origin.

SAND MINERALOGY

Light minerals.-The light minerals compose nearly 

all the sand fraction in the Potomac Formation. A 

binocular examination of these minerals revealed that 

most have subangular to angular shapes and hence are 

probably first-cycle sediment. The light minerals in the 

very fine sand fractions were studied under the petrographic microscope, and the results are shown 

graphically in figure 4A. Quartz is the major mineral, 

although feldspar (largely K-feldspar) is also very abundant.

It has long been known that feldspar is relatively 

unstable in a strongly oxidizing environment for any extended period of time. As figure 4 shows, there is no 

significant decline in the total percentage of feldspar 

throughout the entire section. Nevertheless, the feldspars in the upper meter of the profile are more 

weathered than those below. The K-feldspars in the upper beds are very turgid, and the plagioclase crystals are 

extensively embayed. A binocular examination of the 

grains also reveals that most of the feldspar grains have 

a dull white coating, which suggests at least some surface alteration of the grains.

Heavy minerals. - Zircon and small amounts of tourmaline are the major heavy minerals present (fig. 5A). 

Because these minerals are commonly thought to be 

some of the most resistant to subaerial oxidation, they 

could not be used to determine the effects of postdepositional weathering on these beds. Much smaller amounts 

of epidote and staurolite are also present, along with 

even smaller amounts of garnet and kyanite. The 

epidote, staurolite, and kyanite typically are altered, but 

whether the weathering was a provenance effect or a 

postdepositional effect is unknown. Regardless, the 

heavy-mineral assemblages in the Potomac Formation 

would be considered a mature assemblage.

CLAY-SILT MINERALOGY

X-ray studies of the clay-silt fraction in the upper sand 

bed are summarized in figure 6. In general, illitesmectite dominates the lower, less weathered part of the 

section and decreases upward into the orange-brown 

zone, where kaolinite and, to a lesser degree, illite 

become more abundant. About 1.2 m from the surface, 

both illite and kaolinite appear to decrease. There, dioctahedral vermiculite becomes prominent and accounts

for the kaolinite-illite decrease. Figure 7 shows the 

mineral distribution throughout the upper sand beds 

and, although it is not quantitative, illustrates the clay 

mineral changes upward through this section, particularly the change from illite-smectite to more stable 

clay minerals (kaolinite and dioctahedral vermiculite).

INTERPRETATION

The Potomac Formation at the Hayfield site appears 

to be a first-cycle sediment derived from a very feldspathic, coarse crystalline metamorphic or igneous rock. 

The close proximity of the Occoquan Granite to the 

Potomac Formation suggests that this rock is the major 

source for the Potomac sediments. The Potomac Formation does not, however, contain the high percentage of 

plagioclase reported by Seiders and others (1975) to be 

characteristic of the Occoquan Granite. If they are correct, then a large amount of plagioclase was lost during 

the chemical and mechanical disintegration of the 

adamellite. Nevertheless, the relatively fresh state of 

the feldspar in the Potomac Formation and the especially abundant illite-smectite in a zone of strong 

subaerial oxidation are incompatible with the Cretaceous age of these sediments. Perhaps these beds were 

exhumed in recent times. The near-surface position of 

the relatively unweathered beds of Cretaceous age in 

this region probably came about as a result of faulting 

described by Mixon and Newell (1977) or is perhaps 

related to Quaternary eustatic sea-level changes known 

to have affected this area.

The principal factors involved in positioning these 

beds at the surface are not particularly relevant to our 

study. What is important are the character or degree of 

weathering of the sediments and the length of time 

necessary to produce the degree of mineral alteration at 

the Hayfield site.

Alteration of minerals in the Potomac Formation appears to be minimal. Some weathering of the feldspars 

was observed optically, but the only significant change 

in the clay minerals was the alteration of some of the 

illite-smectite to kaolinite and dioctahedral vermiculite 

in the uppermost beds. This slight degree of alteration in 

well-drained sands under the present climatic conditions 

in this area (particularly the relatively high rainfall and 

humidity) suggests a very youthful weathering profile. 

The best guess is that the weathering could have begun 

in the middle Pliocene but is probably much younger.

BOWLING GREEN, VA.

YORKTOWN FORMATION, LOCALITY NO. 

BOWLING GREEN 1

The upper Coastal Plain of Virginia is mantled by a 

widespread cover of gravelly sands (fig. 1), which for a
F8 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

DEPTH,

IN FEET

(METERS)

0 —i

(0)

10,- 

(3.0)

20 -

(6.1)

30 - 

(9.1)

40 - 

(12.2)

50- 

(15.2)

60 -I 

(18.3)

0 —i 

(0)

10 - 

(3.0)

20- 

(6.1)

30 - 

(9.1)

PERCENT PERCENT PERCENT PERCENT PERCENT PERCENT 

0 50 100 0 50 100 0 50 100 0 50 100 0 50 100 0 50 100

PERCENT 

0 50 100

PERCENT 

0 50 100

PERCENT 

0 50 100

H

PERCENT 

100 0 50 100

Quartz 

K-feldspar 

Plagioclase 

Rock fragments

FIGURE 4.-Distribution of light minerals (<2.85 specific gravity) in formations in the study area. The size fraction studied is from 0.177 to 

0.074 mm (fine-grained to very fine grained sand). A, Hayfield, Va.; B, Bowling Green, Va.; C, Round Bay, Md.; D, Betterton, Md.; E, 

Whaleysville, Md.; F, Germantown, Md.; G, Worton Point, Md.; H, Pittsville, Md.; /, Hammonton, N.J., J, Bernardsville, N.J.; K, Van Sciver 

Lake, Pa.
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F9

DEPTH,

IN FEET

(METERS)

0-

(0)

10- 

(3.0)

20- 

(6.1)

30-

(9.1)

40- 

(12.2)

50- 

(15.2)

60- 

(18.3)

PERCENT PERCENT PERCENT PERCENT PERCENT PERCENT 

0 50 100 0 50 100 0 50 100 0 50 100 0 50 100 0 50 100

D

PERCENT 

0 50 100

PERCENT 

0 50 100

PERCENT 

50 100

PERCENT 

0 50 100

PERCENT 

0 50 100

PERCENT 

50 100

(0)

10- 

(3.0)

20- 

(6.1)

30- 

(9.1)

40- 

(12.2) H

EXPLANATION

ZTR—Z, zircon; T, tourmaline; 

R, rutile

HEGAT—H, hornblende; E, epidote; G, garnet; A, actinolite; 

T, tremolite

SSK—S, staurolite and sphalerite; K, kyanite

OTHER—All other heavy minerals (such as chlorite, andalusite, pyroxene, etc.)

FIGURE 5.-Distribution of heavy minerals (>2.85 specific gravity) in formations in the study area. The size fraction studied is from 0.177 to 

0.074 mm (fine-grained to very fine grained sand). A, Hayfield, Va.; B, Bowling Green, Va.; C, Round Bay, Md.; D, Betterton, Md.; E, 

Houston, Del.; F, Whaleysville, Md.; G, Germantown, Md.; H, Worton Point, Md.; /, Pittsville, Md.; J, Hammonton, N.J.; K, Bernardsville, 

N.J.; L, Van Sciver Lake, Pa.
F10 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

DEPTH,

IN FEET

(METERS)

0

(0)1

5- 

(1.5)

10- 

(3.0)

15 — 

(4.6)

20- 

(6.1)

25- 

(7.6)

30- 

(9.1)

35—' 

(10.7)

PERCENT 

50 100

I I

100 100

FIGURE 6.-Calculated clay mineral concentrations in some formations in the study area. Vermiculite, halloysite, and gibbsite were not 

calculated with the other clays because no method has been devised to determine, with any degree of assurance, the amount of these minerals 

in a sample. Therefore, those samples that contained significant concentrations of these minerals are not shown in this type diagram. A, 

Hayfield, Va.; B, Bowling Green, Va.; C, Round Bay, Md.; D, Whaleysville, Md.; E, Pittsville, Md.; F, Van Sciver Lake, Pa. (vermiculite 

estimated on the basis of peak height).
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS Fll

DEPTH,

IN FEET

(METERS)

(Oi

(1.5)

10- 

(3.0)

15-

(4.6)

20- 

(6.1)

25 H

(7.6)

30 H 

(9.1)

35-

(10.7)

40-| 

(12.2)

45 -I 

(13.7)

PERCENT 

50

I I I I I I

100

PERCENT 

50

I I I I I I

^^

o

o

o

0

- • •* 

• +' 

•'.'•»

: +.• 

-*• . • -*• • +' '

+ +

+ +

X

X 

X

PERCENT 

50

I I I I I I

100

EXPLANATION

Kaolinite

Illite

Illite-smectite

Percentage expandable layers 

in illite-smectite

Vermiculite (+ chlorite) 

Halloysite
F12 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

146 13.0

1.2

1.4

1.8

3.32 3.12

I/S GO 2.3

FIGURE 7.-X-ray traces of the <2-/* fraction in sand of the Potomac 

Formation at Hayfield, Va. (locality no. Anna 1). Traces illustrated 

are of unoriented and untreated clay. This untreated type of clay 

pattern is used for other units throughout the report. The X-ray 

identification discussed in the text, however, was data derived 

after the clay had been subjected to the standard series of heating 

and chemical tests. Measurements of peaks in the X-ray traces are 

in angstroms. Depths of samples are given in meters. V is vermiculite, I is illite, K is kaolinite, L is lepidocrocite, G is gibbsite, 

GO is goethite, and I/S is illite-smectite.

long time was considered to be a single unit ("upland 

gravels" or Brandywine Formation, Pliocene?). These 

beds could be equivalent to the "upland gravels" at the 

Hayfield site. Detailed field studies near the Rappahannock River, however, have shown that these "upland 

gravels" are of more than one age and were deposited in 

many environments (Wayne Newell, written commun., 

1978). The gravels at Bowling Green (fig. 1) are mapped 

as Yorktown Formation (lower and middle(?) Pliocene). 

The lithology of the upper part of this unit as exposed in 

a roadcut is shown in figure 8. The most obvious lithic 

characteristics of this unit are abundant gravel and 

sand, poor stratification, extensive but irregularly 

distributed iron oxide staining, and the presence of 

relatively large Ophiomorpha burrows. In general, the 

deposits appear to be well-drained, permeable sand.

SAND MINERALOGY

Light minerals.-Figure 4B shows the light-mineral 

distribution in the sand fraction at this locality. The bulk 

of the sand fraction is quartz. K-feldspar totals about 25 

percent of the sand fraction at depth and decreases to 

about 7 percent near the surface. All of the K-feldspar 

grains examined, irrespective of depth, appear to be 

altered to some degree (turgid and ragged edged). A few 

rock fragments are also present in the light-mineral 

fraction. Most of these fragments appear to be mediumgrained gneiss. The subangularity of most of the grains 

suggests that they are first-cycle material. Compositionally, the sands at this locality are subarkose to protoquartzite.

Heavy minerals.-The heavy-mineral assemblages in 

this unit are dominated by the more stable forms: zircon, 

tourmaline, and rutile (ZTR group) (fig. 5B). Zircon is 

especially abundant in this group of minerals. The next 

most abundant minerals are the SSK group (staurolite, 

sillimanite, and kyanite). Staurolite is the most abundant in this group, kyanite being the next most common.

The least abundant mineral group present, HE GAT 

(hornblende, epidote, garnet, actinolite, and tremolite), 

accounts for up to 7 percent of the heavy-mineral concentrate. This group contains minerals considered to be 

the least stable in strongly oxidizing environments. 

There is no consistent pattern to the distribution or concentrations of these minerals in the profile studied. 

Surprisingly, hornblende, considered to very unstable in 

oxidizing zones, occurs as fresh grains in the sample collected nearest the surface.

CLAY-SILT MINERALOGY

Figure QB shows the distribution of the clay minerals 

in the profile sampled. In this profile, kaolinite is by far 

the most abundant clay mineral. Illite occurs in small
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F13

DEPTH BELOW 

SURFACE, 

IN FEET 

(METERS)

(0)

r

I

>

E 

D

'. (3.0)

» c — ^

3

<.

c

•>r»

'-^--^"ZrZHr?

r"C2~i_m^rijrliir^:

••j : :=:-: : ------:-.:. :.---|-

r 

•••••• ••::•::

• - , i . . . r •--.'•.•;-•.•

. • ' .-\- '-•.--•:•. :v:'.' - •

".:••:::'••;.'• :f '•'.'..••'..•

',"•« - .°. 0 -°"o° 0 °; 1

. - . ' "•.'.."•

"•'•• \°-°- ' :; :v.

:v" - = ?o=°--

'. ".- :°'0 ^ ',"•'•' i

•/•'°-° -"'."'o

(6.1)

Semiconsolidated mottled red and yellowbrown, slightly clayey sand; massive 

grading downward to moderate reddish 

brown (1 OR 4/6)

Sand, crossbedded, loose moderate reddish orange (10 R 6/6). Extensively cut by 

small circular, white clay-lined burrows 

(Ophiomorpha type)

Sand, crossbedded, dark yellowish orange 

(10 YR 6/6) medium grained, abundant 

small gravel

Sand, gravelly (1 inch maximum) medium 

to coarse, dark yellowish orange (10 YR 

6/6)

EXPLANATION 

Clay 

Sand

I'i

Gravel

Burrows

Crossbedded 

sand

FIGURE 8. -Columnar section showing the geology at Bowling Green, Va. Exposure is in a roadcut on State Route 2, 0.6 km 

(0.4 mi) northeast of Bowling Green in the Bowling Green 7.5-minute quadrangle. Locality no. Bowling Green 1. Arrows 

indicate sample locations in profile. Surface elevation is 64 m (210 ft) above sea level.

amounts throughout the profile, and illite-smectite occurs only in the lowest beds. Vermiculite is present 

throughout.

Figure 9 shows the X-ray traces of untreated samples 

from this profile. There appears to be very little variation in the peak heights of the minerals in this profile, 

except for a tendency for vermiculite to increase toward 

the surface. Free aluminum oxides were not detected, 

but small amounts of iron oxides (goethite) occur at 

depth.

INTERPRETATION

In general, the clay mineral content (kaolinite dominant) and the decrease in feldspar and the increase in 

the stable heavy-mineral assemblages (ZTR) toward the 

surface indicate that the Yorktown Formation at this 

locality has been subjected to weathering of intermediate intensity.

Samples also were obtained from the capping gravels 

near the Fall Line at Fredericksburg, Va. These beds lie 

at higher elevations than those at Bowling Green and 

are farther updip. These gravels are considered to be the 

fluviatile facies of the Yorktown Formation (again lower 

and middle(?) Pliocene) (Wayne Newell, written commun., 1978). In general, the clay minerals in the sand at 

Fredericksburg are very similar to those at Bowling 

Green-that is, kaolinite and vermiculite dominant and

no illite-smectite. Again, the supermature weathering 

minerals, gibbsite and hematite, were not observed at 

this locality.

It would appear, therefore, that, in this part of the 

Virginia Coastal Plain, feldspathic surficial sand of early 

and middle(?) Pliocene age is weathered but has not 

reached compositional maturity or, if it has, that the 

deposits have undergone undetected stripping or 

resilicification or both.

ROUND BAY, MD.

CALVERT AND AQUIA FORMATIONS, 

LOCALITY NO. R.B. 51

A series of samples were collected from a section on 

the northern bank of the Severn River, about 1.44 km 

(0.9 mi) south of Round Bay and about 8 km (5 mi) west 

of Annapolis, Md. This locality is a naturally cut bank 

approximately 24.3 m high that is gradually retreating 

and thus exposing relatively fresh material. This area 

has been mapped recently (Minard, 1980); the stratigraphy at this site is shown in figure 10. Two formations 

are present, the Calvert Formation of early and middle 

Miocene age and the Aquia Formation of early(?) and 

late Paleocene age. Samples were collected from the 

Calvert and the upper part of the Aquia to a depth 

shown in figure 10.
F14 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

7.16 3.55

17.0

17.0 7.16 3.55

V I/S

FIGURE 9.-X-ray traces of clay minerals in the Yorktown Formation at Bowling Green, Va. (locality no. Bowling Green 1). The intensity of the kaolinite (K) reflection (7 A) is apparent in this 

diagram. The increase in dioctahedral vermiculite (V) (14.6 A) in 

samples taken nearest the surface also can be seen. I/S is illitesmectite, and GO is goethite. Measurements of the peaks of the 

X-ray traces are in angstroms. Depths of samples are in meters.

SAND MINERALOGY

Light minerals.-The light-mineral fraction in both 

these formations is shown in figure 4C. In both these 

units, quartz is the major light mineral. Not shown, 

however, is glauconite, which is particularly abundant 

(a major sand constituent) in the Aquia Formation. 

K-feldspar averages about 10 percent of the size fraction 

examined, and plagioclase occurs only in trace amounts. 

Most of the rock fragments in these beds are gneiss. The 

feldspar content in these two formations is considerably 

less than that in the Potomac Formation at the Hayfield 

site and about the same as that in the Yorktown Formation at the Bowling Green site. The feldspar content 

does not decline toward the surface in either the Aquia 

or the Calvert. In both units, the K-feldspar grains all 

appear to be altered to some degree, their general appearance being turgid.

Heavy minerals.-The heavy-mineral content at this 

locality is shown in figure 5C. All the assemblages except OTHER (which includes all common heavy minerals

such as chloritoid, andelusite, and pyroxene) are present 

in major amounts. In the HE GAT group, epidote and 

garnet compose nearly the entire fraction. No hornblende, actinolite, or tremolite was found in any 

samples. In the ZTR group, zircon is the major mineral, 

and, in the SSK group, staurolite is the major mineral. 

In the OTHER group, chloritoid is the major mineral.

Like the light minerals, the heavy-mineral assemblages of the Calvert and Aquia Formations are very 

similar. There is no significant variation in the percentages of the heavy-mineral assemblages, irrespective of 

depth within the formation. The one notable exception is 

at the top of the Aquia Formation, where the most 

stable of the heavy-mineral groups (ZTR) is unusually 

abundant. One explanation is that this particular zone 

represents a paleosol formed on the upper beds of the 

Aquia (upper Paleocene) before Calvert (lower and middle Miocene) deposition.

The heavy-mineral assemblages in these two formations have much less zircon than those in the Potomac 

Formation. There is a marked increase in the HE GAT 

(notably, epidote), SSK (notably, staurolite), and 

OTHER (notably, chloritoid) contents. Clearly, the 

sediments in these formations had a provenance different from that of the sediments of the Potomac Formation (Lower Cretaceous) at Hayfield or the "upland 

gravels" (lower and middle Pliocene) at Bowling Green.

CLAY-SILT MINERALOGY

The clay mineral distribution at this locality is summarized in figure 6C. In general, there is a decrease in 

illite-smectite upward through the section and a concomitant increase in kaolinite. In addition, vermiculite 

and chloritized vermiculite are developed in the upper 

part of the Calvert Formation. Illite shows no marked 

changes in concentration upward through the section.

X-ray traces showing the distribution of clay-sized 

minerals at this locality are shown in figure 11. The 

overall crystallinity of the minerals in both formations is 

poorer than that at the previously described localities. 

Mixed layering is very common, and glauconite is present in the Aquia Formation. Differentiating between illite and glauconite in X-ray traces is particularly difficult. For that reason, part of the illite percentage 

shown in figure 11 in the Aquia Formation is probably 

glauconite.

INTERPRETATION

The Calvert and Aquia Formations were originally 

protoquartzite in composition. They had, therefore, a 

feldspar content considerably lower than that of the 

Potomac Formation at Hayfield. Because the heavy and 

light minerals in the Calvert and Aquia Formations do
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F15

DEPTH BELOW 

SURFACE, 

IN FEET 

(METERS)

B ->

§ — C5 — 

< (1.5)

5

r

2 c-»

r

LJ

? 10-

J (3.0)

D ->

^

5 

§ 20

| (6.lT

3

L

X X X X X

: ':>- •;;::•;•:: '

-^-^r-^v^^T^--^ <

::-:-^ ;.-::••

^^:-:-;-:-.

Medium-dark-gray (N 4) organic concentrations

Pale to moderate yellow (10 YR 2/4) very 

fine to fine-grained sand. Loose

Sand very fine to fine-grained, silty; 

micaceous glauconite sand and dark 

opaque minerals concentrated in base of 

formation. Very pale orange (10 YR 3/2)

Yellowish brown (10 YR 5/4) fine to 

medium grained. Sand 10 percent glauconite

Grayish red (10 R 4/2) to dark reddish 

brown (10 R 3/4) with pockets of moderate yellowish-brown (10 YR 5/4), very 

glauconitic sand

EXPLANATION

X X 

X

Sand 

Peat

Clay 

lamallae

Clay

Glauconite 

sand

FIGURE 10.-Columnar section showing the geology at Round Bay, Md. Exposure in the northern bank of the Severn 

River, 1.44 km (0.9 mi) south of Round Bay, Md., and 8 km (5 mi) west of Annapolis,Md.,in the Round Bay 7.5-minute 

quadrangle. The lower part of the lower and middle Miocene Calvert Formation and the upper part of the lower(?) and 

upper Paleocene Aquia Formation are exposed at this locality. Locality no. R.B. 51. Arrows indicate sample locations 

in profile. Surface elevation is about 30 m (100 ft) above sea level.

not show any pronounced variation from the top to the 

base, these beds may not have been subjected to any prolonged subaerial oxidation in relatively recent time.

The data from the clay minerals, however, show a 

trend toward more compositional maturity from the 

lowermost part of the Aquia to the uppermost part of 

the exposed Calvert. Kaolinite and dioctahedral vermiculite increased toward the surface, and the percentage of illite-smectite shows an inverse relationship 

decreasing in the same direction. The compositional 

maturity of the clays, however, appears to be only in the 

aluminous silicates, not in the aluminum oxides. The 

resultant difference in the clay mineralogy of the 

Calvert and Aquia Formations and that of the Potomac 

Formation may be related the original lower feldspar 

content in the Calvert and Aquia Formations rather 

than to the effects of subaerial oxidation.

SUMMARY OF WEATHERING EFFECTS WEST OF 

CHESAPEAKE BAY

In the three sample localities west of Chesapeake Bay, 

the weathering effects were studied on the surface and 

near the surface of formations ranging in age from Early Cretaceous to middle Pliocene. The weathering effects indicated by the mineral assemblages (clay and 

sand) present in near-surface beds varied between sites, 

but none approached the maturity that might be 

predicted for deposits of this age from Jackson's (1965) 

weathering model. All the surfaces seem to be stripped 

postdepositionally, but how much and when?

The Yorktown Formation (Bowling Green site) appears to have the most mature profile if the concentration of illite-smectite in the clay assemblage is interpreted to reflect a strongly oxidizing near-surface environment. By the same criterion, the Calvert Formation appears to be more weathered than the Potomac 

Formation. In general, the weathering, as described by 

the Jackson model, would range from mild (Potomac) to 

intermediate (Yorktown).

Sand minerals show the effect of weathering less than 

clay minerals. The quartz-feldspar ratios show a base-tosurface decrease that is best seen in the Yorktown Formation. This preferential loss of feldspar relative to 

quartz upward through a section is to be expected in a 

well-developed weathering profile. Marked changes in 

the quartz-feldspar ratios were not evident in the 

Calvert and Potomac Formations; therefore, these
F16

14.0

3.55 3.33

0.05

VI/S I

4.6

6.1

GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

BETWEEN CHESAPEAKE AND DELAWARE BAYS

Six sites were sampled between Chesapeake and 

Delaware Bays.

BETTERTON, MD. 

PENSAUKEN FORMATION, LOCALITY NO. BET. 3

A series of high bluffs borders the Sassafras River in 

the northwestern part of the Delmarva Peninsula. Exposed in a few of these bluffs are broad channels filled 

with yellow gravelly sand that has cut into the older 

Cretaceous formations. This gravelly sand has been 

assigned to the Pensauken Formation (upper Miocene) 

(Owens and Minard, 1979). Figure 12 shows a section 

through a channel just west of Betterton, Md., that was 

sampled for study. Just over 18 m of the channel is exposed, from which six samples were collected for 

analysis.

The channel fill is composed of cross-stratified, 

moderately sorted, medium- to coarse-grained sand and 

horizontally stratified, poorly sorted gravelly sand. No 

trace fossils are present. The fill in these channels appears very permeable. Iron oxide staining and locally 

weak cementation occur throughout the entire section, 

although most of the iron oxides are in the upper beds of 

the channel fill (fig. 12).

SAND MINERALOGY

Light minerals.-The light-mineral distribution in the 

sand fraction is shown in figure 4D. In the size fraction 

studied (0.177 to 0.074 mm), K-feldspar is more abundant than quartz, although the relationship is reversed 

in the coarser and more abundant size fractions. Smaller 

amounts of plagioclase (mostly oligoclase), rock 

fragments, mica, and glauconite are also common constituents. In general, almost all the feldspar grains are 

weathered to some degree. Compositionally, the Pensauken Formation at this locality is an arkose unit, 

similar in this respect to the Potomac Formation at 

Hayfield, Va.

Heavy minerals.-The heavy-mineral assemblage in 

the Pensauken Formation at this locality is immature, as 

its high percentage of HEGAT minerals shows (fig. 5Z>). 

The formation here has high concentrations of actinolite 

in comparison with the formation in other parts of the 

Delmarva Peninsula. Otherwise, the Pensauken heavymineral assemblages are very similar throughout the 

Delmarva Peninsula. Studies of the heavy minerals upward through the section at Betterton show a general 

decline in the more labile constituents, although the 

feldspar content relative to quartz remains about the 

same.

FIGURE 11.-X-ray traces of untreated, unoriented specimens in 

samples of the Calvert (0.05, 0.3, and 4.2 m) and Aquia (4.6 and 6.1 

m) Formations at Round Bay, Md. (locality no. R.B.51). The 

preponderance of minerals in the high-angle range is characteristic 

of both formations. Mineralogic trends are difficult to see in these 

traces because of extensive mixed layering, but, in general, vermiculite (V) (14 A) increases toward the surface. Other minerals 

present are illite-smectite (US), illite (I), and kaolinite (K). 

Measurements of peaks in the X-ray traces are in angstroms. Depths 

of samples are given in meters.

minerals could not be used to detect any effects of 

weathering superimposed on these formations.

The heavy minerals followed much the same mineral 

trends as the light minerals. In the Yorktown Formation, the ZTR assemblage (the most resistant minerals) 

increases from the base to the top. In the Calvert and 

Potomac Formations, no such trend is evident.

In conclusion, the weathered profiles tested in this 

region are less mature (younger) than the formations on 

which they were developed. Additionally, the fact that 

formations are weathered to different depths and varying intensities suggests a different rate of erosion at 

each site. The interpretation that we favor for the lack 

of compositional maturity is that these deposits have 

been uplifted postdepositionally, the result being that 

the uppermost weathered beds have been stripped from 

much of this area.
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F17

DEPTH BELOW 

SURFACE, 

IN FEET 

(METERS)' 

0 

(0)

B 10- 

(3.0)

20 

(6.1)

(9.1)

40 

(12.2)

E

(15.2)

F 60 

(18.3)

o":

-

°°

'a.

1

W^S

m$*^

^':t ''-°.'":\.''

° •£*.'.' I.

.•:.;..'%;•'.•. ••'•.-:'-..'•

=-° °- ?'" = «';V

'.v^-'-V.-:-''^1

S.Q.O^o^p-o^

Sand semi-indurated, reddish brown (10 R 

3/4) medium-grained massive clay

Sand, banded, iron oxide cemented in 

layers, moderate reddish brown (10 R 

4/6) with pale yellowish-orange (10 YR 

8/6), slightly clayey, medium-grained 

feldspathic sand

Sand, extensively cross-stratified with thin 

gravel layers, mostly light brown (5 YR 

6/4), locally pale orange (10 YR 8/2). 

Mainly medium to coarse grained; loose

EXPLANATION 

Sand

Crossbedded 

sand

Gravel 

Iron oxide

Iron oxide cemented in base

FIGURE 12.-Columnar section showing the geology as exposed in a bluff along the southern side of the Sassafras 

River 0.5 km (0.9 mi) west of Betterton, Md., in the Betterton 7.5-minute quadrangle. Locality no. Bet. 3. Arrows indicate sample locations in profile. Surface elevation is 24.4 m (80 ft) above sea level.
F18 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

CLAY-SILT MINERALOGY

The clay minerals interstitial to the sand of the Pensauken Formation are shown in figure 13. At a depth of 

18.3 m below the surface, these minerals are poorly 

crystalline. The assemblage at this level appears to be 

characterized by quartz, halloysite, goethite, and 

feldspar. At 15.2 m, halloysite increases in crystallinity 

and apparent concentration. Detectable amounts of 

gibbsite and dioctahedral vermiculite also make their 

first appearance in this assemblage dominated by 

halloysite. From this level to the surface, gibbsite and, 

particularly, vermiculite increase, and halloysite tends 

to decrease. Small amounts of illite are also present 1.5 

to 4.6 m below the surface.

TEM plates illustrating the morphology of the 

minerals at various levels in the formation are shown in 

figure 14. In the two basal samples (figs. 14E", F), 

halloysite tubes are abundant and very well formed. 

Thin, transparent plates (kaolinite) are scattered 

throughout these samples. In figure 14D, most of the 

well-formed halloysite tubes are not present. At this 

level, unrolled halloysite tubes are the major form, and 

the thin anhedral plates are more common than they are 

below. In figure 14C, none of the well-developed 

halloysite tubes are present, and the bulk of the sample 

is the unrolled tubes and anhedral plates. In figure 14A, 

the platy minerals (vermiculite, kaolinite, and perhaps 

gibbsite) are the major phase, and only a few poorly 

formed tubes are present.

INTERPRETATION

The Pensauken Formation contains large concentrations of feldspar and thus resembles the arkosic 

Potomac Formation at Hayfield. Samples taken from 

the Pensauken at Betterton throughout its entire 

thickness are stained by iron oxides to varying degrees, 

an indication that the Pensauken is much more leached 

than the Potomac at Hayfield. The occurrence of abundant halloysite and especially gibbsite in the Pensauken, 

but not in the Potomac, indicates that the Pensauken 

has been intensively leached. Additionally, a comparison 

of the Pensauken with its near-age equivalent (the 

Yorktown Formation at Bowling Green) shows that both 

these upper Tertiary formations have widespread iron 

oxide staining, which superficially, indicates a comparable degree of subaerial alteration. This weathering 

equivalency is not borne out in the mineralogy, however. 

All the mature weathering products-gibbsite or halloysite or both-are present in the Pensauken but are 

notably absent in the Yorktown. Perhaps these mineralogic differences are related to the fact that the original 

feldspar content in the Pensauken was higher than that

in the Yorktown, but, at present, we favor the interpretation that the Pensauken is much more intensely 

weathered. In summary, the Pensauken is an intensely 

leached unit, the first formation discussed thus far that 

contains significant amounts of the supermature 

weathering mineral gibbsite.

HOUSTON, DEL.

BEAVERDAM SAND AND PENSAUKEN FORMATION, 

LOCALITY NO. HARR. 5

At the Houston, Del., locality, the Pensauken Formation (upper Miocene) is overlapped by the Beaverdam 

Sand (upper Pliocene) (fig. 15). The upper beds of the 

Beaverdam in turn are extensively dissected and 

overlain by younger, much more quartzose sand apparently derived from a reworking of the Beaverdam 

Sand. The Pensauken and Beaverdam are equally 

feldspathic units (arkose to subarkose).

The Pensauken at this locality is lithologically similar 

to the beds at Betterton (cross-bedded sand, local gravel 

beds, extensive iron oxide staining, and local cementation). Near the contact with the overlying Beaverdam, 

the Pensauken is cemented irregularly by iron oxides into a hard ironstone. This ironstone forms a highly irregular surface in the Pensauken. The much lighter colored sand in the overlying Beaverdam is characterized 

by small- to large-scale crossbedding and by an upwardfining sequence. The sand is typically a light gray but is 

normally stained by iron oxides along some of the crossstrata. The light red staining of the upper 30 cm of the 

formation suggests that the original weathered surface 

of this unit is not intact. Apparently, the upper part of 

the Beaverdam was removed before the deposition of 

the younger quartz sand that overlies the Beaverdam 

here.

SAND MINERALOGY

Light minerals. -No mineral counts of the Beaverdam 

or Pensauken were made at this locality. Spot checks of 

the mineralogy in the sand indicate that both units are 

very feldspathic (mostly K-feldspar) and have about the 

same feldspar content. The Beaverdam, like the Pensauken, is therefore an arkose unit.

Heavy minerals.-The heavy-mineral assemblages in 

the Beaverdam and Pensauken at this locality have a 

high HEGAT (immature) content (fig. 5#). Within this 

HEGAT group, hornblende is especially abundant. The 

ZTR context of the Beaverdam is higher than that of the 

Pensauken, and the Beaverdam thus is probably a more 

mature assemblage. The hornblende content (high) in 

the Pensauken differs markedly from the hornblende 

concentration in the Pensauken at Betterton (low).
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F19

1455 3345

1.5

15.2

18.3

GO

FIGURE 13.-X-ray traces showing clay minerals in sand of the Pensauken Formation at Betterton, Md. (locality no. Bet. 3). In this profile, kaolinite + halloysite (K,H) decreases in concentration from base 

to top. Vermiculite (V) increases in abundance in the uppermost 

beds, as does gibbsite (G), although this mineral is less abundant than 

vermiculite in these upper beds. Illite (I) occurs only in a few samples 

and then only in small amounts. Goethite (GO) is a common constituent in all samples, as is quartz (Q). Measurements of peaks in the 

X-ray traces are in angstroms. Depths of samples are given in 

meters.

CLAY-SILT MINERALOGY

The clay minerals in the sand of the Beaverdam and 

Pensauken are shown in figure 16. Generally, X-ray patterns of the Pensauken at 3.2 m are similar to those of 

the Beaverdam at 2.7 m. The uppermost sample of the 

Pensauken at 4.2 m is more poorly crystalline than 

either of the two samples mentioned above. The 1.5-m 

sample has significantly higher concentrations of 

goethite (iron oxide). This result can be expected

because the sample came from the iron oxide zone 

shown in figure 15. Overall, several trends can be seen 

in figure 16. The general increase in vermiculite content 

upward through the weathering profile is found at many 

of the previously described localities. Gibbsite appears to 

increase from the base to the top, but this trend is less 

pronounced than the vermiculite increase. Illite also 

shows an increase upward through the section and appears to combine with vermiculite to form a mixed-layer 

clay in the sample taken nearest the surface.

INTERPRETATION

Mineralogic studies of the Beaverdam Sand and the 

Pensauken Formation at this locality confirm field 

observations that the unit nearest the surface, the 

Beaverdam, has been stripped postdepositionally. After 

this stripping (probably in the late Quaternary on the 

basis of general field relations throughout the Delmarva 

Peninsula), a second weathering profile developed on 

the Beaverdam; during this phase, vermiculite and, to a 

lesser degree, illite were formed in the uppermost beds. 

Gibbsite formed during a previous weathering cycle appears to have been relict in these beds. The presence of 

gibbsite in the nonvermiculite-illite beds of the Pensauken and through the Beaverdam favors such an interpretation.

The heavy-mineral suite and, to a lesser degree, the 

feldspar percentages indicate that neither the Beaverdam nor the Pensauken has undergone intensive 

subaerial oxidation after stripping. Hornblende in 

heavy-mineral assemblages is particularly soluble in 

mild to intensive subaerial oxidation. This mineral is 

very abundant even in the Beaverdam sample taken 

nearest the surface. The fact that feldspar percentages 

do not show any significant decline in the upper beds 

again attests to the relatively mild leaching of these formations.

Therefore, our interpretation of this section would be 

that the Beaverdam (upper Pliocene) and the Pensauken 

(upper Miocene) have been through at least two cycles of 

weathering. In the earlier phase, the assemblage 

kaolinite-gibbsite-goethite was formed. The Beaverdam 

was reexposed, and the uppermost intensely weathered 

bed (characterized by a thick, upper, red-colored zone) 

was stripped. A second weathering cycle began producing a vermiculite-illite-amorphous iron oxide(?) 

assemblage in the upper beds.

This last weathering cycle has hardly affected the 

underlying Pensauken. The clay minerals in this part of 

the section tend to resemble those in the more 

weathered parts of the Pensauken at Betterton (fig. 13), 

especially those beds between 1.5 and 4.6 m (kaolinitegibbsite-goethite assemblage). The only exception is the
F20 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

D

FIGURE 14.-Transmission electron microscope photomicrographs of the <2-/t fraction in sand of the Pensauken Formation at Betterton, Md. 

(locality no. Bet. 3). Depths of samples are as follows: A, 1.5 m; B, 3 m; C, 6.1 m; D, 9.1 m; E, 15.2 m; F, 18.3 m. Letters correspond to sample 

designations in figure 12. V is vermiculite, and H is halloysite.
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F21

DEPTH BELOW

SURFACE,

IN FEET

(METERS)

0-

(0) T

0

z 

<

V)

5 < 

o

IT

m 

I

E

10- 

(3.0)

20 — 

(6.1)

Quartz sand, grayish orange (5 YR 7/2)

Sand massive at top, crossbedded below; 

pale yellowish orange (10 YR 8/6)

Iron oxide staining along some of crossstrata

Thin to thick irregular-shaped ironstone 

layer; grayish-red (10 R 4/2) semi-consolidated, crossbedded sand

Grayish-red (10 R 4/2) semi-consolidated, 

crossbedded sand

Pale-green clay breccia

Moderate reddish-brown, (10 R 4/6) loose, 

medium to coarse sand, fine to coarse 

gravel

EXPLANATION

Gravel 

Sand

Crossbedded 

sand

FIGURE 15.-Columnar section showing the geology in a pit on the northern side of the Murderkill 

River 8 km (5 mi) northeast of Houston, Del., in the Harrington 7.5-minute quadrangle. Locality no. 

Harr. 5. As interpreted here, three units are present: an upper, very quartzose unit; a middle, lightcolored, very feldspathic sand (Beaverdam Sand); and a lower, moderate-reddish-brown-stained unit 

(Pensauken Formation). Arrows indicate sample locations in profile. Surface elevation is 9.1 m (30 ft) 

above sea level.

vermiculite-illite assemblage apparently superimposed 

on the older weathered beds.

WHALEYSVILLE, MD.

OMAR FORMATION AND BEAVERDAM SAND, 

LOCALITY NO. WH. 1A

One of the most widespread coastal units in the 

Delmarva Peninsula is the Omar Formation (Owens and 

Denny, 1979). This formation occurs at elevations of 9 to 

15 m above sea level. The unit was deposited in a 

marginal marine environment and characteristically 

consists of several lithofacies. Drill holes through the 

unit at several localities show that the unit typically has 

the same types of lithofacies stacked in a vertical sequence. A thin (as much as 1 m thick) basal brown peat 

to peaty clay is overlain by a massive, black, very clayey 

silt to silty clay (commonly containing the oyster 

Crassostrea virginica) that grades upward into a 

massive, white, slightly clayey and silty sand. Macrofossils here include Merceneria sp. (clam), Ensis sp. 

(clam), Donax sp. (clam), and Busycon sp. (snail). Commonly, the upper beds are a medium-dark-gray, 

weathered, silty, fine-grained sand.

In general, this assemblage indicates saline water 

deposition (open bay to shallow shelf). The dark-gray 

sand is overlain by a light-colored, extensively crossbedded sand indicative of a barrier-to-beach depositional 

site.

The Omar beds are characteristically more the 

lagoonal or back-barrier muddy sediments in the 

Maryland part of the Delmarva Peninsula, whereas the 

Omar beds near Accomack, Va., are a shallow shelfbarrier (sandy) complex.

The Whaleysville samples taken at Longridge, Md., 

just west of Whaleysville, are from the Omar-type 

sediments. At this locality, both the Omar and the 

underlying Beaverdam were sampled (fig. 17). In all, 

four samples were analyzed, two from the Omar (one 

sand and one clay-silt) and two from the Beaverdam 

(both sand).
F22 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

14.2 7.26

3.57

3.34

.5 PS

V,C I 3.2 PS

FIGURE 16.-X-ray traces of clay minerals in the Beaverdam Sand 

and the Pensauken Formation northeast of Houston, Del. (locality 

no. Harr. 5). Vermiculite (V) shows typical near-surface increase in 

concentration in the upper part of the Beaverdam between 0.5 and 

1.5 m below the surface. Kaolinite ( + halloysite) (K,H) and gibbsite 

(G) seem little changed in concentration throughout both formations. 

Goethite (GO) (4.19 A), on the other hand, is present only in the Pensauken (PS) and is absent or poorly developed in the Beaverdam. C is 

chlorite, Q is quartz, and I is illite. Depths (in meters) are keyed to 

columnar section. Measurements of peaks in the X-ray traces are in 

angstroms.

SAND MINERALOGY

Light minerals.-The bulk of the sand in the Omar 

Formation is quartz (fig. 4F). K-feldspar, largely 

microcline, is the next most abundant mineral. No 

plagioclase was observed in the Omar at this locality. 

Rock fragments are a small but persistent constituent in 

all of the Omar samples. Compositionally, the Omar is 

protoquartzite.

The Beaverdam Sand, on the other hand, has, in 

general, more feldspar than the Omar, although quartz 

is still the major light mineral. K-feldspar is the major 

feldspar, but plagioclase (oligoclase) is present in small 

amounts. The Beaverdam at Whaleysville is an arkose 

unit, similar to the Beaverdam at the Houston site.

Heavy minerals.-The heavy minerals in both units 

are somewhat similar, although the Omar is slightly less 

mature (fig. 5F). Field relationships (Beaverdam deeply 

eroded prior to the emplacement of Omar beds) suggest 

that the Omar at this site may have been derived largely 

from the Beaverdam-hence, the general mineral 

similarity in both assemblages. The HE GAT assemblage 

in both units has low hornblende content relative to 

tremolite and actinolite. The heavy-mineral assemblages 

in both units are considered to be moderately immature 

because the more labile constituents such as amphibole 

are present in only small amounts. In the samples examined, no selective removal of the more labile constituents by intrastratal solution was observed. However, 

no very near surface samples were analyzed from this 

locality. Farther southwest, however, such near-surface 

sand was examined from the Omar beds. As at 

Whaleysville, no selective removal of the more labile 

heavy minerals could be discerned.

CLAY-SILT MINERALOGY

Four samples of the clay-silt fraction in the sand from 

this locality were X rayed. Two samples were from the 

Omar (3.7 to 4.6 m and 7.6 to 9.1 m), and two samples 

were from the Beaverdam (10.7 to 12.2 m and 12.2 to 

13.7 m). The two assemblages are different (fig. 6D). 

The Beaverdam assemblage is mainly halloysite 

(+kaolinite) and smaller amounts of illite and illitesmectite (fig. 6D). The overlying Omar has much more illite and less kaolinite and illite-smectite than the 

underlying Beaverdam. The Omar sample taken nearest 

the surface also has vermiculite (fig. 18). Like the sand 

fraction, the clay mineral assemblages in both formations are moderately immature.

INTERPRETATI ON

The effects of subaerial oxidation on the Omar Formation near Whaleysville are slight. Except for the appearance of vermiculite in the sample taken nearest the 

surface, the Omar appears relatively unweathered. At 

this site (the only one studied in the Omar), however, the 

upper 3.6 m of the formation was not analyzed, so that 

the weathering effects in this interval are not known.

It appears, therefore, that subaerial oxidation has had 

little effect on the part of the Omar Formation sampled. 

The underlying Beaverdam also shows few visual alteration effects in drill cuttings (no iron oxide formation),
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F23

DEPTH BELOW

SURFACE,

IN FEET

(METERS)

o-

(0)

10 — 

(3.0)

20 — 

(6.1)

30-

(9.1)

40- 

(12.2)

Medium dark-gray (N 4) mottled reds and 

white silty fine-grained sand

White (N 9) slightly clayey, coarse-grained 

sand; slightly feldspathic

Dark-gray (N 3) sandy clay

Dark-gray (N 3) silty sand

Grayish-brown (5 YR 3/2) peaty somewhat 

sandy clay-silt. Wood fragments common

- Unconformity

Pale greenish-yellow (10 YR 3/2) mediumto coarse-grained, pebbly, feldspathic 

quartz sand

EXPLANATION 

Sand

Peat

FIGURE 17.-Columnar section in an auger hole at Longridge 2 km (1.3 mi) west of Whaleysville, Md., in the 

Whaleysville 7.5-minute quadrangle of Maryland and Delaware. Locality no. Wh. 1A. The Omar Formation and the 

Beaverdam Sand are present in this auger hole. Arrows indicate sample locations in profile. Surface elevation is 

10.6 m (35 ft) above sea level.
F24 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

10.0

10.7-12.2

H 12.2-13.7

FIGURE 18.-X-ray diffractograms of the untreated <2-^ fraction in 

sand of the Omar Formation and the Beaverdam Sand at 

Whaleysville, Md. (locality no. Wh. 1A). I/S is illite-smectite, I is illite, H is halloysite, K, is kaolinite, and V,C is vermiculite 

( + chlorite). Measurements of peaks in the X-ray traces are in 

angstroms. Depths of samples are given in meters.

but the X-ray traces indicate that the clay mineral 

assemblage (halloysite dominant) in this unit is more 

weathered than that in the Omar. Although the Beaverdam Sand near Whaleysville is weathered, it is less 

altered than the Beaverdam at Houston. One explanation is that the Beaverdam beds at Whaleysville are a 

less weathered zone lying below the weathering level 

represented by the Beaverdam at Houston. The upper, 

more weathered beds of the Beaverdam were stripped 

during emplacement of the Omar Formation.

The point to be made at this locality is that the upper 

Pleistocene Omar Formation (about 190,000 years old) is 

much less altered than the Beaverdam (Pliocene) or the 

Pensauken (Miocene).

GERMANTOWN, MD.

IRONSHIRE FORMATION, UPPER PLEISTOCENE, 

LOCALITY NO. BER. 2

The Omar Formation has been eroded into and 

overlapped along its eastern margin by a dominantly 

sandy unit called the Ironshire Formation (Owens and 

Denny, 1979). Along the Atlantic Coast, this unit occurs

as a narrow band of sand having elevations of as much 

as 10 m above sea level (fig. 1).

Figure 19 is a stratigraphic section typical of many 

seen in exposures of the sand. The Ironshire Formation 

consists of three lithofacies distinguished primarily by 

the type of cross-stratification. The lower unit is a loose, 

well-sorted sand having long, gently inclined crossbeds. 

Black, heavy-mineral laminae are abundant and commonly cut by numerous short, circular borings. This unit 

is overlain by a loose, poorly sorted gravelly (quartz 

clasts) sand in which the scale of the trough crossbedding is very large. Locally, this sand has a large number 

ofCallianassa burrows. This unit grades up into another 

sandy unit. The sand is extensively crossbedded (trough 

type), but the cross sets are much smaller than those in 

the gravelly sand below. Only a few burrows were 

observed in this facies.

Overall, the Ironshire Formation appears to have the 

lithofacies found in a regressive beach sequence (beach, 

tidal channel, and tidal flat (ridge and runnel)). To the 

south, all of the sand is overlain by a back-barrier silty 

clay. This formation is considered to be late Sangamon 

(about 60,000 to 80,000 years) in age (Owens and Denny, 

1979).

SAND MINERALOGY

Light minerals.-Seven samples from this site were 

analyzed. Quartz is the major sand constituent, and 

K-feldspar, plagioclase, and rock fragments (mica 

gneiss) are less abundant (fig. 4F). The feldspar content 

in the fraction analyzed is about 25 percent. K-feldspar 

is the most abundant, but plagioclase is very common. In 

the sampled pit, plagioclase shows the most marked 

trend, decreasing from the base to the top; quartz increases upward in the same interval. Compositionally, 

the Ironshire sand is a subarkose unit.

Heavy minerals. - The heavy-mineral assemblage in 

this unit is noteworthy because of the large number of 

well-rounded grains in all the samples examined. Hornblende is particularly abundant (fig. 5G) and appears exceptionally fresh, even in the samples taken nearest the 

surface. Pyroxene (hypersthene) is a common constituent in the sample taken nearest the surface, but these 

grains have a "washed out" appearance (weathered). 

This mineral is the only indication in the heavy-mineral 

assemblage that any chemical weathering of these beds 

has taken place.

CLAY-SILT MINERALOGY

The X-ray results from this unit were very surprising 

because of the large concentrations of gibbsite in many 

of the traces (fig. 20). The trace from the lowermost 

sample (7.3 m) is almost totally gibbsite. This
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F25

DEPTH BELOW

SURFACE,

IN FEET

(METERS)

0

(0)

-^ G

Sand, clayey, massive light brown (5 YR 

5/6)

Sand, crossbedded, light brown (5 YR 6/4); 

clay lamellae interstratified with sand

Sand with thin beds of gravel (1 inch or 

less diameter, crossbedded trough, 

small scale; sets less than 18 inches 

thick, color mostly very pale orange (10 

YR 9/2), stained locally moderate orange 

pink (5 YR 8/4)

Sand, crossbedded, large-scale troughs 

(sets typically greater than 3 feet thick). 

Locally contains abundant Callianassa 

burrows

Sand, with long inclined beds, white (N 9), 

black heavy mineral laminae, extensively 

burrowed

-—Unconformity 

Beaverdam Sand

EXPLANATION 

Sand

Crossbedded 

sand

Gravel 

Burrows

Clay 

lamellae

FIGURE 19.-Columnar section showing the geology in a pit near Berlin, Md., 0.4 km (0.6 mi) east of Germantown, Md., in the Berlin 7.5-minute quadrangle. Locality no. Ber. 2. The Ironshire Formation and the Beaverdam 

Sand are exposed in this pit. The Ironshire is typically a sandy unit bevelled into the underlying Beaverdam along the 

coast. Arrows indicate sample locations in profile. Surface elevation is 9 m (30 ft) above sea level.

mineralogy persists to within 3.7 m of the surface. 

Above this interval, the clay minerals show a marked 

change; vermiculite, illite, and kaolinite are present in 

fair abundance from here to the surface. Gibbsite is still 

a major constituent at 3.7 m but decreases in abundance 

(or crystallinity or both) above this level.

One of the most difficult minerals to identify morphologically under the electron microscope is gibbsite. 

Because of the unusual concentration of this mineral in 

the base of the Ironshire, a series of SEM pictures were 

taken at various magnifications to ascertain what morphologies were present (fig. 21). The dominant shapes 

are what appear: to be unrolled tubes of halloysite (fig. 

2L4.). At increased magnification (fig. 2LB), halloysite 

and the other major shapes (thin anhedral plates) are 

better displayed. SEM-EDAX analyses of this form 

revealed it to be almost all aluminum and some traces of 

silica and thus confirmed the X-ray analyses of these 

samples.

INTERPRETATION

The overall lithology of the Ironshire (feldspathic sand 

and a very immature heavy-mineral suite) suggests a 

fresh first-cycle sediment. The presence of abundant 

amphiboles and smaller amounts of pyroxene 

throughout the formation favors such an interpretation. 

In outcrop, the formation appears to be somewhat 

weathered in the upper beds, as evidenced by iron oxide 

staining in the upper 2.4 m (8 ft).

The distribution of clay minerals in the formation is 

unusual, however. The lower half of the outcrop is 

characterized by an abundance of gibbsite, whereas the 

upper half shows the soil development noted at other 

localities-that is, a general increase in vermiculite, illite, and possibly kaolinite from about 2.4 to 0.9 m below 

the surface (intermediate weathering).

Thus, the clay minerals in the upper half of the profile 

appear to belong to the normal weathering profile 

observed at all the sites described previously. The gibb-
F26

14.20

GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

1450 r 7.20 

\f^^^/ff\Mflf^f\ J

V,C I

FIGURE 20.-X-ray traces of clay minerals in the Ironshire Formation at Germantown, Md. (locality no. Ber. 2). The lower half of the 

profile is dominated by gibbsite (G) (4.85 A), a mature weathering 

mineral. The upper half is characterized by progressive development 

of vermiculite (V) (14.2 A) and, to a lesser degree, of illite (I) and 

kaolinite (K), which suggest a less mature weathering profile. C is 

chlorite. Measurements of peaks in the X-ray traces are in 

angstroms. Depths of samples are given in meters.

site, however, presumably a more mature weathering 

mineral, seems out of place in the profile. The fact that 

this mineral is most abundant in the basal sample suggests derivation from an intensely weathered terrane 

and is present as a detrital weathering product rather 

than as an in-place weathering product. At this locality, 

the Ironshire has bevelled into the Beaverdam Sand (upper Pliocene) and the Omar Formation (upper 

Pleistocene). As illustrated earlier, the Beaverdam, 

which has significant concentrations of gibbsite at 

Houston, Del., probably was the source for gibbsite in 

the Ironshire. The clay minerals in the Ironshire, 

therefore, show that knowledge of the geologic history

of a deposit is necessary before its clay mineral content 

can be interpreted.

WORTON POINT, MD.

KENT ISLAND FORMATION, UPPER PLEISTOCENE, 

LOCALITY NO. HANESVILLE 1

The eastern side of Chesapeake Bay is flanked by a 

flat surface or terrace that slopes gently from north to 

south. In the northern Chesapeake Bay area near the 

mouth of the Susquehanna River, this terrace is very 

dissected but has maximum elevations of 12 to 15 m 

(40-50 ft). The Chesapeake Bay has cut into this terrace 

at Worton Point, Md. (fig. 1) and exposed about 12 m (40 

ft) of section. The lithologies in this bluff are shown in 

figure 22. The section includes two clay-silt units 

separated by a gravel and sand unit. Pollen studies from 

the clay-silt beds indicate that two palynomorph zones 

are present, the upper dominated by a cool assemblage 

(pine-hemlock) and the lower by a warm assemblage 

(oak-hickory) (L. A. Sirkin, written commun., 1975). A 

thick gravel and sand layer separating the two silt beds 

suggests an unconformity, and we conclude that two 

formations are present. Such a two-bed configuration 

(cool flora-warm flora) also has been seen at Kent Island 

in Chesapeake Bay and possibly includes Omar or Ironshire Formation equivalents (warm) as mapped in the 

lower bay region (Owens and Denny, 1979). Wood obtained from the lower silt was dated at more than 45,000 

years B.P. (U.S. Geological Survey Radiocarbon 

Laboratory Sample W-1920) (Meyer Rubin, written 

commun., 1973). The upper unit is possibly middle 

Wisconsinan (about 30,000 years B.P.), whereas the 

underlying unit is either about 60,000 years (Ironshire 

equivalent) or 190,000 years (Omar equivalent). The 

sediments at Worton Point, therefore, are probably late 

Pleistocene in age.

SAND MINERALOGY

Light minerals.-Figure 4G shows the light minerals 

observed at this locality. The concentrations of light 

minerals in this unit are different from those in units 

described heretofore. Rock fragments, typically 

micaceous gneiss or schist, are the major light minerals 

observed. Quartz and feldspar, both K-feldspar and 

plagioclase, are also very common sand constituents. At 

a few localities, such as the mouth of the Susquehanna 

and as far south as Kent Island, coarse gravel is particularly abundant. The gravel suite is heterogeneous 

and contains many different rock types, mostly 

crystalline and metamorphic. This heterogeneity and 

the closeness of Worton Point to the source of these 

rocks (the Piedmont province) explain the high content 

of rock fragments in the sand. Compositionally, the beds 

at Worton Point are a high-rank graywacke.
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F27

FIGURE 21. - Scanning electron microscope (A) and transmission electron microscope (B) micrographs of gibbsite (G) from the < 2-/* fraction in 

sand of the Ironshire Formation 7.3 m (24 ft) below the surface at locality no. Ber. 2. Siliceous film, Si. Scale is 1 cm= 1 /x.

The apparent lack of any significant variation in 

feldspar content from top to bottom in this sample suggests only slight postdepositional mineral alteration 

here.

Heavy minerals.-The heavy-mineral assemblages in 

the beds at this locality (fig. 5H) are immature. In the 

nonopaque fraction, highly weatherable amphiboles, 

notably hornblende, are abundant and fresh throughout 

the section. Pyroxenes, mostly orthopyroxene (hypersthene), are relatively abundant in these beds, quite 

comparable to the abundance in the Pleistocene units 

(Omar and Ironshire Formations) along the Atlantic

Coast. In the opaque fraction, magnetite as well as ilmenite is very abundant throughout the sampled section.

As was true of the light minerals, there is little variation in the heavy-mineral assemblages throughout this 

section.

CLAY-SILT MINERALOGY

The clay mineral assemblage in the Worton Point beds 

consists of vermiculite, illite, and kaolinite. Vermiculite 

is particularly abundant in all the samples examined, irrespective of depth or palynomorph zone. In this
F28 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

DEPTH BELOW

SURFACE,

IN FEET

(METERS)

•D

JL

(0)

A—

10 —

(3.0)

20 — 

(6.1)

£ >

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F->

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111

:r^^~tLr^jr^r^r~zi

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Moderate reddish-brown (10 R 4/6) sand 

semi-consolidated, massive, mostly with 

irregular moderate brown (5 YR 3/4) clay 

lamellae

Distorted beds

Sand, crossbedded, dark yellowish orange 

(10 YR 6/6), loose medium grained

Medium-gray (N 5) laminated silts grading 

down to very clayey massive silt

Very light gray (N 8) crossbedded sand

Sand, crossbedded, dark yellowish orange 

(10 YR 6/6), loose, medium to coarse

Gravel to 5 inches (12.7 cm)

Medium dark-gray (N 4), massive to thickbedded clayey silt and clayey sand. 

Abundant woody fragments

Beach level (high tide) 

Covered interval

EXPLANATION 

Sand

Crossbedded 

sand

Silt

Clay 

Gravel

Clay 

lamellae

FIGURE 22.-Columnar section showing the Kent Island Formation at Worton Point, Md. The section was 

measured in a bluff on the eastern side of Chesapeake Bay 3.5 km (2.2 mi) northwest of Newtown, Md., in the 

Hanesville 7.5-minute quadrangle. Locality no. Hanesville 1. Arrows indicate sample locations in profile. Surface 

elevation is 12.2 m (40 ft) above sea level.

respect, the Worton Point beds differ from all the 

deposits discussed to this point.

As we observed for the heavy- and light-mineral 

assemblages, there is little or no variation in the clay 

mineral assemblage throughout the section (fig. 23).

Figures 244 and 245 are electron micrographs from 

the Worton Point beds. Figure 244 shows the platy but 

otherwise anhedral forms of vermiculite. Figure 24B 

shows a kaolinite-dominant sample in which the hexagonal edges of the plates are well defined. Neither sample, however, has tubular halloysite.

INTERPRETATION

The beds of the Kent Island Formation at Worton 

Point compositionally show only minor subaerial alteration effects, as suggested by the general absence of iron 

oxide staining. One of the more common clay minerals
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F29

14.5

0.9

V,C I 11.3

FIGURE 23.-X-ray traces of the clay fraction in sand of the Kent 

Island Formation at Worton Point, Md. (locality no. Hanesville 1). 

The most conspicuous feature of these patterns is the persistence 

of vermiculite (+chlorite) (V,C) throughout the profile. In addition, 

kaolinite (K) and illite (I) are persistent minerals throughout the 

section. There is very little evidence of significant subaerial oxidation reflected in clay minerals at this locality. Measurements of 

peaks in X-ray traces are in angstroms. Depths of samples are 

given in meters.

formed in the upper zone of alteration at most of the 

other sites discussed is vermiculite. The abundance of 

this mineral throughout an entire 11.2-m (37 ft) Worton 

Point section suggests that this mineral is detrital

rather than authigenic. Apparently, the concentration 

of the mineral here is because of the close proximity of 

the Worton Point beds to probable source rocks (metamorphic and crystalline) in the nearby Piedmont province. The biotite and chlorite in the metamorphic rocks 

were probably weathered to vermiculite before stripping, transportation, and deposition in the Coastal 

Plain. The fact that downbay age equivalents of the 

Worton Point beds contain considerably less vermiculite 

suggests that this mineral was deposited rapidly by 

rivers after they entered the Coastal Plain or that the 

percentages were reduced because of the addition of 

clay minerals from other sources, sucli as the reworked 

Coastal Plain sediments.

If the Kent Island beds at Worton Point are late 

Pleistocene in age, as interpreted, and are in part either 

Ironshire or Omar Formation equivalents, a correlation 

of the weathering effects in the Ironshire and Omar Formations with the Worton Point beds is not possible. In 

the coastal beds of late Pleistocene age, subaerial alteration is expressed by the development of vermiculite and 

illite. Both these minerals appear to be original depositional components in the Kent Island beds at Worton 

Point; therefore, weathering effects could not be 

detected because of the original mineralogy in these 

beds;

The heavy and light sand minerals, however, can be 

used to determine the intensity of subaerial oxidation in 

this unit. The heavy and light sand minerals show few 

alteration effects from the base to the top of the section. 

Intensive weathering or leaching (intrastratal solution) 

does not appear to have been an important factor in the 

postdepositional history of this unit. Therefore, this unit 

is only mildly weathered, or, simply stated, the weathering profile here is compatible with the age of the upper 

beds.

PITTSVILLE, MD.

PARSONSBURG SAND (UPPER PLEISTOCENE) (COULD

INCLUDE PLIOCENE TO HOLOCENE SAND DEPOSITS),

LOCALITY NO. PITT.8

Large parts of the Delmarva Peninsula are underlain 

by a thin to thick blanket of sand called the Parsonsburg 

Sand (Denny and Owens, 1979). The age of these sand 

deposits is uncertain in many areas but could be as old as 

late Pliocene. Most of the sand, however, was deposited 

in late Wisconsinan time (Sirkin and others, 1977).

Some of these sand deposits occur on the higher elevations in the southern Delmarva Peninsula, called by 

some "the Parsonsburg high" (Rasmussen and 

Slaughter, 1955). One of the sandy bodies on this high 

was sampled (fig. 25). Only 1 m of section was available 

for study, but a drill hole showed the deposit to be approximately 8.2 m thick. The exposed beds of the deposit
F30 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

FIGURE 24.-Electron micrographs of clay fractions from the Kent Island Formation at Worton Point, Md. (locality no. Hanesville 1), showing (A) vermiculite flakes (V) from a depth of 2.7 m and (B) characteristic hexagonal kaolinite aggregates (K) from a depth of 3.35 m. Both of 

these forms are readily identifiable on the basis of morphology, and their presence is corroborated in X-ray traces.

typically are a massive, loose, medium-grained sand. 

Many of the grains are rounded to well rounded and 

have a frosted or pitted surface. The upper meter is 

stained by iron oxide, but there is no well-developed B 

horizon having a pronounced clay accumulation. Below 

this iron oxide zone, accumulations of stained, irregular, 

thin, wiggly brown clay (clay lamellae of other workers) 

are present. Clay lamellae are common throughout the 

Parsonsburg Sand in the Delmarva Peninsula.

SAND MINERALOGY

Light minerals. —The light minerals in the 0.074- to 

0.177-mm fraction are shown in figure 4H. Quartz and 

lesser amounts of K-feldspar comprise nearly this entire 

fraction. No plagioclase was found in any samples. 

Minor amounts of rock fragments too small to be shown 

in figure 4 were detected in most samples.

The quartz-feldspar ratio showed very little variation in the section sampled. The feldspar content of
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F31

DEPTH BELOW

SURFACE,

IN FEET

(METERS)

0

10- 

(3.0)

20 -

(6.1)

Moderate brown (5 YR 4/4) massive 

slightly clayey medium sand

Light - brown (5 YR 5/6) crossbedded 

medium sand

Very pale orange (10 YR 8/2) crossbedded 

medium sand with abundant thin (less 

than 1 inch) light-brown (5 YR 5/6) clay 

lamellae

Moderate brown (5 YR 3/4) peaty clayey 

silt

Grayish-brown (5 YR 3/2) silty clay with 

scattered small pieces of carbonized 

wood

Grayish-brown (5 YR 3/2) clayey peat. Two 

C 14 dates on peat; upper, 25,690 ±600 

years B.P., lower 28,330 ±600 years B.P.

—~—~^~—-~ I Walston Silt (upper Pliocene)

EXPLANATION

Sand

Crossbedded 

sand

Clay 

lamellae

30 

(9.1)

FIGURE 25.-Columnar section of the Parsonsburg Sand near Pittsville, Md., about 11.2 km (7 mi) east of Salisbury, 

Md., in the Pittsville 7.5-minute quadrangle. Locality no. Pitt. 8. Solid lines show the section seen in outcrop; dashed 

lines indicate lithologic data obtained from an auger hole at the outcrop site. Arrows indicate sample locations in profile. Surface elevation is 24 m (80 ft) above sea level.

samples from the base of the unit in the subsurface (15 

percent) was much larger than that of samples from the 

upper beds (less than 5 percent). The Parsonsburg Sand 

here is protoquartzite, a composition typical of most 

Parsonsburg samples from other localities.

Heavy minerals. -The heavy minerals in the 0.074- to 

0.177-mm fraction are shown in figure 57. The ZTR 

minerals are the most common; the HE GAT and SSK 

minerals are present in about equal but lesser amounts. 

In a vertical section, the ZTR minerals show a small 

tendency to increase toward the surface, whereas the 

HE GAT minerals tend to decrease slightly toward the 

surface. The heavy-mineral assemblage in the Parsonsburg Sand is moderately mature.

CLAY-SILT MINERALOGY

The X-ray traces of the clay minerals in this unit are 

shown in figure 26. There is no dramatic change in the 

clay mineralogy vertically in the section sampled. In 

general, vermiculite and kaolinite are the major 

minerals in the profile. Gibbsite, illite, and locally 

goethite are minor minerals. Gibbsite appears to increase toward the surface, whereas kaolinite and illite 

decrease upward.

INTERPRETATION

The Parsonsburg Sand at this locality yielded 

radiocarbon ages of 26,000 to 30,000 years B.P. The
F32 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

14.4

3.34

3.56

1.8

FIGURE 26.-X-ray traces of the clay-silt fraction in the Parsonsburg 

Sand near Pittsville, Md. (locality no. Pitt. 8). In general, the clay 

mineral assemblage is mature (gibbsite bearing) and changes little 

throughout the sampled section. In view of the very young late 

Pleistocene age of this unit, such an assemblage is unusually 

mature. V,C is vermiculite (+chlorite), I is illite, K,C is kaolinite 

(+chlorite), G is gibbsite, GO is goethite, and Q is quartz. 

Measurements of peaks in the X-ray traces are in angstroms. 

Depths of samples are given in meters.

composition of the sand and its probable aeolian origin 

suggest that it was derived from the nearby Beaverdam 

Sand. The Parsonsburg, therefore, is at least a secondcycle sediment, and its sand mineral assemblage (both 

light and heavy) is more mature than that of the underlying Beaverdam.

The clay minerals are unusual in comparison with the 

others discussed thus far in this paper because of a small 

variation in a vertical profile. The clay mineral 

assemblage is also unusual, in view of the late Wisconsinan age of the deposit, because of its relative compositional maturity (moderate percentage of gibbsite and no 

illite-smectite). The percentage of gibbsite in the Parsonsburg is similar to that found in the upper beds of the 

Beaverdam at the Houston, Del, site (Harr. 5) but not 

found in Quaternary sediment at the Worton Point or 

Whaleysville sites, for example. It seems likely that 

most of the Parsonsburg gibbsite is detrital, similar to 

that found in the base of the Ber. 2 sample (fig. 19). 

Whereas the gibbsite at Berlin was derived from the 

Beaverdam in an aqueous environment, the gibbsite in 

the Parsonsburg probably was introduced as loess. The 

gibbsite-bearing clay lamellae common in the Parsonsburg probably are loess translocated through this 

dominantly sandy deposit by illuviation.

SUMMARY OF WEATHERING EFFECTS BETWEEN 

CHESAPEAKE AND DELAWARE BAYS

In this general region, six sites ranging in age from 

late Pleistocene to late Miocene were examined. A variety of formations were sampled, some from the surface 

down and others only at depth. Some sections contained 

more than one formation in the vertical sequence.

The clay mineral assemblages in the formations seem 

to follow a normal sequence in most places, the older formations having the more mature assemblages. At Betterton, for example, the Pensauken Formation (upper 

Miocene) has a profile characterized by aluminous 

silicates (kaolinite, halloysite, and vermiculite) and, to a 

lesser degree, by aluminous oxides (gibbsite). Illitesmectite is notably absent, even 18 m below the surface. 

In contrast, at Worton Point, the upper Pleistocene beds 

have a much more diverse assemblage consisting of vermiculite, chlorite, illite, and only small amounts of 

kaolinite. Even smaller amounts of gibbsite are possibly 

present at the surface. The Worton Point clay 

assemblage is much less mature than the Pensauken 

clay assemblage but does show some degree of weathering.

The light and heavy sand minerals in those units 

thought to have relatively in-place authigenic clay 

mineral assemblages follow the same trend toward 

mineralogic maturity from the base to the top of the 

unit. At Betterton, feldspar declines upward through 

the section, and the ZTR assemblage increases upward 

in the Miocene Pensauken Formation. At Worton Point 

in the Pleistocene Kent Island beds, the feldspar 

decreases from the base to top, but the heavy minerals 

show no significant change in the same interval. Apparently, the geochemical conditions necessary to break 

down the feldspars did not affect the heavy minerals in 

any significant manner during this time interval.

The Beaverdam (Harr. 5) and Omar (Wh. 1A) sites 

represent sections in which the upper original
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F33

weathered surface was either stripped away or was not 

sampled. In the upper Pleistocene Omar Formation, the 

clay mineral assemblage is unweathered, but the upper 

3.7 m was not sampled. However, any weathering effects in this upper 3.7-m section obviously do not extend 

to a depth as great as that of subaerial oxidation in the 

Beaverdam at Houston, Del. At the Houston site, the 

upper Pliocene Beaverdam is overlain by a Pleistocene 

quartz sand and, therefore, has been stripped 

postdepositionally. The Beaverdam, nonetheless, is 

weathered throughout to a significant degree (the 

presence of gibbsite throughout indicates an intensive 

weathering history before the deposition of the quartz 

sand). Additionally, the fact that the underlying Pensauken was bevelled before Beaverdam deposition suggests a similar intensive weathering history before 

emplacement of the Beaverdam. The light and heavy 

sand minerals seem to follow the same weathering pattern noted in the Worton Point and Betterton beds.

Two of the sampled sites have clay mineral 

assemblages that are unusual relative to their age. 

Abundant gibbsite is the only clay mineral in the base of 

the Ironshire Formation, and its concentration decreases upward to the surface. The distribution of this 

mature weathering mineral suggests that it was derived 

from the reworking of the underlying Beaverdam Sand 

during the transgression associated with the Ironshire 

Formation. A similar case can be made for the presence 

of gibbsite in the Parsonsburg Sand (a 30,000-year-old 

deposit). This unit is, in large part, a dune deposit that, 

for the most part, overlies deeply weathered (gibbsitebearing) surfaces. The presence of gibbsite (as an 

aerosol product) in such young deposits is attributed to 

wind action. These two sites and their unusual clay 

mineral assemblages indicate that clay mineral maturity 

should be used cautiously as a guide in determining the 

age of a deposit.

The effects of weathering deduced from the dissolution of feldspar could be determined only in the Ironshire. In this unit, there is a general decrease in 

plagioclase and, to a lesser degree, in K-feldspar from 

the base to the top. Apparently, the weathering shown 

by the clay mineral assemblage at the top was sufficient 

to partially remove some of the feldspar. No such relationship is evident in the Parsonsburg Sand, possibly 

because of the youthfulness of its beds. The heavy 

minerals in both these units seem little affected by the 

intensity of the subaerial oxidation to which both have 

been subjected.

NORTHEAST OF DELAWARE BAY

Three sites were sampled from this general region, 

two containing materials thought to be Quaternary and 

one containing material thought to be late Miocene.

HAMMONTON, N.J.

BRIDGETON FORMATION, UPPER MIOCENE, 

LOCALITY NO. NEWTONSVILLE 1

Much of southern New Jersey and part of the SalemAmboy valley along the inner edge of the New Jersey 

Coastal Plain are'mantled by gravelly deposits called the 

Bridgeton Formation (Owens and Minard, 1979). This 

gravelly sand varies in thickness from area to area but 

may be as much as 30 m thick. All exposures of this formation are weathered to some degree. Not uncommonly, the upper beds are deep red, massive, and very clayey 

and typically have a thick B horizon.

One site was sampled in Hammonton, N.J.; figure 27 

is a columnar section showing the geology. The sand 

beneath the massive B horizon is cross-stratified. 

Platelets centered by iron oxide are common in some of 

the sand; all the sand beds are stained by iron oxides. 

Locally small, roughly circular black masses are scattered throughout the sand below the B horizon.

SAND MINERALOGY

Light minerals.-Most of the Bridgeton Formation 

throughout the outcrop belt is sand. The sand grains, 

particularly quartz, are subangular to subrounded. The 

feldspar grains, which are abundant, are more angular 

than the quartz grains, and all are coated by a dull white 

film. Mica, mostly muscovite, is present locally, especially southwest of Philadelphia, Pa. Glauconite is a common sand constituent in the Bridgeton between Amboy 

and Camden, N.J.

The light-mineral distribution at the Hammonton site 

is shown in figure 47. The lowest sample, taken 5.4 m (18 

ft) below the surface, is from the Cohansey Sand of probable early to middle Miocene age. This unit is typically 

an orthoquartzite (Owens and Sohl, 1969). In the basal 

Bridgeton samples, there is a marked increase in 

feldspar and rock fragments. This section, in fact, illustrates one of the easier methods for distinguishing 

between the Cohansey Sand and the Bridgeton Formation. No plagioclase was observed in the Bridgeton in 

this sample or in any of the southern New Jersey 

samples from this formation. Plagioclase, however, is 

common in samples from this formation near New York, 

N.Y. Feldspar shows a general decline from the base to 

the top in figure 47.

The high concentrations of feldspar are characteristic 

of the Bridgeton throughout its outcrop. The composition of this unit varies from a subarkose to an arkose 

and, in this report, is similar to the samples of the Pensauken, Beaverdam, and Potomac discussed earlier.

Heavy minerals.- Heavy minerals in the Bridgeton, 

for the most part, account for less than 0.5 percent of 

the sand fraction. The distribution of these minerals is
F34 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

DEPTH BELOW 

SURFACE, 

IN FEET 

(METERS)

-i— ft —— , ————— = ———— r-. ————————— , ~

OHANSEY 

SAND i

(0)

^

I

»

:

L

10 — 

5 (3.0)

LI

3

3 C-» 

i

9ft

g?feg|

:^'^v>.'-'^::\t::

^: *:M^-:<&

i I

Massive dark-reddish-brown (10 YR 3/4), 

very clayey, very gravelly sand

Sand, crossbedded, medium to coarse 

grained, very feldspathic, very light gray 

(N 8) to very pale orange (10 YR 6/6) 

stained iron red by iron oxides

-Gravel to 3 inches (7.6 cm)

Very light gray (N 6) crossbedded sand, 

abundant dark opaque heavy minerals

EXPLANATION 

Sand

Crossbedded 

sand

Clay 

Gravel

(6.1)

FIGURE 27.-Columnar section showing the geology in a borrow pit at Hammonton, N.J., 3 km (1.9 mi) northeast of 

Folsom, N.J., in the Newtonsville 7.5-minute quadrangle. Locality no. Newtonsville 1. Most of the exposure is the 

Bridgeton Formation. The Cohansey Sand (Miocene) is locally exposed in the base of the pit. Arrows indicate sample 

locations in profile. Surface elevation is 36.5 m (120 ft) above sea level.

remarkably uniform throughout the outcrop. In comparison with the relatively immature light-mineral 

assemblage, the heavy minerals are strikingly more 

mature (fig. 5J). The ZTR assemblage is the major 

group, SSK being the next most abundant. The more 

labile HE GAT mineral group is relatively unimportant 

throughout.

In the Hammonton section, the more stable ZTR 

minerals increase from the base to the top, and the SSK 

minerals decrease proportionally. The trend evident in 

the light minerals, therefore, exists here as well; that is, 

the stable constituents are more abundant in the intensely weathered upper beds.

CLAY-SILT MINERALOGY

The clay minerals in the Bridgeton perhaps illustrate 

best the effects of prolonged leaching. The mineralogy 

of this fine fraction is shown in figure 28. Vermiculite 

and gibbsite increase from the base to the top in this profile. Kaolinite + halloysite decreases somewhat, as does 

illite. The widespread occurrence of gibbsite as a major 

clay-sized phase characterizes the Bridgeton throughout 

its outcrop more than any other formation sampled in 

our study. A few samples of the silt fraction also show

that gibbsite is even more abundant in this size range 

than figure 28 shows. The iron oxides in the Bridgeton 

also deserve some mention. Goethite occurs as a major 

iron oxide mineral in many of the X-ray traces of the 

Bridgeton Formation. The particular iron oxide phase 

also is accompanied locally by significant concentrations 

of hematite not shown in figure 28. The presence of 

hematite in significant concentrations in the soil zone 

appears to be unique to the Bridgeton.

Figure 29 is a set of a TEM micrographs showing the 

morphology of the clays in the Bridgeton and the 

Cohansey. The presence of halloysite in the Cohansey is 

anomalous because this unit is an orthoquartzite (no 

feldspar). Apparently, the halloysite migrated 

downward from the base to the Bridgeton, where 

halloysite is abundant. Upward through the section, 

halloysite tubes give way to more amorphous forms, 

which, according to the X-ray results, are mainly gibbsite and vermiculite. The bulk of the sample shown in 

figure 29A consists of anhedral plates. Some halloysite 

tubes persist into this level.

SEM micrographs of the same samples (fig. 30) show 

the minerals in three dimensions. The tubular nature of 

the halloysite is particularly striking in this series of 

photographs (figs. 3QA, B). .
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F35

485

3.57

14.5 3.345

V I K,H GO

FIGURE 28.-X-ray traces of the clay-silt fraction in the Bridgeton 

Formation at Hammonton, N.J. (locality no. Newtonsville 1). Gibbsite (G) and vermiculite (V) increase in abundance from base to top. 

Kaolinite (K) decreases in the same interval. I is illite, K,H, is 

kaolinite (+halloysite), GO is goethite, and Q is quartz. The clay 

mineral assemblage is mature, the most mature, in fact, of any 

discussed in this report. Measurements of peaks in the X-ray traces 

are in angstroms. Depths of samples are given in meters.

INTERPRETATION

For a long time, the Bridgeton was considered to be 

Pleistocene in age. The deeply weathered nature of this 

deposit, taken in conjunction with the reported presence 

of gibbsite, led Owens and Minard (1975) to postulate a 

late Tertiary age (Miocene and Pliocene?) for this unit. 

Mapping in the southern Delmarva Peninsula later 

showed that the Pensauken (which is unconformable on 

the Bridgeton) was late Miocene in age (Owens and Denny, 1979). It was then apparent that the Bridgeton was 

pre-Pleistocene, in fact, pre-Pliocene. The mature clay 

mineralogy and the thick B horizon in this unit, 

therefore, are readily understandable. The assemblage 

gibbsite-goethite-hematite-halloysite, the alteration 

toward iron and aluminum oxides, and the degradation

of kaolinite to halloysite all suggest leaching over a long 

period of time. The development of dioctahedral vermiculite, a complex ferroaluminum, does not follow this 

leaching (that is, the stripping of silica from basic sheet 

or chain crystal structures). The mineral, in effect, increases in abundance toward the surface, a situation 

noted in most other profiles.

When the other, very feldspathic formations are compared, the weathering of the Bridgeton is seen to resemble that of the Beaverdam and the Pensauken. The 

Bridgeton has a more mature clay mineral assemblage, 

which we interpret to indicate a longer period of 

subaerial oxidation. The weathering of the Bridgeton 

certainly is much more mature than that of the equally 

feldspathic Potomac Formation, this maturity again 

pointing to the deeper weathering of the pre-Quaternary 

feldspathic deposits east of Chesapeake Bay.

The sand minerals in the Bridgeton also show the effects of interstratal solution. In both the light- and the 

heavy-mineral fractions, concentrations of the more 

weatherable minerals decrease from the base to the top 

of the section. Thus, both the clay and the sand minerals 

exhibit the effects of prolonged leaching in a thick vertical section through this unit.

BERNARDSVILLE, N.J. 

PLEISTOCENE, ILLINOIAN(?), LOCALITY NO. BERN. 1

Scattered bodies of glacial deposits south of the 

Wisconsinan terminal moraine in New Jersey appear to 

be more weathered than the Wisconsinan deposits 

(Minard and Rhodehamel, 1969). Nearly everyone who 

has discussed these deposits considers them to be preWisconsinan and most commonly Illinoian. All that can 

be determined, however, with any degree of assurance is 

that they are pre-Wisconsinan in age.

Overall, these deposits are very gravelly in the upper 

part where the samples were collected. However, the 

surface of this deposit has high relief, and the sampled 

section was not from the highest surface.

All the exposed beds of the Bernardsville deposit have 

a general yellowish cast, unlike the typical light to 

medium gray of the Wisconsinan deposits or the red of 

the Miocene deposists. The feldspathic gravel in this unit 

was saprolitized throughout the 6 m (20 ft) of section 

that we studied. Figure 31 is a columnar section of the 

lithology at the Bernardsville site between Basking 

Ridge and Bernardsville, N.J.

SAND MINERALOGY

Light minerals.-The light minerals in this unit are 

mostly rock fragments and smaller amounts of 

K-feldspar and plagioclase (fig. 4J). Free quartz grains 

are notably few in all the samples studied. The fact that
F36 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

V V

^->/

0.9—4.5 meters—Bridgeton Formation 

5.4 meters—Cohansey Sand

FIGURE 29.-Transmission electron microscope micrographs of the 

clay fraction of sand of the Bridgeton Formation (A-D) and the 

Cohansey Sand (E) at Hammonton, N. J. (locality no. Newtonsville 1), 

showing the morphology of the minerals. Abundant well-developed 

halloysite tubes in the base of the Bridgeton (D) gradually decrease 

upward through the section (C and E). The presence of small 

amounts of halloysite in the Cohansey sample (E) is probably the 

result of downward migration from the overlying Bridgeton. Depths 

of samples are as follows: A, 0.9 m; B, 1.8 m; C, 3.6 m; D, 4.9 m; E, 

5.4 m.
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F37

FIGURE 30. - Scanning electron microscope micrographs of the clay fraction of the Bridgeton sand at Hammonton, N. J. (locality no. Newtonsville

l).The halloysite tube at H is hollow; platy vermiculite is present in both A and B.

the rock fragments are typically micaceous or 

feldspathic suggests derivation from metamorphic or igneous rocks. The very high rock-fragment content in 

this unit is somewhat similar to that in the Worton Point 

beds near the mouth of the Susquehanna River. The high 

percentage of rock fragments plus the feldspar indicates 

that this sand is a high-rank graywacke in composition. 

A binocular examination of the sand grains reveals that 

they are subangular to angular, and they are thus interpreted as being a first-cycle sediment. The light 

minerals show very little variation from the top to the 

bottom of the exposed section; hence, no intensive 

weathering effects are indicated.

Heavy minerals.-The heavy-mineral assemblages in 

this unit have nearly equal amounts of the HEGAT and 

ZTR groups. Minerals of the SSK group are present in 

only small amounts (fig. 5X). In the HEGAT group, 

hornblende is especially abundant, and epidote is also 

very common. Zircon dominates the ZTR group. The 

heavy-mineral assemblage overall is immature.

The heavy-mineral assemblage suggests derivation 

from a largely granitic terrane. The low amounts of 

staurolite, sillimanite, and kyanite show the small contribution from metamorphic rocks. The heavy minerals 

show very little variation through the section sampled.

CLAY-SILT MINERALOGY

The clay minerals in the sand fraction are shown in 

figure 32. Kaolinite ( +halloysite) and illite are the major

minerals and are more or less present in the same abundance throughout the section. The kaolinite 

(+halloysite) appears to be poorly ordered. Vermiculite 

is not present in the lowest sample (6 m) but is present at 

3 m and is very abundant in the upper samples (0.9 m). 

These three minerals are the only ones present in the 

X-ray traces.

TEM plates were prepared for the three samples to 

examine the morphology of the clay minerals. Figure 33, 

from the basal sample, shows that the bulk of the sample 

is transparent, thin, anhedral plates. Small, incipient^?) 

halloysite tubes are also abundant. There is no apparent 

change in the morphology of the clay minerals from the 

base to the top of the unit.

INTERPRETATION

Weathering in the pre-Wisconsinan deposits in New 

Jersey seems intermediate. No pronounced changes in 

the light- or heavy-mineral assemblages were observed. 

The clay minerals, however, show some evidence of surficial subaerial oxidation, notably the development of 

vermiculite in the upper beds. The kaolinite 

( +halloysite) appears little affected throughout the profile; that is, no distinct upward change takes place. In 

fact, although the X-ray traces indicate that the 

aluminum silicates of the kaolinite family are disordered 

(poorly crystalline), halloysite tubes are few. The persistence of disordering in the kaolinite formation from 

the base to the top of the unit suggests that this mineral
F38 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

DEPTH BELOW 

SURFACE, 

IN FEET 

(METERS)

o-

(0)

(3.

- 20_ 

'(6.1)

Dusky yellow (5 Y 6/4) interbedded 

gravelly sands and crossbedded sands. 

Little color change throughout. Gravel 

assemblage heterogeneous (quartz, 

quartzite, red sandstone, and red shale). 

Crystalline rocks, mostly granitic, common. Crystalline gravel mostly saprolitized EXPLANATION

! Sand

Clay 

Gravel

Crossbedded 

sand

FIGURE 31.-Columnar section showing the geology in a roadcut near Bernardsville, N.J., on the northern side of 

Interstate 287 between Bernardsville and Basking Ridge, N.J., in the Bernardsville 7.5-minute quadrangle. Locality no. 

Bern. 1. Arrows indicate sample locations in profile. Surface elevation is 121 m (400 ft) above sea level.

is detrital rather than diagenetic. Whatever the case, 

the pre-Wisconsinan (Illinoian?) beds sampled in this 

area are not intensely altered. If these beds are mostly 

intact, then, in this region, the profile of the preWisconsinan drift (which is about 200,000 years old) is 

considerably different from that of the pre-Sangamon 

beds in the Delmarva Peninsula. Novak and others 

(1971), discussing beds similar in appearance and interpreted to be Illinoian drift elsewhere in New Jersey 

(Rockport Soil Series), reported a mineralogy somewhat 

different from ours (more chlorite and no halloysite, for 

example). They did, however, report that vermiculite 

and kaolinite are major minerals in samples taken very 

near the surface; thus, an overall similarity exists between this mineralogy and that at Bernardsville.

"VAN SCIVER LAKE BEDS" 

SANGAMON(?), LOCALITY NO. TW 15A

A thick deltalike mass of unconsolidated coarse 

gravelly sands and sandy gravel occurs where the 

Delaware River leaves the Piedmont physiographic 

province and enters the Coastal Plain at Trenton, N. J. 

Parts of these beds are included with the "Van Sciver

Lake beds" by Owens and Minard (1979). These beds lie 

beneath a broad, relatively undissected terrace that has 

surface elevations near 6.1 m (20 ft) above sea level. Extensive mining of the terrace for its sand and gravel content has provided abundant fresh exposures of this unit.

A profile showing a typical lithology in this unit is 

presented in figure 34. As shown, this unit consists of 

light- to medium-gray, horizontally bedded gravels and 

thinner crossbedded sands. No evidence of iron oxide 

staining was observed in these beds. The gravel in this 

unit is heterogeneous, containing quartz and many rock 

types: quartzite, granite, gneiss, schist, and, less commonly, limestone. A coating of calcium carbonate on 

some of the gravels suggests at least partial solution of 

some of the limestone clasts. Another feature of this formation is the abundant boulders, some as much as 1.5 m 

in maximum dimensions. In this respect, this unit 

resembles the beds near the mouth of the Susquehanna 

River in Chesapeake Bay.

The formation is considered to be Sangamon (about 

60,000 to 80,000 years) in age, probably the fluviatile 

equivalent, at least in part, of the Ironshire Formation 

at the coast and the lower part of the Worton Point beds 

in the upper Chesapeake Bay region.
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F39

14.0

3.32

6.1

'FIGURE 32.-X-ray traces of three samples collected from a roadcut near Bernardsville, N.J. (locality no. Bern. 1). The most significant weathering effect seen in this profile is the increase in dioctahedral vermiculite (V) (14 A) from base to top. I is illite, and K,H is 

kaolinite (+halloysite). Measurements of peaks in the X-ray traces 

are in angstroms. Depths of samples are given in meters.

SAND MINERALOGY

Light minerals.-The light minerals in this unit are 

mostly rock fragments (mostly granitic gneiss) and 

quartz (fig. 4K). Two feldspars (K-feldspar and 

plagioclase) are present, but they comprise only a small 

percentage of the light-mineral fraction. Compositionally, the "Van Sciver Lake beds" are a high-grade 

graywacke. There is no marked increase or decrease in 

the various light minerals of this assemblage in a vertical section.

Heavy minerals.-The heavy-mineral assemblages 

have nearly equal proportions of ZTR and HE GAT 

minerals (fig. 5L). The SSK and OTHER minerals are 

only minor constituents. In the HEGAT assemblage, 

hornblende is very abundant, and hypersthene is present in the OTHER group. The heavy-mineral assemblage is this unit is immature and shows little variation 

throughout the studied profile.

CLAY-SILT MINERALOGY

The clay minerals in this unit are shown in figure QF. 

Basically, the only minerals present in varying abundance are chlorite, illite, and vermiculite. Illite-smectite 

and kaolinite were not found in the samples analyzed. 

Vermiculite is present throughout the profile. Chlorite 

increases in concentration toward the top. In the upper 

beds, chlorite is probably interlayered to some degree

FIGURE 33.-Transmission electron microscope micrograph of the 

clay-silt fraction in the sand of the "older drift" at Bernardsville, N.J. 

(locality no. Bern. 1). The elongate, incomplete halloysite tubes are 

believed by some investigators to be intermediate in the transformation of halloysite from allophane. The broadened peak in the X-ray 

trace at the characteristic spacing for halloysite is also indicative of 

poor crystallinity.

with vermiculite. Illite shows a general decrease from 

the base to the top.

X-ray patterns showing these trends are given in 

figure 35. The decrease in illite, especially in the (001) 

and (002) reflections, is especially pronounced. Vermiculite, as evidenced by the 14-9 peak, shows the 

upward increase in the concentration of this mineral.

The presence of chlorite and the absence of the more 

mature aluminous silicates (kaolinite, for example) indicate that this assemblage is very immature.

Figure 36 is an SEM micrograph of the clay minerals. 

These samples were studied by electron microscope 

because they presumably represent relatively unweathered clays introduced into the Coastal Plain from 

the source lands. The anhedral clay morphologies in this 

unit contrast markedly with the clay forms in the Bernardsville sample (fig. 33) and especially with those in 

the Bridgeton sample (fig. 30). Essentially, the dominant form in all the samples is thin anhedral plates. The 

SEM micrograph emphasizes the platy or tabular nature 

of the minerals. Because there is no evidence of 

halloysite-type minerals in these samples, the results obtained by the X ray are confirmed.
F40 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

T

CO 

Q 

LU 

CD

LU

cc

LU

o

CO

I

J_

DEPTH BELOW 

SURFACE, 

IN FEET 

(METERS) °n ————— ^

B -+

D -> 

E ->

10 F-> ———— —————— -

„ . - J

•'.•„• -V;°'%'.;;0;:

y^^jio^'-^

"«°."« ? *-".*•%'*•*

(3.0)

Sand, very fine- to fine-grained, massive

Interbedded horizontal gravel layers and 

crossbedded sand. Medium gray, loose, 

poorly sorted

EXPLANATION 

Sand

Crossbedded 

sand

Gravel

FIGURE 34.-Columnar section showing the geology in the pits at Van Sciver Lake, Pa. Pit is 3 km 

(1.9 mi) south of Morrisville, Pa., in the Trenton West 7.5-minute quadrangle of New Jersey and Pennsylvania. Locality no. TW 15A. Arrows indicate sample locations in profile. Surface elevation is 6 m (20 ft) 

above sea level.

INTERPRETATION

In outcrop, the beds comprising this unit do not appear to have any obvious weathering except for the 

redeposition of calcite on some of the siliceous clasts. 

The heavy- and light-mineral assemblages show no 

evidence of alteration through the sampled section. The 

clay minerals, however, change, as the increase in vermiculite and decrease in illite upward through the profile show. Apparently, illite in this profile is transformed 

into vermiculite. It is difficult to determine what is happening to the chlorite in this section, but the suggestion 

is that part of the vermiculite is a vermiculite-chlorite 

mixed-layer clay.

Novak and others (1971) studied the clay mineralogy 

in the B horizon in Wisconsinan drift in New Jersey 

(Nassau Soil Series). Their clay mineral assemblage is a 

mica (illite?)-kaolinite-chlorite mixed-layer clay and vermiculite, in that order of abundance. Except for the 

presence of kaolinite, a concentration of vermiculite 

probably greater than that in our samples, and a lesser 

abundance of illite, the two assemblages are somewhat 

similar. The weathering profiles of the "Van Sciver Lake 

beds" and those of their age equivalent at the coast 

(Ironshire Formation) appear to be compatible again, 

except for the development of kaolinite in the Ironshire 

Formation. Another point to be mentioned regarding 

the clay minerals is the persistence of vermiculite 

throughout the section. The distribution of this mineral 

in these beds is similar to its distribution in the Worton 

Point beds. Essentially, the vermiculite in the "Van 

Sciver Lake beds" suggests that a high percentage of 

this mineral is detrital. Like that at Worton Point in the 

Chesapeake region, the high concentration of vermiculite appears to be a function of proximity to rocks of 

the Piedmont province.

SUMMARY OF WEATHERING EFFECTS NORTHEAST OF 

DELAWARE BAY

The three sites studied northeast of Delaware Bay include two units that are relatively young (Pleistocene) 

and close to each other in age (the "Van Sciver Lake 

beds" and the "older drift" at Bernardsville) and one unit 

(Bridgeton Formation) that is much older (Miocene). All 

seem to follow what is considered a normal weathering 

pattern relative to the age of the deposits.

The Bridgeton Formation of southern New Jersey has 

the most mature weathering profile of any unit studied. 

We would interpret this profile as indicating that the 

Bridgeton is the oldest sampled unit in which the 

original surface is still relatively intact.

The clay mineral assemblage in this unit is characterized by the increase of the supermature weathering 

minerals from the base of the section to the top. Halloysite-endellite and vermiculite are also main minerals in 

the upper Bridgeton beds. Feldspar (K-feldspar) decreases from the lower part of the formation to the upper part; in the heavy minerals, the SSK minerals show 

a decline, and the more stable ZTR minerals increase upward through the section. Overall, the Bridgeton would 

be interpreted as being intensely weathered.

The "older drift" beds at Bernardsville (middle Pleistocene?) are much less weathered than the beds at the 

Bridgeton. The clay minerals in the unit are characterized by halloysite, vermiculite, and illite. The extensive 

halloysite suggests an intermediate intensity of weathering. The heavy and light minerals in this unit show few 

weathering effects under this type of leaching regime.

The youngest unit sampled (the "Van Sciver Lake 

beds," probably late Pleistocene, Sangamon, in age) i,:> 

less weathered than other units sampled northeast of 

Delaware Bay. The clay minerals are characterized by
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F41

14.2

3.325

V,C I K,C

FIGURE 35.-X-ray traces of untreated samples in the "Van Sciver 

Lake beds" (locality no. TW 15A) showing the upward increase in 

vermiculite (V) concentration. A decrease in the illite (I) content is 

also apparent. K,C is kaolinite ( + chlorite). This assemblage suggests 

that vermiculite is detrital but that subsequent weathering increases 

the amount of this mineral in the upper beds. Measurements of peaks 

in the X-ray traces are in angstroms. Depths of samples are given in 

meters.

vermiculite, chlorite, and illite. Much of the vermiculite 

at this locality is detrital but generally increases toward 

the surface. This increase in vermiculite concentration 

upward in the section is thought to be the best indicator 

of weathering in this assemblage. No pronounced trend 

toward the more stable species in the heavy- or lightmineral fractions in sand was observed.

Thus, in this general region, the weathering mineral 

assemblages are considered normal relative to the age of 

the deposit on which they were formed.

-s

FIGURE 36.-Transmission electron microscope micrograph of the 

clay fraction in sand of the "Van Sciver Lake beds" in Pennsylvania 

(locality no. TW 15A). Vermiculite, chlorite, and illite are difficult to 

resolve in electron micrographs because of their intricate admixture 

and their lack of truly characteristic morphology. In addition to 

platiness, some vermiculite may still show hexagonal edges; chlorite 

is platy and irregular in outline; extremely fine and platy particles 

are interpreted as illite. The presence of all three minerals in varying 

amounts is confirmed by X-ray identification. Magnification 

x 15,000.

CONCLUSIONS

The purpose of this study was to determine whether 

the depth and intensity of subaerial oxidation in welldrained sand could be used to estimate the age of the 

surficial beds in the Middle Atlantic States. In all, 12 

sites were sampled, and the sand and clay mineralogy of 

the surficial units present at each locality was studied in 

the laboratory.

We interpret the results of this study to suggest that 

there are three general categories of mineral alteration 

in the surficial beds of the Middle Atlantic States: (1) 

those deposits that have a normal weathering profile 

relative to their age, (2) those deposits that have an abnormally immature profile relative to their age, and (3) 

those deposits that have an abnormally mature profile 

relative to their age.
F42 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

Deposits that have normal mineral alteration relative 

to their age contain the following mineral assemblages:

late Quaternary: 

(60,000-80,000 years)

Worton Point beds 

"Van Sciver Lake beds" 

Ironshire Formation

chlorite + illite—vermiculite 

Clay- feldspar — illite-smectite —kaolinite — 

sized (halloysite)

material ferromagnesian minerals —lepidocrocite— 

goethite

immature heavy-mineral suite—no proSand- nounced change

sized immature (feldspathic) light-mineral suite-* 

material some weathering of feldspar grains, particularly plagioclase, in near-surface beds

In this assemblage, the most pronounced effect of subaerial oxidation in the clay-sized material is the development of vermiculite and hydrated iron oxides (some 

lepidocrocite but mostly goethite), especially in the beds 

nearest the surface. Kaolinite is present but appears less 

stable than vermiculite or goethite in this uppermost 

zone. An objection to using vermiculite as an in-place 

weathering indicator is the possibility that this mineral 

has been inherited from the Piedmont crystalline rocks 

(for example, in the Worton Point beds and the "Van 

Sciver Lake beds").

Of the sand-sized material, feldspar (plagioclase particularly) shows the most obvious weathering effects. 

Concentrations of this mineral typically are reduced in 

the beds nearest the surface in most units of late Quaternary age. The heavy minerals show far fewer weathering effects than the light minerals do. In general, in the 

profiles, the heavy minerals show little variation in type 

or concentration. In Jackson's (1965) model, these sediments have been subjected to mild desilication under low 

weathering intensity.

middle(?) Pleistocene 

(about 200,000 

years or 

perhaps older)

"Jerseyan drift," 

Bernardsville 

site

The clay mineral transformation in this unit is as follows:

illite—vermiculite

feldspar — illite-smectite — kaolinite — halloysite

ferromagnesian minerals—goethite

In the sand-sized minerals, the percentages of feldspar 

do not decrease throughout the profile, but the feldspar 

grains in the shallower beds are much more weathered

than those at the base of the section. The heavy minerals 

show few effects of subaerial oxidation throughout the 

profile studied. In addition to the formation of vermiculite in the near surface, halloysite appears to have 

formed from kaolinite in the clay mineral fraction. 

Halloysite in these glacial sediments may have been derived from the source rocks, but the weathered nature of 

the feldspathic crystalline gravel (weathering presumably occurred postdepositionally) suggests that the 

halloysite is also an in-place weathering product. If this 

is true, then the weathering in these beds is more advanced than that in the upper Pleistocene deposits. The 

transformation of kaolinite to halloysite suggests such a 

possibility.

In Jackson's (1965) model, the weathering in the middle Pleistocene beds would represent intermediate desilication under intermediate weathering intensity.

late Tertiary: Beaverdam Sand (late Pliocene?)

Pensauken Formation (late Miocene) 

Bridgeton Formation (late Miocene)

The following clay-mineral assemblages occur in these 

beds:

illite—vermiculite endellite 

feldspar—illite- smectite(?) — kaolinite ^ halloysite—

gibbsite 

ferromagnesian minerals—lepidocrocite—goethite—

hematite

The following sand-mineral assemblages occur in these 

beds:

immature heavy-mineral assemblages—more mature 

assemblages (higher concentrations of ZTR)

immature light-mineral assemblages (two feldspars)— 

more mature (feldspar mainly K-feldspar; percentage reduced near surface)

Beds of this age probably span an interval of between 

2 and 8 million years. The near-surface beds in the oldest 

upper Tertiary deposits (Bridgeton Formation) essentially are characterized by the vermiculite-gibbsitehematite assemblage; gibbsite and hematite are present 

in much smaller amounts in the younger Pensauken and 

Beaverdam. Halloysite (+endellite locally) in these upper Tertiary beds is well developed at depths greater 

than those in the middle Pleistocene(?) beds. A preQuaternary age for such mature clay mineral 

assemblages in Coastal Plain sediments elsewhere was 

observed in deposits in the Southeastern United States 

(Clarke, 1971).
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F43

The heavy and light minerals show considerable variation from zones of less intense weathering to those of 

more intense weathering. Plagioclase, hornblende, and 

hypersthene are selectively depleted upward through 

the section. In Jackson's (1965) model, these sediments 

would have been subjected to intensive desilication 

under high weathering intensity.

On the basis of the examples cited above, it would 

seem that the maturation of mineral alteration suites 

can be used as a guide to the age of what were originally 

fairly fresh sediments.

In the younger units (60,000 to 80,000 years old), the 

typical weathering mineral assemblage is characterized 

in the uppermost weathering profile by vermiculite and 

small amounts of gibbsite. Kaolinite tends to increase 

from the base of the profile to the middle and then to decrease upward. Illite decreases from the base to the top. 

No illite-smectite was found in the samples tested, so the 

effect that subaerial alteration had on this mineral during this time frame is conjectural. Most likely, illitesmectite follows the same pattern as illite. In general, 

the sand minerals show little change as the result of intrastratal solution except for a weathering rind on the 

feldspar grains.

The middle Pleistocene beds are characterized by the 

breakdown of feldspar, which produces large quantities 

of halloysite, kaolinite, and locally(?) moderate amounts 

of gibbsite. Vermiculite is again abundant in the upper 

zone of oxidation. Illite again decreases from the base to 

the top. The increase in gibbsite concentration and the 

abundance of halloysite are the significant differences 

between the 80,000- and the 200,000-year-old beds.

In the pre-Quaternary units, the trends established in 

the middle Pleistocene are accentuated. Gibbsite increases in both concentration and the depth at which it 

is found. Halloysite is formed to greater depths in these 

units than it is in the Quaternary beds. Vermiculite is 

still very common in the uppermost beds. The iron 

phases goethite and, to a lesser degree, hematite are 

more abundant and better crystallized in beds of this 

age.

Overall, therefore, the transformation from silicates 

to oxides seems to follow a systematic age trend. 

Specifically, the concentration and depth distribution of 

gibbsite appear to be good indicators of the relative age 

of a formation, particularly where the age spread between formations is long. Time, therefore, is an important element in the generation of mature weathering 

mineral assemblages.

The Coastal Plain deposits that have abnormally immature assemblages for their age all occur west of 

Chesapeake Bay: the Potomac Formation at the Hayfield site, the Yorktown Formation at the Bowling

Green site, and the Calvert and Aquia Formations at the 

Round Bay site.

The clay mineral assemblage in these units suggests 

the following reactions:

illite -* vermiculite

feldspar—illite-smectite—kaolinite

ferromagnesian minerals—lepidocrocite —> goethite

The sand minerals apparently are affected in the following manner:

mature heavy minerals—mature heavy minerals 

immature light minerals (two feldspars)-*

immature light minerals (two feldspars slightly

more weathered at the surface)

The clay mineral assemblages in all of these units are 

poorly crystalline. Vermiculite, which is so abundant in 

all the samples of late Pleistocene age taken nearest the 

surface, is less common in all of these deposits west of 

Chesapeake Bay. Other common alteration minerals 

such as goethite and kaolinite are also present in small 

amounts in these beds.

The heavy and light sand minerals show little alteration in a vertical section in these beds. The lack of thick 

alteration zones on these older beds (Pliocene to Lower 

Cretaceous), which lie at the surface at relatively high 

topographic elevations, suggests that the beds have 

been stripped in relatively recent time. Certainly, the 

deposits at the Hayfield site, where they are overlain by 

the "upland gravels" (Pliocene?), point to such an interpretation. If these beds were stripped after deposition of 

the "upland gravels," their "normal" alteration profile as 

outlined earlier points to a late Pliocene or perhaps an 

early Quaternary tectonic uplift and an associated 

period of stripping of the uppermost mantle of weathered beds.

It is apparent, therefore, that an understanding of 

local tectonics (and perhaps associated eustatic changes) 

is very important if the mineral alteration-age technique is applied areally. Additionally, this mineral alteration-age technique could be used as a tool in regional 

tectonic studies. From the data already presented, it 

would appear that uplift in the area of immature mineral 

alteration west of Chesapeake Bay has been greater 

than that in the areas of mature mineral alteration to 

the east or northeast in the Delmarva Peninsula and 

New Jersey.

The Coastal Plain deposits that have abnormally 

mature alteration zones for their age are best exemplified by the Parsonsburg Sand (Pittsville sample, late 

Wisconsinan Age, about 26,000 to 30,000 years B.P.)
F44 GEOLOGIC STUDIES IN EMERGED COASTAL PLAIN OF MIDDLE ATLANTIC STATES

(Sirkin and others, 1977). Deposits of this type form a 

thin but widespread veneer over much of the central 

Delmarva Peninsula. The clay mineral assemblage in 

these beds suggests the following relationships:

mica —• vermiculite

vermiculite—more ordered vermiculite

feldspar —• illite-smectite(?)—kaolinite —• halloysite—

gibbsite 

halloysite—gibbsite (less ordered) —• gibbsite (more

ordered) 

ferromagnesian minerals—goethite

The sand minerals indicate the following relationship:

relatively immature heavy-mineral assemblage —• no significant change

relatively immature light-mineral assemblage (feldspar) 

—no significant change

The presence of gibbsite + kaolinite + halloysite + 

goethite, a mature mineral assemblage for upper 

Wisconsinan deposits, seems anomalous if such minerals 

indicate that a given deposit is old (pre-Quaternary). As 

we have noted, however, some of the more diagnostic 

weathering minerals can be inherited from older units. 

For example, reworked gibbsite in the base of the Ironshire Formation (Ber. 2 sample) or vermiculite in the 

Worton Point beds and "the Van Sciver Lake beds" was 

apparently derived from saprolites formed on Piedmonttype rocks. The eolian origin of part of the Parsonsburg 

Sand, therefore, would require that the weathered 

minerals be introduced into this unit by the wind. Apparently, the source beds, on the basis of regional 

geology, have been the Beaverdam Sand, which the Parsonsburg Sand overlies. Upper weathered beds in this 

upper(?) Pliocene unit contain significant concentrations 

of gibbsite, halloysite, and goethite (Harr. 5 sample) and 

thus provide a nearby supply of these minerals to be 

eroded and transported by wind action.

In conclusion, we feel that the depth and intensity of 

subaerial oxidation have much promise as tools in determining the relative age of otherwise unfossiliferous, unconsolidated sediments in the Coastal Plain. It is important to note, however, that, if this technique is to be applied regionally, the depositional and tectonic history of 

deposits should be understood before the laboratory 

results are interpreted.

APPENDIX

Anna 1, Hayfield site. Annandale 7.5-minute quadrangle, Virginia, lat 38°4515" N., long 77°08'35" W. 

Pit adjacent to Telegraph Road (State Route 611) at

Hayfield, Va. Surface elevation about 66 m (220 ft) 

above sea level.

Bowling Green 1. Bowling Green 7.5-minute quadrangle, Virginia, lat 38°05'00" N., long 77°20'00" W. 

Roadcut on eastern side of country road, 1,500 m 

north of Bowling Green, Va. Surface elevation about 

60 m (200 ft) above sea level.

R.B. 51. Round Bay 7.5-minute quadrangle, Maryland, 

lat 39°02W N., long 76°32'00" W. Bluff on eastern 

side of Severn River just south of Arnold Point, 

1,350 m southwest of Maryland State Highway 2. 

Surface elevation 30 m (100 ft) above sea level.

Bet. 3. Betterton 7.5-minute quadrangle, Maryland, 

lat 39°22'32" N., long 76°05'00" W. Bluff along 

southern side of Sassafras River, 1,000 m west of 

Betterton, Md. Surface elevation of bluff about 27 m 

(90 ft) above sea level.

Harr. 5. Harrington 7.5-minute quadrangle, Delaware, 

lat 38°45'00" N., long 75°31'15" W. Pit on northern 

side of Murderkill River, 7,500 m northwest of 

Houston, Del. Surface elevation of pit about 12 m 

(40 ft) above sea level.

Wh. 1A. Whaleysville 7.5-minute quadrangle, MarylandDelaware, lat 38°2315" N., long. 75°16'05" W. 

Auger hole is at crossroads called Longridge, 2,000 

m east of Whaleysville, Md. Auger hole spudded in 

at about 11 m (36 ft) above sea level.

Ber. 2. Berlin 7.5-minute quadrangle, Maryland, lat 

38°19'10" N., long 75°12'00" W. Pit near Germantown, Md., 1,500 m east of U.S. 113. Surface elevation of pit about 11 m (35 ft) above sea level.

Hanesville 1. Hanesville 7.5-minute quadrangle, Maryland, lat 39°19'00" N., long 76°11'00" W. Bluff at 

Worton Point on eastern side of Chesapeake Bay, 

3,600 m northwest of Newtown, Md. Surface elevation about 12 m (39 ft) above sea level.

Pitt. 8. Pittsville 7.5-minute quadrangle, MarylandDelaware, lat 38°25'10" N., long 75°27'45" W. 

Shallow pit along western side of country road, 

5,100 m northwest of Pittsville, Md. Surface elevation of pit 15 m (75 ft) above sea level.

Newtonsville 1. Newtonsville 7.5-minute quadrangle, 

New Jersey, lat 39°37'18" N., long 74°49'10" W. 

Gravel pit between llth and 12th Streets in 

Hammonton, N. J. Surface elevation about 33 m (110 

ft) above sea level.

Bern. 1. Bernardsville 7.5-minute quadrangle, New 

Jersey, lat 40°33'45" N., long 74°3315" W. Roadcut 

on northwestern side of Interstate Highway 287 between Basking Ridge and Bernardsville, N.J. Surface elevation of cut about 128 m (420 ft) above sea 

level.

TW 15A. Trenton West 7.5-minute quadrangle, Pennsylvania-New Jersey, lat 40°10'00" N., long
SURFACE AND NEAR-SURFACE MINERALS IN SELECTED COASTAL PLAIN FORMATIONS F45

74°48'10" W. Gravel pit on eastern side of Van 

Sciver Lake adjacent to Ford Mill Road, 400 m 

northwest of Turkey Hill. Surface elevation 6 m (20 

ft) above sea level.

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