Geologic and Paleoecoogic

Studies o the

Nebraska Sand Hills

Geologic and Paleoecologic 

Studies of the 

Nebraska Sand Hills

Eolian Deposits in the Nebraska Sand Hills

By THOMAS S. AHLBRANDT and STEVEN G. FRYBERGER

Paleoecology of Nonmarine Mollusca from some 

Paleointerdune Deposits in the Nebraska Sand Hills

tfyJOHN H. HANLEY

Late Quaternary Vegetation History of the Central Great Plains 

and its Relationship to Eolian Processes in the Nebraska Sand Hills

By J. PLATT BRADBURY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1 1 2 0-A,B,C

From study of stratification and biota and 

interdune deposits, new information is obtained 

regarding the origin of the Nebraska Sand Hills

UNITEDSTATESGOVERNMENTPRINTINGOFFICE, WASHINGTON: 1980
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Geologic and paleoecologic studies of the Nebraska Sand Hills.

(Geological Survey Professional Paper 1120)

Bibliography: p. 35

1. Geology Nebraska Sand Hills region. 2. Paleoecology Nebraska Sand Hills region.

3. Sand-dunes-Nebraska-Sand Hills region. I. Ahlbrandt, Thomas S. II. Title. III. Series: United

States Geological Survey Professional Paper 1120. 

QE136.S27U54 1979 557.82'? 79-4127

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

Washington, D.C. 20402 

Stock Number 024-001-03290-2
CONTENTS

[Letters designate the chapters. "Index" follows Chapter C on page 37]

Page

(A) Eolian deposits in the Nebraska Sand Hills, by Thomas S. Ahlbrandt and Steven G.

Fryberger .................................................................. 1

(B) Paleoecology of nonmarine Mollusca from some paleointerdune deposits in the

Nebraska Sand Hills, by John H. Hanley...................................... 25

(C) Late Quaternary vegetation history of the central Great Plains and its relationship to

eolian processes in the Nebraska Sand Hills, by J. Platt Bradbury............... 29

ill

Eolian Deposits in the 

Nebraska Sand Hills

By THOMAS S. AHLBRANDT and STEVEN G. FRYBERGER

GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1120-A
CONTENTS

Abstract.........................................

Introduction .....................................

Distribution of the dune types .....................

Thickness of the eolian sand .......................

Past sand transport directions .....................

Relationship of past sand transport to present wind . Orientation of laminae within dunes ................

Sedimentary structures in dunes...................

Primary structures ...........................

Page

1

1

3

5

5

7

7

8

8

Sedimentary structures in dunes Continued 

Secondary structures ..................

Dissipation structures .................

Interdune deposits ........................

Degradations! processes in the Sand Hills ...

Sedimentary petrography ..................

Loess deposits ............................

Acknowledgments .........................

References cited...........................

13

13

15

19

19

21

23

23

ILLUSTRATIONS

Page

FIGURE 1. Index map of study localities in the Nebraska Sand Hills and loess hills........................................... 2

2. Mosaic of Landsat imagery of the snow-covered Nebraska Sand Hills during winter ............................... 3

3. Stratigraphic cross-sections through the Sand Hills ............................................................. 4

4. Sand roses and stereonet plots of past sand transport in the Sand Hills ........................................... 6

5. Graph of directional and energy properties of wind regimes ...................................................... 7

6. Stereonets and histograms of strike and dip data for barchan, transverse ridge, and blowout dunes ................. 8

7. Diagram of dune terminology ................................................................................. 9

8. Diagram of measured sections in en echelon barchan dunes at Merritt Reservoir................................... 10

9-12. Photographs of:

9. Large-scale structures in dunes of the Sand Hills ...................................................... 11

10. Sedimentary features in dune and interdune deposits .................................................. 12

11. Small-scale structures .............................................................................. 14

12. Secondary sedimentary structures ................................................................... 16

13. Photograph, histograms, and graphs showing dissipation structures ............................................. 17

14. Gas chromatogram of Nebraska Sand Hills interdune deposit.................................................... 17

15. Graphs and histograms of textural contrasts of eolian sand samples .............................................. 18

16. Graphs of textural parameters of 93 eolian sand samples ........................................................ 19

17. Photographs, graph, and histogram of sedimentary features in loess ............................................. 20

18. Well logs and lithologies of cross section showing loess deposits .................................................. 22

TABLE

TABLE 1. Organic analyses of interdune sample,

Page

15
GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE 

NEBRASKA SAND HILLS

EOLIAN DEPOSITS IN THE NEBRASKA SAND HILLS

By THOMAS S. AHLBRANDT and STEVEN G. FRYBERGER

ABSTRACT

The Nebraska Sand Hills are an inactive, late Quaternary, most 

probably Holocene, dune field (covering 57,000 km2 ) that have been 

eroded along streams and in blowouts, resulting in excellent lateral 

and vertical exposures of the stratification of dune and interdune 

sediments. This paper presents new data on the geometry, primary 

sedimentary structures, modification of sedimentary structures, 

direction of sand movement, and petrography of these eolian 

deposits.

Eolian deposits of the Sand Hills occur as relatively thin (9-24 m) 

"blanket" sands, composed of a complex of dune and discontinuous, 

diachronous interdune deposits unconformably overlying fluviolacustrine sediments. The internal stratification of large dunes in 

the Sand Hills (as high as 100 m), is similar to the internal stratification of smaller dunes of the same type in the Sand Hills, differing 

only in scale. Studies of laminae orientation in the Sand Hills indicate that transverse, barchan, and blowout dunes can be differentiated in rocks of eolian origin using both the mean dip angle of 

laminae and the mean angular deviation of dip direction.

A variety of secondary structures modify or replace primary 

eolian stratification in the Sand Hills, the more common of which 

are dissipation structures and bioturbation. Dissipation structures 

in the Sand Hills may develop when infiltrating water deposits clay 

adjacent to less permeable layers in the sand, or along the upper 

margins of frozen layers that form in the sands during winter.

Cross-bed measurements from dunes of the Nebraska 

Sand Hills necessitate a new interpretation of the past sand 

transport directions. The data from these measurements indicate a 

general northwest-to-southeast drift of sand, with a more southerly 

drift in the southeast part of the Sand Hills. A large area of small 

dunes «100 m high) described by Smith (1965) as linear or seif in 

the central part of the Sand Hills was interpreted by him on the 

basis of morphology only. We interpret these as transverse-ridge 

dunes that were generally moving to the south. Further, our 

measurements indicate that dunes in the western part of the Sand 

Hills did not develop in response to present-day effective wind 

regimes. The presence of "transverse" and en echelon barchan 

dunes in the Sand Hills corresponds to a developmental sequence of 

barchan to linear dunes proposed by Tsoar (1978).

Dune and interdune deposits of the Sand Hills are 

subfeldsarenites to feldsarenites. Sand grains are commonly coated 

with montmorillonitic clay, which may be the local source of the clay 

concentrated in the dissipation structures. Textures of sand 

samples taken from adjacent layers within a dune were as dissimilar 

as textures of samples taken from widely separated dunes. This

common occurrence indicates that textural data must be used 

carefully and in combination with other data to recognize ancient 

rocks of eolian origin.

Organic material derived from a variety of flora and fauna that inhabit the interdunes (chapters B and C) generated both oil and gas 

upon heating. Thus, interdune sediments may be an indigenous 

hydrocarbon source if buried in eolianites.

The twofold stratigraphy of loess and correlative dune deposits in 

the Sand Hills proposed by Reed and Dreeszen (1965) could not be 

confirmed by the present study. Rather, available data indicate that 

the dunes represent a single formation as suggested by Lugn (1935).

INTRODUCTION

The Nebraska Sand Hills are the largest dune field in 

the Western Hemisphere, occupying 57,000 km2 in central Nebraska (fig. 1). The dune field is now stabilized 

by vegetation, and erosion of the Sand Hills has produced many large outcrops that permit the detailed examination of the stratification of eolian deposits in this 

inland sand sea. In this paper, we present new data on 

the geometry, direction of sand transport, sedimentary 

structures, and modification of structures and 

petrography of these dunes and interdune deposits. 

These data should be useful to geologists in interpreting eolianites.

The Sand Hills are bordered by through-flowing 

streams the Niobrara River to the north and the 

North Platte and Platte Rivers to the south. Some 

perennial streams originate within the dune field (for 

example, the Snake River, Middle and North Loup 

Rivers, and Dismal River) (fig. 1). Precipitation in the 

Sand Hills ranges from 406 mm/yr on the western 

margin of the dune field to 610 mm/yr on the eastern 

margin of the dune field. The dunes occur at an elevation of from 670.5 to 1,310.6 m in a semiarid, cool 

climate with a mean annual temperature of 8.9 ° C and 

a range of -40 ° C to 43.3 ° C (Keech and Bentall, 1971).

The Sand Hills seem to have developed in the late 

Pleistocene, probably during the late Wisconsin or 

Holocene. A 14C date of 12,600 years B.P. (before the 

present), obtained for basal sediments in a core hole, is
GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

r

SOUTH DAKOTA. 

"NEBRASKA

l CO 

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D

Scottsbluff

EXPLANATION

A§ Study locality and n 

O Test holes used in c 

sections

Freshwater interdun 

ponds

Area prospected for 

during World Wai

lumber

potash

B

NEBRASKA 

COLORADO 1

D Ogallala

North Platte O 75 KILOMETERS _

FIGURE 1. Study localities in the Nebraska Sand Hills and loess hills. Base modified from Keech and Bentall (1971).

the oldest age of dated material of which we are aware 

in the Sand Hills (Watts and Wright, 1966). Valley fill 

beneath dune sand along the southeastern margin of 

the Sand Hills in Blaine County was dated by 14C at 

8,400±250 yrs. B.P. by Brice (1964). During our field 

work, two nondiagnostic fragments of bison bones 

were collected in place at two dune localities (loc. 32 

and 89). The bones from both localities were identified 

as IBison (Bison] bison (Linnaeus] of probable 

Holocene age by G. E. Lewis (written commun., 1975) 

of the U.S. Geological Survey. Faunal and floral 

analyses of samples from three interdune ponds at 

higher elevations than those of the present interdune 

surface provide data on the more recent history of the 

Sand Hills (chapters B and C) and indicate a Holocene 

age for the Sand Hills.

The upper Tertiary Ogallala Formation in original or 

reworked form has been suggested as the source of the 

dune sand by Lugn (1935, 1960, 1962). Stanley and 

Wayne (1972) and Reed and Dreeszen (1965), among 

others, suggested a lower Pleistocene alluvial source. 

We conducted a mineralogic study of 7 dune and interdune sand samples, and textural analyses were made 

of 93 samples. Available mineralogic and textural data 

are too limited to ascertain the source sediments for 

the Sand Hills.

Several studies of dunes in the Sand Hills describe 

mainly dune morphology (Lugn, 1935; and Smith, 

1965, 1968) or morphology and texture of the dune

sand (Warren, 1968). The interdune areas, in particular 

freshwater and alkaline ponds and lakes, have been 

studied both hydrologically and geologically. The 

works of Condra (1918, 1932) and Hicks (1921) summarize the economic importance of the alkaline lakes in 

the production of potash during World War I. 

Freshwater ponds have been analyzed for mollusks 

(chapter B), for pollen and seed profiles (Sears, 1961; 

Watts and Wright, 1966; chapter C), and for algae and 

water chemistry (Anderson and Walker, 1920; Bradley 

and Rainwater, 1956).

Lugn (1935) named the dune sand in the Sand Hills 

the Sand Hills Formation. Reed and Dreeszen (1965) 

divided the dune sand into the Peoria Dunesand and 

Bignell Dunesand, which they correlated with the 

medial Wisconsin Peoria Loess and the upper Wisconsin and Holocene Bignell Loess; the fluviatile 

equivalents were called the Peoria Formation and 

Bignell Formation respectively. The question of 

whether the loess is genetically related to the Sand 

Hills or to some other source (such as glacial or fluvial) 

is widely debated. The source of the loess and relative 

ages of the loess and dune sand are discussed by E. C. 

Reed and A. L. Lugn (in Schultz and Frye, 1968). Lugn 

(1968) and Wehrman (1961) indicated that loess and 

dune sand are interlayered within a transition zone between the Sand Hills and Loess Hills in central 

Nebraska (figs. 1, 2). We studied this transition zone in 

Custer and Logan Counties in an attempt to define the 

loess-dune sand relationship.
EOLIAN DEPOSITS

101°00'

FIGURE 2. Mosaic of Landsat imagery of the snow-covered Nebraska Sand Hills during winter. Both large dunes (Series I of Smith, 1965) 

and relatively smaller dunes (Series II of Smith, 1965) can be seen between the North Platte and Niobrara Rivers. Note the en echelon 

arrangement of barchan and barchanoid-ridge dunes, suggesting an early stage of evolution of barchan dunes to linear dunes.

DISTRIBUTION OF THE DUNE TYPES

The Sand Hills dunes can be classified as simple or 

compound (primarily transverse) types including dome 

(the small variety described by McKee, 1966; 

Ahlbrandt, 1975), barchan, barchanoid-ridge (McKee 

and Moiola, 1975), transverse-ridge, parabolic, and 

blowout. Some dunes in Custer County have two slipfaces dipping in opposite directions and may be reversing dunes, but internal stratification of these 

dunes were not well enough exposed for certain identification.

Barchan, barchanoid-ridge, and transverse-ridge 

dunes as high as 91 m are widespread throughout the 

Sand Hills region (fig. 3). A group of the largest of 

these dunes extends roughly from north-northwest to 

south-southeast across the western part of the dune 

field. Dune heights are greatest in the central part of 

the dune field, decreasing in size to the north and south

(fig. 3, section D-D'). The large dunes are compound in 

form; for example, small transverse-ridge dunes occur 

on large transverse-ridge dunes. Large barchans are 

common at the margins of the dune field, as well as in 

the interior (fig. 2). Some large dunes, straight or gently curving in plan view (fig. 2), superficially resemble 

linear or seif dunes; but their internal stratification indicates that they are barchanoid-ridge and transverseridge dunes. Some of these dunes are alined oblique to 

the regional direction of the sand transport. Many 

developed from en echelon barchans (fig. 2) and may 

represent an early stage of evolution of barchan dunes 

to sinuous-crested linear dunes, a hypothesis proposed 

by Tsoar (1978).

Many low mounds as much as 5 m high, with gently 

dipping, curved, parallel internal stratification, occur 

throughout the Sand Hills atop larger dunes. They 

may represent remnants of windward-slope or crestal 

deposits of older dunes, blowout deposits, or small
GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

20-B-70

UJ

12-B-72 10-B-72

24^6-70 17-B-70 16-B-70

20 40 KILOMETERS Deposits 

Eolian

EXPLANATION

15-B-72

Test-hole and number

Contact Dashed to separate thickness of 

eolian sands measured from test-hole 

data in interdune areas from thickness of 

dune sands above. Queried where contact 

uncertain. Dune heights above interdunes 

measured from topographic maps

FIGURE 3. Stratigraphic cross sections through the Nebraska Sand. Hills. The test-hole numbers used in the cross section are from data 

available at the Conservation and Survey Division, University of Nebraska, Lincoln. The height of dunes at each test-hole site is shown 

on each section. Vertical exaggeration X 86.

dome dunes, although dome dunes have not previously 

been described in compound association with other 

dune types.

The larger dunes visible in figure 2 are the Series I 

(large-scale transverse) dunes of Smith (1965). The 

Series II dunes (narrow longitudinal dunes of Smith,
EOLI AN DEPOSITS

1965) were examined in trenches and road cuts 

throughout McPherson, Logan, Custer, Thomas, and 

Hooker Counties, where they are best developed. In all 

examples, the Series II dunes seem to be normal 

transverse-ridge dunes with nearly all cross-beds dipping steeply southward; thus they are not modified upsiloidal (parabolic) or longitudinal (seif) dunes as suggested by Smith (1965). The large dunes north of the 

Niobrara River (fig. 2), described by Smith (1968) as 

possibly analogous to large dome dunes (probably star 

dunes) in North Africa, are here interpreted as intensely reworked barchan dunes. The horns of several 

barchans can be distinguished in an illustration by 

Smith (1968, p. 40) and also in figure 2.

Blowout and parabolic dunes, the Series III of Smith 

(1965), are ubiquitous in the Sand Hills. They are 

secondary features that developed after the largest 

dunes were formed. Most blowouts are 3-5 m deep, 

although some are deeper. The maximum depth 

measured in a blowout was 12 m. Blowouts and 

resulting deposits are oriented in many directions 

throughout the dune field, reflecting the present-day 

complex wind distributions over much of the Sand 

Hills.

THICKNESS OF THE EOLIAN SAND

The Sand Hills of Nebraska form a thin "blanket" 

deposit unconformably overlying either a southwardthickening wedge of unconsolidated Pleistocene fluvial 

deposits or consolidated sediments primarily of the 

Tertiary Ogallala Formation (fig. 3; Swinehart, 1972). 

In the southeastern portion of the dune field (Custer 

and Logan Counties), dune sand overlies loess in both 

outcrop and subsurface (fig. 3, Section D-D', test-hole 

16-B-70). In general, the height of the dunes above the 

interdune surfaces is greater than the depth of eolian 

sand beneath the interdune surfaces.

The thickness of eolian sand below interdune surfaces generally ranges from 9 to 24 m, with an observed maximum thickness of 37 m (fig. 3, 7-B-73), as 

determined by analyses of lithologic descriptions and 

of electric logs of 35 test holes along the four cross sections. Spontaneous potential and resistivity electrical 

logs from the test holes were calibrated with lithologic 

descriptions. The depth at which pebbles, silts, clays, 

or indurated rocks were found was used as a lower 

boundary of eolian sand. The inferred sand thicknesses 

were then checked by measuring sections of complete 

exposures of dune and underlying material along the 

major streams. Along the Middle and North Loup 

Rivers and Dismal River, dune sand rests on fluvial 

sand. These test holes and lithologic descriptions are 

part of a cooperative drilling program by the U.S. 

Geological Survey and the Conservation and Survey

Division of the University of Nebraska. Test-hole data 

is available at the Conservation and Survey Division, 

University of Nebraska, Lincoln.

Dunes and eolian sand deposits do not occur at many 

localities south of the present-day through-flowing 

Niobrara River and North Platte and Platte Rivers 

(fig. 3, 13-B-73, 24-B-70). Dunes north of the Niobrara 

River are more heavily reworked than are those to the 

south.

Interdune deposits that contain abundant organic 

material are widespread throughout the Sand Hills, 

but with the exception of silty layers in some test holes 

in the western part of the Sand Hills, they are not extensive in the subsurface. This indicates that the 

organic-rich interdune deposits, although diachronous 

(chapter C), represent culminating events in the 

history of the dune field, and that such deposits did not 

occur or were not preserved extensively during the 

development of the dune field. Fine-grained, evaporitic 

paleointerdune deposits, where preserved as in the 

western Sand Hills, are local permeability barriers 

(Bradley and Rainwater, 1956).

PAST SAND TRANSPORT DIRECTIONS

The direction of dune-building winds and the inferred sand transport directions in a dune field are indicated both by the external morphology of a dune in 

particular, the directions of dip of the slipface in 

transverse forms and by the direction of dip of internal cross-bedding. Internal dip direction is more 

reliable than slipface orientation, because internal 

structures constitute a record of dune deposits 

preserved through time and thus represent a more 

complete record than does the slipface. The slipface of 

a stabilized dune may represent the effects of the last 

dune-building storm or even later reworking.

Data for analysis of sand tranport directions in 

figure 4 are based on approximately 1,000 strike and 

dip measurements of cross-beds in deep exposures 

within the dunes, along streams, in road excavations, 

in gullies, and in a few deep blowouts. All measurements were made on bedding exposed in trenches cut 

at one-meter vertical intervals. Although 

measurements were made in dunes north of the 

Niobrara River and in the western part of the Sand 

Hills, these data are not considered reliable owing to 

the intensive reworking of dunes in those regions. Only 

data from cross-beds deep within dunes and overlain 

by soil at least 0.6 m thick were used in the analysis. 

These deposits were distinctly more indurated than 

those in recently active or surficially reworked dune 

sand. These data then were plotted on stereonets 

(fig. 4).
GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

North Platte . 

(DP not available)

41

50 

i

100 KILOMETERS

EXPLANATION

Sand rose arm—Proportional in length to amount of sand potentially moved by present-day 

winds: points into effective wind

Drift potential—Relative amount of potential sand movement 

Resultant drift direction—Direction all sand will tend to move

FIGURE 4. Past sand transport in the Sand Hills shown on lower hemisphere stereonet plots of dip-and-strike data from internal 

dune cross-beds. Stereonets cover the portion of the map area from which data were collected. Present effective wind regimes 

are indicated by sand rose (Fryberger, 1979).

Analysis of the stereonet plots indicates a general 

northwest-to-southeast drift of sand, except in the 

vicinity of North Platte where the drift was 

southward. Our interpretation differs from previous interpretations of the past sand transport in the Sand 

Hills. Two principal directions of sand transport to 

the southwest and directly to the east were inferred 

by Smith (1965) from dune morphology. We now interpret the large area of small linear or seif dunes in the 

southeastern part of the Sand Hills, described by 

Smith (1965), to be transverse-ridge dunes that 

migrated predominantly to the south.

Despite the great length of many dunes with 

straight or gently curving plans, none were found to be 

linear (seif) dunes in the sense that they were constructed from major sets of opposite-dipping slipface 

deposits as described by McKee and Tibbitts (1964). 

At some locations, dip directions of cross-beds suggested slipface growth at an angle oblique to the trend

of the dune as a whole (compare resultant drift direction, fig. 4, with dunes near Valentine, fig. 2). These 

data, as well as morphological evidence, show that 

some seemingly straight dunes have developed from en 

echelon barchans (fig. 2), as previously discussed, and 

perhaps represent an early stage of evolution of barchan dunes into linear dunes using Tsoar's (1978) concepts as to the origin and relative age of linear dunes.

The bimodal dip-directions in the North Platte and 

Arnold vicinity (fig. 2) reflect the occurrence of sets of 

small transverse ridge dunes facing in nearly opposite 

directions.

The trend of past sand transport direction in the 

Sand Hills is roughly similar in magnitude and curvature to similar trends south of latitude 30 ° north in 

Algeria and at latitude 30° north in Saudi Arabia 

(Fryberger, 1979). These trends parallel circulation 

patterns of typical midlatitude high pressure cells.
EOLIAN DEPOSITS

RELATIONSHIP OF PAST SAND 

TRANSPORT TO PRESENT WIND

Present-day effective winds were evaluated using 

sand roses circular histograms (fig. 4) in which the 

"arms" of each rose are proportional in length to the 

amount of sand that can be moved by the wind from a 

given direction toward the center of the rose 

(Fryberger, 1979). The arrow near each rose indicates 

the net direction of sand transport, or resultant drift 

direction. The terms used to describe relative amounts 

of sand potentially moved by winds at a station are 

drift potential, which is the total potential sandmoving power of all winds, and resultant drift potential, which is the magnitude of the net potential sand 

transport in a given direction when the effects of wind 

from various directions are considered as vectors. The 

principal advantage of using sand roses is that wind 

regimes can be described quantitatively and classified 

according to properties of direction and energy (fig. 5).

If present-day wind regimes are compared with dune 

types in the Sand Hills, a wide discrepancy is found for 

some stations (fig. 5). For example, the wind regime at 

Alliance, a short distance from transverse dunes along 

the western margin of the dune field, is more compatible with the star-dune type than with the transverse 

type (fig. 5). Similarly, the present-day wind regime at 

Ainsworth seems more compatible with linear dunes 

than with the transverse dunes in this area. Presentday wind regimes in the Sand Hills mostly have high 

drift potentials (MOO) and low resultant drift potentials. Were it not for the rainfall of the region, which

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RESULTANT DRIFT POTENTIAL/DRIFT POTENTIAL 

(<—- WIND VARIABILITY INCREASES)

FIGURE 5. Approximate directional versus energy properties of 

wind regimes associated with transverse, linear, and star dunes, 

based on data from Fryberger (1979). Low-energy wind regimes 

are 0-199 vector units (V.U.); intermediate energy, 200-399 V.U.; 

and high energy, 400 V.U. or greater. Present-day wind regimes in 

the Nebraska Sand Hills are indicated by dots. Present wind 

regimes are more characteristic of star or linear dunes than of the 

transverse type preserved in the Sand Hills. Dashed lines indicate 

approximate boundaries of dune type with wind regime.

supports a stabilizing vegetation, the sand sea would 

be very active, and, in some areas, the dune forms 

would be different from those existing today.

The nature of the change in wind circulation from the 

time of the dune building to the present cannot be 

determined from available data. However, if the southerly to southeasterly component of the modern wind 

regimes were not present, wind regimes would be compatible with the regionally common transverse dune 

types. A shift from an older regime of westerly effective winds to a younger regime of southerly effective 

winds has been documented for southern Oklahoma, 

western Texas, and southeastern New Mexico by 

Melton (1940). The wind drift type dunes built by an 

older westerly wind regime were considered by Melton 

(1940) to have formed at least 15,000 years B.P. 

(although this figure is not based on a radiometric 

determination), so possibly the introduction of the 

southerly-southeasterly component of the wind 

regimes in the region Melton studied and in Nebraska 

may have been roughly contemporaneous but more recent than previously reported (chapter C).

If the southerly component of present-day winds 

were removed, resultant drift directions would be more 

southerly (fig. 4). Present-day resultant drift directions 

compare favorably, although not perfectly, with 

transport directions indicated by internal stratification of the Sand Hills dunes. The present analysis of internal cross-stratification does not agree with the suggestion by Smith (1965) that a major shift in effective 

wind direction occurred during the building of the sand 

sea. Our interpretation is that resultant drift directions remained steady during the growth of the dunes, 

forming an arc from southeast through south. 

Anomalous trends of transport, such as that indicated 

by northeast-facing dunes in the Arnold area (loc. 110, 

fig. 1; see also stereonet for dunes near North Platte, 

fig. 4), may represent the results of a single storm 

(perhaps the later southerly effective winds) prior to 

dune stabilization. Although blowout deposits (Series 

III, Smith, 1965) clearly are younger than the Series I 

and II dunes, we found no evidence to indicate that 

larger dunes (Series I, Smith, 1965) represent a different period or cycle to activity than that of the 

smaller dunes (Series II of Smith, 1965).

ORIENTATION OF LAMINAE 

WITHIN DUNES

Detailed analysis of laminae dip direction and degree 

was undertaken in this study for barchan, transverseridge, and blowout deposits to see if any diagnostic 

strike and dip relationships would emerge. These data 

are similar to those typically available from cores and
8 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

dip-meter logs. Strike and dip measurements from a 

number of sites in the same dune type were combined 

as shown in figure 6. Dune type in each area was 

diagnosed on the basis of both external morphology 

and internal structure as revealed in the best exposures. Topset deposits were not used in this 

analysis, because they conform to the topography of 

the dune and are rarely preserved within dunes. 

Failure to recognize upwind-dipping topset beds in 

shallow exposures may result in transverse dunes being incorrectly identified as linear dunes. The relation 

of topset and slipface deposits is schematically shown 

in figure 7.

Strike and dip were measured systematically along 

the entire length and height of a dune outcrop. To 

avoid apparent-dip problems, measurements were 

made in pits dug at 1-m vertical intervals and spaced 

at equal horizontal intervals to cover the entire exposure at 30.5-m spacings.

The mean dip and mean angular deviation of dip, as 

computed by the statistical method described by Till 

(1974, p. 38-42), are as follows (see also fig. 6):

Dune type

Blowout .................

Meandip(°)

24

22

16

Mean angular 

deviation) °)

32

54

54

Total dip 

spread! °)

QO

180

180

Transverse-ridge dunes have a narrower spread of 

dip directions than do barchan dunes. The wide spread 

of dips in barchan dunes reflects the curvature of the 

slipface of that type of dune. The narrow spread of dips 

in the transverse-ridge dune similarly is the result of a 

relatively straight slipface.

Although laminae within blowout dunes have the 

same mean angular deviation of dip directions as those 

in barchan dunes, the mean dip is much lower than 

that of laminae within either barchan or transverseridge dunes. The low mean dip value of laminae within 

blowout dunes reflects the general lack of slipface 

development on blowout dunes. The 180 ° total spread 

of dip directions of laminae in blowout dunes is considerably less than the 270 ° total spread of dip directions observed in parabolic dunes by McKee (1966) and 

by Bigarella (1975), although the growth of both 

blowout and parabolic dunes in the Sand Hills is controlled by vegetation. The narrower spread of dip directions in blowout dunes, of the Sand Hills relative to 

parabolic dunes elsewhere, may reflect the absence of 

long trailing arms (which characterize parabolic 

dunes), and the concentration of accretion deposits on 

the dune noses of the blowouts. Thus, identification of 

dune type in the rock record, or when unknown, may be 

ascertained by determining both the mean dip angle 

and mean angular dip deviation of laminae.

NORTH

MEAN DIP 22 DEGREES

0 5 10 15 20 25 30 35 

BARCHAN

TOTAL SPREAD 

r=0.55 

S=54

LU

o

DC 

LU

Q_

30 -I 

20- 

10-

O-z.

LU

ID

a

LU 

DC

0

MEAN DIP 24 DEGREES

0 5 10 15 20 25 30 

TRANSVERSE-RIDGE

35

MEAN DIP 16 DEGREES

r=0.55 

S=54

0 5 10 15 20 25 30 35 

BLOWOUT

DIP OF CROSS STRATA 

IN DUNES, IN DEGREES

FIGURE 6. Mean angular deviation (S) in degrees; estimate of 

spread of angular values around unit circle (r); and histograms of 

dip distribution for strike and dip data in selected barchan, transverse-ridge, and blowout dunes. Statistical computations are described in Till (1974, p. 38-43). Stereonet plots (dots) depict intersection of plunge of lamination dip with lower hemisphere. 

Outer margin of stereonet circle is 40 degrees.

SEDIMENTARY STRUCTURES IN DUNES 

PRIMARY STRUCTURES

Many excellent exposures of internal structure of the 

dunes were examined throughout the Sand Hills. The 

best exposures are along the margins of Merritt Reservoir in Cherry County, southwest of Valentine, 

Nebraska (loc. 17, 24, 52-54), where the dunes have
EOLIAN DEPOSITS

Slipface deposits

Topset deposits

Wedge-planar 

cross bed set Tabular-planar 

cross bed set

Interdune deposits

DIRECTION OF DUNE MIGRATION

FIGURE 7. Schematic diagram illustrating terminology used in this report and internal stratification in dunes that have one slipface and migrate principally in one direction, such as barchan, barchanoid-ridge and transverse-ridge dunes in the Sand Hills.

been undercut by the Snake River. Vertical outcrops as 

high as 37 m expose the structures within en echelon 

barchan dunes for several kilometers along the northern margin of the reservoir (fig. 8). Exposures also were 

examined at many localities along the North, Middle, 

and South Loup, Dismal, Niobrara, Snake, and North 

Platte Rivers.

In general, the two types of deposits originally called 

"avalanche" and "accretion" deposits by Bagnold 

(1941) are easily recognized in dunes of the Sand Hills. 

Observations by a number of workers have shown that 

deposition on the lee side of a dune ("avalanche" 

deposits) may occur in a number of ways, including (1) 

avalanching (both slumps and grain flows; McKee and 

others, 1971); (2) direct fall of grains (Hunter, 1977); 

and (3) minor reworking of these two types of deposits 

by ripples oriented up and down the slipface that 

migrate normal to the direction of dune migration. 

Similarly, "accretion" deposits may form by saltation 

or by grain fall. "Accretion" deposits may dip either upwind or downwind. In this paper, the general descriptive terms "slipface" and "topset" are used to avoid 

the genetic implications of the definite processes of 

origin that are ascribed to "avalanche" and 

"accretion" by Bagnold (1941).

Topset deposits are common in dunes of the Sand 

Hills. Where present in barchan, barchanoid-ridge, or 

transverse-ridge dunes, they constitute a small percentage of the dune relative to slipface deposits; but 

they may still be very thick (as much as 10 m) in a large

dune. Dune types such as dome, blowout, and 

parabolic may not develop slipface deposits and may 

be composed almost entirely of topset deposits. Topset 

deposits are rarely preserved in dunes containing slipface deposits, because they are very susceptible to 

reworking (Reiche, 1938; McKee, 1934). Topset 

deposits in the Sand Hills form a relatively thin 

blanket over the top of a dune and may dip upwind 

(windward-slope deposits) or downwind (to the brink) 

from the crest (fig. 7). Laminae within topset beds have 

dips less than 25 °, and thus do not contain avalanche 

structures. Laminae within topset deposits commonly 

are gently curving and conform to the topography of 

the dune or may dip at a low angle to the dune 

topography. Topset deposits may unconformably 

overlie slipface deposits.

Figure 7 illustrates the vertical sequences of 

deposits that can be preserved within a dune having 

one slipface and migrating principally in one direction. 

A complete vertical succession would contain slipface 

deposits overlain successively by downwind-dipping 

topset and finally upwind-dipping topset deposits (fig. 

$A). However, slipface deposits may be buried by only 

one topset sequence or topsets may be absent (fig. 9B, 

9Z>). The maximum observed thicknesses of upwinddipping topset beds, downwind-dipping topset beds, 

and slipface beds are 2.1 m (loc. 68), 10.4 m (loc. 68), 

and 26.2 m (loc. 54), respectively.

Slipface deposits in the Sand Hills are wedge- or 

tabular-shaped and generally comprise most of a dune.
10 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

NORTHWEST

25

N. 18 W., 24 S.

SOUTHEAST

EXPLANATION

Strike and dip of lamination, 

in degrees

Strike and dip of erosional 

bounding surface between 

sets of laminations, in degrees

Bounding surface—Dashed 

where estimated

HORIZONTAL AND VERTICAL SCALE

Dissipation structures

48 E., 05 E.

Bounding surfaces dip 

in direction of transport

Weak dissipation 

structures. Isolated 

medium-scale trough 

cross bedding

N.07E.,27S 

^-—— 

E-W, 08 S.

06 W., 19 N. 

N. 18 W., 24 S.

Thinner beds

toward top

of dune

ation structures

Base of dune exposure along highest lake-terrace level

FIGURE 8. Measured sections in en echelon barchan dunes at Merritt Reservoir (loc. 54). Sections shown in close proximity on diagram

were measured on different dunes along the lake front.

Slipface deposits mostly consist of even parallel 

laminae, which become tangential at the lower 

bounding surface and are convex downward. Sand-flow 

lobes or toes are distinguishable near the lower 

bounding surface of such deposits (fig. 1(XA). Convex 

upward cross-bed sets occur in blowout and parabolic 

dunes, which are the result of vegetational control and 

general lack of slipfaces on the lee side (nose) of these 

dunes.

On a large scale, bounding surfaces between crossbed sets may be broadly curving and troughlike 

(McKee, 1966; and fig. 8); however, laminae between 

such surfaces meet the lower bounding surface and not 

the upper bounding surface and are more properly 

referred to as wedge-planar cross-bed sets. Although 

some bounding surfaces are flat, most show gentle, 

convex-downward curvature in the direction of dune 

migration, at angles less than those of enclosing 

laminae, and are continuous over distances of 6 m or 

more (fig. 8).

Trough (festoon) cross-bedding is uncommon in the 

Sand Hills (fig. 105). The trough cross-bed set shown 

in figure IOB resulted from reworking (scour and fill) of 

the uppermost part of a dune. Stacked small- to 

medium-scale troughs, such as those described in

aqueous deposits by Harms, MacKenzie, and McCubbin (1963), were not observed in the Sand Hills dunes. 

Sets of cross-strata generally are progressively thinner toward the top of a dune, their dip directions are 

more variable, and their dip inclinations are lower (fig. 

8). The laminae within a cross-bed set generally are 

steepest near the top of the set (fig. 8).

A wide variety of small-scale primary structures 

occur in dunes of the Sand Hills. Common primary 

sedimentary structures include normally graded, inversely graded, and nongraded beds and laminae, and

FIGURE 9.(facing page). Large-scale structures in dunes of the 

Sand Hills. A, Slipface deposits dipping to the left, overlain successively by downwind-dipping topset deposits and upwind-dipping topset deposits (loc. 15). B, Slipface deposits dipping to the 

right, not overlain by topset deposits (loc. 45). C, A "nickline" 

(Walker and Harms, 1972) in topset deposits is shown in a barchan dune (loc. 132). D, Slipface deposits overlain by downwinddipping topset deposits (loc. 77). E, Three sets of wedge-planar 

cross-bed sets, one dipping to the left, one toward the reader, and 

one to the right (loc. 54). The latter cross-bed set is a slipface 

deposit which is little affected by dissipation structures. F, Detail 

of E showing dissipation structures in a cross-bed set. Note clipboard for scale in A, D, Et and F; the bar on the clipboard is 20 cm 

long.
EOLIAN DEPOSITS 11

*- •r'-'- TM - *,
12 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

I "f ft f
EOLIAN DEPOSITS 13

coarse-textured deposits along erosional surfaces 

within dunes. The few ripples observed were in flatbedded interdune deposits. Ripple laminae (McKee, 

1957) and adhesion ripples were relatively common, 

the latter in interdune sediments only (fig. 1QE). 

Graded, laminated, and unlaminated beds commonly 

are juxtaposed. Thinning-upward inversely graded 

beds occur in topset deposits (fig. II A) and overlie 

thicker, normally graded beds in slipface deposits (fig.

SECONDARY STRUCTURES

Secondary structures that have modified or 

destroyed primary dune structures, are common in the 

Sand Hills. Modification of primary structures ranges 

from slight to complete. Secondary structures include 

faults; contorted bedding; dissipation structures 

(discussed in the following section); desiccation cracks; 

and biogenic structures such as burrows, dikaka (root 

tubules), and other tubular structures. Bioturbation 

traces are of many sizes and shapes, and burrows are 

infilled in a variety of ways. For example, the large 

burrow in figure I2A is unstratified and contains fecal 

pellets. The small-diameter tubular structures in figure 

12C have a meniscate internal structure. Burrows are 

both normal (fig. 12Q and oblique to bedding (fig. 

12A), and some traces (dikaka) have spiral forms (fig. 

125). The surface features shown in figure 12Fare not 

burrows or dikaka but freeze-thaw-induced structures 

produced at the brink of an active dune which formed 

along the shoreline of Merritt Reservoir. Structures of 

unknown origin (fig. I2E) are present in flat-bedded 

dune sand and may reflect snow melt. Infilled desiccation cracks(?) also were observed within dunes (fig. 

12D).

Contorted beds occur at the base of some slipface 

deposits, reflecting compressional deformation of 

cohesive sand similar to that described by McKee, 

Douglass, and Rittenhouse (1971; fig. 1LD). Contorted 

beds caused by loading were more common in interdune deposits than in dune deposits (fig. IQD). Primary 

dune bedding is preserved in the contorted bed shown

FIGURE 10 (facing page).—Sedimentary features in dune and interdune deposits. A, Tabular planar cross-bed with pronounced 

sand-flow toes (arrows) (loc. 68). B, Rare occurrence of trough 

cross-bedding, in this case due to reworking (loc. 27). C, Lenticular 

organic-rich interdune deposit (loc. 71; sample NP-7 was taken 

from this deposit). D, Interdune deposits containing dissipation 

structures overlain by unaffected dune sand; contorted bedding 

occurs at the dune-interdune contact. Pencil is 13 cm long. E, Interbedded adhesion-rippled layers (ledges) with flat-bedded interdune sediments (loc. 68). Pen is 13 cm long. F, Alluvial-sand fan 

filling interdune (loc. 62).

in figure 1LD, but in figure 11C it has been destroyed 

by dissipation structures. A topset bed with burrows, 

dissipation structures, and contorted bedding, is 

shown in figure 11F.

DISSIPATION STRUCTURES

Throughout the Sand Hills, the laminae and bedding 

in the upper parts of a dune exposure commonly are in 

various stages of modification by "dissipation structures" a term originally used by Bigarella (1975) to 

describe this feature in Brazilian coastal dunes. The 

dissipation structures from a series of dark, discontinuous, wavy bands that superficially resemble contorted bedding (figs. 9E, 9F, 1(XD, 11Q but have a different origin. Dissipation structures are layers 

resulting from the concentration of fine material, and 

are superimposed upon original stratification. They do 

not result from the contortion of previously existing 

laminations. In the tropical climate of Brazil, Bigarella 

(1975) observed dissipation structures that formed in 

response to infiltrating waters from heavy rains 

causing the redistribution of colloidal material within 

eolian deposits.

During winter field investigations in the Sand Hills, 

dissipation structures were observed along the upper 

margins of frozen sand layers (fig. 13). Textural 

analyses for three samples from adjacent frozen, unfrozen, and dissipation structure layers were made 

using sieves (weight frequency) and a Quantimet 720 

Automatic Image Analyzer (A.I.A)1 . The grain shape, 

(area/perimeter2), is similar for each of the three 

samples (fig. 13), but texture, size, and sorting are different. The material within the dissipation structures 

contains 3.1 percent silt and clay, whereas the frozen 

sand layer contains 0.4 percent silt and clay, and the 

unfrozen layer contains 0.75 percent silt and clay. 

Another dissipation structure layer contains 16.1 percent silt and clay, compared to an adjacent unaltered 

layer with 2.6 percent silt and clay. Thus, dissipation 

structures are finer grained and more poorly sorted 

than are adjacent layers as determined by both weightand number-frequency data (fig. 13). The silt and clay 

fraction is the pan fraction of the sieve that is 

predominantly clay as determined by the Automatic 

Image Analyzer following disaggregation of this fraction with an ultrasonic device.

A source of clay which may become concentrated 

within dissipation structure layers is present within 

the dunes as clay coatings on sand grains. These 

coatings are mainly montmorillonite with some mixed-

'Use of trade or company names is tor descriptive purposes only and does not constitute an 

endorsement of the product or company by the U.S. Geological Survey.
14 

t

GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS 

J
EOLIAN DEPOSITS 15

layer montmorillonite-illite as determined by X-ray diffraction and scanning electron microscope techniques. 

Dissipation structures most commonly occur in the upper part of an outcrop and along the upper margin of 

frozen sand layers. Infiltration of water may concentrate clay preferentially in or along less permeable 

layers within the dune sands. Frozen sand layers may 

form a barrier to such infiltration and cause clay to be 

deposited above them. After the frozen layer melts, the 

dissipation structure (layer) is less permeable than surrounding layers due to increased clay content. This 

process would promote the continued deposition of 

clay in and adjacent to the dissipation structure. The 

reduced permeability in dissipation structure layers 

relative to surrounding unaffected layers is discussed 

in the Sedimentary Petrography section of this 

chapter.

INTERDUNE DEPOSITS

A continuing question in eolian studies is whether interdune deposits are extensive or strictly local (McKee 

and Moiola, 1975). Interdune pond deposits and waters 

comprise a total of 266.33 km2 in the Sand Hills (Steen, 

1961). Interdune pond deposits that crop out in the 

Sand Hills seem to be isolated and lenticular at 

localities 2, 60, and 71, where they intertongue with 

dune sand. A 2,590-km2 area of enclosed drainage and 

alkaline interdune pond deposits in the western Sand 

Hills was drilled extensively in search of potash during 

World War I (hachured area, fig. 1). In test holes, two 

or three buried hardpan layers were separated by 

sands containing alkaline water, but no continuous 

hardpan horizon in the western part of the Sand Hills 

was found (Condra, 1918; Bradley and Rainwater, 

1956; fig. 3, this chapter).

For this study, samples from three interdune 

deposits were collected for paleontological, 

palynological, and orgamc-geochemical analyses. Two 

samples are from an alkaline interdune deposit in 

northwestern Cherry County (NS-2, 3, loc. 2), and the 

third sample is from a lenticular, organic interdune 

deposit in Hooker County (NP-7, loc. 71). The results of 

the analyses of mollusks from these samples are

FIGURE 11 (facing page).—Small-scale structures in the Nebraska 

Sand Hills. A, Inversely graded, thinning-upwad beds in topset 

deposits (loc. 116); centimeter rule shown for scale. B, Normally 

graded slipface deposits underlying deposits shown in 1L4 (loc. 

116). C, Intense development of dissipation structures; relict 

laminae near bottom of photograph (loc. 52). D, Contorted bed at 

base of slipface deposit (loc. 52). E, Brecciation of interdune sediment (loc. 71). F, Intense disruption of topset deposits by contorted bedding, dissipation structures, tensional fault (just left of 

pencil), and meniscate burrow (loc. 70).

discussed in chapter B, and the analyses of diatoms, 

ostracodes, and pollen for the same samples are 

discussed in chapter C.

Interdune deposits in the Sand Hills differ from 

nearby dune sands in color, thickness, texture, internal 

structures, and composition. Interdune pond deposits 

are commonly richer in organic matter than are dune 

topset and slipface deposits (fig. 14); they are dark 

gray to black, whereas the dune sands have lighter 

hues. Thickness of interdune sediments in the Sand 

Hills ranges from a few meters in surface exposures 

(fig. 10Q to 15 m in some core samples (see chapter C). 

Nearby dunes have thicknesses of 60-90 m. The depth 

of organic silt, sand, and other sediment was 6.5 m 

(Watts and Wright, 1966), and 5 m (Sears, 1961). Interdunes with similar deposits were cored to depths of 3.5 

m in Krause and Jesse Lakes in Sheridan County in 

1953 (H. S. Tourtelot, oral commun., 1976).

Interdune deposits generally are finer grained and 

more poorly sorted than are dune deposits. (Interdune 

samples shown in figure 16 are plotted for their sand 

fractions only; compare with figure 15C which includes 

the silt and clay fractions; also see McKee and Moiola, 

1975.) The adverse effects of interdunes as permeability barriers on sandstone reservoirs (for both water 

and petroleum) are described by Bradley and Rainwater (1956).

Horizontal to subhorizontal laminae are numerous in 

the interdune deposits of the Sand Hills. Interdune 

deposits commonly contain adhesion ripples (fig. 10.E), 

dissipation structures, and convolute bedding (fig. 

WD). The interdune sample from Hooker County 

(NP-7) was analyzed for organic content by combustion and a thermal analysis-gas chromatography 

technique. The results of analyses of coarse- and fineorganic fractions by G. E. Claypool (written commun., 

1975) are shown in table 1.

TABLE I.—Organic analyses of interdune sample NP-7

Carbon (in Oil yield

weight percent) _________________

Total Organic Gal/ton Weight percent

Organic concentrates: 

Coarse ..............

Fine ................

1.71 0.9 0.25

14 1

................ 6.7

0.1

5.4

2.6

The sample was heated from 30° to 355° C and produced 8-10 major hydrocarbon compounds distilled 

from the organic matter. A second analysis was performed on material evolved from the sample at 

temperatures of 355°-800° C (fig. 14). The decomposition of the solid organic matter during the second 

analysis produced the whole range of normal paraffin 

hydrocarbons, and, thus, could produce petroleum
16 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS
EOLIAN DEPOSITS 17

50-

ZZ 30 _

Uj |jj OLI

£32

UJ LU

DS-1

50- 

40-

DS-2

01234 01 2 345 

GRAIN SIZE, IN PHI

50- 

40- 

30- 

20- 

10- 

0

DS-3

012345

I|o.6H

Z **

< > 0.5- 

W Q 0.4

.DS-2 

.DS-1 

I

.DS-3

2.0 2.5 3.0 

MEAN GRAIN SIZE, IN PHI

'Sphericity 

increases2.0 3.0

Fine sand 

GRAIN SIZE, IN PHI

0.5 0.6 0.7 0.06 0.07 

Moderately well (Moderate GRAIN SHAPE 

SORTING COEFFICIENT (AREA/PER I METER2)

FIGURE 13.—A dissipation structure along the upper margins of a 

frozen sand layer. Mean grain size, sorting, and shape factors for 

three adjacent samples are shown. Sample DS-3, from the margin 

of the frozen sand, is finer grained and more poorly sorted than 

either unfrozen sand (DS-1) or sand from the center of the frozen 

layer (DS-2).

.<XI FIGURE 12 (facing page).—Secondary sedimentary structures. A, 

Fecal pellets within unstratified, filled, large-diameter burrow 

(loc. 52). B, Spiral bioturbation traces and plant molds; area 

shown is 12 cm across (loc. 116). C, Small-diameter meniscate burrow crossing a preserved ripple (loc. 52). D, Infilled desiccation 

cracks exposed in bottom of blowout near base of transverse dune 

(loc. 68). E, Collapse structured) in flat-bedded dune sand (loc. 54). 

F, Top view of freeze-thaw structure produced by melting of a 

thin layer of snow beneath a 5-cm-thick layer of sand.

upon burial and heating (G. E. Claypool, written commun., 1975) (fig. 14).

The pyrolysis product of the interdune sediment 

(sample NP-7) is comparable to hydrocarbons produced from lacustrine deposits of the Eocene Green 

River Formation in the western United States. 

Pyrolysis products from interdune sediments and from 

the Green River Formation may have a common 

organic source; namely, nonmarine algae (G. E. 

Claypool, written commun., 1975). The presence of 326 

species of algae in the Sand Hills lakes has been 

established by Anderson and Walker (1920). The 

pyrolysis products of interdune sediments resemble 

saturated hydrocarbons in crude oils from the 

Pineview Field in Wyoming, which produces from the 

Triassic(?) and Jurassic(?) Nugget Sandstone, considered to be, in part, an eolian deposit.

Using a pyrolytic oil yield for the coarse organic concentrate of 14.1 gal/ton (60 liters/metric ton) and a 0.9 

percent organic carbon content for the whole rock will 

give a pyrolytic oil yield for the original sediment sample of about 0.25 gal/ton (1.07 liters/metric ton). If a 

density of 0.08 lb/in3 (2.2 g/cm3) is assumed, then 436 

unit volumes of source rock would be required to produce one unit volume of oil. If expulsion of oil is inefficient, then 2 to 4 times more rock volume (872 to 

1,744 unit volumes) would be required to. produce one 

unit volume of oil (G. E. Claypool, written commun., 

1975).

100

RETENTION TIME

FIGURE 14.—Gas chromatogram of Nebraska Sand Hills interdune 

deposit (NP-7, loc. 71). The sample was heated from 355° to 800° 

C. Numbers along selected peaks refer to the number of carbon 

atoms per molecule of normal-paraffin hydrocarbons. The whole 

range of normal-paraffin hydrocarbons, both oil and natural gas, 

was generated.
18

LLJ

>

ID 

U

95

84

75

50

25

16

5

I I I T

SK|= + .396 

SK|=-.167>

GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

50

-1.0 

A

2.0 4.0

O 

DC 

LLJ 

Q_

95

> 84 

O 75

w 50

O 25

16

SK,=-.194

i i

-1.0

B

2.0 4.0

95

84

75

50

25

16

- SK,= -. 

SK,=+.041

U 

QC

CO 

CO

-1.0 2.0 4.0

50

CO 40

£ 30

20

Mz =2.618f 

o-, =0.8231

Mz =2.644<£

<T,=0.586

O 10

a. 0

a: -1-0

UJ 

DC

o

__L I I

2.0 4.0

50

40

30

20

10

Mz=2.314? 

L a. =0.324

-1.0 2.0 4.0 -1.0 

C GRAIN SIZE, IN PHI (</>)

EXPLANATION

>4.0 Silt and clay fraction combined 

SK Skewness 

M Mean grain size 

o- Standard deviation

2.0 4.0

FIGURE 15.—Textural contrasts of eolian sand 

samples. A, Adjacent topset deposits, loc. 75; a 

light-colored layer (thin line on cumulative curve, 

patterned area on histogram) adjacent to a darkcolored layer that contains dissipation structures 

(thick line). B, Loc. 40; topset deposits (thin line, 

patterned histogram) compared with slipface 

deposits (thick line). C, Poorly sorted, sandy mud 

from interdune deposit (thin line, patterned 

histogram, loc. 25) versus very well sorted slipface sand (thick line, loc. 10). Cumulative frequency curves were recalculated on the sand fraction if either gravel or pan fraction was greater 

than five percent.
EOLI AN DEPOSITS 19

0.3

0.2

u3 0.1

Z

LU 0

-0.1 

-0.2

n o

•^ |

-

_ 9

A

-

I

I

A

A

»A %V

S 2y ••

K 'l^-.

x *%

"" t^

A

I

I I

Strongly fine skewed

Fine-skewed —

Nearly symmetrical —

Coarse-skewed —

I I

MEDIUM

SAND 1.0 —— — ——

z 0.9

O

< 0.8

^

Qj n

Q U- 7

§ 0.6

Q

V/>O

</> 0.4

n i

1 —

—

A

-

flf^

-

1

FINE

SAND

1

A ^x

. 1

J^**

"A $$l

» ^ ^^:* •

A • •

"*/ "

x I

VERY FINE SAND

I I —

Moderately sorted

—

Moderately well sorted ~

Well sorted _

I | Very well sorted

1.0 2.0 3.0 4.0 

MEAN GRAIN SIZE, IN PHI (</>)

EXPLANATION

GRAIN POPULATION 

x Slipface 

A Topset

• Undifferentiated dune

• Interdune

FIGURE 16.—Textural parameters of 93 eolian-sand samples divided 

into topset, slipface, undifferentiated dune, and interdune populations. Values for interdune samples reflect the sand fraction only.

An indigenous hydrocarbon source for the eolian 

Nugget Sandstone in western Wyoming has been proposed by Picard (1975). He found that many reservoirs 

in the Nugget are not filled to their spill points; that is, 

the effective pay zone is much less than subsurface 

closure. He further suggested that the characteristic of 

the Nugget oils indicate an indigenous source; namely, 

lacustrine intervals in the basal part of the Nugget 

Sandstone. Interdune sediments in the Nebraska Sand 

Hills could possibly provide upon burial a source of 

petroleum for nearby surrounding reservoir rocks.

Thus, these interdune deposits are possible analogs for 

source rocks in the Nugget.

DEGRADATIONAL PROCESSES IN THE 

SAND HILLS

Although much of the Sand Hills region is covered 

by a protective mantle of grass, the forming of soil, 

erosion by wind and water, and mass wasting are continually modifying the landscape and internal structures of the dunes.

Wind erosion produces parabolic dunes and blowout 

dunes (previously described) and, in general, reduces 

the relief of the old dune topography. In some places, 

wind erosion results in yardangs, and, in the western 

Sand Hills, the denudation of dry salt-encrusted interdunes in summer.

Water erosion probably is the most important cause 

of landscape alteration. Dissection of the steeper lee 

slopes and slipfaces of dunes by gullies is a common occurrence and deposition from these gullies creates 

alluvial fans, particularly in front of the dune slipface 

(fig. 10F). The sand deposited as alluvial fans was 

originally accumulated through eolian processes and 

has been moved only a short distance by water. When 

carried to extremes, the dissection results in slumping. 

Abundant rainfall has caused the formation of organicrich interdune ponds and the development of thin soils 

on the dune sands. Thus, both aqueous and subaerial 

processes are currently eroding the dunes and infilling 

the topographically low interdune areas.

SEDIMENTARY PETROGRAPHY

A suite of 93 samples from topset, slipface, undifferentiated dune, and interdune deposits was collected 

from below the soil zone in outcrops throughout the 

Sand Hills. The samples were sieved on 1/4<|> intervals; 

and graphic measures of mean grain size (Mz), sorting 

(o7), skewness (SKj) and kurtosis (both Kc and transgraphic kurtosis Kl c), as defined by Folk (1968), were 

determined.

The analysis of 93 sand samples showed that there is 

as much textural variation from one bed to another 

within a single dune as among dunes in widely 

separated localities (fig. 15A). One layer of topset beds 

(fig. 15A) is a moderately sorted, strongly fine skewed, 

medium-grained sand with a silt and clay content of 

2.6 percent. The overlying topset bed, containing incipient dissipation structures, is noticeably darker and 

is a moderately well sorted, coarse-skewed, finegrained sand with a silt and clay content of 16.1 per-
20 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

84

i£O ou 

LU Ul

g a 25

I III

Sand

Loess

I I I

-1.0 2.0

GRAIN SIZE, IN PHI

4.0

50

40

_ LU

£

0 

<r

10

Silt

and

Xlay

-1.0 2.0 4.0 

GRAIN SIZE, IN PHI

Mz

CTl

SK|

Layer

Sand

3.037^,

0.667

-0.168

Loess

2.4280

0.693

+0.055
EOLI AN DEPOSITS 21

cent. Textural differences are also found between 

topset and slipface sand (fig. 15B). The extreme sorting 

differences between very poorly sorted sandy interdune mud and very well sorted slipface sand are shown 

in figure 15C. The sample of slipface sand shown in 

figure 15C is the only very well sorted sand sample of 

the entire 93-sample suite.

The plot of mean grain size versus sorting 

demonstrates that the samples are predominantly finegrained, moderately well sorted sands (fig. 16). The 

plot of skewness versus mean grain size shows a wide 

distribution of values, both positive and negative (fig. 

16), and is a characteristic of other inland dune fields 

(Ahlbrandt, 1974). Kurtosis values were widely scattered and will not be presented.

Seven thin sections were cut from 2.5-cm-diameter 

plugs taken in the field for permeability tests. The field 

sampling procedure consisted of a standard softsediment-permeability sampling device provided by 

Core Laboratories, Inc. After the permeability of a 

sample was determined, the plug was injected with 

blue epoxy, thin-sectioned, and stained for K-feldspar; 

600 grains per slide were counted.

The sand that composes both dune and interdune 

deposits is predominantly a feldsarenite as defined by 

Folk, Andrews and Lewis (1970). The sandy interdune 

samples have more feldspar (36.1 percent feldspar 

average for four interdune samples) than the dune 

sands (19.3 percent feldspar average for three 

samples). The detrital components of these eolian 

deposits in decreasing frequency include quartz (50-75 

percent), feldspar (about equal amounts of K-feldspar 

(9-25 percent) and plagioclase (5-24 percent)), chert 

(3-9 percent), rock fragments (1-4 percent), and clay 

(trace-4 percent in dune sand, 2-32 percent in interdune sand). Montmorillonite clay coatings occur on 

grains of all compositions.

The permeability of 13 dune-sand samples ranged 

from 2.4 to 9.9 darcies (D). Large permeability differences were found during a bed-to-bed comparison. 

For example, analysis of adjacent samples from a 

topset deposit showed 5.1-D permeability for a fine 

sand, whereas the medium sand bed below had 9.4-D 

permeability (see fig. 15A). A similar contrast was 

present in slipface deposits; a fine sand bed had 2.8-D

FIGURE 17 (facing page).—Sedimentary features in loess (loc. 128). 

A, Loess deposits before smoothing and brushing, left, and after, 

right. B,Scour-and-fill features in loess (numbers on scale in centimeters). C, Low-index ripples in sandy loess. D, Scour feature 

along base of sand intercalated in loess. Textural analyses for a 

sand sample within a loess sequence and loess sample subjacent 

to the sand in D. Cumulative frequency curves were recalculated 

on the sand fraction if either gravel or pan fraction was greater 

than five percent.

permeability whereas a medium sand bed 5.1 cm below 

had 6.6-D permeability. Although the internal permeability contrasts initially seemed of little importance, 

their influence on the development of secondary structures was recognized later. The finer grained, less 

permeable layers were the first to develop dissipation 

structures, as discussed in a preceding section. The differential cementation of laminae observed in eolianites 

may relate to these initial permeability (and 

presumably porosity) contrasts.

LOESS DEPOSITS

The stratigraphic relationship of the loess sequence 

to the eolian deposits in the Sand Hills (fig. 1) was 

determined in a subsidiary study. After a summer of 

field investigations, an aerial reconnaissance showed 

the closest proximity of dune and loess deposits to be 

in the vicinity of Arnold, Nebraska, in Custer and 

Logan Counties. Subsequent field investigations of 

these areas indicate that the dunes overlie the eroded 

remnants of the loess. For example, dunes occur in the 

valley below the cliffs of the loess hills northwest of 

Arnold and also on top of the cliffs (fig. 3, section 

D-D1). Whereas datable material to relate the two was 

not available, the only evidence that directly related 

the loess and eolian deposits was the presence of sands 

intercalated within the loess section. Lugn (1935,1960, 

1962, 1968), Wehrman (1961), and Reed and Dreeszen 

(1965) considered these sands to be eolian, and assigned these deposits to the Peorian Loess and Peorian 

Dunesand and the Bignell Loess and Bignell Dunesand.

Although loess has generally been described as 

structureless, we observed loess in this area with both 

large- and small-scale sedimentary structures intercalated with sequences of structureless loess. Largescale laminations inclined as much as 10° with an apparent dip to the south were in loess at localities 120, 

128, 129 in Custer and Logan Counties. After scraping 

an outcrop with a machete and then brushing it with a 

soft-bristled paint brush, numerous small-scale structures were apparent (fig. 17A). Small-scale structures such as high-amplitude ripples (fig. 11B), scourand-fill structures with well-preserved foresets (fig. 

17C), parallel to discontinuous wavy nonparallel 

laminae, and small-scale channel-fill structures were 

present. Structureless loess occurred at many localities 

where burrows and dikaka (oxidized root tubules) had 

destroyed primary bedding. Mollusks were present in 

such sequences as further described by Frye, Willman, 

and Glass (1968) and Frankel (1957a, b).

Sands intercalated in the loess may reflect only locally reworked deposits; but, where we observed them,
22 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

they are not eolian deposits and are most probably 

fluvial deposits. The scour along the base of one such 

sand bed is shown in figure 17D (note the local relief 

and abrupt textural change at the loess-sand contact). 

Within the sand deposits are small-scale structures 

that confirm a subaqueous origin. Figure 17D shows a 

channel, which is locally filled with trough crossbedding and contains high-amplitude ripples (fig. 17C). 

The sands grade vertically upward into loess with intercalated sand and loess, and above these only loess 

(fig. 17£>). The correlation of such sands within the 

loess sequence is difficult, as is illustrated in figure 18 

where three test holes extend through a loess section 

(Section E-E1). Sand occurrence is sporadic and 

therefore suggestive of channel-sand development.

Lugn (1968) and Wehrman (1961) suggested that 

loess and dune deposits were intercalated. However, 

our observations in Logan and Custer Counties suggest that younger dune sand unconformably overlies 

loess deposits: (1) sedimentary structures in loess outcrops in the Arnold area (Logan and Custer Counties) 

demonstrate that those sands intercalated in the loess 

were deposited in a subaqueous, not subaerial, environment; (2) sand dunes override the eroded loess 

topography in the Arnold area; (3) a twofold 

stratigraphy in the dune sand cannot be traced laterally through the Sand Hills, as evidenced by analysis 

of test- hole data (figs. 3, 18). A similar relationship of 

younger dune sand mantling loess deposits that are 

"remarkably free of interbedded dune sand" is noted 

by Brice (1964, p. D9) in the Brewster area (Blaine 

County). He further noted that dune sand overlies 

valley fill of Peoria (Illinoian) age. We suggest that 

Lugn's (1935) original term for the dune sand in the 

Sand Hills, the Sand Hills Formation, be used 

(although not adopted by the U.S. Geological Survey2 ) 

until the problems just mentioned are resolved.

2Since this paper was originally completed in 1976, new radiometric age determinations of 

sediment beneath the Sand Hills Formation by University of Nebraska personnel confirm a 

Holocene age for the Sand Hills (James B. Swinehart II, oral commun., 1978).

NORTH

E ELEVATION 819.5 m 

TEST HOLE 10-B-70

METERS 

0

10-

20 H

30-

40-

50-

60 J

E-LOG, IN OHMS

'———40 80

LITHOLOGY

Resistivity 

curve

Fluvial

gravels and

sands

ELEVATION 826.8 m

TEST HOLE 11-B-70

E-LOG, IN OHMS LITHOLOGY

80

Fluvial

gravels and

sands

19.3 KILOMETERS

-5-0*

, b -o

a °:

o- o

SOUTH

ELEVATION 887.8 m E' 

TEST HOLE 12-B-70

E-LOG, IN OHMS LITHOLOGY —r~ 

40

—r

80

Peoria 

Loess

Sand

Sandy 

loess

Loveland 

Loess

Sand

6.4 KILOMETERS

GROUND LEVEL

,Gilman Canyon

Sand and gravel

EXPLANATION

'^T^C' Silt ZErZ-^El Clay

FIGURE 18.—Cross-section^-E'(see fig. 1) showing loess deposits (Illinoian Loveland Loess and Wisconsin Peoria Loess) along

the southeastern margin of the Sand Hills.
EOLIAN DEPOSITS 23

ACKNOWLEDGMENTS

Textural analyses were graciously provided by R. J. 

Moiola and W. Phillips of Mobil Research and 

Development Corporation. This paper was improved 

by the careful reviews of James B. Swinehart II and 

Vincent H. Dreeszen of the Conservation and Survey 

Division of the University of Nebraska, Ray Bentall, 

and Edwin D. McKee of the U.S. Geological Survey, 

and James R. Steidtmann of the University of Wyoming. The director and staffs of the Nebraska 

Geological Survey and the Conservation and Survey 

Division of the University of Nebraska were most 

helpful during all phases of this study.

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39-57.

____1975, Comparison of textures and structures to distinguish 

eolian environments, Killpecker dune field, Wyoming: Mtn. 

Geologist, v. 12, no. 2, p. 61-73.

Anderson, E. N., and Walker, E. R., 1920, An ecological study of 

the algae of some Sand Hills lakes: Am. Microscop. Soc. Trans., 

v. 39, p. 51-85.

Bagnold, R. A., 1941, The physics of blown sand and desert dunes: 

Methuen & Co., London, 265 p.

Bigarella, J. J.,1975, Lagoa dune field, State of Santa Catarina, 

Brazil—A model of eolian arid pluvial activity, in International 

symposium on the Quaternary, southern Brazil, July 15-31, 

1975: Boletim Paranaense Geocigncias, no. 33, p. 133-167.

Bradley, Edward, and Rainwater, F. H., 1956, Geology and groundwater resources of the upper Niobrara River basin, Nebraska 

and Wyoming: U.S. Geol. Survey Water-Supply Paper 1368, 

70 p.

Brice, J. C., 1964, Channel patterns and terraces of the Loup Rivers 

in Nebraska: U.S. Geol. Survey Prof. Paper 422-D, 41 p.

Condra, G. E., 1918, Preliminary report on the potash industry of 

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Survey Bull. 8, 39 p.

___1932, The ground waters and lakes of the Sand Hills region, 

Nebraska: Nebraska Irrigation Assoc. Proc., p. 42-48.

Folk, R. L., 1968, Petrology of sedimentary rocks: Austin, Tex., 

Hemphill, 170 p.

Folk, R. L., Andrews, P. B., and Lewis, D. W., 1970, Detrital sedimentary rock classification and nomenclature for use in New 

Zealand: New Zealand Jour. Geology and Geophysics., v. 13, no. 

4, p. 937-968.

Frankel, L., 1957a, The value of Pleistocene mollusks as index fossils of Wisconsin sub-ages in Nebraska: Jour. Paleontology, v. 

31, no. 3, p. 641-647.

____1957b, Nebraska's loess deposits—grassland or woodldnd 

environment?: Jour. Paleontology, v. 32, no. 3, p. 638-639.

Fryberger, S. G., 1979, Dune forms and wind regime, in McKee, 

E. D., ed., A study of global sand seas: U.S. Geol. Survey Prof. 

Paper 1052, p. 137-169.

Frye, J. C., Willman, H. B., and Glass, H. D., 1968, Correlation 

of midwestern loesses with the glacial sequence, in Schultz, C. 

B., and Frye, J. C., eds., Loess and related eolian deposits of the 

world: Lincoln, Nebr., Nebraska Univ. Press, p. 3-22.

Harms, J. C., MacKenzie, D. B., and McCubbin, D. G., 1963, Stratification in modern sands of the Red River, Louisiana: Jour.

Geology, v. 71, noi. 5, p. 566-580. 

Hicks, W. B., 1921, The potash resources of Nebraska: U.S. Geol.

Survey Bull. 715-1, p. 125-139. 

Hunter, R. E., 1977, Basic types of stratification in small eolian

dunes: Sedimentology, v. 24, no. 3, p. 361-387. 

Keech, C. F., and Bentall, Ray, 1971, Dunes on the plains—The

Sand Hills region of Nebraska: Nebraska Univ., Conserv. and

Survey Div. Resource Rept. 4,18 p. 

Lugn, A. L., 1935, The Pleistocene geology of Nebraska: Nebraska

Geol. Survey Bull. 10, 2nd ser., 223 p. 

___1960, The origin and sources of loess in the Great Plains

in North America: Internat. Geol. Cong., 21st, Copenhagen,

1960, Rept., pt. 21, p. 223-235. 

___1962, The origin and sources of loess in the central Great

Plains and adjoining areas of the central lowland: Nebraska

Univ. Studies, new ser., no. 26, Pt. XI, 105 p. 

.1968, The origin of loesses and their relation to the Great

Plains in North America, in Schultz, C. B., and Frye, J. C., eds.,

Loess and related eolian deposits of the world: Lincoln, Nebr.,

Nebraska Univ. Press, p. 139-182. 

McKee, E. D., 1934, The Coconino Sandstone—Its history and

origin: Carnegie Inst. Washington, Pub. 440, p. 77-115. 

____1957, Primary structures in some recent sediments: Am.

Assoc. Petroleum Geologists Bull., v. 41, no. 8, p. 1704-1747. 

___1966, Structures of dunes at White Sands National Monument, New Mexico (and a comparison with structures of dunes 

from other selected areas): Sedimentology, v. 7, no. 1, Spec. 

Issue, p. 3-69.

McKee, E. D., Douglass, J. R., and Rittenhouse, Suzanne, 1971,

Deformation of lee-side laminae in eolian dunes: Geol. Soc.

America Bull., v. 82, no. 2, p. 359-378. 

McKee, E. D., and Moiola, R. J., 1975, Geometry and growth of

the White Sands dune field, New Mexico: U.S. Geol. Survey

Jour. Research, v. 3, no. 1, p. 59-66.

McKee, E. D., and Tibbetts, G. C., Jr., 1964, Primary structures of 

a seif dune and associated deposits in Libya: Jour. Sed. 

Petrology, v. 34, no. 1, p. 5-17.

Melton, F. A., 1940, A tentative classification of sand dunes—Its 

application to dune history in the southern High Plains: Jour. 

Geology, v. 48, no. 2, p. 113-174.

Picard, M. D., 1975, Facies, petrography and petroleum potential 

of Nugget Sandstone (Jurassic), southwestern Wyoming and 

northeastern Utah, in Bolyard, D. W., ed., Symposium on deep 

drilling frontiers in the central Rocky Mountains: Denver, Colo. 

Rocky Mtn. Assoc. Geol., p. 109-128.

Reed, E. C., and Dreeszen, V. H., 1965, Revision of the classification of the Pleistocene deposits of Nebraska: Nebraska Geol. 

Survey Bull. 23, 65 p.

Reiche, Parry, 1938, An analysis of cross-lamination—the Coconino 

sandstone: Jour. Geology, v. 46, no. 7, p. 905-932.

Schultz, C. B., and Frye, J. C., eds., 1968, Loess and related eolian 

deposits of the world: Lincoln, Nebr., Nebraska Univ. Press, 

345 p.

Sears, P. B., 1961, A pollen profile from the grassland province: 

Science, v. 134, no. 3495, p. 2038-2039.

Smith, H. T. U.', 1965, Dune morphology and chronology in central 

and western Nebraska: Jour. Geology, v. 73, no. 4, p. 557-578.

___1968, Nebraska dunes compared with those of North Africa 

and other regions, in Schultz, C. B. and Frye, J. C., eds., Loess 

and related eolian deposits of the world: Lincoln, Nebr., 

Nebraska Univ. Press, p. 29-47.
24 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

Stanley, K. O., and Wayne, W. J., 1972, Epeirogenic and climatic 

controls of early Pleistocene fluvial sediment dispersal in 

Nebraska: Geol. Soc. America Bull, v. 83, no. 12, p. 3675-3690.

Steen, M. O., 1961, Sand Hill Lake survey: Nebraska Game, Forestation and Parks Commission Kept, for period July 1954 to 

Dec. 31,1960.

Swinehart, J. B., 1972, Preliminary results of shallow drilling in the 

Nebraska Sand Hills: Nebraska Acad. Sci. Proc., no. 82, p. 83.

Till, Roger, 1974, Statistical methods for the earth scientist, an 

introduction: New York, John Wiley, 154 p.

Tsoar, Haim, 1978, The dynamics of longitudinal dunes: Hebrew 

University, Ph.D. thesis, 250 p.

Walker, T. R., and Harms, J. C., 1972, Eolian origin of flagstone 

beds, Lyons Sandstone (Permian), type area, Boulder County, 

Colorado, in Environments of sandstone, carbonate, and 

evaporite deposition: Mtn. Geologist, v. 9, no. 2-3, p. 279-288.

Warren, Andrew, 1968, Dune volume and trend measurements in 

the Nebraska Sand Hills [abs.]: Nebraska Acad. Sci. Proc., v. 78, 

p. 23.

Watts, W. A., and Wright, H. E., Jr., 1966, Late-Wisconsin pollen 

and seed analysis from the Nebraska Sand Hills: Ecology, v. 47, 

no. 2, p. 202-210.

Wehrman, K. C., 1961, A study of the transition zone between the 

Loess Hills and Sand Hills in central Nebraska: Nebraska Univ. 

M. S. thesis.
Paleoecology of Nonmarine Mollusca 

from some Paleointerdune Deposits 

in the Nebraska Sand Hills

By JOHN H. HANLEY

GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1120-B
CONTENTS

Page

Abstract........................................................................... 25

Introduction ....................................................................... 25

Previous work...................................................................... 25

Fauna ............................................................................. 25

Localities .......................................................................... 25

Paleoecology ....................................................................... 26

Age ............................................................................... 27

Conclusions ........................................................................ 27

Acknowledgments.................................................................. 27

References cited.................................................................... 27

ILLUSTRATIONS

[Plates follow index]

PLATES 1-2. Mollusks from paleointerdune deposits in the Nebraska Sand Hills.

TABLES

TABLE 2. Taxonomic composition of paleointerdune samples .............................................................. 26

3. Habitat indications of paleointerdune mollusks.................................................................. 27
GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE 

NEBRASKA SAND HILLS

PALEOECOLOGY OF NONMARINE MOLLUSCA FROM SOME 

PALEOINTERDUNE DEPOSITS IN THE NEBRASKA SAND HILLS

By JOHN H. HANLEY

ABSTRACT

Three assemblages of nonmarine Mollusca from paleointerdune 

deposits in the Nebraska Sand Hills inhabited shallow, quiet, 

vegetated, subpermanent or temporary, freshwater interdune 

ponds and adjacent terrestrial habitats. Analysis of factors affecting the taxonomic composition, diversity, and abundance of 

species in living assemblages of mollusks support this interpretation. The mollusks have long biostratigraphic ranges and broad 

biogeographic distributions. They fail to establish precise age relations of the faunas other than middle or late Pleistocene to 

Holocene.

INTRODUCTION

This paper documents the molluscan fauna of some 

paleointerdune deposits in the Nebraska Sand Hills 

and interprets their paleoecology. Such documentation 

is needed to clarify depositional environments within 

interdune areas that have been inadequately studied 

and are of potential economic significance (chapter A).

PREVIOUS WORK

Pleistocene and Holocene mollusks of the Great 

Plains have been studied extensively. (Taylor, 1975, includes index of genera and species and extensive 

bibliography.) Although the Quaternary mollusks of 

Nebraska have been discussed by many authors 

(Taylor, 1975, p. 14-15, summary), the mollusks of the 

Nebraska Sand Hills have not been adequately 

studied. Taylor's summary (1960, p. 42-44) of 

Holocene mollusks from 14 aquatic and terrestrial 

habitats in the Nebraska Sand Hills and adjacent High 

Plains, and his discussion (Taylor, 1960, p. 32-36; 

1966, p. 95-96) of the Sand Draw local fauna (preNebraskan?) of north-central Nebraska provide important faunal and habitat data for interpretation of 

paleointerdune mollusks.

FAUNA

Taxonomy of mollusks reported here has been 

discussed by many authors, including Herrington and 

Taylor (1958), Taylor (1960), Hibbard and Taylor 

(1960), Herrington (1962), Miller (1966), and LaRocque 

(1968, 1970). The taxonomic composition, rank abundance, and number of specimens of each species in a 

collection are summarized in table 2. The fauna is illustrated in plates 1 and 2 (following index).

LOCALITIES

Following is a summary of locality and lithologic and 

stratigraphic data for the paleontologic samples from 

interdune deposits. The distribution of localities in central and north-central Nebraska is shown in figure 1 of 

chapter A.

USGS Cenozoic locality D1116NM:

NEV4, SWV4, Sec. 19, T. 34 N., R. 39 W., Cherry County, 

Nebraska; Irwirt 15-minute quadrangle. Feldsarenite collected 

1.2 m below surface of ground from second inferred interdune 

deposit above base in a series of five inferred interdune deposits 

that are interbedded with dune sand. Locality 2 (sample NS 2) of 

Ahlbrandt and Fryberger (chapter A). The deposit yielding the 

fauna is unnamed.

USGS Cenozoic locality D1117NM:

NEW, SWW, Sec. 19, T. 34 N., R. 39 W., Cherry County, 

Nebraska; Irwin 15-minute quadrangle. Muddy sand 

feldsarenite collected 0.9 m below surface of ground from third 

inferred interdune deposit above base in a series of five inferred 

interdune deposits that are interbedded with dune sand. Locality 2 (sample NS 3) of Ahlbrandt and Fryberger (chapter A). The 

deposit yielding the fauna is unnamed and is 0.3 m 

stratigraphically above sample D1116NM.

25
26 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

USGS Cenozoic locality D1119NM:

SEW, NWy4 , Sec. 10, T. 22 N., R. 35 W., Hooker County, 

Nebraska; Dismal River 15-minute quadrangle. Clay stone collected from inferred interdune deposit which is interbedded 

with unconsolidated dune sand. Locality 71 (sample NP-7) of 

Ahlbrandt and Fryberger (chapter A). The deposit yielding the 

fauna is unnamed.

TABLE 2.—Taxonomic composition of paleointerdune samples. The 

two numbers given for each species indicate the rank abundance 

and number of specimens in a collection, respectively

USGS Cenozoic locality

D1116NM D1117NM D1119NM

5-1 

5-1

3-46 2-11 3-19

5-7

Class Bivalvia

Order Veneroida

Family Pisidiidae

Pisidium casertanum (Poli) Sphaerium sp. indet. —------

Class Gastropoda

Order Basommatophora 

Family Lymnaeidae

Stagnicola reflexa (Say) -— 

Family Planorbidae

Gyraulus circumstriatus

(Tryon)

Gyraulus parvus (Say) ———— 1-93 

Promenetus exacuous (Say) ~ 7-3 

Armiger crista (Linnaeus)—— 2-70 4-3 

Helisoma trivolvis (Say) -----— — 4-3

Family Physidae

Physa gyrina Say, form 4-8 3-10

hildrethiana Lea. 

Order Stylommatophora 

Family Succineidae

Succineal sp. indet. —---——- 6-5 3-10 4-2 

Family Pupillidae

Vertigo ovata Say ——————-- 8-1

Family Zonitidae

4-2 

1-83 1-45

2-42

Hawaiia minuscula (Binney) - 7-3

PALEOECOLOGY

Analysis of factors affecting the taxonomic composition, diversity, and abundance of Mollusca is critical in 

the interpretation of nonmarine paleoenvironments. 

Paleoecologic interpretations should be preceded by 

reconstruction of the pre- and post-burial history 

(taphonomy) of the fossil assemblage, to determine if 

the mollusks could have lived in the same habitat and 

if they were preserved in the environment in which 

they had lived (that is, whether they represent a biocoenosis or life-association). Taylor (1960, 1965) provided an excellent review of principles of paleoecologic 

interpretation of late Pliocene and Pleistocene nonmarine mollusks.

Although the taphonomy of mollusks in the 

paleointerdune samples is poorly documented, several 

factors suggest that reliable paleoecologic interpretations can be made. All taxa in table 2 are extant, have 

broad biogeographic distributions, and have been 

reported from Pleistocene and Holocene deposits in 

Nebraska. The ecologic compatibility of these living

species is well documented and suggests that the 

samples differ from molluscan biocoenoses only in the 

minor admixture of terrestrial gastropods (Succinea, 

Vertigo ovata, and Hawaiia minuscula) from adjacent 

habitats.

The habitat distributions of the mollusks are 

discussed by many authors, but are concisely summarized by Hibbard and Taylor (1960), Taylor (1960), 

and LaRocque (1968, 1970). Primarily on the basis of 

Taylor's work (1960), habitat preferences are summarized in table 3. The mollusks from the three 

paleointerdune deposits inhabited shallow, quiet, 

vegetated, subpermanent or temporary freshwater, interdune ponds. The presence of Pisidium casertanum 

and(or) Armiger crista suggests that the ponds may 

have been seasonally ephemeral. Vertigo ovata probably lived in moist leaves and humus at the margin of 

the pond. Hawaiia minuscula, which can withstand 

arid conditions, also lived adjacent to the pond but in a 

somewhat drier terrestrial habitat under leaves, logs, 

or rocks.

Aquatic pulmonate gastropods (Planorbidae, Lymnaeidae, and Physidae), which dominate the collections 

(rank abundances of taxa, table 2), are excellently 

adapted for life in local, even ephemeral, aquatic 

habitats. The mantle cavity, which normally contains 

the gills, has been modified into a pulmonary sac. The 

gills are replaced by a plexus of blood vessels in the 

roof of the pulmonary sac. Oxygen may pass into the 

sac through a single opening, the pneumostome. 

Physidae and Lymnaeidae come to the surface and obtain atmospheric oxygen by bringing the pneumostome into contact with the air-water interface. 

This trait is advantageous in allowing them to tolerate 

reduced oxygen concentration in their aquatic habitat. 

Lymnaeid gastropods can also breathe oxygen directly 

from the water through their skins by a process termed 

cutaneous respiration. Planorbidae also exhibit a 

secondary, external gill termed the pseudobranch. 

These gastropods are able to respire subaqueously 

using their false gills.

Aquatic pulmonates often exhibit remarkable 

tolerance to environmental stress, such as desiccation 

of their aquatic habitat (for example, Helisoma 

trivolvis). Many are able to reduce their metabolism 

and aestivate, as do terrestrial pulmonate gastropods. 

Some pisidiid bivalves (for example, Pisidium casertanum) are also able to withstand desiccation of their 

habitat by burrowing into moist sediment, often 

beneath stones. Their ovoviviparity promotes survival 

of offspring in that the young are released from the 

parent as fully developed juvenile bivalves.

High-dispersal potential of aquatic pulmonates and 

pisidiids promotes rapid colonization of local habitats.
PALEOECOLOGY OF NONMARINE MOLLUSCA FROM SOME PALEOINTERDUNE DEPOSITS 27

TABLE 3.—Habitat indications of paleointerdune mollusks, and comparison with a portion of the Sand Draw local fauna and Holocene

mollusks from northern Nebraska, based on Taylor (1960, p. 36)

Occurrence

Habitat

Permanent to temporary water 

Permanent or subpermanent ——————

Temporary pond or marginal pool — — — —

Species 

I

Promenetus exacuous -—————-——

...... {jryrctitlus circu,m<imlu>s ••• ----•~TM~TM»— ---

.. ... f\unig@r cnsta «•— ------- - —«««..—«««•— ... 

Pisidium casertanum —— — — —— ——

USGS Cenozoiclocality

D1116NM

X 

X 

X 

X 

X 

X

X 

X

X

D1117NM

X

X 

X 

X 

X

X

D1119NM

X 

X

X 

X 

X

X 

X

Sand Draw 

local fauna

X 

X X1

X 

X 

X 

X 

X

Recent

X 

X 

X 

X 

X

X 

X 

X 

X 

X 

X

(1960) recognizes Stagnicola cf. S. reflexa in the Sand Draw local fauna.

Aquatic pulmonates typically lay their eggs on shallow 

aquatic vegetation, thereby increasing the chance of 

aerial dispersal on the legs of water birds (Rees, 1965). 

Pisidiids are known to be locally dispersed by insects 

(Fernando, 1954; Rees, 1965). The abundance of aquatic pulmonates in the presumed interdune pond habitat 

is enhanced by their hermaphroditic reproduction.

AGE

Table 3 illustrates the similarity between the 

paleointerdune faunas, a portion of the Sand Draw 

local fauna, and Holocene mollusks reported from 

northern Nebraska by Taylor (1960). Helisoma 

trivolvis, Promenetus exacuous, Gyraulus circumstriatus, and Armiger crista are unknown in 

deposits as old as the Sand Draw local fauna (preNebraskan?) in North America.

The paleointerdune mollusks are all extant and have 

long biostratigraphic ranges and broad biogeographic 

distributions. They are of little utility in determining 

precise age relations of the paleointerdune deposits, as 

summarized below:

USGS Cenozoic locality D1116NM: The presence of Promenetus 

exacuous (equivalent to P. exacuous form exacuous of Miller, 

1966, p. 233-235) suggests that this fauna is late Pleistocene (IIlinoian) to Holocene in age.

USGS Cenozoic locality D1117NM: Armiger crista is unknown in 

North America in deposits older than middle Pleistocene (Hibbard and Taylor, 1960). This fauna is middle Pleistocene to 

Holocene in age.

USGS Cenozoic locality D1119NM: Gyraulus circumstriatus is 

unknown in deposits older than middle Pleistocene (Kansan) 

(Hibbard and Taylor, 1960). G. circumstriatus in association 

with Armiger crista suggests that this fauna is of middle 

Pleistocene (Kansan) to Holocene age. The deposit yielding this 

fauna is C14 dated at 500±200 years B.P. (before the present) 

(USGS Sample No. W-185).

CONCLUSIONS

Three assemblages of nonmarine Mollusca from 

paleointerdune deposits in the Nebraska Sand Hills inhabited shallow, quiet, vegetated, subpermanent or 

temporary freshwater interdune ponds and adjacent 

terrestrial habitats. Ecology and adaptations of living 

representatives of these species support this interpretation. The mollusks have long biostratigraphic 

ranges and fail to establish precise age relations of the 

faunas.

ACKNOWLEDGMENTS

Thomas S. Ahlbrandt and Bruce R. Wardlaw reviewed the manuscript and offered suggestions for its 

improvement. Leonard A. Wilson, Robert O'Donnell, 

and Robert E. Burkholder assisted in photography of 

mollusks. I am especially grateful to Aurele LaRocque, 

Ohio State University, who examined gastropods and 

provided insight into problems of molluscan taxonomy 

and paleoecology. However, the responsibility for taxonomy of the mollusks and paleoecologic interpretation rests solely with the author.

REFERENCES CITED

Fernando, C. H., 1954, The possible dispersal of Pisidium by 

Corixidae (Hemiptera): Jour. Conch., v. 24, p. 17-19.

Herrington, H. B., 1962, A revision of the Sphaeriidae of North 

America (Mollusca; Pelecypoda): Michigan Univ. Mus. Zoology 

Misc. Pub. 118, 74 p.

Herrington, H. B., and Taylor, D. W., 1958, Pliocene and Pleistocene Sphaeriidae (Pelecypoda) from the central United States: 

Michigan Univ. Mus. Zoology Occasional Paper 596, 28 p. \

Hibbard, C. W., and Taylor, D. W., 1960, Two late Pleistocene 

faunas from southwestern Kansas: Michigan Univ. Mus. 

Paleontology Contr., v. 16, no. 1, 223 p.
28 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

LaRocque, Aurele, 1968, Pleistocene Mollusca of Ohio: Ohio Div. 

Geol. Survey Bull. 62, pt. 3 (of 4 parts), p. 357-553.

___1970, Pleistocene Mollusca of Ohio: Ohio Div. Geol. Survey 

Bull. 62, pt. 4 (of 4 parts), p. 555-800.

Miller, B. B., 1966, Five Illinoian molluscan faunas from the southern Great Plains: Malacologia, v. 4, no. 1, p. 173-260.

Rees, W. J., 1965, The aerial dispersal of Mollusca: Malacological

Soc. London, Proc., v. 36, p. 269-282. 

Taylor, D. W., 1960, Late Cenozoic molluscan faunas from the High

Plains: U.S. Geol. Survey Prof. Paper 337, 94 p.

_1965, The study of Pleistocene nonmarine mollusks in North 

America, in Wright, H. E., Jr., and Frey, D. G., eds., The 

Quaternary of the United States: Princeton, N.J., Princeton 

Univ. Press, p. 597-611.

_1966, Summary of North American Blancan nonmarine 

mollusks: Malacologia v. 4, no. 1, p. 1-172.

_1975, Index and bibliography of late Cenozoic freshwater 

Mollusca of western North America: Michigan Univ. Papers on 

Paleontology 10, 384 p.
Late Quaternary Vegetation History 

of the Central Great Plains and its 

Relationship to Eolian Processes 

in the Nebraska Sand Hills

By J. PLATT BRADBURY

GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1120-C
CONTENTS

Page

Abstract............................................................................ 29

Introduction ....................................................................... 29

Late Pleistocene and Holocene vegetation history of the Great Plains ................... 29

Paleoecological records from the Sand Hills ........................................... 30

Discussion ......................................................................... 34

References cited.................................................................... 35

ILLUSTRATIONS

FIGURE 19. Index maps of the Great Plains and the Nebraska Sand Hills........................................................ 31

20. Selected pollen profiles from sites near the Nebraska Sand Hills..................................................... 32

21. Map of prairie vegetation versus rainfall in drought years .......................................................... 33

22. Pollen profile from Hackberry Lake ............................................................................... 33

TABLES

Page

TABLE 4. Paleoecologic analysis of pond deposits ........................................................................... 34
GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE 

NEBRASKA SAND HILLS

LATE QUATERNARY VEGETATION HISTORY OF THE

CENTRAL GREAT PLAINS AND ITS RELATIONSHIP TO EOLIAN PROCESSES

IN THE NEBRASKA SAND HILLS

By J. PLATT BRADBURY

ABSTRACT

A review of the vegetation history of the Great Plains during the 

late Pleistocene indicates that boreal coniferous forests containing 

substantial amounts of spruce (Picea) surrounded the Nebraska 

Sand Hills. Probably similar vegetation existed in the Sand Hills as 

well. The eolian mechanisms that produced the present Sand Hills 

topography could not operate compatibly with forest vegetation, 

and it is hypothesized that the latest major epoch of sand dune formation occurred after the forests left, in the middle Holocene. 

Perhaps this eolian activity coincided with the Altithermal, a warm 

and dry period between 8,000 and 4,000 years B.P. (before the present) that is recorded in pollen records of the eastern Great Plains. 

C14 dates in the Sand Hills suggest that sand movement and deposition occurred in different areas at different times, and that the dune 

field has a complex history.

INTRODUCTION

The environmental history of the Nebraska Sand 

Hills (fig. 19) can be considered from two viewpoints. 

The first involves the eolian processes that 

transported and deposited the sand across northern 

Nebraska, and the second concerns the biological environments that existed during and after the time of 

dune deposition. To a large extent, the geomorphology, 

internal structure, thickness and distribution of the 

eolian deposits provide the most relevant information 

about the nature of the processes involved in sand 

deposition. However, information about the absolute 

timing of such events must come from biological 

materials synchronously deposited within the dunes 

that can be radiocarbon dated, or from dated fossil 

sequences near the dune fields that suggest paleoenvironments appropriate to eolian deposition. Traditionally, pollen sequences from lake sediments and 

fossil molluscan faunas in loess and pond muds provide biological evidence for paleoecological analysis of

these environments, and thus form the basis for dating 

by correlation. Unfortunately, Pleistocene and 

Holocene environments are not well studied in the 

Sand Hills or in the areas immediately surrounding 

them, and ecological inferences and correlations suffer 

because of the great distances that separate the Sand 

Hills from better known regions in the eastern and 

southern portions of the Great Plains. A compounding 

problem is that the paleoecological records, especially 

for pollen, are mostly restricted to late Wisconsin and 

Holocene times, whereas the Sand Hills dune deposits 

perhaps extend to the early Wisconsin (Smith, 1965), 

or medial Wisconsin (Reed and Dreeszen, 1965). A 

brief review of relevant late Wisconsin and Holocene 

paleoecology will, nevertheless, provide a framework 

in which Sand Hills paleoenvironments can be studied. 

The paleoecological discussion deals with eight sites 

within the Sand Hills—Rosebud, Swan Lake, Hackberry Lake, the North Loup River peat deposits, and 

four pond deposits associated with sand dunes or 

alluvium in Hooker, Cherry, and Thomas Counties, 

Nebraska (fig. 19). A regional vegetation history is 

derived from pollen sites in South Dakota, Minnesota, 

Iowa, Kansas, Missouri, Nebraska, and Texas.

LATE PLEISTOCENE AND HOLOCENE 

VEGETATION HISTORY 

OF THE GREAT PLAINS

Late Pleistocene vegetation records derived from 

pollen analysis of lake and bog sediments in the central 

Great Plains (fig. 19) indicate that at the close of the 

Wisconsin glacial maximum (about 12,000 years ago) 

boreal forests covered much of the area. The sediment 

records contain as much as 80 percent spruce (Picea}

29
30 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

pollen (fig. 20) and, because most authorities 

acknowledge that only very small quantities of spruce 

pollen are subject to long distance transport, closed 

spruce forests are thought to have occurred during this 

time in southern Minnesota (Jelgersma, 1962; Waddington, 1969), southern South Dakota (Watts and 

Bright, 1968; Watts and Wright, 1966), northeastern 

Kansas (Gruger, 1973), west-central Missouri (King 

and Lindsay, 1976), and northwestern Iowa (Van Zant, 

1976). Even values of 10-15 percent spruce pollen, 

which occur in the late Wisconsin pollen records at 

Vigo Park of the Llano Estacado, Texas (fig. 19), reflect 

a substantial colonization of spruce in the immediate 

area (Oldfield and Schoenwetter, 1975).

With the close of the Pleistocene, the spruce forests 

retreated northward. They disappeared from Kansas 

(Gruger, 1973), and, presumably, also from Missouri 

(King and Lindsay, 1976), about 12,000 years ago, and 

left South Dakota and southern Minnesota about 

10,000 years ago (Jelgersma, 1962; Watts and Bright, 

1968; Waddington, 1969). To the east (Kansas, Minnesota, and Iowa), the boreal forests were replaced by 

deciduous forests (Gruger, 1973; Jelgersma, 1962; Van 

Zant, 1976), while on the Llano Estacado, pine forests 

persisted after spruce disappeared (Oldfield and 

Schoenwetter, 1975). The boreal spruce forest of 

Manitoba, near the northern edge of the Great Plains 

was replaced about 9,500 years ago directly by prairie 

vegetation (Wright, 1970).

The warming trend that was responsible for the 

deterioration of the boreal forests and their replacement by thermophilous forests of deciduous trees and 

pine continued into the early Holocene. Between 8,000 

and 4,000 years ago prairie vegetation expanded 

eastward into southern Minnesota and Iowa (Wright, 

1968; Van Zant, 1976). A shrunken remnant of this expansion exists today—the so-called Prairie Peninsula—(fig. 21), which corresponds geographically with 

the position of a mass of dry western air that lies between areas of heavy winter precipitation to the northeast and to the southeast. When this air is not displaced during the summer by moist Gulf of Mexico air 

masses moving northward, drought conditions follow, 

and summer precipitation deficiencies increase to the 

west (fig. 21) (Wright, 1968). The eastward expansion of 

prairie vegetation 8,000 to 4,000 years ago—the middle Holocene xeric interval—climaxed about 7,000 

years ago, and it probably correlates with an increase 

in the number and intensity of summer droughts 

(Wright, 1968). Establishment of modern vegetation in 

the Great Plains began about 4,000 years ago.

PALEOECOLOGICAL RECORDS FROM 

THE SAND HILLS

Rosebud is the only site within the Sand Hills that 

provides a pollen record of late Pleistocene vegetation. 

The Rosebud site is near the northern edge of the Sand 

Hills on the Nebraska-South Dakota border at about 

101° W. longitude (fig. 19). The pollen and plant 

macrofossil records from this site indicate that a 

boreal spruce forest existed at that location about 

12,600 years ago, and that soon after that time a pine 

forest and then prairie vegetation rapidly replaced the 

spruce (Watts and Wright, 1966, fig. 20). Seeds and 

leaves of aquatic macrophy tes at the Rosebud site suggest that a fresh, open-water basin existed when 

spruce was prevalent, and that conditions changed to a 

species-poor, alkaline reed swamp with the change to 

prairie vegetation. This vegetation and limnologic 

history implies a change from cooler, probably 

somewhat moister climates to one of increased aridity 

and higher temperatures that characterizes the Sand 

Hills today. The pollen record of prairie vegetation at 

Rosebud does not significantly differ from that of 

modern surface samples in this area (Watts and 

Wright, 1966).

Subsequent vegetation history at Rosebud is difficult to interpret because the upper sediments lack 

pollen and do not provide a continuous record. The 

rapid disappearance of spruce pollen and its immediate 

replacement by pollen of pine and prairie herbs (fig. 20) 

suggest a depositional hiatus, although apparently no 

other stratigraphic or chronologic evidence supports 

this. All that is clear is that prairie vegetation existed 

sometime after 12,600 years ago, and that the lake 

subsequently dried up and either the upper pollenbearing sediments were destroyed, or intermittent 

fluvial deposition with poor pollen preservation occurred.

FIGURE 19 (facing page).—Index maps of the north-central Great 

Plains (A) and the Nebraska Sand Hills (shaded, B). Site localities 

(A): Pi, Pickerel Lake; Ma, Madelia; Rb, Rosebud; WO, West Lake 

Okoboji; Mus, Muskotah; BS, Boney Spring; and VP, Vigo Park. 

Localities in the Nebraska Sand Hills include deposits (NP-4, 

NP-7, NS-2, and NS-3), pollen sites (Hackberry Lake and 

Rosebud), and organic deposits (Swan Lake and North Loup 

River peat deposit). The pond deposits correspond to the following study localities of Ahlbrandt and Fryberger, chapter A, fig. 1: 

NS-2, loc. 2; NS-3, loc. 3, NP-4, loc. 32; and NP-7, loc. F1. The 

figures on the Nebraska Sand Hills sites indicate the radiocarbon 

age, in years, at the base of the deposit. A is modified from Wright 

(1970), and B from Keech and Bentall (1971).
VEGETATION HISTORY AND ITS RELATIONSHIP TO EOLI AN PROCESSES 31

niferous

NORTH DAKOTA

SOUTH DAKOTA

Black

ROSEBUD / / 

12,600 101° '

SOUTH DAKOTA

Area of

poor drainage

and alkali

lakes 

Box Butte

Alliance •

': NP-7 Dismal ' */ ."./BOO

ORTH 4.0UP

RIVER PEAT

DEPOSIT

8400
32 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

Herb or nonarboreal pollen 

Madelia, Minn. (Jelgersma,1962)

years B. P. 

9300 —

1 11,250 — 

12,650 —

n

h—n |—n Hi—i

Pickerel, S. Dak. (Watts and Bright,1968)

10,670

Rosebud, S. Dak. (Watts and Wright,1966)

I I

12,580- 

12,630-

r i

Muskotah, Kans. (Griiger, 1973)

11,3401

West Lake Okoboji, Iowa (Van Zant,1976)

9075 ——

11,800——

13,990-

F 7 I

Boney Spring, Mo. (Mehringer and others, 1968)

,13,500 ^|H III II I I II

pi I I I I I I I'll I I I Jill pi pi

D I I

T I I—I I I I i f I | f I 'I

0 20 40 60 80010010 6 20 0 20 0 20 6 20 6 20 010 010 6 20 40 60 0 20 0 20 0 20

PERCENT OF TOTAL POLLEN

FIGURE 20. _Selected pollen profiles from sites near the Nebraska Sand Hills. 1-4, 6 modified 

from Wright (1970); 5, modified from Van Zant (1976).
VEGETATION HISTORY AND ITS RELATIONSHIP TO EOLIAN PROCESSES 33

FIGURE 21.—Extent of prairie vegetation (the so-called Prairie 

Peninsula, stippled) compared to percent of normal rainfall 

in average July of major drought years. Modified from 

Wright (1968).

Another source of paleoenvironmental information 

comes from peat beds and logs, radiocarbon dated 

from 10,500±250 to 8,400±250 years B.P. (before the 

present), in valley fill associated with the North Loup 

River (fig. 19). The peat is buried by alluvium which is 

mantled by dune sand (Brice, 1964). The stratigraphic 

association of these deposits and the presence of marsh 

plants like Equisetum (horsetails) indicate that, locally, fluvial processes and riparian environments, 

similar to those that exist today, were followed by 

sand movement.

On the southwestern margin of the Sand Hills at 

Swan Lake (fig. 19), H. E. Wright has taken a core that 

has a basal radiocarbon date of about 8,000 years B.P. 

Sedimentation in Swan Lake appears to be continuous 

to the present, and preliminary pollen analyses indicate a prairie vegetation with minor fluctuations of 

herbs and grasses throughout this time (H. E. Wright, 

written commun., 1975).

A subsequent paleoecological record comes from 

Sears' (1961) pollen diagram from Hackberry Lake in 

the north-central part of the Sand Hills (fig. 19 and 22). 

A radiocarbon date indicates that organic deposition 

began at this site about 5,040 years ago, and the 

sediments also record a fluctuating dominance of

prairie vegetation .that persists to the present. The 

sand dunes that enclose the Hackberry Lake basin are 

well-preserved barchan and barchanoid-ridge dunes 

(chapter A) that indicate prevailing wind directions to 

the southeast.

Among the most recent paleoecological records in 

the Sand Hills are buried interdune organic deposits 

no longer associated with current interdune basins. A 

sample from one such deposit (NP-7, fig. 19, this 

chapter) yields a radiocarbon date of 500 ±200 years, 

and testifies to comparatively recent hydrologic 

and(or) climatic changes in the Sand Hills.

The pollen, diatom, and ostracod assemblages of 

these deposits (table 4) all contain extant species, and

POLLEN TYPES

* -

No core recovery

i i

No core recovery i i i

No core recovery

No core recovery

No core recovery

0 25 50 75 100 

PERCENT OF TOTAL POLLEN

FIGURE 22.—Pollen profile from Hackberry 

Lake, near Valentine, Nebraska. Modified 

from Sears (1961). Numbers in profile represent C14 ages of sediments in years B.P.
34 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

do not provide a firm date for the interdune and fluvial 

deposits. The pollen data suggest an arid to semiarid 

climate, but the poor preservation of the pollen grains 

demands caution in interpreting the pollen assemblage 

in terms of paleoclimate. Nevertheless, pollen from 

sample NP-7 (500±200 years B.P.) strongly resembles 

the prairie vegetation of assemblage zone R-2 of the 

Rosebud site (Watts and Wright, 1966). All the 

samples compare closely to collections of modern surface pollen near the Rosebud site (Watts and Wright, 

1966). Although sample NS-2 has a high Pinus frequency (50 percent, excluding Cyperaceae), the very 

poor preservation of pollen in this sample suggests 

that this frequency might be the result of differential 

destruction of the more delicate pollen types.

The diatom flora of samples NP-7, NS-2, and NS-3 

are moderately well preserved. The diatoms of sample 

NP-4 are badly broken and corroded. All the samples 

contain diatoms indicative of shallow, alkaline, and 

sometimes rather saline water—an environment that 

characterizes the upper part of the Rosebud core 

(Watts and Wright, 1966). NS-2 and NS-3 contain 

forms that suggest fresher and deeper water (for example, Melosira italica, and Fragilaria vaucheriae), but 

this may be the result of local hydrologic differences 

rather than climatic (temporal) differences. The admixture of brackish-water and freshwater diatoms suggests that the ponds underwent seasonal changes in 

salinity.

NP-4 is from pond sediments associated with 

alluvium stratigraphically beneath the eolian dune 

deposits. The dominance of Denticula elegans in this 

sample indicates warm, slightly shallow, brackish 

water (specific inductance of modern analogs ranges 

from 1100 to more than 4000). Although the 

stratigraphic context of the calcareous, diatombearing nodules from NP-4 has not been studied in 

detail, this diatom association would imply that arid 

environments existed during some of the time when 

fluvial processes were active in the Sand Hills region.

The ostracod fauna of NP-7, NS-2, and NS-3 has been 

identified, and ecological determinations indicate an 

environment of shallow, alkaline, freshwater ponds, 

with salinities generally under 3%o. Brackish-water 

species of the genus Limnocythere are not present, 

possibly suggesting that saline water did not persist in 

the ponds long enough for an appropriate ostracod 

fauna to establish itself.

TABLE 4.—Paleoecologic analysis of pond deposits associated with 

interdune and fluvial sediments in the Nebraska Sand Hills

JSample NP-7, Dismal River Ranch quadrangle, SE'/iNW'/i sec. 10, T. 22 N., R. 35 W., 

Hooker County. USGS Paleobotany No. D5439. Samples NS-2 and NS-3, Irwin quadrangle, SW/4 sec. 19, T. 34 N., R. 40 W., Cherry County. NS-2 is approximately 30 cm 

below NS-3. USGS Paleobotany No. D5440A and D5440B. Sample NP-4, Seneca 

quadrangle, NE'/SNE'/i sec. 20, T. 24 N., R. 30 W., Thomas County. USGS Paleobotany 

No. D5441]

Sample numbers--- —————————

Pollen types

JrlTlUS EW — " —————————————— * ———

/"^ n**nfmrm

Compositae — - — — - — — — -

Chenopodiineae — — — — -- —

Diatom dominants

Amphora ovalis v. lybica —

Anomoeoneis cos to to? - — -

Cocconeis placentula ———

Denticula elegans —————

Fragilaria vaucheriae -——

Gomphonema lanceolatum

Gomphonema spp. 

Hantzschia amphioxys -----

Melosira italica --—-——— ------

Nitzschia amphibia —— -- — -

Nitzschia frustulum -——---

Rhopalodia gibba 2--— — — —

Ostracods

r> "A v;

Dx>+sv*OTX>S»A**«*W ft «**

Potamocypris smaradina •—

NP-7 NS-2 NS-3 NP-4

Percent total pollen

16 (20)'

14 (17)'

18

3 (3.3) 1

19 (23) 1

26 (32) 1

42 (50) 1

6(7)'

16 —

18 (21) 1

18 (21) 1

Trace..

Trace..

...

—

—

—

. Barren

...

—

...

—

Percent total diatoms

3.4

7.6

2.1

4.7

...

1.3

2.9 

10.2

2.1

20.3

13.6

1.3

19.3

6.4

...

—

11.6

5.4

10.2 

1.9

16.0

7.7

1.7

0.7

4.0

3.2

5.8

4.4

30.1

2.0

1.0 

1.6

0.2

12.0

4.3

5.0

...

—

...

77.5

—

...

...

...

5.6 —

8.4

Presence (X)

X

—

-

X

X

X

-

X

X

Barren

-

'Percent calculated excluding Cyperaceae.

DISCUSSION

Ahlbrandt and Fryberger (chapter A) indicate that 

the dune forms in the main body of the Sand Hills 

(south of the Niobrara River) were deposited by winds 

blowing to the southeast. This wind direction can account for all the common dune types, and thus they envision deposition occurring within a single paleoclimatic regime, probably during one continuous 

period of time.

Although additional paleoecological data is certainly 

needed, the present information on vegetation history 

appears to place several constraints on the time of 

eolian deposition, the source of sand for the presently 

existing dunes, and the locations in which deposition 

occurred.
VEGETATION HISTORY AND ITS RELATIONSHIP TO EOLIAN PROCESSES 35

The Rosebud site, with spruce pollen and macrofossils in levels dated at 12,600 years B.P., must postdate 

an epoch of sand-dune formation, because the depositional basin containing the pollen record is formed by 

sand dunes now considerably modified by deflation 

(chapter A). A boreal spruce forest environment is not 

consistent with the deposition of barchan and 

barchanoid-ridge sand dunes. It is likely that the dunes 

enclosing the Rosebud site predate the Wisconsin maximum (about 18,000 years B.P.) because of evidence of 

boreal forests during the Wisconsin maximum completely surrounding the Sand Hills; and it seems probable that similar vegetation existed at that time in 

much of the rest of Nebraska as well.

The North Loup River peat deposits that existed between 10,500 and 8,400 years ago were probably local 

environments in both time and space which might not 

preclude approximately contemporaneous environments of eolian deposition. At a minimum these 

deposits tell us that some sand deposition occurred 

after 8,400 years ago. On the other hand, the apparently continuous 8,000-year lacustrine record from 

Swan Lake indicates that, at least locally, hydrologic 

conditions were stable and that this lake basin was not 

engulfed by moving sand dunes. These deposits, plus 

the 5,000-year limnologic history at Hackberry Lake 

and the intermittent records of lakes and ponds 

represented by buried interdune organic sediments, 

suggest that aquatic environments in the Sand Hills 

have variable histories. They persist for longer or 

shorter periods of time, and they are both preceded by 

and followed by periods of sand deposition. A major 

episode of eolian deposition that simultaneously affected the entire Sand Hills region seems quite unlikely for the past 12,000 years, and perhaps for the 

past 24,000 years.

The location of the Rosebud site also places a 

geographic constraint on sand sources. If a distant 

sand source is required, it must have been to the northwest to conform with the paleowind directions (chapter 

A). Several authors have suggested Miocene Ogallala 

Formation or the Pleistocene alluvium as sand sources 

(chapter A). However, it would seem difficult to 

transport the sand from northwest to southeast across 

the Rosebud site (and the Niobrara River) after 12,000 

years B.P. without burying these depressions, and no 

stratigraphic evidence indicates that this occurred. 

Burial and subsequent exhumation would seem unlikely. Pleistocene dunes such as those that enclose the 

Rosebud site would likely have existed south of the

Niobrara River, but fluvial activity accompanied by 

soil and forest development during the late Wisconsin 

and early Holocene could have destroyed most of the 

older dune forms and their internal structure. Much of 

the current eolian topography of the Sand Hills may 

have been established in the middle Holocene, during 

the xeric interval (8,000-4,000 B.P.) that was synchronous with the maximum expansion of prairie 

vegetation in southern Minnesota and Iowa. During 

such times, intensification of summer droughts as 

predicted by Wright (1968) could have reduced the 

dune-stabilizing prairie vegetation to such a point that 

northwesterly winds could rework deposits of preexisting eolian and fluvial sand. Some sand may have 

been added from the Niobrara River itself, if it were 

reduced to an intermittent stream at this time. This 

eolian activity, however, did not encompass the entire 

Sand Hills region. The Rosebud site persisted throughout the Holocene, although stratigraphic evidence suggests desiccation during some of this time. Perhaps the 

dunes enclosing Rosebud were partially reworked and 

modified by blowouts while active sand transport occurred south of the Niobrara River. Ground water 

moving from the Pine Ridge Escarpment toward the 

Niobrara River may have aided in the stabilization of 

the Rosebud dunes and others north of the Niobrara. 

In a similar sense, the dunes near Swan Lake may have 

been spared complete reorganization during the middle 

Holocene xeric interval because they occupy an area of 

closed drainage (fig. 19) where surface water accumulates and promotes stabilization. Sand dunes 

generally stabilize first at the upwind margins, and 

both Rosebud and Swan Lake are in appropriate locations for early sand-dune stabilization. In the central 

portion of the Sand Hills south of the Niobrara River, 

dunes reach the greatest thickness (chapter A), and 

this area probably witnessed the most intense eolian 

activity during the middle Holocene.

Additional cores and paleoecological studies in the 

Sand Hills will be necessary to test these assumptions 

and will likely provide important information about 

Pleistocene and Holocene climatic changes in the 

Great Plains.

REFERENCES CITED

Brice, J. C., 1964, Channel patterns and terraces of the Loup Rivers 

in Nebraska: U.S. Geol. Survey Prof. Paper 422-D, 41 p.

Griiger, J., 1973, Studies on the late Quaternary vegetation history 

of northeastern Kansas: Geol. Soc. America Bull., v. 84, no. 1, p. 

239-250.
36 GEOLOGIC AND PALEOECOLOGIC STUDIES OF THE NEBRASKA SAND HILLS

Jelgersma, S., 1962, A late-glacial pollen diagram from Madelia, 

south-central Minnesota: Am. Jour. Sci., v. 260, no.7, p. 

522-529.

Keech, C. F., and Bentall, R., 1971, Dunes on the plains; the Sand 

Hills region of Nebraska: Lincoln, Nebr., Nebraska Univ. Conservation and Survey Division, Resource Rept. 4,18 p.

King, J. E., and Lindsay, E. H., 1976, Late Quaternary biotic 

records from spring deposits in western Missouri, in Prehistoric 

man and his envionments, a case study in the Ozark Highland: 

New York, Academic Press, p. 63-78.

Mehringer, P. J., Jr., Schweger, C. E., Wood, W. R., and McMillan, 

R. B., 1968, Late-Pleistocene boreal forest in the Ozark Highlands?: Ecology, v. 49, no. 3, p. 567-568.

Oldfield, F., and Schoenwetter, J., 1975, Discussion of the pollen 

analytical evidence: in Wendorf, F., and Hester, J. J., eds., Late 

Pleistocene environments of the southern High Plains: N. Mex., 

Ranches de Taos, Fort Burgwin Research Center Pub. 9, 290 p.

Reed, E. C., and Dreeszen, V. H., 1965, Revision of the classification of the Pleistocene deposits of Nebraska: Nebraska Geol.

Survey Bull. 23, 65 p. 

Sears, P. B., 1961, A pollen profile from the grassland province:

Science, v. 134, no. 3495, p. 2038-2039. 

Smith, H. T. U., 1965, Dune morphology and chronology in central

and western Nebraska: Jour. Geology, v. 73, no. 4, p. 557-578. 

Van Zant, Kent, 1976, Late- and post-glacial vegetational history

of northern Iowa: Iowa Univ., Ph.D. Thesis, 197 p. 

Waddington, J. C. B., 1969, A stratigraphic record of the pollen

influx to a lake in the Big Woods of Minnesota in Schumm, S.

A., and Bradley, W. C., eds., United States contributions tc

Quaternary research: Geol. Soc. America Spec. Paper 123, p.

263-282. 

Watts, W. A., and Bright, R. C., 1968, Pollen, seed, and mollusk

analysis of a sediment core from Pickerel Lake, northeastern

South Dakota: Geol. Soc. America Bull., v. 79, no. 7, p. 855-876. 

Watts, W. A., and Wright, H. E., 1966, Late-Wisconsin pollen and

seed analysis from the Nebraska Sand Hills: Ecology, v. 47, no.

2, p. 202-210.
INDEX

A

Abstract .........................

Alliance, wind regime ............

Alluvial fans ....................

Amphora avails lybica ...........

Anomoeoneis costata ............

Aquatic macrophytes ............

Aquatic pulmonate gastropods . . .

Armiger crista ...................

Arnold ...........................

Artemisia ........................

Avalanche deposits ..............

B

depth .................. 

dip ..........................

topset deposits ............... 

wind erosion ................. 

Boreal forests ....................

Brewster .........................

C

Clay .............................

Cvoridopsis vidua ...............

Page 

.......... 1, 25, 29

.......... 8, 9

.......... 34

.......... 7

.......... 17

.......... 7

.......... 19

.......... 34

.......... 34

........... 34

.......... 34

.......... 30

.......... 26

...... 26, 27; pi. 2

..........6,21,22

.......... 34

.......... 9

.......... 9

oo 07 qc

.......... 2 

.......... 2

.......... 5 

.......... 8

.......... 9 

.......... 19 

.......... 29, 30

.......... 13

.......... 22

.......... 34

.......... 34

.......... 34

...... 26, 27; pi. 2

.......... 34

.......... 8, 29

.......... 15

.......... 21

...... 26, 27; pi. 1

........ 13, 19, 21

.......... 13,21

3

,

.......... 34

...... 26, 27; pi 2

.......... 17

3

C O1 00

34

.......... 34

D

.

D 1 m t

Dikaka ........................

Dismal River ..................

Dissipation structures ..........

Dome dunes ...................

topset deposits .............

Drift potential .................

Dunes, barchan ................

dip ....................

slipface deposits .......

barchanoid-ridge ...........

slipface deposits .......

blowout ....................

cross-bed sets ..........

depth ..................

topset deposits .........

wind erosion ...........

dome ......................

topset deposits .........

en echelon barchan ........ 

heights ....................

longitudinal ...............

wind erosion ...........

E

exacuous, Promenetus ..........

Page

............ 8, 9

............ 9

5

1 o ic i Q qq

1 ^

............ 21

8 Q 1 Q 91

8 Q 1 Q 91

1 Q

............ 15

............ 13,21

............ 1,5,9

.......... 13, 15, 19

........... 4

............ 9

............ 7

.....3,5,6,7,33,35

............ 8

............ 9

............3, 33, 35

............ 9

............ 3, 5, 7

............ 10

............ 5

............ 9

............ 19

............ 4

........... 9

............ 3, 6, 9 

............ 3

............ 4 

............ 3, 5, 8

............ 10

............ 9

............ 19

............ 3

............ 4

............ 4

............ 5

............ 3

............ 3, 4

. ....... 3, 5, 6, 7

............ 8

............ 9

............ 2, 21

............ 2, 21

............ 34

............ 1

............ 3, 6, 9

............ 29

............ 34

............ 33

............ 19

............ 19

............ 35

........ 26, 27; pi. 1

F Page

Faults ..................................... 13

Fauna, molluscan .......................... 25

ostracod ............................... 34

paleointerdune, age .................... 27

Feldsarenite ............................... 21

Feldspar................................... 21

Flora, diatom .............................. 34

Fluvial deposits............................ 22

Forests .................................... 29, 30

Formation, Bignell......................... 2

Green River............................ 17

Ogallala ............................... 2, 5, 35

Peoria ................................. 2

Sand Hills ............................. 2, 22

Fragilaria vaucheriae ...................... 34

frustulum, Nitzschia ....................... 34

G

Gastropods, aquatic pulmonate.

terrestrial..................

gibba, Rhopalodia .............

Glacial maximum, Wisconsin .. 

Gomphonema lanceolatum .....

spp. .......................

Gramineae.....................

Great Plains, environment .....

mollusks...................

Green River Formation ........

Groundwater ..................

26

26

34

29

34

34

34

29

25

17

35

Gyraulus circumstriatus ............... 26, 27; pi. 1

parvus ............................. 26, 27; pi. 1

gyrina, Physa ......................... 26, 27; pi. 2

H

Habitat distributions....................... 26

Hackberry Lake ........................... 33, 35

Hantzschia amphioxys..................... 34

Hawana minuscula .................... 26, 27; pi. 2

Heights, dune.............................. 3

Helisoma trivolvis ..................... 26, 27; pi. 1

High Plains, Holocene mollusks ............ 25

hildrethiana, Physa ........................ 26; pi. 2

History, environmental .................... 29

Hooker County ............................ 5, 29

organic interdune deposit .............. 15

Hydrocarbons ............................. 17

I, J, K

Interdune deposits .................. 5, 13, 15, 19, 33

localities............................... 25

thickness .............................. 15

Interdune ponds ......................... 19, 26, 27

Introduction ............................... 1, 25, 29

Iowa, northwestern, spruce pollen .......... 30

prairie vegetation ...................... 35

italica, Melosira ........................... 34

Jesse Lake, interdune deposits .....

Kansas, northeastern, spruce pollen 

Krause Lake, interdune deposits....

15

30

15

37
38 INDEX

L Page

lactea, Candona ........................... 34

Lakes, alkaline ............................ 2

freshwater ............................. 2

Laminae................................ 7, 9, 15, 21

ripple .................................. 13

lanceolatum, Gomphonema ................ 34

Limnocythere.............................. 34

Linear dunes .............................. 3, 6

Location ................................... 1

Loess ...................................... 2, 5, 21

Bignell ................................ 2, 21

Peoria ................................. 2, 21

Logan County .............................5, 21, 22

Longitudinal dunes ........................ 4

lybica, Amphora oualis .................... 34

Lymnaeidae ............................... 26

Macrofossils ............................... 35

Macrophytes, aquatic ...................... 30

Manitoba, boreal spruce forests ............ 30

Melosira italica ............................ 34

Merritt Reservoir .......................... 8, 13

Middle Loup River ......................... 1, 5, 9

Minnesota, southern, prairie vegetation .... 35

spruce pollen .......................... 30

minuscula, Hawaiia.................... 26, 27; pi. 2

Missouri, west-central, spruce pollen........ 30

Mollusks................................... 21

habitat distributions ................... 26

Holocene .............................. 27

Great Plains ....................... 25

High Plains ....................... 25

Sand Draw ........................ 25

nonmarine............................. 26

paleointerdune......................... 27

taphonomy ............................ 26

taxonomy.............................. 25

Montmorillonite ........................... 13, 21

Montmorillonite-illite ...................... 15

Morphology, dune.......................... 2, 5, 8

N, O

Niobrara River ............................ 9, 35

Nitzschia amphibia ........................ 34

frustulum .............................. 34

North Loup River .......................... 1, 5, 9

peat deposits........................... 33, 35

North Platte River ......................... 6, 9

Nugget Sandstone ......................... 17

Ogallala Formation ........................ 2,5,35

oualis lybica, Amphora .................... 34

ovata. Vertigo ......................... 26, 27; pi. 2

P Page

Paleoecology............................... 26

Paleointerdune deposits .................... 25, 26

Paleointerdune fauna, age ................. 27

Paleointerdune mollusks ................... 27

Parabolic dunes............................ 3, 5, 8

cross-bed sets .......................... 10

topset deposits ......................... 9

wind erosion ........................... 19

paruus, Gyraulus ...................... 26, 27; pi. 1

patzcuaro, Candona........................ 34

Peat deposits .............................. 33, 35

Peoria dunesand ........................... 2, 21

Peoria Formation .......................... 2

Peoria Loess ............................... 2, 21

Permeability............................... 21

Petrography ............................... 19

Physa gyrina .......................... 26, 27; pi. 2

hildrethiana ........................... 26; pi. 2

Physidae .................................. 26

Picea ...................................... 29

Pine forests ................................ 30

Pine Ridge Escarpment .................... 35

Pineview Field ............................. 17

Pinus ...................................... 34

Pisidiid bivalves ........................... 26

Pisidium casertanum .................. 26, 27; pi. 2

placentula, Cocconeis ...................... 34

Plagioclase ................................ 21

Planorbidae ............................... 26

Plants, marsh ............................. 33

Pollen ..................................... 30, 34

spruce ................................. 29, 35

Ponds, alkaline ............................ 2

freshwater .............................2, 26, 27

interdune ............................ 19, 26, 27

faunal analysis .................... 2

floral analysis ..................... 2

Potash..................................... 2, 15

Prairie peninsula .......................... 30

Prairie vegetation ..................... 30, 33, 34, 35

Precipitation ............................... 1, 17, 19

Promenetus exacuous .................. 26, 27; pi. 1

Pyrolysis products ......................... 17

Q, R

Quartz. 21

reflexa, Stagnicola ..................... 26, 27; pi. 2

Rhopalodia gibba .......................... 34

Ripples .................................. 13, 15, 21

Rock fragments ............................ 21

Rosebud ................................... 30, 35

Sand Draw, Holocene mollusks. 

local fauna, age............

Page

Sand Hills Formation ...................... 2, 22

Sand layers, frozen ........................ 13

Sand roses ................................. 7

Sand transport directions .................. 5, 6

Sandstone, nugget ......................... 17

Sedimentary structures .................... 8

Series I dunes.............................. 4

Series II dunes............................. 4

Series III dunes ............................ 5

Sheridan County........................... 15

Silt ........................................ 13, 19

Simple dunes .............................. 3

Slipface deposits ........................ 8, 9, 19, 21

Slumping .................................. 19

Snake River ............................... 1, 9

South Dakota, southern, spruce pollen ...... 30

Sphaerium sp. ............................. 26, 27

Spruce forests.............................. 30

Spruce pollen .............................. 29, 35

Stagnicola reflexa ..................... 26, 27; pi. 2

Succinea sp. ........................... 26, 27; pi. 2

Swan Lake ................................ 3,3, 35

Taphonomy, mollusks...................... 26

Temperature ............................... 1

Texas, Llano Estacado, spruce pollen....... 30

Thermophilous forests ..................... 30

Topset deposits ......................... 8, 9, 19, 21

Transport, sand............................ 7

Transport, wind ........................... 7

Transverse dunes .......................... 3, 4, 7

Transverse-ridge dunes .................... 3, 5, 6

dip .................................... 8

slipface deposits ....................... 9

triuolvis, Helisoma ..................... 26, 27; pi. 1

Trough cross-bed sets ...................... 10

vaucheriae, Fragilaria ..................... 34

Vegetation................................. 8, 30

prairie ............................ 30, 33, 34, 35

records ................................ 29

Vertigo ovata .......................... 26, 27; pi. 2

vidua, Cypridopsis ......................... 34

Virgo Park, spruce pollen .................. 30

W, Y

Water erosion . Wind erosion . Wind regime ., 

Wyoming .....

Yardangs .
PLATES 1 AND 2
PLATE 1

FIGURES 1-3. Helisoma trivolvis (Say).

Right side, left side, apertural view, USNM1 210232, USGS Loc. D1117NM, X4. 

4-6. Gyraulus circumstriatus (Tryon).

Right side, apertural view (note apertural callus), left side, USNM 210233, USGS Loc. D1116NM, X10. 

7-9. Promenetus exacuous (Say).

Right side, apertural view, left side, USNM 210234, USGS Loc. D1116NM, X10. 

10-12. Gyraulus parvus (Say).

Right side, apertural view, left side, USNM 210235, USGS Loc. D1116NM, X 10.

'USNM, United States National Museum, in Washington, D.C., where specimens are deposited.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1120-B PLATE 1

HELISOMA, GYRAULUS, AND PROMENETUS
PLATE 2

FIGURES 1-2. Pisidium casertanum (Poll).

Internal and external views of right valve, USNM1 210236, USGS Loc. D1119NM X 20. 

3. Vertigo ovata Say.

Apertural view. Specimen inadvertently destroyed. USGS Loc. Dl 116NM, X 20. 

4-7. Armiger crista (Linnaeus).

4-6, Right side. Apertural view, left side, USNM 210237, USGS Loc. D1116NM, X 10; 7, Right side (note peripheral 

costae), USNM 210238, USGS Loc. D1116NM, X10. 

8-9. Physa gyrina Say, form hildrethiana Lea.

Abaperturaland apertural views, USNM 210239, USGS Loc. D1117NM, X 6. 

10-12. Hawaiia minuscula (Binney).

Apical, umbilical, and apertural views, USNM 210240, USGS Loc. Dl 116NM, X10. 

13-14. Succineat sp. indet.

Abaperturaland apertural views, USNM 210241, USGS Loc. D1117NM, X6. 

15-16. Stagnicola reflexa (Say).

Abapertural and apertural views, USNM 210242, USGS Loc. Dl 117NM, X 2.

'USNM, United States National Museum, in Washington, D.C., where specimens are deposited.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1120-B PLATE 2

PISIDIUM, VERTIGO, ARMIGER, PHYSA, HAWAIIA, 

SUCCINEA1, AND STAGNICOLA

*U.S. GOVERNMENT PRINTING OFFICE: 1980-677-129/34