Heavy-Mineral Dispersal and 

Deposition in Sandy Deltas 

of Glacial Lake Quinebaug, 

Connecticut 

U.S. GEOLOGICAL SURVEY BULLETIN 1874 . 
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Heavy-Mineral Dispersal and 

Deposition in Sandy Deltas 

of Glacial Lake Quinebaug, 

Connecticut 

By ERIC R. FORCE and BYRON D. STONE 

Two deltas in the lake had similar depositional 

parameters but separate source terranes. Interaction 

between source and depositional factors determined 

the mineralogy of each foreset bed 

U.S. GEOLOGICAL SURVEY BULLETIN 1874 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1990 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 1 Box 25425 

Denver 1 CO 80225 

Library of Congress Cataloging in Publication Data 

Force, Eric R. 

Heavy-mineral dispersal and deposition in sandy deltas of glacial Lake Quinebaug, Connecticut. 

(U.S. Geological Survey bulletin ; 1874) 

Bibliography: p. 

Supt. of Docs. no.: 119.3:1874 

1. Heavy minerals-Connecticut-Quinebaug, Lake. 2. Lake sedimentationConnecticut-Quinebaug, Lake. 3. Geology, Stratigraphic- Pleistocene. 

I. Stone, Byron D. II. Title. Ill. Series: Geological Survey bulletin ; 1874. 

QE75.B9 no. 1874 557.3 s [549.9746'45] 88-600492 

[QE364.2.H4] 
CONTENTS 

Abstract 1 

Introduction 1 

Ice-Marginal Glaciolacustrine Deltas 2 

Study Area 5 

Bedrock Geology 5 

Glacial Deposits 5 

Methods of This Study 7 

Stratigraphic Sections 8 

Kitt Brook Delta 8 

Packerville Delta 10 

General Comparison of Textures and Bedding 11 

Heavy-Mineral Distribution 11 

General Character of Heavy-Mineral Grains 11 

Heavy-Mineral Assemblages and Sediment Sources 11 

Heavy-Mineral Distribution Within the Deltas 12 

Influence of Grain Size 13 

Factors Controlling the Heavy Mineralogy of Each Bed 13 

Grain-Size Distributions of Heavy Minerals Supplied to Each Delta 14 

Sorting by Shape and Density Within Each Bed 15 

Factor Interrelation and Consequent Predictive Capacity 17 

Mode of Heavy-Mineral Deposition 18 

Ice-Marginal Supply and Dispersal System 19 

Acknowledgments 20 

References 20 

FIGURES 

1. Photograph showing the topset-foreset disconformity and sets of foreset beds 

separated by disconformities of a typical glaciolacustrine delta in the study area 2 

2. Map showing the bedrock geology, metamorphic isograds, and glacial Lake 

Quinebaug and its deltas 3 

3. Stratigraphic columns showing sedimentary features, grain size of primary mode, 

and heavy-mineral contents 4 

4. Grain-size histograms for light and heavy minerals of six beds 9 

5-9. Graphs showing: 

5. Heavy-mineral content as a function of grain size 12 

6. Heavy-mineral percentage versus gravel percentage at Kitt Brook 13 

7. Variation of mineral abundance and median grain size 14 

8. Concentration of heavy-mineral species in grain-size fractions of channel 

samples in the Kitt Brook and Packerville deltas 16 

9. Mineral density versus the difference between median mineral grain size and 

median sample grain size 17 

Contents Ill 
IV Contents 

10. Grain-size distribution histograms and mineral cumulative curves for sample 

K12 18 

11. Graph showing the relation of size distributions of supplied debris and of any given 

sample and its contained minerals 19 

12. Map showing ice-marginal supply and dispersal directions in the study area 20 

TABLES 

1. Rock-type comparisons of bedrock and gravel samples, glacial Lake Quinebaug 6 

2. Relative abundance of heavy minerals in bedrock terranes, tills, and delta channel 

samples, Kitt Brook and Packerville deltas 7 

3. Mineral percentages by weight in some heavy-mineral concentrates of the most 

completely analyzed samples, Kitt Brook and Packerville deltas 8 

4. Average arithmetic difference between median grain sizes of whole samples and of 

individual constituent minerals, Kitt Brook and Packerville deltas 15 
Heavy-Mineral Dispersal and Deposition in Sandy 

Deltas of Glacial Lake Quinebaug, Connecticut 

By Eric R. Force and Byron D. Stone 

Abstract 

Heavy minerals in sandy foreset beds were studied in 

two Pleistocene glaciolacustrine deltas. The deltas were 

built at about the same time into different sides of glacial 

Lake Quinebaug and rest on different bedrock terranes. 

Our aims were to determine a dispersal pattern for the 

heavy minerals and the mode of their deposition. 

The dipping foreset beds form sets bounded by 

erosion surfaces and consist largely of moderately wellsorted sands and subordinate bimodal gravelly sands. 

Sedimentary structures show deposition by suspension, 

traction currents, and subordinate avalanching, probably 

from continuous dense turbulent underflows. 

The heavy-mineral assemblages of the two deltas are 

quite distinct, and each is closely related to the mineralogy of the underlying bedrock terrane. Apparently little 

mixing of debris from different sources occurred anywhere in the dispersal system. Despite heavy-mineral 

contents averaging more than 5 percent and reaching 

almost 20 percent, heavy-mineral content of the delta 

sands is no greater than that of the source rocks. 

Several factors appear to have no influence on 

heavy-mineral distribution within foreset beds: (1) there 

are no trends of heavy-mineral content with stratigraphic 

position within foreset sequences; (2) there is no orderly 

relation between sorting and heavy-mineral content, 

except in gravelly bimodal deposits; and (3) there is no 

relation between sedimentary structures and heavymineral content. 

The only variable correlating well with heavy-mineral 

percentage and mineral assemblage within a delta is grain 

size of the host bed. In each delta, a particular modal grain 

size is associated with a heavy-mineral maximum. Grainsize variation also controls the concentration of individual 

heavy-mineral species; each species shows a maximum 

concentration at a particular grain size. Within a delta, 

concentration of a given heavy mineral was found to vary 

in coarse versus fine beds by as much as an order of 

magnitude. 

In this depositional environment, heavy minerals 

were deposited as would be predicted from suspension 

equivalence. The heavy-mineral fraction is finer than the 

Manuscript approved for publication October 25, 1988. 

bulk sample. Each heavy-mineral species forms a wellsorted population that is always in the same position 

relative to the size distribution of the whole sample and 

relative to other heavy-mineral species. The calculated 

sorting coefficient of any whole sample is increased by its 

mixed-density population. 

The interaction of two factors determines the mineralogy of each bed; the first is the size distribution of 

supply for each mineral, and the second is the grain size of 

the bed. The debris of each source terrane has a characteristic proportion of minerals, each having a characteristic size distribution. Each foreset bed can draw only on 

this population. The size distribution of each bed implies 

a suspension-equivalent size in demand for each heavymineral species. Where this optimal size for a mineral 

matches a size interval of abundant supply, a concentration of that mineral species forms. Where that mineral 

dominates supply or where size of supply and demand 

match simultaneously for several minerals, high total 

heavy-mineral contents result. 

INTRODUCTION 

Glaciolacustrine deltas of late Pleistocene age, characterized by thick sets of steeply dipping sandy foreset 

beds, are the dominant type of ice-marginal deposit in the 

northeastern United States. This is a region of moderate 

relief where numerous, relatively shallow glacial lakes were 

impounded in front of retreating ice margins of the Laurentide ice sheet (Schafer and Hartshorn, 1965; Stewart and 

MacClintock, 1970; Koteff and Pessl, 1981; Stone and 

Peper, 1982; Stone and Borns, 1986). The preserved 

morphology of the deltas and the distribution of related 

lacustrine facies, shorelines, and lake spillways permit 

detailed reconstructions of basin morphometry and descriptions of specific depositional environments. Detailed 

regional studies (for example, Stone and Randall, 1978; 

Stone and Peper, 1982) clearly show that the bulk of 

glacially produced sand of late Wisconsinan age was 

deposited in subaqueous deltaic foreset and related environments. 

The variety of sedimentary features in glacial deltas 

has received considerable study (Jopling and Walker, 1968; 

Introduction 
Aario, 1971; Stone, 1974; Gustavson and others, 1975; 

Shaw, 1975; Cohen, 1979, 1983; Serrat and others, 1983; 

Smith and Ashley, 1985). However, few studies have 

addressed the sedimentology of the entire delta system, and 

none has included thorough considerations of sediment 

source or an integrated concept of the sediment distribution 

systems that operated within these sandy deltas. 

The mineralogy of glaciolacustrine sands has been 

studied in bulk samples to address economic potential of 

contained heavy minerals (Force and others, 1976; Stone 

and Force, 1980), but no detailed mineralogic studies have 

been done in this depositional environment. In related till 

and glaciofluvial lithologies, mineralogy has locally been 

studied (for example, Krynine, 1937). Dreimanis and Vagners ( 1969) showed that some mineral species in till are 

concentrated in a "terminal (size) grade," related to the 

mineral's resistance to glacial abrasion. 

This study (1) describes the distribution of heavy 

minerals in two typical ice-marginal deltaic deposits that 

overlie contrasting lithologic bedrock terranes and relates 

the heavy-mineral composition of these sediments to possible sediment sources and dispersal patterns; (2) relates 

heavy-mineral species to stratigraphic position, grain size, 

sorting, and sedimentary structures of host sands; and (3) 

isolates factors affecting hydrodynamic separation of sand 

grains of different mineralogy in glaciofluvial and deltaic 

environments. The study thus examines separately the 

textural and mineralogic immaturity of glacial sediments 

and includes an account of many heavy-mineral species 

across the entire sand interval of grain size. By tracking all 

aspects of lithology (that is, composition, texture, and 

sedimentary structures), this study explores the interrelation 

between sediment supply and hydraulic sorting within the 

deltaic dispersal system. 

ICE-MARGINAL GLACIOLACUSTRINE DELTAS 

Tripartite deltaic sequences (Gilbert, 1885), consisting of silty sand bottomset beds, thick sets of inclined sandy 

to gravelly foreset beds, and gravel topset beds, are the 

characteristic stratigraphic motif of most ice-marginal 

deposits of late Pleistocene age in the northeastern United 

States (examples in Jopling and Walker, 1968; Stone, 1974; 

Gustavson and others, 1975; summarized by Koteff and 

Pessl, 1981; Stone and Peper, 1982). This characteristic 

stratigraphy was produced by progradation of fluvial topset 

beds over subaqueous sequences of foreset and bottomset 

beds that were deposited on delta slopes and lake-bottom 

plains, respectively. The planar contact between delta 

topset and foreset beds (fig. 1) is at the approximate level of 

the former lake-water plane, and the approximate 

paleodepth of any delta foreset sample can be specified 

from this contact. 

The depositional framework of these deltas can be 

specified from their relict morphology. The delta plains, the 

Figure 1. Typical glaciolacustrine delta of the study area, 

showing topset-foreset disconformity and sets of foreset 

beds separated by disconformities. Exposure about 5.5 m 

high. 

upper surfaces of coarse glaciofluvial topset beds, commonly extend from proximal ice-contact slopes to distal 

digitate borders. The delta foreset slopes beneath these 

borders merge tangentially with delta toeset slopes or 

bottomset plains in front of the delta. In many valleys, 

contacts of successive ice-marginal deltas show the retreatal 

positions of the edge of a stagnant-ice zone that was 

marginal to the Laurentide ice sheet. These ice-contact 

slopes show the trend and some details of the edge of 

supporting, stagnant-ice walls. The chronology of icemargin recession in late Wisconsinan time (Stone and 

Borns, 1986) implies that each ice-marginal delta was 

deposited in no more than a few decades, probably in a few 

years. 

Coarse-grained glaciolacustrine deltas in the region of 

this study (fig. 2) consist of an overall coarsening-upward 

sequence of horizontal silty and sandy bottomset beds, 

overlain by inclined sandy to gravelly foreset beds, which in 

2 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
41 

0 

0 

q 

Eastern 

lowland 

terrane 

2 MILES 

2 KILOMETERS 

Central //", 

. Village 1 

·v ~' 

... 

hva 

... ! 

EXPLANATION 

W 

Canterbu~ Gneiss-Includes Hebron 

Format1on 

Tatnic Hill Formation 

Quinebaug Formation 

Hope Valley Alaskite Gneiss 

;- /,.. Bedrock outcrops 

Area of glacial Lake Quinebaug 

Delta-Hachures indicate eroded delta front 

Contact between bedrock lithologic units 

Metamorphic isograd 

.....--. Dip direction of delta foreset beds 

at measured section 

+-- Striation 

--o- Drumlin or glacially streamlined 

till rampart 

!::::. Till sample locality-PT. Packerville till; 

KBT, Kitt Brook till 

42° 

! 

i 

i 

~~ t 

.,.. ~~ 

( 25 KILOMETERS 41 ° 

Figure 2. Bedrock geology, metamorphic isograds, and glacial Lake Quinebaug and its deltas. 

tum are disconformably overlain by gravel-dominant glaciofluvial delta topset beds (Stone, 1974; Stone and Force, 

1982, 1983). The glaciofluvial delta topset gravel facies 

includes massive to indistinctly bedded, clast-supported, 

pebble to cobble gravel or even boulder gravel, having 

locally well-developed imbrication, and pebble or cobble 

gravel in tabular crossbeds or trough crossbeds. Gravel beds 

range from 0.2 to 1.2 min thickness. Subordinant sand beds 

are chiefly coarse sand having pebbles and granules in 

trough and tabular crossbeds. Medium- and fine-sand 

ripple-laminated beds are locally present. 

Deltaic foreset beds characteristically have diverse 

textures and sedimentary structures. Foreset sequences tens 

to hundreds of meters downstream from the ice contact of 

the delta typically are alternating coarse- and fine-sand beds 

and pebbly sand beds, in thick (>2 m) sets of foreset 

cross-strata that are inclined from about 15° to 30°. In most 

sections, these inclined strata do not form a simple sequence 

but consist of multiple sets of foreset beds. Each set of delta 

foresets is bounded by disconformities but contains con·· 

formable beds (Stone and Force, 1982, 1983). These foreset 

bedding relations are illustrated in measured stratigraphic 

sections (fig. 3). Local changes in grain size within and 

between sets of foreset strata imprint a variable pattern on 

the coarsening-upward textural trend. This overall textural 

trend in the area of this study is substantiated by augur-hole 

subsurface data (Stone and Randall, 1978). 

Characteristic foreset lithologies include medium- to 

fine-sand beds having ripple cross-laminations or planar 

laminations, fine silty sand in sets of draped laminations, 

and pebbly sands having planar laminations or, less commonly, cross beds. Steeply dipping pebble to cobble gravel 

foresets have variable amounts of coarse-sand matrix. 

Deltaic foreset sequences consist mostly of sand beds 

that contain a variety of current bedding features that 

resulted from traction- and suspended-load deposition on 

the delta foreset slope (Jopling and Walker, 1968; Aario, 

1971; Stone, 1974; Gustavson and others, 1975; Stone and 

Force, 1982, 1983; Smith and Ashley, 1985). Currents that 

flowed down and across these foreset slopes were continuous but nonsteady density underflows, or turbidity currents, 

driven by the mass of their suspended loads. In the upper 

Ice-Marginal Glaciolacustrine Deltas 3 
KITT BROOK DELTA 

.. ~.o·.·~,.~ .. 

0 

K21 

K17 

6 

PACKERVILLE DELTA 

r 

DELTA 

TOPSET 

BEDS 

t 

DELTA 

FORE SET 

BEDS 

EXPLANATION 

SEDIMENTARY STRUCTURES 

Topset Beds 

Imbricate gravel clasts 

Trough crossbeds 

Foreset Beds 

Planar beds 

P7 

P6 

Type- A climbing ripple cross -lamination 

Type- B climbing ripple cross -lamination 

Solitary ripple cross -lamination 

Disconformity between sets 

of foreset strata 

K12 Sample numbers (table 3, figs. 4 and 10) 

Figure 3. Stratigraphic columns showing sedimentary features and grain size of primary mode. Right column shows the 

heavy-mineral fraction (p (specific gravity) >2.85). 

4 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
delta foreset sequences in the study area, we have seen no 

-deposits of interflow origin (using criteria of Smith and 

Ashley, 1985). Lower flow regime bedforms are probably 

dominant in these sequences and are interbedded with 

subordinate thinly laminated silt and fine sand that accumulated chiefly from suspended-load fallout. Vertical 

sequences of climbing ripple cross-laminations consist of 

gradations from type-A to type-B cross-laminations to 

draped laminations. Theoretical (Allen, 1971) and experimental (Ashley and others, 1982) studies of such ripple 

successions indicate that tens of centimeters of these beds 

probably accumulated in only hours of sedimentation. 

Sharp contacts between beds and especially between discordant sets of foreset strata indicate erosion related to 

variable dispersal patterns (Cohen, 1983) on the foreset 

slope. Gradational or indistinct bed contacts and some sharp 

contacts probably reflect variability of diurnal and (or) 

seasonal flow parameters (Smith and Ashley, 1985). Larger 

bedforms in deltaic subaqueous environments, such as sand 

megaripples, transverse dunes, and gravel crossbeds, are 

less common but suggest larger lower flow regime currents. 

Turbidite beds in the classical sense are present but unusual. 

In some sections, especially those close to ice-contact 

proximal parts of deltas, steeply dipping gravel and coarsesand beds accumulated in planar foreset strata. Some of 

these gravelly foreset beds were probably deposited by 

continuous avalanching (Allen, 1971) on the upper foreset 

slope of the delta. 

Judging from the distribution of individual deltaic 

deposits (for example, Stone and Randall, 1978), most 

sediment was transported less than 3 km in braided meltwater streams before it was deposited in the various 

environments of the delta. Most sand was transported 

through the delta fluvial topset environment and into the 

foreset depositional environment where subaqueous meltwater currents flowed as density underflows on the foreset 

slopes. Within the foreset parts of the sequence, we find 

that many sand or gravel beds are nevertheless quite well 

sorted especially where particles of the same density are 

considered. Thus the mineralogic immaturity of these sediments does not necessary imply textural immaturity. 

STUDY AREA 

Glacial sediments of late Wisconsinan age form a 

surficial cover of irregular thickness over the Quinebaug 

River valley and adjacent uplands of eastern Connecticut 

(fig. 2), about 70 km north of the terminal moraine on Long 

Island. Glacially eroded debris in the Quinebaug River 

lowland area was transported in a south-southeast direction, 

as shown by the general direction of striations. Detailed 

mapping (Stone and Randall, 1978) revealed that glacial 

and meltwater deposits contain boulders and gravel clasts 

that are conspicuously similar to lithologies of local bedrock 

outcrops. In addition, aeroradioactivity maps of the area 

show that the contoured pattern of radiation, derived from 

the surficial sediments and subordinate rock outcrop, is 

similar to the mapped pattern of contrasting bedrock lithologies (Goldsmith and others, 1977). This relation supports 

the conclusion that most of the glacial sediment was derived 

locally and was not diluted significantly by far-transported 

erratic debris. Field relations thus indicate that the mineralogic compositions of glaciogenic deposits should be 

closely related to the composition of local bedrock. 

Bedrock Geology 

The study area is part of a metamorphic belt of 

Paleozoic age. Detailed bedrock maps of the area (Dixon, 

1965; Dixon and Shaw, 1965) show a major north-south 

lithologic boundary that divides the study area into two 

gneiss terranes of contrasting mineralogies (fig. 2). Rocks 

in the western upland terrane are medium-grained leucocratic gneiss and pelitic schist of the Tatnic Hill Formation, minor calc-silicate rocks (Fly Pond Member), and 

mafic rocks (table 1). Two north-south-trending metamorphic isograds within the Tatnic Hill terrane define the 

boundaries of a staurolite zone to the west, a sillimanitemuscovite zone in the center, and a sillimanite-orthoclase 

zone to the east. Thus the Tatnic Hill terrane contains garnet 

and staurolite to the west and garnet, sillimanite, and local 

kyanite to the east (table 2). Small but mappable calcsilicate units contain abundant pyroxene (mostly diopsidic), 

amphibole (mostly hornblende), epidote, and sphene. 

Rocks of the eastern terrane that underlie the Quinebaug lowland are dark, fine- to medium-grained hornblende 

gneiss of the Quinebaug Formation and minor leucocratic 

gneiss units. Most of the Quinebaug Formation is within a 

sillimanite-muscovite zone, and its dense minerals include 

amphibole (hornblende), lesser amounts of pyroxene, finegrained garnet and epidote, and minor sphene and sillimanite (table 2). 

Rocks of both terranes contain opaque magnetite and 

ilmenite; leucocratic units in each terrane contain a minor 

amount of zircon. In both terranes, rutile is present in 

sillimanite-muscovite-grade or, more commonly, sillimaniteorthoclase-grade rocks (Goldsmith and Force, 1978). 

H.R. Dixon (written commun., 1985) has estimated 

the average percentage of heavy minerals from about 100 

thin sections of rocks from each terrane. Her estimates, 

converted to weight percentages, are about 34 percent (plus 

10 percent biotite) for the Quinebaug Formation and 15 

percent (plus 14 percent biotite) for the Tatnic Hill Formation. Minerals are ranked by abundance in table 2. 

Glacial Deposits 

Glacial sediments of the area consist of thin till and 

local meltwater deposits on the bedrock uplands and numerStudy Area 5 
Table 1. Rock-type comparisons of bedrock and gravel samples, glacial Lake Quinebaug 

[Rock types are modified by principal minerals (Dixon, 1965), listed in increasing order. Accessory minerals are shown in parentheses. Bedrock rock types 

are listed in order of outcrop area and proximity to ice-contact source of sediments in deltaic deposits. Map unit symbols are from Dixon (1965)] 

WESTERN UPLAND TERRANE AND KITT BROOK DELTA 

Bedrock, Tatnic Hill Formation 

Rock type [map unit] 

Gneisses 

Garnet-biotite gneiss [tb,tr] 

(Pyroxene)-hornblende gneiss [tr] 

Sillimanite-kyanite gneiss [tb] 

Sillimanite gneiss [ts] 

Calc-silicate, biotite-hornblende gneiss [tr,tc,tfp,tb] 

(Staurolite) gneiss [ty?] 

Schists 

Rusty-weathering garnet-muscovite schist [tr] 

Rusty-weathering muscovite-biotite schist[tr] 

Other rock types 

Amphibolite [tr,tb] 

Gamet granulite [ tr] 

Area, in percent 

75 

20 

5 

Kitt Brook gravel 

Rock type [map unit] Percent of 

I gravel 

I Gneisses 74 

I (Garnet)-biotite gneiss [tb] 51 

1 

Green amphibolite gneiss [tr,tb,qu?] 19 

Amphibolite gneiss [tb,tfp?] 2 

1 

Sillimanite-kyanite gneiss [tb] 2 

I 

I Schists 21 

(Garnet)-muscovite-biotite schist [tb] 20 

[Rusty schist [tr] 1 

Other rock types 5 

Granulite [ tr?] 5 

EASTERN LOWLAND TERRANE AND PACKERVILLE DELTA 

Bedrock, Quinebaug Formation 

Rock type [map unit] 

Gneisses 

Epidote-biotite gneiss [ql] 

Biotite-hornblende gneiss [ql] 

Biotite-epidote gneiss [ql] 

Biotite-hornblende gneiss [qu] 

Epidote-biotite gneiss [qu] 

Amphibolites 

Epidote-hornblende amphibolite [ql] 

Greenish-gray amphibolite [qu] 

Granulites 

Biotite-muscovite granulite [qbg] 

Hornblende-biotite granulite [ qbg] 

Schists 

(Calcite)-biotite schist [qb] 

(Biotite)-muscovite schist [qb] 

Other rock types 

Cataclasites [ qlc] 

(Areas unknown) 

ous deltaic deposits on the Quinebaug lowland. Till derived 

from the resistant gneiss of the Tatnic Hill Formation is 

sandy; the matrix of sand and finer grain sizes from our one 

sample contains 25 percent silt and clay. A slightly siltier 

till, which overlies bedrock in the lowland, has a matrix 

which contains 35 percent silt and clay. 

Glaciolacustrine deposits in the Quinebaug lowland 

consist of a series of ice-marginal deltas deposited in glacial 

Lake Quinebaug (Stone, 1978; Stone and Randall, 1978). 

Lake Quinebaug extended as a proglacial lake from its 

bedrock-floored spillway at the narrow southern part of the 

valley (fig. 2) to the northern part of the basin where it was 

about 5 km wide. Ice-marginal deltas, related to six retreatal 

Packerville gravel 

Rock type [map unit] 

Gneisses 

Pyribole gneiss [ql] 

(Gamet)-biotite gneiss [ ql] 

Leucocratic gneiss [ql,hv] 

Sillimanite-muscovite-garnet gneiss [ql,tr,ts] 

Granulites 

Granulite [qbg] 

Schists 

Muscovite-biotite schist [qb] 

Other rock types 

Granitoid rock [qn,ql,hv] 

[ Cataclasite [qlc,qlg] 

Percent of 

gravel 

44 

19 

8 

2 

11 

4 

11 

1 

positions of the margin of the ice sheet, prograded into the 

lake as the margin retreated northward. Delta topset-foreset 

contacts indicate the altitude of the isostatically tilted lakewater plane, at the maximum extent of the lake, shown in 

figure 2. Bedrock-surface contours on the bottom of the 

basin (Stone and Randall, 1978) show that the lake was 

generally less than 35 m deep. Ice-marginal deltas were 

deposited on the sides of the basin or near bedmck islands 

where the lake was 10 to 20 m deep. Lake-bottom sand is 

not extensive but is distributed around and between some of 

the deltas. 

The two ice-marginal deltaic deposits studied in this 

report are in the northern part of the lake basin (fig. 2). The 

6 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
Table 2. Relative abundance of heavy minerals in bedrock terranes, tills, and delta channel samples, Kitt Brook and 

Packerville deltas 

Bedrock1 

(Tatnic Hill Formation) 

Garnet 

Biotite 

Sillimanite 

Hornblende 

Diopside 

Other pyroxenes 

Kyanite3 

Epidote 

"Opaques" (ilm, mag, hem) 

Staurolite3 

Sulfides 

Apatite 

Zircon 

Rutile 

Bedrock1 

(Quinebaug Formation) 

Hornblende 

Epidote 

Biotite 

Diopside 

Garnet 

"Opaques" 

Allanite 

Sphene 

Zircon 

Apatite 

Rutile 

Western upland terrane and derived sediments 

Till 

(Kitt Brook) 

Garnet ............................ . 

Sillimanite ........................ . 

Light pyriboles .................... . 

Dark pyriboles .................... . 

Epidote ........................... . 

Magnetite ......................... . 

Ilmenite ........................... . 

Rutile ............................. . 

Kyanite3 .......•...•........•...... 

Staurolite3 •.......•...•............ 

Hematite .......................... . 

Tourmaline ........................ . 

Volume, 

in percent2 

23 

22 

16 

16 

8 

6 

4 

2 

1 

1 

tr 

tr 

Delta channel samples 

(Kitt Brook) 

Garnet ............................ . 

Dark pyribole ..................... . 

Sillimanite ........................ . 

Light pyriboles .................... . 

Epidote ........................... . 

Ilmenite ........................... . 

Staurolite3 ........................ . 

Kyanite3 .•......•...•...•......•..• 

Tourmaline ........................ . 

Magnetite ......................... . 

Sphene ........................... . 

Rutile ............................. . 

Zircon ............................ . 

Hematite .......................... . 

Eastern lowland terrane and derived sediments 

Till 

(Quinebaug) 

Dark pyribole ..................... . 

Epidote ........................... . 

Garnet ............................ . 

Light pyribole ..................... . 

Sillimanite ........................ . 

Ilmenite ........................... . 

Magnetite ......................... . 

Sphene ........................... . 

Rutile ............................. . 

Kyanite 3 ....•........•............. 

Zircon ............................ . 

Corundum ........................ . 

Tourmaline ........................ . 

Volume, 

in percene 

33 

24 

18 

11 

7 

3 

3 

1 

1 

1 

tr 

tr 

tr 

Delta channel samples 

(Packerville) 

Dark pyribole ..................... . 

Epidote ........................... . 

Light pyribole ..................... . 

Garnet ............................ . 

Sillimanite ........................ . 

Magnetite ......................... . 

Ilmenite ........................... . 

Tourmaline ........................ . 

Sphene ........................... . 

Rutile ............................. . 

Zircon ........................... . 

Kyanite3 .•......•...•..........•... 

Corundum ........................ . 

1 Listed in apparent order of abundance by volume. 

Volume, 

in percent2 

29 

12 

11 

10 

7 

5 

3 

1 

1 

1 

1 

1 

tr 

tr 

Volume, 

in percent2 

35 

17 

13 

11 

5 

5 

3 

1 

1 

tr 

tr 

tr 

tr 

2 Listed in volume percent of heavy minerals, exclusive of biotite, to facilitate comparison to bedrock. Values rounded to whole percent, tr <1 

percent. 3 Minerals that have sources restricted to the western terrane. 

Kitt Brook delta is on the western side of the lowland; 

related ice-contact deposits and coarse glaciofluvial sediments that were deposited at the ice-marginal source of the 

delta extend up into the upper reaches of Kitt Brook in the 

western upland terrane. The Packerville delta, 2.5 km east 

of the Kitt Brook delta, is in the axial part of the Quinebaug 

lowland in the eastern lowland terrane. The deposit was fed 

by ice-channel streams in stagnant ice that fringed the front 

of the ice sheet in the lowland. The delta contains a broad, 

ice-contact-bounded linear ridge of ice-channel origin. The 

positions of both deltaic deposits, altitudes of delta topsetforeset contacts within each section, and stratigraphic relations of lake-bottom sediments clearly show that sediments 

in each delta were deposited in glacial Lake Quinebaug. 

The two units are related to retreatal ice-margin positions 

that are closely related in relative age (Stone and Randall, 

1978). 

METHODS OF THIS STUDY 

Measured stratigraphic sections (fig. 3) include the 

exposed upper foreset and topset beds of each delta. At least 

one sample was taken from each bed, except those beds less 

than 1 em thick. A channel sample from each delta 

integrated lithologies from the entire foreset sequence. 

Grain-size analyses were based on standard sieving procedures at I/2-<l> intervals in sandy beds, and results were 

expressed in weight percent. For purposes of heavy-mineral 

identification, a bromoform-separated (specific gravity (p) 

2.85) coarse fraction, 1 to 2.5 <J>, and fine fraction, 2.5 to 

4.0 <J>, were reseparated by using methylene iodide (p 3.3), 

and each of the four size-density fractions was separated 

into five magnetic subfractions. Each subfraction was 

weighed and examined under binocular and petrographic 

microscopes. The relative abundance of each mineral 

Methods of This Study 7 
Table 3. Mineral percentages by weight in some heavy-mineral (p (specific gravity) >2.85) concentrates of the most 

completely analyzed samples, Kitt Brook and Packerville deltas 

[K samples from Kitt Brook; P samples from Packerville; -, not identified] 

Sample no. K1 K4 K5 K10 K11 

Magnetite ................. 0. 7 0.7 1.0 1.5 } 9.3 Ilmenite ................... 4.3 3.0 13.1 3.6 

Garnet. .................. .47.0 55.6 59.1 26.1 32.7 

Dark pyribole .............. 3.8 7.7 8.5 11.6 7.9 

Light pyribole .............. 2.2 1.9 2.6 5.1 7.5 

Biotite .................... 1.2 1.8 1.5 17.5 8.9 

Epidote ................... 5.1 3.2 .7 4.4 6.6 

Staurolite .................. .6 .9 1.1 1.2 2.4 

Sphene ................... 1.0 1.3 .3 1.2 2.0 

Sillimanite ................. 6.1 6.0 5.1 14.5 11.1 

Kyanite ................... .5 .5 1.1 1.1 1.9 

Zircon .................... .2 .3 .2 .1 

Rutile .................... .4 .3 .1 .4 .7 

Tourmaline ................ 2.8 .7 .2 2.8 1.3 

Aggregates ................ 12.6 15.9 5.2 8.7 7.6 

Percentage of .............. 5.1 5.2 5.5 6.9 6.5 

heavy minerals 

Host character 

Median (Md) (<j>) ....... 1.5 1.2 -0.5 2.5 2.25 

Sand-sized modal ....... 1.5-2 .5-1 1-2 2.5-3 2-2.5 

classes {<j>) .5-1 1.5-2 

Trask sorting ........... 1.8 1.5 5.2 1.3 1.4 

coefficient (So) 

Folk-Ward sorting ...... 1.00 .77 2.6 .74 .85 

species was estimated by point counts and visual comparison charts. The weight of each mineral species, adjusted for 

specific gravity, was then summed for all 20 size, density, 

and magnetic fractions to determine the weight percentage 

of each mineral in each sample (table 3). For sample Kl2, 

and for the channel samples and two till samples, more 

work was done; heavy minerals were separated by magnetism and density and identified by point counts for each Ih-<f> 

grain-size split. These intricate procedures thus relied as 

much as possible on weighed fractions based on physical 

properties, and as little as possible on point counting, for 

which error is much larger. 

Sources of error included small errors in weighing 

and significant-figure errors, errors from sample separation, 

and errors associated with point counts. In most samples, 

errors due to incomplete density separations were less than 

10 percent; these were corrected in counted samples. The 

largest source of error was estimation of mineral abundance 

by point-count (150 to 320 grains per fraction) methods. 

Weight percentage of magnetite was established by magnetic properties and was not subject to point -count error. 

For sparse minerals having lower magnetic susceptibilities, 

such as rutile, probable errors are as much as 50 weight 

percent of listed mineral abundance. 

Kitt PackerK12 K14 K17 K21 P1 P6 P7 Brook ville 

channel channel 

sample sample 

1.2 } 7.8 } 4.3 } 3.6 2.9 7.5 7.3 1.4 7.5 

4.6 .6 1.3 2.0 6.2 4.0 

70.6 43.8 21.3 8.8 9.1 11.3 21.5 33.7 13.0 

4.0 15.9 12.2 7.1 34.0 36.9 35.3 13.0 33.5 

1.8 3.5 10.1 9.5 8.0 4.6 5.9 8.2 11.2 

.8 20.0 11.3 .6 .8 .7 9.4 1.4 

3.4 5.3 4.8 7.2 16.4 27.9 21.3 6.0 16.2 

1.7 3.3 1.9 3.2 

1.3 1.5 .4 .6 .8 .7 

2.5 6.3 12.9 31.9 1.8 2.9 1.8 9.8 4.5 

1.2 2.9 1.9 2.5 .4 .4 .2 1.3 .3 

.1 .4 

.2 .1 2.3 .4 .7 .3 .8 .5 

1.0 2.7 4.0 8.2 .7 3.6 .2 1.0 1.3 

5.4 6.8 6.3 6.5 24.3 1.5 3.4 4.4 6.7 

12.7 9.7 3.5 3.8 11.4 18.7 15.6 5.7 10.7 

1.25 1.4 2.25 3.2 1.5 2.3 1.8 2.3 2.2 

1.5-2 1.5-2 2-2.5 3-3.5 .5-1 2-2.5 2-2.5 

1.5-2 

1.5 1.3 1.3 1.4 1.7 1.4 1.7 

.80 .71 .76 .65 .81 .67 1.06 

STRATIGRAPHIC SECTIONS 

The measured sections in both deltas are composite, 

because of the method of quarrying in benches. Both 

measured sections show horizontally bedded glaciofluvial 

gravel and sand beds that disconformably overlie dipping 

delta foreset strata (fig. 3). The foresets consist of sets of 

conformable beds separated by angular discordances. True 

dip angles of foreset beds are shown in figure 3. No delta 

bottomset beds were exposed in either pit, so the total 

thickness of foreset beds is not known. 

Kitt Brook Delta 

The Kitt Brook delta was deposited at the western 

margin of Lake Quinebaug (fig. 2). Ice-marginal meltwater 

streams drained the upper Kitt Brook drainage in the 

western upland Tatnic Hill terrane, and the delta prograded 

eastward into the lake. High-angle reverse and normal faults 

downthrown to the east are exposed in the pit wall and 

indicate that the delta accumulated in contact with melting 

ice that was marginal to the edge of the ice sheet. 

Gravel beds in the delta topset sequence total1.6 min 

thickness (fig. 3). Cobble clasts are as large as 12 em 

8 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
KITT BROOK SANDS 

<I> 0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 

mm 1 .707 .5 .354 .25 .177.125 .088 .063 .044 .031 

40 

30 

20 

10 

<!> 0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 

mm 1 .707 .5 .354 .25 .177 .125 .088 .063.044 .031 

KITT BROOK GRAVELS 

w 

...J 40 40 K5 K6 a.. 

:2 

<( 30 30 en 

u.. 

0 20 20 

tz 

w 10 10 

u 

a: 

w 0 0 a.. <!> -5 -4 -3 -2 -1 0 1 2 3 4 5 <I> -5 -4 -3 -2 -1 0 1 2 3 4 5 

mm38 16 8 4 2 1 .5 .25 .125 .062 .031 mm 38 16 8 4 2 1 .5 .25 .125 .062 .031 

PACKERVILLE SANDS 

40 

30 

20 

P3 40 P6 

30 

20 

10 

OL__l __ ~_J==~--

<I> 0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 <I> 0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 

mm1 .707 .5 .354 .25 .177 .125 .088 .063 .044 .031 mm 1 .707 .5 .354 .25 .177 .125 .088 .063 .044 .031 

GRAIN SIZE, IN PHI (<!>) AND MILLIMETERS (mm) 

Figure 4. Grain-size histograms for light and heavy minerals (dark pattern) of six beds. Note differing scale and <!> 

spacing for sands and gravels. K10 is a typical ripple-laminated fine sand; K4 is a typical planar-laminated bimodal 

coarse sand; K6 is an unusual openwork gravel having few heavy minerals; KS is a typical bimodal gravel, here 

framework supported; P6 is a typical ripple-laminated fine sand; P3 is a typical planar-laminated fine sand. 

intermediate diameter. Scoured bases of channels show an 

east-southeasterly paleocurrent direction. The delta topset 

beds disconformably overlie 4. 7 m of delta foreset beds that 

consist of four sets of east- or northeast-dipping foreset 

strata. The sets of foreset strata are separated by erosion 

surfaces. In the fore set sequence, sand beds predominate 

over gravel beds. Two sets of foreset strata coarsen upward, 

another shows no definite vertical trend in texture, and one 

set fines irregularly upward. From bottom to top, this 

composite foreset sequence becomes finer grained. 

The lowest set of foreset beds coarsens upward and 

dips 40°. The lowest beds measured in the set are medium 

sand and contain two vertical sequences of type-A climbing 

ripple cross-laminations and overlying draped laminations. 

These beds are overlain by a thin bed of planar-laminated 

medium sand (K4 of fig. 4). These sequences have average 

total heavy-mineral contents of 5 to 6 percent. Bimodal 

gravel and sand beds overlie the rippled sequences (K5 of 

fig. 4). The sand grain-size mode is similar to the mode of 

the underlying sand beds. A set of openwork, imbricate 

gravel beds is at the top of this set of foresets (K6 of fig. 4). 

Pebbles in these beds are as long as 7 em, and the gravel 

grain-size mode of these beds is similar to the gravel mode 

of the underlying bimodal beds. Both the openwork gravel 

and the rippled sands are moderately well sorted (sorting 

coefficient (So) 1. 6). 

The second set of foreset beds fines upward and 

consists of interbedded sand and gravel in 0.1- to 0.3-m 

Stratigraphic Sections 9 
beds dipping 16°. The sands are well sorted (So about 1.4), 

are fine (median (Md) about 2.25 <P), and have planar and 

type-A ripple laminae (K10 of fig. 4). Heavy-mineral 

contents average about 6.5 percent. The gravels in this set 

are poorly sorted (So 4.5) and have poorly defined modes. 

Imbricate pebbles are as long as 14 em. The heavy-mineral 

content of the gravel beds is low. Bases of gravel beds are 

minor erosional surfaces~ sand beds commonly overlie silt 

drapes. 

Beds in the third set of foresets dip 21 o. At the base 

is a thin bed of planar laminated coarse to medium sand that 

contains 12.5 percent total heavy minerals (K12). Overlying beds consist of interbedded sand and gravel beds 

separated by sharp erosional contacts. Some sand beds are 

granular and contain trough cross beds. These sands are well 

sorted (So 1.3-1.4) and contain 3 to 10 percent heavy 

minerals. Interbedded gravel beds are poorly sorted and 

have indistinct modes. Clasts are as long as 8 em. The 

heavy-mineral content of the gravel beds is only 1 to 2 

percent. 

The uppermost set of foreset beds coarsens upward 

and consists almost entirely of well-sorted (So 1.4) sand. 

The very fine sand beds at the base contain a type-A to typeB climbing ripple cross-lamination vertical sequence. This 

sequence is disconformably overlain by a thin bed of fine 

sand containing type-A ripples. Granular coarse sand in 

planar beds overlies this bed and extends to the base of the 

topset beds. The dip of these foreset beds is 9°. Heavymineral content of the lower beds averages about 4 percent. 

The composition of the sediments in the Kitt Brook 

delta is closely related to the known bedrock lithologies of 

the western upland terrane. Pebbles in the foreset sequence 

of the Kitt Brook delta (table 1) are composed chiefly of 

banded (gamet)-biotite gneiss, similar to the dominant rock 

type of the Tatnic Hill Formation. Other pebble lithologies, 

such as green amphibole gneiss, (gamet)-muscovite-biotite 

schist, and rusty schist are also common minor rock types of 

the Tatnic Hill Formation. 

The mineral composition of sand in the Kitt Brook 

delta also compares closely with bedrock of the western 

upland terrane and with a local till sample (table 2). The 

channel sample of the Kitt Brook foreset sequence has a 

median grain size of 2. 3 <P and contains 5. 7 percent heavy 

minerals. 

Heavy-mineral pan concentrates from the Kitt Brook 

delta sands are pink, because of abundant garnet. The 

heavy-mineral assemblages in all bed samples from the Kitt 

Brook delta sediments are broadly similar; they are dominated by garnet and lesser components of sillimanite, 

ilmenite, and biotite (table 3). Pyriboles and epidote also 

are ubiquitous components. Staurolite, unique to the westem bedrock terrane, is a characteristic constituent and is 

zoned in coarse grains. Variation in the heavy-mineral suite 

from bed to bed is closely related to varying bed grain size 

(table 3). The assemblage of heavy minerals in the channel 

sampl~ (table 3) integrates the bed-by-bed variation and is 

therefore representative of the suite of sand-sized minerals 

that were supplied to meltwater streams throughout deposition of the upper part of the delta. 

Packerville Delta 

The Packerville delta was constructed over a shallow 

bedrock area in the axial northern part of Lake Quinebaug. 

The hills north of the deposit were islands in the lake (fig. 

2). These hills and the surrounding lowland area are 

underlain by the Quinebaug Formation. The delta prograded 

westward within an ice-channel drainage system. 

Topset strata in the Packerville delta comprise 

pebble-cobble gravel beds that total 2.8 min thickness (fig. 

3). Three sets of foreset strata, separated by disconformities 

and totaling 3. 3 m in thickness, disconformably underlie the 

topset beds. The entire foreset sequence coarsens upward 

from sand beds in the lowest set to interbedded sand and 

gravel in the uppermost set. Only the uppermost set 

coarsens upward internally. 

The lowest set of foreset strata, dipping 24 °, consists 

of interbedded ripple-laminated sand (mostly type-A) and 

planar-bedded sand. The grain-size range of the ripplelaminated sands (Md 2.0 to 4.0 <P; fine and very fine sand) 

overlaps the grain-size range of the planar-bedded sands 

(Md 1.5 to 2.3 <P; medium and fine sand). Grain-size 

distributions of samples P3 and P6 are shown on figure 4. 

Sorting of most beds is good (So about 1.3 except for 

samples taken over several laminae). Heavy-mineral contents range from 3. 7 to 18.8 percent; both ripple- and 

planar-laminated beds have high values. 

The middle set of foresets was measured near the 

edge of the set where it is thin. In the measured section, this 

erosionally bounded set consists of sand .and pebbly sand 

beds and contains 15.6 percent heavy minerals. 

The upper set of fore set strata dips 22° and consists of 

a coarsening-upward sequence of sand and pebbly sand 

beds, the latter strongly bimodal and consequently poorly 

sorted (So 4.1). 

Lithologies of pebbles in the Packerville foreset beds 

are dominated by dark gneiss from the Quinebaug Formation, including banded pyribole (chiefly hornblende) gneiss, 

(gamet)-biotite gneiss, granulite, and minor pelitic lithologies. Granitoid rocks and leucocratic gneiss make up 19 

percent of the clasts; these lithologies may have been 

derived from the upland terrane to the east, as well as from 

leucocratic layers in the Quinebaug Formation. 

The mineralogy of Packerville sands also reflects 

derivation from the Quinebaug Formation and is similar to 

that of a local till sample (table 2). The channel sample of 

the entire Packerville foreset sequence has a median grain 

size of 2.2 <P and contains 10.7 percent heavy minerals. 

10 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
Heavy-mineral pan concentrates from Packerville 

delta sands are green, reflecting a dominance by pyriboles 

and epidote. The assemblage of heavy minerals, broadly 

similar throughout the Packerville section, is dominated, in 

order of abundance, by pyribole (mostly hornblende), 

epidote, and garnet, and a ubiquitous lesser component of 

magnetite (table 3). Staurolite was not identified in the 

Packerville sediments, and ilmenite, biotite, and sillimanite 

are far less abundant than in the Kitt Brook delta. Variation 

in mineralogy between beds is related to grain size (table 3). 

The channel sample represents the suite of sand-sized 

minerals supplied to the Packerville delta during sedimentation of the exposed foreset sequence. The suite contrasts 

strongly in mineral proportions and sizes with the mineral 

suite of the Kitt Brook delta (table 3). 

General Comparison of Textures and Bedding 

The foreset sequences of the two deltas are texturally 

similar except that the Kitt Brook delta has a greater 

proportion of gravel beds. The median grain size of the sand 

fraction of the Kitt Brook channel sample, 2.3 <!:>, is 

virtually identical to the median value, 2.2 <1:>. of the 

Packerville channel sample. Figure 4 presents some typical 

grain-size distributions of beds from both deltas, including 

bimodal gravelly beds. 

Sorting coefficients of the fore set beds range from 1. 3 

(well sorted) to 5.2 (poorly sorted) (table 3) in Trask's 

(1932) terminology. Folk and Ward (1957) sorting coefficients are 0.65 to 2.6. The better sorted beds, having So 

values of 1.6 or less, include beds of openwork gravels, 

grits, and coarse and fine sands and constitute well over half 

of the foreset sequences in both deltas. Sand beds having 

either planar- or ripple-laminated structures have So values 

as low as 1.3, although some planar-bedded sands have 

higher So values because of a tendency toward a subsidiary 

coarse mode. 

There is some correspondence between sedimentary 

structure and grain size. Ripple-laminated beds have 

median grain sizes that range from 1.4 to 4.0 <1:>, and 

planar-laminated beds have median grain sizes that range 

from -0.25 to 2.3 <!:>.The overlap is thus in the medium and 

fine sands (fig. 5). The coarsest sands that contain ripple 

laminae are in the Kitt Brook section. 

HEAVY-MINERAL DISTRIBUTION 

General Character of Heavy-Mineral Grains 

Heavy-mineral grains in both deltaic sequences are 

fresh and angular to subangular, and some species are 

euhedral. Jagged grain edges and sharp conchoidal fractures 

are preserved on most grains. Subrounded grains constitute 

only a small proportion of the heavy-mineral suites. Magnetite is octahedral in most grains of all grain sizes. A few 

grains of gamet contain euhedral faces. Minerals that have 

prismatic habit, such as tourmaline, are either euhedral or 

show broken terminations. Light-mineral grains are 

unweathered and are angular or subangular, commonly 

preserving conchoidal fractures or cleavage faces. The 

morphology of virtually all sand-sized mineral constituents 

thus clearly shows the first-cycle origin of these glacial 

sediments. Heavy minerals are present largely in polymineralic rock fragments in gravel-sized fractions and to a 

lesser extent even in the very coarse sand-sized fraction. In 

fractions finer than 0.0 to 1.0 <j:>, heavy minerals occur 

predominantly as separate grains. Heavy-mineral-bearing 

polymineralic rock aggregates persist as minor constituents 

in grain sizes as fine as 3.0 <j:>. 

Heavy-Mineral Assemblages and Sediment 

Sources 

The assemblages of heavy minerals in samples from 

each delta are relatively homogeneous, the relative abundance of minerals varying with differences in grain size 

(table 3). Between the two deltaic sections, proportional 

abundances of heavy minerals are strikingly different. The 

most obvious difference is in the variation of dominant 

minerals. For example, the ratio of garnet to pyribole + 

epidote in the Kitt Brook delta ranges from 7. 7 in the 

coarsest sample (K12) to 0.37 in the finest sample (K21); 

this ratio is 1.24 for the Kitt Brook channel sample. In the 

Packerville sequence this ratio ranges from 0.16 to 0. 34 and 

is 0.21 for the channel sample. The contrast between deltas 

is also exemplified by the ratio of ilmenite to magnetite. In 

the Kitt Brook samples, this ratio ranges from 2.4 to 13.1 

(4.4 in the channel sample), whereas in the Packerville 

sediments, this ratio ranges from 0.17 to 0.27 (0.53 in the 

channel sample). Biotite, sillimanite, and kyanite are common in the Kitt Brook section but are notably less important 

in the Packerville sequence. Staurolite is common in Kitt 

Brook samples but was not observed in Packerville samples. Varietal mineral characters also are distinct; for 

example, many epidote grains in samples from Packerville 

contain magnetite inclusions. 

Each deltaic deposit contains a characteristic suite of 

heavy minerals that is similar to the mineral suites from the 

adjacent bedrock terrane and local till samples (table 2). 

Garnet is the principal mineral in Kitt Brook sediments, 

especially in coarse-sand samples. Its abundance is attributed to the corresponding abundance of coarse-grained 

garnet in rocks of the Tatnic Hill Formation. In the rocks of 

the eastern lowland terrane, garnet is a lesser and finegrained constituent and is found chiefly in the fine fraction 

of the Packerville samples. Pyribole (mostly hornblende) 

and epidote are the predominant minerals in the dark 

gneissic rocks of the Quinebaug Formation and are also the 

Heavy-Mineral Distribution 11 
22 

20 

1-

z 18 w 

u 

a: 

w 

a.. 16 

~ 

i:O 14 

co 

c-.i 12 (\ 

...::-

(J) 10 _J 

<( 

a: 

w 8 z 

~ 

>- 6 

> 

< w 4 J: 

2 

0 <I> -5 mm 38 

A 

PACKERVILLE 

SAMPLE MAXIMUM 

KITT BROOK 

SAMPLE MAXIMUM 

-4 -3 -2 -1 0 2 3 4 5 

16 8 4 2 1 .5 .25 .125 .062 .031 

MEDIAN GRAIN SIZE OF BED, IN PHI (<!>) 

AND MILLIMETERS (mm) 

oL_~--~---L---L--~--~--~--L---~~ 

<I> -5 -4 -3 -2 -1 0 2 3 4 5 

mm 38 16 8 4 2 1 .5 .25 .125 .062 .031 

GRAIN SIZE FRACTION OF CHANNEL SAMPLE, 

IN PHI (<\>) AND MILLIMETERS (mm) 

Figure 5. Heavy-mineral content as a function of grain size. A, Heavy-mineral content of sands of differing median 

grain sizes. Grain sizes of rippled beds in each delta are delineated by diagonal lines. Table 3 shows the relation of 

median to modal grain size of these sands. B, Heavy-mineral content of grain-size classes in the channel samples. 

Open circles, Kitt Brook samples; open squares, Packerville samples; p, specific gravity. 

predominant constituents of the Packerville samples. Pyribole in Kitt Brook sand was probably derived from the Fly 

Pond Member and other calc-silicate or mafic units within 

the Tatnic Hill Formation. The small amount of sillimanite 

in samples from Packerville may have derived from reportedly sparse (Dixon, 1965) sillimanite-bearing lenses of the 

Quinebaug Formation. The presence and relative abundance 

of all other mineral species likewise are related to the 

mineralogic composition of the bedrock terranes. Thus, 

only limited mixing of minerals across the bedrock terrane 

boundary is indicated. 

The distribution of pyribole, sillimanite, and kyanite 

(tables 2, 3) could be interpreted as a result of limited 

mixing of sand by transport across the bedrock terrane 

boundary, either by glacial or fluvial processes. Some 

cross-boundary transport is expected. However, the presence of staurolite in the Kitt Brook samples, and its absence 

in the sand at Packerville, suggests that such crossboundary sediment mixing is minimal in the study area. 

Staurolite in Kitt Brook delta sands is derived from the part 

of the Yantic Member of the Tatnic Hill Formation that is at 

staurolite metamorphic grade (Dixon, 1964, written commun., 1979; Dixon and Shaw, 1965); staurolite is absent in 

rocks to the east due to higher metamorphic grade. 

The total heavy-mineral abundance in the channel 

samples further contrasts the two deltaic sections. At Kitt 

Brook, the total heavy-mineral content in the sand fraction 

is 5. 7 percent. At Packerville, heavy minerals make up 10.7 

percent of the sand. Because the grain-size distributions of 

the channel samples are nearly identical, the difference in 

heavy-mineral contents cannot be attributed to differences 

in sample texture. The contrasting heavy-mineral contents 

of the two deltas correspond to differences in abundance of 

dense minerals in source rock terranes. Minerals denser 

than p 2.85 average about 15 percent by weight in the 

Tatnic Hill Formation. Such minerals average about 34 

percent in the Quinebaug Formation. This contrast is 

reflected in the heavy-mineral contents of local till; our 

sample of Kitt Brook till contains 7. 9 percent, whereas our 

Quinebaug till sample contains 10.1 percent. No overall 

concentration of heavy minerals is apparent in the sand of 

either delta. In fact, sand fractions of these coarse deltaic 

sediments are enriched in quartz and feldspar relative to 

bedrock. 

Heavy-Mineral Distribution Within the Deltas 

The abundance of heavy minerals shows no systematic relation to stratigraphic position in the foreset 

sequences (fig. 3). Because the topset-foreset contact represents the former lake surface, there is no correlation 

between heavy-mineral content and paleowater depth. 

12 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
There is no systematic distribution of minerals within 

individual sets of foreset strata, with the exception of one 

thin enriched unit, sample K12, which is above an unconformity at the base of a set. Sedimentary structure likewise 

appears to have little influence on heavy-mineral content in 

samples of equal grain size. Sands that have higher heavymineral content in each section may be planar- or ripplelaminated or crossbedded (fig. S). 

Influence of Grain Size 

Total heavy-mineral content.-The highest heavymineral contents in the Packerville section (fig. SA) are in 

sand beds having median grain-size diameters of 1.8 to 2.3 

<V (medium to fine sand), whereas in the Kitt Brook section 

heavy minerals are most abundant in beds having median 

grain-size values of -O.S to l.S <V (very coarse to medium 

sand). The difference corresponds to a difference in the size 

distribution of heavy minerals in the channel samples (fig. 

SB); that is, it is related to the nature of supply. 

Gravelly bimodal samples have lower heavy-mineral 

contents than unimodal sand samples. Modal grain size of 

the heavy-mineral fractions appears to correspond to the 

sand-sized mode rather than to the gravel-sized mode of 

gravelly bimodal samples (fig. 4). This correspondence 

results because the supplied monomineralic heavy minerals 

are too fine and not sufficiently dense to correspond 

hydraulically to pebbles. Therefore, the gravel fraction 

merely dilutes the heavy-mineral content (fig. 6). Heavymineral concentrations in the sand fraction of gravelly 

samples from Kitt Brook average 7. S percent, comparable 

to an average of 6. 7 percent for unimodal Kitt Brook sands. 

Sediment sorting appears to have limited influence on 

heavy-mineral content. The higher heavy-mineral contents 

in each section are in beds that have So values of 1. 7 or 

lower (Folk-Ward 1.2 or lower). However, only bimodal 

gravelly foreset beds have So values higher than 1. 7, so 

most beds in the delta are sufficiently well sorted to have 

high heavy-mineral contents. The best sorted deposits (So 

1.3) have heavy-mineral contents ranging from 3.S percent, 

which is notably below the average at Kitt Brook, to 17.7 

percent, which is above the average at Packerville. Plots of 

heavy-mineral content of Kitt Brook sands versus sorting 

coefficients show no trend. If gravels are included, the most 

poorly sorted deposits have low heavy-mineral contents, but 

this correlation is only the result of dilution by coarser 

material as discussed above. In a following section, sorting 

is further analyzed. 

Heavy-mineral assemblage.-Differences in relative 

abundance of heavy-mineral species as a function of bed 

grain size are quite intricate and are comparable in total 

magnitude to the provenance effect on variation of mineral 

abundance between the two deltas. At Kitt Brook, the most 

obvious correspondence between mineralogy and grain size 

i:O 

00 0 

C"i 8 

1\ 

-= 

(/) 0 ...J 

<( 

a: 

w 

z 

~ 2 0 0 

>- 0 > <( 0 w 

I 0 10 20 30 40 50 60 70 80 90 100 

GRAVEL (>4 mm), IN PERCENT 

Figure 6. Heavy-mineral percentage versus gravel percentage at Kitt Brook; p, specific gravity. 

is the degree of dominance by garnet, which is much greater 

in the coarser sands than in the finer sands (fig. 7A). The 

coarser Md of heavy-mineral-rich Kitt Brook sands (fig. 

SA) is consistent with their dominance by coarse garnet. 

Apparently little fine-grained garnet was supplied to the Kitt 

Brook delta. The finer sands at Kitt Brook tend to concentrate heavy minerals of two types: (1) the minerals that are 

normally supplied as fine grains (such as rutile) and (2) the 

intermediate-density minerals biotite, sillimanite, tourmaline, and epidote (which here includes feldspar only partially replaced by epidote). 

In the Packerville section, based on fewer data, 

minerals more abundant in finer sands are magnetite, 

ilmenite, epidote, sillimanite, rutile, and toum1aline (table 3 

and fig. 7C). Only pale pyriboles are markedly more 

abundant in coarser sands. As at Kitt Brook, the finer sands 

contain either less dense minerals, such as epidote, or those 

likely to be supplied as fine grains. 

FACTORS CONTROLLING THE HEAVY 

MINERALOGY OF EACH BED 

The pervasive control of relative heavy-mineral abundance by bed texture is intriguing, and this study, with its 

well-constrained paleogeographic variables, allowed for 

effective isolation and testing of this effect. In this section 

we discuss the effect in terms of two variables, the nature of 

sediment supply to each delta and the nature of hydraulic 

sorting of each bed. The two variables interact in such a 

way that, given only the shape and density properties of 

each mineral, the entire heavy-mineral assemblage of each 

bed is determined. 

Factors Controlling the Heavy Mineralogy of Each Bed 13 
en 

...J 

<t: 

a: 

w 

z 

~ 

>-

> <t: 

w 

:I: 

LL. 

0 

Iz 

w 

u 

a: 

w 

a.. 

70 

60 

50 

40 

30 

20 

10 

0 

50 

40 

30 

20 

10 

0 

A 

~ \ 

'o 

0 \ 

\\GARNET 

'\ 

'\ 0 '\. 

'\. 

'\. 0 

" '\. / 0 / 

X / " / 4 ..... /.6. 

SILLIMANITE, ,.. .......... .6. ..... 

.6. .6..6. - .,., ..... 

6 

<f> 1.0 1.5 2.0 2.5 

mm .5 .35 .25 .18 

c 

O PYRIBOLE 

--o..L.....-0 

EPIDOTE / ~ 

> 

JY 

/ 

!::/ 

MAGNETITE .cr-----o 

\."' 

o· 

6 

I 

I 

I 

/ 

/ 

" '\. 

'D 

' 

3.0 

.125 

o~----L_ ____ L_ ____ L_ ____ L_ __ ~ 

<I> 1.0 

mm .5 

1.5 2.0 2.5 3.0 

.35 .25 .18 .125 

3.5 

.09 

8 ~ 8 I 

( 

I 

7 ~ A 

D /I 

/ I 

/ ,' 

6 / I 

EPIDOTE,/ I 

I % /7 I 

I 

5 / I 

/ 0 I 

I 

/ d 

I . I 

/ I I 

of I 

I 

I 

0 I 

3 I 

• I • I 

I 

'\ 

2 / TOURMALINE / 

/ 

I 

/ • / .I / 

., / 

0 

<f> 1.0 1.5 2.0 2.5 3.0 3.5 

mm .5 .35 .25 .18 .125 .09 

MEDIAN GRAIN SIZE OF BED, IN PHI (<f>) AND MILLIMETERS (mm) 

Figure 7. Variation of mineral abundance (as a percent of heavy concentrate) and median grain size. A, Kitt Brook delta, 

major constituents. B, Kitt Brook delta, minor constituents. C, Packerville delta. 

Grain-Size Distributions of Heavy Minerals 

Supplied to Each Delta 

The two deltas differ not only in relative and total 

abundance of heavy minerals but also in the grain-size 

distributions in which each mineral is supplied. The sizes in 

which each mineral is supplied to each delta are best shown 

by size distribution of the mineral in the channel sample of 

each delta (fig. 8), because the channel samples integrate 

foreset sediments and represent the sand-sized component 

of sediment supply to the delta. These size distributions in 

the channel samples are quite different for different miner14 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
als within one delta and differ for the same mineral between 

deltas. The size distributions correspond closely (with a 

correction for mineral density, discussed below) to the 

variation of relative mineral abundance in beds of varying 

median grain sizes (fig. 7). That is, differences in relative 

availability of a mineral in different grain sizes are reflected 

in different abundances of that mineral in different beds. 

Thus a primary control of the mineralogy of a bed is the 

characteristic grain-size distribution of each mineral inherent in the nature of supply. 

Sorting by Shape and Density Within Each Bed 

Figure 4 shows the relation of total heavy-mineral 

size distributions to size distributions of whole samples in 

some typical foreset beds. Heavy-mineral distributions are 

normal and resemble those of the sand-sized portions of the 

whole samples but are typically shifted about 1

h <!> toward a 

finer grain size. A shift of this magnitude and direction is 

expected where all the grains in the sample have similar 

settling velocities. That is, the grains are approximate 

hydraulic equivalents for deposition from suspension (in the 

sense of Rubey, 1933; Rittenhouse, 1943). 

In more detail, each heavy-mineral species has a 

predictable grain-size distribution relative to the grain-size 

distribution of the whole sample. An array of size distributions for all the heavy minerals in a bed sample shows an 

intricate dependence on mineral density and shape. Such 

arrays were generated in this study in two ways. First, for 

those samples in which the 0.177-mm (2.5 <P) grain-size 

split for mineral identification was nearly coincident with 

the median grain size of a particular mineral, the measured 

difference between the median for that mineral and the 

median of the whole sample was determined (see table 4 

and figure 9 for computed values). The values obtained 

from beds of all grain sizes and structures in both deltas are 

quite consistent, being sensitive only to the physical properties of the minerals. The behavior of biotite is unusual for 

heavy minerals; it tends to form grains coarser than the 

sand-sized median of the whole sample. Because biotite 

departs markedly from equant shape, the shape factor must 

have as much importance in its transport as does its density. 

More equant heavy-mineral species show median grain size 

about 0.5 <P to more than 1 <!> finer than the sample mode, 

as a function of mineral density (fig. 9). The progression is 

similar to that documented by Rittenhouse (1943) for fluvial 

deposits. 

A more detailed technique using only one sample was 

applied to the same problem. For sample Kl2, a heavymineral-rich sand with subsidiary coarse mode, minerals 

were identified in four size fractions, and a grain-size 

distribution of each mineral was determined (fig. 10). The 

results are generally similar to these obtained from all 

Table 4. Average arithmetic difference between median 

grain sizes of whole samples and of individual constituent 

minerals, Kitt Brook and Packerville deltas 

Mineral 

Magnetite • • • •• 0 •••• 

Ilmenite ............ 

Gamet ............. 

Dark pyribole ....... 

Light pyribole ...... 

Biotite .............. 

Epidote ..... .. . ... . 

Staurolite ........... 

Sillimanite . . .. . .. .. 

Kyanite ............ 

Zircon •••• 0 00 •••••• 

Tourmaline ......... 

Average 

<!> separation 

toward fines 

All samples K12 

1.05 ...... 1.05 ........ 

1.00 ······ .95 ........ 

. 74 ...... .5 ......... 

.76 ...... }.45 . 71 ....... ...... 

>.5 coarser .45 coarser. 

. 65 0 ••••• .55 ........ 

. 73 0 ••••• .45 ........ 

.48 ...... .50 ........ 

. 60 ...... .20 ........ 

1.00 ······ .80 ........ 

. 58 . ..... .65 ........ 

Number of 

observations 

3 

3 

7 

6 

7 

2 

5 

6 

5 

4 

2 

5 

samples (table 4), and the array again is a function of 

mineral density and shape (note kyanite in fig. 9). 

Figures 9 and 10 strongly suggest that deposition of 

heavy minerals in the foreset beds occurred in conditions of 

suspension equivalence (that is, that grains of the same 

settling velocity occur together). This suspension equivalence in turn is consistent with our bulk compositional data 

that show no enrichments of heavy minerals in foresets 

compared to source rocks. Enrichment generally involves 

more complex types of hydraulic equivalence (Rittenhouse, 

1943; Force, 1976; Komar and Wang, 1984; Slingerland 

and Smith, 1986). 

Implications regarding sorting studies. -Figure 10 

shows that sample Kl2, although moderately well sorted 

(So 1.5, Folk-Ward 0.80), actually contains a mixture of 

mineralogic size populations, each of which is much better 

sorted (So 1.2-1.3, Folk-Ward 0.28-0.52) than the whole 

bed. The heavy minerals together form a heavy-mineral 

fraction having So 1.3 (Folk-Ward 0.52). Thus this sample 

is a mixed population both texturally (admixed coarse 

mode) and mineralogically (heavy minerals), and both 

factors contribute to lesser sorting for the whole sample. 

Where grains of the same shape and density are 

measured, the sorting of glacial lake delta sands can be 

exquisite. The size distribution of the whole sample is only 

a weighted average of a series of tighter distributions of 

individual minerals. Among unimodal samples, polymineralic sands that have minerals differing in density and shape 

are necessarily more poorly sorted than monomineralic 

sands deposited under similar conditions. Although this 

effect is probably minor in most polymineralic sands, it 

works contrary to the purpose of sorting investigations. We 

suggest that, in studies of mineralogically immature sands, 

Factors Controlling the Heavy Mineralogy of Each Bed 15 
3 

GARNET 

2 

z 0~----~------~----~------~----~ 

Q <f> 0 

t)mm1 

<{ 

a: 

u. 

w 

N 

en 

LL. 

0 

1-

z 

w 

1 

.5 

ffi 4 EPIDOTE Q.. 

Cl) 

<( 

...J 

<{ 

a: 

~ 3 

~ 

2 

2 

.25 

3 

.125 

4 

.062 

5 

.031 

10 

PYRIBOLE 

9 

8 

7 

6 

5 

3 

2 

o~----~------~----~------~--~ 

<f> 0 1 2 

mm 1 .5 .25 

3 

MAGNETITE 

2 

3 

.125 

4 

.062 

5 

.031 

o o~----~--~~------~----~----~ 

<f>O 2 3 4 5 <f>O 1 2 3 4 5 

mm1 .5 .25 .125 .062 .031 mm 1 .5 .25 .125 .062 .031 

GRAIN SIZE FRACTION OF CHANNEL SAMPLE, IN PHI (<f>) AND MILLIMETERS (mm) 

Figure 8. Concentration of heavy-mineral species in grain-size fractions of channel samples of exposed foreset 

sequences in the Kitt Brook and Packerville deltas. Mineral abundance is shown as a percentage of each 

grain-size class. 

16 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
z 

<( 

a: 

1.5~ 

0 

w 

~ 

~1.0 

u:::: u. 

0~~ z-a: oClw 

- w :z 5 ~-~- . <( ~ 

a:w <(.....J 

Q..Cl. 

w~ en<( 

~en 

-~a: 

-ow 5: a: en 

u.a: 

0 

.....J <( 

a: <( 0 u ~· ~ <( .5 

~ a: 

w 

z 

~ 

EXPLANATION 

e Light fraction (Quartz and Feldspar) 

b. Biotite 

0 Kyanite in sample K12 0 

0 Other heavy minerals Cf3 

• 

00 00 

oo 

Jto oo 

0 

0 

1.0~--~----~--~----~----~---l___j 

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 

MINERAL DENSITY (p) 

>- u 

z 

w 

::> 

a 

w 

a: 

u. 

SIZE DISTRIBUTION 

OF ENTIRE SAMPLE 

GRAIN SIZE (1/2 <!> INTERVAL SHOWN) 

Figure 9. Mineral density versus the difference between median mineral grain size and median sample grain size, 

derived from all samples from the Kitt Brook and Packerville deltas. Inset (right) shows idealized relation to frequency 

diagram of a whole sample. 

sorting of minerals of similar density be measured to avoid 

confusing textural and mineralogic immaturity. 

Implications regarding heavy-mineral study techniques. - The common technique of comparing the heavy 

mineralogies of only one standard size interval among 

samples would have had inadequate or misleading results if 

employed for these sands (and for others, as first noted by 

Rubey, 1933). Any given size interval falls in differing 

relation to the grain-size distributions of various samples 

and thus enriches different parts of the density-shape 

spectrum of mineral species. Two samples having identical 

bulk mineral assemblages but different grain-size distributions will yield different mineral assemblages if only one 

size fraction is examined. We emphasize that this common 

technique is misleading except where ( 1) sediment is 

unsorted, (2) all samples have the same sand-sized mode, or 

(3) relative abundance only of minerals of the same density 

is considered. 

Factor Interrelation and Consequent Predictive 

Capacity 

In the study area, each source terrane and its icemarginal drainage system contributed debris that had a 

characteristic proportion of minerals. Grains of each mineral were supplied in a characteristic size distribution. The 

supply distributions for Kitt Brook are shown in figure llA, 

which was generated from information found in figures 7 

and 8. Each bed (or lamina) draws grains from the population supplied. 

As a result of hydraulic factors, each bed (or lamina) 

has a certain grain-size distribution for light minerals and a 

family of related heavy-mineral distributions (fig. liB). A 

particular heavy mineral is concentrated where the size of 

the mineral that can be deposited by the flow (fig. llB) 

corresponds with a size supplied in abundance (fig. llA). 

For the fine-sand sample shown in figure llB (solid 

curves), very fine-grained ilmenite and medium-grained 

Factors Controlling the Heavy Mineralogy of Each Bed 17 
w 40 

...J 

a.. 

~ 30 (/) 

u. 

0 20 

1-

z 

w 10 u 

a: 

w 

a.. 0 

40 

(/). 

...J 

<( 1- 30 a::z 

Ww 

zu 

~ ffi 20 

~a.. 

<( ~ 10 w 

I 

100 

1-

~ 80 u a::...J 

w<( 

a.. ffi 60 

~~ 

i= ~ 40 ~u. ::)0 

3 20 

u 

mm 2 

8 

0 2 3 

1 .5 .25 .125 

MEDIAN GRAIN SIZE OF MINERALS 

IN PHI (<!>) AND MILLIMETERS (mm) 

4 

.062 

Figure 10. Grain-size distribution histograms for sample 

K12 of, A, Whole sample, B, Heavy minerals, and, C, 

Cumulative curves for whole sample and several mineral 

species. Dark pattern denotes heavy minerals. 

biotite are concentrated. For a coarser sample, the whole 

grain-size distribution, including all the component heavymineral curves, would be shifted to the left so that different 

components of mineral supply would be tapped. In a sample 

having Md -0.5 <f> (dashed, fig. liB), coarse garnet would 

be concentrated instead of biotite and ilmenite. Where the 

nature of the supply is different, as it is at Packerville, the 

minerals concentrated at each median grain size would also 

be different. 

Given the grain-size distribution of any sample and 

the size distributions of mineral supply in its delta, we 

should be able to predict abundance and grain-size information for each heavy-mineral species. The modal grain 

size of a given heavy-mineral species is calculated relative 

to the sand-sized mode of the whole sample, by use of 

figures 9 and 10 and table 4. The abundance of this mineral 

in this sample is proportional to the height of the supply 

distribution of the mineral at its modal grain size. Our 

prediction method embodies the hydraulic ratio concept of 

Rittenhouse (1943) but, in our opinion, is easier to use. 

MODE OF HEAVY-MINERAL DEPOSITION 

The grain-size relation of heavy-mineral species to 

light minerals and to other heavy minerals in the foreset 

beds of the two deltas strongly suggests that deposition from 

suspension was an important process, as the grains have 

similar settling velocities. There is no evidence in the 

grain-size distributions for enrichment by reentrainment, as 

described by Slingerland and Smith (1986), for this process 

selects more by grain size than by density and produces less 

size separation among the array of mineral populations than 

we observed. The little heavy-mineral enrichment that we 

observed in some beds is explained by the interrelation of 

bed texture and the size distribution of mineral supply. 

Observations from sedimentary structures are consistent with an important suspension component of deposition 

and suggest that this component varied from bed to bed. In 

those beds or intervals showing type-B climbing ripples, 

traction transport must be minor, and deposition was largely 

from suspension (Jopling and Walker, 1968; Ashley and 

others, 1982). Type-A ripples show that traction transport 

was more important, that reentrainment occurred, but that 

accumulation from suspension was still important. Some 

foreset beds having moderate dip show transitions from 

planar to very low-angle type-A rippled beds; these beds 

have still higher components of traction transport. In all 

beds regardless of structure, however, suspension equivalence is suggested by the grain-size distributions of constituent minerals. Sample Kl2, from a planar bed just above a 

disconformity, is our best studied example of suspension 

equivalence. 

The sandy foreset beds are rather well sorted. Minerals of equal density are locally very well sorted (even in 

the terminology of Folk and Ward, 1957). The depositional 

mechanism must explain not only suspension equivalence 

but also this locally excellent sorting. 

We envision deposition from continuous but nonsteady turbidity currents moving down foreset slopes as 

turbid suspensions denser than lake water. On upper fore set 

slopes of 10° to 30° where deposition is occurring, there is 

little evidence of either deceleration or acceleration of flow 

at a scale of individual outcrops. Only grains having a 

certain minimum settling velocity can settle out from such a 

suspension. In poorly sorted coarse beds, all such grains are 

deposited with bedload. However, most sand beds show a 

narrow spectrum of settling velocities. Finer grains were 

deposited elsewhere. The role of traction transport varied 

from bed to bed. 

18 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
7 

en 

...J 

<( 

a: 6 w 

zw 

-o 

~<( 

>-a: 5 

>(.!) 

<Cw WN :I:-en 4 

!z~ wUa: ::I: wa.. 3 a..--0 ww 

r-::J 

<(0.. 2 ::!:0.. 

-:::::> X en 0 

a: 

a.. 

a.. 

<( 

0 

50 

z 

Q 40 w .... ...J::> 

0..~ 

~a: 

<( .... 30 en~ 

._o 

Z>-

~ ~ 20 a:w 

w::> 

0..0 

w 10 a: 

!: 

0 

A 

I 

I 

/ 

8 

/-

/ " 

/ 

/ 

I 

I 

I 

I 

/ 

/ 

I 

/ 

/ / 

100 

<j> -3 -2 -1 0 2 3 4 

mm 8 4 2 1 .5 .25 .125 .062 

GRAIN SIZE OF MINERALS, IN PHI (<!>) AND MILLIMETERS (mm) 

Figure 11. Relation of size distributions of supplied 

debris and of any given sample and its contained minerals. A, The graph for supplied debris is a function of, and 

varies with, the source terrane and erosion agents. The 

distribution shown is for the Tatnic Hill terrane and is 

calculated from the varying mineralogies of beds of 

differing grain sizes in the Kitt Brook delta (see fig. 7) and 

from its channel sample (fig. 8). Each mineral is supplied 

in the range of size intervals shown. B, The size distribuICE-MARGINAL SUPPLY AND DISPERSAL 

SYSTEM 

The contrast in mineral assemblages of the two deltas 

provides constraints on reconstructed dispersal patterns of 

the glacial sediment in the study area. The characteristic 

mineral abundance of each delta is directly related to that of 

the immediately adjacent bedrock source terrane. Distinct 

mineral assemblages and mineral size distributions in each 

delta imply very little mixing of sediment across the 

bedrock terrane boundary. Further, the mineral suites of till 

tion of a sample varies from bed to bed or part thereof. A 

fine sand with its constituent heavy minerals is shown in 

solid lines; this size distribution should be considered 

mobile in its entirety from right to left to represent 

samples of coarser grain size (dashed). Enrichments of 

particular heavy minerals occur where the cumulative 

curve for that mineral in the sample (B) can be made to 

match an interval of abundant supply (A). 

samples from the two source terranes (table 2) are closely 

related to the mineralogy of the two deltaic deposits. 

Accordingly, the transport scheme must be as diagramed 

in figure 12. During deglaciation, glacial transport of till 

was only slightly oblique to the terrane boundary, and little 

debris was dispersed across that boundary. For some 

minerals, for example, magnetite and garnet in euhedral 

grains, grain size in the deltas represents original grain size 

in source rocks. 

Along the stagnant ice margin, meltwater carrying 

locally derived glacial debris converged on Lake QuineIce-Marginal Supply and Dispersal System 19 
WESTERN EASTERN 

(TATNIC HILL) (QUINEBAUG) 

TERRANE TERRANE 

l i ~ ~~\ \ l>rZ)> 

CJ)(") 

-ool> 

:D' 

-I 

N 

0 t 2 MILES 

0 2 KILOMETERS 

Figure 12. Ice-marginal supply and dispersal directions 

in the study area. 

baug. Sand- and gravel-sized sediment was entrained in 

meltwater streams and carried across the delta braidedstream topset plain where most gravel remained. Meltwater 

flow continued into the lakes as nonsteady continuous 

underflows on the delta foreset slopes; the hydraulic parameters of these flows determined the grain size of each foreset 

bed, and with the size distribution of mineral supply, 

determined its mineralogy. 

ACKNOWLEDGMENTS 

We thank Kimberley Winkler for performing many 

mineral separations and Katharine Schindler, John Peper, 

Harry Tourtelot, Norman Smith, and Curt Larsen for 

editing and reviewing the manuscript. Jane Dodge rescued 

the samples from a Connecticut railroad platform. 

REFERENCES 

Aario, Risto, 1971 , Associations of bed forms and paleocurrent 

patterns in an esker delta, Haapajarvi, Finland: Annales 

Academiae Scientiarum Fennicae, ser. A., pt. 3, no. 111, 55 

p. 

Allen, J.R.L., 1971, A theoretical and experimental study of 

climbing-ripple cross-lamination, with a field application to 

the Uppsalaesker: GeografiskaAnnaler, v. 53A, p. 157-187. 

Ashley, G.M., Southard, J.B., and Boothroyd, J.C., 1982, 

Deposition of climbing-ripple beds: A flume simulation: 

Sedimentology, v. 29, no. 1, p. 67-69. 

Cohen, J .M., 1979, Deltaic sedimentation in glacial Lake Blessington, County Wicklow, Ireland, in Schltichter, Christian, 

ed., Moraines and varves: Rotterdam, A.A. Balkema, p. 

357-367. 

---1983, Subaquatic mass flows in a high energy ice marginal 

deltaic environment and problems with the identification of 

flow tills, in Evenson, E.B., and others, eds., Tills and 

related deposits: Rotterdam, A.A. Balkema, p. 255-267. 

Davis, W.M., 1980, Structure and origin of glacial sandplains: 

Geological Society of America Bulletin, v. 1, p. 195-202. 

Dixon, H.R., 1964, The Putnam Group of eastern Connecticut: 

U.S. Geological Survey Bulletin 1194-C, 12 p. 

---1965, Bedrock geologic map of the Plainfield quadrangle, 

Windham and New London Counties, Connecticut: U.S. 

Geological Survey Geologic Quadrangle Map GQ-481, scale 

1:24,000. 

Dixon, H.R., and Shaw, C.E., Jr., 1965, Geologic map of the 

Scotland quadrangle, Connecticut: U.S. Geological Survey 

Geologic Quadrangle Map GQ-392, scale 1:24,000. 

Dreimanis, Alexis, and Vagners, V.J., 1969, Bimodal distribution 

of rock and mineral fragments in basal tills, in Goldthwait, 

R.P., ed., Till, a symposium: Columbus, Ohio, Ohio State 

University Press, p. 237-250. 

Folk, R.L., and Ward, W.C., 1957, Brazos River bar: A study in 

the significance of grain size parameters: Journal of Sedimentary Petrology, v. 27, p. 3-26. 

Force, E.R., 1976, Metamorphic source rocks of titanium placer 

deposits: U.S. Geological Survey Professional Paper 959-B, 

16 p. 

Force, E.R., Lipin, B.R., and Smith, R.E., 1976, Heavy mineral 

resources in Pleistocene sand of the Port Leyden quadrangle, 

southwestern Adirondack Mountains, New York: U.S. Geological Survey Miscellaneous Field Studies Map MF-728-B, 

scale 1:24,000. 

Gilbert, G.K., 1885, The topographic features of lake shores: 

Fifth Annual Report, U.S. Geological Survey, p. 69-123. 

Goldsmith, Richard, and Force, E.R., 1978, Distribution of rutile 

in metamorphic rocks and implications for placer deposits: 

Mineralium Deposita, v. 13, p. 329-343. 

Goldsmith, Richard, Zietz, Isidore, and Dixon, H.R., 1977, 

Correlation of aeroradioactivity and geology in southeastern 

Connecticut and adjacent New York and Rhode Island: 

Geological Society of America Bulletin, v. 88, p. 925-934. 

Gustavson, T. C., 197 5, Sedimentation and physical limnology in 

proglacial Malaspina Lake, Southeastern Alaska, in Jopling, 

A.V., and McDonald, B.C., eds., Glaciofluvial and glaciolacustrine sedimentation: Society of Economic Paleontologists and Mineralogists Special Publication 23, p. 249-263. 

Gustavson, T.C., Ashley, G.M., and Boothroyd, J.C., 1975, 

Depositional sequences in glaciolacustrine deltas, in Jopling, 

A.V., and McDonald, B.C., eds., Glaciofluvial and glaciolacustrine sedimentation: Society of Economic Paleontologists and Mineralogists Special Publication 23, p. 264-280. 

Jopling, A.V., and Walker, R.G., 1968, Morphology and origin 

of ripple-drift cross-lamination with examples from the Pleistocene of Massachusetts: Journal of Sedimentary Petrology, 

v. 38, p. 971-984. 

Komar, P.D., and Wang, Chi, 1984, Processes of selective grain 

transport and the formation of placers on beaches: Journal of 

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20 Heavy-Mineral Dispersal and Deposition in Sandy Deltas of Glacial Lake Quinebaug, Connecticut 
Koteff, CarL and Pessl, Fred, Jr., 1981. Systematic ice retreat in 

New England: U.S. Geological Survey Professional Paper 

1179, 20 p. 

Krynine, P.D., 1937, Glacial sedimentology of the QuinnipiacPequabuck lowland in southern Connecticut: American Journal of Science, v. 33, no. 194, p. 111-139. 

Rittenhouse, Gordon, 1943, Transportation and deposition of 

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v. 54, p. 1725-1780. 

Rubey, W.W., 1933, The size distribution of heavy minerals 

within a water-laid sandstone: Journal of Sedimentary Petrology, v. 3, p. 3-29. 

Schafer, J.P., and Hartshorn, J.H., 1965, The Quaternary of New 

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

Quaternary of the United States: Princeton, New Jersey, 

Princeton University Press, p. 113-127. 

Serrat, David, Vilaplana, J.M .. and Marti, C.E., 1983, Some 

depositional models in glaciolacustrine environments (southem Pyrenees), in Evenson, E.B., and others, eds., Tills and 

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16, p. 135-216. 

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Jewett City quadrangles, central eastern Connecticut: Baltimore, Maryland, The Johns Hopkins University, Ph.D. 

dissertation, 217 p. 

---1978, Surficial geologic map of the Jewett City quadrangle, New London County, Connecticut: U.S. Geological 

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interglacial stratigraphy of New England, Long Island, and 

adjacent Georges Bank and Gulf of Maine, in Sibrava, 

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Stone, B.D., and Force, E.R., 1980, The Port Leyden, New 

York, heavy mineral deposit: New York State Museum 

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---1982, Sedimentary sequences and petrology of glaciolacustrine deltas, eastern Connecticut, U.S.A.: 11th International Congress on Sedimentology, Hamilton, Ontario, Aug. 

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Trask, P.D., 1932, Origin and environment of source sediments of 

petroleum: Houston, Texas, Gulf Publishing Co., 323 p. 

References 21 



SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

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Professional Papers are mainly comprehensive scientific reports of 

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