Holocene alluvial stratigraphy in the upper Susquehanna River Basin, New York

QUATERNARY

RESEARCH

15,

327-344 (1981)

Holocene Alluvial Stratigraphy in the Upper Susquehanna River Basin, New York’ RICHARD W. SCULLY~ AND RICHARD W.AR&OLD~ Department

of Agronomy,

Cornell

University,

Ithaca,

New

York

14853

Received February 3, 1978 Two alluvial terraces and the present flood plain were studied at two locations along the Susquehanna and Unadilla Rivers in south-central New York state. They have formed since deglaciation and incision of the stream channels into the valley train deposits. The higher terrace has noncumulative soil profiles with well-developed color B horizons predominantly of silt loam and very fine sandy loam. The terrace is weathered to a degree similar to nearby glacial outwash terraces that have caps of similarly textured sediments. Incision that produced the terrace occurred before 9705 5 130 yr B.P. The lower terrace is characterized by relatively thick, vertical-accretion deposits of silt loam that contain sequences of thin, buried A, color B, and C horizons. They were formed between about 3240 ? 110 (‘“C date of soil humin) and 235 t 80 yr B.P. Deposits above the 235 ‘-’ 80 yr B.P. stratum are unweathered. The soil stratigraphy and r4C dates of soil humin from buried A horizons are surprisingly well correlated between sites. Most sediments of the present flood plain have been deposited since 1120 f 80 yr B.P. Incipient A horizons and oxidation of inherited organic matter in the subsoil are the only evidence of pedogenesis in the flood-plain deposits that are older than 275 2 80 yr B.P. The most recent flood-plain till deposited since then is unaltered. These youngest sediments of the flood plain along with the youngest veneer of verticalaccretion deposits on the lowest terrace are associated with an increased rate of deposition largely attributable to clearing of the forests by settlers, beginning in the late 1700s. Comparison of the alluvial stratigraphy with the radiocarbon-dated pollen stratigraphy of southwestern New York (Miller, 1973) reveals some apparent time correlations between alluvial events and vegetation changes. This gives reason to speculate that climatic change or forest catastrophes such as disease or drought are causes of some of the alluvial events.

INTRODUCTION

geomorphologists if it could be related to the age or stability of an alluvial surface. The localities with alluvial deposits were selected because soil map units thought to represent different terraces and ages of parent material in well-drained alluvium had been mapped by the soil survey then in progress, and buried, dark-colored soil horizons could be observed. By selecting these particular localities we are aware that some areas of buried soil horizons may be anomalous and maximum terrace expression may represent only those areas of greatest stream incision or migration, but this is where the stratigraphic record is most apparent. This paper deals primarily with the stratigraphy. More detailed analysis of the soils, particularly the significance to soil classification, is presented in another paper (Scully and Arnold, 1979).

The impetus for the study came from a desire to improve the effectiveness of soil map units for flood-frequency interpretation. It was our belief that an improved understanding of how soil profiles are related to the stratigraphy of the soil parent material and topography would help soil surveyors make more meaningful soil maps of alluvial deposits and those maps would be more useful for flood-plain management. In a similar manner, soil morphology might be used more as a tool in terrace mapping by ’ Agronomy Paper No. 1229. Department of Agronomy, Cornell University, Ithaca, N.Y. 14853. * Present address: 1865 Norwood Ave., Boulder, Colo. 80302. ’ Present address: Soil Conservation Service, U.S. Department of Agriculture, Washington, D.C. 20013. 327

0033-5894/81/030327-18$02.00/O Copyright All rights

0 1981 by the University of Washingu of reproduction in any form reserved.

3”.

328 GEOMORPHOLOGY

SCULLY

OF STUDY

AND

SITES

The two localities are in Chenango County, New York. One is along the Unadilla River (U-site, Fig. l), 5.6 km north of the present confluence of the Unadilla and Susquehanna Rivers, and about 48 km northeast of Binghamton, New York. The other site is along the Susquehanna River (S-site, Fig. l), 4.5 km downstream from the same confluence. The drainage of the Unadilla River above the Rockdale gaging station (Fig. l), 2.5 km upstream from the

ARNOLD

U-site, is about 1350 km2. Above the Bainbridge gage on the Susquehanna River, 2.7 km downstream from the S-site, the drainage area is about 4200 km2. Both areas are located in the glaciated Appalachian Plateau within glacially scoured valleys that have truncated spurs and steep valley walls. From 15 to more than 75 m of glacial drift dating from the Woodfordian Stade of the Late Wisconsin Glaciation fills the valley bottoms (Cadwell, 1972). Glacial deposits occupy the larger portion of the valley as valley trains, kame

N

FIG.

1. Map

of study

area in New

York

State.

HOLOCENE

ALLUVIAL

terraces, kames, and proglacial lake terraces and beds. The postglacial terraces and flood plain occupy the smaller portion of the valley. The bedrock of the watershed is predominately noncalcareous shale, sandstone, and siltstone. A small percentage of limestone in the glacial drift was carried in by glaciers from outcrops on the northern edge of the watershed. Cadwell (1972) found that the percentage of limestone clasts in the glacial drift in the Unadilla River and Susquehanna River valleys averaged 5.4 and 1. I%, respectively. The pH values of the flood-plain sediments are slightly acid and medium acid (Scully and Arnold, 1979). The deposits are acid enough that contamination of radiocarbondated samples by ancient carbonates is not thought to be a problem. METHODS

A reconnaissance of the localities was made by boring on a 60-m grid. A study site, extending from the river to at least the upper limit of postglacial alluvium, was then selected within each locality to include all the soils and alluvial surfaces present. Detailed topographic maps of the study sites were prepared and from these maps transects were selected for sampling. Two transects were made at the S-site and three at the U-site. Sampling sites along these transects included every ridge and swale. Sampling was done by small depth increments rather than by horizons to objectively test the system of horizon nomenclature and concepts (Soil Survey Staff, 1951) which are not easily applied to cumulative soils (Riecken and Poetsch, 1960). Each sample combined the same depth increment from four borings placed within a square meter. Except where abrupt changes were observed, sampling increments were (a) Ap horizon--one sample; (b) bottom of Ap to 75 cm-one sample per 5-cm increment; (c) 75 cm+--one sample per 12.5cm increment. Where encountered, buried organic-rich

STRATIGRAPHY

329

horizons and charcoal fragments were sampled from backhoe excavations. Plant debris preserved below the water table at the contact between sandy lateral-accretion deposits and gravelly channel-lag deposits was sampled from excavations and borings. Samples for radiocarbon dating included wood, charcoal, and soil (Table 1). The soil samples were pretreated by a procedure modified after Campbell et al. (1967) and humin (including hydrolyzable and nonhydrolyzable fractions) was the residue dated. Those samples taken below the water table were very well preserved with the exception of the sample at site 9 (880 + 130 yr B.P.) which was in an advanced state of decomposition. Certainly the soil humin and possibly the charcoal samples are subject to contamination by root and mobile humic acid additions of young carbon. However, the close stratigraphic context of the samples and the remarkable agreement of dates (Tables 2 and 3) from the same stratigraphic position suggest that contamination is not as serious as might be expected. Where the chronology is based on radiocarbon dates of soil humin from A horizons it is noted because those are the samples which are most likely to suffer from contamination. USE OF SOILS IN ALLUVIAL STRATIGRAPHY

The geologic maps presented here (Figs. 2 and 3) use units defined primarily on the basis of alluvial surfaces that also correspond to major soils. The units are further subdivided by more-detailed soil and topographic characteristics. The older postglacial and glacial terrace deposits in New York and Pennsylvania have not been differentiated on the basis of soil properties related to age (Denny and Lyford, 1963; Peltier, 1949). Similarly the soils on the outwash terraces and oldest postglacial terrace (V2, Vl, and T2 in Table 2 and Fig. 4) at our sites are noncumulative and have similar degrees of development. This study concentrates on the alluvial de-

46-58 64-66 84-89 102-107 135-140 460 86-109 460 230 230

112-122 215 140 150 110 150 180

30-36 42-46 68-71 76-86

Sample depth (cm)

Charcoal Soil humin Soil humin Soil humin Soil humin Wood Charcoal Wood Wood

Soil humin Soil humin Soil humin Soil humin Soil humin Wood Wood Wood Charcoal Wood Wood

Sample material Unadilla site

I-9640 I-9515 I-9516 I-9526 I-9514 l-9527 I-9528

130 80 80 80 80 80

k tf 2 2 +

I-9685 I-9681 I-9642 I-9683

Lab No.

-c 100 2 110

2 95 k 85 2 85

235 f 80 6601?:90 2195 -c 95 2225 2 90 2840 f 105 4670 2 95 615 2 80 7220 r 120 880 k 130 280 2 125

I-9512 I-9684 I-9641 I-%82 I-9639 l-9529 I-9513 I-9531 I-9530 I-9638

Susquehanna site

665 1490 2130 2430 3240 9705 1120 505 295 615 275

Radiocarbon age (yr B.P.)

1760-1435

1770-1470

1650- 1460

1650-1450

Corrected date” (A.D.)

1. RADIOCARBON DATESAND VERTICAL ACCRETION RATES

20-16 31-23 155-57

O-230 O-230

(7.9-4.1)

37-18 (3.1-1.3) (1.7-1.3)

13-12 35-26 51-29 25-8 92-51

(6.1-4.6) (1.6-1.0) (5.3-3.1) (13-3.6) (5.9-3.6)

Accretion rate (cm/centuryb~e)

O-109

O-58 58-66 66-89 89-107 107- 140

O-180

O-110 1 lo- 150

O-150

O-140

O-36 36-46 46-71 71-86 86-122

Accretion depth (cm)

n Radiocarbon age corrected by means of a dendrochronology correction curve (Ralph et al., 1973). * Accretion rates calculated using radiocarbon ages. Differences between these accretion rates and accretion rates calculated using corrected ages are much less than the error introduced by the radiocarbon date error. c Rates in parentheses are calculated using soil humin radiocarbon dates.

7 8 9 10

6

5

2 3 4

1

Sample site (Figs. 2 and 3)

TABLE

HOLOCENE TABLE

ALLUVIAL

331

STRATIGRAPHY

2. SUMMARY OF RELATIONSHIPS BETWEEN TIME-STRATIGRAPHIC UNITS, LANDFORMS, AND SOI t.s

Timettratiorcmhic

“k veers

‘%

Dates

Q.P.

I” lateral occretlo” U-site S-site

280

-

14C

Dotes

B.P.

in vertical occrstion U-site S-sit*

. 295

Hop FiQ.

units 2 6 3)

-

a3

-

Flood

F-2

Plain

F --

-----_---ACT C

F-3

--

---

Ab COX -----,

----------.

;2130) ,243O)

Typical I22 (2840)

Subfills %aa Old

,324O)

Ab Bb Ab Bb COX

Tl

‘leistocene wries

Second T2

V1.2,3 K L

alley train terraces cllley train me ocustrine tsrrac*

B Ab Bb COX

SWQlEZ AP Ab Bb Ab Bb Ab C Ab C Ab COX

AP

Terrace -----.

Nate. Radiocarbon

types

Ridgo

1

B COX ------_--_.

AP B COX

dates of soil humin in parentheses.

posits of the flood plain and lowest terrace (Tl and F). These deposits have received enough recent deposition to visibly affect the development of soil profiles. Leopold et al. (1964, p. 467) said that because of the irregular surface of both the lowest terrace and the flood plain in many areas, their differentiation may be difficult. That problem was solved at these sites by using pedologic criteria to define the depositional units comprising the first terrace and flood plain. The pedologic criteria presented here are not like those usually used in soil-stratigraphic studies (Birkeland, 1974, p. 258; Leopold et al.. 1964, p. 471; Morrison,

1967, p. 9) because these soils are not simple A - B-C profiles. The Holocene alluvial surfaces, which are constructional, include the flood plain (first or low bottom in soilsurvey terminology) and the first terrace (second or high bottom). Deposition on these surfaces has been episodic enough to allow the use of soil sola (plural of solum) to distinguish deposits of different age or origin. In this case the sola are thin, incipient soil profiles. The sola are recognized as thin, buried A horizons or buried A and color B horizons but lack the so-called zonal development because they were young when buried, having been formed on accreting surfaces. The resulting soil pro-

92-112 112-127

127+

A12b2 B2b2 Alb3

C3 Alb4

C4 Alb5

B2b6’

312 414 2/l

412 312

412

412

71-76 76-92

3240 2 110 (112-122)

2430 2 100 (76-86)

2130 k 85 (68-71)

1490 + 85 (42-46)

665 + 95 (30-36)

yr B.P. (Depth, cm)

COMPARISON

IDENTICAL

5

4 4

4 4

4 4 4

3

3

1-2 3

Time-stratigraphic units

FROM

413

313 312

312 3/l

312 413 2.511

2.511

3/l

312 312.5

Dominant color 10 YR

SHALLOW

Note. Both positions were chosen for maximum expression of soil stratigraphy. ’ Munsell Color Chart designations of hue (IOYR), value and chroma (V/C). * Superscripts indicate the solum number within the profile. ’ Very compact, stiff, and with bright mottles.

3.512

42-48

Allb*

311

48-58 58-68 68-71

36-42

B2b’

414

O-30 30-36

Depth (cm)

AP Alb’

Soil horizon designation*

U-site

3. SOIL STRATIGRAPHIC

312 3/l

Dominant color 10 YR”

TABLE

B2b5 or C5

C4 Alb5

C3 Alb4

A12b” B2b2 Alb3

AllbZ

AP C

Depth (cm)

S-site

157+

109- 119 119-157

89-97 97- 109

68-78 78-83 83-89

61-68

46-61

2840 2 105 (135-140)

2225 k 90 (102- 107)

2195 + 95 (84-89)

235 k 80 (46-58) 660 ‘- 90 (64-66)

yr B.P. (Depth, cm)

THE FIRSTTERRACE

O-36 36-46

POSITIONSON

Soil horizon designation*

SWALE

4 4

4

3-4 4

3

2

1 I

Time-stratigraphic units

(Tl)

334

SCULLY AND ARNOLD

0 I

loo

200 4

maters Approximate fcole

[3

E vertwial

exaggeration

15X

FIG. 4. Schematic cross section showing relationships Table 2.

files in the top 1.25 m of sediment are cumulative soils, often comprised of several sola, not easily described with the A-B-C horizon nomenclature (Riecken and Poetsch, 1960). The degree of color expression and chemical development of these sola or miniature buried soils is thought to be directly related to the rate of accretion of the surface (Leeder, 1975) and that, together with the sequences they comprise, serve as criteria for differentiation among the postglacial fills. Legend

of Geologic Units Shown in Figures 2 and 3 Holocene Series C-Present channel deposits C-c-Point bars and channel bars C-d-Tributary deltas F-Flood plain F-l-Youngest subfill F-2-Intermediate subfill F-3-Oldest subtill F-a-Abandoned channel, undifferentiated F-s-Swale, undifferentiated Tl-First terrace Tl -Undifferentiated Tl-l-Ridge, multiple Ab horizons

Soil Vertical

r

Lateral

m

Channel

fz!J

Lacustrono

accretion accretion

deposits deposits

log gravels deposits

between landforms and deposits. See also

Tl-2-Ridge, single Ab horizon Tl-r-Ridge or interswale flat Tl-s-Swale Pleistocene Series T2-Second terrace T2 -Undifferentiated TZr-Ridge TZs-Swale Glacial Drift Vl-c -Low valley train terrace, abandoned channel with silt cap Vl-si -Low valley train terrace, silt cap V2-sa-High valley train terrace, sand cap VZsi -High valley train terrace, silt cap v3 -Valley train, undissected L -Lacustrine terrace K -Kame or kame terrace n-p Detailed transect 14C date location oASSUMPTION OF SYNCHRONY Underlying the discussion of the alluvial chronology is the assumption of synchrony of events at the localities, as the stratigraphic sequences of deposits from the two sites have been used to formulate a single chronological sequence. The correspon-

HOLOCENE

ALLUVIAL

STRATIGRAPHY

335

pedologic age and radiocarbon date corredence of most deposits at both localities lations rather than only on geomorphic bounded by acceptably correlative radiocarbon dates (Table 2) is the basis for surfaces. For the practical purposes of flood-plain the assumption. Though events were simimapping, it should be determined whether lar in time and space, they may not have the terraces are nonpaired or paired bebeen synchronous, and possibly were out of phase by a few centuries. Such time intercause that will likely have an effect on whether the frequency of flooding of the vals become more important when intersecond-bottom soil-map unit (first terrace, preting the younger events which, because of a more bountiful geologic record, can be Tl) has a wide or narrow range. In our analyzed on a more detailed time scale on view, paired terraces are more likely to corthe order of hundreds of years. There may respond to a specific flood-frequency be a finite limit to the detail with which al- height. luvial events can be correlated. Local conALLUVIAL STRATIGRAPHY ditions affecting the time when a geomorDeglaciation phic threshold was surpassed (Schumm, 1973), minimum errors in radiocarbon dates The area was last glaciated shortly before (here +-80 yr), and second-order fluctuathe Valley Heads Moraine was formed to tions in the relationship between real years the north, about 14,000-12,000 yr B.P. as determined by dendrochronology (Ralph (Coates, 1971; Cadwell, 1972). Proglacial et al., 1973) and radiocarbon years may lacustrine deposits locally form a high termake correlation difficult for alluvial perirace (L in Fig. 4) of thick, well-sorted silt and very fine sand at the S-site. The valley ods during the past 1000 yr which were on the order of 200- to 600-yr long. train (V) that was formed during ice retreat To illustrate the fact that the deposits of a was incised deeply, compared to later postsingle episode cross the geologic map glacial incision, probably after meltwater boundaries in Figures 2 and 3 the deposits ceased contributing to the sediment load. are subdivided into informal time-stratiThe glacial drift comprises time-stratigraphic units (Fig. 5). This is done with graphic unit 7 (Fig. 5 and Table 2). depositional markers of charcoal seams and soil horizons, and with numerous ra- Late Pleistocerle Alluvium The late Pleistocene alluvium includes all diocarbon dates. The correlation of alluvial terraces on the the lateral-accretion deposits and some of basis of topographic position may be inapthe vertical-accretion deposits of the secpropriate if they are nonpaired. Nonpaired ond terrace (T2). These deposits formed alluvial terraces can be formed by steady after the channels incised following demigration of a degrading channel and may glaciation and prior to 9705 +- 130 yr B.P. not be related to a specific degradational The Holocene/Pleistocene boundary is event following a period of stability, as taken as 10,000 yr B.P. paired terraces are (Schumm, 1977, p. 212). Following the major postglacial incision, The area1 extent of this study (Figs. 2 and 3) a period of stability in channel elevation ocis insufficient to determine whether the curred, indicated by paired terrace remlowest terrace (Tl) is paired or unpaired. nants (T2 in Fig. 2) on opposite sides of the Also, the undulating surfaces and small river at the U-site. These deposits now comprise the second terrace. The fill is not amount of relief (as little as 0.5 m average difference in elevation between the first or always a distinct terrace where the next lowest terrace (Tl) and the second terrace younger fill has been accreted to nearly the (T2)) make such a determination difficult. same height or where colluvium covers the Synchrony is based primarily on inferred second terrace. Even at the U-site where

\

v2

,

I

I

-4670t85

FIG. 5. Schematic cross section showing relations among the time-stratigraphic

RIVER SITE

RIVER SITE

SUSQUEHANNA

UNADltlA

VI

RAOlOCARl3ON

~-2

DATE

:

I

F-f

VERTICAL EXAGGERATION 15x units. No. 1 is the youngest and No. 7 is the oldest.

I

I I I

HOLOCENE

ALLUVIAL

the terrace is best expressed it is an average of only 0.5 m higher than the next younger terrace. Soils on the second terrace usually possess simple A/color B/C profiles that have no distinct buried horizons except where swales adjacent to the valley wall trap colluvial sediment. In some profiles darker colors at the base of the Ap horizon suggest that a buried A horizon may have been incorporated into the present Ap horizon by plowing. Early -Middle

Holocene

Alluvium

The early-middle Holocene alluvium includes the lateral-accretion deposits of the first terrace (Tl) as well as much of the vertical-accretion deposits of that terrace and probably some on the second terrace. The deposits formed from before 9705 ? 130 to roughly 1500 yr B.P. The first terrace is an undulating surface with a few swales, that at the S-site separate subtills of differing ages. As best as can be determined by the undulating topography of the sand/gravel contact (Fig. 6) the channel-lag gravels of the first terrace are incised slightly below those of the second terrace. The lateral-accretion deposits of the first terrace were deposited as the channel migrated laterally at a stable elevation from before 9705 +- 130 to after 4670 2 95 yr B .P. and possibly as late as about 1500 yr B.P. At the S-site, while new lateral-accretion deposits were forming the old ones were covered by vertical-accretion deposits and the older subtill was thus built up. By the time of channel incision that marked the start of formation of the flood plain the surviving sublills of the first terrace there had been built up to a common height. Thus a single terrace was formed from two main subtills of different age. The older subfill at the S-site has received less recent deposition and soil development is more advanced than in the younger subtill. The older fill has an A/ color B horizon sequence (solum) buried

STRATIGRAPHY

337

beneath a thinner A/color B horizon sequence. The buried solum has not been dated but would probably be correlated with some buried horizon in the younger till. The younger fill contains a complex sequence of buried A/color B and C horizons that are remarkably similar to the ones developed in similar silty vertical-accretion deposits at the U-site (Table 3). The number of distinct horizons is greatest in the swales described in Table 3. On the ridges the horizons merge or thin. Some of the Ab horizons at the S-site can be traced over an area of 8 hectares on the ridges. Similar kinds of sola sequences occur on the first terrace at the U-site but there is no orderly pattern of soils on subfills. Soil variability here on the interswale areas is apparently erratic and buried horizons cannot be traced very far laterally. The early-middle Holocene alluvium is divided into two time-stratigraphic units (Fig. 5). The boundary between the two is chosen at the base of the oldest Ab horizon on the first terrace (Table 3) dated at 2840 ZL 105 and 3240 +: 110 yr B.P. on soil humin (referred to below as roughly 3000 yr B.P.). This assumes the Ab horizon in the older subtill at the S-site is no older. Time-stratigraphic unit 5 includes all the lateral-accretion deposits and the older vertical-accretion deposits of the first terrace. The vertical-accretion deposits lack buried soil horizons and charcoal seams, so their age is deduced by position. There are probably vertical-accretion deposits of the same age on the second terrace that have not been identified as such. At the U-site there is only a thin deposit from this period, suggesting that lateral accretion was dominant there. The age of the unit is pre-9705 2 130 to roughly 3000 yr B.P. Time-stratigraphic unit 4 includes a series of three Ab horizons alternating with lighter-colored, less-altered horizons and other Ab and Bb horizons above in the first terrace swales (Table 3) and time-equivalent horizons elsewhere on the first terrace. Burial of the A/color B horizon se-

338

SCULLY

AND

ARNOLD

UNADILLA RIVER Transect n -0

0

qo

SUSQUEHANNA Transect

R I VER j-k

SITE

S ITE

FIG. 6. Cross sections of generalized texture of sediments. Vertical exaggeration is 15 x Data for the “C sites are in Table 3 and Figure 7. Textural groupings are: (SI) silt loam with inclusions of loam and small lenses of sand; (CSI) silt loam with significant amount of very fine sand; (LO) loam with significant inclusions of very fine sandy loam and some inclusions of tine sandy loam, silt loam, and sandy loam; (SA) sand and loamy sand. Without a modifier the texture is too variable or data insufficient to classify sand sizes: (G) very gravelly and gravelly sands, loamy sands, and sandy loams. Modifiers indicate dominant size of sand fraction; where several modifiers they indicate dominance and subdominance. (VF) Very fine; (Ft tine: (M) medium; (C) coarse and very coarse.

quence on the older subfill of the first terrace at the S-site most likely occurred at this time. Again, some vertical-accretion deposits of the second terrace probably belong in this unit. The unit spans from roughly 3000 yr B.P. to the time of channel incision that started the formation of the present flood plain. The flood-plain initiation probably correlates with the slowing of vertical accretion and the first formation of color B horizons (Fig. 7) in the younger part of the first terrace (in Table 3 horizon B2b2 at the U-site and B2b2 at the S-site) around

1500 yr B.P. (1490 + 85 yr B.P. on soil humin on horizon Allb* at the U-site, Table 3). Late Holocene Alluvium

The late Holocene alluvium includes the flood-plain deposits as well as a veneer of vertical-accretion deposits on the terraces that were formed from roughly 1500 yr B.P. (see above) to the present. The topography of the flood plain is undulating, with a network of swales that carry floodwater. The nature of the

HOLOCENE

ALLUVIAL -ected

STRATIGRAPHY 14C yrs

339

B.P.

M-

U-site S-site

-____

FIG. 7. Accretion-rate curves for comparable shallow swale positions on the first terrace (TI). Curves are orimarilv based on radiocarbon dates of soil humin. See Figures 5 and 6 for landscape positions and Table 3 for stratigraphic sections.

vertical-accretion deposits differs between the two sites. A the U-site the verticalaccretion deposits are relatively thin and more sandy. On the same alluvial surface at the S-site soil development is entirely within silty vertical-accretion deposits which are as thick on the flood plain as on the terraces. At both sites the flood plain can be subdivided into three fills (F-3, F-2, F-l) on the basis of soil properties that are related to age of the fill’s lateral-accretion deposits. At the S-site each of the three fills is separated from the others by swales. Increasing height with age gives them a subtle, stepped appearance. At the U-site the subfills lack topographic expression and are recognized solely by soil properties. The F-3 fill, which has the oldest lateralaccretion deposits, is characterized by a faint Ap horizon that is one to one-half chroma darker than the subsoil. The subsoil contains a laterally traceable, but discontinuous, very dark grayish-brown to black,

organic-rich horizon interpreted to be a buried A horizon. The rest of the subsoil has had much of its inherited organic matter oxidized, yet there are no bright colors attributable to the formation of free iron oxides. Faint soil structure is present. Alteration is thought to have been primarily oxidation of inherited sedimentary organic matter and of whatever organic matter formed at the surface as the sediments rapidly accumulated. These subsoils depleted of inherited organic matter are designated as Cox (oxidized) horizons. This differs from the original use of the term by Birkeland (1974) for color evidence of alteration in subsoils that do not qualify as cambit horizons. As used here Cox horizons are fundamentally different from the more-weathered color B horizons of the first terrace and show some chemical evidence of pedogenic alteration in contrast to unaltered C horizons in younger sediment (Scully and Arnold, 1979). The F-2 till, which has lateral-accretion

340

SCULLY

AND

deposits of intermediate age, is characterized by a faint Ap horizon, one to onehalf chroma darker than the subsoil which exhibits partial oxidation of its inherited organic matter. There are still thin textural stratifications of pink silt laminae and sand seams present indicating that there has been little pedoturbation of the original sedimentary strata. The F-l fill, which has the youngest lateral-accretion deposits, is characterized by its lack of soil development. It is unaltered, structureless alluvium with a uniform, very dark grayish-brown color with depth. In some places at the U-site the upper part of the fill contains more medium and coarse sands than do the older fills at an equivalent elevation. These sands are probably sand splay deposits similar to one of coarse to medium sand deposited in the spring of 1976 on the F-2 fill at the U-site. This is evidence for increased overbank deposition of sands since the beginning of the F-l fill, about 270 + 80 yr B.P. (see below). The late Holocene alluvium is subdivided into three time-stratigraphic units. Time-stratigraphic unit 3 (Fig. 5) consists of all the lateral-accretion and the older vertical-accretion deposits of the F-3 fill and a veneer of vertical-accretion deposits on the first terrace (Table 3). The soil horizons, also shown in Table 3, are thought to have developed when formation of the flood plain by incision and lateral migration of the channel decreased the flood frequency and vertical-accretion rate on the first terrace (Fig. 7). A minimum age for the beginning of formation of the F-3 lateralaccretion deposits comes from a log dated at 1120 t 80 yr B.P. The buried A horizons on the first terrace are dated at about 1500 and 660 yr B.P. (soil humin) (Table 3). The upper limit of the F-3 fill, at the S-site, that is included in the unit is the Ab horizon that lies immediately below a charcoal-rich strata dated at 615 ? 80 yr B.P. The maximum age of time-stratigraphic unit 3 is the beginning of formation of the Ab hori-

ARNOLD

zon dated at about 1500 yr B.P. and the minimum age is 615 + 80 yr B.P. Time-stratigraphic unit 2 (Fig. 5) consists of the lateral-accretion deposits of the F-2 fill, a veneer of vertical-accretion deposits above the Ab horizon of the F-3 fill, and possibly a thin layer of vertical-accretion deposits on the first terrace of the S-site (Table 3). The maximum age is given by two 615 ? 80 yr B.P. dates. One is from the charcoal above the Ab horizon in the F-3 subsoil and the other is from the basal, channel-lag gravel of the F-2 fill. The 505 + 80 yr B.P. date also on the gravel is in a major flood-conducting swale and is thought to be too young because the swale may have been scoured out since its inception. The upper limit of the unit in the F-2 till is recognized by the subtle contact with the overlying sediment which is less compact, higher in organic matter, and, at the U-site, has more plant debris. The older strata has been slightly affected by pedogenesis. A charcoal-rich seam at this contact is dated at 295 -+- 80 yr B.P. (Fig. 5). Because charcoal and plant debris are common at the contact between timestratigraphic units 1 and 2, a total of four 14C dates were made of these materials (Table 1). The average of the dates is about 270 2 80 yr B.P., so this is taken as the time boundary between the two units. Time-stratigraphic unit 1 consists of all the deposits of the F-l fill and a veneer of nearly unaltered (with the exception of the Ap horizon) vertical-accretion deposits upon the F-2 till, the F-3 fill, and the first terrace. The veneer is thicker than the underlying layers of time-stratigraphic units 2 and 3 that took longer to be deposited. This is evidence of accelerated overbank deposition since about 270 + 80 yr B.P. The accretion rates (Table 1) at sample site 6 (a swale on the first terrace) and sample site 4 (a minor swale in the F-2 till) support this conclusion but the data from sample site 1 (a minor swale on the first terrace) are less convincing. Accretion rates of different

HOLOCENE

ALLUVIAL

sample sites should probably not be compared because rates vary greatly with landscape position. ACCRETION

RATES

Table 1 shows that accretion rates calculated with radiocarbon dates are subject to errors resulting from limitations of the dating method, not to mention other errors involving interpretation of the dates. These radiocarbon dates have a minimum laboratory error of +80 years. This error has the greatest effect on the accretion rates calculated using the youngest dates. Deviations between radiocarbon ages and real ages deduced by dendrochronology (Ralph et al., 1973) significantly alter the range in values of accretion rates and also the interpretations of paleohydrologic events for dates less than 300 yr B.P. Because of this and the closeness of the younger radiocarbon dates to historical time, the younger dates were corrected to real dates using the dendrochronology correction curve of Ralph et al. (1973). Vertical accretion rates are generally greater for the younger alluvial fills close to the rivers and in the swales. The rates given here are all from swales with the exception of sample site 5 (Table 1 and Fig. 2). It is vitally important that the landscape position be given when vertical-accretion rates are reported for areas similar to these study sites. CAUSES

AND CORRELATIONS ALLUWAL EVENTS

OF THE

Before 9705 of: 130 yr B.P. incision terminated deposition of the lateral-accretion sediments of the second terrace (Table 4). The time of incision corresponds closely with a climatic change evidenced by a change in pollen stratigraphy from predominantly spruce (A zone) to pine (B zone) between 10,500 and 9500 yr B.P. (Miller, 1973). The climatic change may have had hydraulic effects that caused incision. Alternatively, the incision may have

STRATIGRAPHY

341

been an adjustment to an increase in channel slope caused by postglacial isostatic uplift of the region. A stable channel elevation during the period when the lateral-accretion deposits of the first terrace were laid down corresponds with the stability of the regional hemlockhardwoods forest (C- 1 pollen zone) between 8000 and 4400 yr B.P. (Miller, 1973). The abrupt decline of hemlock at 4400 yr B.P. correlates broadly with the beginning of the period for which only vertical-accretion deposits are found at the sites (after about 4700 yr B.P.). The widespread hemlock decline in the eastern United States has been interpreted variously as a response to drought (Miller, 1973) or a widespread disaster, such as spread of a pathogen (Likens and Davis, 1975). A reduction in flood discharges from drought could have decreased the competence of the stream to carry coarse sediment. This would increase the relative significance of vertical accretion by reducing stream migration and lateral accretion. An alternative explanation is that a serious reduction in vegetative cover, with consequent upland erosion, could increase suspended sediment loads. The incision before 1100 yr B.P. may have been just a continuation of the process of lateral migration with some downcutting, but it coincided closely with the return to prominence of hemlock in the pollen record (C-3 zone) about 1270 2 95 yr B.P. This change was possibly a result of cooler and moister conditions (Miller, 1973) that could have increased the competence of rivers. The first terrace had been built up by vertical accretion and possibly had confined the channel too much. Several authors have suggested that Indians may have been an important geomorphic agent by burning, clearing, and cultivating forests before European cultivation (Alexander and Prior, 1971; Gooding, 197 1; Nelson, 1966). Miller (1973, pp. 79, 80) reported low percentages of Ambrosia (rag-

342 TABLE4.

SCULLY

AND

ARNOLD

CORRELATIONOFTHEALLUVIALHISTORYOFTHEUNADILLAANDTHENORTHBRANCHOF THE SUSQUEHANNARIVERSWITHTHEPOLLEN STRATIGRAPHYOFSOUTHWESTERN NEW YORK(MILLER, 1973) This yr

B.P.

4

atudy Lateral-accretion depeaits

Pollen Southwestern (Miller,

accelerated

F-l

23xles in New York 1973) European

C-3b

cultivation Indian

opriculturs?

i F-2

500

return

F

C-30

to

prominence of Hemlock

F-3 1000

slight incision

I

slowing vertical accratim -a------

-’ of

----

----

no Lateralxcretioa yc-;s .----

Hemlock minimum

c-2

Hemlock

abrupt

decline

5000 i

1

Tl

incision

-

C-l

stable Hemlockih-dwoods

B

Pine dominant

,-------i

10.000

Spruce-Pine

T2

12,000

7

i

-

major

incision

_

T .-B-B----

---V

weed) and Rumex (dock) pollen in the C-3a zone which could be attributed to Indian cultivation. Charcoal is ubiquitous in alluvium at these sites that is less than 2000 yr old and may have resulted from increased Indian activity after that time. The F-l fill began forming about 275 & 80 yr B.P. (A. D. 1460-1650). The first permanent settlements in Chenango County were Afton and Bainbridge, founded in 1784 (Sullivan, 1927). The dated sample, a small log with less than 50 growth rings,

Tundra?

deglaciation

could have lain in the stream a long time before burial or it could have been retransported. The age of this sample suggests that the F-l fill may have begun forming before European settlement. CONCLUSIONS

Deposits of the second terrace and the valley train appear to have the same degree of soil development as determined by field examination of soil morphology. Both have noncumulative soil profiles with well-

HOLOCENE

ALLUVIAL

developed color B horizons. Darker colors at the base of the plow layer (Ap horizon) in the second terrace suggest that there may have been an Ab horizon before disturbance . The first terrace and flood plain have received enough recent deposition to visibly affect the development of soil profiles. These alluvial surfaces can be differentiated on the basis of topography, radiocarbon dates, and, at the U-site, texture of the deposits. They also are easily separated, and even subdivided into fills of different ages, by pedologic criteria. The pedologic criteria are for the most part not simple A/B/C profiles but rather sequences of soil sola. The sola are recognized, at both the surface and in the subsoil, as thin A horizons or as A and color B horizons in a sequence. They are immature sola because they were young when buried or are on very young sediments. It is believed that the degree of color expression and chemical development of the thin, buried sola are directly related to the time before subsequent burial. They are useful in interpreting the more recent (less than about 3500 yr B-P.) depositional history. Together with 14C dates they demonstrate that the mappable alluvial surfaces are underlain by several overlapping timestratigraphic units and that each of these units can be present under several alluvial surfaces. The timing of channel incisions show a close correspondence to events in the radiocarbon dates pollen stratigraphy of southwestern New York (Miller, 1973). This allows some speculation about the causes. In particular, the return to prominence of hemlock at 1270 + 95 yr B.P. (Miller, 1973) may reflect cooler and moister conditions that could have increased river competence by increasing discharges or flood frequencies. This corresponds closely with the slight incision and beginning of formation of the present flood plain before 1180 + 80 yr B.P. The change in the rivers’ behavior is also shown by the development of A and color B horizons on the

343

STRATIGRAPHY

first terrace at that time, suggesting decreased flooding on that terrace as a consequence of the formation of the lower flood plain. There is a possible long range correlation of this event with a similar event in southeastern Indiana (Gooding, 1971). Although Gooding believed that the whole first bottom (called the flood plain here) there formed in historic time, he reported a minimum date of 1000 2 150 yr B.P. from the base of the high bottom (first terrace here). The high bottom there has incipient soil development that he attributed to termination of high-bottom accretion by slight entrenchment and formation of the first bottom. Gooding’s high bottom and the older two flood plain subfills (F-3 and F-2 reported here) are time equivalent. ACKNOWLEDGMENTS The authors wish to thank P. W. Birkeland and S. C. Porter for their many helpful suggestions. This work was supported in part by funds provided by the U.S. Department of Interior, Offtce of Water Research and Technology, project A-063-NY, and the research program of Cornell University.

REFERENCES Alexander, C. S., and Prior, J. C. (1971). Holocene sedimentation rates in overbank deposits in the Black Bottom of the lower Ohio River, southern Illinois. American Journal of Science 270, 361-362. Birkeland, P. W. (1974). “Pedology, Weathering, and Geomorphological Research.” Oxford Univ. Press. New York. Cadwell, D. H. (1972). “Late Wisconsin Chronology of the Chenango River Valley and Vicinity, New York,” Ph.D. thesis. State University of New York, Binghamton. Campbell, C. A., Paul, E. A., Rennie, D. A., and McCullum, K. J. (1967). Applicability of the carbon-dating method of analysis of soil humus studies. Soil Science 104, 217-224. Coates, D. R. (1971). Reappraisal of the glaciated Appalachian Plateau. In “Glacial Geomorphology” (D. R. Coates, Ed.), pp. 205-243. Publications in Geomorphology, State University of New York. Binghamtom. Denny, C. S., and Lyford, W. H. (1963). “Surticial geology and soils of the Elmira-Williamsport region, N.Y. and Pa.” U.S. Geological Survey Professional Paper 379. Gooding, A. M. (1971). Postglacial alluvial history in

344

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AND ARNOLD

the upper Whitewater Basin, southeastern Indiana, and possible regional relationships. American Journalof.Science 271, 389-401. Leeder, M. R. (1975). Pedogenic carbonates and flood sediment accretion rates: A quantitative model for alluvial arid-zone lithofacies. Geological Magazine 112, 257-270. Leopold, L. B., Wolman, M. G., and Miller, J. P. (1964). “Fluvial Processes in Geomorphology.” Freeman, San Francisco. Likens, G. E., and Davis, M. B. (1975). Post-glacial history of Mirror Lake and its watershed in New Hampshire, U.S.A.: An initial report. International Association Proceedings

of Theoretical

and Applied

Limnology

19, 982-993. Miller, N. G. (1973). Late-glacial and postglacial vegetation change in southwestern New York State. New York letin 420.

State

Museum

and Science

Service

Bul-

Morrison, R. B. (1967). Principles of Quatemary soil stratigraphy. In “Quatemary Soils, Proceedings of the 7th INQUA Congress” (R. B. Morrison and H. E. Wright, Eds.), Vol. 9, pp. l-69. Nelson, J. G. (1966). Man and geomorphic process in the Chemung Valley, New York and Pennsylvania. Annals

of the Association

56, 24-32.

of American

Geographers

Peltier, L. G. (1949). Pleistocene terraces of the Susquehanna River. Pennsylvania Topographic and Geologic

Survey

Bulletin

G-23.

Ralph, E. K., Michael, H. N., and Han, M. C. (1973). Radiocarbon dates and reality. MASCA Newsletter 9, No. 1. Applied Science Center for Archaeology, University of Pennsylvania. Riecken, F. F., and Poetsch, E. (1960). Genesis and classification considerations in some prairie-formed soil profiles from local alluvium in Adair County, Iowa. Iowa Academy of Science Proceedings 67, 268-276. Schumm, S. A. (1973). Geomorphic thresholds and complex response of drainage systems. In “Fluvial Geomorphology”

(M.

Morisawa,

Ed.),

pp.

299-310. Publications in Geomorphology, State University of New York, Binghamton. Schumm, S. A. (1977). “The Fluvial System.” Wiley-Interscience, New York. Scully, R. W., and Arnold, R. W. (1979). Soilgeomorphic relationships in postglacial alluvium in New York. Soil Science Society of America Journal 43, 1014- 1019. Soil Survey Staff (1951). “Soil Survey Manual.” U.S. Dept. Agriculture Handbook No. 18. Sullivan, J. (1927). “History of New York State.” Lewis Historical Publishing, New York.