Re-evaluation of Antevs' New England varve chronology and new radiocarbon dates of sediments from glacial Lake Hitchcock JOHN C. RIDGE Department of Geology, Tufts University, Medford, Massachusetts 02155 FREDERICK D. LARSEN Department of Earth Science, Norwich University, Northfield, Vermont 05663 ABSTRACT A new varve record from sediments of glacial Lake Hitchcock in the Connecticut River Valley along Canoe Brook in Vermont matches and provides a test of Antevs' New England varve chronology for a span of more than 530 yr. Antevs' methods of correlation and for constructing the varve chronology appear to be valid. The varve record at Canoe Brook records weather-controlled variations in meteoric (nonglacial) discharge as well as glacial runoff. Organic sed- iment from the Canoe Brook site, which includes twigs, leaf debris, conifer needles, and fine disseminated organic detritus, lies 460-470 couplets above the base of the section and was deposited about 500 yr after déglaciation. The organic sediment was radiocarbon dated at 12,355 ± 75 yr B.P. (GX-14231), 12,455 ± 360 yr B.P. (GX-14780), and 12,915 ± 175 yr B.P. (GX-14781). Our radiocarbon dates are the first from sediments of Lake Hitchcock, and they provide the first real calibration of the New England varve chronology. The dates place the inception of Lake Hitchcock in central Connecticut at before 15,600 yr B.P. and déglaciation of the Canoe Brook site at about 12,900 yr B.P. An abrupt change in sediment types and thickness of varves 50 yr above the radiocarbon dates (about 12,400 yr B.P.) corresponds to a basin-wide change in the New England varve chronology and records the initial breaching of the dam for Lake Hitchcock at Rocky Hill, Connecticut. Nonglacial lakes, lower than Lake Hitchcock, persisted in the northern Connecticut Valley until at least 400 yr after the incur- sion of marine waters into the Champlain Valley. INTRODUCTION In the early 1920s, Ernst Antevs (1922) formulated the New England (NE) varve chronology from glacial lake sediments deposited during late Wisconsinan ice recession in New England and eastern New York. The NE varve chronology was part of an attempt to create a master chronology for North America, similar to a detailed chronology for Scandinavia (De Geer, 1912), and to determine the time and rate of recession of the Lauren- tide ice sheet (Antevs, 1922, 1925, 1928). Correlation with deposits in Europe was also attempted (De Geer, 1921; Antevs, 1928). Antevs (1922) measured the thicknesses of individual varve couplets (from bottom of silty summer bed to top of winter clay bed) in 73 exposures in the Connecticut Valley from Hartford, Connecticut, to St. Johnsbury, Vermont (Fig. 1). Additional varve records, one from sedi- ments of Lake Ashuelot at Keene, New Hampshire, 17 from Lake Merri- mack in south-central New Hampshire, and 10 from Lake Albany in the Hudson Valley of New York, were also constructed. The Connecticut Valley measurements were mostly from sediments of Lake Hitchcock Figure 1. Location of the Champlain Sea and glacial lakes used by (Lougee, 1939), the highest lake level in the Connecticut Valley. Lake Antevs (1922) to formulate the New England varve chronology (modi- Hitchcock was dammed behind ice-contact stratified deposits at Rocky fied from Larsen, 1987). Geological Society of America Bulletin, v. 102, p. 889-899, 4 figs., July 1990. 889 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/102/7/889/3380905/i0016-7606-102-7-889.pdf by guest on 01 October 2021 890 RIDGE AND LARSEN Hill, Connecticut (Fig. 1), and its level was controlled by a stable bedrock Hartshorn, 1965). Summaries of the Quaternary geology of New England spillway at New Britain (Schafer and Hartshorn, 1965; Stone and others, (Schafer and Hartshorn, 1965; Hartshorn, 1976) and sedimentologic stud- 1982). The lake expanded northward in front of the receding ice sheet to at ies of Lake Hitchcock (Ashley, 1972, 1975) acknowledged the least Lyme, New Hampshire (Lougee, 1939; Goldthwait and others, disagreement between radiocarbon interpretations and the NE varve chro- 1951). Deltas of Lake Hitchcock have topset-foreset contacts that define a nology, but they could offer no solution to the problem. Disfavor with the planar, tilted surface and are now known to extend up the Connecticut NE varve chronology was marked by exclusion of any reference to it in the Valley to Littleton, New Hampshire (Koteff and others, 1987; Koteff and latest textbooks by Hint (1957, 1971). Antevs' (1962) final appraisal of Larsen, 1989). Initial failure of the Rocky Hill dam caused lowering, but the radiocarbon chronology of deglaciation in North America appeared to not complete drainage, of water in the Connecticut Valley (Schafer and carefully avoid any mention of discrepancies with the NE varve Hartshorn, 1965). chronology. Antevs constructed "normal curves" of varve thickness for separate Interpretations of the age of Lake Hitchcock based on radiocarbon regions by matching thickness records from individual sections and calcu- dates in the 1950s should be scrutinized, especially when one considers lating the average thickness of varve couplets for overlapping intervals. A that not one of the radiocarbon dates was from Lake Hitchcock sediment. large number of sections were matched to account for irregularities (miss- There also have been significant improvements in the laboratory treatment ing or extra couplets) in individual sections, and Antevs (1922) reported of samples for radiocarbon dating. More recent geologic evidence and close agreement between distant varve localities. Antevs was confident radiocarbon dating place doubt on the time constraints of Flint (1956). A that contemporaneous normal curves, from separate regions and lakes, radiocarbon date of 12,200 ± 350 yr B.P. (W-828, Colton, 1960) was matched because thickness variations on all normal curves were a function obtained from a log in a buried peat bog in one of many depressions on the of regional weather patterns that controlled glacial melting and runoff. surface of Lake Hitchcock sediments in Connecticut. The depressions are The NE varve chronology is composed of two continuous sequences probably permafrost features that formed shortly after the drainage of with a total of 4,152 varves. The varve chronology arbitrarily begins with Lake Hitchcock (Stone and Ashley, 1989). Lake Hitchcock, therefore, had NE varve 3001 and ends at NE varve 7400. Antevs was able to match to drain before 12,000 yr B.P. Ashley (1972) recognized that the persis- Connecticut Valley normal curves with curves constructed from sediments tence of glacial ice in the Connecticut Valley, and the persistence of Lake of Lakes Albany, Merrimack, and Ashuelot (Fig. 1). These correlations Hitchcock as a glacial lake as late as 10,700 yr B.P. was incompatible with allowed Antevs to cover gaps between normal curves constructed from the invasion of marine waters into the Champlain Valley about 1,000 yr varves in the Connecticut Valley. Only one gap, estimated by Antevs to be earlier (Parrott and Stone, 1972; Cronin, 1979; Lowdon and Blake, 1979). 200-300 yr (NE varves 6353-6600), was not covered by normal curves The contemporaneity of the Middletown Readvance and non- from outside the Connecticut Valley. arboreal pollen zones south of Middletown (Hint, 1956) cannot be dem- Since the 1950s, when the NE varve chronology was first challenged onstrated. This interpretation ignores the possibility of considerable lags in (Flint, 1956), many Quaternary geologists have viewed it with skepticism. organic sedimentation and very slow sedimentation rates for non-arboreal Our objective is to test the validity of Antevs' NE varve chronology by pollen-zone sediments (Cotter and others, 1983). Furthermore, recent comparing it with a new varve record from Canoe Brook, Vermont. We detailed surficial mapping has led to a different interpretation of sediments also present the first radiocarbon dates of Lake Hitchcock sediments and previously identified as those of the Middletown Readvance (Stone and the first real calibration of the NE varve chronology. The NE varve chro- others, 1982; London, 1985), and the existence of thg*readvance has been nology, the Canoe Brook varve record, and the radiocarbon dates together questioned. provide an important framework for studying the chronology of déglacia- tion in New England. THE NEW ENGLAND VARVE CHRONOLOGY AND PALEOMAGNETIC DATA THE VARVE CHRONOLOGY VERSUS RADIOCARBON INTERPRETATIONS Validity of the varve chronology is supported by successful attempts to use it as a chronologic framework for constructing high-resolution The NE varve chronology was challenged in the 1950s on the basis of records of late Pleistocene paleomagnetic declination and inclination. two sets of radiocarbon dates from southern New England. One set of McNish and Johnson (1938), and Johnson and others (1948) located and dates, from deposits at the southern end of the New Britain spillway remeasured varve sections studied by Antevs' (1922) and matched them channel and from fluvial deposits overlying the lacustrine sediments of with the NE varve chronology. Paleomagnetic declination records were Lake Hitchcock, was interpreted to constrain the drainage of Lake Hitch- constructed that had smooth changes in remanent declination over time, as cock in the Hartford area to about 10,700 yr B.P. (Flint, 1956). The would be expected for a continuous sequence of varves deposited under second set of dates was obtained from spruce pollen zones in cores of bogs time-varying geomagnetic field conditions. Verosub (1979a, 1979b) stud- south of Middletown (Fig. 1) and was interpreted to constrain the begin- ied the first 2,500 yr of the Antevs' chronology and was able to reproduce ning of Lake Hitchcock to 13,000 yr B.P. or later (Suess, 1954; Flint, the declination record of Johnson and others (1948) and to construct an 1956). The dates south of Middletown were from materials overlying inclination record.