Strand-plain evidence for late Holocene lake-level variations in Lake Michigan

Todd A. Thompson* Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, Steve J. Baedke } Indiana 47405-1401

ABSTRACT INTRODUCTION that form at or near lake level; most are caused by fluctuations in lake level (Olson, 1958; Thompson Lake level is a primary control on shoreline Shorelines along Great Lakes coastlines are and Baedke, 1995). That is, beach ridges form in behavior in Lake Michigan. The historical products of the interaction among three factors: many parts of the Great Lakes basin after a fall in record from lake-level gauges is the most accu- wave climate, sediment supply, and lake level. Of lake level from a highstand. Facies and facies con- rate source of information on past lake levels, these three factors, lake level is the primary con- tacts within beach ridges preserve information on but the short duration of the record does not trol on shoreline behavior because of its rapid lake-level maxima, and their sequential develop- permit the recognition of long-term patterns of month to month and year to year variation and ment yields information on their relative age. Ac- lake-level change (longer than a decade or immediate influence on the shoreline system tual ages of the ridges can be estimated with ra- two). To extend the record of lake-level change, (Hands, 1983). Knowledge of lake-level varia- diocarbon dates from basal organic sediments of the internal architecture and timing of devel- tion in the Great Lakes is based on the historical wetlands that commonly occur in the swales be- opment of five strand plains of late Holocene record from lake-level gauges (cf. Bishop, 1990). tween ridges. Because the age (relative or ab- beach ridges along the Lake Michigan coast- The historical record of the lakes extends from solute) and lake-level elevation of formation can line were studied. Relative lake-level curves for A.D. 1860 to the present; the record of some of the be readily obtained from the study of beach each site were constructed by determining the lakes (e.g., Lake Michigan) can be semiquantita- ridges, strand plains of beach ridges may contain elevation of foreshore (swash zone) sediments tively extended to the early nineteenth century one of the best records of late Holocene lake level in the beach ridges and by dating basal wet- (Quinn and Sellinger, 1990). Larsen (1985), how- of all of the coastal geomorphic features pre- land sediments in the swales between ridges. ever, showed that the historical record may under- served around the Great Lakes. These curves detect long-term (30+ yr) lake- estimate lake-level extremes. Furthermore, the Strand plains of beach ridges are common fea- level variations and differential isostatic ad- historical record, 135 yr, may be too short to rec- tures along the margins of Lake Michigan. Most justments over the past 4700 yr at a greater ognize significant long-term patterns of lake- occur in the northern part of the lake, where nu- resolution than achieved by other studies. level behavior (DeCooke and Megerian, 1967; Liu, merous embayments into glacial deposits and The average timing of beach-ridge develop- 1970; Cohn and Robinson, 1975, 1976; Thomp- bedrock are present and where a supply of sand- ment for all sites is between 29 and 38 yr/ridge. son et al., 1991). An alternative data source, the sized sediment is plentiful. The largest strand This correspondence occurs in spite of the em- geologic record, is needed to extend the lake- plain of beach ridges, however, occurs at the bayments containing the strand plains being level record further in time and provide informa- southern tip of Lake Michigan along the entire different in size, orientation, hydrographic tion on long-term lake-level change. coast of Indiana and the southern coast of Illinois. regime, and available sediment type and cal- The onshore geologic record consists of coastal This strand plain contains more than 100 individ- iber. If not coincidental, all sites responded to a geomorphic features and sedimentary deposits ual beach ridges that record the position of the for- lake-level fluctuation of a little more than three that occur at the present lake margin or several mer shoreline of southern Lake Michigan and the decades in duration and a range of 0.5 to 0.6 m. kilometers inland. Such features and deposits in- elevation of the lake at the time of beach-ridge Most pronounced in the relative lake-level clude wave- and stream-cut terraces, delta plat- formation. Other areas of beach-ridge develop- curves is a fluctuation of 120Ð180 yr in dura- forms, valley and river-mouth fills, spits, dunes, ment occur along the eastern shore of the Door tion. This ≈150 yr variation is defined by and beach ridges. The elevation of these coastal Peninsula of Wisconsin, the southern shore of the groups of four to six ridges that show a rise and features and deposits may be used to estimate the Upper Peninsula of Michigan, and the northwest- fall in foreshore elevations of 0.5 to 1.5 m elevation of lake level; or, where the relationship ern coast of the Lower Peninsula of Michigan. For within the group. The 150 yr variation can be of these features and deposits to actual lake level example, southwest of Manistique, Michigan, correlated between sites in the Lake Michigan cannot be established with certainty, their stratig- more than 90 beach ridges arc between bedrock basin. The ≈30 and 150 yr fluctuations are su- raphy can be used to determine the behavior of and glacial headlands, capturing Indian Lake perimposed on a long-term loss of water to the lake level when the feature or deposit was devel- from the Lake Michigan basin. Smaller embay- Lake Michigan basin and differential rates of oping. The relative ages of the geomorphic fea- ments containing partial chronosequences of isostatic adjustment. tures and sedimentary deposits can be determined beach ridges occur throughout the area. by spatial and stratigraphic relationships, and es- We studied five strand plains along the margin timates of their absolute ages can be approxi- of the Lake Michigan (Fig. 1) to determine, at mated by radiometric dating (commonly 14C). each site, (1) the physical limits of lake-level vari- *E-mail: [email protected] Beach ridges are sandy depositional features ation during the late Holocene, (2) the timing of

GSA Bulletin; June 1997; v. 109; no. 6; p. 666Ð682; 9 figures; 1 table.

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high lake levels, and (3) long-term patterns of shoreline behavior and beach-ridge development in response to changes in lake level. The purpose of this paper is to describe the lake-level informa- tion obtained from the stratigraphy and timing of development of the beach ridges within the five strand plains. Data were obtained from a coring program aimed at determining the elevation of foreshore (swash zone) deposits within beach ridges, and the age of the beach ridges from radio- carbon dates on basal wetland sediments in the swales between ridges. Because we rely on radio- carbon dates from basal wetland deposits to deter- mine the age of the ridges, the absolute age control of the beach ridges is not ideal. However, we feel Figure 1. Map of Lake Michi- that the elevation data and our treatment of the age gan showing the five study areas data permits us to detect lake-level variations at a and other sites referenced in the time scale much shorter than those achieved by text. See Figures 3 and 5 for de- other studies of Great Lakes levels (e.g., Dalrym- tailed maps of the study areas. ple and Carey, 1990; Dott and Mickelson, 1995; Fraser et al., 1975, 1990; Flint et al., 1988; Larsen, 1985, 1994). This report provides information on long-term behavior of the shoreline at the five sites under natural conditions. Unfortunately, human modifications to the depositional systems at many of the sites during the nineteenth and twentieth centuries prohibit continuation of the unaltered coastal processes and patterns of sediment accu- mulation that we describe.

METHODS

Two types of data are needed to construct a lake-level curve from a strand plain of beach ridges. The first is the elevation of the lake when each ridge formed. One of the best methods of measuring lake level is based upon the elevation of foreshore (swash zone) sediments preserved in each ridge (Fig. 2). At the five study sites one or more transects were established perpendicular to the depositional strike of the beach ridges. Vibra- cores were collected on the lakeward margin of accessible ridges along the transects to recover foreshore sediments (Fig. 2). All vibracores were collected at the break in slope between the ridge and the wetland that occurs lakeward of it. At this position, the foreshore sediments are at their highest collectable elevation within each ridge (Thompson, 1992). The elevation of each core site was surveyed with a transit to a precision of 0.003 m and tied into the International Great Lakes Datum (IGLD) of 1955 using benchmarks (3Ð4.5 m) and actual lake level. The cores (256 total) were returned to the laboratory to be split, described, (1Ð2.5 m) photographed, and sampled. Latex peels were made of each core to preserve the core and to en- hance the ability to see stratification. Grain-size Figure 2. Schematic diagram illustrating the terminology used in this report and the location analyses were conducted on 4010 samples to aid of cores used in determining foreshore elevations and obtaining the peat samples for radiocar- in the identification of foreshore sediments. Iden- bon dating. Diagram not to scale. tification of foreshore sediments was based on a

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TABLE 1. PHYSICAL CHARACTERISTICS OF GENETIC FACIES OBSERVED IN CORES opment of the beach ridges lakeward of them. At Facies and properties Description this time we have no information on the lag time Dune Eolian deposits capping the beach ridge and wind-worked backshore deposits between beach-ridge formation and the onset of Texture and composition Moderately to well-sorted lower medium- to lower fine-grained quartz sand Sedimentary structures Generally unstratified, but may contain low- and high-angle, landward- and organic accumulation. Ongoing paleobotanical lakeward-dipping parallel laminations at the base of the dune sequence and paleoecological research may provide infor- Internal organization Laminae defined by heavy minerals or slight alternations in grain size; no recognizable grading in laminae or within the entire dune sequence mation on the wetland response (Stephen T. Jack- Other features Rootlets and minor soil horizons son, 1994, personal commun.). Organic samples Bounding units Overlies foreshore deposits; contact is sharp to gradational with foreshore were collected from the base of 10 to 25 wetlands Foreshore Swash-zone sediments per site by vibracoring or by hand coring. The Texture and composition Moderately to poorly sorted upper fine-grained to granular quartz sand, and wetlands were probed before collecting the core sandy gravel up to cobble size; gravels consist of oblate siltstone, shale, to ensure that the deepest and presumably oldest limestone, and dolostone clasts Sedimentary structures Horizontal and lakeward-dipping subhorizontal parallel laminations; some low- to part of each wetland sequence was obtained. All high-angle parallel laminations in the upper part and occasionally at the base samples were removed from the cores, immedi- Internal organization Laminae and beds defined by alternations in grain size; some laminae-scale inverse grading, but most laminae are ungraded or normally graded; coarser ately dried in an oven, and sent to GeoChron laminae and beds occur in the base of the unit (plunge point) with some coarse Laboratories for dating with 13C correction. At horizons at the top (berm) GeoChron, modern rootlets were removed and Thickness 1.1 to 1.5 m average thickness of all sites; beds of gravel from 0.1 to 0.6 m thick Other features Shell fragments, plant debris, charcoal grains samples were treated with hot dilute HCl to re- Bounding units Foreshore deposits overlie upper shoreface sediments; the contact is sharp to move carbonate minerals. The dates were cali- erosional and marked by an abrupt change in grain size brated and corrected for variations in atmos- 14 Upper shoreface Longshore trough and bar sediments pheric C and converted to calendar years (0 cal Texture and composition Moderately sorted upper very fine- to lower fine-grained quartz sand with B.P. = A.D. 1950) using bidecadal tree-ring data stringers and flasers of silt and clay; some beds of coarse-grained sand and sandy gravel from A.D. 1950 to 7210 B.C. (Stuvier and Reimer, Sedimentary structures Horizontal, subhorizontal, low-angle and high-angle parallel laminations, ripple 1993, Revision 3.0.3). bedding, and microtrough cross-stratification Sampling error, calibration error, laboratory Internal organization Laminae defined by alternations in grain size; entire sequence fines, and coarser beds and laminae are lost downward error, possible contamination from modern root- Other features Shell and plant debris, charcoal grains lets, humic acids, and dead carbon, and sediment mixing in the swale (Olsson, 1986) potentially cause variation from the true age of the base of the wetland. We have attempted to minimize these errors by collecting a large number of radio- combination of physical characteristics, includ- and Superior to indicate actual lake level. The con- carbon dates at each site so that meaningful trends ing visual description, measured grain-size distri- tact in a beach ridge between the foreshore and are observable in the data and that outliers are ap- butions, and sedimentary structures displayed in overlying dune (foreshore thickness) records the parent. Because the radiocarbon dates are mini- the latex peels (Table 1). wave setup from storms and seiches. For the areas mum ages on the development of the beach ridges Of particular interest in this study is the recog- studied in this report, this contact is 1.1 to 1.5 m lakeward of them, the dates for each site should nition of basal foreshore sediments in the cores. above the foreshore base. The thickness of the define an upper envelope of minimum beach The base of the foreshore occurs at the position foreshore is an indication of the wave climate that ridge age. Unfortunately, contamination from where the wave breaks (plunge point or plunge affected the shoreline during its development (cf. hard water at all sites and possible petroleum for step) and rushes up the beach face, separating the Howard and Reineck, 1981). Foreshore thickness the Toleston Beach study area can shift dates upper shoreface (barred part of the nearshore) from is highly variable between sites and varies through older than the expected envelope. We have calcu- the exposed foreshore (Fig. 2). Because these sed- time at each site. This contact and horizons and po- lated a least-squares linear regression directly iments form at lake level, they create a marker for sitions above the foreshore base (i.e., soils, dune through the dates for each site. Outliers, where the elevation of the lake at the time of their depo- crests) overestimate actual lake level. they are significantly different from the overall sition (Thompson et al., 1988). Along many Lake The second type of information needed to con- trend, were removed. Michigan coastlines, the plunge point is the coars- struct a lake-level curve is the age of the ridges. Larsen (1994) expressed concern about the est part of the nearshore lithosome with grain Because the five sites are within progradational methodology of calculating a regression line sizes ranging from upper medium-grained sand to sequences, ridges become sequentially younger through radiocarbon measurements. The concern gravel (cf. Fox et al., 1966; Fraser and Hester, lakeward, producing a chronosequence of late is founded on his opinion that there is unaccept- 1974, 1977; Fraser et al., 1991). Holocene shoreline behavior. However, the rela- able scatter in the Toleston Beach data presented Dott and Mickelson (1995) used the elevation tive lake-level curve that can be produced from by Thompson (1992), and that similar wetland of vibracore foreshore sediments in beach ridges this horizontal stratigraphy yields little informa- dating by Hansel et al. (1990) was unsuccessful to determine late Holocene lake level at Two tion on the actual timing of lake-level events. To in the Zion beach-ridge plain, Illinois (Fig. 1). We Rivers, Wisconsin. They felt that resolving lake- obtain a more accurate age for the beach ridges, believe that the variability seen by Thompson level changes for their area of less than ±0.5 m peat and organic sediment samples of palustrine (1992) is inherent in the dating technique and is would be difficult, and attributed some of the vari- deposits from the bases of swales between the only observable because of the large numbers of ability to foreshore identification and site-leveling ridges were radiocarbon dated. The assumption in dates collected by Thompson (1992). Pilcher errors. We calculated an average error for all of our radiocarbon dating these samples is that the wet- (1993), in a review of the precision and accuracy sites of ±0.3 m. Larsen (1994) apparently used the land could not form before the development of of radiocarbon dating, concludes that within a upper contact of the foreshore (his “upper fore- the ridge lakeward of it. That is, the radiocarbon stratigraphic framework, absolute ages are less shore zone”) in beach ridges of Lakes Michigan dates are minimum age estimates for the devel- accurate than the relative-age relationships be-

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tween samples. We have maximized the accuracy ground-water focusing. Consequently, a water SITE DESCRIPTION AND FORESHORE of our age determinations by using a large num- table significantly above the elevation of Lake ELEVATIONS ber of samples corrected with regressions. Michigan in the most lakeward swales during a Larsen’s (1994) second concern addresses lake-level fall would not exist. Visocky (1977) Toleston Beach: Northwestern Indiana problems of radiocarbon dating at the Zion showed that water levels in the landward part of beach-ridge plain. We believe that a chronose- the Zion beach-ridge plain (1.5 km landward of Toleston Beach is a strand plain 68 km long and quence of radiocarbon measurements cannot be the shoreline) mirrored fluctuations in lake level as wide as 9.8 km that parallels the southern tip of obtained at this site because of the ground-water and were only 0.6 to 0.8 m higher than the level Lake Michigan. Toleston Beach began to form flow system of the area. Cherkauer and McK- of Lake Michigan. In addition, Hansel et al. about 6300 yr ago, when lake level rose from the ereghan (1991) showed that shoreline curvature (1990) noted that “the youngest and most-lake- extreme low of the Chippewa phase of ancestral in embayments realigns ground-water gradients ward swales in the [Zion] beach-ridge complex Lake Michigan to establish the Nipissing I phase so that flow converges into the embayment, in- appear to have been dominated by eolian sedi- (Hansel et al., 1985; Thompson, 1989). Internally, creasing ground-water flow by as much as mentation rather than organic matter accretion.” Toleston Beach consists of a single 45-m-high 500% over straight stretches of shoreline. The These observations lead us to expect that the dune ridge in its eastern part that splits westward movement of such large volumes of water may first period of organic accumulation for the most into more than 100 dune-capped beach ridges west cause water levels in embayments to rise signif- lakeward wetlands coincides with extreme lake of Ogden Dunes, Indiana (Fig. 3). Beach ridges in icantly higher than the level of Lake Michigan. levels that may flood all the wetlands. Radiocar- Toleston Beach are from 1.5 to 4.5 m high. In the In the embayments we studied, water levels in bon data for the Zion beach-ridge plain (Hansel lakeward half of Toleston Beach, beach ridges are wetlands immediately landward of the youngest et al., 1990) shows clustering of ages during pe- spaced ≈45 m apart. This spacing decreases land- beach ridge were 1.8 to 2.4 m higher than the el- riods of lake-level highs (cf. Dott and Mickel- ward to ≈23 m at an erosional discontinuity that evation of the lake. High ground-water levels son, 1995; Thompson, 1992; Larsen, 1985). The occurs in the landward part of the strand plain are needed to form and sustain wetlands be- methodology described by Thompson (1992) (Fig. 3). There are only 25 ridges landward of the tween beach ridges that ultimately accumulate and used in this paper can most successfully be erosional discontinuity, whereas more than 80 organic matter. The Zion beach-ridge plain, applied to embayments that support ground- beach ridges are lakeward of it. Chrzastowski and however, is a promontory that does not produce water focusing. Thompson (1992) and Thompson (1992) noted

Figure 3. Map of Toleston beach at the southern end of Lake Michigan, showing beach ridges (arcuate bold lines), dunes (arcs), and core sites (dots). The dashed bold line in the landward part of Toleston beach marks a low-angle truncation between Algoma and older beach ridges and ridges formed later. Note the approximate location of the transect (straight line perpendicular to the modern shoreline).

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that the Nipissing phases occur in the landward 25 ridges are wetlands that are wider than those wet- gan (Fig. 1). The embayment is bounded by the ridges of Toleston Beach. That is, record of the first lands within the groups. The grouping of ridges Point Betsie moraine to the south, and an unnamed 2500 yr are compressed in the first set of ridges, indicates that the lake-level fluctuation needed to moraine and the Platte River to the north (Calver, and the record of the following 2600 yr are in the produce a single ridge is superimposed on a 1947). The northwest opening to the embayment next 80 or more ridges. longer term and possibly larger amplitude varia- is 4.5 km wide and rimmed with 10-m-high para- Olson (1958) showed that a beach ridge is tion. The overall geomorphic distribution of the bolic dunes. Internally, there are ≈60 beach ridges formed along the southern shore of Lake Michi- ridges suggests that lake-level variations longer (Fig. 5A) extending ≈4 km inland from the land- gan whenever lake level falls from a highstand. than Olson’s (1958) 30 yr occur in Lake Michi- ward side of the parabolic dunes to Big Platte Lake The fall in lake level is instrumental in abandon- gan and that these events are preserved in the pat- (Big Platte Lake is not shown in Fig. 5A). Calver ing the high-water berm, widening the backshore, tern of ridge development in Toleston Beach. (1947) showed that the first beach ridges that and possibly exposing an ephemeral bar. The An approximately shore-perpendicular transect formed in the Platte Lake embayment isolated berm is enhanced by eolian accumulation as it be- was established through several areas near the Long, Rush, and Big Platte Lakes from Lake comes colonized by marram grass and other pio- Gary Regional Airport (Gibson Woods, Clark and Michigan during the early Nipissing phases of an- neer plants (Olson, 1958). With time, a continu- Pine, and Shell Oil Nature Preserves; Ivanhoe cestral Lake Michigan. The beach ridges in the ous dune-capped beach ridge is formed westward property of the Chicago and Southshore Railroad; lakeward part of the embayment are ≈0.5 to 2 m from Ogden Dunes to the Illinois-Indiana state and the Clark Avenue property of Bongi Trucking) high and are spaced ≈65 m apart. They decrease in line. The next subsequent lake-level rise may cre- (Fig. 2). Urban and industrial development relief along the depositional strike of the embay- ate a scarp on the newly formed beach ridge, but throughout this area in the twentieth century re- ment from parabolic dunes in the south-southwest it is unable to remove the ridge because of the moved most of the ridge and swale topography to the Platte River in the east-northeast. Similar to large volume of sediment that was added to the from the landscape. Consequently, a single straight Toleston Beach, groups of four to six beach ridges foreshore and dune during the lake-level fall and shore-normal transect that crosses the entire Tole- that vary in relief, elevation, and spacing occur lowstand. Thompson and Baedke (1995) showed ston Beach could not be established. In our analy- across depositional dip. The groupings are less on a theoretical basis that the high-water berm sis, the offsets are projected onto a shore-normal pronounced than those in Toleston Beach because probably forms in the final stages of lake-level transect through the areas. The transect extends of the low relief of the ridges and extensive devel- rise, and it is abandoned and colonized by grasses landward from the modern shoreline, but only tra- opment of small parabolic dunes along the crest of during the subsequent lake-level fall. For exam- verses approximately three-fourths of the entire most ridges. ple, Hunter et al. (1990) documented the develop- width of Toleston Beach. No data were collected We collected 49 cores crossing 52 beach ridges ment of a new beach ridge at Miller, Indiana, fol- from sites on Nipissing phase beach ridges. along an arcuate transect that roughly followed lowing the high lake levels of 1985Ð1986. By the Foreshore deposits were collected and identi- the central axis of the embayment (Fig. 3A). Be- end of 1989, the ridge was more than 3 m high, fied in 62 cores crossing 78 ridges along the Tole- cause the dune sediments capping the beach and the shore had prograded more than 70 m. ston Beach transect (Fig. 4A). These data include ridges are thin, most cores began directly in fore- The successive development of beach ridges in the 47 cores of Thompson (1992) and 15 addi- shore sediments and stopped in the sandy gravel Toleston Beach causes the southern shore of Lake tional cores. Gaps in the record from 0 to 750 m at the base of the foreshore. The elevations of the Michigan to prograde northward with fluctuations and 1900 to 2700 m landward are parts of the foreshore sediments in the Platte Lake embay- in lake level. The continuous progradation pro- strand plain for which no ridges remain. All cores ment show a lake-level fall in the landward part of duces a horizontal stratigraphy of nearshore and but one recovered the entire foreshore sequence. the transect of ≈2.5 m (Fig. 5B). From the middle onshore deposition. Beach ridges in Toleston The elevations of the foreshore deposits show a part of the strand plain to the landward edge of the Beach, therefore, form a chronosequence of past long-term lake-level fall reaching the historical parabolic dunes, basal foreshore sediments are at highstands of lake level, and the elevation of average for Lake Michigan (176.7 m, IGLD about the same elevation as the historical record nearshore sediments in the ridges provides infor- 1955, data from 1819 to 1990) at about midway for Lake Michigan. A long-term lake-level rise of mation on the upper limit of lake level throughout during the development of the strand plain. The ≈1.5 m is observed from 900 to 2500 m landward. the late Holocene in southern Lake Michigan. four most landward cores are landward of the Superimposed on the long-term lake-level trend Olson (1958, p. 479) suggested that in Toleston erosional discontinuity in Toleston Beach. A drop are groups of four to six ridges that are defined by Beach “the average interval between successive of ≈2 m in foreshore elevation occurs lakeward of a rise and fall in foreshore elevation of ≈0.5 to beach ridges would have been of the order of three the discontinuity. Superimposed on the long-term 1 m. These foreshore patterns are similar in mag- decades, prior to shore-line disturbance by man in lake-level fall are groups of four to six ridges that nitude and number of included beach ridges to the the twentieth century.” Beach ridges of shorter are defined by rises and falls in the elevation of groups observed in Toleston Beach. term development may form and be eroded in re- the top and bottom of the foreshore. The groups sponse to short-term lake-level rises and falls of are typically broad highs with commonly single Baileys Harbor Embayment: several years, but only one ridge is preserved along point lows and range from 0.5 to 2 m in ampli- Ridges Sanctuary, Wisconsin southern Lake Michigan about every 30 yr (Olson, tude. These groups of ridges mirror patterns of el- 1958). If Olson (1958) is correct, the shortest pos- evation, relief, and spacing recognized in the ge- Baileys Harbor embayment is the southern- sible interval that lake level can be measured in omorphology of the ridges. most of four bays along the eastern margin of the Toleston Beach is roughly 30 yr. northern Door Peninsula, Wisconsin (Fig. 1). Changes in elevation, relief, and spacing be- Platte Lake Embayment: Sleeping Bear The 2.5-km-wide embayment opens southward tween ridges can be used to define groups of Dunes National Lakeshore, Michigan and is bounded on both its east and west sides by beach ridges in Toleston Beach. Four to six ridges Silurian dolostones of the Niagaran Series (Sher- show sequential rises and falls in the elevation of The Platte Lake embayment is the central of rill, 1978). Internally, ≈30 dune-capped ridges the crests of the ridges and relief above the sur- three embayments into the Manistee moraine arc between the bedrock uplands (Fig. 5B). Most face of the swales. Between successive groups of along the western shore of Benzie County, Michi- ridges are of low relief, extending 0.5 to 2 m

670 Geological Society of America Bulletin, June 1997

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Figure 5. Map of study areas in northern Lake Michigan, showing beach ridges (arcuate bold lines), parabolic dunes (arcs), and core locations (solid dots). Areas are: Platte Lake embayment (A), Baileys Harbor embayment (B), Manistique and Thompson embayments (C), and Sturgeon Bay embayment (D).

above the surface of the wetlands in the swales, land. Several truncations of older beach ridges sediments in the swales between ridges. They and narrowly spaced ≈37 m apart. The ridges are by younger beach ridges occur along the western showed that the elevation of the crest of the anchored on their western margin to a prominent margin of the strand plain. ridges decreases only slightly lakeward and that cobble ridge and fan out and decrease in relief Johnson et al. (1990) profiled the ridges and most of the ridges formed over the past 1000 and elevation eastward toward a bedrock head- collected nine radiocarbon dates from wetland radiocarbon years from nearshore accretion dur-

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ing a fall from a highstand of lake level. Johnson gle erosional truncations and slightly wider stone and limestone peninsula to the north to a 24- et al. (1990) did not collect foreshore-elevation swales. The central axis of the wedges shifted to m-high bluff of sand- and gravel-rich glacial de- data; therefore, a lake-level curve for the Baileys the southern edge of the embayment during posits in the south. Ridges are typically 1 to 4 m Harbor embayment cannot be constructed di- strand-plain evolution. The wedges indicate that high; most ridges are only ≈1.5 to 2 m high. rectly from their data. some erosion has occurred in the Thompson em- Beach ridges are narrowly spaced in the Sturgeon Foreshore deposits were collected in 24 cores bayment and that a complete record of lake-level Bay embayment, averaging only ≈30 m apart. Ex- crossing 29 ridges, following a transect along the variation may not be preserved. tensive parabolic dune development occurs in the west-central part of the embayment (Fig. 5B). Several early twentieth-century studies investi- landward and southern parts of the embayment. The transect begins two ridges back from the gated the development of the beach ridges in the Lichter (1993, 1994) profiled the ridges and modern shoreline and roughly follows transect 2 Manistique-Thompson area. Scott (1921), Steven- collected radiocarbon dates and paleobotanical of Johnson et al. (1990). We were unable to take son (1930), and Bergquist (1936) concluded that data. He showed that the dune cap on the ridges vibracores of the landward-most ridge because the ridges near Indian Lake formed as lacustrine formed during falls in lake level and suggested the foreshore contained cobbles that stopped the sand bars that were exposed as lake level fell. The that parabolic dune development along the vibracorer from penetrating the sediments. A bars were moved landward to their present posi- ridges is associated with highstands. Like John- foreshore top elevation, however, was established tion by eolian processes. Stevenson (1930) sug- son et al. (1990), Lichter (1993, 1994) did not at the top of the gravels (Fig. 4C). All cores col- gested the possibility that the ridges formed in situ collect foreshore-elevation data. A relative lake- lected the entire foreshore sequence, and most by a repetitious process of lake-level lowering that level curve cannot be constructed directly from cores extended a meter or more into the upper exposed an area of sand that is blown into dunes in Lichter’s data. shoreface. front of older ones, but discounted this possibility Cores were collected along two transects in the The foreshore elevations in the Baileys Harbor on the basis of the morphology of dunes. However, embayment (Fig. 5D). The first transect crosses embayment show a slight lakeward decrease of Henderson (1993) showed that the beach ridges 26 ridges along the northern edge of the strand ≈0.5 m along the entire transect (Fig. 4C). Most are composed of nearshore sediments overlain by plain. This transect begins 13 ridges back from basal foreshore elevations are at or near the his- eolian deposits, and indicated that the ridges and the modern shoreline. The second transect fol- torical average for Lake Michigan during the de- their dune cap formed in place during progradation lows the central axis of the embayment and velopment of the entire strand plain. Similar to of the shoreline. crosses an additional 26 beach ridges. All but the other sites, there are shorter term rises and Four transects that extend from the modern three of the cores sampled the entire foreshore se- falls in foreshore elevation of 0.5 to 1.2 m among shoreline to near Indian Lake (Fig. 5C) were es- quence. The foreshore is consistently the most four to six ridges in the data. The foreshore ele- tablished in the Manistique and Thompson em- coarse grained of all the areas studied. vations show potentially five groups (Fig. 4C), al- bayments. Ninety-two vibracores crossing 87 The elevations of the upper and lower contacts though the fourth group is not well defined. beach ridges were collected along the transects, of the foreshore show a lake-level fall of ≈4 m representing ≈85% of the entire strand plain. throughout the development of the strand plain Manistique and Thompson Embayments: Most cores penetrated the entire foreshore se- (Fig. 4E). Rises and falls in foreshore elevation of Manistique, Michigan quence, but in the landward part of the Manis- 0.5 to 1 m, represented by three to six ridges, are tique embayment thick dune sediments prevented common. The groups are less pronounced here The Manistique and Thompson embayments penetration into the upper shoreface deposits. than in the more southern study areas because of are two indentations (2.5 and 3 km wide) into the The upper and basal foreshore contacts in the the steep gradient of the foreshore elevations and Lake Michigan shore southwest of Manistique in Manistique-Thompson embayments show a long- because of several overthickened foreshores that Schoolcraft County, Michigan (Fig. 1). The two term lake-level fall of 13 m during the develop- occur along the transect (Fig. 4E). These thicker embayments are separated by Stony Point, a bed- ment of the combined strand plains (Fig. 4D). A foreshores commonly occur in the landward part rock headland of Devonian dolostones (Dorr and rapid decline of ≈6 m occurs in the landward of a group of ridges. Grain-size analyses and sed- Eschman, 1970), and are bounded to the south- third of the transect (2200 to 2800 m landward), imentary structures indicate that the thicker fore- west by a morainal upland and to the northeast by followed by a slower fall of 2 m (800 to 2200 m shores formed from the stacking of two or more Indian River (Fig. 5C). During the late Nipissing landward) through the middle third. Foreshore el- foreshores. That is, the foreshore of one beach phases of ancestral Lake Michigan, the two em- evations decline another 5 m in the 800 m of the ridge is stacked upon the previously formed ridge. bayments were combined, but they separated into strand plain nearest the modern shoreline. The This is the only area in which we have consis- two strand plains when continued development data suggest that smaller-term rises and falls in tently observed the amalgamation of beach ridges of beach ridges intercepted Stony Point. foreshore elevation also occur at the Manistique- in the landward part of a group of ridges. Combined, the embayments contain ≈90 indi- Thompson embayments. The groups are difficult vidual beach ridges (Fig. 5C). Beach-ridge relief to recognize because of the steep slope of the Summary varies considerably throughout the complex and foreshore elevations. ranges from 0.5 m to more than 10 m. On an av- Changes in the upper limit of the level of Lake erage, beach ridges are spaced ≈45 m apart; how- Sturgeon Bay Embayment: Wilderness Michigan through time can be determined from a ever, landward of where the two embayments are State Park, Michigan systematic coring program that measures the ele- joined, the ridges narrow to a spacing of ≈15 m. vation of foreshore (swash zone) sediments within Groups of four to six beach ridges defined by sys- The Sturgeon Bay embayment is westward beach ridges. The basal foreshore elevations mea- tematic changes in relief, elevation, and spacing opening, 2.8 km wide, in Emmit County, Michi- sured across a series of beach ridges indicate long- are common in the Manistique embayment. In the gan (Fig. 1). The embayment is entirely confined term patterns of lake-level change during shoreline Thompson embayment, however, the groups exist within Wilderness State Park, and contains ≈60 progradation (Fig. 4). At all of the sites, the fore- in map view as arcuate wedges of four to six arcuate beach ridges (Fig. 3D). The ridges extend shore elevations indicate a long-term fall in the beach ridges. The wedges are defined by low-an- from Big Sucker Creek along a Devonian dolo- elevation of Lake Michigan during the develop-

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ment of the strand plains. The Toleston Beach and of these sources of variability causes the reported lakeward decrease in age. The oldest date deter- Platte Lake embayment sites approach and follow ages to vary from the expected lakeward decrease. mined by Johnson et al. (1990) is 1020 14C B.P. the historical average for Lake Michigan about Any model that supports a continuous lake- We dated the next lakeward wetland at 1110 14C midway through their progradational history. The ward decrease in beach-ridge age may character- B.P. (980 cal B.P.). Similar correspondences of short record at Baileys Harbor shows only a slight ize strand-plain development. Polynomial and ages occur throughout the strand plain. We have lake-level fall with all elevations near the historical exponential functions can be used as models to not, however, incorporated their dates into our average. The Manistique-Thompson and Sturgeon describe long-term rates of shoreline prograda- analysis to maintain consistency in dating tech- Bay embayments show long-term falls that are tion. However, polynomial functions greater than niques between all areas studied. The age versus much greater than the observed rates of fall in the the first order that force a short-term lakeward in- distance regression through these data yields more southern sites. crease or no change in age as the beach ridges 0.94 yr/m (1.1 m/yr progradation rate). The slope Groupings of beach ridges are apparent in forms cannot explain these systems. That is, in a of the age versus beach ridge regression is 31 ± most sites. These groups typically consist of four progradational system, a beach ridge cannot form 10 yr/ridge. to six ridges that show a systematic rise and fall that is older than the one landward of it; nor can it of foreshore elevations that mirror relief and ele- form without time passing. For simplicity and Manistique and Thompson Embayments: vation changes for the crests of the ridges. Where ease of comparison between locations, we have Manistique, Michigan they are well defined, the highs are typically adopted a linear model (first-order polynomial) broad with sharp, commonly single-point lows to interpolate ages for wetlands that were not We obtained 25 radiocarbon ages for basal (Fig. 4). The groups suggest a lake-level fluctua- dated and to extract a representative rate of shore- wetland sediments in the Manistique and tion longer than the lake-level rise and fall needed line progradation for Toleston Beach. Thompson embayments (Fig. 6D). Two addi- to make a single beach ridge. These two varia- A least-squares regression of best linear fit of tional ages were determined for the second and tions are superimposed on the overall lowering of beach-ridge age versus distance landward from third ridge back from the modern shoreline by the elevation of Lake Michigan. The timing of the shoreline was calculated (Fig. 6A). The re- counting tree rings of white pines on the ridges beach-ridge and group development is addressed gression yielded a slope of 0.58 yr/m for the east (Douglass A. Wilcox, 1994, personal commun.). in the next section. central part of Toleston Beach. The inverse of this The estimated ages of all the ridges show a lake- slope, 1.7 m/yr, represents the approximate long- ward decrease; however, unlike the Toleston SHORELINE AGES AND TIMING OF term rate of shoreline progradation along the Beach, and Platte Lake and Baileys Harbor em- BEACH-RIDGE DEVELOPMENT transect. An additional least-squares regression bayments data, the Manistique-Thompson data was calculated between the age of the ridges and show three distinct sets of ages (Fig. 6D). Along Toleston Beach: Northwestern Indiana a number assigned sequentially to the ridges. The the transect in the Thompson embayment, two slope of this line, 32 ± 6 yr/ridge, indicates the offsets in the ages, each of ≈1000 yr in duration, The basal ages of 21 wetlands between beach average time between beach-ridge formation. occur at 200 and 950 m landward of the shore- ridges were determined along the Toleston Beach The 95% confidence interval about the slope sug- line. At both offsets, the ridge landward of the transect (Fig. 6A). Three additional radiocarbon gests that beach ridges were formed in the east- offset is several times greater in relief than the dates were added to the data of Thompson (1992). central part of Toleston Beach roughly every 23 to ridge lakeward of the offset. This is especially The calibrated dates show an overall lakeward 41 yr (Fig. 6F). The 32 yr between beach ridges true for the beach ridge landward of the second decrease in age. This lakeward decline confirms is similar to the “three decade” timing of beach- offset, where the ridge is 13 m higher than the the progradational nature of the shoreline. Previ- ridge formation suggested by Olson (1958). ridge lakeward of it. The presence of the time off- ous studies of late Holocene lake level in Lake set and the thick dune cap on the beach ridge Michigan (Fraser et al., 1975, 1990; Larsen, 1973, Platte Lake Embayment: Sleeping Bear landward of the offset indicate that the formation 1985) have treated individual radiocarbon dates Dunes National Lakeshore, Michigan of beach ridges halted for ≈1000 yr, or that ridges as “absolute” age indicators of the material being formed and were eroded back to the high ridge dated and correspondingly the deposits from We cored 20 wetlands along the Platte Lake during this time interval. Large quantities of sed- which the sample were extracted. However, transect (Fig. 6B). Radiocarbon dates from the iment were allowed to be blown into the beach Thompson (1992) and this study have found that base of each core show a general lakeward de- ridge’s dune cap. This scenario is similar to the treating individual dates as absolute fact can lead crease in the age of the beach ridge, reflecting the modern beach at the Platte Lake embayment, to apparent age reversals that are inconsistent long-term progradation of the shoreline in the em- where no new beach ridges are forming and sed- with the process of strand-plain development. bayment. Three wetlands along the transect were iment is being added only to dunes. Regardless of This apparent conflict results from errors in age dated twice, and calibrated ages between samples the cause of the missing ridges, these offsets estimates, which can arise from sampling, calibra- of the same wetland can differ by 200 to 520 yr. show that the Thompson embayment did not al- tion, and laboratory errors; contamination from Regressions calculated through all the dates yield ways preserve a continuous record of lake-level modern rootlets, humic acids, and dead carbon a progradation rate of 2.08 m/yr (0.48 yr/m) and variations. Lake-level studies that do not use ex- (hard-water effect); and depositional and hydro- an average timing of beach-ridge formation of tensive radiocarbon dating as a means of deter- logic processes within the wetland basin that 29 ± 5 yr/ridge. mining the ages of beach ridges in similar em- cause organic sediment mixing or delays in accu- bayments may not observe this loss in their data. mulation (see Geyh and Schleicher, 1990, for a Baileys Harbor Embayment: Linear least-squares regressions were calcu- discussion of factors influencing 14C age deter- Ridges Sanctuary, Wisconsin lated through the two landward sets of data. The minations). The reported laboratory error (a min- age versus distance regression for the older set imum of ±65 yr in this study) alone is greater The basal ages of 12 wetlands were deter- yields a value of 0.89 yr/m, and the younger set than the average timing of beach-ridge develop- mined along the Baileys Harbor transect yields a value 0.97 yr/m (1.1 and 1.0 m/yr progra- ment. The individual and combined effect of each (Fig. 4C). Like the other sites the dates show a dation rate, respectively). The age versus beach-

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Figure 6. Graphs of calibrated ridge age versus distance landward of the shoreline for the Toleston beach (A), Platte Lake (B), Baileys Harbor (C), Manistique and Thompson (D), and Sturgeon Bay (E) transects, and summary of age versus ridge number regressions (F). Data points and error bars for AÐE are calibrated radiocarbon dates of basal wetland sediments from swales between ridges (unweighted least-squares regressions are shown). Data points and error bars for F are average timing of beach-ridge development (solid box), standard error (small cross tick), and 95% confidence-interval (large cross tick). The sites in F are Toleston beach (T), Platte Lake embayment (P), Baileys Harbor embayment (B), landward part of the Manistique and Thompson embayments (M1), lakeward part of the Manistique and Thompson embayments (M2), and Sturgeon Bay embayment (S). The results of the spectral analyses of Liu (1970) and Cohen and Robinson (1975) on the historical record are shown (H).

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ridge number regression has a slope of 38 ± lake level. The average timings suggest that a pe- over, the CCBHD (1977) data indicate that the 16 yr/ridge and 32 ± 4 yr/ridge, respectively. riodic or quasiperiodic lake-level fluctuation be- Platte Lake and Baileys Harbor embayments are tween 29 and 38 yr (32.9 yr average) was occur- roughly in line with a zero isobase that would ex- Sturgeon Bay Embayment: Wilderness ring in the Lake Michigan basin during the late tend through the Port Huron outlet for Lakes State Park, Michigan Holocene, and that this variation was of sufficient Michigan and Huron, and that suggests that these magnitude and duration to permit individual embayments may preserve lake-level variations Radiocarbon ages were determined for 12 wet- beach ridges to begin form at the same time at that occurred at the outlet. Deviations of water- lands in the Sturgeon Bay embayment (Fig. 6E). each of the sites. Moreover, the groupings of four level elevations at other sites from the Platte The age versus beach-ridge regression yields an to six ridges suggest that a longer term lake-level LakeÐBaileys Harbor data are a function of dif- average timing of beach-ridge development of 47 fluctuation with a duration between 120 to 190 yr ferential isostasy or tectonism. We have combined ± 11 yr/ridge. This regression, however, does not also occurs in the basin. data from the Platte Lake and Baileys Harbor em- consider the missing beach ridges indicated by bayments into a single curve. Although the two the stacked (over-thickened) foreshores. When LATE HOLOCENE LAKE LEVEL data sets do not directly overlap, the connection the data are adjusted to account for these stacked between the two curves is apparent (Fig. 7B). foreshores, the age versus beach-ridge regression Late Holocene lake-level curves can be cre- The CCBHD (1977) also indicate that during the yields a value of 36 ± 9 yr/ridge. This value is ated from the data presented in Figures 4 and 6. 40 yr prior to A.D. 1970, the southern shore of more similar to the values determined for the Lake-level curves (Fig. 7, AÐD) were constructed Lake Michigan was falling (0.10 m/100 yr) with other sites. Correspondingly, when the distances for each site by assigning ages to the beach ridges respect to Goderich, Ontario (112 km north of the are also corrected for the missing beach ridges, from the age-distance regressions (Fig. 6, AÐE) outlet), and that the northern shore was rising the age versus distance landward of the modern and plotting these ages against the foreshore ele- (0.094 m/100 yr). If the trends in these data ex- shoreline regression yields a value of 1.1 yr/m vations identified from the facies analyses of the tend into geologic time, one would expect the rel- (0.91 m/yr progradation rate). vibracores (Fig. 4, AÐE). Because of differential ative lake-level curve for Toleston Beach to show rates of isostatic adjustment between the study a long-term lake-level rise and that the Manis- Summary areas (Coordinating Committee on Great Lakes tique-Thompson and Sturgeon Bay curves Basic Hydraulic and Hydrologic Data [CCBHD], should show a long-term lake-level fall during The age of basal wetland sediments in the 1977), these lake-level curves are relative only to the late Holocene. swales between adjacent beach ridges provides a the immediate transect areas. Within the limita- minimum age for the beach ridge lakeward of tions of the dating technique, long-term and some Long-Term Lake-Level Variation each wetland. Under ideal conditions, the ages of shorter term lake-level variations, however, the wetlands should sequentially decrease lake- should be recognizable and correlatable between This study. Only the Manistique-Thompson ward. However, the short amount of time separat- shoreline of Lake Michigan. curve extends back more than 3100 calendar ing the formation of individual beach ridges Combined, the relative lake-level curves en- years, so discussion of lake level for Lake Michi- (roughly 30 yr) and errors inherent in age esti- compass a time frame from the present to about gan prior to 3100 yr ago is confined to the mates based on 14C dating cause deviations from 4700 cal B.P. Additional study in the landward Manistique-Thompson curve. The Manistique- the true ages. All of the sites show a variability in parts of several of the study areas may extend the Thompson curve shows a double-peaked lake- ages away from the simple lakeward decrease. To data set to the early Nipissing phase of ancestral level maximum from 4400 to 4600 cal B.P. determine representative rates of shoreline pro- Lake Michigan (pre-5000 cal B.P.). The Manis- (Fig. 7C). This high, centered at 4500, is followed gradation and to estimate ages for ridges that tique and Thompson embayments contain the by a rapid lowering to ca. 4000 yr ago. This low- were not dated, linear least-squares regressions longest record of lake-level variation (Fig. 6C), ering is about five times greater than the rate of were calculated for each transect. The regression but gaps occur in the record from 50 to 950 and fall observed in the rest of the curve. Although between the calibrated ages and distance land- 1700 to 2700 cal B.P. These gaps are a real re- difficult to recognize because of the extreme ward from the shoreline to the beach ridge lake- sponse of the shoreline, unlike the gaps in the steepening of the curve, a 300-yr-long double- ward of the wetland provides an estimate of the other curves (e.g., Toleston Beach, Fig. 7A; Platte peaked lake-level high occurs in the Manistique- calendar age of each beach ridge (Fig. 6, AÐE). Lake embayment, Fig. 7B) where ridges were not Thompson data from 4000 to 4300 cal B.P. Similarly, the age of the basal wetland sediments sampled because they were inaccessible or de- (Fig. 7C). Following this high, basal foreshore versus a sequential beach-ridge number yields stroyed. The gaps indicate that the Thompson elevations in the Manistique-Thompson curve the average timing of beach-ridge development embayment either did not form ridges or formed continues to show a lake-level fall, but at a much (Fig. 6F). and eroded ridges during the two 1000-yr-long reduced rate, until lake level begins rising again The five strand plains show an average timing time-periods (Thompson and Baedke, 1995). about 3300 cal B.P. of beach-ridge development ranging from 29 to The CCBHD (1977) examined vertical uplift The Toleston Beach, Platte LakeÐBaileys Har- 38 yr/ridge (Fig. 6F). The average timing and er- throughout the Great Lakes by comparing water- bor, and Manistique-Thompson curves indicate ror overlap between all sites, and a pair-wise level gauge data. They showed that the Platte a broad lake-level high from 2300 to 3200 cal t-test indicates that none of the average timings of Lake and Baileys Harbor embayments under- B.P. (Fig. 7, AÐC). This high consists of three or beach-ridge development are statistically differ- went roughly the same vertical uplift in the 40 yr four individual peaks. Unfortunately, the data ent from each other. Similar average timings of before A.D. 1970. Assuming that these two sites from all of the sites are not complete and cannot beach-ridge development are surprising, because have undergone the same isostatic change over adequately define the high lake stage. The Tole- the embayments containing the strand plains dif- the past several thousand years, data from Bai- ston Beach curve exhibits the most variability fer in size, shape, orientation, available sediment leys Harbor embayment can be combined with (Fig. 7A). Much of this variability may be attrib- supply and caliber, and hydrographic regime. the data from the Platte Lake embayment, pro- uted to the erosional discontinuity that occurs be- The only factor that is common to all sites is the ducing a longer relative lake-level curve. More- tween the fourth and fifth ridge from the land-

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Figure 7. Graphs of foreshore top and base elevations versus calendar year for the Toleston Beach (A), Platte Lake and Baileys Harbor (B), Manistique and Thompson (C), and Sturgeon Bay (D) transects. Opposing triangles bracket the upper and lower parts of the foreshore.

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ward end of the curve (Fig. 3). It is possible that beach ridges were only created during the lake- time (1Ð2 m during the past 3000 cal B.P.). Al- some of the record may be missing at this point, level fall from the 1700 yr ago high (Fig. 7C). though the altitude of organic material in the and that the four ridges on the end of the curve Other studies. Numerous researchers have swales between beach ridges has little quantifi- should actually be shifted older in time. addressed the topic of lake level in ancestral Lake able relationship to actual lake level, and the age Following the broad high from 2300 to 3200 Michigan. At the turn of the century, most studies data are presented without regard to relative-age cal B.P., lake level fell to a low at 2000 to 2200 yr focused on late Pleistocene lake-level variations. relationships, the curve suggests periods of high ago. In the Toleston Beach and Platte LakeÐ Study of late Holocene lake level at this time was lake levels at 400, 900, 1500, 2300, 3600, 4400, Baileys Harbor curves, the elevation of this low is primarily oriented toward recognizing Nipissing and 5100 cal B.P. (Fig. 8B). Moreover, Larsen at the elevation of the historical average for Lake phase and Algoma phase coastal features and re- (1985) assigned lake phase names to the 3600, Michigan (Fig. 7, A and B). Basal foreshore ele- constructing isobases (cf. Hough, 1958). More 4400, and 5100 peaks as the Algoma, Nipissing vations for the Platte LakeÐBaileys Harbor curve recent original studies of late Holocene lake level II, and Nipissing I phases of ancestral Lake continue to follow the historical average from in Lake Michigan were conducted by Fraser et al. Michigan. These data are in broad agreement 2200 cal B.P. to present (Fig. 7B), whereas the (1975, 1990), Larsen (1985, 1994), Thompson with the long-term trends and some short-term Toleston Beach curve extends below the histori- (1992), and Dott and Mickelson (1995). The data patterns observed in this study. Our high at 4500 cal average by 1500 cal B.P. and reaches extreme from the Gary Airport transect of Thompson cal B.P. is slightly older than Larsen’s (1985) lows at 600 and 400 cal B.P. (Fig. 7A). The Platte (1992) are incorporated into this study and are Nipissing II peak, but our high starting at 3200 is LakeÐBaileys Harbor elevations at the historical not discussed separately. Recent studies of late at least 400 yr younger than his Algoma peak. average supports the conclusions of the CCBHD Holocene lake level for Lake Ontario were con- Larsen (1994), however, moved the Algoma peak (1977), that the Platte Lake and Baileys Harbor ducted by Flint et al. (1988), McCarthy and forward 800 yr, to about 2800 cal B.P. This shift embayments are on or near the zero isobase for McAndrews (1988), and Dalrymple and Carey more closely matches our data. Lakes Michigan and Huron. The lows at 600 and (1990). Several of these studies only present the Dott and Mickelson (1995) created a compos- 400 cal B.P. for Toleston Beach suggest levels be- time scale of their lake-level curves as radiocar- ite curve for two strand plains of beach ridges at low the elevation of the historical average for the bon years before present. We discuss their curves Two Rivers, Wisconsin. Using a technique simi- southern shore of Lake Michigan. These low lev- in calendar years using a cross-reference scale lar to that of Thompson (1992), they produced a els would be expected for an area rebounding created from the bidecadal data set of Stuvier and curve covering the past 5700 cal B.P. The curve more slowly than the outlet for the basin. The Reimer (1993). suggests highs at 1200, 1500, 2300, 2800, 3700, data, however, indicate that the relative lake-level Fraser et al. (1975) were among the first to 4200, and 5300 cal B.P. (Fig. 8C). The oldest rise for the southern shore of Lake Michigan pre- quantify lake-level fluctuations in Lake Michigan peak may represent the Nipissing I phase, the dicted by the CCBHD (1977) occurred during on time scales shorter than the major Nipissing double peak at 3800 representing the Nipissing II only the past 600 yr. In addition, the relative lake- and Algoma lake phases. They examined the tim- phase, and the high at 2800 representing the Al- level curve for Toleston Beach suggests that the ing of shoreline development in the Zion beach- goma phase (Dott and Mickelson, 1995, interpre- area was rising relative to the outlet prior to about ridge plain by dating 23 peat, organic soil, and tation I). The Nipissing II peak is 600 yr younger 600 yr ago. wood samples from cores collected in the wet- and the Algoma peak is 200 yr younger, respec- The Sturgeon Bay curve records the elevation of lands between beach ridges. Using these data and tively, than the 4500 and 3000 highs indicated by the 2000 to 2200 low at an isostatically elevated information about the stratigraphic sequences in the curves in this study. 3.5 m above the historical average (Fig. 6D), and which the samples were deposited, periods of Three studies used a different geological ap- like the Manistique-Thompson curve shows a con- high and low lake level were inferred as relating proach to determining past lake-level change in tinued lake-level fall from the 2200 low to the pre- to cool and wet and warm and dry climates, re- Lake Ontario (Flint et al., 1988; McCarthy and sent. The fall is steeper for the Sturgeon Bay curve, spectively. In the Fraser et al. (1975) treatment of McAndrews, 1988; Dalrymple and Carey, 1990). supporting the conclusion of CCBHD (1977) that the data, no absolute elevations were assigned to These studies employed stratigraphic and sedi- the northern tip of the Lower Peninsula of Michi- the lake-level curve. They suggest periods of high mentologic relationships in ponds and lagoons to gan is isostatically rebounding faster than the west- lake levels at 40Ð180, 340Ð600, 725Ð850, suggest periods of rising and falling lake level ern end of the Upper Peninsula. The rate of isosta- 1025Ð1375, 1550Ð1700, and 2300Ð3500 cal B.P. over the past 3800 cal B.P. Although slightly tic rise is 0.16 m/100 yr. The interpolated value for (Fig. 8A). Many of these highs are roughly coin- different in the actual timing and magnitude of the northern tip of the Lower Peninsula of Michi- cident with the lake-level highs recorded in this lake-level variation, they suggest high lake levels gan to the Port Huron outlet from the CCBHD study. They do not, however, resolve discrete from about 800 to 1800, 2000 to 3000, and prior (1977) is ≈0.14 m/100 yr. lake-level events before 2300 cal B.P., and they to 3500 cal B.P. (Fig. 8D). These highs are very The relative lake-level curves for all of the sites split the 1700 high observed in this study into two similar to the highs suggested in this study and show a broad lake-level high from 1200 to 2000 events. indicate that Lakes Michigan and Ontario were cal B.P. that is centered around 1700 yr ago. The Using the elevations of the dated material from behaving synchronously. This observation is con- Platte LakeÐBaileys Harbor curve indicates that the Fraser et al. (1975) study, additional age dat- trary to the conclusion of Dalrymple and Cary lake level rose and fell ≈1.5 m. The high is less ing at the Zion beach-ridge plain, and elevation (1990). pronounced for the other areas because of their and age data from northwestern Indiana and the isostatic adjustments. Thompson and Baedke Chicago area, Larsen (1985) produced a lake- Short-Term Lake-Level Variation (1995) suggested that the rise to the 1700 yr ago level curve containing both elevation and age high was instrumental in causing the loss of rec- data. In addition to identifying long-term intervals Although the four relative lake-level curves ord in the Manistique-Thompson curve. They ar- of high and low levels of Lake Michigan during produced in this study do not cover the same time gued that there was insufficient sediment supply the past 7000 yr, this curve showed that Lake frame, there is sufficient overlap to recognize two to the area to counteract the landward translation Michigan has had significantly higher and lower temporal scales of lake-level variation. The of the shoreline as lake level rose. Consequently, water levels than those observed during historic shorter of these variations is represented by the

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Figure 8. Graphs of lake-level curves for Lake Michigan from (A) Fraser et al. (1975), (B) Larsen (1985), (C) Dott and Mickelson (1995), and (D) Dalrymple and Carey (1990).

timing of development for individual beach of the historical data set, these calculated fluctua- the resolution of the dating technique used in this ridges. At all the sites these ridges are quasiperi- tions cannot be statistically validated. The corre- study, we cannot correlate all 30 yr events basin- odically formed every 29 to 38 yr; the average is spondence of their observations of the historical wide (Fig. 9). Moreover, no data are available on 33 yr/ridge (Fig. 7F). Liu (1970) and Cohn and record with the timing of beach-ridge develop- the amplitude of lake-level rise and fall, because Robinson (1976), using spectral analyses, ment observed in this study supports our inter- only lake-level highs are preserved by the beach showed a 32 and 36 yr cyclic variation, respec- pretation that a lake-level fluctuation of ≈33 yr ridges. The historical record, however, indicates tively, in the lake-level gauge data for Lake occurs in the Lake Michigan basin. Because the an amplitude of 0.5 to 0.6 m (Thompson, 1992). Michigan (Fig. 7F). Because of the short length duration of this 30 yr fluctuation is smaller than The longer scale variation is suggested by the

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Figure 9. Graphs of relative late Holocene lake level for the study areas. Data for this graph are the basal foreshore elevations of Figure 7. Note that the Platte Lake and Baileys Harbor curves are combined. Opposing arrows mark some of the 150 yr events.

groupings of four to six beach ridges identifiable nineteenth century, falling to lows in the 1930s, though individual strand plains may not preserve in most areas by a systematic rise and fall in fore- and a steady rise in the mid- to late twentieth cen- all lake-level variations, combining information shore elevation within the group. Surficially, the tury. Other researchers have attributed the falling from several sites can identify patterns of lake- groups show an increase followed by a decrease lake levels in the early 1900s to dredging of the level change outside the temporal limits of the in elevation and relief. These groups are com- Detroit River (cf. Bishop, 1990). The pervasive historical record. monly separated by wider wetlands than those nature of the 150 yr variation recognized in this We have focused our study on gathering infor- that occur within a group. Consisting of four to study suggests that the dredging hypothesis may mation needed to pinpoint actual lake level by six ridges, they suggest a lake-level fluctuation of not account for the entire lake-level fall in the rigorously collecting sedimentological data. ≈150 yr in duration and a range of 120 to 180 yr. early 1900s. More than 250 beach ridges were cored across This fluctuation is observable at all of the sites five strand plains to obtain the elevation of basal back to 4500 cal B.P. with a range of lake-level CONCLUSIONS foreshore deposits. These sediments are the most rise and fall of 0.5 to 1.5 m (Fig. 8). Many 150 yr reliable and accurate approximation of actual variations can be directly correlated basinwide. The behavior of any reach of Great Lakes lake level that can be obtained from a strand plain This is especially true for the 150 yr events on the shoreline is a complex interaction of many forc- of beach ridges. The elevation data presented in 1700 high. Across this high phase of Lake Michi- ing factors. These factors can be simplified into this study improve upon estimates of lake level gan, we observe six 150 yr fluctuations and an al- wave climate, relative rate of sediment supply, interpreted from the elevation of geomorphic fea- most peak for peak match between areas (Fig. 9). and relative rate of lake-level change. The quanti- tures (e.g., Johnson et al., 1990; Lichter, 1994) However, we see that 150 yr events are not uni- tative interaction of these three factors is not well and organic samples (e.g., Fraser et al., 1975, form in period or amplitude between sites and at known. However, changes in lake level are the 1990; Larsen, 1973, 1985). individual sites. Some of the variability between most quantifiable, and for Great Lakes shore- We have systematically determined the age of sites is a function of the resolution of the dating lines, they may have the most profound influence beach ridges by dating basal wetland sediments technique, but it may be that the 150 yr variation on shoreline response (Hands, 1983). Along the in swales between beach ridges. The ages are is simply quasiperiodic in nature. Thompson coasts of Lake Michigan, fluctuations in lake more variable than expected, but close temporal (1992) suggested that the 150 yr variation may be level throughout the late Holocene produced correspondence in peaks among the relative lake- in part reflected in the historical record for Lake strand plains of beach ridges and associated in- level curves indicates that our dating technique is Michigan: high lake levels in the mid- to late terridge wetlands in numerous embayments. Al- reliable. Caution should be used in applying our

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dating technique to areas that do not undergo and cost sharing to the Indiana Geological Sur- p. 1175Ð1183. ground-water focusing (e.g., Hansel et al., 1990). vey at Indiana University. We appreciate the re- Fox, W. T., Ladd, J. W., and Martin, M. K., 1966, A profile of the four moment measures perpendicular to a shore line, In these areas the assumption that the wetland views by Robert W. Dalrymple, D. Mickelson, South Haven, Michigan: Journal of Sedimentary Petrol- formed soon after the development of the beach and Orrin Pilkey that improved the manuscript. ogy, v. 35, p. 1126Ð1130. ridge lakeward of it is probably not valid. In ad- We thank personnel at the Indiana Dunes and Fraser, G. S., Larsen, C. E., and Hester, N. C., 1975, Climati- cally controlled high lake levels in Lake Michigan and dition, care should be taken to make sure that no Sleeping Bear Dunes National Lakeshores, Mead Lake Huron basins: Anais de Academia Brasileira de erosion had occurred in the strand plain if the Paper Company, Ridges Sanctuary, and Wilder- Ciencias, Supplement 47, p. 51Ð66. Fraser, G. S., Larsen, C. E., and Hester, N. C., 1990, Climatic technique of Larsen (1994) is applied. This tech- ness State Park for access to the study areas and control of lake levels in the Lake Michigan and Lake nique is similar to ours because it uses distance as logistical support. Numerous field and laboratory Huron basins, in Schneider, A. F., and Fraser, G. S., eds., a time line. However, having no way to determine associates worked on portions of these projects Late Quaternary history of the Lake Michigan basin: Ge- ological Society of America Special Paper 251, p. 75Ð89. accurately if continuous preservation occurs in during the past 7 yr: Paul K. Doss, Linda Pride Fraser, G. S., and 12 others, 1991, Sediments and sedimentary the strand plain, ages may be assigned to ridges Thompson, Allen W. Archer, Zinta Smidchens, structures of a barred, nontidal coastline, southern shore that do not reflect their true age. Charlotte Tanner, William Henderson, Jennifer of Lake Michigan: Journal of Coastal Research, v. 7, p. 1113Ð1124. Common observations between the relative Wilson, Clayton Millard, Ann Zawistoski, Wes- Geyh, M. A., and Schleicher, H., 1990, Absolute age determi- lake-level curves are as follows. ley Boberg, Barbara Cermak Baedke, and Ann nation: Berlin, Springer-Verlag, 503 p. Hands, E. B., 1983, The Great Lakes as a test model for profile (1) Lake-level highs occurred at 4400Ð4600 Pahmeier. We also thank Douglas A. Wilcox, responses to sea level changes, in Komar, P. D., ed., CRC (Nipissing II phase), 4000Ð4300, 2300Ð3200 Stephen T. Jackson, Gordon S. Fraser, Robert K. handbook of coastal processes: Boca Raton, Florida, (Algoma phase), and 1200Ð2000 cal B.P. Rel- Schwartz, and S. Jeff Williams for helpful com- CRC Press, p. 167Ð189. Hansel, A. K., Mickelson, D. M., Schneider, A. F., and Larsen, ative lake-level curves for the northern sites ments throughout the collection and writing C. E., 1985, Late Wisconsinan and Holocene history of the (Manistique-Thompson, and Sturgeon Bay phases of this project. Permission to distribute Lake Michigan basin: Geological Association of Canada curves) show that isostatic rebound was more this paper was granted by the State Geologist and Special Paper 30, p. 39Ð53. Hansel, A. K., Chrzastowski, M. J., Riggs, M. H., Miller, M. V., rapid than at the Port Huron outlet, whereas the Publications Committee of the Indiana Geologi- and Follmer, L. R., 1990, New 14C ages on Late Holocene Platte LakeÐBaileys Harbor curves show little cal Survey. peat accumulations in beach-ridge swales at Illinois Beach State Park: Geological Society of America Abstracts with differential isostatic rebound with respect to the Programs, v. 22, no. 5, p. 12. outlet. The Toleston Beach curve shows a long- Henderson, W. A., 1993, Comparison of lateral facies charac- term fall in the older part of the curve, suggesting REFERENCES CITED teristics in a modern nearshore with vertical facies se- quences in adjacent beach ridges [Bachelor’s thesis]: that the area has rebounded faster than the outlet. Bergquist, S. G., 1936, The Pleistocene history of the Tahqua- Meadville, Pennsylvania, Allegheny College, 39 p. The lake-level rise measured for the southern menon and Manistique drainage region of the northern Hough, J. 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A., 1992, The late Wis- igan basin: Geological Society of America Special Paper vidual shorelines preclude this variation from be- consinan and Holocene coastal evolution of the southern 251, p. 67Ð74. shore of Lake Michigan, in Fletcher, C. H., and Wehmiller, Larsen, C. E., 1973, Late Holocene lake levels in southern Lake ing directly correlatable everywhere in the basin. J. F., eds., Quaternary coasts of the United States: Marine Michigan: Illinois State Geological Survey Guidebook This lake-level fluctuation is present in the his- and lacustrine systems: SEPM (Society for Sedimentary Series 12, p. 46Ð55. torical record from lake-level gauges with a range Geology) Special Publication 48, p. 397Ð413. Larsen, C. E., 1985, A stratigraphic study of beach features on Cohen, B. P., and Robinson, J. E., 1976, A forecast model for the southwestern shore of Lake Michigan: New evidence of 0.5 to 0.6 m. 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C., 1970, Statistics of Great Lakes levels: Proceedings of Dorr, J. A., Jr., and Eschman, D. F., 1970, Geology of Michi- the 13th Conference on Great Lakes Research, p. 360Ð368. gan: Ann Arbor, University of Michigan Press, 476 p. McCarthy, F. M. G., and McAndrews, J. H., 1988, Water levels This report is a summary of two studies par- Dott, E. R., and Mickelson, D., 1995, Lake Michigan water in Lake Ontario 4230Ð2000 years B. P.: Evidence from level and the development of Holocene beach-ridge com- Grenadier Pond, Toronto, Canada: Journal of Paleoclima- tially or completely funded by the U.S. Geologi- plexes at Two Rivers, Wisconsin: Stratigraphic, geomor- tology, v. 1, p. 99Ð113. cal Survey, Coastal Geology Program, and the phic, and radiocarbon evidence: Geological Society of Olson, J. S., 1958, Lake Michigan dune development. 3. 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Chichester, United Kingdom, Wiley & Sons, p. 273Ð298. Stevenson, E. B., 1930, The dunes of the Manistique area: Pa- opment in Lake Michigan, shoreline behavior in response Pilcher, J. R., 1993, Radiocarbon dating and the palynologist: pers of the Michigan Academy of Science, Arts, and Let- to quasi-periodic lake-level events: Marine Geology, A realistic approach to accuracy, in Chambers, F. M., ed., ters, v. 14, p. 475—485. v. 129, p. 163Ð174. Climate change and human impact on the landscape: Stuvier, M., and Reimer, P. J., 1993, Extended 14C data base Thompson, T. A., Fraser, G. S., and Olyphant, G., 1988, Estab- Studies in palaeoecology and environmental archaeology: and revised Calib 3.0 14C age calibration program: Ra- lishing the altitude and age of past lake levels in the Great New York, Chapman and Hall, p. 23Ð32. diocarbon, v. 35, p. 215Ð230. Lakes: Geological Society of America Abstracts with Quinn, F. H., and Sellinger, C. E., 1990, Lake Michigan record Thompson, T. A., 1987, Sedimentology, internal architecture, Programs, v. 20, no. 5, p. 392. levels of 1838: A present perspective: Journal of Great and depositional history of the southeastern shore of Lake Thompson, T. A., Fraser, G. S., and Hester, N. C., 1991, Lake- Lakes Research, v. 16, p. 133Ð138. Michigan, [Ph.D. dissert.]: Bloomington, Indiana Univer- level variation in southern Lake Michigan: Magnitude and Schneider, A. F., 1966, Natural features of Indiana, Chapter sity, 295 p. timing of fluctuations over the past 4000 years: Illinois- 3—Physiography, in Indiana sesquicentennial volume: Thompson, T. A., 1989, Anatomy of a transgression along the Indiana National Oceanic and Atmospheric Administra- Indianapolis, Indiana Academy of Science, p. 40Ð56. southeastern shore of Lake Michigan: Journal of Coastal tion Sea Grant Special Report IL-IN-SR-91-2, 19 p. Scott, I. D., 1921, Inland lakes of Michigan: Michigan Geolog- Research, v. 5, p. 711Ð724. Visocky, A. P., 1977, Hydrologic study of Illinois Beach State ical and Biological Survey Publication 30, Geological Se- Thompson, T. A., 1992, Beach-ridge development and lake- Park: Illinois State Water Survey Circular 128, 48 p. ries 25, p. 281Ð286. level variation in southern Lake Michigan, in Donoghue, Sherrill, M. G., 1978, Geology and ground water in Door J. F., Davis, R. A., Fletcher, C. H., and Suter, J. R., eds., County, Wisconsin, with emphasis on contamination po- Quaternary coastal evolution: Sedimentary Geology, MANUSCRIPT RECEIVED BY THE SOCIETY JUNE, 13, 1995 tential in the Silurian dolomite: U.S. Geological Survey v. 80, p. 305Ð318. REVISED MANUSCRIPT RECEIVED SEPTEMBER 13, 1996 Water-Supply Paper 2047, 38 p. Thompson, T. A., and Baedke, S. J., 1995, Beach-ridge devel- MANUSCRIPT ACCEPTED OCTOBER 17, 1996

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