ABSTRACT This field guide provides an updated synthesis of the stratigraphy and chronology of glacial deposits in central Indiana near the southern limit of glaciation in the midcontinent. Central Indiana contains evidence of multiple glaciations—deposits from the last two glaciations (Oxygen Isotope Stages [OIS] 2 [Wisconsin Episode] and 6 [Illinois Episode]) have been the focus of recent stratigraphic and chronologic investigation. New radiocarbon and optically stimulated luminescence (OSL) dating from outcrop and core has refined the timing of OIS 2 and OIS 6 ice sheet advances, outwash/slackwater aggradation, glacial lake formation, and eolian activity. Radiocarbon ages within or below late Wisconsin till from three sites within 5 km (3 mi) of the late Wisconsin maximum limit indicate an age of 24.0 k cal yr B.P. for maximum OIS 2 ice sheet extent in central Indiana, consistent with chronology from Illinois and Ohio. A subsequent >50 km (31 mi) readvance (21.6 k cal yr B.P.) across central Indiana came within 10 km (6 mi) of the maximum limit and in the western part of the field-trip area, terminated in glacial Lake Eminence. The start of outwash aggradation and associated slackwater sedimentation in the West Fork White River valley and tributaries began ca. 27 k cal yr B.P. and continued until ca. 20.5 k cal yr B.P., representing the timing of ice sheet advance into and out of the paleo–White River drainage basin. Ice sheet advance and retreat rates average ~40 m/yr before and after the global Last Glacial Maximum (ca. 26−21 k cal yr B.P.) when ice was within ~50 km of the late Wisconsin maximum. OSL dating of pre-Wisconsin outwash and glacio-lacustrine sediment return ages between ca. 218 and 127 ka, confirming deposition during OIS 6. These ages document spatially complex sedimentation in bedrock valleys beyond the Wisconsin limit.

ABSTRACT The Sidney Geosol in Ohio and Indiana is believed to have developed between marine isotope stage (MIS) 5 and MIS 2. Development stopped when the Laurentide ice sheet extended south of the Great Lakes during MIS 2. Prior reported data and new chronological information are employed here to show that pedogenesis of the Sydney Geosol started prior to 50 cal ka and ended time-transgressively through burial by sediment of the Laurentide ice sheet. Near Sidney, Ohio, the termination age is ca. 25.9 cal ka, whereas at Snyder, Indiana, near the limit of the ice-sheet expansion, the age is ca. 21.9 cal ka. However, at Oxford, Ohio, an interstadial organic accumulation between till units may imply that the upper portion of the Sidney Geosol formed under different conditions than the remainder. At a third site, Huffman Park, Ohio, glacially transported tree remains represent a landscape older than 50 cal ka, which is currently difficult to correlate with any specific paleosol, but which suggests that further insights about conditions prior to ca. 25.9 cal ka may be preserved in the record.

ABSTRACT Based on the interpretation of 893 finite radiocarbon ages, we have revised the time-distance diagram for the Lake Michigan Lobe of the Laurentide ice sheet in Illinois. The data set contains 507 reliable ages determined using standard benzene synthesis–liquid scintillation, including “legacy” ages determined in the 1950s and 1960s at the inception of the radiometric radiocarbon dating method. In addition, the data set includes 278 radiocarbon ages determined by accelerator mass spectrometry. We analyzed the data set based on context, precision, and accuracy to vet minimum or maximum age estimates of diachronic phases. The last glaciation in Illinois is marked by a local maximum margin in northeastern Illinois during the Marengo Phase (modal probability 28,000 cal [calibrated] yr B.P.), and subsequent glacial maximum culminating during the Shelby Phase (24,200 cal yr B.P.). From about that point, the Lake Michigan Lobe entered an overall retreat mode, with significant advances at ~22,200 and 21,100 cal yr B.P. (the Marseilles and Minooka Subphases of the Livingston Phase) and at 20,500 cal yr B.P. (Woodstock Phase). The latter age is also the conservative estimate of the onset of the lacustrine Milwaukee Phase, with referent deposits located as far north as Milwaukee, Wisconsin. This phase ended as the Lake Michigan Lobe made its final advance into Illinois during the Crown Point Phase (18,490 to ca. 16,500 cal yr B.P.), interfingering with the proglacial lacustrine Glenwood Phase deposits (16,900–15,000 cal yr B.P.).

ABSTRACT The glaciated terrain along the northern edge of the Appalachian Plateau in the eastern Finger Lakes of central New York has long been recognized as an important location for meltwater routing and for proglacial lake development in the Great Lakes region. Despite recognition of multiple ice margins formed by the Ontario Lobe of the Laurentide ice sheet during the late Wisconsinan, numerical age control of several margins has been elusive, particularly in regard to regional readvances of the Port Bruce (ca. 16,980–18,000 cal [calibrated] yr B.P.) and Port Huron (ca. 14,300– 16,000 cal yr B.P.) Phases. Utilizing light detection and ranging (LiDAR) terrain models in the eastern Finger Lakes area, we identified and described the Mapleton, Tully, and Labrador Hollow moraines. Associated ice-marginal landforms include push moraines, fans, and hummocky topography. In places, these features intrude into the northern heads of through valleys. Coring of three basins directly associated with these landforms yielded more than 20 samples of boreal tree needles and twigs, and Dryas leaves. Accelerated mass spectrometry (AMS) radiocarbon assay results indicate that poststadial lacustrine sedimentation began at ca. 15,000 cal yr B.P., consistent with ages of the Port Huron Phase.

Since 1890, Bering Glacier has been retreating from its Little Ice Age position near the Gulf of Alaska. Although this retreat has been punctuated by spectacular surge events, areas previously under the ice have regularly become exposed following surges. Sedimentary deposits above the current level of Vitus Lake are well dated to the past 2200 a. Older deposits eroded from the floor of the previous fjord are deposited above lake level by ice advance, and these sediments and fossils allow us to reconstruct the past history of Bering Glacier. Bering Glacier extended past the modern Pacific coastline during the Late Glacial Maximum (LGM), but retreated up its fjord by 13,000 a ago, leaving an embayed coastline inhabited by marine invertebrates until 5000 a ago. The shoreline was then uplifted, and terrestrial sandy outwash with intermittent peat bogs covered the landscape. Forests covered the area by 4000 a ago, with evidence of 800 a of continuous forest occupation (from 200 B.C. to A.D. 600) found at the Ancient Forest site. This forest was buried by rising lake levels, and between A.D. 600 and 1000, active gravel outwash deposition alternated with thin peats growing on more stable surfaces. Subsequently, active outwash deposits aggraded to 21 m above the current level of Vitus Lake as glacier outwash covered the forelands. A thin till capping the advance out-wash is the only indicator of the Little Ice Age advance that occurred sometime after A.D. 1100. The sediment record does not hold evidence for multiple advances of Bering Glacier during the past 2200 a.

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Reconnaissance surficial mapping in the upper St. John River area of northwestern Maine has shown that the latest Wisconsin events in the region were ice-flow reversal and southeastward ice marginal retreat. Widespread erratics derived from the Canadian Shield substantiate ice movement from the west or northwest into Maine prior to these events. Striations, rattails, and small-scale stoss-and-lee forms, all indicating northward and subsequently northwestward ice flow, are superimposed over earlier evidence showing eastward ice movement. Recessional ice-margin positions, delineated by lakes, drainage routes, and moraine segments, demonstrate that the ice margin retreated to the southeast following the emergence of the Notre Dame Mountains as nunataks near the present International Border. Marginal drainage was generally northeastward—perpendicular to topographic slope—via short-lived lakes and spillways. One major stillstand of the ice margin interrupted overall recession in northernmost Maine; however, no conclusive evidence suggests a north or northwestward readvance during this phase. Evidence for north and northwestward ice flow requires a late-glacial dome located over north-central Maine. One explanation for such dome formation is that a late-glacial ice stream developed in the St. Lawrence Valley and drained most of the ice from central Maine before marine calving isolated an independent ice mass. Rapid areal deglaciation ensued with only rare stillstands interrupting extensive disintegration.