Surficial Geology of the Bradford, NH 7.5-minute Quadrangle Gregory A. Barker and Joshua A. Keeley New Hampshire Geological Survey Surficial geology mapped during the 2017-2018 field season Geologic History New Hampshire has been subject to multiple ice ages, but only evidence of the most recent one, the Wisconsin Glaciation and the Laurentide ice sheet, is well preserved in the glacial sediments and landforms that were left behind as the ice melted. The Laurentide Glacier generally advanced into the area from the northwest to the southeast. The ice was at least 2000 meters thick through much of the region, covering even the highest summits (Bierman et al. 2015), and the weight of the ice and its slow but constant motion led to significant erosion of the pre-glacial landscape. Stoss and lee topography is common in many glaciated landscapes, where the leading, up-ice (stoss) side of a hill has a gentler slope while the down-ice side (lee) is much steeper resulting from plucking or erosion by the ice. Photograph 1 shows a bedrock striation or a gouge across the bedrock surface, an indicator that the ice sheet passed over this area of New Hampshire. Beginning around 14,500 years ago, the area began to become ice free as the glacier both retreated and thinned (Hodgson and Licciardi 2016) exposing the summit of nearby Mt. Cardigan to solar radiation. The high summit of Mount Kearsarge likely caused ice to stagnate and downwaste against its northwestern edge. In this scenario, ice front positions were controlled by pre-existing bedrock controls and not by climatic conditions (Caldwell 1978). Within the mapping area, meltwater initially flowed south through the Lake Massasecum area and east through the Warner River channel. Ice contact deposits, including an esker and kame, positioned against the southwest side of the valley leading to Lake Massasecum, indicate that meltwater exited the quadrangle here. The depth of Lake Massasecum suggests that an ice block occupied the basin to prohibit the meltwater and sediments from entering the basin. Rather the meltwater and sediment were deposited against the ice or along the ice block’s western edge. The lack of deposits at the center of the area between the Warner River and Lake Massaseum suggest that ice occupied the area and directed meltwater toward Lake Massasecum. See Photos 2 and 3 for examples of sediment found along this deposit. Photograph 4 shows a typical glacial till deposit, adjacent this kame deposit. Ice eventually pulled back fully exposing the Warner River channel and it became the main meltwater outlet for the southern half of the quadrangle. Comparison of elevated terraced sediments within the Warner to a constriction point just east of Bradford center, indicate that these deposits likely graded to this constriction. Two areas at the western edge of the Warner system, although ultimately drained to the Warner, are considered to be separate deposits. The first is in the area of the West Warner River. This area contains several terraces, designated Qst, that extend off quadrangle. Comparison of these terrace elevations with a constriction just east indicates this system likely graded to this constriction. The second area around the Newbury, NH town center and designated Qnv, predominantly consists of ice contact deposits in the form of a kame and several eskers. Photographs 5 and 6 show exposed sediments of a kame just to the southwest of Newbury center. There is a small area of low outwash deposits just to the east of the town center. As the glacier melted back across the central hills of the quadrangle, till was predominantly deposited with a few areas of ice contact material accumulating along the south facing portion of these hills. Once the glacier reaches a nick point in the Lane River, at the eastern edge of south Sutton, NH, ice contact and glaciofluvial deposits begin to occur. These deposits have been collectively identified as the Middle Lane River Deposits (Qmlr). See Photograph 7 for a view looking north from the Lane River nick point. As the glacier retreated further north, the upper reaches of the Lane River and Stevens Brook became exposed and provided valleys for meltwater to drain through. Sediments deposited along the lower two thirds of Stevens Brook are predominantly ice contact in origin, particularly at the immediate valley margin with Holocene alluvium occupying the center around the current stream position. The upper third of Stevens Brook has greater thickness and contains fully formed ice contact features such as eskers and kames. Photographs 8 and 9, respectively, show a large drop stone within the deposit and a small esker. The Upper Lane River Deposit, in the vicinity of Kezar Lake and North Sutton, NH, was formed behind two meltwater channels. The easternmost channel is the current day outlet of the Lane, while the other channel, immediately west, was at a slightly higher elevation. A third channel exists to the west but is too high in elevation and so must have captured meltwater directly from the ice or subglacially. Behind the two outlets, sediments grade as an outwash plain to the outlets. As the ice pulled back beyond Kezar Lake, an ice block appears to have remained within the lake. Evidence for this are location and depth of Kezar Lake, the abrupt termination of outwash plain against the lake margin and a meltwater channel and associated deposits along the southwestern edge of the lake. Photograph 10 shows this edge of Kezar Lake. It should also be noted that the topographic constriction to the south of Gile Pond, just southeast of Kezar Lake, was the location of an early higher elevation meltwater channel. The use of this meltwater channel was rapidly terminated, as there are no terraced deposits leading to the channel and sediments in the channel consist primarily of basal till. References Barker, G.A. and Olson, N.F., 2017, Surficial Geology of the New London 7.5 minute Quadrangle: New Hampshire Geological Survey, Map Geo-120-024000-SMOF, scale 1:24,000. Bierman, P.R., Davis, P.T., Corbett, L.B., Lifton, N.A., Finkel, R.C., 2015, Cold-based Laurentide ice covered New England’s highest summits during the Last Glacial Maximum, Geology v. 43, n. 12 pp. 1059- 1062. Caldwell, D.H., 1978, Bedrock control of ice-marginal positions in central New York, Geology v. 6 pp. 278- 280 Goldthwait, and Stewart, unpublished data. Harte, Philip T., Johnson, William, Geohydrology and Water Quality of Stratified-Drift Aquifers in the Contoocook River Basin, South-Central New Hampshire, USGS, Water-Resources Investigation Report 92-4154, 1995. Hodgdon, Taylor, and Licciardi, Joseph, 2016, Developing a chronology for thinning of the Laurentide Ice Sheet in New Hampshire during the last deglaciation, Northeast GSA annual meeting, Abstracts with Programs. Koteff, Carl, 2012, Surficial Geologic map of the Warner Quadrangle, New Hampshire: New Hampshire Geological Survey, Map Geo-134-024000-SMOF, scale 1:24,000. Quantum Spatial, 2016, LiDAR data for Connecticut River Watershed with FEMA HQ - Winnipesaukee AOI and WMNF AOI QL2 LiDAR, New Hampshire State Plane Data Set USGS Contract: G10PC00026 Task Order Number: G15PD00886 CT_River_Watershed_2015. Description of Map Units af – Artificial fill (Holocene) Areas where surficial sediments may have been disturbed or removed and /or material transported from another location. Qaf – Alluvial Fan (Holocene and Pleistocene) Poorly sorted sand to boulder sized materials with some rounding, deposited in fan structures at the base of high sloping drainages. These fans may be the result of historic or periodic precipitation events that mobilized sediment down steep slopes. The resulting deposits can show some sorting but have limited amount of rounding to particles. These fans often overlie till at their upper, steeper sloped ends and valley bottom deposits, glaciofluvial or alluvium, at the distal end. Qal - Alluvium (Holocene) Sand to cobble, well rounded, poorly sorted deposits within the modern day floodplain. Qic - Ice Contact (Pleistocene) Glaciofluvial deposits laid down within or in close proximity to the ice margin. Deposits are generally poorly sorted, ranging from sands to moderately rounded cobbles with occasional boulders that may become increasingly stratified and may also grade to stratified deposits. Ice contact deposits can take the form of kames, eskers, ice channel fills and short braided stream plains. Qls – Land Slide (Holocene and Pleistocene) Deposit formed by a mass failure of sediment moved downslope. Originally deposited sediment is typically glacial till remobilized downslope to form a compact, poorly sorted diamicton. These deposits were found along the western edge of Mount Kearsarge within the quadrangle. Qmlr – Middle Lane River Deposit (Pleistocene) This deposit is located near the center of the quadrangle and largely consists of poorly sorted sand, gravel and cobble sediments up to 50 feet thick, although in most areas is less than 20 feet. A bedrock nick point for this area of the Lane River basin exists at the southeastern edge of this deposit. This nick point likely reduced the gradient of melt streams along this system providing the opportunity to build terraced fluvial sediments. However, most of the deposited sediments consist of ice contact deposits with eskers and kames being typical deposit morphologies. Qnv – Newbury Village Deposit (Pleistocene) This deposit is located around the center of Newbury, New Hampshire at the western terminus of the Warner River basin. The deposit predominantly consists of sand and gravel sediments with some cobbles and can be as much as 75 feet thick. There is one large kame within the deposit that exhibits stratified fluvial sediments that mostly dip to the north. There are also two eskers, immediately to the east of this kame, that also trend to the north. The remaining portion of this deposit, to the north, is dominated by eskers and outwash deposits that have a southerly trend.