Geochronology and Geomorphology of the Jones

Home , Dunderberg Mountain, Gat (landform)

Geomorphology 321 (2018) 87–102

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Geomorphology

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Geochronology and geomorphology of the Jones Point glacial landform in Lower Hudson Valley (New York): Insight into deglaciation processes since the Last Glacial Maximum

Yuri Gorokhovich a,⁎, Michelle Nelson b, Timothy Eaton c, Jessica Wolk-Stanley a, Gautam Sen a a Lehman College, City University of New York (CUNY), Department of Earth, Environmental, and Geospatial Sciences, Gillet Hall 315, 250 Bedford Park Blvd. West, Bronx, NY 10468, USA b USU Luminescence Lab, Department of Geology, Utah State University, USA c Queens College, School of Earth and Environmental Science, City University of New York, USA article info abstract

Article history: The glacial deposits at Jones Point, located on the western side of the lower Hudson River, New York, were Received 16 May 2018 investigated with geologic, geophysical, remote sensing and optically stimulated luminescence (OSL) dating Received in revised form 8 August 2018 methods to build an interpretation of landform origin, formation and timing. OSL dates on eight samples of quartz Accepted 8 August 2018 sand, seven single-aliquot, and one single-grain of quartz yield an age range of 14–27 ka for the proglacial and Available online 14 August 2018 glaciofluvial deposits at Jones Point. Optical age results suggest that Jones Point deposits largely predate the glacial Lake Albany drainage erosional flood episode in the Hudson River Valley ca. 15–13 ka. Based on this Keywords: fi Glaciofluvial sedimentary data, we conclude that this major erosional event mostly removed valley ll deposits, leaving elevated terraces Landform evolution during deglaciation at the end of the Last Glacial Maximum (LGM). Our analysis supports the earlier 15 ka date Late Quaternary geochronology for the flood occurrence and suggests that more recent overlying glaciofluvial deposits formed in the lee-side Lower Hudson Valley of the Jones Point promontory. © 2018 Elsevier B.V. All rights reserved.

1. Introduction recent synthesis of local studies of glacial deposits and landforms in New Jersey, Long Island, and the Hudson valley, revision of the The lower Hudson River Valley in New York state has a well-known routing of the Hudson River, and the effect of the moraine's breaches glacial history beginning with work by Merrill (1891) and continuing and sea level rise on the history of glacial lakes was done by Stanford into the twenty-first century (Peet, 1904a, 1904b; Fuller, 1914; (2010). This study in addition to varve chronology by Ridge (2004) Thwaites, 1946; Newman et al., 1969; Markl, 1971; Merguerian and for the northeastern region of the USA, place deposition of the Sanders, 1990, 1992; Sanders and Merguerian, 1998; Cadwell et al., terminal moraine (Ronkonkoma) between 21,500 and 20,000 YBP, 2003). The evidence for multiple glacial episodes during the Pleistocene confirming dates previously reported by Sirkin and Stuckenrath Epoch (Fuller, 1914) was supported by studies of Sanders and (1980). The details of within-valley deglaciation processes following Merguerian (1998). The major glacial advance and retreat of the terminal moraine breach and climate change causing northward Laurentide Ice Sheet (LIS) in North America left substantial late shrinkage of the LIS are less constrained. Nonetheless, they are Quaternary sedimentary records in mid-lower Hudson River Valley, critically important to understanding the development of soils, New York, partially reworked and eroded by sudden meltwater revegetation, and ecological successions that eventually supported discharge (Uchupi et al., 2001; Donnelly et al., 2005; Rayburn et al., agriculture and subsistence for first settlers. 2005; Stanford, 2010). One of the earliest and widely used interpretations of deglaciation in The maximum ice extent in this region is limited to the south by New York State, including mid-lower Hudson River Valley, was summa- the Ronkonkoma moraine (Fuller, 1914)onLongIsland(Fig. 1), rized by Connally and Sirkin (1986). In their model of northward glacial and the upper age limit for the late Wisconsinan glacial maximum retreat, a series of ice-dammed lakes and associated glaciofluvial (LGM) is 21,750 ± 750 YBP, a 14C date based on bulk material of deposits such as deltas, kames, moraines, and terraces were deposited. unfossiliferous silt from the moraine (Sirkin and Stuckenrath, In addition, Ozsvath (1985) and Cadwell et al. (2003) emphasized the 1980; Cadwell and Dineen, 1987; Muller and Calkin, 1993). More effect of bedrock topography and relief on the formation of glacial features and their distribution; this helped to explain ice flows and glacial lake formation along the Hudson River. These interpretations are still ⁎ Corresponding author. being used in recent publications on deglaciation in New York, including E-mail address: [email protected] (Y. Gorokhovich). research on the role of the freshwater discharge from glacial lakes into

Fig. 1. General deglaciation benchmarks in mid-lower Hudson River Valley (adapted from Muller and Calkin, 1993; Ridge, 2004). A more detailed and larger geomorphological framework of the area, including glacial lake extents, can be found on maps in Ridge (2004), Stanford (2010),andMoss (2016). the Atlantic shelf (Uchupi et al., 2001; Donnelly et al., 2005; Rayburn Geomorphic and detailed sedimentary studies using limited bulk et al., 2005; Stanford, 2010). radiocarbon samples in the northeastern US have contributed to under- According to Connally and Sirkin (1986), northward LIS retreat and standing and interpretation of existing glacial features. Cosmogenic melting behind the Ronkonkoma moraine formed proglacial Lake radionuclide surface exposure (10Be) and 14C dating techniques helped Hudson, which was bounded to the north by the Shenandoah/Pellets establish better constraints on its deglaciation history. Surface exposure Island Moraine (Fig. 1). The Harbor Hill moraine, located to the north dating using 10Be by Balco and Schaefer (2006) on boulders from of Ronkonkoma moraine on Long Island (Fig. 1), is a result of the late moraines in eastern Connecticut, in conjunction with the previously Wisconsinan ice advance (Cadwell et al., 2003). Connally and Sirkin published New England varve chronology, place deglaciation within also proposed that the glacier had receded to the Shenandoah/Pellets a range of 18,500–19,000 YBP. In southern New York, boulder ages Island Moraine position by 17.95 cal. ka BP and a subsequent advance from Bear Mountain State Park area (Fig. 1) range from 18,000 to (Rosendale) took place about 16.1 cal. ka BP. After 16.1 cal. ka BP the 22,000 YBP (Schaefer pers. comm.). Peteet et al. (2012) used new accel- ice retreat continued northward, providing space for southern-derived erated mass spectrometer (AMS) 14C dates from 13 sites, including one ecological succession of plants and animals. near Jones Point in the area of Harriman State Park (Fig. 1), that show a With continued glacial retreat, proglacial Lake Hudson that occupied range of deposits dating to 15–16 cal. ka BP. The discrepancy in 10Be and areas of the lower Hudson (Fig. 1) connected with proglacial Lake 14C geochronologies led Peteet et al. (2012) to propose a hypothesis of Albany (stretched from the Mid-Hudson to the north); features and severe climatic conditions in North America that postponed complete landforms associated with this process are ice contact deltas from deglaciation until 16 cal. ka BP, the oldest 14Cdateobtainedinthe tributaries that mark paleolake levels (Connally and Sirkin, 1986). region. This can be possibly associated with Rosendale readvance that Sanders and Merguerian (1998) reported evidence of loess deposition took place ≈16,100 YBP (Connally and Sirkin, 1986). (however, no geochronological data is available) at Croton Point In this paper, we report the first optically stimulated luminescence (Fig. 1), an important indicator of ice sheet absence at this location. (OSL) dates of quartz sand and glacial sediments exposed in the Other loess locations were recorded in Long Island (de Laguna, 1963) lower Hudson River Valley near Jones Point, New York. Integration of but also not dated. Ridge (2004) compiled varve data from Antevs the OSL data with geomorphic methods used in this study helped to (1928) and Stanford and Harper (1991) to establish Haverstraw identify landform morphology, structure, and evolution since LGM. and Hackensack deglaciation margins in the lower Hudson River Data incorporated from previous studies helped place the geomorphic Valley (Fig. 1). evolution of the studied landform in a regional context of major Timing and interpretation of the deglaciation process is also im- deglaciation events: catastrophic breach of the Narrows moraine releas- portant to understanding evolution of species in the lower Hudson ing Lake Albany cold waters into the Atlantic and possible triggering of Valley. For example, separate fish studies on incipient speciation in glacial readvance. subwatershed tributaries demonstrated the existence of genetic changes in four freshwater fish species (Arcement and Rachlin, 1.1. Luminescence dating of glacial sediments 1976; Miller, 2015), which is attributed to their isolation by saltwater intrusion from the Atlantic Ocean. Because of the limited age control The long continental deglaciation process produces variable envi- on glacial deposits in the mid-lower Hudson Valley, such research ronmental conditions and depositional features, some of which are currently lacks a detailed chronological time frame in which these better suited for luminescence dating than others (Rhodes, 2011; events occurred. Wyshnytzky et al., 2015). Luminescence dating, described in more Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102 89

techniques to Patagonian, Russian, North American and Norwegian glacial material (respectively) by taking into account detailed sedimentology and stratigraphy, comparison to 14C ages, use of a minimum age model (Galbraith and Roberts, 2012), single-grain dating, and/or examination of residual luminescence signals in modern glacially-derived sediments. The effect of transport distance sedimentary history on luminescence dating of glacial sediments is twofold, bleachability (already mentioned) and sensitivity (Rhodes, 2011). Sensitivity is described by the OSL intensity, and a lack of luminescence intensity (or ‘dim’ signals) has been identified in glacial quartz from the New Zealand Alps (Preusser et al., 2006). The authors attributed these low detectable quartz OSL signals to short transport history and lack of luminescence traps. The notion of sensitiza- tion is likely derived from sedimentary cycling, which exposes grains to radiation over time and increases the number of available luminescence traps (Sawakuchi et al., 2011). Another noteworthy observation for glacial quartz is the lab-induced increase in sensitivity and thermal transfer that can occur with repeated laboratory dosing and stimulations (Rhodes, 2000; Preusser et al., 2006). The OSL ages may be overestimated if left uncorrected for such a shift in sensitivity or if it is too dominant to correct for (Rhodes, 2000). Fig. 2. Glacial landform (JP_2001) exposed after the landslide in 2001, facing southwest. Route 9W passes on the left; letters refer to sedimentary deposits To summarize, sediments farthest from the glacial front or sampled for granulometric analysis; layers D, G, I, and J were sampled for OSL (see Table 1 supraglacial sediments typically have a better chance of luminescence for sedimentology). signals being completely reset prior to burial than those deposited subglacially, intraglacially, or proximal to the glacial front, though this is detail later, is applied to sedimentary grains of quartz and feldspar somewhat complicated by bedrock lithology; this closely links OSL to determine an age estimate of the last time sediment was exposed dating and its interpretation with deglaciation processes and landforms. to sunlight or thermal exposure N300 °C (Huntley et al., 1985). In this paper, we combine geochronologic data from OSL dating and After removal from the stimulation source (light/heat), the mineral from geologic and geophysical methods in order to describe in detail dosimeters acquire and retain a dose of environmental radiation the glacial depositional landform at Jones Point, NY, and place it in the equivalent to time spent in burial and subject to surrounding radioactive framework of deglaciation history of the region. decay (Aitken, 1998). Complete removal of a previous dose (known as bleaching) during 1.2. Study area: Jones Point, New York sedimentary transport is ideal, and if not achieved, understanding the degree to which that previous dose has been removed is essential Two exposures near Bear Mountain State Park at Jones Point (Fig. 1) for accurate age determination (Alexanderson and Murray, 2007; are the focus for this study. Following a landslide in 2001, site JP_2001 Preusser et al., 2007). A review by Fuchs and Owen (2008) emphasized was exposed on the flank of the slope next to New York State route the importance of transport distance on dose resetting and related this 9W (Cusick and Gorokhovich, 2003)(Fig. 2). Due west across route to glacial deposits. They conclude that partial resetting is a likely 9W is site JP_2002, located in an abandoned gravel quarry (Fig. 3). scenario for glaciofluvial, glaciolacustrine, and glaciomarine deposits. Nu- Currently, both sites are heavily modified by surface erosion and merous independent studies have substantiated this (e.g., Glasser et al., slumping. These deposits are juxtaposed on the steep granite and gra- 2006; Thomas et al., 2006; Lepper et al., 2007; Rittenour et al., 2015; nitic gneiss bedrock (New York State Geologic Map, 1:250,000) slope King et al., 2014). These studies successfully applied luminescence dating of Jones Point where the Hudson River is channeled through an abrupt

Fig. 3. Repeat photograph of glacial landform JP_2002 in 2002 and 2016. Exposure is south facing, route 9W passes on the right, the bedrock of Jones Point is on the left behind the trees; upper layer of boulders and gravel (layer K) was considered as a marker in the two locations. Two samples for OSL were taken here in 2016, one above and one below layer K that dips in western direction. 90 Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102

Fig. 4. Oblique LIDAR model of the terrain at Jones Point, Rt 9W cuts across from NE to SW. Locations: 1 – JP_2002; 2 – JP_2001; 3 and 4 – unidentiﬁed potential components of original glacial terrace described by Merrill (1891) and Peet (1904a, 1904b). bend around Dunderberg Mountain (Fig. 4). The ﬁrst descriptions of continued exposure to nuclear radiation within the surrounding sedi- glacial deposits at Jones Point can be found in Merrill (1891) and Peet ment (Aitken, 1989). The decay of this radiation is converted to a dose

(1904a, 1904b). Both authors described deposits as a terrace, less than rate DR, in this case through chemical analysis such as inductively a mile long, composed of stratified subrounded gravel, sand, and little coupled mass spectrometry (ICP-MS) and known conversion factors clay. The original deposit morphology was cut through at the end (Adamiec and Aitken, 1998; Aitken, 1998; Guérin et al., 2011). of the nineteenth century by the construction of route 9W; however, The OSL age (ka) is the quotient of the DE (Gy) and DR (Gy/ka). no records or documentation were available from New York State One main assumption for OSL dating is that the material sampled was Department of Transportation. thoroughly exposed to sunlight or high heat to reset, or zero out, any and all previously acquired dose prior to the most recent burial or 2. Methodology event of interest. If mineral grains are not thoroughly zeroed, they will retain an antecedent dose (Murray et al., 1995), a phenomena known To study the timing and deglaciation environments at Jones Point, NY, as partial bleaching or incomplete zeroing. If left unaccounted for, we employed OSL dating, sedimentary and petrographic analysis, electri- partially bleached material will overestimate the latest burial dose and cal resistivity geophysics, and remote sensing (LiDAR). Sedimentary tex- age of an OSL sample (i.e., Olley et al., 1999). This problem can be ampli- ture and sorting were used to identify suitable layers for OSL dating and fied in glacial settings as transport distances may be short and transport to determine the onset of fluvial activity during glacial retreat. Addition- energy and sediment load typically are high and/or occur subglacially ally, the boulder/gravel layer K was analyzed by petrographic analysis of (Fuchs and Owen, 2008; Wyshnytzky et al., 2015). Methods are thin sections to determine the source (local vs. distant) of its material. employed to mitigate partial bleaching effects in these OSL samples, Bare-earth (i.e., without vegetation cover) LiDAR data were used to inves- and those are discussed in the Results section. tigate the overall morphology of the landform. Electrical resistivity was employed to conduct a subsurface investigation of the landforms and to 2.1.1. OSL sample collection verify the continuity of boulder layer K between our two sites. The OSL samples were collected in 2014 and 2016 from two exposures of a continuous outcrop of interbedded sand and pebble/cobble/boulder 2.1. Optically stimulated luminescence (OSL) dating stratigraphy at site JP_2002 (n 2) and Site JP_2001 (n 6) at Jones Point,

Luminescence dating can be applied to sedimentary quartz and feldspar in a variety of Quaternary geomorphic deposits (Aitken, 1998). Upon burial or removal from the heat source, these minerals are capable of storing a measurable dose of radiation in which they become natural dosimeters (Huntley et al., 1985). While OSL is complementary to radiocarbon and cosmogenic nuclide dating in terms of timescale over which it is applied (late Quaternary), OSL dating requires no organic material, is minimally inﬂuenced by subsequent erosion or aggradation, and it can date widespread surﬁcial geologic material beyond the limit of radiocarbon and below the typical limit with cosmogenic exposure dating (Duller, 2000). Standard OSL dating of quartz sand utilizes blue-green wavelengths to release excited electrons back to their natural energy orbital (Huntley et al., 1985). Upon ejection from geologically stable traps, some electrons recombine in luminescence centers to produce a measureable amount of light. These photons make up the luminescence signal measured in a dark room laboratory and are calibrated through irradiation cycles in order to calculate an equivalent dose DE in units of gray (Gy, where 1Gy = Joule/kg) of radiation (Murray and Wintle, 2000). Fig. 5. OSL sampling location at JP_2002 (USU-2422): sampling tube and 15-cm radius of

Electrons become ionized and trapped in mineral defects through DR sediment collection; image also shows parallel lamination. Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102 91

NY (Figs.2,3). Thick sand beds and lenses (N30 cm) were the main targets sieved to a grain size range between 125 and 250 μm. The quartz for OSL sampling to avoid DR heterogeneity; however, some thinner sand mineral fraction was isolated by using 10% hydrochloric acid and bleached lenses between pebble/cobble/boulder units were sampled given the gla- to dissolve carbonates and organic material, sodium polytungstate cial context that often lacks abundant sand deposits. Layers with original (2.7 g/cm3) to separate out the heavy minerals, and concentrated sedimentary structures, i.e., planar laminations, were sought after to min- hydrofluoric and hydrochloric acids to remove the feldspars, etch the imize post-depositional mixing and/or high energy and rapid deposition, outer quartz grain, and prevent formation of fluorite precipitates (see though massive sands were also sampled. Metal conduits cut into 8-inch Wintle, 1997 for details). Aliquots were checked for feldspar contamina- pieces were hammered horizontally into targeted layers for DE samples tion using infrared (IR) stimulation on all aliquots following the SAR (Fig. 5). The DR sediment was uniformly collected within a 15-cm radius protocol. Single-grains were checked for feldspar following the OSL IR of the DE sample; cobbles and gravels were included where they depletion ratio protocol of Duller (2003). intersected the DR sphere of influence. 2.1.3. Dose rate (DR) determination 2.1.2. OSL sample processing Representative subsamples of bulk DR material were uniformly di- Eight OSL samples were processed and analyzed at the Utah State vided into ~30 g samples and sent to the ALS Minerals Laboratory in University Luminescence Laboratory in Logan, UT, USA, for small- Elko, Nevada, to measure the radioelemental concentrations of K, Rb, aliquot and single-grain single-aliquot regenerative dose (SAR) analysis Th, and U using ICP-MS and ICP-AES analyses. In situ gravimetric mois- of quartz sand (Duller et al., 1999; Murray and Wintle, 2000). Samples ture content was measured at the USU Luminescence Lab on all samples. were opened under subdued amber safe lighting (~590 nm) and wet Dose rate calculations include cosmic contribution by using sample

Fig. 6. Proposed source areas I, II, and Catskills Mountains. These areas potentially contributed material to layer K at Jones Point. More detailed description of rock lithologies within each source area are in Tables 1 and 2. 92 Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102

Table 1 Results of granulometric analysis.

Layer Thickness (cm) Depth (cm) Mean (mm) Median (mm) Sorting Sediment type Sedimentary structure

A 135 135 4.82 8.39 2.83 Fine gravel Glacial drift deposits B 18 153 4.58 8.22 2.90 Fine gravel Glacial drift deposits C 16 169 1.13 1.15 1.99 Very coarse sand Cross-bedding D 20 189 0.39 0.34 1.55 Medium sand Cross-bedding E 76 265 1.81 2.15 1.93 Very coarse sand Plane beds F 5 270 0.04 0.06 2.98 Very coarse silt Flood/melt-out deposit (?) G 85 355 0.67 0.64 1.99 Coarse sand Massive beds H 63 418 0.48 0.55 1.70 Medium sand Massive beds I 20 438 0.15 0.16 2.26 Fine sand Massive beds J 95 533 0.22 0.26 1.55 Medium sand Massive beds K 200 733 Analyzed for petrographic identiﬁcation only Boulder/cobble/gravel Matrix supported gravel/boulder L 400 1133 1.3 1.36 2.46 Very coarse sand Massive beds depth, elevation, and longitude/latitude following Prescott and Hutton saturating-exponential or saturating-exponential plus linear ﬁts to

(1994),influence of water attenuation (Aitken and Xie, 1990), uncer- calculate individual aliquot DE values. tainty in elemental measurements, and dose rate conversion factors Single-grain dating was applied to USU-1768 and analyzed using the (Guérin et al., 2011). SAR technique (Duller et al., 1999; Murray and Wintle, 2000)onaRisø TL/OSL Model DA-20 reader with single-grain attachment (Duller et al., 2.1.4. Optical measurements 1999; Bøtter-Jensen et al., 2003). Grains were heated to 125 °C then 2 Individual aliquot DEs on quartz were calculated using the SAR tech- stimulated with a green laser (532 nm) at 90% power (45 W/cm ) for nique of Murray and Wintle (2000) on 1–2 mm diameter small-aliquots 0.8 s with a 0.1 s pause before and after stimulation. The luminescence (~10 grains per disk) for seven out of the eight samples. Optical mea- signal was detected through a 7.5-mm UV filter (U-340). Following surements were performed on Risø TL/OSL Model DA-20 readers with natural and regenerative doses, the preheat temperature was 240 °C blue-green light-emitting diodes (LED) (470 ± 30 nm) as the stimula- and held for 10 s, and test dose preheat treatments were 220 °C tion source. The luminescence signal was measured through 7.5-mm also held for 10 s. Dose response curves were fit within saturating- UV filters (U-340) over 40–45 s (250 channels) at 125 °C with LED exponential and saturating-exponential plus linear fits to calculate 2 diodes at 70–90% power (~45 mW/cm ), and calculated by subtracting individual grain DE values. the average of the last 5 s (background signal) from the first 0.7 s of the signal decay curve. Aliquots were heated to N180 °C prior to all op- 2.2. Electrical resistivity geophysics tical measurements to remove the thermally unstable traps around the 110 °C TL peak in quartz (Rhodes and Bailey, 1997). Preheat tempera- To investigate the three-dimensional morphology of the terrace tures at 240 °C (held for 10 s) followed natural and regenerative beta stratigraphy at JP_2001 (Fig. 2), a geophysical survey was designed doses, and test dose preheat treatments were 160–220 °C (held for using the electrical resistivity method, which is commonly used to 10 s). Two samples (USU-1765 and USU-1766) required a high temper- distinguish coarser (more resistive) from finer (less resistive) clastic ature (280 °C) optical stimulation (bleach) with blue LEDs held for 40 s sediments. The survey was conducted using an AGI Supersting at the end of each cycle to clear out high levels of recuperation (Wintle 28-electrode DC resistivity unit, with two-dimensional inverse and Murray, 2006). Dose response curves were fit within linear, modeling of the subsurface, and included two perpendicular profiles

Fig. 7. Results of sedimentary analysis vs. depth (max value) of sediments; alphabetical labels refer to individual layers and their max depth (cm). Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102 93

Fig. 8. Glacioﬂuvial features of the site JP_2001: cross-bedding (layer C), horizontal layers (E), and meltwater deposits of layer F; blue arrows indicate location of these features on the landform exposure. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)

along the ridge behind the bluff exposure and across a saddle to another vary between 17 and 26 cm (Hodgson and Bresnahan, 2004). ridge overlooking the Hudson (Fig. 4). With a 3-m electrode spacing, American Society for Photogrammetry and Remote Sensing (ASPRS) apparent resistivity pseudosections were corrected for topography has standard categories on LiDAR vertical accuracy from 5 cm (quality and generated using the Schlumberger and Dipole-dipole configura- level 0) to 18.5 cm (Quality Level 3) (USGS, 2014). tions, and the data were inverted using EarthImager2D (Advanced LiDAR data for this study were obtained from U.S. Geological Survey Geosciences Inc., Austin, TX) to produce subsurface distributions of (USGS) data application EarthExplorer (see: http://earthexplorer.usgs. apparent resistivity for interpretation. Data were not excessively gov/) in the American Society for Photogrammetry and Remote Sensing noisy, and standard inversion error criteria such as RMS and normalized (ASPRS) LAS format that stores three-dimensional point cloud data and L2 were low (b3% and 2.4 respectively). associated attributes. A LiDAR LAS file usually contains information on signal returns (e.g., first, second, third, fourth, last, etc.) and its classifi- 2.3. Remote sensing (LiDAR) application cation (e.g., unassigned, ground, noise, water, reserved, etc.) with a number of associated points in the point cloud. To map the surface of LiDAR (light detection and ranging) is widely used in remote sensing the bare earth, we used ground class points and created an image of for mapping earth surfaces and the shallow subsurface (Carter et al., Jones Point with bare earth elevation, i.e., without vegetation cover 2001; Slob and Hack, 2004). Vertical accuracy of measurements (Fig. 4). This helped to visualize the terrain as a geomorphologic entity depends on data interpolation and horizontal displacement and can and interpret the glacial landform.

Fig. 9. An example of the sample and corresponding thin section of the sample from layer K. 94 Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102

2.4. Sedimentary and petrographic analyses Table 2 Rock types identiﬁed at the JP_2002 location.

Field descriptions of sedimentary units exposed at JP_2001 and Sample Identiﬁed rock Possible source area JP_2002 include color, texture, sedimentary structure, and contact type (Fig. 6) appearance. JP1-1 Quartz-rich granitoid Source area I Twelve layers were targeted at site JP_2001 for granulometric JP1-2 Metamorphic quartzite Source area I analysis using freely available software package GRADISTAT (Blott and JP1-3 Low grade metamorphic quartzite Source area I (?) Pye, 2001) developed for Microsoft Excel. with carbon grains/calcite veins JP1-4 Sedimentary metamorphic sandstone Source area II Layer K is a coarse-grained sedimentary marker bed containing JP1-5 Sedimentary metamorphic sandstone Source area II small boulders and is observed at similar elevations at both sites JP1-6 Sandstone Source area II; (~25–31 m asl, Figs. 2, 3). Both locations were mapped with high- Catskills Mountains precision differential correction GPS (Trimble Pro). We targeted 12 JP1-7 Granite Source area I JP1-8 Fine-grained limestone Catskills Mountains boulders (N10 cm diameter) of unique lithology and had thin sections JP1-9 Sandstone (with carbonate inclusions) Catskills Mountains, prepared for petrographic analysis with a petrographic microscope to source area II identify minerals and rock types. Using the 1:250,000 digital geologic JP1-10 Altered sericite granite Source area I map (Fisher et al., 1970) in geographic information systems (GIS) JP1-11 Quartz monzonite breccia Source area II (Dicken et al., 2005), we grouped lithologies and identiﬁed three main JP1-12 Monzosyenite Source area II source areas (source areas I, II, and Catskills Mountains, Fig. 6)to which we matched the rock types.

3.3. LiDAR analysis 3. Results LiDAR data analysis was conducted to establish geomorphology 3.1. Sedimentary (granulometric) analysis of the area of study to verify potential connection between JP_2001 and JP_2002 and their relationship with the bedrock side of the valley. Detailed sedimentary analysis was done only for the site JP_2001 Fig. 4 shows rendering of the surface topography without vegetation because JP_2002 was not accessible at the time. Table 1 includes results cover. Route 9W is shown and cuts through the large terrace that was of field descriptions on unit thickness, sedimentary structure, and possibly one feature before construction and development of the area, granulometric analysis conducted with GRADISTAT; we used Folk and mentioned by Merrill (1891) and Peet (1904a, 1904b). Lower right Ward (1957) graphic measures for mean, median, and sorting. part of the image displays railroad tracks from the New York Hudson Mean particle size of sediments ranges from 0.04 to 4.82 mm. One Line. Flat surfaces (terraces) are evident at locations 1, 2, 3, and 4. sample (layer F) was primarily silt (0.04 mm), seven samples represent fine to coarse sand, and two upper samples represent fine gravel. 3.4. Geophysical analysis Sorting in all layers is moderate (≤1.62) to poor (≥1.62) with only two samples exhibiting moderate sorting: layers J and D. Layer H has sorting The resistivity surveys were conducted at sites 2 and 3 (Fig. 4), coefficient 1.7 on the borderline, close to 1.62. where LIDAR imagery shows remnant terraces of glaciofluvial materials Fig. 7 shows distribution of main granulometric parameters with extending east from the valley wall consisting of gneiss and diorite depth, from layers A to J. Median diameter in all layers follows closely bedrock beyond route 9W. The profiles extended NNE-SSW across the mean size distribution. Layers A and B exhibit poor sorting and large terrace behind JP_2001 at site 2 (Fig. 10) and WNW-ESE perpendicular mean/median grain size. Improvement of sorting coefficient and corre- across the saddle to site 3 (Fig. 11). These orientations were designed to sponding reduction in mean/median grain size is noticeable in layers C, distinguish whether boulder horizons were laterally continuous and D, E. Farther down, layer F shows finest mean/median grain size but whether the horizon geometries were subhorizontal, draped, or steeply poor sorting, the pattern similar to layer I. Other layers (G, H, I, and angled (Eaton et al., 2017). J) show that increase in grain size corresponds to decrease in sediment The survey configurations (dipole-dipole and Schlumberger) at each sorting (i.e., increase in sorting coefficient). location essentially show the same subsurface geometries, with high- Specific sedimentary structures such as plane beds and cross- resistivity materials (interpreted as the boulder horizon) mainly as bedding were observed in sedimentary layers C, D, and E. Layer F represents a thin fine-grained lens, possibly left by rapid meltwater. Fig. 8 shows examples of these features documented at site JP_2001. Granulometric analysis and stratigraphy of sedimentary units Table 3 helped to group 12 studied layers in three main facies (Table 1): glacial Unique occurrences of rock types in source areas I, II and Catskills (Fig. 6). drift (layers A–B), glaciofluvial (C–F) and proglacial deposits (G–J Source area II unique rocks Source area I unique rocks Catskills mountains and L). Glacial drift in top layers A and B is a matrix-supported diamict, (not existing in source area I) (not existing in source area II) rocks containing rounded and subrounded gravel material, poorly sorted. Anorthosite Diorite Limestone Glaciofluvial layers C–F contain cross-bedding structures; whereas the Argillite Gabbro Dolostone thickest basal layer L shows massive, coarse, planar beds. Black shale Granodiorite Sandstone Felsic gneiss Norite Mudstone Granulite Pelitic schist Conglomerates Lamprophyre Pyroxenite 3.2. Petrographic analysis Lava flows Quartzite Mafic metavolcanic Schist Analysis of thin sections made from rock samples (Fig. 9)found Metasedimentary rocks Metavolcanic in the JP_2002 site showed a list of rock types (Table 2)thatwere Monzonite õcompared to source areas I and II and to the Catskills Mountains. Mudstone õColumn possible source area contains matched choices of a specific Paragneiss rock type source. Table 3 shows unique occurrences of rock types within Sandstone Trachyte source areas I, II, and Catskills Mountains (Fig. 6). Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102 95

Fig. 10. Inversion models of subsurface resistivity distributions using dipole-dipole (upper) and Schlumberger (lower) conﬁgurations for NNE-SSW proﬁle at site 2. High resistivity values shown in white (note: resistivity values are relative, not absolute).

noncontinuous and limited to one end of the profile. In the case of the 3.5. OSL dating analysis terrace remnant at site 2 closer to the valley wall (Fig. 4), the higher resistivity materials are at the NNE (left) end, and at site 3 they are In luminescence dating, aliquots or grains may be removed from found at the ESE (right) end of traverse 2 (Fig. 11). The depth of the further age analysis if they do not meet acceptance criteria relating to high-resistivity materials (~3 m from the land surface) is consistent steps in the SAR protocol, such as repeated or no dose measurements with the location of the boulder horizon where it appears in the or nonsaturating exponential luminescence signal growth with given southern bluff of site 2; however, no similar bluff outcrop was identified doses. For the Jones Point OSL samples, individual aliquots were at site 3. Given the likely ice-proximal deglaciation scenario of the accepted in age calculation if they had no feldspar contamination, Hudson River Valley, it seems probable that the high-resistivity deposits repeated dose ratio within 40% of unity (USU-1766 and USU-1767 have longitudinal axes parallel to the valley wall and the geophysical omitted), recuperation at the zero dose SAR step b15% of the natural sig- profiles crossed them at high angles if not perpendicularly in the nal, and if the natural and test doses fell within the nonsaturating part of case of site 3 (Fig. 11). Although the profiles appear subhorizontal the dose response curve (Fig. 12). In addition, grains were rejected from at the site-scale, a comparison of similar boulder horizons at sites analysis if the initial signal (0.1–0.13 s) was b3 times the background

JP_2001 and JP_2002 suggests that the larger scale geometry is (0.67–0.90 s) after receiving a beta dose. Cumulative DE values were dipping in the downvalley direction (see Fig. 3). Therefore, the calculated using the central age model (CAM) or three-parameter boulder horizon seems unlikely to be a planar horizontal topset bed minimum age model (MAM-3) of Galbraith and Roberts (2012) of as originally hypothesized (Eaton et al., 2017). at least nine acceptable aliquots or grains of quartz sand (Table 4).

Fig. 11. Inversion models of subsurface resistivity distributions using dipole-dipole (upper) and Schlumberger (lower) conﬁgurations for WNW-ESE proﬁle at site 3. High resistivity values shown in white (note: resistivity values are relative, not absolute). 96 Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102

Fig. 12. Luminescence dose-response curves (left) and OSL response (right) for two 1-mm small-aliquot examples (USU-2422 and USU-1765) and one single-grain example from USU- 1768. Top example (USU-2422) is an exceptionally sensitive aliquot, while the middle example (USU-1765) is less sensitive to luminescence and more common for OSL samples presented here. The lower sensitivity and greater DE distribution has led to increased total error in OSL age estimates. Luminescence-responsive single grains were even less common, and the bottom example is one of a kind. The 675 out of 700 (96%) grains stimulated were not included in further analysis because initial response was b3 times background level. Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102 97

The chosen age model was based on sedimentology and stratigraphic cosmogenic contribution to the total dose rate following Prescott and context, overdispersion parameter, and skewness of aliquot or grain dis- Hutton (1994). tribution (Fig. 13; Table 5). All samples had overdispersion, or variance in the DE data, ≥40%, a sign that the distribution may contain some por- 4. Discussion tion of partially bleached grains (i.e., Arnold et al., 2007). Wyshnytzky et al. (2015) had showed this to be a common scenario in glaciofluvial In this work, we employed a variety of methods at Jones Point to sediments and that high overdispersion values do not always warrant better understand the geomorphic and sedimentary history of the use of the MAM when considering sedimentology that suggests lower glacial landform as it fits in the framework of the last deglaciation energy deposition and stratigraphic context such as thinner sand layers period. In terms of morphology, the LiDAR survey revealed a set of and discontinuous lenses. Table 5 lists OSL sample sedimentology, four distinguishable terraces (locations 1, 2, 3, and 4) along the flank overdispersion, and skewness in stratigraphic order. All but three of the Jones Point bedrock (Fig. 4) valley side. It is possible that construc- samples were calculated with the MAM (Galbraith and Roberts, 2012) tion of the railroad and a highway (route 9W) caused changes in their and are in stratigraphic order given error limits. original shape. At the same time, flat surfaces and almost equal eleva-

Errors on DE and age estimates are reported at 2δ standard error and tion levels in all four locations make it possible to conclude that it was include errors related to instrument calibration; and dose rate and indeed the large terrace described by Merrill (1891) and Peet (1904a, equivalent dose calculations were calculated in quadrature using the 1904b),previouslyidentiﬁed as a kame terrace left behind by the methods of Aitken and Alldred (1972) and Guérin et al. (2011). downwasting process of deglaciation.

The largest contributor to OSL age error is that from the DE values, not Studies by Ozsvath (1985) and Cadwell et al. (2003) showed depen- surprising given the spread of individual measurements (Fig. 13). dency of the deglaciation process in New York on topography of its Error estimates on measured aliquots or grains were higher because bedrock. Cadwell et al. (2003) indicated that “recession of the ice mar- of the lower peak signals (b500 counts/s) at the small mask size gin was accompanied by thinning and regional downwasting thus (1-mm). Initial test aliquots were run at 2-mm mask, but many of uncovering upland summits” (Fig. 14). Later work (Moss, 2016; these DEs were likely overestimated from the presence of partially Stanford, 2010) showed that the Hudson River Valley has been deeply bleached grains. The smaller 1-mm mask size was chosen to mitigate is- eroded by multiple glaciations and that sediments have been deposited sues with partial bleaching, though signal resolution was reduced. and removed by multiple ice-dam glacial lake release episodes since Single-grain dating is preferable for partially bleached glacial sediments the LGM. If the Jones Point sediments were deposited in contact with (Duller, 2006; Thrasher et al., 2009); however, we were only moder- ice as it was retreating back up the narrow Hudson River Valley, one ately successful with single-grain dating on USU-1768 given the low would expect more fine-grained glaciolacustrine sediments in this se- signal response of these samples. Fig. 12 displays dose-response curves quence of Hudson Valley deposits at this elevation (+25 m asl). Indeed, and optically stimulated luminescence decay from three samples. such sediments are likely to have been emplaced early but could have One aliquot from USU-2422 has an exceptionally bright fast component been eroded and removed if we assume that the Hudson River Valley to the total signal (N600 counts/s) and low DE error. While the example became the major regional drain of the receding ice sheet, generating from USU-1765 was more commonly found, resulting in greater high volume meltwater flows down the constricted valley, removing (worsened) recycling ratios, poorly fit dose-response curves and glaciolacustrine and other fine sediments, and depositing and eroding thus higher DE errors. These dimmer signals, in the example given existing proglacial massive sandy deposits (Fig. 14). b200 counts/s for a 78 Gy beta dose, are commonly found in sediments Sedimentary results (Moss, 2016) from deep borings for the new with shorter transport history and less time spent in the sedimentary bridge (Haverstraw Ice Margin location, Fig. 1) over the Tappan Zee cycle prior to burial (Preusser et al., 2006). While it would have been (a broad section of Hudson River Valley just south of Jones Point) advantageous to apply single-grain dating to all samples in this study, provide new insight into the chronology of these events. The boundary given the poor dose response and large percentage of grains (675/700 between varved silt and clay glaciolacustrine deposits and overlying = 96%) that were rejected on USU-1768 for low signal response, sands and gravels similar to Jones Point is at a considerable depth single-grain dating is not feasible for the samples. of −60 m bsl (below sea level) underneath the modern river. Dose rate values range from 2.08 to 2.91 Gy/ka, and the lack of signif- Furthermore, these sands and gravels in turn have been eroded to a icant outliers in the chemistry data (Table 6) suggest little heterogeneity depth of −39 m bsl where they are overlain by more modern estuarine amongst the dose rate environment for the samples collected along this organic sediments. The analysis of two 14C samples (bulk analysis) dual outcrop exposure. Moisture content values ranged from 1.6–19.2%, from the fragmentary organic matter at the base of these sediments, and because of desiccation effects at the outcrop exposure and season interpreted as a marine incursion,weredatedto10,790–12,598 YBP of sampling (mid-summer), those with b7% water content had an (Donnelly et al., 2005). average value of 7.9% applied to the DR calculation. Geographic data At Jones Point (Table 7) two major lithofacies are present: a more (41.28° N, 73.95° W, 0.03 km) were used with burial depth to calculate massive, plane-bedded facies attributed to proglacial processes

Table 4 Optically stimulated luminescence (OSL) age information.

a b Sample num. USU num. Grain size (μm) Num. of aliquots or grains Dose rate (Gy/ka) DE ±2σ (Gy) OSL age ± 2σ (ka) Age model D USU-1765 125–212 9 (26) 2.91 ± 0.14 41.4 ± 17.3 14.2 ± 6.1 CAM G USU-1766 150–250 10 (27) 2.81 ± 0.13 45.6 ± 15.2 16.2 ± 5.6 MAM I USU-1767 125–212 13 (25) 2.08 ± 0.14 46.6 ± 17.1 22.4 ± 8.6 MAM J USU-1768 125–250 12 (700)c 2.20 ± 0.17 58.5 ± 23.6 26.6 ± 11.2 MAM JP1 USU-2422 150–250 12 (30) 2.19 ± 0.10 55.3 ± 15.2 25.3 ± 7.4 CAM JP2 USU-2423 150–250 12 (33) 2.55 ± 0.12 69.5 ± 12.8 27.3 ± 5.7 CAM JP3 USU-2424 150–250 14 (32) 2.32 ± 0.11 39.7 ± 12.8 17.2 ± 5.8 MAM JP4 USU-2425 125–250 17 (32) 2.53 ± 0.12 56.0 ± 18.6 22.2 ± 7.7 MAM

a Age analysis using the single-aliquot regenerative-dose procedure of Murray and Wintle (2000) on 1–2 mm small-aliquots of quartz sand unless otherwise noted. Number of aliquots used in age calculation and number of aliquots analyzed in parentheses. b Equivalent dose (DE) calculated using the central age model (CAM) or minimum age model (MAM) of Galbraith and Roberts (2012). c Age analysis using the single-aliquot regenerative-dose procedure of Murray and Wintle (2000) on single-grains of quartz sand. Number of grains used in age calculation and number of grains analyzed in parentheses. 98 Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102

(G–J, L) and an upper secondary glacioﬂuvial facies showing cross- (clays or silts, characteristic of glaciolacustrine or ice-contact bedding (C–F). The dominance of the massive facies, the presence sediments) suggests winnowing by transport processes during of the coarse boulder facies K, and the relative lack of ﬁner sediments deposition.

Fig. 13. Radial plots of equivalent dose (DE) distributions on accepted aliquots or grains for eight OSL samples from Bear Mountain, NY. Skew values with * are signiﬁcantly positive following Bailey and Arnold (2006). Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102 99

Table 5

OSL sample location, sedimentology, and DE distribution statistics.

USU num. Depth Sedimentology (thickness cm) Depositional ODa (%) Skewb OSL age ± 2σ Age Layerd (m) environment (ka) modelc

USU-1765 1.69 Sand, medium, well sorted (20 cm) Glacioﬂuvial 56.8 ± 15.9 0.38 14.2 ± 6.1 CAM D USU-1766 2.7 Sand, coarse, well sorted (85 cm) Proglacial melt-out 58.5 ± 15.4 0.82* 16.2 ± 5.6 MAM G USU-2424 3.5 Sand, coarse, well sorted (85 cm); Proglacial melt-out 28.5 ± 8.3 0.75* 17.2 ± 5.8 MAM G massive sand USU-1767 4.18 Sand, ﬁne, moderately sorted (20 cm) Proglacial 45.3 ± 11.5 0.48 22.4 ± 8.6 MAM I USU-2425 5.5 Med-coarse sand above Proglacial 32.8 ± 8.0 −0.22 22.2 ± 7.7 MAM J boulder/cobble/pebbles (30 cm) USU-1768 (SG) 4.38 Sand, medium, well sorted (95 cm) Proglacial 25.5 ± 11.2 −0.03 26.6 ± 11.2 MAM J USU-2423e 4 Sand over boulder/cobble/pebbles Proglacial 24.9 ± 7.9 0.54 27.3 ± 5.7 CAM J USU-2422e 5.3 Coarse-med sand lens below Pre-LGM proglacial 41.6 ± 10.8 0.51 25.3 ± 7.4 CAM L boulder/cobble/pebbles (32 cm)

a Overdispersion (OD) represents variance in DE data beyond measurement uncertainties, OD N 20% may indicate signiﬁcant scatter caused by depositional or post-depositional processes. b Skew values with * are signiﬁcantly positive following Bailey and Arnold (2006). c Equivalent dose (DE) calculated using the central age model (CAM) or minimum age model (MAM) of Galbraith and Roberts (2012). d Layers listed in stratigraphic order; see Table 1 for granulometic details. e Samples were taken at JP_2002 site.

Given that most of our OSL ages at Jones Point (Table 7)considerably Originally we hypothesized that this could be a local feature created predate this erosional event, the Jones Point deposits are likely to be by filling subglacial cavity (Boulton, 1982); however, its petrographic all that remains from a more extensive valley-fill proglacial deposit composition supports the alternative hypothesis that layer K, containing (Lonne and Nemec, 2004; Winsemann et al., 2007;). Although they a variety of material from distant sources, is most likely the remnant of a differ on timing, Donnelly et al. (2005) and Stanford (2010) provide a lateral moraine dating to the end of the LGM (according to OSL) from mechanism for such an erosional event: the catastrophic glacial lake which the fines have been winnowed by subsequent massive meltwater draining as a result of the breach in the terminal moraine at the Narrows discharge. in New York City. We interpret the boundary between Jones Point The formation of overlying glaciofluvial layers (F–A) is most likely proglacial and glaciofluvial deposits as an indicator of this flood erosion associated with reworking of proglacial deposits following the flood- event that, according to our OSL data, could possibly occur between 14 erosional event described earlier. Bedforms within the upper part of and 16 ka. This time interval is consistent with dates of 13 or 15 ka, the sequence and flow indicators from multiple directions suggest according to conclusions of Donnelly et al. (2005) and Stanford (2010). that the preservation of the Jones Point terraces was in part because Layer K, within the massive proglacial sequence, is present at of their location in the lee of the Dunderberg Mountain massif, while the JP_2001 and JP_2002 locations; it was considered a marker bed, the same sediments were being eroded in the center of the valley possibly derived from a lateral moraine related to the LGM period. (Fig. 14). Layers C (above) and E (below) have characteristic cross- Four ages (±2δ standard error) surrounding this layer (Table 5) bedding and planar bedding structures. Layer F is a silt, poorly sorted, are 22.2 ± 7.7 ka (layer J, above), 26.6 ± 11.2 ka (layer J, above), that forms a thin (5 cm) layer between coarse sand layers, indicating 27.3 ± 5.7 ka (layer J, above), and 25.3 ± 7.4 ka (layer L, below). sharp change in surrounding fluvial conditions, probably a localized Location 3 (geophysical site 3, Fig. 11) did not reveal a continuous flood by the meltwater. Layers G, H, I, and J maintain massive bedding connection of layer K with the same layer at location 2. The coarse with a decrease of mean/median grain size from J to I, making a typical nature of the boulders in layer K are inconsistent with an in-place graded bedding sequence going up from layer K to I. Fig. 14 summarizes lateral moraine as described by Lukas and Sass (2011),whichretains in four panels our proposed morphologic development at the site. considerable fine-grained, poorly sorted material. It is likely that The OSL dating results show sequentially younger ages from coarse deposits of layer K stretch along the bedrock flank as an the bottom of the terrace (layer J) to the upper glaciofluvial layer D elongated feature, partially eroded and detached. At site JP_2002, providing a range between 27 and14 ka. The youngest OSL age of it dips in a western direction toward the bedrock exposure (Fig. 3), layer D (Table 7) in this suite is 14.2 ± 6.1 ka. The OSL ages of layer G revealing an asymmetry characteristic for other lateral moraines are 16.2 ± 5.6 and 17.2 ± 5.8 ka; three ages for the lower I layer and (e.g., Lukas and Sass, 2011). the J layer are 22.4 ± 8.6, 22.2 ± 7. 7, 26.6 ± 11.2, and 27.3 ± 5.7 ka. Petrographic analysis of boulders from layer K indicated multiple To place the OSL ages provided here into the overall deglaciation sources of petrographic material (Fig. 6, Tables 2, 3) from the Catskills context, we compare them to other geochronologic data available in and Adirondack Mountains, ~60 and 120 km north correspondingly. the vicinity of the study area. On a highland part of the lower Hudson

Table 6 Dose rate information.

a b b b b c Sample num. USU num. In situ H2O (%) Depth (m) K (%) Rb (ppm) Th (ppm) U (ppm) Cosmic (Gy/ka) D USU-1765 7.7 1.69 2.05 ± 0.05 79.8 ± 3.2 8.4 ± 0.8 1.5 ± 0.1 0.17 ± 0.02 G USU-1766 7.7 2.70 2.04 ± 0.05 81.7 ± 3.3 7.6 ± 0.7 1.5 ± 0.1 0.15 ± 0.01 I USU-1767 15.1 4.18 1.51 ± 0.04 66.4 ± 2.7 6.4 ± 0.6 1.5 ± 0.1 0.12 ± 0.01 J USU-1768 19.2 4.38 1.62 ± 0.04 70.6 ± 2.8 7.8 ± 0.7 1.7 ± 0.1 0.12 ± 0.01 JP1d USU-2422 2.2 5.3 1.56 ± 0.04 73.3 ± 2.9 6.1 ± 0.6 1.3 ± 0.1 0.11 ± 0.01 JP2d USU-2423 1.6 4 1.92 ± 0.05 79.9 ± 3.2 6.3 ± 0.6 1.3 ± 0.1 0.13 ± 0.01 JP3 USU-2424 4.3 3.5 1.76 ± 0.04 75.8 ± 3.0 5.2 ± 0.5 1.2 ± 0.1 0.14 ± 0.01 JP4 USU-2425 5.3 5.5 1.85 ± 0.05 81.5 ± 3.3 6.9 ± 0.6 1.4 ± 0.1 0.11 ± 0.01

a Assumed average of all samples, 7.9 ± 2.4%, as moisture content over burial history for samples with b7%. b Radioelemental concentrations determined by ALS Minerals (Elko, NV) using ICP-MS and ICP-AES techniques. c Following Prescott and Hutton (1994). d Samples were taken at JP_2002 site. 100 Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102

Fig. 14. Proposed historical morphologic development at Jones Point. Panel (A) shows early time when ice covered everything except the major bedrock summits: Dunderberg and Manitou Mountains on either side of the Hudson Valley. By about 17,000 BP, in panel (B), ice is retreating back past Jones Point and revealing the older (boulder layer K and older proglacial) sediments, before the breach of the Narrows dam and catastrophic ﬂooding event (approx. 15,000 BP). Panel (C) (about 12,000 BP) shows the deep valley carved into those sediments (which appear as terraces) with the proto-Hudson River greatly incised compared to modern sea level. Note incipient vegetation colonization on the rocky highlands. Panel (D) shows about 5000 BP, predevelopment view of modern river.

Valley in Harriman State Park (Fig. 1), Peteet et al. (2012) obtained four at sampling sites. It is possible that the UH-1 location was subject to AMS-based 14Cdatesfrombogs(Picea needles, twigs, clay) with a range more active glaciofluvial conditions. of 14–15.1 cal. ka. According to those authors, these findings represent The uncertainty of OSL results is in part associated with partial (the initial colonization of the landscape coincident with widespread sunlight resetting as seen with the high dispersion and skew toward climatic amelioration and ice-free condition). In the nearby Bear Moun- higher doses in most DE distributions, often a side effect of tain State Park (Fig. 1) surface exposure dates based on 10Be (Schaefer, OSL when applied to glacial deposits. Adding to the uncertainty pers. comm.) produced a range of 18–22 cal. ka. These data were ob- is the low sensitivity of the quartz grains to optical stimulation, tained from large boulders on the ridges, indicating the time when ice noted in Fig. 12 and supported by the high amount of luminescence- retreat exposed the bedrock and erratic boulders to cosmogenic nuclide dead single grains (N96%). These luminescence ages and characteris- accumulation. tics combined with sedimentology and geomorphology support Two kilometers northwest from Jones Point, at Iona Island marsh, at our interpretation of proglacial deposits having experienced some a depth of 28 m below modern sea level, bulk 14C date based on twigs transport. (oak, pine, spruce) were recovered from organic silt-sand interface (bore UH-1; Newman et al., 1969) and produced a date of 12,500 YBP 5. Conclusions (or 14,700 cal. YBP). Interestingly enough, Peteet et al. (2012) samples do not contain any sand or silt, indicating stable depositional conditions This study aimed to interpret and date glacial deposits found at Jones Point, New York, and place them in the framework of the deglaciation Table 7 process on the lower Hudson River Valley. Data obtained from various Glacial facies interpreted from sedimentary layers. techniques (OSL, sedimentary analysis, LiDAR, geophysics, and petro- Facies (layers) Thickness (cm) OSL age (ka) Lithofacies codea graphic analysis) and synthesis of available information on the deglaciation process in the lower Hudson Valley allow us to make following Glacial drift (A–B) 153 NA Dcm Glaciofluvial (C–F) 117 14.2 ± 6.1 Sh, Sp conclusions: Proglacial (G–J) 263 16.2 ± 5.6 Sm 17.2 ± 5.8 • New OSL ages on proglacial massive sandy sediments at ~25 m asl 22.4 ± 8.6 from 16,000 to 27,000 YBP at Jones Point predate current estimates 22.2 ± 7.7 fl 26.6 ± 11.2 of a proglacial lake-draining ood episode between 13,000 and 27.3 ± 5.7 15,000 YBP (Donnelly et al., 2005; Stanford, 2010). Our interpretation Lateral moraine remnant (K) 200 NA Gcm suggests that these sandy proglacial valley fill deposits were Proglacial (L) N300 25.3 ± 7.4 Sm probably much more extensive but were eroded by proglacial lake a Codes for lithofacies used from (Eyles et al., 1983; Benn and Evans, 1998). drainage as shown by stratigraphy and ages of deep valley fill below Y. Gorokhovich et al. / Geomorphology 321 (2018) 87–102 101

sea level underneath the modern river. A boulder/cobble/pebble layer Arnold, L.J., Bailey, R.M., Tucker, G.E., 2007. Statistical treatment of fluvial dose distributions from southern Colorado arroyo deposits. Quat. Geochronol. 2, 162–167. (K) embedded in these massive sands may be a remnant of lateral mo- Bailey, R.M., Arnold, L.J., 2006. Statistical modelling of single grain quartz De distributions and raine with a distant source of rock material, most likely from the an assessment of procedures for estimating burial dose. Quat. Sci. Rev. 25 (3475-2502). Catskills and Adirondack mountains. Balco, G., Schaefer, J.M., 2006. Cosmogenic-nuclide and varve chronologies for the • fl deglaciation of southern New England. Quat. Geochronol. 1, 15–28. At Jones Point, the overlying glacio uvial sediments show bedforms Benn, D.I., Evans, D.J.A., 1998. Glaciers and Glaciation. Arnold, London (734 pp.). indicating a quieter glaciofluvial environment starting ca. 14.2 ± Blott, S.J., Pye, K., 2001. GRADISTAT: a grain size distribution and statistics package for the 6.1 ka, sheltered in the lee of Dunderberg Mountain. Therefore, analysis of unconsolidated sediments. Earth Surf. Process. Landf. 26, 1237–1248. attribution of the lake-draining flood to the earlier 15 ka date Bøtter-Jensen, L., Andersen, C.E., Duller, G.A.T., Murray, A.S., 2003. Developments in radiation, stimulation and observation facilities in luminescence measurements. (Stanford, 2010) is more suitable in the context of Jones Point OSL Radiat. Meas. 37, 535–541. data. Moreover, this interpretation supports the theory of interruption Boulton, G.S., 1982. Subglacial processes and the development of glacial bedforms. In: fl of the deglaciation process (Peteet et al., 2012) and Rosendale Davidson-Arnott, R., et al. (Eds.), Research in Glacial, Glacio- uvial, and Glacio- Lacustrine Systems. Proceedings of the 6th Guelph Symposium on Geomorphology, readvance (Connally and Sirkin, 1986) ca. 16 ka because massive 1980. Geo Books Norwich. cold flood water contribution to the Atlantic could likely cause local Cadwell, D.H., Dineen, R.J., 1987. Surficial Geologic Map of New York: Hudson—Mohawk climatic fluctuations (Donnelly et al., 2005). Sheet, New York State Museum. Geological Survey Map and Chart Series #40The • University of the State of New York, Albany. The appearance of cross-bedding (layers C and D) coincides with Cadwell, D.H., Muller, E.H., Fleisher, P.J., 2003. Geomorphic history of New York state. In: continuous ice retreat from Jones Point by 14 cal. ka BP, as evident Cremeens, D.L., Hart, J.P. (Eds.), Geoarchaeology of Landscapes in the Glaciated from 14C calibrated data by Peteet et al. (2012) and Newman et al. Northeast. New York State Museum, Bulletin 497, pp. 7–14 edited by. Carter, W., Shrestha, R., Tuell, D., Bloomquist, D., Sartori, M., 2001. Airborne laser swath (1969); ice-free conditions and ensuing ecological succession mapping shines new light on earth's topography. EOS Trans. Am. Geophys. Union 14 triggered the formation of organic matter analyzed by C. A future 82 (46), 549–550 (555). OSL target in the area should be loess deposits described by Sanders Connally, G.G., Sirkin, L., 1986. Woodfordian ice margins, recessional events, and pollen stratigraphy of the Mid-Hudson valley. In: Cadwell, D.H. (Ed.), The Wisconsinan and Merguerian (1998) at Croton Point. Stage of the First Geological District, Eastern New York. New York State Museum • Results of this study allows reconstructing the following sequence Bulletin 455, pp. 50–72. of morphogenetic events at the Jones Point site: glacial advance Cusick, L.C., Gorokhovich, Y., 2003. Reconstruction of Paleogeographic History of the during LGM-deposited lateral moraine (layer K); glacial retreat Hudson River at newly exposed Pleistocene strata at Bear Mountain. Section I: 1–32. In: Waldman, J.R., Nieder, W.C. (Eds.), Final Reports, Tibor T. Polgar Fellowship reworked and covered lateral moraine by proglacial deposits that Program, 2002. Hudson River Foundation. were deeply eroded during the break of the terminal moraine dam Dicken, C.L., Nicholson, S.W., Horton, J.D., Kinney, S.A., Gunther, G., Foose, M.P., Mueller, of Lake Albany (~15 ka); possible interruption of deglaciation by cli- J.A.L., 2005. Preliminary integrated geologic map databases for the United States: Delaware, Maryland, New York, Pennsylvania, and Virginia. USGS Open-File Report mate change caused by the release of cold water from Lake Albany (2005-1325) (Updated August 2008). into the Atlantic and continued ice retreat recorded by glaciofluvial, Donnelly, J.P., Driscoll, N.W., Uchupi, E., Keigwin, L.D., Schwab, W.C., Thieler, E.R., Swift, cross-bedded deposits. S.A., 2005. Catastrophic meltwater discharge down the Hudson Valley: a potential – • trigger for the Intra-Allerød cold period. Geology 33 (2), 89 92. The combination of methods used in this study proves to be an invalu- Duller, G.A.T., 2000. Dating methods: geochronology and landscape evolution. Prog. Phys. able tool in glacial research in developed urbanized areas, such as the Geogr. 24 (1), 111–116. lower Hudson Valley. Specifically, LiDAR and geophysical surveys Duller, G.A.T., 2003. Distinguishing quartz and feldspar in single grain luminescence measurements. Radiat. Meas. 37, 161–165. helped to map and interpret Jones Point terraces and stratigraphy Duller, G.A.T., 2006. Single grain optical dating of glacigenic deposits. Quat. Geochronol. 1, with high spatial resolution. Future work will be planned to recognize 296–304. and characterize more of these features using LiDAR data. Duller, G.A.T., Bøtter-Jensen, L., Murray, A.S., Truscott, A.J., 1999. Single grain laser luminescence (SGLL) measurement using a novel automated reader. Nucl. Instrum. Methods B 155, 506–514. Eaton, T.T., Gorokhovich, Y., Soule, D., 2017. Electrical resistivity survey and interpretation Acknowledgements of glacial deposits at Jones Point, Lower Hudson River Valley, NY. GSA Abstracts w/Programs, Vol. 49, No.2, NE Section Meeting. Geological Society of America, Funding for this study was provided by two PSC-CUNY grants from Pittsburgh, PA (March 20, 2017). Eyles, N., Eyles, C.H., Miall, A.D., 1983. Lithofacies types and vertical profile models; an al- the City University of New York (2013, 2015). We are also grateful to ternative approach to the description and environmental interpretation of glacial Dr. Dax Soule for his contribution to the geophysical field survey and diamict and diamictite sequences. Sedimentol. 30, 393–410. to Dr. Dorothy Peteet for her contribution to the discussion of material Fisher, D.W., Isachsen, Y.W., Rickard, L.V., 1970. Geologic Map of New York State, presented in this paper. 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