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Ronald J. Litwin

Publications and source records attributed to Ronald J. Litwin.

13 recordsLinked to original sources
USGS2021

Stratigraphy and age of a prominent paleosol in a late Pleistocene sedimentary sequence, Mason Neck, Virginia

The High Point paleosol is 2.28-meters-thick aggradational soil developed in fining upward estuarine-alluvial sand and loess. The paleosol is exposed in a few shoreline cliff faces of Mason Neck, Virginia. Although a former A horizon is missing, the E, Bw, Bt, and C horizon sequence seen in the sediments indicates subaerial pedogenesis. Pedogenesis began with initial estuarine-alluvial floodplain emergence as sea level was lowering in late marine isotope stage 5 (MIS5) and MIS4, continued during eolian silt deposition accompanied by incorporation of the silt into the estuarine-alluvial sand, and ended with a period of loess and eolian sand deposition, erosion, and development of periglacial(?) features. Six optically stimulated luminescence ages provide an age range from 86 to 56 ka (thousand years ago) for sedimentary units below and above the paleosol. These ages indicate a 10,000- to 30,000-year interval in late MIS5 and MIS4 for these events to have occurred.

Virginia↗
USGS2017

100,000-year-long terrestrial record of millennial-scale linkage between eastern North American mid-latitude paleovegetation shifts and Greenland ice-core oxygen isotope trends

We document frequent, rapid, strong, millennial-scale paleovegetation shifts throughout the late Pleistocene, within a 100,000+ yr interval (~ 115–15 ka) of terrestrial sediments from the mid-Atlantic Region (MAR) of North America. High-resolution analyses of fossil pollen from one core locality revealed a continuously shifting sequence of thermally dependent forest assemblages, ranging between two endmembers: subtropical oak-tupelo-bald cypress-gum forest and high boreal spruce-pine forest. Sedimentary textural evidence indicates fluvial, paludal, and loess deposition, and paleosol formation, representing sequential freshwater to subaerial environments in which this record was deposited. Its total age"depth model, based on radiocarbon and optically stimulated luminescence ages, ranges from terrestrial oxygen isotope stages (OIS) 6 to 1. The particular core sub-interval presented here is correlative in trend and timing to that portion of the oxygen isotope sequence common among several Greenland ice cores: interstades GI2 to GI24 (≈ OIS2–5 d). This site thus provides the first evidence for an essentially complete series of "Dansgaard"Oeschger" climate events in the MAR. These data reveal that the ~ 100,000 yr preceding the Late Glacial and Holocene in the MAR of North America were characterized by frequently and dynamically changing climate states, and by vegetation shifts that closely tracked the Greenland paleoclimate sequence.

Quaternary Research↗
USGS2015

Synthesis on Quaternary aeolian research in the unglaciated eastern United States

Late-middle and late Pleistocene, and Holocene, inland aeolian sand and loess blanket >90,000 km 2 of the unglaciated eastern United States of America (USA). Deposits are most extensive in the Lower Mississippi Valley (LMV) and Atlantic Coastal Plain (ACP), areas presently lacking significant aeolian activity. They provide evidence of paleoclimate intervals when wind erosion and deposition were dominant land-altering processes. This study synthesizes available data for aeolian sand deposits in the LMV, the Eastern Gulf Coastal Plain (EGCP) and the ACP, and loess deposits in the Middle Atlantic Coastal Plain (MACP). Data indicate: (a) the most recent major aeolian activity occurred in response to and coincident with growth and decay of the Laurentide Ice Sheet (LIS); (b) by ∼40 ka, aeolian processes greatly influenced landscape evolution in all three regions; (c) aeolian activity peaked in OIS2; (d) OIS3 and OIS2 aeolian records are in regional agreement with paleoecological records; and (e) limited aeolian activity occurred in the Holocene (EGCP and ACP). Paleoclimate and atmospheric-circulation models (PCMs/ACMs) for the last glacial maximum (LGM) show westerly winter winds for the unglaciated eastern USA, but do not resolve documented W and SW winds in the SEACP and WNW and N winds in the MACP. The minimum areal extent of aeolian deposits in the EGCP and ACP is ∼10,000 km 2 . For the LMV, it is >80,000 km 2 . Based on these estimates, published PCMs/ACMs likely underrepresent the areal extent of LGM aeolian activity, as well as the extent and complexity of climatic changes during this interval.

Aeolian Research↗
USGS2014

Interagency partnership to assess and restore a degraded urban riverine wetland: Dyke Marsh Wildlife Preserve, Virginia

The narrow-leaved cattail wetland known as Dyke Marsh formally became a land holding of George Washington Memorial Parkway (GWMP, a unit of the national park system) in 1959, along with a congressional directive to honor a newly-let 30-year commercial sand and gravel dredge-mining lease at the site. Dredging continued until 1974 when Public Law 93-251 called for the National Park Service and the United States Army Corps of Engineers to “implement restoration of the historical and ecological values of Dyke Marsh.” By that time, about 83 acres of the marsh remained, and no congressional funding accompanied the passage of the law to effect any immediate conservation or restoration. Decades of dredge mining had severely altered the surface area of Dyke Marsh, the extent of its tidal creek system, and the shallow river bottom of the Potomac River abutting the marsh. Further, mining destabilized the marsh, causing persistent erosion, shoreline retreat, and tidal channel widening after mining ceased. Erosion has continued unchecked until the present; approximately 50 acres of the original marsh are now estimated to remain. The specific cause of persistent erosion had been unknown prior to this collaborative study but previously was assumed to be due to flooding by the Potomac River.

Virginia↗
USGS2013

Rates and probable causes of freshwater tidal marsh failure, Potomac River Estuary, Northern Virginia, USA

Dyke Marsh, a distal tidal marsh along the Potomac River estuary, is diminishing rapidly in areal extent. This study documents Dyke Marsh erosion rates from the early-1860s to the present during pre-mining, mining, and post-mining phases. From the late-1930s to the mid-1970s, Dyke Marsh and the adjacent shallow riverbottom were mined for gravel, resulting in a ~55 % initial loss of area. Marsh loss continued during the post-mining phase (1976–2012). Causes of post-mining loss were unknown, but were thought to include Potomac River flooding. Post-mining areal-erosion rates increased from 0.138 ha yr −1 (~0.37 ac yr −1 ) to 0.516 ha yr −1 (~1.67 ac yr −1 ), and shoreline-erosion rates increased from 0.76 m yr −1 (~2.5 ft yr −1 ) to 2.60 m yr −1 (~8.5 ft yr −1 ). Results suggest the accelerating post-mining erosion reflects a process-driven feedback loop, enabled by the marsh's severely-altered geomorphic and hydrologic baseline system; the primary post-mining degradation process is wave-induced erosion from northbound cyclonic storms. Dyke Marsh erosion rates are now comparable to, or exceed, rates for proximal coastal marshes in the same region. Persistent and accelerated erosion of marshland long after cessation of mining illustrates the long-term, and potentially devastating, effects that temporally-restricted, anthropogenic destabilization can have on estuarine marsh systems.

Virginia↗
USGS2011

Analysis of the deconstruction of Dyke Marsh, George Washington Memorial Parkway, Virginia-Progression, geologic and manmade causes, and effective restoration scenarios

This report is a synthesis of the latest findings from an ongoing study of Dyke Marsh, an eroding freshwater tidal wetland that is scheduled for federal restoration. Its purpose is to provide an accurate and up-to-date temporal and geological framework for the marsh, of which most is new information (plus a compilation of historical and recent information), that is directly relevant to the restoration effort and also is relevant to short-term and long-term land management decisions regarding this natural resource. Analysis of field evidence, aerial photography, and published maps has revealed an accelerating rate of erosion and marsh loss at Dyke Marsh, which now appears to put at risk the short term survivability of this marsh. The destabilization of Dyke Marsh is outlined here, spanning an approximately 70-year time interval (1940-2010). This freshwater tidal marsh has shifted from a semi-stable net depositional environment (1864-1937) into a strongly erosional one, during a time when it currently is in early-phase planning for comprehensive restoration. The marsh has been deconstructed over the past 70 years by a combination of manmade and natural causes. The marsh initially experienced a strong destabilizing period between 1940 and 1972 by direct dredge mining of the marsh surface. By 1976 the marsh had entered a net destructive phase, where it remains at present. Photoanalysis of time-sequence aerial photographs of Dyke Marsh enabled us to calculate shoreline erosion estimates for this marsh over 19 years (1987-2006), as well as to quantify overall marsh acreage for 6 calendar years spanning an ~70 year interval (1937-2006). Photo overlay of a historic map enabled us to extend our whole-marsh acreage calculations back to 1883. Both sets of analyses were part of a geologic framework study in support of current efforts by the National Park Service (NPS) to restore this urban wetland. Two time intervals were selected for our shoreline erosion analyses, based on image quality and availability: 1987 to 2002, and 2002 to 2006. The more recent time interval shows a marked increase in erosion in the southern part of Dyke Marsh, following a wave-induced breach of a small peninsula that had protected its southern shoreline. Field observations and analyses of annual aerial imagery between 1987 and 2006 revealed a progressive increase in wave-induced erosion that presently is deconstructing Hog Island Gut, the last significant tidal creek network within the Dyke Marsh. These photo analyses documented an overall average westward shoreline loss of 6.0 to 7.8 linear feet per year along the Potomac River during this 19-year time interval. Additionally, photographic evidence documented that lateral erosion now is capturing existing higher order tributaries in the Hog Island Gut. Wave-driven stream piracy is fragmenting the remaining marsh habitat, and therefore its connectivity, relatively rapidly, causing the effective mouth of the Hog Island Gut tidal network to retreat headward visibly over the past several decades. Based on our estimates of total marsh area in the Dyke Marsh derived from 1987 aerial imagery, as much as 12 percent of the central part of the marsh has eroded in the 19 year period we studied (or ~7.5 percent of the original ~78.8 acres of 1987 marshland). Shoreline loss estimates for marsh parcels north and south of our study area have not yet been analyzed, although annual aerial photos from 1987 to 2002 confirm visible progressive shoreline loss in those areas over this same time interval.

Open-File Report↗
USGS2009

Paleontological interpretations of crater processes and infilling of synimpact sediments from the Chesapeake Bay impact structure

Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of watersaturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dinoflagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As a result, intact Paleogene clasts in Eyreville cores are rare, but clasts of semilithified Potomac Formation silts and clays are common.

Chesapeake Bay↗
USGS1997

An 800,000-year pollen record from Owens Lake, California: Preliminary analyses

A long sequence of fossil palynomorph assemblages from a 323-m-long core taken at Owens Lake has enabled us to evaluate the gross vegetational trends for the Owens Valley region of California over the past ~800,000 years. Shifts in vegetation composition and abundance in the study area during the Pleistocene were indicated in core sediments by marked fluctuations in the pollen frequencies of pines, junipers, and, to a lesser extent, of big sagebrush, composites, and chenopods/amaranths. The modern vegetation distribution and modern pollen rain on the eastern flank of the Sierra Nevada indicate that maximal abundances of these taxa generally characterize higher elevation subalpine and montane coniferous forests, lower elevation coniferous woodland, steppe, and desert scrub environments. Pollen frequencies in the upper part of core OL-92 corroborate vegetational trends documented previously from late Wisconsin and Holocene Neotoma middens in the Great Basin. These trends and evidence from this study suggest that woodland taxa expanded their range down the slope of the eastern flank of the Sierra Nevada and were established in (and immediately adjacent to) Owens Valley during moderated climates of the late Wisconsin, apparently in response to decreases in temperature and increases in precipitation, but retreated upslope toward their present position starting as long ago as ca. 20 ka. More importantly, pollen evidence from core OL-92 documents that the southern Sierra Nevada has experienced nine major cool-to-warm vegetation shifts (in addition to the late Wisconsin-early Holocene warming) during the time interval spanning the middle Pleistocene to early Holocene (Brunhes Normal Polarity Chron). We believe that at least six consecutive cool-to-warm shifts (the most recent ones) represent transitions from full-glacial to full-interglacial conditions on the basis of the magnitude of vegetation change in this portion of the pollen record. These marked changes in the frequency curves of dominant palynomorph taxa enabled us to identify boundaries that define 19 (?20) pollen zones in OL-92. The excursions of the pollen frequency curves within and across zone boundaries approximate the nature, duration, and timing of the middle and late Pleistocene climatic trends documented by geochemical (δ 18 O) evidence from OL-92 and from Devils Hole (DH-11) in the Amargosa Desert of Nevada.

California↗