Cover image for The Nature and Pace of Change in American Indian Cultures: Pennsylvania, 4000 to 3000 BP Edited by R. Michael Stewart, Kurt W. Carr, and Paul A. Raber

The Nature and Pace of Change in American Indian Cultures

Pennsylvania, 4000 to 3000 BP

Edited by R. Michael Stewart, Kurt W. Carr, and Paul A. Raber

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2015

Recent Research in Pennsylvania Archaeology

The Nature and Pace of Change in American Indian Cultures

Pennsylvania, 4000 to 3000 BP

Edited by R. Michael Stewart, Kurt W. Carr, and Paul A. Raber

“A true synthesis of the most recent and cutting-edge interpretations of this enigmatic time period to date. Perhaps what is most impressive about this volume, however, is how the information is clearly embedded in archaeological, environmental, and technological contexts. It truly fills a gap in our understanding of the archaeological record.”

 

  • Description
  • Reviews
  • Bio
  • Table of Contents
  • Sample Chapters
  • Subjects
Three thousand to four thousand years ago, the Native Americans of the mid-Atlantic region experienced a groundswell of cultural innovation. This remarkable era, known as the Transitional period, saw the advent of broad-bladed bifaces, cache blades, ceramics, steatite bowls, and sustained trade, among other ingenious and novel objects and behaviors. In The Nature and Pace of Change in American Indian Cultures, eight expert contributors examine the Transitional period in Pennsylvania and posit potential explanations of the significant changes in social and cultural life at that time.

Building upon sixty years of accumulated data, corrected radiocarbon dating, and fresh research, scholars are reimagining the ancient environment in which native people lived. The Nature and Pace of Change in American Indian Cultures will give readers new insights into a singular moment in the prehistory of the mid-Atlantic region and the daily lives of the people who lived there.

The contributors are Joseph R. Blondino, Kurt W. Carr, Patricia E. Miller, Roger Moeller, Paul A. Raber, R. Michael Stewart, Frank J. Vento, Robert D. Wall, and Heather A. Wholey.

“A true synthesis of the most recent and cutting-edge interpretations of this enigmatic time period to date. Perhaps what is most impressive about this volume, however, is how the information is clearly embedded in archaeological, environmental, and technological contexts. It truly fills a gap in our understanding of the archaeological record.”
The Nature and Pace of Change in American Indian Cultures is an important contribution to the archaeological literature of Pennsylvania and the central Middle Atlantic region. It provides new perspectives on important anthropological and archaeological topics of prehistoric culture change that will appeal to those interested in the local region as well as those interested in broader comparative studies of ancient culture change.”
“Since John Witthoft’s 1953 publication on ‘Broadspear’ cultures in Pennsylvania, archaeologists have been fascinated by the so-called Transitional or Terminal Archaic. Building on earlier research, the contributors to this volume provide important new data and interpretive perspectives on Native American material culture, lifeways, and society in the mid-Atlantic region circa 4000–3000 years before the present.”
“An essential read for anyone researching the Transitional Archaic Period in Pennsylvania and a useful resource for all archaeologists studying the end of the Archaic period in Eastern North America.”

R. Michael Stewart is Associate Professor Emeritus at Temple University and Archaeologist, New Jersey Historic Preservation Office.

Kurt W. Carr is Senior Curator of Archaeology at the State Museum of Pennsylvania.

Paul A. Raber is Vice-President and Director of Archaeological Services at Heberling Associates, Inc.

Contents

List of Figures

List of Tables

Introduction: Working with the Archaeological Record of 4500–2700 BP

R. Michael Stewart

1 Evidence for Climate Variability During the Sub-Boreal/Transitional Archaic Period: Fact or Fiction?

Frank J. Vento

2 The End of the Late Archaic Period in the Upper Susquehanna Valley of Pennsylvania: Lamoka and Its Variants

Robert D. Wall

3 The Evolution of Cultural Adaptations During the Transitional Period in the Delaware and Susquehanna River Valleys in Pennsylvania

Kurt W. Carr

4 The Transitional Archaic Period in the Susquehanna River Valley

Patricia E. Miller

5 Rethinking the Transitional Archaic Period in the Upper Delaware Valley: A View from the “Orient”

Joseph R. Blondino

6 Transitional Archaic Settlement Density in Eastern Pennsylvania

Heather A. Wholey

7 The Transitional Dilemma in Pennsylvania: Hearths, Fish, and Pottery

Roger Moeller

List of Contributors

Index

<CN>1

<CT>Evidence for Climate Variability During the Sub-Boreal/Transitional Archaic Period

<CST>Fact or Fiction?

<CA>Frank J. Vento

<1>Abstract

This chapter will focus solely on the responses of river systems to climate change during the Sub-Boreal climate interval or Transitional Archaic period in the Middle Atlantic region and, specifically, in Pennsylvania. For my purposes, this period begins at approximately 4200 BP and ends at 3000 BP. The Sub-Boreal, much like the preceding Younger Dryas (ca. 11,200 BP) and later Little Ice Age (700–400 BP) climate intervals, was a time of renewed stream channel migration and active overbank deposition. Unlike the Younger Dryas or Little Ice Age interval, however, when fluvial erosional disconformities were associated with either cold and dry or cooler and wetter climatic conditions, respectively, the Sub-Boreal interval, which coincides with the Transitional Archaic, occurred during a 1,200-year period of decreased effective precipitation associated with climatic conditions that are warmer and drier overall than those present today, for example. The following discussion examines both archaeological and paleoenvironmental lines of evidence in the Middle Atlantic region and elsewhere for the above assertions.

<1>Archaeological Evidence

Archaeologically, the Transitional Archaic period is defined by broadspears, which date to between approximately 4,000 and 3000 BP. In addition, and following the lead of several researchers, this period is distinguished from the Late Archaic and Early Woodland periods by the preferential use of certain, usually nonlocal lithic types, for example, metarhyolites, that were typically available in massive bedrock formations, as opposed to tabular chert or pebble sources. This period is also documented by a change to bifacial core technology, a staged biface reduction process, the caching of bifaces, curated tools, steatite bowls, large and numerous fire-cracked rock (FCR) features, the beginning of fired clay pottery, occasional burial ceremonialism, and a preference for riverine environments. Based on the current recorded site database, Transitional Archaic populations appear to have preferred encampments along larger perennial streams rather than smaller first- or second-order tributaries. Could this preference for larger perennial streams reflect the fact that, during sustained warm and dry periods, small streams would have been more affected by a lower input of water from base flow and surface runoff and thus have been less attractive to Transitional Archaic populations? As Kurt Carr has argued for at least two decades, the change from an expedient flake-and-blade technology during the Late Archaic to a biface technology during the Transitional Archaic period, concomitant with greater mobility, argues for a food economy procurement strategy that reflects environmental stress due to warmer and drier climatic conditions and lower discharges along streams in the Middle Atlantic region.

Effects of the warmer and drier climate included a decrease in the number of low-order streams, lower water volume in streams generally, a decrease in biomass on ridges, and a lowering of the water table (Graetzer 1986; Watts 1979). Evidence provided by correlations of pollen core data with pollen from surface samples of known vegetation types suggests that the overall composition of the vegetation did not change radically (Bradstreet and Davis 1975). On the other hand, changes in hydrology and decreases in productivity would likely have had some effect on the distribution of prehistoric populations. Specifically, upland areas would have become less attractive, whereas major riverine areas such as the Ohio, Delaware, and Susquehanna River floodplains and associated terraces would have been more attractive (Miller et al. 2003).

Although there is some disagreement regarding the occurrence of a Middle Holocene climatic optimum in the Northeast, there is still greater disagreement regarding the climate following 5000 BP. A number of researchers have presented evidence indicating an environment characterized by severe climatic fluctuations, including a warm and dry, or xerothermic, period between 5000 and 2600 BP (Carbone 1976; Curry and Custer 1982; Custer 1988; Vento and Rollins 1989; Vento et al. 2008). Arthur Joyce (1988) notes that researchers have presented a variety of dates within the Middle Holocene for the proposed xerothermic period. Dennis Curry and Jay Custer (1982) argue that the xerothermic corresponds to the warm and dry conditions of the Atlantic/Sub-Boreal period in the Blytt-Sernander system (Figure 1.1; described in Zeuner 1952; see also Vento et al. 2008), originally developed to describe European climatic change but frequently applied without reservation to North America. In contrast, other researchers argue that, although there were undoubted fluctuations in temperature and moisture after 5000 BP, these were no more than low-amplitude fluctuations of short duration (Beckerman 1986; Joyce 1988; Watts 1979).

<insert fig. 1.1 about here>

Patricia Miller and colleagues (2003) have argued that the impacts on vegetation were likely minimal and the composition of the forest, as a result, was similar to the present-day forest in many respects. Custer (1984, 1988) points to a decrease in hemlock and an increase in hickory in many of the major pollen studies of the northeastern United States. Hickory, in this sense, is considered an indicator of relatively dry conditions. But, as both Jay Custer (1988) and Victor Carbone (1976) remark, the inability to identify pollen to the species level renders such an interpretation problematic. Mesic species of hickory exist (Carya cordiformis, C. ovata) and are common in the modern biota (Joyce 1988). Most xeric hickory species also grow and thrive in moist, fertile soils. The sudden and synchronous decline of hemlock across a wide range of latitudes, cited as an indicator of dry conditions, strongly supports disease rather than climatic change as the cause (Bhiry and Filion 1996; Davis 1983; Watts 1979, 1983). Likewise, pollen profiles do not show the significant increases in nonarboreal pollen, such as grasses, amaranth, and Chenopodium, that would suggest a major decline in overstory vegetation resulting from decreasing precipitation and increasing temperatures (Miller et al. 2003).

Carbone’s (1976) quantitative analysis of data from the Shenandoah Valley is often cited to support the proposition that warm and dry conditions were present in the Middle Atlantic region during the Late Holocene. His analysis followed a methodology developed by Thompson Webb and Reid Bryson (1972), who took modern pollen samples and modern climatic data from seventy-three sample locations in the Midwest and, using canonical correlation, calculated a set of mathematical transfer functions relating pollen frequency to climatic variables, which they then applied to three fossil pollen cores located within the same region. Carbone applied this methodology to raw data from Hack Pond, located in the Shenandoah Valley of Virginia, concluding in his 1976 study that the climate of the Shenandoah Valley involved a warm and dry period that culminated around 4350 BP (Miller et al. 2003). This period was characterized by “increased temperatures, increased desiccation and moisture stress” (Carbone 1976:106). It is not clear in Carbone’s discussion when temperature and precipitation reached modern levels, although he states “the climatic shifts of the last 4,000 to 5,000 years can be better understood as perturbations of the modern pattern rather than as actual long-term shifts” (Carbone 1976:107). Problems in dating these shifts may arise from the fact that the most recent radiocarbon sample from Hack Pond was from a depth of approximately 140 centimeters and returned a date of 9520 ± 200 BP (11,262–10,251 BP or 9313–9302 BC calibrated). Although Carbone does not explicitly say so, he apparently assumes a constant rate of deposition over the last 9,000 years, an assumption that may be invalid, given what is known of variation in alluvial deposition during this period (Vento and Rollins 1989; Vento et al. 2008).

Webb and Bryson (1972) assume that climate can be considered the primary controlling factor for the composition of past vegetation within their Midwestern study region. This assumption is likely based on the proposition that other factors controlling vegetation, such as topography and soils, are constant between the modern and fossil samples. Carbone’s 1976 study violates the assumption, however, in that he uses the same mathematical transfer functions developed by Webb and Bryson for the Midwest, rather than developing transfer functions from sample sites in the Shenandoah Valley, where factors such as soil and topography are radically different from those in the Midwest (Miller et al. 2003).

Noting Webb and Bryson’s caution that climatic factors controlling pine in the Midwest are different from those controlling pine in the Southeast, Carbone (1976:100) reasons that, because deciduous vegetation in the two regions was similar, the pine problem is unlikely to significantly affect the overall results. However, any number of similar, but unrevealed, problems may exist as a result of applying transfer functions developed in the Midwest to the Middle Atlantic region (Miller et al. 2003).

Alluvial stratigraphy has also been cited as evidence for warm and dry conditions in the Late Holocene. Increases in overbank deposition rates have been interpreted as indicating increased runoff resulting from decreased vegetative cover. Such an interpretation is based in part on James Knox’s (1983) study of the morphology of stream channels and floodplains in southwestern Wisconsin and on investigations within the Susquehanna, Ohio, and Delaware River valleys (Vento et al. 2008). Knox interprets increased alluviation prior to 6000 BP as resulting from a warm and dry period, whose climate was primarily influenced by dry westerlies. This period is well documented in the pollen profiles of the Midwest, which indicate an eastward migration of the Midwestern prairie prior to 6000 BP (King 1980). Knox (1983) theorizes that increasing rainfall and vegetation after 6000 BP would have resulted in a decrease in the magnitude and frequency of peak flows, thus also a decrease in overbank deposition. Knox notes that the period of greatest sediment yield during the climatic fluctuation from humid to arid to humid conditions would have occurred at the end of the warm and dry period, during which vegetation was at a minimum despite an increase in rainfall (Miller et al. 2003).

Studies of alluvial stratigraphy in the Middle Atlantic region indicate that overbank deposition was rapid during the period between approximately 5000 and 3000 BP. Frank Vento and Harold Rollins (1989) and Vento and colleagues (2008) have identified rapid vertical accretion in the Ohio, Upper and Middle Delaware, and Susquehanna Basins, consisting of sediments with Late and Transitional Archaic cultural material. Richard Scully and Richard Arnold (1981) found evidence of increasing vertical accretion in the Upper Susquehanna Basin after 4900 BP. Carbone (1976) points to the rapid deposition of culturally sterile, sandy-clay loam between 5,000 and 2,700 BP as evidence that vegetation was at a minimum due to increased temperatures and decreased rainfall (Miller et al. 2003).

Despite the significance of Knox’s (1983) study for understanding the relationship between changes in the climatic optimum and changes in the stream channels and floodplain characteristics of the Midwest, the presence of similar alluvial characteristics in the Late Holocene (Sub-Boreal) of the Middle Atlantic region does not necessarily indicate that the same climatic changes were in progress. Hydrological studies show that the decrease in precipitation needed to substantially affect sediment yield and flood size is quite large. According to data gathered by Walter Langbein and Stanley Schumm (1958), a decrease in precipitation causing vegetation change from forest to grassland would result in only a 30% increase in sediment yield. Late and Transitional Archaic overbank deposition apparently increased to at least this degree, yet there is no evidence in pollen profiles of grassland vegetation during this period. Data presented by Knox (1983) indicate that changes in mean annual precipitation above 650 millimeters per annum have little effect on flood size. Modern precipitation in the Susquehanna, Delaware, and Ohio Basins is approximately 900 millimeters per annum. Thus, for decreased rainfall to affect either the sediment yield of drainage basins or the magnitude of overbank flooding, arid conditions would have been required, but, as noted above, there is no evidence of vegetation changes in the Late Holocene pollen data of the Middle Atlantic region that would indicate a change to such conditions. At most, the pollen data cited as evidence for a warm and dry period would indicate a shift in overstory forest composition involving an increase in xeric species, although, again as noted above, this interpretation of the pollen profile is subject to challenge (Miller et al. 2003).

Vento and Rollins (1989) and Vento and colleagues (2008) accept the hypothesis of a warm and dry Sub-Boreal, and they attribute rapid vertical accretion to changes in atmospheric circulation patterns. Based on Knox’s (1983) discussion of the effects of zonal versus meridional circulation, Vento and colleagues (2008) and Joyce (1988) point to an increase in meridional circulation that resulted in more frequent cyclonic storms, causing more frequent overbank flooding. Patricia Miller, Frank Vento, and James Marine (2007) note that such an interpretation does not depend on an overall decrease in either precipitation, vegetation, or both to explain the increase in alluvial deposition. Although there are at present no independent supporting data for a warm and dry Sub-Boreal, the hypothesis is consistent with the pollen data, as is the hypothesis of severe climatic change (Miller et al. 2003).

Miller and colleagues (2003) further note that there is no conclusive evidence of a widespread warm and dry climate such as that hypothesized by Carbone (1976) and by Curry and Custer (1982) for the period between 5000 and 2600 BP. Rather, data suggest that modern levels of temperature and precipitation generally prevailed in both the eastern United States and the Ohio River drainage basin. Cyclonic storms, as evidenced by flood scouring and the deposition of coarse-grained material on the floodplain, likely occurred with greater frequency than in previous periods. Floodplain and terrace soils supported mesophytic species such as beech, oak, tulip tree, ash, sugar maple, and walnut. Upland soils supported forest communities dominated by chestnut, hickory, and oak (Figures 1.1–1.4). The Late Holocene forest differed from the modern forest primarily in age structure, containing trees of all ages, with a mosaic of gaps caused by falls of trees in senescence and in various stages of regeneration. These gaps gave rise to a variety of edible resources that grow best in the open, including blackberries, raspberries, and a variety of tubers (Miller et al. 2003).

<insert figs. 1.2–1.4 about here>

<1>Geomorphic Fluvial Evidence

With regard to the fluvial geomorphic evidence, based on more than thirty years of personal experience in the region, I see a clear patterning in the stratigraphic record that supports my contention that rivers and streams in the region responded to these warm and drier climatic conditions by undergoing more active lateral channel migration along smaller drainage lines or more rapid vertical accretion along the major drainage lines, often reflected in the stratigraphic profiles by distinct autogenic flood events. If we briefly examine some representative sites that have a lengthy Holocene record from the Ohio, Susquehanna, and Delaware Basins, it becomes clear that the Sub-Boreal, and thus also Transitional Archaic, culture period was one of environmental change. All of these sites occur on Late Wisconsin terraces that contain a thick Holocene package of vertical accretion and Transitional Archaic artifacts in variably thick cambic B horizons. At some sites, the cambic B horizons are immediately overlain by a surface A horizon; at others, they are capped by a cumulic A horizon that dates to the Sub-Atlantic climate interval (3000–1750 BP). The stratigraphic horizons and thickness of the Holocene soils that cap the Transitional Archaic horizons reflect variables such as channel morphology, height of the terrace above the active stream channel, valley morphology, and stream order.

The Leetsdale Site (Miller 2012) and Point State Park Site (Blades et al. 2008) on the Ohio River at Pittsburgh document rapid rates of late Middle Holocene vertical accretion. At the Leetsdale Site, the Transitional Archaic period encompasses, in places, more than 1 meter of overbank deposition in less than 1,100 years. This soil package, or defined allostratigraphic unit, in Area 1 consists of a series of nested lamellae (stacked AC/C couplets) that document a series of relatively high magnitude flood events. The rates of vertical accretion for the Sub-Boreal at the Leetsdale Site are much higher than those for deposits in the preceding Atlantic or subsequent Sub-Atlantic climatic phase. In addition, in Area 2, which is situated closer to the active river channel, the soil profiles show clear evidence for channel migration and incision of the terrace.

In the upper reach of the Allegheny River near Tionesta, Pennsylvania, recent investigations (Verbka, Vento, and Shaffer 2013) at the Hunter Station Bridge Site identified more than 2.5 meters of Holocene alluvium with artifacts occurring throughout the profile. Once again, the Transitional Archaic horizons at the site include a cambic B horizon documenting continuous slow vertical accretion of the terrace.

At the Jacobs, Gould Island, and Memorial Park Sites on the North and West Branches of the Susquehanna River (Vento et al. 2008), the Sub-Boreal phase alluvial deposits form a thick cambic B horizon documenting continuous slow vertical accretion of the terrace between 4200 and 3000 BP. In the Route 11/15 corridor, extending from near Selinsgrove to Liverpool, Pennsylvania, along the main stem of the Susquehanna River, all of the excavated sites contained Transitional Archaic artifacts associated with thick cambic B horizons that, in places, were intercalated with coarse-grained autogenic flood events (C horizons).

Soil profiles at the Smithfield Beach, Frenchtown, and Shohola Bridge Sites in the Delaware River valley document increased rates of overbank deposition during this time. At the Shohola Bridge Site, much like at Leetsdale, multiple AC/C horizons represent continuous flood deposition between very short lived episodes of stability for the period 4200 to 3000 BP. At the Frenchtown Site on the Middle Delaware River, the Transitional Archaic is evidenced by slow vertical accretion of the floodplain. I contend that the higher rates of vertical accretion along the larger drainage lines, the absence of cumulic A horizons documenting long episodes of stability, and the more active lateral channel migration along smaller internal drainages all support the presence of generally warmer and drier climatic conditions favoring increased rates of surface runoff, higher sediment yield to streams, and thus also higher rates of vertical accretion.

In the Upper Delaware River valley, the Transitional Archaic period (4000–3000 BP) coincides with the late Middle Holocene (5000–3200 BP) phase (Phase IV) of reworking and aggradation (Stinchcomb et al. 2012). Following Middle Holocene (6000–5000 BP) incision, average flood deposit grain size decreases, and widespread soil formation occurs along the higher T2a alluvial terrace. Adjacent to the T2a is a lower T2b terrace that contains evidence of rapid sedimentation and multiple weakly developed buried soils. Because overbank sediment was accumulating along the lower surfaces (active floodplain), the higher, less flood-prone T2a surface became more suitable for habitation. This T2a buried soil often holds evidence of Late and Transitional Archaic occupation. Carbon isotope composition of organic matter from Delaware River alluvial soils suggests that the Transitional Archaic period follows a shift from higher to lower C4:C3 plants, centered at 4500 BP (Stinchcomb et al. 2013). This shift may be related to major climate reorganization (the 4200 BP event and Middle to Late Holocene transition), incision and riparian development after 6000–5000 BP, or both.

Geomorphic evidence (not associated with fluvial geomorphology) for a 1,200-year period of warm and dry climatic conditions comes from the recent excavations at the Beech Ridge Site near Dover, Delaware (Barse and Marston 2006), where a deep, strongly weathered paleosol containing Dalton Hardaway points is overlain by a thick package of windblown sands. The late Middle Holocene component of these overlying sands is thicker and slightly coarser grained than that of sands at lower and higher levels. In fact, much of the aeolian sand package appears to have been emplaced during the late Middle Holocene. The increased rates of aeolian deflation and deposition during this time were in response to warm and dry climatic conditions. Over the years, Dennis Curry, much to his credit, has argued for aeolian deflation and subsequent burial of prehistoric sites during the Holocene on the Maryland Coastal Plain. There is now strong evidence along the entire eastern Coastal Plain for a period of late Middle Holocene aeolian deflation, proving him correct.

<1>Geomorphic Evidence Outside the Middle Atlantic Region

In Georgia, David Hurst Thomas’s extensive work on Late Archaic settlements on Saint Catherines Island (e.g., Bishop, Rollins, and Thomas 2011) documents a shift in settlement due to a potential marsh regression of 1.5 meters in the period 4000 to 3500 BP. Frank Vento and Patricia Stahlman (2011), working on now-buried paleosols on Saint Catherines Island, have documented, in places, more than 3 meters of Holocene aeolian sands, with a thick portion of this package occurring during the Sub-Boreal climatic phase.

Other researchers in the region, conducting sea level and tidal channel migration studies, argue for a late Middle Holocene sea level regression or standstill at this time (e.g., Gayes et al. 1992). Timothy Chowns (2009) notes that, around 4000 BP, sea levels regressed, changing the coastal processes from tidal to wave dominated, which in turn favored tidal channel migration and spit development. Recent studies in central Florida indicate drying on the basis of a change from mangrove swamps to yellow and loblolly pines during the late Middle Holocene (e.g., Rich, Vento, and Vega 2011).

<1>Faunal and Floral Evidence

At present in the Middle Atlantic region, there is a large set of data that documents a clear decrease in hemlock pollen as a proxy for warm and dry conditions during the period 4200 to 3000 BP. Recent pollen studies completed on cores extracted from Chesapeake Bay (Willard and Bernhardt 2004) show clear decreases in pine pollen in association with atmospheric cooling at 8000 BP and again during the Little Ice Age (700–400 BP). In the data for the period 4200 to 3000 BP, there is a large increase in pine pollen, suggesting warmer and probably drier climatic conditions. In their recent paper on pollen extracted from a deep core along Sandy Run Creek on the Georgia Coastal Plain, Heidi LaMoreaux, George Brook, and John Knox (2009) show wetter conditions than now from 4500 to 1000 BP and a sharp decrease in groundwater levels, aridity, and lower stream discharges beginning at 4500 BP. LaMoreaux, Brook, and Knox argue that this drying reflected increased winter solar radiation that raised winter temperatures, with the replacement of oak by southern pine. They further state that, with the absence of the Laurentian ice sheet, there would have been less orbitally induced seasonality, thus weakening both the polar and subtropical jet streams and opening the door for other climate change processes such as the El Niño–Southern Oscillation (ENSO). Consistent with a less stormy jet stream pattern, there was a decrease in meridional flow of moist Gulf air into eastern North America and the Upper Mississippi Valley after the Middle Holocene climatic optimum, or hypsithermal, leading to drier conditions and reduced river discharges. That said, much of the problem to date is the dearth of detailed and comprehensive archaeobotanical studies for the Transitional Archaic period in the Middle Atlantic region. If warming and drying did dominate the climate, then we should see evidence in the form of grassland expansion, an increase in pine, evidence for lower water tables, and the desiccation of swamps and bogs. Clearly, there need to be additional pollen, macrobotanical, and phytolith studies on soils that target the period 4200 to 3000 BP.

<1>Discussion

Increased frequency of cyclonic storms after the Atlantic climatic episode (beginning as early as 6000 BP) and resultant high alluvial deposition fit with data from the Upper Ohio and Upper and Middle Susquehanna and Delaware River drainage basins. Stratigraphic evidence, in the form of coarse-grained vertical and lateral accretionary deposits, especially along the first-, second-, and third-order streams within the basins, documents the increased occurrence of large storms after 6000 BP. Similar stratigraphic evidence in the northern Midwest supports the idea of more frequent large floods after 6000 BP (Knox, McDowell, and Johnson 1981). The increased rates of overbank deposition along the major drainage lines (i.e., the Delaware and Susquehanna Rivers) and more active lateral channel migration and incision along their tributary streams precluded the development of cumulic A horizons during the Sub-Boreal climatic phase (4200–3000 BP).

Not surprisingly, the incision of the Pre-Boreal and Boreal valley-fill deposits in most areas of these basins occurred about 6000 BP, coincident with increased meridional circulation, a condition that promoted strong cyclonic storms via the lifting and mixing of warm, moist Gulf air masses by cool, dry air masses out of Canada (Grissinger, Murphey, and Little 1981; Vento and Fitzgibbons 1987). This episode of Middle Holocene incision and more frequent large floods may be responsible for the general paucity or near absence of Paleoindian, Early Archaic, and Middle Archaic sites in low-terrace contexts along most of the streams in these basins. On the other hand, there are sites along the major rivers in the Middle Atlantic region such as Leetsdale, Point State Park, Shawnee Minisink, Shawnee Island, City Island, Smithfield Beach, Cremard, Memorial Park, High Bank, Piney Island, and Canfield Island, as well as the Route 11/15 sites (Bressler, Maietta, and Rockey 1983; Hart et al. 1995; Kent 1996; Miller et al. 2003; Miller, Marine, and Vento 2007; Schuldenrein and Vento 2002; Vento and Rollins 1989; Vento et al. 1992, 2008; Kurt Carr, personal communication 2014) that clearly contain intact artifact-bearing remnants of fine-grained overbank deposits from the Late Pleistocene through the Atlantic climatic phase (see Figures 1.1–1.4).

During the period 4200 to 3000 BP, the genetic stratigraphic package on the lowermost Port Huron and Valley Heads terraces in the Ohio, Susquehanna, and Delaware Basins marks various episodes of erosion and deposition that can be attributed to atmospherically induced changes in climate. The typically thick, often mottled, cambic B horizons or C horizons of the Sub-Boreal were likely emplaced during warm and dry conditions, probably in association with meridional stabilization of the Bermuda-Azores anticyclone over eastern North America and the increased importance of warm and dry zonal flow (much as in the 1930s) that reduced vegetative cover, increased surface runoff, and promoted vertical accretion on low terraces within the basin. This situation occurs when the Bermuda-Azores high becomes particularly large and strong and retrogrades westward over the eastern portion of North America. This decreases the likelihood of precipitation while simultaneously advecting warm, dry air from the Southwest. Such conditions often occur during present-day summers.

As noted earlier, the decline of hemlock (Pollen Zone C-2) during the Sub-Boreal climatic interval (4200 to 3000 BP) supports the presence of warm and dry conditions during this time. The absence of well-developed cumulic A horizons and associated floodplain instability in the period 4200 to 3000 BP may also be attributed to these conditions. The forest of the Sub-Boreal (Pollen Zone C-2) was dominated by oak and hickory, and there is a marked reduction in pine, birch, and alder (Prentice, Bartlein, and Webb 1991:2047). A dramatic decline in hemlock that began around 5000 BP (Haas and McAndrews 2000:81) continued throughout this interval, whose cultures include those of the Late and Transitional Archaic periods (Figure 1.1). The warm and dry climate of the Sub-Boreal phase, which reduced vegetative cover and increased erosion, is associated with floodplain instability and the formation of mottled Bw horizons and C horizons along larger streams in the Middle Atlantic region (Figure 1.1; Vento and Rollins 1989; Vento et al. 1992, 2008:22).

By 3000 BP, the climate abruptly transitioned to warm and moist conditions. The Sub-Atlantic (3000–1750 BP), Scandic (1750–1200 BP), and Neo-Atlantic (1100–750 BP) climatic episodes mark a transition to warm and moist, cool and moist, and warm and moist conditions, respectively. The transition from the previous climatic episode allowed for several hundred years of floodplain stability and subsequent long-term development of A horizons. Clearly, the effect of meridional circulation, and the associated cyclonic and convectional storms, was much reduced during these climatic periods; a subsequent return to more abundant hemlock pollen from its low levels during the warm and dry Sub-Boreal indicates lowered rates of evapotranspiration and more effective precipitation.

Cooler and moister climatic phases such as the Scandic (1750–1200 BP) and Pacific (700–400 BP) effectively arrested development of A horizons as a result of frequent large floods that favored rapid vertical accretion (cambic B horizons and autogenic units of coarse-grained C horizons) on low terraces within the Middle Atlantic region. This may be a result of an increase in tropical storm (i.e., hurricane) frequency or more frequent cool-season flood events associated with more meridional flow conditions. Heavy precipitation from intensive low-pressure cells, such as those of the 1955 and 1972 tropical cyclone–induced floods, could have been rather common during these climatic phases as atmospheric flow characteristics approached those of modern times. Prior to 6000 BP, blocking effects induced by the presence of the Laurentian ice sheet would have precluded such tropically induced flood events. All of these data provide a strong argument for a marked change in the environment during the late Middle Holocene and especially during the Transitional Archaic period.

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