A reported early-man site adjacent to southern Alaska's continental shelf: A geologic solution to an archeologic enigma

An extensive ancient archeologic site containing lithic artifacts and associated with mammoth remains was reported at Chinitna Bay, southern Alaska in 1943. The presence of such a site adjacent to the continental shelf at the base of the rugged Aleutian Range suggested that humans may have inhabited the inner shelf environment during the late Pleistocene at times of lowered sea level. Because of the site's potential significance, an interdisciplinary research team relocated and reinvestigated the area in 1978, but failed to find evidence of prehistoric human habitation. Geologic studies and radiocarbon dating indicate that the strata reported at the site are intertidal in origin, very late Holocene in age, and have undergone significant tectonic movement in the recent past. These observations indicate that the previously published observations of the Chinitna Bay site are probably invalid.     

A late quaternary record of eolian silt deposition in a maar lake, St. Michael Island, western Alaska

Recent stratigraphic studies in central Alaska have yielded the unexpected finding that there is little evidence for full-glacial (late Wisconsin) loess deposition. Because the loess record of western Alaska is poorly exposed and not well known, we analyzed a core from Zagoskin Lake, a maar lake on St. Michael Island, to determine if a full-glacial eolian record could be found in that region. Particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian. Silt deposition took place from at least the latter part of the mid-Wisconsin interstadial period through the Holocene, based on radiocarbon dating. Based on the locations of likely loess sources, eolian silt in western Alaska was probably deflated by northeasterly winds from glaciofluvial sediments. If last-glacial winds that deposited loess were indeed from the northeast, this reconstruction is in conflict with a model-derived reconstruction of paleowinds in Alaska. Mass accumulation rates in Zagoskin Lake were higher during the Pleistocene than during the Holocene. In addition, more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape. The thinner loess record on land may be due to the sparse, herb tundra vegetation that dominated the landscape in full-glacial time. Herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height. The lack of abundant, full-glacial, eolian silt deposition in the loess stratigraphic record of central Alaska may be due, therefore, to a mimimal ability of the landscape to trap loess, rather than a lack of available eolian sediment.     

Late Pliocene to late Pleistocene environments preserved at the Palisades Site, central Yukon River, Alaska

The Palisades Site is an extensive silt-loam bluff complex on the central Yukon River preserving a nearly continuous record of the last 2 myr. Volcanic ash deposits present include the Old Crow (OCt; 140,000 yr), Sheep Creek (SCt; 190,000 yr), PA (2.02 myr), EC (ca. 2 myr), and Mining Camp (ca. 2 myr) tephras. Two new tephras, PAL and PAU, are geochemically similar to the PA and EC tephras and appear to be comagmatic. The PA tephra occurs in ice-wedge casts and solifluction deposits, marking the oldest occurrence of permafrost in central Alaska. Three buried forest horizons are present in association with dated tephras. The uppermost forest bed occurs immediately above the OCt; the middle forest horizon occurs below the SCt. The lowest forest bed occurs between the EC and the PA tephras, and correlates with the Dawson Cut Forest Bed. Plant taxa in all three peats are common elements of moist taiga forest found in lowlands of central Alaska today. Large mammal fossils are all from common late Pleistocene taxa. Those recovered in situ came from a single horizon radiocarbon dated to ca. 27,000 ¹⁴C yr B.P. The incongruous small mammal assemblage in that horizon reflects a diverse landscape with both wet and mesic environments.     

Geochronology of paleoenvironmental change,clovis type site,Blackwater draw,New Mexico

Geoarchaeological investigations at the Clovis type site, Blackwater Locality No. 1, in 1983 and 1984 included core drilling, archaeological test excavations, stratigraphic profiling, sedimentary analyses, and radiocarbon dating. Six lines of core holes transverse to the outlet channel clearly defined the subsurface configuration and stratigraphy of the prehistoric spring run. Pieces of large animal bone from units B, C, D, and E that elsewhere in the site contain Paleoindian artifacts suggest occurrences of additional buried sites along the ancient spring run. Four Paleoindian projectile points recovered during archaeological testing confirm these prospects. The Clovis type site, located in an abandoned gravel pit, is in a natural depression initially occupied by a late Pleistocene lake. After breaching of the depression by overflow or sapping, it became a springhead and was enlarged by slumping and slopewash. Detailed stratigraphic profiling of the south wall of the abandoned gravel pit provided precise stratigraphic control for sediment sampling and radiocarbon dating, and revealed more complex microstratigraphy and facies relationships than heretofore known for the site. The interfingering of dune facies around the depression with lacustrine and spring-laid facies within it aid paleoclimatic interpretation. Deflational contacts within the depression appear to correlate with adjacent wedges of dune sand reflecting relatively arid intervals. Between these arid episodes occur intervals of increased ground water level attended initially by deposition of spring-laid sands of unit B during the late Pleistocene (13,000–11,500 yr B.P.). As the water table rose following a period of severe deflation, slumping and gravity flow deposited clayey sand, Unit C, on the floor of the blowout between 11,500 and 11,000 yr B.P. During this time Clovis people first appeared at the site. After another brief period of deflation, a lake rose causing sand of Unit D₀ to be washed in from shore followed by deposition of diatomities, units D₁ and D₂. These were separated by a brief influx of eolian sand, unit D_2z. Between 10,800 and 10,000 yr B.P. outflow from the lake was reduced by accumulation of eolian sand in the outlet while Folsom people and later Agate Basin people arrived to hunt bison during this time. Cody complex people appeared during and after a brief erosional episode that preceded deposition of eolian silt and sand of units E and F from 10,000 to 8000 yr B.P. Eolian deposition during post-Folsom time converted the pond to a wet meadow and eventually, during Cody time, to a grassy swale. Some of these deposits were blown out during the Altithermal arid period (ca. 8000-5000 yr B.P.), a time when prehistoric Archaic peoples excavated wells in the floor of the depression. Subsequent eolian activity has resulted in deflation and dune migration during the late Holocene. The best prospects for Paleoindian finds are along the buried outlet south of the south wall and in early Holocene dune sands on the uplands around the depression. © 1995 John Wiley & Sons, Inc.     

Age of Sheep Creek Tephra (Pleistocene) in Central Alaska from Thermoluminescence Dating of Bracketing Loess

The age of the Sheep Creek tephra (SCt), a widespread marker ash bed in eastern Alaska and western Yukon Territory, has been ambiguous and controversial. We have obtained three reliable thermoluminescence age estimates from bracketing loess near Fairbanks that imply a deposition age of about 190,000 ± 20,000 yr for SCt. Three of six loess samples near and closely bracketing the SCt beds near Fairbanks yielded younger age estimates (∼117,000 and ∼135,000 yr), most likely (based on field aspects) because of reworking and contamination by translocated grains. The new, reliable age assignment of 190,000 yr confirms independent stratigraphic evidence of a pre-last interglaciation age, and stratigraphic evidence from one site (Upper Eva Creek) that SCt is older than the more-widespread 140,000-yr-old Old Crow tephra. The SCt age also has implications for regional correlations of glacial and nonglacial deposits. In particular, it supports the stratigraphic and geomorphic interpretation that the Delta Glaciation in the east-central Alaska Range and the Reid Glaciation in western Yukon Territory are older than the last interglaciation (isotope substage 5e).     

Revised age of deglaciation of Lake Emma based on new radiocarbon and macrofossil analyses

Previous radiocarbon ages of detrital moss fragments in basal organic sediments of Lake Emma indicated that extensive deglaciation of the San Juan Mountains occurred prior to 14,900 yr B.P. (Carrara et al., 1984). Paleoecological analyses of insect and plant macrofossils from these basal sediments cast doubt on the reliability of the radiocarbon ages. Subsequent accelerator radiocarbon dates of insect fossils and wood fragments indicate an early Holocene age, rather than a late Pleistocene age, for the basal sediments of Lake Emma. These new radiocarbon ages suggest that by at least 10,000 yr B.P. deglaciation of the San Juan Mountains was complete. The insect and plant macrofossils from the basal organic sediments indicate a higher-than-present treeline during the early Holocene. The insect assemblages consisted of about 30% bark beetles, which contrasts markedly with the composition of insects from modern lake sediments and modern specimens collected in the Lake Emma cirque, in which bark beetles comprise only about 3% of the assemblages. In addition, in the fossil assemblages there were a number of flightless insect species (not subject to upslope transport by wind) indicative of coniferous forest environments. These insects were likewise absent in the modern assemblage.     

Geoarchaeological context of late Pleistocene and early Holocene occupation at the Cooper's Ferry site,western Idaho,USA

Archaeological excavations at the Cooper's Ferry site (10IH73), located in the lower Salmon River canyon of western Idaho, revealed a stratified sequence of cultural occupations that included a pit feature containing stemmed points. However, radiocarbon ages determined on charcoal and bone in the pit feature range between ca. 12,000 yr B.P. and 7300 yr B.P. By considering the effects of postdepositional processes on dated samples, and by comparing the lithostratigraphy, pedostratigraphy, and stable isotope geochemistry of pedogenic carbonates from Cooper's Ferry with other well‐dated stratigraphic sections in the canyon, site geochronology is clarified. Based on the presence of key radiocarbon ages and distinctive stratigraphic criteria, we argue that the initial occupation and interment of lithic artifacts in a pit feature at Cooper's Ferry occurred during the late Pleistocene, between ca. 11,410 and 11,370 yr B.P., and not during the early Holocene. Records of geomorphic change and paleoenvironmental proxy data from the site reveal that early occupation in the lower Salmon River canyon corresponds with evolving riparian ecosystems, which must be considered as a contextual aspect of local prehistoric cultural ecology. © 2004 Wiley Periodicals, Inc.     

Late Quaternary Stratigraphy, Glacial Limits, and Paleoenvironments of the Marresale Area, Western Yamal Peninsula, Russia

Stratigraphic records from coastal cliff sections near the Marresale Station on the Yamal Peninsula, Russia, yield new insight on ice-sheet dynamics and paleoenvironments for northern Eurasia. Field studies identify nine informal stratigraphic units from oldest to youngest (the Marresale formation, Labsuyakha sand, Kara diamicton, Varjakha peat and silt, Oleny sand, Baidarata sand, Betula horizon, Nenets peat, and Chum sand) that show a single glaciation and a varied terrestrial environment during the late Pleistocene. The Kara diamicton reflects regional glaciation and is associated with glaciotectonic deformation from the southwest of the underlying Labsuyakha sand and Marresale formation. Finite radiocarbon and luminescence ages of ca. 35,000 to 45,000 yr from Varjakha peat and silt that immediately overlies Kara diamicton place the glaciation >40,000 yr ago. Eolian and fluvial deposition ensued with concomitant cryogenesis between ca. 35,000 and 12,000 cal yr B.P. associated with the Oleny and the Baidarata sands. There is no geomorphic or stratigraphic evidence of coverage or proximity of the Yamal Peninsula to a Late Weichselian ice sheet. The Nenets peat accumulated over the Baidarata sand during much of the past 10,000 yr, with local additions of the eolian Chum sand starting ca. 1000 yr ago. A prominent Betula horizon at the base of the Nenets peat contains rooted birch trees ca. 10,000 to 9000 cal yr old and indicates a >200-km shift northward of the treeline from the present limits, corresponding to a 2° to 4°C summer warming across northern Eurasia.     

Holocene loess deposition and soil formation as competing processes, Matanuska Valley, southern Alaska

Although loess–paleosol sequences are among the most important records of Quaternary climate change and past dust deposition cycles, few modern examples of such sedimentation systems have been studied. Stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the Matanuska Valley in southern Alaska show that loess deposition there began sometime after 6500 ¹⁴C yr B.P. and has continued to the present. The silts are produced through grinding by the Matanuska and Knik glaciers, deposited as outwash, entrained by strong winds, and redeposited as loess. Over a downwind distance of 40 km, loess thickness, sand content, and sand-plus-coarse-silt content decrease, whereas fine-silt content increases. Loess deposition was episodic, as shown by the presence of paleosols, at distances >10 km from the outwash plain loess source. Stratigraphic complexity is at a maximum (i.e., the greatest number of loesses and paleosols) at intermediate (10–25 km) distances from the loess source. Surface soils increase in degree of development with distance downwind from the source, where sedimentation rates are lower. Proximal soils are Entisols or Inceptisols, whereas distal soils are Spodosols. Ratios of mobile CaO, K₂O, and Fe₂O₃ to immobile TiO₂ show decreases in surface horizons with distance from the source. Thus, as in China, where loess deposition also takes place today, eolian sedimentation and soil formation are competing processes. Study of loess and paleosols in southern Alaska shows that particle size can vary over short distances, loess deposition can be episodic over limited time intervals, and soils developed in stabilized loess can show considerable variability under the same vegetation.     

Pedoarchaeology of Cactus Hill,a sandy Paleoindian site in southeastern Virginia,U.S.A.

Cactus Hill is located in the Virginia Coastal Plain on a terrace above the Nottoway River. The site has a record of occupation that spans the Holocene and also offers evidence of humans late in the Pleistocene before Clovis time. Soil investigations identified several deposit types, and demonstrated that multisequal eolian sands forming the site's primary core are arrayed in spatially and temporally discrete horizons. Resting atop an ancient paleosol, the earliest sand stratum (19,540 ± 70 ¹⁴C yr B.P.) is marked by a conspicuous but culturally sterile buried surface horizon. Eolian sand above this surface supports another sequum in which Clovis and underlying “Blade” artifacts are associated with a fainter surface horizon and pronounced subsoil lamellae. Early Archaic and successively younger artifacts occur above the Clovis level in a more weakly developed uppermost sequum. This soil and cultural stratigraphy, together with considerations of regional topography, demonstrate that the landscape has evolved incrementally since about the last glacial maximum. © 2004 Wiley Periodicals, Inc.     

Stratigraphy of Pleistocene glaciations in the St Elias Mountains,southwest Yukon,Canada

At least five Middle to Late Pleistocene advances of the northern Cordilleran Ice Sheet are preserved at Silver Creek, on the northeastern edge of the St Elias Mountains in southwest Yukon, Canada. Silver Creek is located 100 km up‐ice of the Marine Isotope Stage (MIS) 2 McConnell glacial limit of the St Elias lobe. This site contains ~3 km of nearly continuous lateral exposure of glacial and non‐glacial sediments, including multiple tills separated by thick gravel, loess and tilted lake beds. Infrared‐stimulated luminescence (IRSL) and AMS radiocarbon dating constrain the glacial deposits to MIS 2, 4, either MIS 6 or mid‐MIS 7, and two older Middle Pleistocene advances. This chronology and the tilt of the lake beds suggest Pleistocene uplift rates of up to 1.9 mm a^?1 along the Denali Fault since MIS 7. The non‐glacial sediment consists of sand, gravel, loess and organic beds from MIS 7, MIS 3 and the early Holocene. The MIS 3 deposits date to between 30–36 ¹⁴C ka BP, making Silver Creek one of the few well‐constrained MIS 3‐aged sites in Yukon. This confirms that ice receded close to modern limits in MIS 3. Pollen and macrofossil analyses show that a meadow‐tundra to steppe‐tundra mosaic with abundant herbs and forbs and few shrubs or trees, dominated the environment at this time. The stratigraphy at Silver Creek provides a palaeoclimatic record since at least MIS 8 and comprises the oldest direct record of Pleistocene glaciation in southwest Yukon.     

Shallow site archaeology: Artifact dispersal,stratigraphy, and radiocarbon dating at the Barger Gulch locality B Folsom Site,Middle Park,Colorado

Shallowly buried archaeological sites are particularly susceptible to surface and subsurface disturbance processes. Yet, because cultural deposition often operates on short time scales relative to geologic deposition, vertical artifact distributions can be used to clarify questions of site formation. In particular, patterns in artifact distributions that cannot be explained by occupation histories must be explained by natural processes that have affected sites. Buried only 10–50 cm beneath the ground surface for 10,450 ¹⁴C yr, the Folsom component at Barger Gulch Locality B (Middle Park, Colorado) exhibits many signs of post‐depositional disturbance. Through examination of variation in the vertical distribution of the artifact assemblage, we are able to establish that only a Folsom component is present. Using vertical artifact distributions, stratigraphy, and radiocarbon dating, we are able to reconstruct the series of events that have impacted the site. The Folsom occupation (˜10,450 ¹⁴C yr B.P.) was likely initially buried in a late‐Pleistocene eolian silt loam. Erosion brought the artifacts to rest on a deflation surface at some time prior to 9400 ¹⁴C yr B.P. A mollic epipedon formed in sediments that accumulated between 9400 and 7000 ¹⁴C yr B.P. Some time after 5200 ¹⁴C yr B.P., this soil was partially truncated, and artifacts that had previously dispersed upward created a secondary lag at its upper contact. This surface was buried again and artifact dispersal continued. © 2005 Wiley Periodicals, Inc.     

Dating Early and Middle (Reid) Pleistocene Glaciations in Central Yukon by Tephrochronology

The late Cenozoic deposits of central Yukon contain numerous distal tephra beds, derived from vents in the Wrangell Mountains and Aleutian arc–Alaska Peninsula region. We use a few of these tephra beds to gain a better understanding on the timing of extensive Pleistocene glaciations that affected this area. Exposures at Fort Selkirk show that the Cordilleran Ice Sheet advanced close to the outer limit of glaciation about 1.5 myr ago. At the Midnight Dome Terrace, near Dawson City, exposed outwash gravel, aeolian sand, and loess, related to valley glaciers in the adjacent Ogilvie Mountains, are of the same age. Reid glacial deposits at Ash Bend on the Stewart River are older than oxygen isotope stage (OIS) 6 and likely of OIS 8 age, that is, about 250,000 yr B.P. Supporting evidence for this chronology comes from major peaks in the rates of terrigeneous sediment input into the Gulf of Alaska at 1.5 and 0.25 myr B.P.     

Holocene stratigraphic and morphological evolution of the Wandandian Creek delta,St Georges Basin,New South Wales

Subaerial exposure beside the Wandandian Creek channel during the last glacial maximum led to the development of red and orange mottling and, in some areas, produced a palaeosol over the Pleistocene land surface. Incision of the palaeo-Wandandian Creek, during the Late Pleistocene, formed a relatively deep steep-sided channel partially infilled with medium-grained fluvial sand. This palaeovalley became drowned as the post-glacial marine transgression impounded the western portion of St Georges Basin and the basal prodelta/lagoonal mud facies was deposited from ca 7 ka. The Wandandian Creek delta prograded down the palaeovalley and reached the study area ～3500 – 4000 years ago with the deposition of delta-front sandy silt and the overlying prograded sand facies. The subaerial portion of the delta is characterised by well-developed floodplains, levees, mouth bars and backswamps. Dredging in Wandandian Creek and land clearing for rural and urban development have had little long-term effect on the growth and morphology of Wandandian Creek delta.     

AMS Radiocarbon Age of the Upper Mississippi Valley Roxana Silt

Accelerator mass spectrometer radiocarbon ages of the Roxana Silt (loess) along the Upper Mississippi Valley of Wisconsin and Minnesota indicate that loess sedimentation of the Roxana Silt occurred between about 55,000 and 27,000 ¹⁴ C yr B.P. However, due to local environmental controls, the basal age at any given site may range from 55,000 to 35,000 ¹⁴C yr B.P. The radiocarbon ages presented here are in agreement with previous radiocarbon ages for the Roxana Silt in its type area of west-central Illinois, but indicate that long-term sedimentation rates along the bluffline of the Upper Mississippi Valley were very slow (4-8 cm/1000 yr) compared to long-term sedimentation rates along the bluffline of the type area (40-70 cm/1000 yr). Comparison of radiocarbon ages for midcontinent middle Wisconsinan loess deposits indicates that sedimentation along the Mississippi River valley may have preceded loess sedimentation along the Missouri River valley by as much as 20,000 yr or that basal ages for middle Wisconsinan loess along the Missouri Valley are erroneously young. The bracketing ages for the Upper Mississippi Valley Roxana Silt indicate that the Mississippi River valley was receiving outwash sedimentation between 55,000 and 27,000 ¹⁴C yr B.P.     

Quaternary stratigraphy and geoarchaeology of the colorado and concho rivers,west texas

Geoarchaeological investigations in an area surrounding the confluence of the upper Colorado and Concho Rivers, Edwards Plateau of West Texas, have produced a detailed landscape evolution model which provides a framework for discussion of the influences of geomorphic processes on the development, preservation, and visibility of the archaeological record. Field mapping within the study area has differentiated six allostrati-graphic units of fluvial origin in both valleys, as well as extensive eolian sand sheets along the Colorado River. Early to middle Pleistocene terrace remnants cap many upland areas, whereas two distinct late Pleistocene terrace surfaces are widespread within the study area at somewhat lower elevations. Fluvial activity during the time period of human occupation is represented by an extensive Holocene terrace and underlying valley fill, which is up to 11 m in thickness. Valley fill sediments can be subdivided into allostratigraphic units of early to middle Holocene (ca. 10,000–5000 yr B.P.) and late Holocene age (ca. 4600–1000 yr B.P.), which are separated by a buried soil profile. The modern incised channels and very narrow floodplains represent the last millennium. Eolian sand sheets of early to middle Holocene age overlie limestone- and shale-dominated uplands, Pleistocene terraces, and in some cases the Holocene valley fill along the Colorado River. Pleistocene terraces have been stable features in the landscape and available for settlement through the time period of human occupation. Archaeological materials of all ages occur at the surface, and the record preserved in individual sites range from that associated with discrete periods of activity to longer-term palimpsests that represent repeated use over millennia. Sites within early to middle Holocene and late Holocene fills represent short-term utilization of constructional floodplains during the Paleoindian through early Archaic and middle to late Archaic time periods respectively. By contrast, those that occur along the buried soil profile developed in the early to middle Holocene fill record middle to late Archaic cultural activity on stable terrace surfaces, and represent relatively discrete periods of activity to longer-term palimpsests that represent repeated use over the 3000–4000 years of subaerial exposure. Late Prehistoric sites occur as palimpsests on soils developed in late Holocene alluvium or stratified within modern floodplain facies. Paleoindian through Late Prehistoric sites occur stratified within eolian sand sheets or along the unconformity with subjacent fluvial deposits. The landscape evolution model from the upper Colorado and Concho Rivers is similar to that developed for other major valley axes of the Edwards Plateau. This model may be regionally applicable, and can be used to interpret the geomorphic setting and natural formation processes for already known sites, as well as provide an organizational framework for systematic surface and subsurface survey for new archaeological records. 0 1992 John Wiley & Sons, Inc.     

Age and significance of the Late Pleistocene Dawson tephra in eastern Beringia

Dawson tephra, recently recognized in the Klondike area of Yukon Territory, records one of the largest Quaternary volcanic eruptions in Beringia. Its composition is similar to that of Old Crow tephra, indicating a source in the Aleutian arc-Alaska Peninsula region of southwestern Alaska. Its primary thickness in central Yukon is nearly twice that of Old Crow tephra, which has an estimated eruption volume of >50 km³. The distribution of Dawson tephra is still poorly known, but based on its source area and occurrence in central Yukon, it should be widespread across southern Alaska, Yukon and the Gulf of Alaska. New radiocarbon ages indicate the eruption occurred at about 24,000 ¹⁴C yr BP (ca 27,000 cal yr BP). The Dawson tephra is a valuable marker bed for correlating late Pleistocene records across large areas of eastern Beringia and adjacent marine records.     

Comparison of sedimentation and occupation histories inside and outside rock shelters,Keep‐River region,northwestern Australia

This paper compares archaeological evidence of Aboriginal occupation inside rock shelters and outside in adjacent sand sheets, focusing on two locations in the Keep‐River region, northwestern Australia. Luminescence and radiocarbon dating reveal that occupation sequences inside rock shelters are generally younger ( < 10,000 yr B.P.) than outside ( < 18,000 yr B.P.). Differences in occupation chronology and artifact assemblages inside and outside rock shelters result from depositional and postdepositional processes and shifts in site function. An increase in regional sedimentation rate from 10 cm/ka ^{− 1} in the Pleistocene to 20 cm/ka ^{− 1} in the Holocene may account for late buildup of sediments within rock shelters, increased artifact accumulation, and reduced postdepositional disturbance in some settings. More intense use of rock shelters in the Late Holocene is indicated from a change in hunting technology and greater production of rock art. The results indicate that some cultural interpretations might be flawed unless archaeological evidence from rock‐shelter and open‐site excavations is integrated. © 2006 Wiley Periodicals, Inc.     

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.     

Geoarchaeology of the Cerro La China locality (Buenos Aires,Argentina): Site 2 and site 3

Cerro La China, within the Tandilia Range, has a long archaeological record in which three different human occupations were identified. The geoarchaeological approach allowed us to correlate the archaeosedimentary columns at Site 2 and Site 3 and place the local stratigraphy in a regional context. The archaeologically rich stratigraphic sequence is composed of three episodes of loess deposition. The first bears a 10,600 yr B.P. Paleoindian occupation with Fishtail or Fell's Cave Stemmed points. It is followed by a soil-forming interval which ended about 5000 yr B.P. with an erosive episode. The second event of loess deposition continued through an unknown span of time until a new soil-forming interval started; it includes triangular stemless medium size projectile points corresponding to a different human group. By the sixteenth century another erosive event interrupted the soil-forming interval. After this, the third short-term eolian episode occurred and bears the most recent archaeological occupation marked by small triangular stemless points.