A chronology for late prehistoric Madagascar

Eolian environmental changes in the Northern Mongolian Plateau during the past ∼ 35,000 yr

Studies on Holocene mangrove ecosystem dynamics of the Bragança Peninsula in north-eastern Pará, Brazil

Late Glacial and Holocene vegetation history and paleoclimate of the Kaibab Plateau, Arizona

Early Holocene glaciation on Mount Baker, Washington State, USA

Water Canyon is a rare buried, multicomponent, stratified Paleoindian site in west‐central New Mexico. This paper presents a geoarchaeological assessment of the site as part of a broader interdisciplinary investigation of its paleoenvironmental history and archaeology. The archaeology is associated with ancient wetland deposits (Stratum 6) within an alluvial fan. The fan formed initially through the late Pleistocene. Formation of the fan stopped and wetland deposition began ~11,31014C yr BP (~13,170 cal yr BP). Stratum 6 evolved via wetland deposition and cut‐and‐fill cycles. The bulk of Stratum 6 dates <10,30014C yr BP (<12,200 cal yr BP). One, or possibly two, beds of bison bone, likely processing‐stations, were found on the margin of the paleowetland and date to ~9,20014C yr BP (~10,400 cal yr BP) (lower bone bed) and ~8,20014C yr BP (~9,150 cal yr BP) (upper bone bed). Farther out in the paleo‐wetland a probable kill site was discovered with an in situ Eden projectile point dated to at least ~8,95514C yr BP (~10,070 cal yr BP). The wetland landscape returned to an alluvial fan system <8,00014C yr BP (<8,900 cal yr BP) with two more cycles of fan deposition by ~6,500 cal yr.

Holocene environmental changes in the Central Amazon Basin inferred from Lago Calado (Brazil)

Palaeoenvironmental changes during the last ca. 8590 calibrated yr (7800 radiocarbon yr) in the dry forest ecosystem of the Patía Valley, Southern Colombian Andes: a multiproxy approach

Vegetation and climate changes around the Lama Lake, Taymyr Peninsula, Russia during the Late Pleistocene and Holocene

Pollen data from a Levinson‐Lessing Lake sediment core (74°28'N, 98°38'E) and Cape Sabler, Taymyr Lake permafrost sequences (74°33'N, 100°32'E) reveal substantial environmental changes on the northern Taymyr Peninsula during the last c. 32000 14C years. The continuous records confirm that a scarce steppe‐like vegetation with Poaceae, Artemisia and Cyperaceae dominated c. 32 000–10300 14C yr BP, while tundra‐like vegetation with Oxyria, Ranunculaceae and Caryophyllaceae grew in wetter areas. The coldest interval occurred c. 18000 yr BP. Lateglacial pollen data show several warming events followed by a climate deterioration c. 10500 14C yr BP, which may correspond with the Younger Dryas. The Late Pleistocene/Holocene transition, c. 10300–10000 14C yr BP, is characterized by a change from the herb‐dominated vegetation to shrubby tundra with Betula sect. Nanae and Salix. Alnus fruticosa arrived locally c. 9000–8500 14Cyr BP and disappeared c. 4000–3500 14Cyr BP. Communities of Betula sect. Nanae, broadly distributed at c. 10000–3500 14Cyr BP, almost disappeared when vegetation became similar to the modern herb tundra after 3500–3000 14Cyr BP. Quantitative climate reconstructions show Last Glacial Maximum summer temperature about 4°C below the present and Preboreal (c. 10 000 14C yr BP) temperature 2–4°C above the present. Maximum summer temperature occurred between 10 000 and 5500 14C yr BP; later summers were similar to present or slightly warmer.

Multiproxy paleoecological investigation of a small lake in the high subalpine zone near Stoyoma Mountain, northern Cascade Mountains of British Columbia, reveals significant change in vegetation, limnic conditions, and inferred climate throughout the Holocene (last 10,000 radiocarbon years). Three zones of distinct pollen, plant macrofossil, and chironomid assemblages are apparent in the sediment core from 3M Pond (informal name). A dry, sparsely vegetated spruce parkland and a warm-adapted chironomid community existed in and around the study sites in the early Holocene (ca. 10,000 to 7000 14C yr BP). Between 7000 and 3500 14C yr BP, Engelmann spruce–subalpine fir forest conditions established and then declined around 3M Pond leading to modern subalpine parkland conditions from 3500 14C yr BP to present. Chironomid communities at 3M Pond between 7000 and 3500 14C yr BP are indicative of warmer waters than present, but show a transition to modern assemblages. Three climatic regimes are identified near Stoyoma Mountain: (1) the early Holocene xerothermic period (10,000 to 7000 14C yr BP, (2) a period of climatic transition in the mid-Holocene (7000 to 3500 14C yr BP), and (3) cool, modern neoglacial conditions (after 3500 14C yr BP). These findings confirm vegetation and inferred climate changes identified at Cabin Lake, British Columbia (a nearby lake in the subalpine forest). Changes in treeline position, plant communities, chironomid communities, and inferred climate are nearly synchronous and validate the multiproxy approach for paleoecological reconstruction. Chironomid-based paleotemperature reconstructions confirm earlier evidence that the early Holocene was significantly warmer than present, with estimated summer water surface temperatures up to 4°C higher than today.

Eolian sand in dune fields and sand sheets cover >10 000 km 2 (∼10%) of the Southern High Plains of northwestern Texas and eastern New Mexico. These deposits are concentrated in three west-east–trending belts of dunes (the Muleshoe, Lea-Yoakum, and Andrews dune fields, from north to south) that appear to be eastern extensions of the Mescalero-Monahans dune system in the Pecos River valley, and in the Seminole sand sheet, a discontinuous accumulation of sheet sands between the Lea-Yoakum and Monahans-Andrews dunes. The most common landforms are parabolic dunes associated with blowouts, coppice dunes, and sand sheets, all typical of sandy, vegetated, semiarid landscapes, barchan dunes, in keeping with a relatively limited sand supply and an underlying surface that is relatively hard (Blackwater Draw Formation, Pleistocene), and fence-row dunes, historic dunes formed along field boundaries. These eolian deposits accumulated episodically in the late Pleistocene and Holocene and provide clues to the history of regional drought and aridity. The earliest phase of sedimentation occurred when sheet sands were deposited between 11 000 and 8000 14 C yr B.P., probably in several phases, based on archaeological data, as a result of episodic drought beginning between 11 000 and 10 000 yr B.P. Eolian deposits dating between 8000 and 3000 yr B.P. are rare, although eolian sediment 8000–4500 14 C yr B.P. is ubiquitous in the draws that cross the region, and paleoenvironmental indicators show that the region was subjected to aridity throughout middle Holocene time. The middle Holocene deposits most likely were remobilized in late Holocene time. Most of the deposits and landforms of the dune fields and sand sheets are late Holocene, dating before 4000 14 C yr B.P. and mostly before 1500 14 C yr B.P. The Muleshoe and Lea-Yoakum dunes and the Seminole sand sheet underwent substantial eastward expansion in late Holocene time. Buried soils and radiocarbon ages show that the eolian sand accumulated in several stages, probably in response to cyclic drought. The Muleshoe dunes accumulated after ca. 1300 cal yr B.P. (ca. 1400 14 C yr B.P.), after ca. 750–670 cal yr B.P. (ca. 850–750 14 C yr B.P.), just after ca. 500 cal yr B.P. (ca. 450 14 C yr B.P.), and during the nineteenth and twentieth centuries. The Lea-Yoakum dunes were active after ca. 3400 cal yr B.P. (ca. 3200 14 C yr B.P.) and historically. The Seminole sand sheet was active ca. 430–330 cal yr B.P. (ca. 360 14 C yr B.P.) and in the twentieth century. The Andrews dunes were subjected to at least two phases of eolian sedimentation after ca. 2320 cal yr B.P. (ca. 2320 14 C yr B.P.). Comparisons with eolian chronologies from other regions on the Great Plains suggest that dune mobilization was a regional phenomenon after ca. 2300 cal yr B.P. (ca. 2300 14 C yr B.P.); after ca. 1500–1400 cal yr B.P. (ca. 1650–1550 14 C yr B.P.); after ca. 700 cal yr B.P. (ca. 800 14 C yr B.P.); between 500 and 300 cal yr B.P. (ca. 450–300 14 C yr B.P.); and in the nineteenth century. The climatic fluctuations responsible for mobilizing the dunes probably were relatively minor, yet the landscape impacts were substantial, resulting in widespread wind erosion and dune construction.

This study of fossils (pollen, plant macrofossils, stomata and fish) and sediments (lithostratigraphy and geochemistry) from the Wendel site in North Dakota, USA, emphasizes the importance of considering ground-water hydrology when deciphering paleoclimate signals from lakes in postglacial landscapes. The Wendel site was a paleolake from about 11,500 14C yr BP to 11,100 14C yr BP. Afterwards, the lake-level lowered until it became a prairie marsh by 9,300 14C yr BP and finally, at 8,500 14C yr BP, an ephemeral wetland as it is today. Meanwhile, the vegetation changed from a white spruce parkland (11,500 to 10,500 14C yr BP) to deciduous parkland, followed by grassland at 9,300 14C yr BP. The pattern and timing of these aquatic and terrestrial changes are similar to coeval kettle lake records from adjacent uplands, providing a regional aridity signal. However, two local sources of ground water were identified from the fossil and geochemical data, which mediated atmospheric inputs to the Wendel basin. First, the paleolake received water from the melting of stagnant ice buried under local till for about 900 years after glacier recession. Later, Holocene droughts probably caused the lower-elevation Wendel site to capture the ground water of up-gradient lakes.

Late Quaternary dynamics of forest vegetation on northern Vancouver Island, British Columbia, Canada

Two sedimentary cores with pollen, charcoal and radiocarbon data are presented. These records document the Late‐glacial and Holocene dry forest vegetation, fire and environmental history of the southern Cauca Valley in Colombia (1020 m). Core Quilichao‐1 (640 cm; 3° 6′N, 76° 31′W) represents the periods of 13 150–7720 14C yr BP and, following a hiatus, from 2880 14C yr BP to modern. Core La Teta‐2 (250 cm; 3° 5′N, 76° 32′W) provides a continuous record from 8700 14C yr BP to modern.Around 13 150 14C yr BP core Quilichao‐1 shows an active Late‐glacial drainage system and presence of dry forest. From 11 465 to 10 520 14C yr BP dry forest consists mainly of Crotalaria, Moraceae/Urticaceae, Melastomataceae/Combretaceae, Piper and low stature trees, such as Acalypha, Alchornea, Cecropia and Celtis. At higher elevation Andean forest comprising Alnus, Hedyosmum, Quercus and Myrica was common. After 10 520 14C yr BP the floral composition of dry forest changed, with extensive open grass vegetation indicative of dry climatic conditions. This event may coincide with the change to cool and dry conditions in the second part of the El Abra stadial, an equivalent to the Younger Dryas. From 8850 14C yr BP the record from La Teta indicates dry climatic conditions relative to the present, these prevailing up to 2880 14C yr BP at Quilichao and to 2720 14C yr BP at La Teta. Severe dryness reached maxima at 7500 14C yr BP and 4300 14C yr BP, when dry forest reached maximum expansion. Dry forest was gradually replaced by grassy vegetation, reaching maximum expansion around 2300 14C yr BP. After 2300 14C yr BP grassy vegetation remains abundant. Presence of crop taxa (a.o. Zea mays), disturbance indicators (Cecropia) and an increase in charcoal point to the presence of pre‐Columbian people since 2300 14C yr BP. After 950 14C yr BP, expansion of secondary forest taxa may indicate depopulation and abandonment of previously cultivated land. After 400 14C yr BP, possibly related to the Spanish conquest, secondary forest expanded and charcoal concentrations increased, possibly indicating further reduction of cultivated land. During the past century, Heliotropium and Didymopanax became abundant in an increasingly degraded landscape. Copyright © 2002 John Wiley & Sons, Ltd.

Wetland dynamics in northern Brazil during the Holocene were studied by pollen analysis and AMS radiocarbon dating of three cores. Near the Amazon mouth region, covered mainly by primary Amazon coastal forest and herbaceous vegetation, the pollen record indicates the dominance of mangroves between 4800 and 1100 cal yr b.p. A contraction of the mangrove area and an expansion of herbaceous and fern vegetation occurred between 1100 and 750 cal yr b.p. The period between 750 and 200 cal yr b.p. is characterized by an expansion of mangrove and a decrease in herbaceous and fern vegetation. This trend continued until the present. On Atalaia Island, the sediment core indicates a period with poor pollen preservation between 830 and 630 cal yr b.p. Between 630 and 330 cal yr b.p., mangroves expanded. Later, up to 45 cal yr b.p., the mangrove area decreased and the herbaceous vegetation expanded. During the last hundred years, the relative sea-level rise most probably favored the mangrove expansion as far as the topographically highest sector on this island, while the herbaceous vegetation decreased. The pollen data from Agua Preta Lake indicate dry conditions, as reflected by the poor pollen preservation between 390 and 240 cal yr b.p. Between 240 and 60 cal yr b.p., restinga and Amazon coastal forest with palms dominated this region. For the last 120 years, the record indicates an expansion of the mangrove area. However, recent confinement of mangrove development to the topographically highest area, and the loss of mangrove areas on the lowest surfaces have led to a net loss of mangrove coverage during the last decades.