Late Holocene paleoenvironment in northern New Caledonia, southwestern Pacific, from a multiproxy analysis of lake sediments

Lithostratigraphic and palynological analysis of two cores recovered from the ‘Grand Lac’ (New Caledonia), combined with 35 ¹⁴C AMS dates, yields a paleoenvironmental record spanning the last 2000 yr. The lithology is represented mainly by clayey or laminated layers. A catastrophic event, which is marked by very coarse deposits, occurred probably between ca 1070-960 cal yr B.P. and possibly is associated with an unusually severe La Niña event. Before and after this event, a similar combination of the two main sediment types is recorded. The repeated alternation of laminated and clayey layers is interpreted as the response to local hydrologic forcing, which may reflect a shift from relatively wet to relatively drier conditions, respectively. Variable amount of micro-charcoal is detected all along the profile. Without additional evidence, notwithstanding the initial local human settlement documented since ca 2900 ¹⁴C yr B.P., micro-charcoal occurrence and variability cannot be linked directly to an anthropogenic origin. No distinct palynological zonations in relation to the lithology are observed, and the vegetation changes may only represent minor transitions across environmental limits.     

Palynology and depositional environment of the Río Ignao nonglacial deposit,province of Valdivia,Chile

In south-central Chile, the Río Ignao nonglacial deposit with a minimal radiocarbon age of 56,000 +2000, ?1700 yr shows the following sequence of pollen assemblages, starting with the oldest: Gramineae (zone 1), Gramineae-Corynabutilon-Lomatia-Ovidia (zone 2), Nothofagus-Embothrium-Gramineae (zone 3A), Nothofagus-Gramineae-Tubuliflorae (zone 3B and D), and Nothofagus-Drimys-Myrtaceae (zone 3A). This sequence implies an initial dry and rather cold climate that later became wetter and somewhat warmer, reached a warm peak, and ultimately became colder and drier. At the warmest time, the Andean tree line is estimated to have been about 900 m lower and average January (summer) temperature about 3–4°C colder than at present. The Río Ignao deposit is believed to represent an early interstade of the last glaciation, known in southern Chile as the Llanquihue Glaciation.     

Sterols of a contemporary lacustrine sediment

C₂₆, C₂₇, C₂₈ and C₂₉ sterols, including Δ⁵-, Δ²²- and Δ^5,22-sterols and both 5α- and 5β-stanols, have been identified in the contemporary lacustrine sediment of Rostherne mere (Cheshire, England). Amounts of total sterols decrease from ca. 400 ppm extracted sediment dry weight for the 0–7 cm sediment section to ca. 40 ppm for the corresponding 18–30 cm section. 5α-stanols are of far greater abundance than the 5α-stanol isomers. The carbon number distributions of unsaturated and saturated sterols and the increase in stanol: Δ⁵-sterol ratio with sediment depth provide indirect evidence for the operation of a sterol hydrogenation process. C₂₉ sterols preponderate at lower sediment depths, suggesting a predominantly higher plant input, whereas C²⁷ sterols are more abundant in the surface sediment.     

The amino acid composition of a deep-water marine sediment from the upwelling region northwest of Africa

The distribution of amino acids with depth have been described for three samples of a core of recent sediment (< 1000–8000 yr) from the continental slope off N.W. Africa. Basic amino acids are more abundant than acidic amino acids in all samples. The amino acid composition of the oldest sample resembles most closely the amino acid composition of planktonic protein. It is suggested that the differences in amino acid composition of the three samples reflect diagenetic changes which are probably controlled by the environment of deposition.     

The Arequipa Massif of Peru: New SHRIMP and isotope constraints on a Paleoproterozoic inlier in the Grenvillian orogen

The enigmatic Arequipa Massif of southwestern Peru is an outcrop of Andean basement that underwent Grenville-age metamorphism, and as such it is important for the better constraint of Laurentia–Amazonia ties in Rodinia reconstruction models. U–Pb SHRIMP zircon dating has yielded new evidence on the evolution of the Massif between Middle Paleoproterozoic and Early Paleozoic. The oldest rock-forming events occurred in major orogenic events between ca. 1.79 and 2.1 Ga (Orosirian to Rhyacian), involving early magmatism (1.89–2.1 Ga, presumably emplaced through partly Archaean continental crust), sedimentation of a thick sequence of terrigenous sediments, UHT metamorphism at ca. 1.87 Ga, and late felsic magmatism at ca. 1.79 Ga. The Atico sedimentary basin developed in the Late-Mesoproterozoic and detrital zircons were fed from a source area similar to the high-grade Paleoproterozoic basement, but also from an unknown source that provided Mesoproterozoic zircons of 1200–1600 Ma. The Grenville-age metamorphism was of low-P type; it both reworked the Paleoproterozoic rocks and also affected the Atico sedimentary rocks. Metamorphism was diachronous: ca. 1040 Ma in the Quilca and Camaná areas and in the San Juán Marcona domain, 940 ± 6 Ma in the Mollendo area, and between 1000 and 850 Ma in the Atico domain. These metamorphic domains are probably tectonically juxtaposed. Comparison with coeval Grenvillian processes in Laurentia and in southern Amazonia raises the possibility that Grenvillian metamorphism in the Arequipa Massif resulted from extension and not from collision. The Arequipa Massif experienced Ordovician–Silurian magmatism at ca. 465 Ma, including anorthosites formerly considered to be Grenvillian, and high-T metamorphism deep within the magmatic arc. Focused retrogression along shear zones or unconformities took place between 430 and 440 Ma.     

Provenance, age, and environment of mid-Wisconsinan slackwater lake sediment in the St. Louis Metro East area, USA

Valleys tributary to the Mississippi River contain fossiliferous slackwater lake sediment (Equality Formation) deposited in response to aggradation of the Mississippi River valley during the last glaciation. In the St. Louis Metro East area, the lower part of the Equality Formation is primarily laminated, fossiliferous silt and clay deposited from about 44,150 to 24,310 ¹⁴C yr B.P. The upper Equality Formation is primarily very fine sand to silt deposited from about 21,200 to 17,000 ¹⁴C yr B.P. Among the four cores that sample this succession in the St. Louis Metro East area, core MNK-3 (38.64EN, 90.01EW) was selected for detailed study. Three sources are distinguished by the following characteristics: (1) gray smectite-quartz-Se-rich, feldspar-poor material of the Des Moines, Wadena, and James lobes; (2) reddish brown kaolinite-Cu-Fe-rich sediment of the Superior and Rainy lobes; and (3) brown illite-dolomite-Sr-rich sediment of the Lake Michigan and Green Bay lobes. The earliest sediments (44,150 to 41,700 ¹⁴C yr B.P.) were derived from the central and western provenances and are chronocorrelative with the lower Roxana Silt. A hiatus occurred from about 41,700 to 29,030 ¹⁴C yr B.P. when much of the middle Roxana Silt (Meadow Member) was deposited on adjacent uplands. The youngest sediment includes evidence of heightened activity of the Superior Lobe at about 29,000 ¹⁴C yr B.P., the Lake Michigan and Green Bay lobes from about 25,000 to 24,000 ¹⁴C yr B.P., and the Wadena-Des Moines-James lobes at about 21,000 ¹⁴C yr B.P.     

Kinetic model options for interpretation of amino acid enantiomeric ratios in Quaternary mollusks: Comments on a paper by Kvenvoldenet al. (1979)

A comparison of linear (to D/L leucine of ca. 0.55) and non-linear (slowing of racemization rates by a factor of ca. 10 × after D/L leucine of ca. 0.25) model kinetics is presented in order to interpret amino acid enantiomeric ratio data in Holocene and Pleistocene marine mollusks from the Pacific coast of the United States. Linear model rate constants for well-dated Holocene and Pleistocene samples are not consistent with probable temperature histories or probable latitudinal differences in effective temperatures for these samples, using reasonable values for the activation energy of racemization. The non-linear model, with a much earlier transition from rapid to slow racemization rates, appears more consistent with available data.     

Photonic dating of prehistoric irrigation canals at Phoenix,Arizona, U.S.A.*

A number of archeological features, including in‐filled irrigation canals of uncertain prehistoric age, occur within the Holocene floodplain of the Salt River at Phoenix, Arizona. In the first attempt to date irrigation‐canal sediments using luminescence methods, we obtained age estimates of 1640 ± 190 yr B.P. (1σ) (multi‐aliquot or MA) and 1621 ± 95 yr B.P. (post‐IR single‐aliquot‐regenerative‐dose or SAR) for a single sample from the base of the oldest canal‐infilling deposits (all IR‐PSL ages reported in this article are in calendar years before A.D. 2001). For the remaining canal samples, weighted mean luminescence ages of 819 ± 45 yr (MA) and 826 ± 32 yr (post‐IR SAR) were obtained. Thus from photonic dating we can resolve the first and last phases of canal use at this Phoenix site: initiation at ca. 1600 years ago and final use at ca. 800 years ago. These results demonstrate the power of SAR luminescence sediment dating to enhance our understanding of prehistoric irrigation‐canal development and usage here and elsewhere in the world. © 2004 Wiley Periodicals, Inc.     

Microbial lipids from a nearshore sediment from Bowling Green Bay,North Queensland: The fatty acid composition of intact lipid fractions

Samples from a sediment core collected in Bowling Green Bay, North Queensland have been analysed for hexane/isopropanol extractable lipids and fatty acids. These data revealed a subsurface lipid abundance maximum at 3–4 cm depth and consistent low total fatty acid abundances (ca 2 μg/g) in the deeper samples ( > 10 cm depth). Lipid phosphate was below the level of detection in all the samples. Bacterial community structure was found to vary markedly in the upper 10 cm of the core, with the 18:1Δ11 bacterial chemotype predominant in the surface sediment and trans-acid chemotypes dominating in the 3–4 cm depth sediment. Based on the fatty acid composition, the bacterial biomass was estimated to vary from 199 μg/g at 3–4 cm depth toca 8 μg/g at 11–13 cm depth, although the fatty acid distributions indicated possible interference from protozoan detritus. In order to test this possibility, a surface sediment sample from a nearby site was extracted and analysed for fatty acids in lipid fractions separated by silica column chromatography. The fatty acid distributions in lipid fractions containing wax/steryl esters, triacylglycerols, glycolipids and phospholipids were markedly different. These analyses were interpreted in terms of fatty acid contributions to the extractable lipids from bacteria, cyanobacteria, protozoan detritus and highly degraded organic matter.     

Regional atmospheric circulation change in the North Pacific during the Holocene inferred from lacustrine carbonate oxygen isotopes, Yukon Territory, Canada

Analyses of sediment cores from Jellybean Lake, a small, evaporation-insensitive groundwater-fed lake, provide a record of changes in North Pacific atmospheric circulation for the last ∼7500 yr at 5- to 30-yr resolution. Isotope hydrology data from the southern Yukon indicate that the oxygen isotope composition of water from Jellybean Lake reflects the composition of mean-annual precipitation, δ¹⁸O_p. Recent changes in the δ¹⁸O of Jellybean sedimentary calcite (δ¹⁸O_ca) correspond to changes in the North Pacific Index (NPI), a measure of the intensity and position of the Aleutian Low (AL) pressure system. This suggests that δ¹⁸O_p variability was related to the degree of fractionation during moisture transport from the Gulf of Alaska across the St. Elias Mountains and that Holocene shifts were controlled by the intensity and position of the AL. Following this model, between ∼7500 and 4500 cal yr B.P., long-term trends suggest a predominantly weaker and/or westward AL. Between ∼4500 and 3000 cal yr B.P. the AL shifted eastward or intensified before shifting westward or weakening between ∼3000 and 2000 cal yr B.P. Rapid shifts eastward and/or intensification occurred ∼1200 and 300 cal yr B.P. Holocene changes in North Pacific atmospheric circulation inferred from Jellybean Lake oxygen isotopes correspond with late Holocene glacial advances in the St. Elias Mountains, changes in North Pacific salmon abundance, and shifts in atmospheric circulation over the Beaufort Sea.     

Archaeomagnetic record from Modoc Rock Shelter,Illinois, for the time range of 6200–8900 B.P.

The Modoc Rock Shelter is located in Randolph County, Illinois at the base of the Mississippi River bluffs, and is documented as having human occupation from 9000 B.P. to as recently as 800 B.P. Two hundred twenty-eight archaeomagnetic samples were collected from 28 surface hearths in two different excavation areas. Pilot samples from each hearth were A.F. demagnetized to 100 mT to establish the optimum demagnetization level for all samples from a specific hearth. The magnetic directions for individual hearths after appropriate demagnetization have high precision with α-95 values between 2° and 4°. Independent inclination and declination records from the two excavations, which were correlated with conventional radiocarbon dates, overlap in time and show good correlation. The composite record shows a prominent eastward declination swing of 15° from 6500–7800 yr B.P., followed by a westward swing of equal magnitude from 8000–8900 yr B.P. The inclination record is less varied. This secular variation record correlates well with soft sediment records from lakes in the north-central United States and is perhaps the longest and oldest archaeomagnetic secular variation record from a single site in North America. © 1997 John Wiley & Sons, Inc.     

Crustal contamination as an indicator of the extent of early Archaean continental crust: Pb isotopic evidence from the late Archaean gneisses of West Greenland

Ph isotopic analyses are reported for 119 samples of late Archaean (ca. 3000-2800 Myr) calc alkaline orthogneisses and associated anorthosites from southern West Greenland. Over most of the area. $\text{Pb}\text{Pb}$ whole rock isotope systematics indicate derivation of the magmatic precursors of the gneisses and anorthosites from a source region with a typically mantle-type $\text{U}\text{Pb}$ ratio (μ₁ value of 7.5) at. or shortly before, ca. 3000-2800 Myr ago. In contrast, in the Godthaabsfjord region, late Archaean Nûk gneisses and associated anorthosites were emplaced into or through early Archaean (ca. 3700 Myr) Amîtsoq gneisses, and crystallised with variable proportions of two isotopically distinct types of Pb which commenced their respective crustal developments at ca. 3000-2800 Myr and at ca. 3700 Myr ago. Isotopic and other geochemical constraints demonstrate that Nûk gneisses and their temporal equivalents were not produced by reworking or melting of Amîtsoq gneisses. Mixing of early and late Archaean Pb results from contamination of the magmatic precursors of Nûk gneisses and anorthosites (characterised by mantle-type Pb at time of emplacement) with ancient, unradiogenic Pb derived from ca. 3700 Myr-old Amîtsoq-type continental crust invaded by the Nûk magmas. The contaminant is considered to be a trace-element enriched fluid phase released from dehydrating older continental crust during progressive burial and heating by emplacement of calc alkaline magmas in the late Archaean ‘accretion differentiation superevent’. This was followed by mixing of the released fluids with younger Nûk magmas.Pb isotopic compositions of late Archaean gneisses and anorthosites outside the Godthaabsfjord region provide no evidence for the presence of early Archaean Amîtsoq-type continental crust in southern West Greenland in areas more than a few tens of km outside the known outcrop of Amîtsoq gneisses. We suggest that early Archaean crust does not exist at depth in late Archaean areas with undisturbed Pb-isotope systematics, either in Greenland or elsewhere in the North Atlantic craton.Pb-isotope evidence for crust magma interaction, involving selective extraction of certain trace elements by a fluid phase from wall rock and subsequent mixing between magma and contaminant fluid, provides a powerful tool for detection, sub-surface ‘mapping’, and geochronological and geochemical characterisation of deep, ancient continental crust.     

Paleohydrological Changes in Highland Desert Rivers and Human Occupation, 7000‐3000 Cal. Yr B.P., South‐Central Andes,Argentina

This article focuses on local paleohydrological changes experienced by the Las Pitas and Miriguaca Rivers in the south‐central Andes of Argentina and their impacts on hunter‐gatherers as they transitioned to food‐producing communities 7000–3000 cal. yr B.P. Paleoenvironmental reconstruction based on geomorphology, alluvial sedimentology, and diatom evidence indicates a dry phase of reduced streamflow between ca. 6700 and 4800 cal. yr B.P. for the Las Pitas River, and 6600 and 3000 cal. yr B.P. for the Miriguaca River. A phase of more humid environmental conditions commenced after ca. 4900 cal. yr B.P. along the Las Pitas River, and after 3000 cal. yr B.P. along the Miriguaca River. Differences in the chronology and magnitude of hydrological changes along both rivers are related to topographic and hydrological characteristics of their respective watersheds. Higher catchment elevation and enhanced orographic precipitation favored greater sensitivity for the Las Pitas River to short humid events during the middle‐to‐late Holocene. The archaeological evidence suggests that the paleohydrological changes within these catchments played a significant role in human occupational dynamics such that the Las Pitas River offered better environmental conditions for human occupation relative to the Miriguaca River as foragers increasingly relied on plant and animal domestication.     

Late-glacial-Holocene climate of the lake district of Chile

Pollen evidence from a 350-cm section of a fen in a moraine belt at Rucañancu (39°33′S, 72°18′W) bears on the controversy regarding interpretation of late-glacial and Holocene climate in midlatitude Chile. Earlier pollen studies, indicating a cooling trend between approximately 11,000 and 10,000 yr B.P., disagreed with observations of glacier fluctuations which show continuous glacier wastage and, by inference, warming after 12,500 yr B.P. and possibly earlier, up until Neoglaciation, beginning after 6850 yr B.P. Fossil beetle assemblage data in this time range support the interpretation of climate made from the observed glacier behavior. At Rucañancu, a pollen assemblage containing upper montane podocarp (Podocarpus andinus) in quantities reaching 34% and dating between 10,440 and 10,000 yr B.P. implies a cold climate with summer temperatures possibly 5–8°C lower than today's. Holocene warming began afterward, later than the glacier and beetle records indicate, and continued until at least 8350 yr B.P., as suggested by the sequence of assemblages dominated by Myrtaceae, by Aextoxicon punctatum, and by Gramineae. A subsequent assemblage of Nothofagus obliqua type implies an increase of moisture until 6960 yr B.P., following which N. dombeyi type, under a cool and humid Neoglacial climate, became dominant.     

Late-glacial vegetation and climate at the Manis Mastodon site,Olympic Peninsula,Washington

As the late Wisconsin Cordilleran Ice Sheet retreated, sediment accumulated in shallow depressions at the Manis Mastodon Archaeological site on the Olympic Peninsula, near Sequim, Washington. Pollen, plant macrofossils, and bones of mastodon, caribou, and bison occur within the lower 47 cm of these deposits. The fossil pollen and seed assemblages indicate persistence for 1000 yr (11,000–12,000 yr B.P.) of an herb-and-shrub-dominated landscape at a time when forest species appear elsewhere in Washington and in adjacent British Columbia.At present, Sequim is near the northern coastal limits of both Cactaceae and Ceratophyllum. Mean annual precipitation is 42.7 cm and summer temperatures average 15°–16°C in July. The absence of coniferous trees and the presence of cactus and Ceratophyllum in late-glacial sediments are explained by a regional climate that was drier and at least as warm as today. These conditions persisted in the rain shadow of the Olympic Mountains until at least 11,000 yr B.P.     

Microfossil evidence for salinity events in the Holocene Coorong Lagoon,South Australia

Nearly 6 m of uncompacted muddy sediment was recovered from the floor of the northern Coorong Lagoon in the core Coorong #5. Radiocarbon analyses of molluscan shells indicate that sedimentation at the core site commenced before 6830 ± 90 yr cal BP, and the presence of Pinus pollen confirms a modern age for the uppermost 0.5 m. Microfossils extracted from the core sediment samples, 2 cm slices at 10 cm intervals, included the foraminifera Ammonia sp., Elphidium excavatum and Elphidium gunteri; the ostracods Osticythere baragwanathi and Leptocythere lacustris; and charophyte oogonia. Shell fragments of the estuarine bivalve Spisula (Notospisula) trigonella in the lowermost 0.7 m of the core are evidence that these sediments were subject to some marine influence, but the absence of foraminifera and ostracods from this same interval indicates that at the core site salinity was not sufficient to support populations of these organisms. Thus, prior to 6830 ± 90 yr cal BP the Younghusband Peninsula was in place, in part isolating the northern lagoon from the Southern Ocean. The initial recorded salinity event is signified by abundant Ammonia sp. at a core depth of 5.2 m. The duration of this event was relatively brief; foraminifera were mostly absent in the immediately overlying 2 m, representing ca 700 yr of sedimentation. This observation is attributed to substantial inflow of freshwater from the River Murray. In the upper 3.0 m, Ammonia sp. was present in most core samples indicating that for most of the past 6000 years the Coorong Lagoon has been sufficiently saline to support a continuing population of this species. At a core depth of 1.3 m, the sediment sample yielded >2000 tests of Ammonia sp., and they were accompanied by maximum pre-modern numbers of E. excavatum, O. baragwanathi and oogonia. Taken together, these data signify the maximum pre-modern salinity event recorded in the core sediments, probably correlating in time with regional drought conditions at ca 3500 yr BP. Elphidium gunteri is confined to the modern sediments where it is abundant and accompanied by equally large numbers of Ammonia sp., E. excavatum, O. baragwanathi and L. lacustris. These data collectively indicate water conditions that are significantly changed from those that prevailed in the Coorong Lagoon for most of the Holocene.     

Four thousand years of environmental change and human activity in the Cochabamba Basin, Bolivia

The Cochabamba Basin (Bolivia) is on the ancient road network connecting Andean and lowland areas. Little is known about the longevity of this trade route or how people responded to past environmental changes. The eastern end of the Cochabamba valley system constricts at the Vacas Lake District, constraining the road network and providing an ideal location in which to examine past human-environmental interactions. Multi-proxy analysis of sediment from Lake Challacaba has allowed a c. 4000 year environmental history to be reconstructed. Fluctuations in drought tolerant pollen taxa and calcium carbonate indicate two periods of reduced moisture availability (c. 4000-3370 and c. 2190-1020 cal yr BP) compared to adjacent wetter episodes (c. 3370-2190 and c. 1020 cal yr BP-present). The moisture fluctuations broadly correlate to El Niño/Southern Oscillation variations reported elsewhere. High charcoal abundance from c. 4000 to 2000 yr ago indicates continuous use of the ancient road network. A decline in charcoal and an increase in dung fungus (Sporormiella) c. 1340-1210 cal yr BP, suggests that cultural changes were a major factor in shaping the modern landscape. Despite undisputable impacts of human populations on the Polylepis woodlands today, we see no evidence of woodland clearance in the Challacaba record.     

Paleohydrology and Paleoclimate of the Past 33,000 Years at the Tamanduá River, Central Brazil

Deposits of the Tamanduá River contain evidence for four major paleohydrologic stages in the last 33,000 years. A wet period between 33,000 and 20,000¹⁴C yr B.P. produced a high water table that allowed organic-rich deposition in the Tamanduá valley. A dry interval 17,000-10,000¹⁴C yr B.P. produced sandy deposits of braided channels and alluvial fans. River aggradation during this period probably resulted from a high sediment load promoted by intense slope erosion and from flash floods. A wet period after 10,000 and before 6000¹⁴C yr B.P. was marked by reduced slope erosion and by high discharge that led to erosion of the valley fill. During that time forests developed widely in Brazil. A drier climate after 6000¹⁴C yr B.P. caused a reduction of discharge but allowed a high water table to be maintained.     

Paleoenvironment of the Folsom archaeological site, New Mexico, USA, approximately 10,500 C yr B.P. as inferred from the stable isotope composition of fossil land snail shells

Well-preserved aragonitic land snail shells (Vallonia) from late Pleistocene Eolian sediment in the Folsom archaeological site in New Mexico exhibit an overall decrease of δ¹⁸O_PDB from maximum values of +2.7‰ (more positive than modern) to younger samples with lower average values of about −3.6‰ (within the modern range). The age of the samples (approximately 10,500 ¹⁴C yr B.P.) suggests that the decrease in δ¹⁸O may manifest climatic changes associated with the Younger Dryas. Some combination of increased relative humidity and cooler temperatures with decreased δ¹⁸O of precipitation during the times of snail activity can explain the decrease in shell δ¹⁸O. A well-known Paleoindian bison kill occurred at the Folsom site during this inferred environmental transition.Average δ¹³C values of the aragonite shells of the fossil Vallonia range from −7.3 to −6.0‰ among different archaeological levels and are not as negative as modern values. This suggests that the proportion of C₄ vegetation at the Folsom site approximately 10,500 ¹⁴C yr B.P. was greater than at present; a result which is consistent with other evidence for higher proportions of C₄ plants in the region at that time.