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1.
Archaeological excavations in deep pre-mound levels at Huaca Prieta in northern Peru have yielded new evidence of late Pleistocene cultural deposits that shed insights into the early human occupation of the Pacific coast of South America. Radiocarbon dates place this occupation between ~ 14,200 and 13,300 cal yr BP. The cultural evidence shares certain basic technological and subsistence traits, including maritime resources and simple flake tools, with previously discovered late Pleistocene sites along the Pacific coast of Peru and Chile. The results help to expand our knowledge of early maritime societies and human adaption to changing coastal environments.  相似文献   

2.
《Tectonophysics》2001,330(1-2):25-43
A detailed gravimetric study has been integrated with the most recent stratigraphic data in the area comprised between the Arno river and the foothills of the Northern Apennines, in northern Tuscany (central Italy). A Plio–Pleistocene basin lies in this area; its sedimentary succession can be subdivided from the bottom, in five allostratigraphic units: (1) Lower–Middle Pliocene shallow marine deposits; (2) Late Pliocene (?)–Early Pleistocene fluvio-lacustrine deposits; (3) late–Early Pleistocene–Middle Pleistocene alluvial to fluvial red conglomerates (Montecarlo Formation); (4) Middle Pleistocene alluvial to fluvial red conglomerates (Cerbaie and Casa Poggio ai Lecci Formations); (5) alluvial to fluvial deposits of Late Pleistocene age. The Bouguer anomaly map displays a strong minimum in the northeastern sector of the basin, and a gentle gradient from west to east. The map of the horizontal gradients permits to recognise three major fault zones, two of which along the southwestern and northeastern margins of the basin, and one along the southeastern edge of the Pisani Mountains. A 2.5D gravimetric modelling along a SW–NE section across the basin displays a thick wedge of sediments of density 2.25 g/cm3 (about 1700 m in the depocenter) overlying a layer of density 2.55 g/cm3, 1000 m thick, which rests on a basement of 2.72 g/cm3. The most of the sediment wedge is here referred to Upper Pliocene (?)–Lower Pleistocene, because borehole data show Pliocene marine deposits thinning northward close to the southern margin of the area. The layer below is referred to Ligurids and upper Tuscan Nappe units; the densest layer is interpreted as composed of Triassic evaporites, quartzites and Palaeozoic basement. According to Carmignani low-angle extensional tectonics began between Serravallian and early Messinian, thinning the Apennine nappe stack. At the end of Middle Pliocene, syn-rift deposition ceased in the Viareggio Basin (west of the investigated area) as demonstrated by Argnani and co-workers, and high-angle extensional tectonics migrated eastward up to the Monte Albano Ridge. A syn-rift continental sedimentary wedge developed in Late Pliocene–Early Pleistocene, until its hanging wall block was dismembered, during late Early Pleistocene, by NE-dipping faults, causing the uplift of its western portion (the Pisani Mountains). This breakup caused exhumation and erosion of Triassic units whose clastics where shed into the surrounding palaeo-Arno Valley in alluvial–fluvial deposits unconformably overlying the Lower Pleistocene syn-rift deposits. In the late Pleistocene SW–NE-trending fault systems created the steep southeastern edge of the Pisani Mountains and the resulting throw is recorded in Middle Pleistocene deposits across the present Arno Valley. This tectonic phase probably continues at present, offshore Livorno, as evidenced by the epicentres of earthquakes.  相似文献   

3.
New pollen, micro-charcoal, sediment and mineral analyses of a radiocarbon-dated sediment core from the Serra Sul dos Carajás (southeast Amazonia) indicate changes between drier and wetter climatic conditions during the past 25,000 yr, reflected by fire events, expansion of savanna vegetation and no-analog Amazonian forest communities. A cool and dry last glacial maximum (LGM) and late glacial were followed by a wet phase in the early Holocene lasting for ca. 1200 yr, when tropical forest occurred under stable humid conditions. Subsequently, an increasingly warm, seasonal climate established. The onset of seasonality falls within the early Holocene warm period, with possibly longer dry seasons from 10,200 to 3400 cal yr BP, and an explicitly drier phase from 9000 to 3700 cal yr BP. Modern conditions with shorter dry seasons became established after 3400 cal yr BP. Taken together with paleoenvironmental evidence from elsewhere in the Amazon Basin, the observed changes in late Pleistocene and Holocene vegetation in the Serra Sul dos Carajás likely reflect large-scale shifts in precipitation patterns driven by the latitudinal displacement of the Inter-Tropical Convergence Zone and changes in sea-surface temperatures in the tropical Atlantic.  相似文献   

4.
A detail investigation was carried out to improve the current knowledge of groundwater salinisation processes in coastal aquifers using hydrochemical and isotopic parameters. Data of major ions for 40 wells located in the Salalah plain aquifer, Sultanate of Oman, were collected during pre-monsoon 2004 and analysed. The groundwater changes along the general flow path towards the coast from fresh (EC < 1500 μS/cm), brackish (EC: 1500–3000 μS/cm) and saline (EC > 3000 μS/cm). Results of inverse modeling simulations using PHREEQC show that dissolution of halite may be the main source of Cl and Na in the study area. Ionic delta calculation indicates that the depletion of Na and K and enrichment of Ca and Mg in groundwater were probably attributed to reverse ion exchange reactions. During a sampling campaign conducted in October 2015, 11 groundwater samples were collected for Cl, Br and isotopic analysis (2H/18O). Molar Cl/Br ratios in fresh groundwater were higher than those of seawater, indicating the impact of halite dissolution on the groundwater quality. For saline groundwater, these ratios were less than those of seawater, showing the influence of anthropogenic input from agriculture on the same. Relatively depleted isotopic signature of all groundwater samples show that the monsoon precipitation is the main source of groundwater recharge in the study area.  相似文献   

5.
This research aims at uncovering the stand-scale Holocene fire history of balsam fir forest stands from two bioclimatic zones of the boreal forest and assessing the existence of a sub-continental shift in past fire activity that could have triggered a change in the Holocene zonal pattern. In eastern Canada, the extant closed-crown boreal forest corresponds to two ecological regions separated along 49°N, the northern black spruce zone and the southern balsam fir zone. We sampled balsam fir stands from the southern fir zone (n = 7) and among the northernmost patches of fir forest located far beyond the fir zone boundary, into the spruce zone (n = 6). Macrofossil analysis of charcoal in mineral soils was used to reconstruct both the stand-scale and regional Holocene fire histories. Data were interpreted in the context of published palaeoecological evidence. Stands of the balsam fir zone were submitted to recurrent fire disturbances between c. 9000 and 5000 cal. yr B.P. Local fire histories suggested that four sites within the fir zone escaped fire during the Holocene. Such fire protected sites allowed the continuous maintenance of the balsam fir forest in the southern boreal landscape. Stands of the spruce zone have been affected by recurrent fires from 5000 cal. yr B.P. to present. Local fire histories indicated that no site escaped fire in this zone. Published palaeoecological data suggested that balsam fir migrated to its current northern limit sometime between 7300 and 6200 cal. yr B.P. A change of the fire regime 5000 years ago caused the regional decline of an historical northern balsam fir forest and its replacement by black spruce forest. The consequence was a sub-continental reshuffling of the fir and spruce zones within the closed-crown boreal forest. The macrofossil analysis of charcoal in mineral soils was instrumental to the reconstruction of stand-scale Holocene fire history at sites where no other in situ fire proxies were available.  相似文献   

6.
Natural gas reservoirs in organic-rich shales in the Appalachian and Michigan basins in the United States are currently being produced via hydraulic fracturing. Stratigraphically-equivalent shales occur in the Canadian portion of the basins in southwestern Ontario with anecdotal evidence of gas shows, yet there has been no commercial shale gas production to date. To provide baseline data in the case of future environmental issues related to hydraulic fracturing and shale gas production, such as leakage of natural gas, saline water, and/or hydraulic fracturing fluids, and to evaluate hydrogeochemical controls on natural gas accumulations in shallow groundwater in general, this study investigates the origin and distribution of natural gas and brine in shallow aquifers across southwestern Ontario. An extensive geochemical database of major ion and trace metal chemistry and methane concentrations of 1010 groundwater samples from shallow, domestic wells in bedrock and overburden aquifers throughout southwestern Ontario was utilized. In addition, select wells (n = 36) were resampled for detailed dissolved gas composition, δ13C of CH4, C2, C3, and CO2, and δD of CH4. Dissolved gases in groundwater from bedrock and overburden wells were composed primarily of CH4 (29.7–98.6 mol% of total gas volume), N2 (0.8–66.2 mol%), Ar + O2 (0.2–3.4 mol%), and CO2 (0–1.2 mol%). Ethane was detected, but only in low concentrations (<0.041 mol%), and no other higher chain hydrocarbons were present, except for one well in overburden overlying the Dundee Formation, which contained 0.81 mol% ethane and 0.21 mol% propane. The highest methane concentrations (30 to >100 in situ % saturation) were found in bedrock wells completed in the Upper Devonian Kettle Point Formation, Middle Devonian Hamilton Group and Dundee Formation, and in surficial aquifers overlying these organic-rich shale-bearing formations, indicating that bedrock geology is the primary control on methane occurrences. A few (n = 40) samples showed Na–Cl–Br evidence of brine mixing with dilute groundwater, however only one of these samples contained high (>60 in situ % saturation) CH4. The relatively low δ13C values of CH4 (−89.9‰ to −57.3‰), covariance of δD values of CH4 and H2O, positive correlation between δ13C values of CH4 and CO2, and lack of higher chain hydrocarbons (C3+) in all but one dissolved gas sample indicates that the methane in groundwater throughout the study area is primarily microbial in origin. The presence or absence of alternative electron acceptors (e.g. dissolved oxygen, Fe, NO3, SO4), in addition to organic substrates, controls the occurrence of microbial CH4 in shallow aquifers. Microbial methane has likely been accumulating in the study area, since at least the Late Pleistocene to the present, as indicated by the co-variance and range of δD values of CH4 (−314‰ to −263‰) and associated groundwater (−19‰ to −6‰ δD-H2O).  相似文献   

7.
《Quaternary Science Reviews》2007,26(13-14):1695-1712
The impact of the 8.2 ka cooling event during the Early–Mid Holocene has not been widely observed in Southern Europe, which in contrast to Northern Europe, was already experiencing a cooler than present climate at this time. Multi-proxy analysis of sediment cores from two closed-basin saline lakes in the Central Ebro Desert (NE Spain) has allowed us to investigate the impact of climatic changes around the time of this event in more detail. Long-term changes in climate between the Early and Mid Holocene indicate a shift in winter to a more positive NAO, resulting in declining lake levels in one lake sensitive to winter groundwater recharge, and cooler winter temperatures reconstructed from pollen–climate analysis. Reconstructed summer temperatures also declined over this period while annual precipitation and forest cover increased, interpreted as a result of enhanced convection-driven summer precipitation association with a northward displacement of the sub-tropical high pressure. Around 8.2 ka, a marked increase in fire frequency is shown between ca 8.8 and 8.0 ka BP, along with an expansion of fire-tolerant evergreen oak and peak in water levels in a second storm run-off fed lake. A maximum in fire intensity occurred with the deposition of a charcoal layer at both lake sites dated to 8150±130 and 8285±135 cal BP, respectively. The increase in fire is largely attributed to a temporary return southward of the summer sub-tropical high pressure over the Mediterranean, which not only increased summer aridity, but also caused a contradictory regional warming before Hemispheric cooling set in.  相似文献   

8.
Stratigraphic analyses and radiocarbon geochronology of alluvial deposits exposed along the Roaring River, Colorado, lead to three principal conclusions: (1) the opinion that stream channels in the higher parts of the Front Range are relics of the Pleistocene and nonalluvial under the present climate, as argued in a water-rights trial USA v. Colorado, is untenable, (2) beds of clast-supported gravel alternate in vertical succession with beds of fine-grained sediment (sand, mud, and peat) in response to centennial-scale changes in snowmelt-driven peak discharges, and (3) alluvial strata provide information about Holocene climate history that complements the history provided by cirque moraines, periglacial deposits, and paleontological data. Most alluvial strata are of late Holocene age and record, among other things, that: (1) the largest peak flows since the end of the Pleistocene occurred during the late Holocene; (2) the occurrence of a mid- to late Holocene interval (~ 2450–1630(?) cal yr BP) of warmer climate, which is not clearly identified in palynological records; and (3) the Little Ice Age climate seems to have had little impact on stream channels, except perhaps for minor (~ 1 m) incision.  相似文献   

9.
Alluvial and lacustrine sediments exposed beneath late Pleistocene glaciolacustrine silt and clay at two sites along the Old Crow River, northern Yukon Territory, are rich in fossils and contain tephra beds. Surprise Creek tephra (SZt) occurs in the lower part of the alluvial sequence at CRH47 and Little Timber tephra (LTt) is present near the base of the exposure at CRH94. Surprise Creek tephra has a glass fission-track age of 0.17 ± 0.07 Ma and Little Timber tephra is 1.37 ± 0.12 Ma. All sediments at CRH47 have a normal remanent magnetic polarity and those near LTt at CRH94 have a reversed polarity — in agreement with the geomagnetic time scale. Small mammal remains from sediments near LTt support an Early Pleistocene age but the chronology is not so clear at CRH47 because of the large error associated with the SZt age determination. Tephrochronological and paleomagnetic considerations point to an MIS 7 age for the interglacial beds just below SZt at CRH47 and at Chester Bluffs in east-central Alaska, but mammalian fossils recovered from sediments close to SZt suggest a late Irvingtonian age, therefore older than MIS 7. Further studies are needed to resolve this problem.  相似文献   

10.
Forty-eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern Vancouver Island, British Columbia. Sea level fell rapidly from its high stand of about +75 m elevation just before 14 000 cal BP (12 000 radiocarbon yrs BP) to below the present shoreline by 13 200 cal BP (11 400 radiocarbon years BP). The sea fell below its present level 1000 years later in the central Strait of Georgia and 2000 years later in the northern Strait of Georgia, reflecting regional differences in ice sheet retreat and downwasting. Direct observations only constrain the low stand to be below ?11 m and above ?40 m. Analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the Cascadia subduction zone, however, places the low stand at ?30 ± 5 m at about 11 200 cal BP (9800 BP). The inferred low stand for southern Vancouver Island, when compared to the sea-level curve previously derived for the central Strait of Georgia to the northwest, generates differential isostatic depression that is consistent with the expected crustal response between the two regions. Morphologic and sub-bottom features previously interpreted to indicate a low stand of ?50 to ?65 m are re-evaluated and found to be consistent with a low stand of ?30 ± 5 m. Submarine banks in eastern Juan de Fuca Strait were emergent at the time of the low stand, but marine passages persisted between southern Vancouver Island and the mainland. The crustal uplift presently occurring in response to the Late Pleistocene collapse of the southwestern sector of the Cordilleran Ice Sheet amounts to about 0.1 mm/yr. The small glacial isostatic adjustment rate is a consequence of low-viscosity mantle in this tectonically active region.  相似文献   

11.
The Holocene and late Pleistocene environmental history of the teri (‘sandy waste’ in local parlance) red sands in the southeast coastal Tamil Nadu was examined using remote sensing, stratigraphy, and optically stimulated luminescence (OSL) dating. Geomorphological surveys enabled the classification of the teri red sands as, 1) inland fluvial teri, 2) coastal teri and, 3) near-coastal teri dunes. The inland teri sediments have higher clay and silty-sand component than the coastal and near-coastal teri, suggesting that these sediments were deposited by the fluvial process during a stronger winter monsoon around > 15 ka. The coastal teri dunes were deposited prior to 11.4 ± 0.9 ka, and the near-coastal dunes aggraded at around 5.6 ± 0.4 ka. We interpret that the coastal dunes were formed during a period of lower relative sea level and the near-coastal dunes formed during a period of higher sea level. Dune reddening is post deposition occurred after 11.4 ± 0.9 ka for the coastal teri dunes and after 5.6 ± 0.4 ka for the near-coastal teri dunes. Presence of microlithic sites associated with the coastal dunes suggest that the cultures existed in the region during 11.4 ± 0.9 ka and 5.6 ± 0.4 ka.  相似文献   

12.
The subalpine to montane zones within the Critical Zone (CZ) of the Colorado Front Range, USA outside Pleistocene glaciation limits are characterized by the abundance of stratified and multilayered slope deposits exhibiting depths >1 m. Initial luminescence dating for the upper sediment layers in different profiles give last glacial ages ranging between 40 and 12 ka. A periglacial origin by solifluction is hypothesized for these slope deposits, which is corroborated by geomorphic and sedimentologic parameters. The stratified slope sediments have a strong influence on the physical and chemical properties as well as on soil forming processes in the CZ. Examples are provided for the sediment derived contribution of some elements and common clay minerals together and the great importance of slope sediments as barriers and pathways for the interflow that runs in sediment layers are shown.  相似文献   

13.
Located on a mountain pass in the west-central Pyrenees, the Col d'Ech peat bog provides a Holocene fire and vegetation record based upon nine 14C (AMS) dates. We aim to compare climate-driven versus human-driven fire regimes in terms of frequency, fire episodes distribution, and impact on vegetation. Our results show the mid-Holocene (8500–5500 cal yr BP) to be characterized by high fire frequency linked with drier and warmer conditions. However, fire occurrences appear to have been rather stochastic as underlined by a scattered chronological distribution. Wetter and colder conditions at the mid-to-late Holocene transition (4000–3000 cal yr BP) led to a decrease in fire frequency, probably driven by both climate and a subsequent reduction in human land use. On the contrary, from 3000 cal yr BP, fire frequency seems to be driven by agro-pastoral activities with a very regular distribution of events. During this period fire was used as a prominent agent of landscape management.  相似文献   

14.
Irene Zembo 《Sedimentary Geology》2010,223(3-4):206-234
The sedimentary record of the Val d'Agri basin is of great importance for understanding the Quaternary tectonic activity and climatic variability in the Southern Apennines. Changes in tectonic controls, sediment supply and climatic input have been identified. The interval from ～ 56 to ～ 43 ka was associated with asymmetric subsidence restricted to the north-eastern actively faulted margin of the basin and development of axial braided river and transverse alluvial fan systems. Short-lasting Mediterranean-type pedogenesis between ～ 43 and ～ 32 ka (MIS Stage 3) coexisted with progradation–aggradation of the southern alluvial fan deposits and southwards tilting of the basin floor. Aggradation ended with consumption of accommodation space after 32 ka. During a subsequent stage of decline of vegetation cover, possibly as a consequence of climatic cooling (probably MIS Stage 2), active progradation of alluvial fans occurred. Breakthrough of the basin threshold and entrenchment of the drainage network must therefore be attributed to a latest Pleistocene to Holocene age. The first stages of basin opening and fill, predating ～ 56 ka have only been inferred by stratigraphic considerations: the earliest lacustrine sedimentation should be middle Pleistocene or older in age. The following south-eastward basin widening allowed progradation of alluvial fan systems, which completely filled the lacustrine area (tentatively late middle Pleistocene). Pedogenesis in “Mediterranean-like” climate conditions caused the final development of a highly mature fersiallitic paleosol at the top of the fan surfaces, in areas of morpho-tectonic stability, plausibly during MIS Stage 5. The study results demonstrate the potential of applying a multidisciplinary approach in an intermontane continental settings marked by a relative rapid and constant tectonic subsidence and a high rate of sediment supply during the Pleistocene glacial–interglacial cycles.  相似文献   

15.
Recent changes along the margins of the Antarctic Peninsula, such as the collapse of the Wilkins Ice Shelf, have highlighted the effects of climatic warming on the Antarctic Peninsula Ice Sheet (APIS). However, such changes must be viewed in a long-term (millennial-scale) context if we are to understand their significance for future stability of the Antarctic ice sheets. To address this, we present nine new cosmogenic 10Be exposure ages from sites on NW Alexander Island and Rothschild Island (adjacent to the Wilkins Ice Shelf) that provide constraints on the timing of thinning of the Alexander Island ice cap since the last glacial maximum. All but one of the 10Be ages are in the range 10.2–21.7 ka, showing a general trend of progressive ice-sheet thinning since at least 22 ka until 10 ka. The data also provide a minimum estimate (490 m) for ice-cap thickness on NW Alexander Island at the last glacial maximum. Cosmogenic 3He ages from a rare occurrence of mantle xenoliths on Rothschild Island yield variable ages up to 46 ka, probably reflecting exhumation by periglacial processes.  相似文献   

16.
《Journal of Structural Geology》2001,23(6-7):1007-1013
The phenomenon of shear-heating is generally difficult to recognise from petrologic evidence alone. Establishing that shear zones attain higher temperatures than the surrounding country rocks requires independent evidence for temperature gradients. In the Musgrave Block, central Australia, there is a clear spatial association between shear zones and interpreted elevated temperatures. Eclogite facies shear zones that formed at ∼550 Ma record temperatures of ∼650–700°C. Outside the high-pressure shear zones, minerals with low closure temperatures such as biotite (∼450°C in the 40Ar–39Ar and Rb–Sr systems), preserve ages >800 Ma, suggesting that these rocks did not experience temperatures greater than about 450°C at ∼550 Ma for any extended period. Thus, the shear zones record temperatures that are ∼200°C higher than the surrounding country rocks. Simple calculations show that the combination of relatively high shear stresses (∼100 MPa) and high strain rates (∼10−11 s−1) for short durations (<1 Ma) can account for the observed apparent temperature variations. The evidence indicates that shear heating is the dominant mechanism for localised temperature increases in the shear zones, while the country rock remained at relatively lower temperatures.  相似文献   

17.
Ancient cave systems in the Northern Calcareous Alps, today located well above the timberline at altitudes of 2400–2500 m, host U-rich speleothems that preserved growth layers on the microscopic scale of presumably annual origin. Two flowstone samples were dated to 2.019 + 0.037/?0.069 Ma and 1.730 + 0.032/?0.068 Ma, respectively, using U–Pb isochron techniques. These ages are corroborated by the Late Pliocene to Early Pleistocene pollen spectrum extracted from one of the samples. We use a multiproxy approach and exploit laminated speleothem sequences to tie high-resolution stable isotope data to a floating lamina-counted chronology. O isotope values of growth intervals when calcite deposition was close to isotopic equilibrium are low compared to modern and Holocene speleothems from other alpine caves and are inconsistent with the current altitudinal setting of the caves. A vegetated but geomorphologically stable alpine catchment (i.e. ～2000 m asl., no (peri)glacial processes) combined with a deep-seated cave (the thickness of the vadose zone might have exceeded 1000 m) is required in order to reconcile the isotopic data with the pollen record and the petrographic evidence. Furthermore, the data can be used to constrain the rate for Quaternary rock-uplift to ≤0.8 mm/annum for this frontal part of the European Alps. Collectively, the data suggest that these speleothems formed both during interglacials (MIS 59 or 61) and interglacial–glacial transitions (MIS 75/74 or 77/76), but the seasonal precipitation pattern was arguably markedly different from today's. Provided that the highly regular microscopic laminae are indeed annual, lamina counts suggest a minimum length of ca 6 ka for interglacials during the earliest Pleistocene.  相似文献   

18.
《Applied Geochemistry》2005,20(1):55-68
In 49 samples of groundwater, sampled in Muzaffargarh District of south-western Punjab, central Pakistan, concentrations of As exceeded the World Health Organisation provisional guideline value, and United States Environmental Protection Agency (USEPA) Maximum Contaminant Level (MCL), of 10 μg L−1 in 58% of samples and reached up to 906 μg L−1. In this semi-arid region canal irrigation has lead to widespread water-logging, and evaporative concentration of salts has the potential to raise As concentrations in shallow groundwater well above 10 μg L−1. In fact, in rural areas, concentrations stay below 25 μg L−1 because As in the oxic shallow groundwater, and in recharging water, is sorbed to aquifer sediments. In some urban areas, however, shallow groundwater is found to contain elevated levels of As. The spatial distribution of As-rich shallow groundwater indicates either direct contamination with industrial or agricultural chemicals, or some other anthropogenic influence. Geochemical evidence suggests that pollutant organics from unconfined sewage and other sources drives reduction of hydrous ferric oxide (HFO) releasing sorbed As to shallow groundwater. The situation is slightly less clear for seven wells sampled which tap deeper groundwater, all of which were found with >50 μg L−1 As. Here As concentrations seem to increase with depth and differing geochemical signatures are seen, suggesting that As concentrations in older groundwater may be governed by different processes. Other data on parameters of potential concern in drinking water are discussed briefly at the end of the paper.  相似文献   

19.
Large-scale fluctuations in global climate and resulting changes in ecology had a profound effect on human evolution and dispersal. Though hominin remains are scarce, studies focussing on the more abundant records of fossil land mammal communities can contribute greatly to our knowledge of the palaeoenvironmental circumstances that influenced and directed the global spread of hominins. To produce a comprehensive and accurate account of the evolution of western Palaearctic habitat diversity between 2.6 and 0.4 Ma BP, information generated from large mammal communities from 221 key sites has been included in this study.The palaeoecological conditions of the western Palaearctic during the Early and early Middle Pleistocene were principally controlled by the following key factors: (1) a widespread trend of temperature decrease, (2) the periodicity of the global temperature record, (3) the intensity of single climatic stages, (4) the temporal pattern of climatic variation, (5) geographical position, and (6) the distribution of continental water resources. A general picture of the evolution of western Palaearctic habitat diversity saw the replacement of extensive forested terrain by an alternating sequence of varied savannah-like and forested habitats during the 2.6–1.8 Ma span, as well as an alternation between different types of predominantly open habitats between 1.8 and 1.2 Ma. Both of these processes were governed by 41 ka temperature periodicity. During the 1.2–0.9 Ma time span, irregular climatic fluctuations were more common and habitat variability increased. The subsequent 0.9–0.4 Ma interval, a period controlled by 100 ka periodicity, was by comparison more stable, with longer climatic cycles alternating between open and forested landscapes. During the entire Early and early Middle Pleistocene, assemblages of large mammal communities reveal a distinct trend of decreasing continentality between Eastern and South-Eastern Europe on the one hand, and South-Western and North-Western Europe on the other. This trend was due to the effect of the Atlantic Ocean, while in Southern Europe the relatively low continentality was balanced by influences from the Mediterranean Sea.When plotted against evidence of hominin occurrence, the data on western Palaearctic habitat diversity inferred from large mammal communities indicate clear environmental stimuli for the earliest human dispersal in Europe. These are: (1) a wide range of habitats, implying a high diversity of resources; (2) mild climates with low seasonality, implying a lack of strong environmental fluctuations. Around 1.8 Ma at the latest, hominins of African origin entered the western Palaearctic for the first time, taking advantage of the diversity of habitats and resources, particularly along large river systems. Their subsequent westward spread between 1.7 and 1.3 Ma was restricted to Mediterranean-influenced areas, which offered a high variability of habitats and relatively low seasonality. The increase in environmental diversity, which occurred from 1.2 Ma onwards, opened up South-Eastern and Eastern Europe for hominin occupation. According to the available records, North-Western and Central Europe were initially colonized during late Early to early Middle Pleistocene interglacials, when these regions experienced periods of low seasonality and considerable habitat diversity.  相似文献   

20.
《Quaternary Science Reviews》2007,26(17-18):2067-2089
The continental vertebrate fauna of Cúllar Baza-1 (Granada, Spain) occur immediately above the Matuyama/Brunhes polarity boundary, and therefore represent an initial record for the Middle Pleistocene. All polarity zones for the Late Pliocene through Middle Pleistocene are found in an 80 m section, which includes this fossil quarry. The existing collection of abundant remains of micro-mammals, macro-mammals and lithic artifacts (indicating human activity) can now be assigned an earliest Middle Pleistocene age of 0.75 Ma. Another section, 25 km across the Neogene Baza Basin, also has the Matuyama/Brunhes polarity boundary. However, in this case the Huéscar-1 fossil quarry and the Puerto Lobo sites are both below the polarity boundary, thus representing a record of the late Early Pleistocene at ∼0.9 Ma. Differences in micro-mammal species across these Matuyama/Brunhes boundaries are significant and justify an approximately coincident biostratigraphic boundary between the Biharian and Toringian stages.  相似文献   

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