首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Palaeontological deposits on Rusinga Island, Lake Victoria, Kenya, provide a rich record of floral and faunal evolution in the early Neogene of East Africa. Yet, despite a wealth of available fossil material, previous palaeoenvironmental reconstructions from Rusinga have resulted in widely divergent results, ranging from closed forest to open woodland environments. Presented here is a detailed study of the sedimentology and fauna of the early Miocene Hiwegi Formation at Waregi Hill on Rusinga Island, Kenya. New sedimentological analyses demonstrate that the Hiwegi Formation records an environmental transition from the bottom to the top of the formation. Lower in the Hiwegi Formation, satin-spar calcite after gypsum in siltstone deposits are interpreted as evidence for open hypersaline lakes. Moving up-section, carbonate deposits – interpreted previously as evidence of aridity – are actually diagenetic calcite cements, which preserve root systems of trees, suggesting a more closed environment; further up-section, the uppermost palaeosol layer contains abundant root traces and tree-stump casts, previously reported as evidence of a closed-canopy forest. These newly interpreted environmental differences are reflected by differences in faunal composition and abundance data from Hiwegi Formation fossil sites R1 and R3. Taken together, this work suggests that divergent palaeoenvironmental reconstructions in previous studies may have been informed by time-averaging across multiple environments. Further, results demonstrate that during the early Miocene local or regional habitat heterogeneity already existed. Rusinga’s Hiwegi Formation varied both spatially and temporally, which challenges the interpretation that a broad forested environment stretched across the African continent during the early Neogene, transitioning later to predominately open landscapes that characterize the region today. This result has important implications for interpretations of the selective pressures faced by early Miocene fauna, including Rusinga Island’s well-preserved fossil primates.  相似文献   

2.
The effect of changing palaeoclimate and palaeoenvironment on human evolution during the Pleistocene is debated, but hampered by few East African records directly associated with archaeological sites prior to the Last Glacial Maximum. Middle to Late Pleistocene deposits on the shoreline of eastern Lake Victoria preserve abundant vertebrate fossils and Middle Stone Age arte‐facts associated with riverine tufas at the base of the deposits, which are ideal for palaeoenvironmental reconstructions. New data from tufas identified on Rusinga Island and on the mainland near Karungu, Kenya are provided from outcrop, thin sections, mineralogical, stable isotopic and U‐series dating analyses. Tufa is identified in four sites: Nyamita (94·0 ± 3·3 and 111·4 ± 4·2 ka); Kisaaka, Aringo (455 ± 45 ka); and Obware. The age ranges of these tufa deposits demonstrate that spring‐fed rivers were a recurrent, variably preserved feature on the Pleistocene landscape for ca 360 kyr. Poor sorting of clastic facies from all sites indicates flashy, ephemeral discharge, but these facies are commonly associated with barrage tufas, paludal environments with δ13C values of ca 10‰ indicative of C3 plants and fossil Hippopotamus, all of which indicate a perennial water source. Other tufa deposits from Nyamita, Obware and Aringo have a mixed C3/C4 signature consistent with a semi‐arid C4 grassland surrounding these spring‐fed rivers. The δ18O values of tufa from Nyamita are on average ca 1‰ more negative than calcite precipitated from modern rainfall in the region, suggesting greater contribution of depleted monsoonal input, similar to the Last Glacial Maximum. Microdebitage and surface‐collected artefacts indicate that early modern humans were utilizing these spring‐fed rivers. The presence of spring?fed rivers would have afforded animals a reliable water source, sustaining a diverse plant and animal community in an otherwise arid environment.  相似文献   

3.
Four genera and one indeterminate genus (total eight species) of fossil rhinoceroses (Mammalia; Perissodactyla; Rhinocerotidae) are recognized from the Neogene of central Myanmar. In the early Miocene, most area of central Myanmar were under the shallow marine condition, and no rhinocerotid remain has been documented yet. During the middle to late Miocene, the rhinocerotid remains are commonly found and are represented by “Diceratherium” naricum, Brachypotherium perimense, Brachypotherium fatehjangense and an indeterminate rhinocerotid. In the latest Miocene, these archaic rhinoceroses became extinct. In the late Neogene, the extant genera, Rhinoceros (late Miocene to Pleistocene) and Dicerorhinus (Plio-Pleistocene) first appeared in Myanmar. They appear to have dispersed to the Island Southeast Asia from the continental Asia during the early Pleistocene to middle Pleistocene when the eustatic sea level became low remarkably.  相似文献   

4.
The evolution of Elephantidae has been intensively studied in the past few years, especially after 2006. The molecular approaches have made great contribution to the assumption that the extinct woolly mammoth has a close relationship with the Asian elephant instead of the African elephant. In this study, partial ancient DNA sequences of cytochrome b (cyt b) gene in mitochondrial genome were successfully retrieved from Late Pleistocene Mammuthus primigenius bones collected from Heilongjiang Province in Northeast China. Both the partial and complete homologous cyt b gene sequences and the whole mitochondrial genome sequences extracted from GenBank were aligned and used as datasets for phylogenetic analyses. All of the phylogenetic trees, based on either the partial or the complete cyt b gene, reject the relationship constructed by the whole mitochondrial genome, showing the occurrence of an effect of sequence length of cyt b gene on mammoth phylogenetic analyses.  相似文献   

5.
Stanford, S. D. 2009: Onshore record of Hudson River drainage to the continental shelf from the late Miocene through the late Wisconsinan deglaciation, USA: synthesis and revision. Boreas, 10.1111/j.1502‐3885.2009.00106.x. ISSN 0300‐9483. Fluvial and glacial deposits in New Jersey, Long Island, and the Hudson valley provide a record of Hudson River drainage since the late Miocene. Late Miocene fluvial deposits record southerly flow across the emerged inner New Jersey shelf. In the late Miocene–early Pliocene this drainage incised, shifted southwesterly, and discharged to the shelf south of New Jersey. During late Pliocene or Early Pleistocene glaciation, discharge to the shelf in the New York City area was established. This drainage incised and stabilized in the Early and Middle Pleistocene and remained open during pre‐Wisconsinan (Oxygen Isotope Stage 6? (OIS‐6?)) and late Wisconsinan (OIS‐2) glacial advances. During late Wisconsinan retreat, moraine deposits dammed the valley at the Narrows to form Lake Albany. From 19 to 15.5 kyr BP (all dates in 14C yr), Hudson drainage was directed eastward into the Long Island Sound lowland. Drainage of Lake Wallkill into Lake Albany at 15.5 kyr BP breached the Narrows dam and initiated the unstable phase of Lake Albany, which was controlled by eroding spillways, first on the moraine dam, then on emerged lake‐bottom in the mid‐Hudson valley. Marine incursion between 12 and 11 kyr BP limited fluvial incision of the lake bottom, stabilizing the Quaker Springs, Coveville, and upper Fort Ann spillways. Lowering sea level between 11 and 10 kyr BP allowed incision from the upper to lower Fort Ann threshold. Sediment eroded by lake outflows between 15 and 10.5 kyr BP was trapped in the glacially deepened lower valley. Little inland sediment reached the shelf after 20 kyr BP.  相似文献   

6.
Competition between taxa related to climate changes has been proposed as a possible factor in Pleistocene megafaunal extinctions, and here we present isotope evidence of the diets of three co-existing bear species [black bear (Ursus americanus), brown bear (Ursus arctos), and the now extinct short-faced bear (Arctodus simus)] from a locale in western North America dating to the Late (Terminal) Pleistocene (~14.5–11.7 ka). The three bear species were found at several sites on Vancouver Island, on the western coast of Canada. To examine the chronological overlap and niche partitioning between these species of bear, we used direct radiocarbon dating, stable isotope analysis and ZooMS proteomic identification methods. Here we present new radiocarbon evidence from Terminal Pleistocene U. americanus, U. arctos and A. simus from several sites on the island, along with both bulk collagen and compound-specific isotope data for these species. Radiocarbon dates confirm the chronological overlap of Arctodus and both Ursus species in the montane regions of the island at the end of the Pleistocene. Stable isotope data reveal niche differentiation between these species, with U. americanus occupying a distinctly lower trophic position than the other two taxa.  相似文献   

7.
Two previously undocumented Pleistocene marine transgressions on Wrangel Island, northeastern Siberia, question the presence of an East Siberian or Beringian ice sheet during the last glacial maximum (LGM). The Tundrovayan Transgression (459,000–780,000 yr B.P.) is represented by raised marine deposits and landforms 15–41 m asl located up to 18 km inland. The presence of high sea level 64,000–73,000 yr ago (the Krasny Flagian Transgression) is preserved in deposits and landforms 4–7 m asl in the Krasny Flag valley. These deposits and landforms were mapped, dated, and described using amino acid geochronology, radiocarbon, optically stimulated luminescence, electron spin resonance, oxygen isotopes, micropaleontology, paleomagnetism, and grain sizes. The marine deposits are eustatic and not isostatic in origin. All marine deposits on Wrangel Island predate the LGM, indicating that neither Wrangel Island nor the East Siberian or Chukchi Seas experienced extensive glaciation over the last 64,000 yr.  相似文献   

8.
The Cape grysbok is endemic to southern Africa's Cape Floral Region where it selectively browses various species of dicotyledonous vegetation. Fossil evidence indicates that the grysbok persisted under glacial and interglacial conditions throughout the late Quaternary and inhabited a range of environments. This study employs mesowear analysis to reconstruct grysbok diets over time and in response to changing environments at Nelson Bay Cave, Die Kelders Cave 1, Klasies River Mouth, and Swartklip 1. Results indicate that the amount of grasses (monocots) versus leafy vegetation (dicots) included in the diet fluctuated over time and largely in agreement with changes in faunal community structure. The case for dietary flexibility is particularly clear at Nelson Bay Cave, where there is a significant trend from mixed feeding towards increased browsing from the late Pleistocene (~ 18,500 14C yr BP) through the Holocene. Dietary shifts at Nelson Bay Cave are consistent with the hypothesis that declining grassland productivity is responsible for the terminal Pleistocene extinction of several large ungulates in southern Africa. Furthermore, the short-term dietary shifts demonstrated here (100s to 1000s of years) provide an important caution against relying on taxonomic uniformitarianism when reconstructing the dietary preferences of fossil ungulates, both extant and extinct.  相似文献   

9.
Palaeolithic people commonly hunted Equus hydruntinus, an extinct species of equid whose cursorial body proportions suggest an adaptation to semi-arid conditions. Despite the frequency with which it is encountered in fossil deposits, only partial cranial remains have been reported until now. As a result, the systematic affiliation of the species remains a subject of controversy. Two nearly complete E. hydruntinus crania are presented here for the first time. These skulls show that E. hydruntinus is a distinct species, more closely related to the hemiones (Asiatic asses) than to any other equid. This suggests that the social organisation of E. hydruntinus followed one of two known equid sociotypes: resource defense territoriality.  相似文献   

10.
At the close of the Pleistocene, fire regimes in North America changed significantly in response to climate change, megafaunal extinctions, anthropogenic burning and, possibly, even an extraterrestrial impact. On California's Channel Islands, researchers have long debated the nature of late Pleistocene “fire areas,” discrete red zones in sedimentary deposits, interpreted by some as prehistoric mammoth-roasting pits created by humans. Further research found no evidence that these red zones were cultural in origin, and two hypotheses were advanced to explain their origin: natural fires and groundwater processes. Radiocarbon dating, X-ray diffraction analysis, and identification of charcoal from six red zones on Santa Rosa Island suggest that the studied features date between ~ 27,500 and 11,400 cal yr BP and resulted from burning or heating, not from groundwater processes. Our results show that fire was a component of late Pleistocene Channel Island ecology prior to and after human colonization of the islands, with no clear evidence for increased fire frequency coincident with Paleoindian settlement, extinction of pygmy mammoths, or a proposed Younger Dryas impact event.  相似文献   

11.
The Clyde Foreland Formation is defined as comprising unconsolidated or only slightly consolidated deposits, varying in grain size from very coarse boulder gravel to clay, situated between the outermost part of Clyde Inlet and the coastal mountains west-northwest of Kogalu River on the northeast coast of Baffin Island, Arctic Canada. They outcrop in an up to 40 m high almost straight-lined coastal cliff facing Baffin Bay and are composed of mainly marine deposits interbedded with glacigenic layers. Investigation of assemblages of fossil foraminifera revealed three main stratigraphical units of the marine deposits, viz., the hlandiella zone, being the youngest, the Cibicides rotundatus zone, and the Nonion tallahattensis zone, being the oldest. The hlandiella zone is supposed to be upper Pleistocene of age, comprising a large Mid-Wisconsinian (Mid-Weichselian) interstadial, and an interglacial that can be correlated with the Sangamonian (Eemian) interglacial. The Cibicides rotundatus zone may comprise Illinoian interstadial deposits as well as deposits of Yarmouthian (Holsteinian) interglacial age. The Nonion tallahattensis zone represents an older (Aftonian?) mild interval.  相似文献   

12.
Discussions of dispersals of early hominins from Africa assume that Southwest Asia and the Arabian Peninsula were the primary passageways for migrations to Eurasia. The Mediterranean is usually viewed as a barrier to early hominin movements because pre‐sapiens hominins were thought to lack the technical means or the cognitive skills to construct boats. The discovery of early Palaeolithic artefacts in an archaeological survey on the Greek island of Crete challenges this view. Here we show that Palaeolithic artefacts in the Plakias region in southwestern Crete are associated with geological contexts that can be dated to the late Middle or early Late Pleistocene. Because Crete has been separated from the mainland throughout the Pleistocene, the presence of Pleistocene age artefacts there suggests that early hominins were able to cross open water. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

13.
Sediment-hosted uranium ores at Henkries in northwest South Africa occur in fine-grained sands, carbonaceous muds and diatomaceous earth within late Pleistocene lake deposits. The lakes are linked by short fluvial channel reaches and these aqueous beds are encompassed in predominant aeolian dune deposits. The late Pleistocene fluvial-lacustrine-aeolian succession is succeeded by a Holocene dune cover. Textural characterisation of lacustrine, fluvial and aeolian sands was based on volume percentages observed in sediment settling tubes. Vortex action during Holocene dune migration contaminated these aeolian cover sands with small amounts of substrate material, whose presence could be detected in settling tube patterns of surface aeolian sediment samples. It was thus possible to map buried lacustrine ore bodies, which were shown, by a successful drilling programme, to be displaced downwind. Received: 28 August 1996 / Accepted: 3 September 1996  相似文献   

14.
A pollen record from a sediment core drilled underneath the Acheulian site of Fontana Ranuccio provides new data on the vegetation characters in central Italy during the late Early Pleistocene, in a forest phase possibly corresponding to a substage of Marine Isotope Stage 21. A number of tree taxa nowadays extinct in Europe (Cathaya, Tsuga, Taxodium type, Carya and Pterocarya) are present at Fontana Ranuccio in a temperate phase characterised by dense forest conditions, dominated by Alnus and Pterocarya. The comparison of the Fontana Ranuccio record with other dated sites distributed along the Italian peninsula indicates that the floristic and vegetational characters of the Mid Pleistocene revolution present a rather distinct succession of biostratigraphic events. Compared to other Early Pleistocene pollen records from southern Europe, the Italian Peninsula shows greater floristic similarities with the Eastern Mediterranean regions than with the Iberian Peninsula. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
The three sedimentary units infilling Lake George provide the longest quasi-continuous sedimentary record of any Australian lake basin. A combination of cosmogenic nuclide burial, magnetostratigraphy and biostratigraphic dating techniques previously has shown that the basal (fluvial) unit, the Gearys Gap Formation, began accumulating at ca 4 Ma, in the early Pliocene (Zanclean), and (ii) deposition had ceased by ca 3 Ma, in the mid-late Pliocene (Piacenzian). The same techniques confirm the middle unit, the (fluvio-lacustrine) Ondyong Point Formation began accumulating in the late Pliocene and deposition continued into the earliest Pleistocene (Gelasian) when a shallow but probably laterally extensive freshwater lake extended across the drillhole site. Our data provide a minimum Gelasian age for tectonic blockage of former spillway(s) and formation of paleo-Lake George. Whether this was the earliest lake to form within the basin is unknown, since the dated intervals are separated by a ferric hardpan, interpreted as representing a prolonged period of erosion or non-deposition. Temperate rainforest angiosperms including Nothofagus growing during the late Pliocene had been extirpated or become extinct during this interval, although a number of gymnosperms, now endemic to New Caledonia, New Guinea, New Zealand and Tasmania still survived in the otherwise sclerophyll-dominated vegetation. The succession of plant communities is considered to be due to effectively drier local conditions, which in turn reflect regional aridification during the Plio-Pleistocene transition, despite the formation of a freshwater lake across the basin. The sequence provides a reliable framework for recognising and correlating Plio-Pleistocene deposits elsewhere on the Southern Highlands.  相似文献   

16.
The Ciemas gold deposit is located in West Java of Indonesia,which is a Cenozoic magmatism belt resulting from the Indo-Australian plate subducting under the Eurasian plate.Two different volcanic rock belts and associated epithermal deposits are distributed in West Java:the younger late Miocene-Pliocene magmatic belt generated the Pliocene-Pleistocene epithermal deposits,while the older late Eocene-early Miocene magmatic belt generated the Miocene epithermal deposits.To constrain the physico-chemical conditions and the origin of the ore fluid in Ciemas,a detailed study of ore petrography,fluid inclusions,laser Raman spectroscopy,oxygen-hydrogen isotopes for quartz was conducted.The results show that hydrothermal pyrite and quartz are widespread,hydrothermal alteration is well developed,and that leaching structures such as vuggy rocks and extension structures such as comb quartz are common.Fluid inclusions in quartz are mainly liquid-rich two phase inclusions,with fluid compositions in the NaCl-H20 fluid system,and contain no or little CO_2.Their homogenization temperatures cluster around 240℃-320℃,the salinities lie in the range of 14-17 wt.%NaCl equiv,and the calculated fluid densities are 0.65-1.00 g/cm~3.The values of δ~(18)O_(H2O-VSMOW)for quartz range from +5.5‰ to +7.7‰,the δD_(VSMOW) of fluid inclusions in quartz ranges from-70‰ to-115‰.All of these data indicate that mixing of magmatic fluid with meteoric water resulted in the formation of the Ciemas deposit.A comparison among gold deposits of West Java suggests that Miocene epithermal ore deposits in the southernmost part of West Java were more affected by magmatic fluids and exhibit a higher degree of sulfldation than those of Pliocene-Pleistocene.  相似文献   

17.
The Plio‐Pleistocene non‐marine sequence in the northeast Guadix–Baza Basin (southern Spain) comprises alluvial and lacustrine deposits (Baza Formation). The results of a revised lithostratigraphical correlation between sections from the middle and upper members of the Baza Formation in the northeast part of the basin, supported by detailed mapping, is presented. The position of micromammal sites in the lithostratigraphical scheme, together with the results of intensive palaeontological sampling for small mammal remains, has allowed us to develop a high‐resolution biostratigraphical framework for the area. This provides an opportunity to refine the biozonation for the Plio‐Pleistocene micromammal faunas, and to define faunal events from the late Villanyian (late Pliocene) to the early Pleistocene. On the basis of the lithostratigraphical and biostratigraphical approaches we obtain the following sequence of biozones for the late Pliocene to early Pleistocene: Kislangia gusii, Mimomys cf. reidi, M. oswaldoreigi, Allophaiomys pliocaenicus and A. burgondiae. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

18.
The end of the Pleistocene in North America was marked by a wave of extinctions of large mammals, with the last known appearances of many species falling between ca. 11,000–10,000 14C yr BP. Temporally, this period overlaps with the Clovis Paleoindian cultural complex (11,190–10,530 14C yr BP) and with sudden climatic changes that define the beginning of the Younger Dryas chronozone (ca. 11,000–10,000 14C yr BP), both of which have been considered as potential proximal causes of this extinction event. Radiocarbon dating of enamel and filtered bone collagen from an extinct American Mastodon (Mammut americanum) from northern Indiana, USA, by accelerator mass spectrometer yielded direct dates of 10,055 ± 40 14C yr BP and 10,032 ± 40 14C yr BP, indicating that the animal survived beyond the Clovis time period and into the late Younger Dryas. Although the late survival of this species in mid-continental North America does not remove either humans or climatic change as contributing causes for the late Pleistocene extinctions, neither Clovis hunters nor the climatic perturbations initiating the Younger Dryas chronozone were immediately responsible for driving mastodons to extinction.  相似文献   

19.
In the middle and lower reaches of the Salawusu River. the Salawusu Formation regarded traditionallyas fluvio-lacustrine deposits actually includes a series of strata which mainly consist of eolian sandy depositsnamed as "Chengchuan Formation" by the authors. The eolian sand of the Chengchuan Formation and theMalan loess distributed in the upper reaches of the Salawusu River are deposits of sand and loess faciesformed by wind action during the same period. The relationship of the Chengchuan Formation and theMalan Loess with the Salawusu Formation which is really of fluvio-lacustrine deposits is that the formertwo superpose the latter. This can be demonstrated by the difference of the extinct species proportion of thefaunas in different strata. In this area. the Salawusu formed during the early period of Late Pleistocene.while the Malan Loess and the Chengchuan Formation deposited during the late period of the LatePleistocene.  相似文献   

20.
River-channel and colluvial deposits, near Marsworth, Buckinghamshire, record a temperate-periglacial-temperate sequence during the late Middle Pleistocene. The deposits of a lower channel contain tufa clasts bearing leaf impressions that include Acer sp., and Sorbus aucuparia and containing temperate arboreal pollen attributed to ash-dominated woodland. The tufa probably formed at the mouth of a limestone spring before being redeposited in a small river whose deposits contain plant remains, Mollusca, Coleoptera, Ostracoda and vertebrate bones of temperate affinities. The sediments, sedimentary structures and limited biological remains above the Lower Channel deposits indicate that fluvial deposition preceded climatic cooling into periglacial conditions. Fluvial deposition recurred during a later temperate episode, as shown by the mammalian bone assemblage in stratigraphically higher channel deposits. The Upper Channel deposits are confidently attributed to Oxygen Isotope Sub-Stage 5e (Ipswichian) on the basis of their vertebrate remains. However, the age of the Lower Channel deposits is less clear. The mammalian and coleopteran remains in the Lower Channel strongly suggest correlation with Oxygen Isotope Stage 7 on the basis of their similarities to other sites whose stratigraphy is better known and the clear difference of the Lower Channel assemblage from well-established faunas of Ipswichian or any other age. By contrast, U–Th dating of the tufa clasts suggests an age post 160 ka BP, while Aile/Ile ratios on Mollusca point to an Ipswichian age and younger. Four ways of interpreting this age discrepancy are considered, the preferred one correlating the Lower Channel deposits with Oxygen Isotope Stage 7.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号