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1.
Excavations at the Wenas Creek Mammoth Site yielded mammoth, bison, and two possible artifacts in a single colluvial stratum, with radiocarbon bone dates ∼17 ka. Eight infrared‐stimulated luminescence (IRSL) samples were collected to establish general ages of site strata, returning multi‐grain estimates consistent with stratigraphic integrity and the radiocarbon dates. Four additional IRSL samples were collected to estimate the depositional age of one artifact found in place. These produced a pooled total of 94 single‐grain estimates from near the artifact, 80% averaging 16.8 ± 0.9 ka, and 20% averaging 5.1 ± 0.5 ka. These results could be interpreted to demonstrate pre‐Clovis age artifact deposition consistent with the bone dates, or a mid to late Holocene intrusion into older deposits, possibly by bioturbation. The single‐grain IRSL dates do not provide proof of pre‐Clovis presence beyond reasonable doubt at this site, but do show that this technique is valuable in assessing the stratigraphic integrity needed for any such claim.  相似文献   

2.
The Dent site provided the first association of fluted points with mammoth bones in the New World. However, the stratigraphic integrity of the site has remained in doubt since the original excavations in 1932 and 1933. Core sampling at the Dent Clovis site indicates that the site, on Kersey terrace gravel, extends under railroad tracks adjacent to the original area of excavation. Four hundred meters south the Kuner strath terrace has been exposed by a roadcut at the Bernhardt site. An Archaic hearth dated 4030 ± 60 B.P. is near the top of a 1-m-thick eolian sand overlying 1 m of fine-grained alluvium dated 5740 ± 60 B.P., which in turn overlies sand and gravel of the Kuner strath terrace with an AMS radiocarbon age of 10,105 ± 90 B.P. The South Platte River appears to have been quasistable at the Kuner level during the Younger Dryas when Paleoindians from Clovis to Cody hunted megafauna on the Kersey terrace. © 1998 John Wiley & Sons, Inc.  相似文献   

3.
The Great Plains contain many of the best‐known Paleoindian sites in North America, and a number of these localities were key to determining the chronology of Paleoindian occupations in the years before, during, and since the development of radiocarbon and other chronometric dating methods. Initial attempts at dating were based on correlation with extinct fauna, the “geologic‐climatic” dating method, and stratigraphic relationships of artifacts within sites. By the time radiocarbon dating was developed (1950), the basic Paleoindian sequence (oldest to youngest) was: Clovis‐Folsom‐unfluted lanceolates (such as Plainview, Eden, and Scottsbluff). Initial applications of radiocarbon dating in the 1950s did little to further resolve age relationships. In the 1960s, however, largely through the efforts of C. V. Haynes, a numerical geochronology of Paleoindian occupations on the Great Plains began to emerge On the Southern Great Plains the radiocarbon‐dated artifact chronology is: Clovis (11,600–11,000 yr B.P.); Folsom and Midland (10,900–10,100 yr B.P.); Plainview, Milnesand, and Lubbock (10,200–9800 yr B.P.); Firstview (9400–8200 yr B.P.); St. Mary's Hall, Golondrina, and Texas Angostura (9200–8000 yr B.P.). The chronology for the Northern Great Plains is: Clovis (11,200–10,900 yr B.P.); Goshen (ca. 11,000 yr B.P.); Folsom (10,900–10,200 yr B.P.); Agate Basin (10,500–10,000 yr B.P.); Hell Gap (10,500–9500 yr B.P.); Alberta, Alberta‐Cody (10,200–9400 yr B.P.); Cody (Eden‐Scottsbluff) (9400–8800 yr B.P.); Angostura, Jimmy Allen, Frederick, and other parallel‐oblique types (9400–7800 yr B.P.). Fifty years after the development of radiocarbon dating, the basic typological sequence has not changed significantly except for the realization that there probably was significant temporal overlap of some point types, and that the old unilinear sequence does not account for all the known typological variation. The chronology has been continually refined with the determination of hundreds of radiocarbon ages in recent decades. © 2000 John Wiley & Sons, Inc.  相似文献   

4.
Cactus Hill is located in the Virginia Coastal Plain on a terrace above the Nottoway River. The site has a record of occupation that spans the Holocene and also offers evidence of humans late in the Pleistocene before Clovis time. Soil investigations identified several deposit types, and demonstrated that multisequal eolian sands forming the site's primary core are arrayed in spatially and temporally discrete horizons. Resting atop an ancient paleosol, the earliest sand stratum (19,540 ± 70 14C yr B.P.) is marked by a conspicuous but culturally sterile buried surface horizon. Eolian sand above this surface supports another sequum in which Clovis and underlying “Blade” artifacts are associated with a fainter surface horizon and pronounced subsoil lamellae. Early Archaic and successively younger artifacts occur above the Clovis level in a more weakly developed uppermost sequum. This soil and cultural stratigraphy, together with considerations of regional topography, demonstrate that the landscape has evolved incrementally since about the last glacial maximum. © 2004 Wiley Periodicals, Inc.  相似文献   

5.
Twenty thin sections were studied from Cactus Hill, a ca. 20 ka stratified sand dune site in Virginia, USA, with a Clovis and hypothesized pre‐Clovis component. The high‐resolution soil micromorphology investigation focused on testing the integrity of Clovis and pre‐Clovis stratigraphy from one location where there is a high density of artifacts. Site formation processes were dominated by eolian (dune) sand formation. There was also ephemeral topsoil development and associated occupation, along with their penecontemporaneous disturbance and dispersal by scavenging animals (assumed) and localized down‐working by small invertebrate mesofauna (as evidenced by aggregates of fine phytolith‐rich humic soil and fine soil‐coated charcoal fragments). Partial erosion of these occupation soils (deflation?) was followed by successive sand burial. Post‐depositional processes affecting these sand‐buried occupations involved only small‐scale bioturbation and overprinting of clay lamellae, suggesting site stratigraphy has been stable for a long time. Soil micromorphological analysis has defined a difference between occupational units (pre‐Clovis and Clovis) and sterile units found between these units as well as above and below. In summary, according to this analysis, the site appears intact with only minor disturbances affecting the long‐term integrity of the stratigraphy. © 2008 Wiley Periodicals, Inc.  相似文献   

6.
An enigmatic circular pit uncovered during archaeological excavations at the Clovis type site, Blackwater Draw, New Mexico, in 1964 has been reexposed and posited as a water well excavated by Clovis people around 11,500 B.C. The prehistoric well, the oldest in the New World, was probably a dry hole. Other Clovis wells may exist in the area. The excavation of wells near where there had been surface water shortly before adds to the evidence for drought during the Pleistocene-Holocene transition. © 1999 John Wiley & Sons, Inc.  相似文献   

7.
The Mockingbird Gap site is one of the largest Clovis sites in the western United States, yet it remains poorly known after it was tested in 1966–1968. Surface collecting and mapping of the site revealed a dense accumulation of Clovis lithic debris stretching along Chupadera Draw, which drains into the Jornada del Muerto basin. We conducted archaeological testing and geoarchaeological coring to assess the stratigraphic integrity of the site and gain clues to the paleoenvironmental conditions during the Clovis occupation. The 1966–1968 excavations were in stratified Holocene eolian sand and thus that assemblage was from a disturbed content. An intact Clovis occupation was found elsewhere in the site, embedded in the upper few centimeters of a well‐developed buried Bt horizon formed in eolian sand, representing the regional Clovis landscape. Coring in Chupadera Draw revealed ∼11 m of fill spanning the past ∼11,000 14C years. The stratified deposits provide evidence of flowing and standing water on the floor of the draw during Clovis times, a likely inducement to settlement. © 2009 Wiley Periodicals, Inc.  相似文献   

8.
Geoarchaeological investigations at the Clovis type site, Blackwater Locality No. 1, in 1983 and 1984 included core drilling, archaeological test excavations, stratigraphic profiling, sedimentary analyses, and radiocarbon dating. Six lines of core holes transverse to the outlet channel clearly defined the subsurface configuration and stratigraphy of the prehistoric spring run. Pieces of large animal bone from units B, C, D, and E that elsewhere in the site contain Paleoindian artifacts suggest occurrences of additional buried sites along the ancient spring run. Four Paleoindian projectile points recovered during archaeological testing confirm these prospects. The Clovis type site, located in an abandoned gravel pit, is in a natural depression initially occupied by a late Pleistocene lake. After breaching of the depression by overflow or sapping, it became a springhead and was enlarged by slumping and slopewash. Detailed stratigraphic profiling of the south wall of the abandoned gravel pit provided precise stratigraphic control for sediment sampling and radiocarbon dating, and revealed more complex microstratigraphy and facies relationships than heretofore known for the site. The interfingering of dune facies around the depression with lacustrine and spring-laid facies within it aid paleoclimatic interpretation. Deflational contacts within the depression appear to correlate with adjacent wedges of dune sand reflecting relatively arid intervals. Between these arid episodes occur intervals of increased ground water level attended initially by deposition of spring-laid sands of unit B during the late Pleistocene (13,000–11,500 yr B.P.). As the water table rose following a period of severe deflation, slumping and gravity flow deposited clayey sand, Unit C, on the floor of the blowout between 11,500 and 11,000 yr B.P. During this time Clovis people first appeared at the site. After another brief period of deflation, a lake rose causing sand of Unit D0 to be washed in from shore followed by deposition of diatomities, units D1 and D2. These were separated by a brief influx of eolian sand, unit D2z. Between 10,800 and 10,000 yr B.P. outflow from the lake was reduced by accumulation of eolian sand in the outlet while Folsom people and later Agate Basin people arrived to hunt bison during this time. Cody complex people appeared during and after a brief erosional episode that preceded deposition of eolian silt and sand of units E and F from 10,000 to 8000 yr B.P. Eolian deposition during post-Folsom time converted the pond to a wet meadow and eventually, during Cody time, to a grassy swale. Some of these deposits were blown out during the Altithermal arid period (ca. 8000-5000 yr B.P.), a time when prehistoric Archaic peoples excavated wells in the floor of the depression. Subsequent eolian activity has resulted in deflation and dune migration during the late Holocene. The best prospects for Paleoindian finds are along the buried outlet south of the south wall and in early Holocene dune sands on the uplands around the depression. © 1995 John Wiley & Sons, Inc.  相似文献   

9.
The eastern Lachlan Orogen in southeastern Australia is noted for its major porphyry–epithermal–skarn copper–gold deposits of late Ordovician age. Whilst many small quartz vein-hosted or orogenic lode-type gold deposits are known in the region, the discovery of the Wyoming gold deposits has demonstrated the potential for significant lode-type mineralisation hosted within the same Ordovician volcanic stratigraphy. Outcrop in the Wyoming area is limited, with the Ordovician sequence largely obscured by clay-rich cover of probable Quaternary to Cretaceous age with depths up to 50 m. Regional aeromagnetic data define a north–south trending linear belt interpreted to represent the Ordovician andesitic volcanic rock sequence within probable Ordo-Silurian pelitic metasedimentary rocks. Drilling through the cover sequence in 2001 to follow up the trend of historically reported mineralisation discovered extensive alteration and gold mineralisation within an andesitic feldspar porphyry intrusion and adjacent volcaniclastic sandstones and siltstones. Subsequent detailed resource definition drilling has identified a substantial mineralised body associated with sericite–carbonate–albite–quartz–(±chlorite ± pyrite ± arsenopyrite) alteration. The Wyoming deposits appear to have formed as the result of a rheological contrast between the porphyry host and the surrounding volcaniclastic rocks, with the porphyry showing brittle fracture and the metasedimentary rocks ductile deformation. The mineralisation at Wyoming bears many petrological and structural similarities to orogenic lode-style gold deposits. Although the timing of alteration and mineralisation in the Wyoming deposits remain problematic, a relationship with possible early to middle Devonian deformation is considered likely.  相似文献   

10.
Six new radiocarbon ages and a pollen sequence are provided for Laguna Stibnite, a small lake on the Taitao Peninsula, Chile (latitude 46°25'S, longitude 74°24'W). The sediments record a late-glacial to present sequence, with a basal age of 14 335 ± 145 yr BP (Q-2840). The radiocarbon ages provide the basis for a sound chronology in a region of Chile where few palynological studies have been made and where previous radiocarbon ages are ambiguous. The chronology from Laguna Stibnite supports the acceptance of a radiocarbon chronology based on wood fragments (rather than bulk analysis) at a site near Puerto Edén further south in the Chilean Channels (49°08'S). These data from Laguna Stibnite provide evidence for an early deglaciation (before 14 000 yr BP) in this region of southern Chile. The sequence provides no evidence for a climatic reversal between 11 000 yr BP and 10 000 yr BP, the so-called Younger Dryas chron.  相似文献   

11.
Seven coprolites of the extinct Shasta ground sloth (Nothrotheriops shastense) were recently discovered in the Los Angeles County Museum collection from Shelter Cave, New Mexico. Three dung balls provided radiocarbon ages of 11,330, 12,330 and 12,430 yr B.P. Packrat (Neotoma) middens disclose a xeric juniper woodland at Shelter Cave during the sloth's occupation. Plant cuticles from the dung indicate that the ground sloth had a diet dominated by mormon tea (Ephedra) and other xerophytic shrubs. Pollen spectra from the coprolites have high representations of anemophilous plants and low representations of the dietary items shown in the cuticle analysis.Fifteen radiocarbon dates of sloth dung obtained since 1974 strengthen the hypothesis that sloth extinction occurred about 11,000 yr B.P. Paleoenvironmental studies indicate that ground sloths lived in juniper woodlands and montane conifer communities. Nothrotheriops commonly dined on shrubs that are still present in these habitats. It is difficult to explain the demise of the Shasta ground sloth by climatic change or dietary stress. Human predation remains as a possible explanation; ground sloth extinction appears to coincide with the time of Clovis mammoth hunters.  相似文献   

12.
New cosmogenic surface-exposure ages of moraine-crest boulders from southwestern Colorado are compared with published surface-exposure ages of boulders from moraine complexes in north-central Colorado and in west-central (Fremont Lake basin) Wyoming. 10Be data sets from the three areas were scaled to a single 10Be production rate of 5.4 at/g/yr at sea level and high latitude (SLHL), which represents the average 10Be production rate for two high-altitude, mid-latitude sites in the western United States (US) and Austria. Multiple nuclide ages on single boulders indicate that this 10Be production rate yields ages comparable to those calculated with a commonly used 36Cl production scheme. The average age and age range of moraine-crest boulders on terminal moraines at the southwestern Colorado and Wyoming sites are similar, indicating a retreat from their positions ∼16.8 36Cl ka (Cosmogenic ages in this paper are labeled 10Be or 36Cl ka or just ka when both 10Be or 36Cl ages are being discussed; radiocarbon ages are labeled 14C ka, calibrated radiocarbon are labeled cal ka, and calendar ages are labeled calendar ka. Errors (±1σ) associated with ages are shown in tables. Radiocarbon ages were calibrated using the data of Hughen et al. (Science 303 (2004) 202). This suggests a near-synchronous retreat of Pinedale glaciers across a 470-km latitudinal range in the Middle and Southern Rocky Mountains. Hypothetical corrections for snow shielding and rock-surface erosion shifts the time of retreat to between 17.2 and 17.5 10Be ka at Pinedale, Wyoming, and between 16.3 and 17.3 36Cl ka at Hogback Mountain, Colorado.  相似文献   

13.
The timing of the extinction of the Australian Megafauna and whether it was simultaneous and widespread has been a much researched topic in Quaternary geoscience. The Black Creek Swamp Megafauna site on Kangaroo Island was thought to be a refugium for Megafauna; however, recent and multidiscipline age determinations have established that the fossils are considerably older than the well-quoted extinction age of 45 kyr. Further radiocarbon age determinations, δ13C isotope analysis and 13C-NMR spectroscopy of the fossil containing organic matter demonstrates that it is highly soluble and accumulated as recently as 31–18 cal. kyr BP. These radiocarbon ages are much younger than the 100–50 kyr age bracket ascertained for the fossil material itself, implying separate episodes of death, deposition and burial. The soluble nature of the organic matter and increasing radiocarbon ages with depth suggests lateral accumulation, probably transported by subsurface waters from elevated areas proximal to the low-lying swamp. Such depositional conditions and 14C age range implies that the site may have experienced an unusually wet Last Glacial Maximum, due maybe to its proximity to the continental shelf and thus to maritime conditions. C3 vegetation dominates the Black Creek Swamp and its organic matter (δ13C; −30‰ and −23‰); however, variations in δ13C may indicate climatic shifts. 13C-enrichment and an abundance of salt-tolerant gastropods within the site's final phase of sediment accumulation (<6 cal. kyr BP) suggest that conditions during this most recent period were not as wet as those of the Last Glacial Maximum.  相似文献   

14.
赵烨 《地学前缘》2002,9(1):137-142
在考察南极菲尔德斯半岛自然地理特征的基础上 ,分析了半岛东侧阿德雷岛西部海拔18 0 0m的海岸阶地上苔藓泥炭层 (0~ 44cm)之沉积特征 ,分别测量了 5 5~ 8cm ,18~ 2 0cm ,36~38cm三个层段泥炭样品的14 C年龄为 :现代、(6 71± 2 0 )aBP、(32 6 5± 12 0 )aBP ,据此推算该苔藓泥炭底层形成的时间大约在 430 0aBP。分析了半岛西北部地质湾海滩沉积层中同种浅海底栖褐藻 (Ha lymeniasp )的14 C年龄 ,即 15~ 17cm和 92~ 95cm层中褐藻的14 C年龄分别为 (885± 70 )aBP、(144 0±75 )aBP ,现代褐藻14 C年龄为 (6 95± 70 )aBP。用不同时段褐藻14 C年龄内差法消除南极海源有机碳的14 C年龄老化问题 ;还分析了地质湾海拔 6 84m海岸阶地古湖相硅藻沉积层的14 C年龄为 (2 430±75 )aBP。从而建立了全新世晚期南极菲尔德斯半岛的海平面变化序列 :在 430 0~ 2 430aBP期间 ,区域海平面快速下降 ,其平均下降速率为 - 0 6 0cm·a-1;在 2 430~ 80 0aBP期间 ,区域海平面继续下降 ,其平均下降速率为 - 0 31cm·a-1;在 80 0~ 2 30aBP期间区域海平面开始缓慢上升 ,其平均上升速率为 0 14cm·a-1;近 2 30a来海平面上升进一步趋缓 ,其平均上升速率为 0 0 7cm·a-1。  相似文献   

15.
In the summer of 1960, mammoth bones were discovered by a dragline operator in southern Wyoming at the Union Pacific (U.P.) Mammoth site. Although subsequent archaeological work during 1960 and 1961 identified artifacts in association with the mammoth remains, many authors have since questioned the nature of that association. Also, little has been published about the site other than a brief article in National Geographic Magazine in 1962. In this paper, we present additional information on the U.P. Mammoth site including stratigraphic profiles from the first author's geoarchaeological work in 1961, stratigraphic and spatial location of bones and artifacts derived from the original field notes, and new radiocarbon dates. Although the precise stratigraphic provenance for many artifacts and skeletal elements remains unclear, a compelling argument can be made for spatial and stratigraphic association of the mammoth remains with the artifact assemblage suggesting some kind of human interaction with the animal.  相似文献   

16.
Camelops have been recorded in a number of Paleo-Indian sites that lack evidence of past procurement methods. Recently, two occurrences of Camelops remains have been recorded in Paleo-Indian animal kills in Wyoming. One kill situation was in a Hell Gap cultural context that produced remains of a single Camelops taken along with about 100 bison in a parabolic sand dune trap. The other Camelops was in a Clovis cultural context and deals with a single animal believed to have been taken in an arroyo trap that was used to take bison at several Paleo-Indian time periods. Identification of geomorphic features involved in these kill sites offers a basis for beginning to interpret Paleo-Indian camel procurement methods.  相似文献   

17.
New radiocarbon dates, carbon and oxygen isotope analyses of mollusks and marl, and palynologic analysis have clarified age relationships at the Corry kettle bog in northwestern Pennsylvania. A 4000-yr difference in radiocarbon dates between basal peat and marl top, previously interpreted as caused by the presence of an unconformity, is reinterpreted as due to “hard-water effects” from carbonate bedrock and glacial deposits. A radiocarbon date of 14,000 yr from basal marl, previously used as a minimum age for glacial deposition, is also likely too old; instead a similar age is estimated for the base of the underlying lake clay. Radiocarbon dates on marl should be used with caution and supported by isotopic and pollen analyses.  相似文献   

18.
Cumulative probability functions (CPFs) for large numbers of radiocarbon age determinations are increasingly being used by scientists as a methodology to discern environmental histories. While the recent compilation of regional databases of the radiocarbon dating control for fluvial sediment sequences has been beneficial for identifying gaps in knowledge and stimulating new research, there are a number of problems that critically undermine the use of these CPFs as sensitive hydroclimatic proxies. (i) The CPF method is underpinned by the assumption that each radiocarbon measurement is a true age estimate for a point in time, whereas each measured age in fact forms a scatter around the true age of the sample; (ii) calibration of radiocarbon ages is responsible for much of the structure in CPFs and compounds the problem of scatter and smears the chronological control; (iii) the databases incorporate multiple types of environmental changes differing chronological relationships between the 14C measurements and the dated events, with pre‐dating, dating or post‐dating chronological control each displaying variable length temporal lags all mixed together in the same analysis; and (iv) the radiocarbon ages from individual case studies need to be more robustly tested before being incorporated into regional databases. All these factors negate the value of CPFs as sensitive proxies of environmental change, because peaks in probability for individual radiocarbon measurements are likely to be an incorrect estimate for the age of a geomorphological event and this problem is compounded by combining probabilities for multiple unrelated events. In this paper we present a critical analysis of CPFs and their interpretation before suggesting alternative approaches to analysing radiocarbon geochronologies of geomorphic events, which include: (i) Bayesian age modelling of river terrace development; (ii) developing regional databases that test specific geomorphic hypotheses; (iii) Bayesian age modelling of palaeoflood records; and (iv) analysis of sedimentation rates. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

19.
Distinguishing between naturally and culturally produced, simply flaked cobbles has been a problem for proponents of a pre‐Clovis occupation in the Americas. Several sites in Alberta have been assigned a pre‐Clovis status based on the presence of simply flaked cobbles found in Late Pleistocene till deposits. Historically, these types of assemblages have been assigned a cultural status based on subjective criteria and appeals to the analyst's expertise. To determine the archaeological status of two such assemblages from Alberta (Varsity Estates and Silver Springs), they were compared to a known natural assemblage and two known cultural assemblages. Chi‐square testing was used to evaluate several lithic attributes. Only those attributes that statistically differentiated between natural and cultural assemblages were used for further analyses. All cobbles were then scored using these attributes. A point was awarded when a statistically significant attribute of human‐manufacture was present. These points were then totaled, providing an aggregate score for each cobble. These scores were plotted to determine whether the test assemblages had closer affinities with the known natural or known cultural assemblages. The results indicate that the proposed pre‐Clovis assemblages have closer affinities to known natural assemblages than to cultural assemblages. Our results suggest that these sites provide no evidence for a pre‐Clovis occupation in the Americas. © 2004 Wiley Periodicals, Inc.  相似文献   

20.
The Fetterman Mammoth locality, eastern Wyoming, U.S.A., produced the remains of a single subadult mammoth and a small lithic assemblage. This paper employs a fine‐grained taphonomic approach to investigate the events responsible for the deposit's creation. No cultural modifications were noted on any of the specimens. Long axis orientations plotted against a reconstruction of the depositional surface suggest limited postdepositional movement of individual disarticulated elements. Weathering patterns based on in situ upside and downside positioning document two discrete episodes of sedimentation. These results suggest that the mammoth remains and the cultural assemblage may be separated by at least one depositional event and, as such, their association is considered equivocal. © 2002 Wiley Periodicals, Inc.  相似文献   

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