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1.
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
2.
The geologic and geomorphic template of Grand Canyon influences patterns in the archaeological record, including sites where apparent increases in erosion may be related to Glen Canyon Dam. To provide geoarchaeological context for the Colorado River corridor and such issues, we explore first‐order trends in a database of field observations and topographic metrics from 227 cultural sites. The patterns revealed may be expected in other river‐canyon settings of management concern. The spatial clustering of sites along the river follows variations in width of the valley bottom and the occurrence of alluvial terraces and debris fans, linking to bedrock controls. In contrast, the pattern of more Formative (Ancestral Puebloan, 800–1250 A.D.) sites in eastern Grand Canyon and Protohistoric (1250–1776 A.D.) sites in western Grand Canyon does not follow any evident geomorphic trends. In terms of site stability, wider reaches with more terrace and debris fan landforms host a disproportionate number of sites with acute erosion. This links most directly to weak alluvial substrates, and the primary erosion process is gullying with diffusive‐creep processes also pervasive. Although Glen Canyon Dam does not directly influence these erosion processes, overall sediment depletion and the loss of major flooding leaves erosion unhampered along the river corridor. 相似文献
3.
Characterising youthful strike-slip fault systems within transtensional regimes is often complicated by the presence of tectonic geomorphic features produced by normal faulting associated with oblique extension. The Petersen Mountain fault in the northern Walker Lane tectonic province exhibits evidence of both normal and strike-slip faulting. We present the results of geologic and geomorphic mapping, and palaeoseismic trenching that characterise the fault's style and sense of deformation. The fault consists of two major traces. The western trace displaces colluvial, landslide, and middle to late Pleistocene alluvial fans and is associated with aligned range front saddles, linear drainages, and oversteepened range front slopes. The eastern trace is associated with a low linear bedrock ridge, a narrow graben, right deflected stream channels, and scarps in late Pleistocene alluvial fan deposits. A trench on the eastern trace of the fault exposed a clear juxtaposition of disintegrated granodiorite bedrock against sand and boulder alluvial fan deposits across a steeply east-dipping fault. The stratigraphic evidence supports the occurrence of at least one late Pleistocene earthquake with a component of lateral displacement. As such, the Petersen Mountain fault accommodates part of the ~7 mm/yr of dextral shear distributed across the northern Walker Lane. 相似文献
4.
东昆仑东段新生代高原隆升重大事件的沉积响应 总被引：10，自引：2，他引：8
根据新生代沉积盆地的地层序列、环境演变及地貌和水系变迁分析将研究区新生代高原隆升过程划分为5个重大事件.首次在研究区内海拔5400m的主夷平面上发现古土壤、岩溶角砾岩及钟乳石等, 认为沱沱河组上段细碎屑沉积及五道梁组石膏沉积(中新世) 是主夷平面形成期的沉积响应, 提出了主夷平面的高程具有东西向排列的盆岭地貌特点, 这种高程差异反映了后期构造隆升的不均衡, 应该是上新世以来差异断块抬升的结果; 早更新世中期(1525.5ka后) 一套河流砂砾卵石沉积是青藏运动C幕的沉积响应, 体现在布尔汗布达山的强烈上升和成山; 早更新世晚期(1113.9~836.3ka) 先湖滨砾石沉积, 后转为河流砂砾卵石沉积, 是昆黄运动在研究区的沉积响应, 并体现在马尔争-布青山的强烈上升和成山, 中更新世早期冰碛物的发育说明昆黄运动后研究区已隆升达到"水汽冻结高度"; 研究区T5阶地沉积前的强烈下蚀, 柴达木盆地内陆水系溯源侵蚀切过布尔汗布达山主分水岭, 袭夺了昆南断裂带原由西向东流向共和古湖的东西向水系并到达阿拉克湖一带, 晚更新世洪冲积角度不整合于中更新世洪冲积之上等是共和运动的具体表现. 相似文献
5.
Jim I. Mead 《Quaternary Research》1981,15(3):311-326
The vertebrate fauna of the last 30,000 radiocarbon years in the Grand Canyon is reviewed. Faunas accompanied with 92 14C dates have been analyzed from nine cave sites (four systematically excavated) and 50 packrat middens. Reasonably precise chronological and environmental data of late Pleistocene and Holocene age were obtained through dung studies in Rampart, Muav, and Stanton's Caves; from the numerous packrat middens; and from a ringtail refuse deposit in Vulture Cave. The desert tortoise, 8 species of lizards, 12 species of snakes, 68 species of birds, and 33 species of mammals are identified. Extinct animals include the avian carrion feeder, Teratornis merriami, and the mammalian herbivores, Oreamnos harringtoni, Camelops cf. hesternus, Equus sp., and Nothrotheriops shastense. There is no apparent abrupt end to the late Pleistocene as observed in the Grand Canyon fossil faunal or floral record. Animal and plant taxa of the Grand Canyon responded individually to the changes in climate of the last 30,000 yr. Both animal and plant fossil assemblages indicate that a pre-full glacial, a full glacial, and a late glacial woodland community with many less dominant desert taxa were slowly replaced by a Holocene desert community. All woodland taxa were absent from the lower elevations of the Grand Canyon by 8500 yr B.P. 相似文献
6.
云南三江一河典型地区河谷第四系发育特征 总被引：6，自引：1，他引：6
三江一河（金沙江、怒江、澜沧江、红河是流经云南境内的４条主体水系，将上述４条河流河谷第四系的野外观察加以总结得出；金沙江河谷局部发育早一中更新世的湖相层和河湖相层，常形成晚期阶地的基座，晚更新世至全新世冲积层构成四级阶地；怒江河谷第四系发育较差，在六库的上游河谷中冲积层极不发育，只有局部地方有少量的河漫滩砂砾层（全新世），在六库至过街河段中，尤其是过街盆地，发育有中更新世至全新世的冲积层和洪积层，前者构成五级阶地，后者形成巨大的洪积扇分布在河流右岸的谷底或苍坡上；澜沧江除景洪、勐罕（橄榄坝）盆地外，其它河段主要为峡谷，第四系很少，在景洪盆地中发育有第二、第一级阶地和河漫滩冲积层；红河的第四系有中更新世至全新世的冲积层，并构成五级阶地。基于上述第四系特点，简要地讨论了这４条河流的形成时代。 相似文献
7.
Donald Lee Johnson 《Quaternary Research》1978,10(2):204-225
Pygmy proboscidean remains of Mammuthus exilis occur abundantly in late Quaternary deposits on the Northern Channel Islands, California. On the assumption that ancestral elephants could not have swum to the islands and must therefore have walked out, various land bridges have been hypothesized that link the northern islands to the mainland by a peninsula. Geological evidence for a land bridge, however, is lacking, and new evidence shows that elephants are excellent swimmers and skilled at crossing watergaps. The Santa Barbara Channel was narrowed to only 6 km during glacially lowered sea levels. Modern elephants swim much further, and at speeds ranging from 0.96–2.70 km/hr. Motives for California elephants to cross Pleistocene watergaps are inferred from motives that lead modern elephants in Asia and Africa to cross watergaps. These are the visual and olfactory sensing of islands and of insular food during times of drought or fire-induced food shortage. Diminutive size of M. exilis principally reflects lack of island predators, an adaption to periodic food stress in a finite forage area affected by periodic drought and fire, and an adaptation for keeping population numbers high to maintain genetic variability and to ensure survival despite accidents. A late Quaternary scenario describes the environmental setting of the Santa Barbara Channel and the conditions that led to proboscidean dispersal to the preexistent super-island Santarosae. 相似文献
8.
第四纪洞庭盆地沅江凹陷东缘鹿角地区构造—沉积演化研究 总被引：7，自引：0，他引：7
沅江凹陷为第四纪洞庭盆地东部的一个次级凹陷。通过地表地质调查和钻孔资料,在沅江凹陷东缘北部鹿角地区第四纪构造、沉积及地貌特征研究基础上,探讨并提出其构造-沉积演化过程：早更新世早期洪湖-湘阴断裂和荣家湾断裂相继活动,断裂以西地区断陷沉降并沉积,以东地区则构造抬升而遭受风化剥蚀。早更新世末期凹陷区东部构造反转抬升并遭受侵蚀。中更新世早期和中期凹陷区断陷沉降并接受沉积。中更新世晚期研究区整体抬升而遭受剥蚀。晚更新世西部主凹陷区在稳定或弱沉降并形成泥质沉积,东部间歇性抬升。在上述中更新世晚期开始的构造抬升的同时,研究区东部产生了自东向西、自南向北的构造掀斜。全新世构造总体稳定,西部洞庭湖区形成湖冲积。区域上,第四纪洞庭盆地构造性质经历了早期断陷到晚期坳陷的转变。 相似文献
9.
Sellicks Beach, located on the eastern shore of Gulf St Vincent, South Australia, is subject to wave-dominated processes and northward longshore transport. During winter, when wave energy is typically vigorous, gravel deposits are exposed across most of the beach, and three step-like berms are well developed. Sand is restricted to a narrow strip that is exposed only at low tide. In contrast, during summer, when wave energy is generally moderate to low, much of the gravel is covered by a thin veneer of sand and only the high berm, on the landward edge of the beach, remains as an obvious feature. Steeply dipping Neoproterozoic to Cambrian strata that outcrop strongly across Sellicks Hill are the original source rocks for the beach gravel; distinctive sedimentary textures, structures and fossils in the cobble-size clasts can be confidently matched with those of the provenance rocks. Much of the sediment entered the modern beach environment as a consequence of coastal erosion of transitional alluvial fan sediments. The oldest alluvial fan sediments are of late Pliocene to earliest Pleistocene age. Mount Terrible Gully provides a conduit for the input of fluvial sediment at the mouth of Cactus Canyon, where clasts as large as boulders accumulate across the beach. Sellicks Beach gravels are subject to longshore transport northwards. Relatively softer clasts, such as those derived from the Heatherdale Shale, are rare beyond Cactus Canyon. In contrast, quartzite clasts are more abundant towards the north. This lithological differentiation is attributed to preferential survivorship of clasts that are physically harder and chemically less reactive. The change in the shapes of clasts northwards, from predominately shingle-like ‘very platy’ and ‘very bladed’ at Cactus Canyon, to more ‘compact’ towards the boat ramp, is in accord with the more massive fabric of the surviving quartzite clasts. At Sellicks Beach, preservation of uplifted, coarse gravels, with entire and comminuted marine molluscan shells, of last interglacial age, provides evidence of neotectonism. At the landward margin of the beach, imbricated gravels in which pore spaces have been infilled with mud, and which show no evidence of modern coastal erosion, may provide evidence of continuing uplift during the recent Holocene. The geological setting, geomorphic framework and modern sedimentary regime at Sellicks Beach combine to provide an exceptionally useful outdoor laboratory for education in field geology. 相似文献
10.
Darrell S. Kaufman Gary O'Brien Jim I. Mead Jordon Bright Paul Umhoefer 《Quaternary Research》2002,58(3):329
One of the most intriguing episodes in the Quaternary evolution of the Grand Canyon of the Colorado River, Arizona, was the development of vast lakes that are thought to have backed up behind lava erupted into the gorge. Stratigraphic evidence for these deep lava-dammed lakes is expectedly sparse. Possible lacustrine deposits at six areas in the eastern canyon yielded no compelling evidence for sediment deposited in a deep lake. At two of the sites the sediment was associated with late Quaternary spring-fed pools and marshes. Water-lain silt and sand at lower Havasu Creek was deposited 3000 cal yr ago. The deposit contains an ostracode assemblage similar to that living in the modern travertine-dammed pools adjacent to the outcrop. The second deposit, at Lees Ferry, formed in a spring-fed marsh 43,000 cal yr ago, as determined by 14C and amino acid geochronology. It contains abundant ostracode and mollusk fossils, the richest assemblages reported from the Grand Canyon to date. Our interpretation of these sediments as spring-fed deposits, and their relative youth, provides an alternative to the conventional view that deposits like these were formed in deep lava-dammed lakes that filled the Grand Canyon. 相似文献
11.
Recent investigations of a limestone solution cave on the Queen Charlotte Islands (Haida Gwaii) have yielded skeletal remains of fauna including late Pleistocene and early Holocene bears, one specimen of which dates to ca. 14,400 14C yr B.P. This new fossil evidence sheds light on early postglacial environmental conditions in this archipelago, with implications for the timing of early human migration into the Americas. 相似文献
12.
澧县凹陷内第四系厚度达200m左右,由早更新世-中更新世中期沉积和全新统组成。早更新世-中更新世中期沉积除顶部为粘土外,主体为砾石层,在凹陷中央夹粉砂、细砂和少量粘土。全新统分布于凹陷南部,为湖冲积粘土。早更新世澧县凹陷区断陷沉降,于河道和冲积扇环境下接受沉积;中更新世凹陷逐渐扩张,沉积范围扩展至凹陷外缘,凹陷主体部位自边缘向中央依次为冲积扇和扇前浅湖环境。中更新世中后期因盆地扩张,自凹陷中央至边缘地带均为静水湖泊环境。中更新世晚期至晚更新世,凹陷及周缘因构造抬升而遭受剥蚀而缺失沉积。全新世凹陷南部受澧水及区域湖面上升影响而发育湖冲积沉积。 相似文献
13.
During the Late Tortonian, shallow‐water temperate carbonates were deposited in a small bay on a gentle ramp linked to a small island (Alhama de Granada area, Granada Basin, southern Spain). A submarine canyon (the ‘Alhama Submarine Canyon’) developed close to the shoreline, cross‐cutting the temperate‐carbonate ramp. The Alhama Submarine Canyon had an irregular profile and steep slopes (10° to 30°). It was excavated in two phases reflected by two major erosion surfaces, the lowermost of which was incised at least 50 m into the ramp. Wedge‐shaped and trough‐shaped, concave‐up beds of calcareous (terrigenous) deposits overlie these erosional surfaces and filled the canyon. A combination of processes connected to sea‐level changes is proposed to explain the evolution of the Alhama Submarine Canyon. During sea‐level fall, part of the carbonate ramp became exposed and a river valley was excavated. As sea‐level rose, river flows continued along the submerged, former river‐channel, eroding and deepening the valley and creating a submarine canyon. At this stage, only some of the transported conglomerates were deposited locally. As sea‐level continued to rise, the river mouth became detached from the canyon head; littoral sediments, transported by longshore and storm currents, were now captured inside the canyon, generating erosive flows that contributed to its excavation. Most of the canyon infilling took place later, during sea‐level highstand. Longshore‐transported well‐sorted calcarenites/fine‐grained calcirudites derived from longshore‐drift sandwaves poured into and fed the canyon from the south. Coarse‐grained, bioclastic calcirudites derived from a poorly sorted, bioclastic ‘factory facies’ cascaded into the canyon from the north during storms. 相似文献
14.
古滦河冲积扇研究的关注点更多在全新世,对其更新世的演化与变迁一直没有进行过系统研究。根据古滦河冲积扇上PZK10、PZK20钻孔的磁性地层学、年代地层学、沉积学、测井沉积学、岩芯色度分析等,对古滦河冲积平原的第四纪三维地质结构、冲积扇体的规模以及迁移规律进行综合研究,结果表明：PZK10孔揭露了上新世时沉积的巨厚洪积成因“泥包砾”地层,早更新世时发育两个冲积扇-湖相旋回,中更新世时发育辫状河沉积,晚更新世发育湖相、冲积扇相、辫状河相沉积。PZK20孔上新世沉积了一套巨厚“泥包砾”层,早更新世为扇前平原-辫状河相沉积,中更新世为辫状河-冲积扇相沉积,晚更新世为辫状河沉积。古滦河发育两期冲积扇,第一期为早更新世早期,在沙流河镇一带出山口形成的规模较大的冲积扇;第二期为早更新世中期,古滦河在现今丘庄水库一带发生分流,在丰润区一带出山口形成的冲积扇。中更新世,第一期冲积扇开始萎缩,第二期冲积扇继续发育,形成巨厚砾石层;晚更新世,古滦河在迁西县城以北发生袭夺,东流迁移出研究区,在西峡口进入迁安盆地,形成以西峡口为顶点的冲积扇。 相似文献
15.
The large Miocene-aged palaeo canyon that extents through the Qiongdongnan basin (QDNB) and Yinggehai basin (YGHB) of Northern South China Sea has been of considerable interest both economically and scientifically over the past decade. Stemmed from this, significant research has been employed into understanding the mechanism for its existence, incision, and sedimentary fill, yet debate remains. In the first case the canyon itself is actually quite anomalous. Alone from the size (over 570 km in length and more than 8 km in width (Yuan et al., 2009)), which is considerably more than most ancient deep-water channels (REFS), the canyon’s sedimentary fill is also distinctly different. Some explanations have been given to explain the canyon’s origin and existence, these include increased sediment supply from the Red River which is genetically linked to uplift of the Tibetan Plateau, lowstand turbidite and mass-transport activity, reactivation and dextral displacement of the Red River Fault zone inducing erosive gravity-flows, regional tilt of the QDNB and YGHB, paleo-seafloor morphology and seal-level fluctuations. With the application of new data obtained from interpretations of a large number of 2D seismic profiles, core and well log data, and tectonic and sedimentary analysis this contribution aims to: (1) Present models to explain the Canyon’s sedimentary fill and basin plain deposits, which provided significant understanding of processes pre-, syn- and post-incision and; (2) review the plausibility and likelihood of each of the controlling mechanisms, hoping to shed light on this controversial aspect. We conclude that the final erosive event that shaped the canyon is dated at 5.5 Ma. The Canyon’s unusual fill is a product of variation in the interaction between turbidity currents and MTD that blocked the canyon’s axis, and the reduction in gravity flow energy through time; and therefore the complete succession represents one major erosive and cut event at 5.5 Ma and thereafter multi-gravity currents fills unlike in most slope channel-fills. 相似文献
16.
深水重要油气储层--琼东南盆地中央峡谷体系 总被引：19，自引：0，他引：19
南海北部海域琼东南盆地发育一个大型中央峡谷体系,平面上呈“S”型NE向展布,西起莺歌海盆地中央拗陷带东缘,横穿琼东南盆地中央拗陷带,向东延伸进入西沙海槽。通过2D及3D地震资料的精细解释和钻井资料综合分析,研究揭示该峡谷体系可以划分为4个区段,不同区段不仅具有明显不同的剖面形态,而且具有不同沉积物构成、沉积微相以及不同沉积物源。不同区域峡谷形态及充填分析表明,自西向东,中央峡谷下切深度越来越大,下切层位越来越老。其下切剖面形态发育有“V”、“U”、“W”和复合型。其中“V”型峡谷下切深度最大,冲刷、削截特征最明显。峡谷西段以浊积水道沉积为主,峡谷东段为浊积水道与块体流沉积互层沉积,但在不同区带不同沉积物所占比例有一定差异。浊积水道沉积的物源主要来自于盆地西侧,块体流沉积的物源主要来自于盆地北部陆坡体系,从而,来自于西部浊积水道沉积与来自于北部块体流沉积在中央峡谷内形成了多源多期发育的复杂的峡谷系统。 相似文献
17.
Torben C. Rick Jon M. Erlandson René L. Vellanoweth Paul W. Collins Thomas W. Stafford Jr. 《Quaternary Research》2009,71(2):93-146
The island fox (Urocyon littoralis) is one of few reportedly endemic terrestrial mammals on California's Channel Islands. Questions remain about how and when foxes first colonized the islands, with researchers speculating on a natural, human-assisted, or combined dispersal during the late Pleistocene and/or Holocene. A natural dispersal of foxes to the northern Channel Islands has been supported by reports of a few fox bones from late Pleistocene paleontological localities. Direct AMS 14C dating of these “fossil” fox bones produced dates ranging from ∼ 6400 to 200 cal yr BP, however, postdating human colonization of the islands by several millennia. Although one of these specimens is the earliest securely dated fox from the islands, these new data support the hypothesis that Native Americans introduced foxes to all the Channel Islands in the early to middle Holocene. However, a natural dispersal for the original island colonization cannot be ruled out until further paleontological, archaeological, and genetic studies (especially aDNA [ancient DNA]) are conducted. 相似文献
18.
《Earth》2006,74(1-4):245-270
New tephrochronologic, soil-stratigraphic and radiometric-dating studies over the last 10 years have generated a robust numerical stratigraphy for Upper Neogene sedimentary deposits throughout Death Valley. Critical to this improved stratigraphy are correlated or radiometrically-dated tephra beds and tuffs that range in age from > 3.58 Ma to < 1.1 ka. These tephra beds and tuffs establish relations among the Upper Pliocene to Middle Pleistocene sedimentary deposits at Furnace Creek basin, Nova basin, Ubehebe–Lake Rogers basin, Copper Canyon, Artists Drive, Kit Fox Hills, and Confidence Hills. New geologic formations have been described in the Confidence Hills and at Mormon Point. This new geochronology also establishes maximum and minimum ages for Quaternary alluvial fans and Lake Manly deposits. Facies associated with the tephra beds show that ∼3.3 Ma the Furnace Creek basin was a northwest–southeast-trending lake flanked by alluvial fans. This paleolake extended from the Furnace Creek to Ubehebe. Based on the new stratigraphy, the Death Valley fault system can be divided into four main fault zones: the dextral, Quaternary-age Northern Death Valley fault zone; the dextral, pre-Quaternary Furnace Creek fault zone; the oblique–normal Black Mountains fault zone; and the dextral Southern Death Valley fault zone. Post − 3.3 Ma geometric, structural, and kinematic changes in the Black Mountains and Towne Pass fault zones led to the break up of Furnace Creek basin and uplift of the Copper Canyon and Nova basins. Internal kinematics of northern Death Valley are interpreted as either rotation of blocks or normal slip along the northeast–southwest-trending Towne Pass and Tin Mountain fault zones within the Eastern California shear zone. 相似文献
19.
西藏林芝地区第四系新知 总被引：3，自引：0，他引：3
对西藏林芝米林盆地的更新世及其以后的沉积进行了调查研究，磁性地层分析表明这些湖积物的历史不到4万年，在米林的古湖泊沉积物中采获Polypodiaceae等晚更新世孢粉，于米林县白过多更新世湖积之上全新统冲积中新发现林芝智人的头盖骨、牙齿及石斧等，为研究青藏高原第四纪地质作用和古环境、古气候变化及古人类活动等提供了新资料。 相似文献