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1.
Radiocarbon dates indicate a Farmdalian through Woodfordian age for fossil white spruce (Picea glauca) in the Tunica Hills, a greater time span than previously documented. These dates, furthermore, require revision of the ages of fluvial terrace deposits in the region. Spruce-bearing Terrace 1 sediments, previously regarded as late Woodfordian to Holocene age, are of Farmdalian to late Holocene age. Terrace 2 sediments, previously assigned a Sangamonian or Farmdalian age, are of probable Altonian age. Plant fossils in Terrace 1 sediments represent two climatically and temporally distinct assemblages: a cool-temperate, Farmdalian-Woodfordian assemblage dominated by white spruce but including deciduous hardwoods suggestive of an oak-hickory association; and a warm-temperate Holocene assemblage composed of southern hardwoods and nonarboreal species representative of the modern flora of the Tunica Hills. Locally, fossils of white spruce have been reworked into younger Terrace 1 sediments containing the warm-temperate plant assemblage. The transition from the cool-temperate flora to the modern warm-temperate flora in the Tunica Hills probably occurred around 12,000 yr B.P.  相似文献   

2.
The age and number of important fossil-producing late Pleistocene terraces in the Tunica Hills have recently become quite controversial. One hypothesis holds that only a single loess-mantled Farmdalian terrace flanks the streams in this area. The other maintains that there are two terraces. The youngest is considered essentially Holocene in age while the older is Sangamon in age. Radiometric and stratigraphic evidence collected for this study indicates that there are two terraces. The youngest is late Woodfordian to Holocene in age while the other is Farmdalian.  相似文献   

3.
In 1938, Clair A. Brown published his classic paleobotanical discoveries from the Tunica Hills of southeastern Louisiana, indicating ice-age plant migrations of more than 1100 km. Brown collected fossils of both boreal trees such as white spruce (Picea glauca) and southern coastal plain plants from deposits mapped as the Port Hickey (Prairie) river terrace by Harold N. Fisk. Subsequent revisions of terrace mapping, radiocarbon dating, and paleoecological analysis reconciled Brown's conceptual and stratigraphic “mixing” of these two ecologically incompatible fossil plant groups. An older Terrace 2 (of Sangamonian to Altonian age) contains the warm-temperate assemblage. A younger Terrace 1 (of Farmdalian, Woodfordian, and Holocene age) includes full-glacial and late-glacial remains of both boreal and cool-temperate plants; and a warm-temperate suite of plants dates from the Holocene interglacial. New plant fossil localities with radiocarbon chronologies are now available from within the Lower Mississippi Valley of Missouri and Arkansas as well as from the adjacent Ozark Plateaus, the Interior Low Plateaus of Kentucky and Tennessee, and the bordering Blufflands of Tennessee, Mississippi, and Louisiana. These studies demonstrate that glacial and interglacial patterns of vegetation have been influenced by regional changes in climate, glacial runoff, and regime of the Mississippi River.  相似文献   

4.
Pleistocene deposits containing the disarticulated skeleton of a mammoth, and associated faunal and floral remains, were discovered in July 1990 at Upper Strensham, Worcestershire. The environmental evidence from the fauna and flora together with limited geological evidence, indicates that the deposits accumulated within a low energy fluvial environment with a surrounding marsh and restricted tree cover on, or close to, the floodplain. The patchy occurrence of trees in a species-rich grassland is discussed, and the climatic significance of the fauna and flora is considered. The Strensham site lies within the valley of the River Avon, which is known to contain at least five altitudinally distinct river terraces. The deposits at Strensham lie beneath a terraced surface that cannot be accommodated within the existing framework of terrace development in the valley, and evidence is presented which may suggest that these deposits form a previously unrecognised fluvial unit, the Strensham Member of the Avon Valley Formation. Amino-acid age estimates from shells taken from the fossiliferous sediments of the Strensham Member suggest a correlation with Oxygen Isotope Stage 7. This correlation suggests that the temperate deposits at this site should be correlated with the temperate phase recorded at Marsworth, Buckinghamshire and Stoke Goldington in the valley of the Great Ouse.  相似文献   

5.
In this paper we present Quaternary stratigraphy of the area around Chennai based on archaeological findings on the ferricrete surface, geomorphological observations supplemented by radiocarbon dating. The coastal landscape around Chennai, Tamil Nadu, has preserved ferruginised boulder gravel deposits, ferricretes and fluvial deposits of varying thickness. The area studied is approximately 150 km east to west and 180 km north to south with a broad continental shelf towards the seaward. Several rivers enter the Bay of Bengal along its shores like the Koratallaiyar, Cooum and the Adyar. Precambrian charnockite and Upper Gondwana sandstone and shale bedrock rim the shelf margin. For the most part, the Upper Pleistocene-Holocene fluvial sediments overlie an erosion surface that has cut into older Pleistocene sediments and ferricrete surface. Incised valleys that cut into this erosion surface are up to 5–6 km wide and have a relief of at least 30 m. The largest valley is that cut by the Koratallaiyar River. Holocene sediments deposited in the incised valleys include fluvial gravels, early transgressive channel sands and floodplain silts. Older Pleistocene sediments are deposited before and during the 120-ka high stand (Marine isotope stage 5). They consist of ferricretes and ferricrete gravel formed in nearshore humid environments. Muddy and sandy clastic sediments dated to the ca. 5 ka highstand suggest that the climate was semi arid at this time with less fluvial transport. The coarsening up sequence indicates deposition by high intensity channel processes. Pedogenic mottled, clayey silt unit represents an important tectonic event when the channel was temporarily drained and sediment were sub aerially exposed. Uplift of the region has caused the local rivers to incise into the landscape, forming degradation terraces.  相似文献   

6.
A complex late Quaternary alluvial history was documented along Henson Creek, a low order tributary on the Fort Hood Military Reservation in central Texas. Three Quaternary alluvial landforms were recognized: terrace 2 (T2), terrace 1 (T1), and the modern floodplain (T0). The late Pleistocene T2 terrace may contain an array of sites spanning the entire known cultural record, while T1 may have sites spanning the last 5000 years only. Five fluvial units, three colluvial facies, two alluvial fan facies, and two buried paleosols were also recognized. Fluvial deposition was occurring approximately 15,000 yr B.P., 10,000-8000 yr B.P., 7000–4800 yr B.P., 1650-600 yr B.P., and during the last 400 years. Colluvial deposition was ongoing mainly in the early and middle Holocene, while alluvial fan aggradation was proceeding primarily in the middle Holocene. Because of erosional unconformities, there is minimal potential for recovering buried sites dating to intervals between depositional eposides for most of the drainage basin. Preservation potentials for buried sites are greatest in fine-grained fluvial deposits dating to the late Pleistocene, early Holocene, and parts of the late Holocene, and in fine-grained colluvial deposits dating to the early and middle Holocene. This investigation demonstrates that within the study area, and perhaps throughout much of central Texas, a greater continuum of sediments and preservation potentials exists in late Quaternary alluvial deposits of rivers than in low-order tributaries.  相似文献   

7.
At Stoke Goldington in the valley of the Great Ouse in Buckinghamshire a river terrace at a height of about 7 m above the floodplain is underlain by fluvial sediments representing climatic fluctuations in the late Middle Pleistocene. Near the base of the succession, at a level only 1 m above the modern floodplain, a fossil assemblage, including pollen, plant macrofossils, molluscs, insects and ostracods, provides evidence for the local development of herb-rich grassland under temperate climatic conditions. The fossil record, amino-acid racemisation ratios and uranium disequilibrium dating all suggest deposition of this material during Oxygen Isotope Stage 7. The deposits containing the temperate assemblage are immediately overlain by typical cold-climate gravels of the Great Ouse. These have been subjected to a later cut-and-fill episode, with the fill accumulating in cool climatic conditions. The cut-and-fill episode was succeeded by aggradation, forming the overlying terrace surface. Amino-acid racemisation ratios indicate that the fill was emplaced, and the terrace surface created, during or after Oxygen Isotope Stage 5. © 1996 John Wiley & Sons, Ltd.  相似文献   

8.
This paper reports new fieldwork at Warsash which clarifies the terrace stratigraphic framework of the Palaeolithic archaeology of the region. Sections were recorded in former gravel pits and at coastal locations, supplemented by the use of ground penetrating radar and luminescence dating techniques. The region’s extensive borehole archive was also analysed to produce a revised terrace stratigraphy at Warsash and for the Test valley as a whole. At Warsash, some of the sediments previously identified as the Mottisfont/Lower Warsash Terrace are reassigned to the Hamble, Belbin/Upper Warsash and Ganger Wood/Mallards Moor Terraces. A luminescence dating programme, using test procedures not utilised in earlier dating studies in the region, yielded age estimates for the Hamble and Mottisfont/Lower Warsash Terraces at Warsash and also highlighted the complicated nature of the fluvial sediments of the River Test, suggesting that published luminescence ages for these deposits should be treated with some caution. This study indicates that the data used to construct terrace stratigraphies also requires careful assessment. The use of bedrock height and sediment thickness data produces more coherent long profile correlations than those produced by terrace surface data alone. The revised terrace stratigraphy provides the framework for the Palaeolithic archaeology at Warsash and clarifies correlations within and between archaeologically important sediments of the Test Valley, enabling it to contribute to discussions on the Lower-Middle Pleistocene settlement history of southern Britain.  相似文献   

9.
Late Pleistocene age terrace deposits are exposed in the narrow cliffed coastal plain of Bahia Coyote, Baja California Sur, resting unconformably on the lagoonal-shallow water volcaniclastics of the early Miocene Cerro Colorado Member of the El Cien Formation. The terrace is dissected by widely spaced arroyos and partically covered by alluvial fans in the inner and central areas. The marine deposits vary in thickness from 0.5 to 10 m and were laid down in pre-existing erosional channels and depressions in the Pleistocene landscape. The sequence begins with a cobble conglomerate with oyster shells, overlain by poorly bedded molluscan-rich bioclastic sands and coral rubble, beds of massive Porites in growth position and coral-rhodolith sands and marls. Beach sands and gravels and coastal dunes cap the sequence.Samples of Porites panamensis selected for U/Th dating are well-preserved aragonite (>95%). Preliminary results yield U/Th ages of 109–209 ka but the corals have initial δ 234U values in excess of modern seawater values. This indicates open-system behavior and uncertainty associated with the ages. A corrected age for the top of the massive Porites unit suggests that the corals grew during the last interglacial, marine isotope stage (MIS) 5e sea level high stand.Assuming global sea level during MIS 5e was ca. 4–5 m above present-day sea level (McCulloch and Esat, 2000) and the growth position of the corals was 1–5 m below sea level, the terraces have been uplifted between 12 and 25 m (12–15 cm/kyr). This is consistent with other terrace-based uplift rates for the central Baja California peninsula, north of the La Paz fault.  相似文献   

10.
在云南石鼓"长江第一湾"附近河段两岸发现了10多处典型的第四纪湖相沉积物露头,它们构成了金沙江第二、三、四级阶地的基座。热释光(TL)和U系法年龄测定及磁性地层学研究结果表明,该套湖相沉积物中上部的时代属于243.3～88.0kaBP的中更新世晚期至晚更新世早期,上覆的第四级阶地沉积物的年龄为88.0～80.9kaBP。湖相沉积物的粒度、地球化学和粘土矿物分析结果表明,其沉积环境有由温湿向湿热转化的趋势。根据对玉龙雪山更新世冰川作用的研究,石鼓古湖最初应是玉龙雪山西麓中更新世早期玉龙冰期冰碛物堰塞金沙江河谷而成的,中更新世晚期丽江冰期的冰水沉积物进一步加以堰塞,直至8万多年前被金沙江侵蚀而再次贯通。  相似文献   

11.
Gao, C. & Boreham, S. 2010: Ipswichian (Eemian) floodplain deposits and terrace stratigraphy in the lower Great Ouse and Cam valleys, southern England, UK. Boreas, 10.1111/j.1502‐3885.2010.00191.x. ISSN 0300‐9483. Thick argillaceous deposits named the Mannings Farm Beds recently uncovered in the third terrace at Mannings Farm near Willingham, Cambridgeshire contain a pollen sequence covering the transitions from Ipswichian/Eemian substages I to II and II to III, when oak and hornbeam expanded, respectively. This is the longest record hitherto obtained in Britain, providing important insight into the major forest successions in this temperate stage. The frequent occurrence of Ipswichian deposits in the third terrace suggests the development of an extensive floodplain on the valley bottom, similar to the case for the present‐day lower Great Ouse and Cam. The Mannings Farm Beds testify to a complete interglacial sequence emplaced between cold‐climate gravels that was directly associated with the terrace development. The third terrace developed during the Ipswichian and the preceding and succeeding cold stages. Major river downcutting, which shaped the third terrace, occurred during the Early Devensian/Weichselian. Previously reported interglacial fossils from this terrace that are inconsistent with an Ipswichian affinity are probably reworked material derived from pre‐Ipswichian interglacial deposits, or their significance as biostratigraphical indicators needs to be confirmed. The second and first terraces developed from the late Early Devensian onwards. Ipswichian deposits filling flood‐scoured deep channels in bedrock are preserved locally below these low terraces.  相似文献   

12.
青海沱沱河地区水系密布、河网交织,沿主干水系河流阶地发育。对沱沱河沿岸不同地段河流阶地进行物质成分及古植物孢粉进行研究,确定了自63.1 kaB.P.(ESR)以来的晚更新世草本植物与木本植物两个古植被演化阶段,相应气候由温凉较干向温和较湿转变。详细的测年(TL、ESR)数据显示,位于基座阶地之上的阶地堆积物为晚更新世97.78 KaB.P.以来堆积而成,推断长江水系在研究区的形成与外泄地质时期为晚更新世早期。  相似文献   

13.
Late Pleistocene glacial features in the Páramo de La Culata region, north-central Venezuelan Andes, include: 1. depositional features: morainic till and fluvio-glacial deposits (terrace gravels); 2. sculptured features: glaciated valleys, cirques, horns, and arêtes; and 3. erosional features: striation and grooving, polished rock, roches moutonnées and whaleback forms, and erratic boulders. Two main levels of moraines were found, an older one at 2600 m elevation, and a younger one between 3000 and 3500 m. The difference in age is reflected by the higher degree of weathering, erosion, and vegetation cover of the lower level, as compared with the higher level. Radiocarbon dating, and a comparison and correlation of these glacial features with those of adjacent regions, indicates that the lower morainic level (2600 m) is probably the result of the main glacial advance of the Late Wisconsin Glaciation. The main morainic level (3000 to 3500 m) was probably formed by the latest Wisconsin glacial advance. The Late Pleistocene snow-line depression reached approximately 1200 m below the present snow-line (i. e., down to approximately 3500 m).  相似文献   

14.
The Quaternary stratigraphy of the Alpine Foreland consists of distinct terrace levels, which have been assigned to four morphostratigraphic units: Höhere (Higher) Deckenschotter, Tiefere (Lower) Deckenschotter, Hochterrasse (High Terrace) and Niederterrasse (Lower Terrace). Here, we focus on the terrace gravels at Hohle Gasse, SSE of Pratteln near Basel, which are mapped as Tiefere Deckenschotter. Petrographic and morphometric data established from clasts allowed to infer the transport mechanisms and sources of the gravels. Sedimentological analyses indicate that the gravels were transported by a braided river and deposited in a distal glaciofluvial setting. In addition, it can be shown that the majority of the clasts display multiple reworking and only a minority maintained a distinct glaciofluvial shape. Cosmogenic multi-isotope dating using 10Be and 36Cl allowed direct dating of the sediments at the study site. A depth-profile age of \(2 70_{ - 1 90}^{ + 8 30}\) ka for 10Be was achieved for the deposits at Hohle Gasse. Unfortunately, no age could be modelled from the 36Cl concentrations as the blank correction was too high. Furthermore, this age proves that the studied terrace level should be assigned to the morphostratigraphic unit Hochterrasse.  相似文献   

15.
One of the most famous blue sapphire deposits in Thailand and SE Asia is from the Bo Phloi District, Kanchanaburi Province, Western Thailand. This paper presents the results of our gemstone investigation as well as establishing the Bo Phloi depositional sequence as one of the Quaternary Type Sections in the region. Relationships among the sedimentology, depositional sequences and geomorphology were investigated in order to understand the gemstone depositional features. Sedimentary structures and textures of the sequences show that the deposition of gemstones is related genetically to fluvial processes. Gemstones are recognized in floodplain and low terrace deposits where gemstone paystreaks concentrate mostly inside layers of gravel beds and foreset-bedded gravels lithofacies. C-14 dating of wood and peat within gemstone-bearing layers indicated that the deposit formed during the middle to late Pleistocene. The gemstone-bearing gravel bed defines a north–south trend along the incised palaeo-channel of an ancient braided river system in the middle part of the basin.  相似文献   

16.
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17.
In the Sierra Nevada, the “Recess Peak Glaciation” has been previously defined on the basis of deposits exhibiting relative-age characteristics intermediate between those of the Little Ice Age deposits and those of early Holocene or older moraines. In the absence of reliable chronological control, the Recess Peak deposits were assigned an early Neoglacial age. Although numerous moraines in the central and southern Sierra have been attributed to this interval, regional snowline gradients reconstructed from these deposits lack internal consistency and appear to represent several distinctly different episodes of glacier advance. As a basis for comparison with the Recess Peak data, modern and late Pleistocene regional snowlines were reconstructed using accumulation-area ratios and cirque-floor altitudes. These reconstructions display regionally consistent gradients, rising gradually southward and more steeply eastward. Based on these data, the full-glacial late Pleistocene snowline depression is estimated to have been ≥800 m. Estimates of Recess Peak snowline depression vary widely, ranging from 140 to 500 m, and a reconstructed regional gradient rises northward, in opposition to the late Pleistocene and modern snowlines. Limited radiocarbon dating and the irregular pattern derived from the Recess Peak snowline data suggest that, even in the type area, these deposits resulted from both pre- and post-Hypsithermal glacier advances.  相似文献   

18.
This paper presents a first approach to using a sediment budget methodology for paired terrace staircase sediments in SW England. Although a budget approach has become firmly established in Holocene fluvial studies, it has not been used in Pleistocene sequences due to the problems of temporal resolution, catchment changes and downstream loss from the system. However, this paper uses a budget approach in a paired non-glaciated basin, primarily as a method of interrogating the terrace record concerning the degree of reworking and new sediment input required to produce the reconstructed terrace sequences. In order to apply a budget approach a number of assumptions have to be made and these are justified in the paper. The results suggest that the Exe system can most parsimoniously be explained principally by the reworking of a Middle Pleistocene floodplain system with relatively little input of new resistant clasts required and a cascade-type model in geomorphological terms. Whilst this maybe partially a result of the specific geology of the catchment, it is likely to be representative of many Pleistocene terrace systems in NW Europe due to their litho-tectonic similarities. This cascade-type model of terrace formation has archaeological implications and sets the context for the Palaeolithic terrace record in the UK. Future work will involve the testing of this and similar budget models using a combination of landscape modelling and chronometric dating.  相似文献   

19.
This study focuses on the Plio‐Pleistocene fluvial deposits preserved in the terrace staircases in the south‐eastern Alpine foreland of the Mislinja (MV) and Upper Savinja valleys (USV) in northern Slovenia. The area is located at the north‐eastern margin of the Adria microplate, where neotectonic activity is the prevailing driving force for the terrace formation. The aim of this study is to determine the morphostratigraphy and provenance of the Pliocene to Early Pleistocene gravels using geomorphic and clast lithological analysis. The established morphostratigraphic framework encompasses three terraces in the MV and five terraces in the USV. Due to the lack of age‐relevant data, the morphostratigraphy of the MV and USV is based on the results of geomorphic analysis, clast petrography and data from the literature. Low‐level, middle‐level and high‐level terrace groups were tentatively attributed to the Late and Middle Pleistocene, Early Pleistocene–Pliocene and Pliocene, and compared with the traditional Quaternary stratigraphy of the Alpine foreland. The results of the clast lithological analysis revealed major provenance areas. Moreover, the evolution of long‐term drainage from the Miocene onward was inferred, which suggests that the system reached conformity with the present‐day drainage pattern at the Miocene to Plio‐Pleistocene transition. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

20.
The Holocene (< 10,000 years old) fossil marine macrofauna (molluscs, polychaetes, mammals and birds) of the Vestfold Hills, Antarctica (68°30'S, 78°00'E) is described. All species are extant, with circumantarctic or wider distributions and wide depth ranges. At Heidemann Bay, Pleistocene-age (> 30 ky old) shell fragments occur in a Holocene moraine. These are interpreted as being glacially reworked fossil shells. Holocene benthic estuarine and coastal molluses and serpulid worm tubes are abundant on the flanks of terraces above saline and hypersaline lakes. Extensive radiocarbon dating gives a chronology of these deposits which were not synchronous. Mummies of seals and penguins, which are concentrated on the shores of the saline lakes and scattered across the Hills, are of no use in dating geomorphological events. Marine fossils in moraines are difficult to interpret because they can be glacially-transported live or fossil shells, or deposited after wind transport. The fossil fauna has such a wide ecological range that it indicates only in general terms that for part of the Pleistocene and most of the Holocene, climatic conditions were broadly similar to the present.  相似文献   

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