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1.
For much of the Middle and all of the Upper Pleistocene the Upper Thames valley has remained outside the limit of ice advance. The main agents of landform evolution have been the River Thames and its tributaries, which have cut down episodically and in so doing have abandoned a series of river terraces. This study reports the findings of an investigation into exposures in the deposits underlying the Floodplain Terrace at Cassington, near Oxford, England. The sequence exposed reveals a stratigraphy of basal, predominantly fine-grained, lithofacies overlain by coarser gravel lithofacies. The fluvial architecture of these deposits indicates a major change in fluvial style from a low-energy (meandering) to a high energy (braided) channel system. The flora and fauna from the lower fine-grained lithofacies display a marked change from temperate at the base, to colder conditions towards the top, indicating a close association between deteriorating climate and changing fluvial depositional style. Amino acid and luminescence geochronology from the basal fine-grained lithofacies suggest correlation with Oxygen Isotope Stage 5 and hence it is argued that the major environmental change recorded at the site relates to the Oxygen Isotope Stage 5–4 transition. Deposition of much of the overlying gravel sequence probably occurred during Oxygen Isotope Stage 4, suggesting that the latter half of the Devensian may be less significant, in terms of fluvial landscape evolution in the Upper Thames valley, than was believed previously. © 1998 John Wiley & Sons, Ltd.  相似文献   

2.
Pleistocene fluvial sediments of the Northmoor Member of the Upper Thames Formation exposed at Latton, Wiltshire, record episodic deposition close to the Churn–Thames confluence possibly spanning the interval from Marine Isotope Stages (MIS) 7 to 2. The sequence is dominated by gravel facies, indicating deposition by a high‐energy, gravel‐bed river. A number of fine‐grained organic sediment bodies within the sequence have yielded palaeoenvironmental and biostratigraphical data from Mollusca, Coleoptera, vertebrates, pollen and plant macrofossils. The basal deposit (Facies Association A) contains faunal material indicating temperate conditions. Most of the palaeontological evidence including a distinctive small form of mammoth (Mammuthus cf. trogontherii), together with the U‐series age estimate of >147.4 ± 20 kyr suggest correlation with MIS 7. The overlying deposits (Facies Associations B and C) represent deposition under a range of climatic conditions. Two fine‐grained organic deposits occurred within Association B; one (Association Ba) in the northern part of the pit as a channel fill and the other (Association Bb) in its southern part as a scour‐fill deposit. The coleopteran assemblages from Ba, indicate that it accumulated under temperate oceanic conditions, while Bb, which also yielded a radiocarbon age estimate of 39 560 ± 780 14C yr BP, was formed under much colder and more continental climatic conditions. The sequence is considered to represent deposition within an alluvial fan formed at the Churn–Thames confluence; a depositional scenario which may account for the juxtaposition of sediments and fossils of widely differing age within the same altitudinal range. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

3.
The relationship between palaeosols and sequence stratigraphy is tested in the Lower Permian Abo Member, south‐central New Mexico, by comparing interfluve and fluvial‐terrace palaeosols with palaeosols that developed within lowstand‐fluvial deposits. Interfluve and fluvial‐terrace palaeosols consist of primary pedogenic features, including vertical root traces, vertic structures, Stage II and III pedogenic calcite and translocated clay (argillans), which are cross‐cut or replaced by low‐aluminium goethite, gley colour mottling, sparry calcite veins and ankerite. The polygenetic character of the palaeosols is consistent with initial development for several thousand to tens of thousands of years on well‐drained interfluves or fluvial terraces, followed by waterlogging due to invasion by a rising water table that locally may have been brackish. In contrast, lowstand‐fluvial sediment that filled incised valleys contains only rooted and vertic palaeosols, whose immaturity resulted from high aggradation rates. Palaeosols similar to those in the Abo Member have been recognized in other ancient strata and, when combined with high‐resolution correlation, provide evidence for interpretation of sequence‐stratigraphic surfaces and systems tracts.  相似文献   

4.
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   

5.
The late Middle Pleistocene fluvial terrace sequence of the lower Trent system, Lincolnshire (eastern England), provides an excellent record of environmental change, including evidence for the last two interglacial episodes. It also provides important stratigraphical evidence for the timing and extent of three separate glaciations. Two of these, the Anglian and Devensian, are well-established correlatives of Marine Isotope Stages (MIS) 12 and 2 respectively; the third is a hitherto un-named post-Anglian-pre-Devensian glaciation in eastern England that has been the subject of much previous speculation, but can now be attributed with some confidence to MIS 8. Crucially, the recognition of MIS 7 interglacial deposits within the Balderton-Southrey terrace of the proto-Trent indicates that the underlying Wragby Till, which is ascribed to this additional glaciation, was emplaced no later than MIS 8. The oldest terrace preserved within the lower Trent staircase, the Eagle Moor-Martin Terrace, is considered to be a complex glacial outwash terrace related to the Wragby Till glaciation. It is suggested that deposits representing MIS 11-9, which are conspicuously absent throughout the Trent system, were removed by this glaciation. This is a departure from previous interpretations, which have suggested MIS 10 or MIS 6 as the most likely stages in which an extensive post-Anglian-pre-Devensian lowland glaciation might have occurred in Britain. However, the widespread preservation of undisrupted post-MIS 8 fluvial sequences throughout the Trent valley and in neighbouring systems, within which MIS 7 interglacial deposits have now been recognized at a number of localities, indicates that ice sheets are unlikely to have advanced further into this catchment during MIS 6 than during the Devensian (MIS 2). Recognition of a British glaciation during MIS 8 corresponds with widespread evidence in Europe, which suggests that glacial deposits classified as ‘Saalian’ represent both MIS 8 and MIS 6; in many areas, distinguishing these remains controversial, as confident correlation with either stage is often only possible where glacial sediments interdigitate with well-constrained fluvial records.  相似文献   

6.
Excellent exposures of thick, multistorey, fluvial deposits from the deltaic Atane Formation on south‐east Nuussuaq, central West Greenland, show the architecture of up to 100 m thick continuously aggrading fluvial depositional complexes. The succession comprises vertically stacked channel belt sandstones separated by thin floodplain deposits, with little to no incision between storeys. Architectural elements and palaeocurrent patterns of channel deposits indicate deposition in large, relatively stable, low‐sinuosity rivers, probably located within an incised valley. Gradual transitions from channel to floodplain deposits accompanied by a gradual change from floodplain to spillover sand suggest avulsion on the floodplain as a possible mechanism for the vertically alternating channel and floodplain deposits. Despite its relative proximity to contemporaneous sea‐level (ca 35 km upstream from the palaeo‐shoreline) the depositional complex is entirely non‐marine. The aggrading nature of the deposits suggests a continuously rising base level coupled with a high and steady sediment supply. Vertical alternations between floodplain and channel deposits may be forced by subtle interruptions in this balance or autocyclic mechanisms on the floodplain. This study provides an example of aggrading lowstand/non‐marine transgressive systems tract deposits.  相似文献   

7.
A new Pleistocene vertebrate assemblage from fluvial deposits of the River Severn in Gloucester, England, has yielded the remains of hippopotamus (Hippopotamus amphibius), a new record for this terrace system, with additional material from probable bison (cf. Bison priscus) and elephant (Elephantidae sp.). The presence of these taxa indicates fully temperate climatic conditions and the occurrence of hippopotamus, a significant biostratigraphical indicator for the British Late Pleistocene, suggests an age for the assemblage within MIS 5e (the Last Interglacial). This would contradict the older MIS 7-6 age for the gravel body that is currently accepted on the basis of deposit mapping and imply a more complex mode of deposition than presently envisaged in the valley.  相似文献   

8.
The influence of palaeodrainage characteristics, palaeogeography and tectonic setting are rarely considered as controls on stratigraphic organization in palaeovalley or incised valley systems. This study is an examination of the influence of source region vs. downstream base level controls on the sedimentary architecture of a set of bedrock-confined palaeovalleys developed along the distal margin of the Alpine foreland basin in south-eastern France. Three distinct facies associations are observed within the palaeovalley fills. Fluvial facies association A is mainly dominated by poorly sorted, highly disorganized, clast-to-matrix-supported cobble-to-boulder conglomerates that are interpreted as streamflood deposits. Facies association B comprises mainly yellow siltstones and is interpreted as recording deposition in an estuarine basin environment. Estuarine marine facies association C comprises interstratified estuarine siltstones and clean, well-sorted washover sandstones. The sedimentary characteristics of the valley fill successions are related to the proximity of depositional sites to sediment source areas. Palaeovalleys located proximal to structurally controlled basement palaeohighs are entirely dominated by coarse fluvial streamflood deposits. In contrast, distal palaeovalley segments, which are located several kilometres downstream, contain successions showing upward transition from coarse fluvial facies into estuarine central basin fines, and finally into estuarine-marginal marine facies. Facies distributions suggest that the fluvial deposits form wedge-shaped, downstream-thinning sediment bodies, whereas the estuarine deposits form an upstream-thinning wedge. The vertical stacking of fluvial to estuarine to marginal marine depositional environments records the fluvial aggradation and subsequent transgression of relatively small bedrock-confined river valleys, which drained a rugged, upland terrain. Facies geometries suggest that a fluvial sediment wedge initially prograded downvalley, in response to high bed load sediment yields. Subsequently, palaeovalleys became drowned during the passage of a marine transgression, with the establishment of estuarine conditions. Initial fluvial aggradation and subsequent marine flooding of the palaeovalleys is a consequence of the interaction of high local rates of sediment supply and relative sea-level rise driven by flexural subsidence of the basin.  相似文献   

9.
Sedimentary sequences within headwater valleys on the landward side of the Great Escarpment of South Africa are elucidated and their significance as indicators of environmental change is assessed. This study focuses on the Sneeuberg Range, the most prominent mountain range in the semi‐arid central Great Karoo. Valley fills of a hitherto unrecognised complexity and of a greater age than any previously recorded in the central Great Karoo are reported. Three phases of deposition spanning the Late Pleistocene up to the present are documented from sites where gully erosion has incised the valley fills. The earliest depositional phase is represented by deeply weathered, calcretised gravel deposits, which probably were emplaced by debris flow and fluvial processes in the form of a fan. These deposits subsequently were buried by finer grained, largely unconsolidated sediment, with much of this emplacement occurring during the Holocene. There is evidence for phases of landscape stability and instability within this facies. Finally, sheetwash has removed fine‐grained sediments from valley flanks and has deposited it either on valley bottoms, or in presently active gullies. This process appears to be ongoing, and is the subject of current investigation. The sedimentary deposits are interpreted as representing a wide range of palaeoenvironmental conditions that have prevailed within the central Great Karoo since the penultimate glaciation. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

10.
There is renewed interest in a series of Carnian-aged sandstone units across the UK because they represent a unique event in the Late Triassic, the Carnian Pluvial Episode (CPE), from 233 to 232 Ma. The North Curry Sandstone Member of the Mercia Mudstone Group in Somerset is of particular importance because it yielded a rich fauna of shark, bony fish and amphibian remains in coarse-grained sandstones to Charles Moore in the 1860s. However, the exact location and age of his important collection had not been identified. Here, we demonstrate that the Moore collection comes from the North Curry Sandstone Member in a location in the village of Ruishton, just east of Taunton, where a new road cutting reveals both the bone-rich units and a complete succession through the CPE, a time of major climatic and biotic upheaval. The 16 m section comprises several sandstones interbedded with red-green mudstones, representing a terrestrial environment with lacustrine, evaporitic mud flat and fluvial deposits.  相似文献   

11.
Eighteen coastal-plain depositional sequences that can be correlated to shallow- to deep-water clinoforms in the Eocene Central Basin of Spitsbergen were studied in 1 × 15 km scale mountainside exposures. The overall mud-prone (>300 m thick) coastal-plain succession is divided by prominent fluvial erosion surfaces into vertically stacked depositional sequences, 7–44 m thick. The erosion surfaces are overlain by fluvial conglomerates and coarse-grained sandstones. The fluvial deposits show tidal influence at their seaward ends. The fluvial deposits pass upwards into macrotidal tide-dominated estuarine deposits, with coarse-grained river-dominated facies followed further seawards by high- and low-sinuosity tidal channels, upper-flow-regime tidal flats, and tidal sand bar facies associations. Laterally, marginal sandy to muddy tidal flat and marsh deposits occur. The fluvial/estuarine sequences are interpreted as having accumulated as a series of incised valley fills because: (i) the basal fluvial erosion surfaces, with at least 16 m of local erosional relief, are regional incisions; (ii) the basal fluvial deposits exhibit a significant basinward facies shift; (iii) the regional erosion surfaces can be correlated with rooted horizons in the interfluve areas; and (iv) the estuarine deposits onlap the valley walls in a landward direction. The coastal-plain deposits represent the topset to clinoforms that formed during progradational infilling of the Eocene Central Basin. Despite large-scale progradation, the sequences are volumetrically dominated by lowstand fluvial deposits and especially by transgressive estuarine deposits. The transgressive deposits are overlain by highstand units in only about 30% of the sequences. The depositional system remained an estuary even during highstand conditions, as evidenced by the continued bedload convergence in the inner-estuarine tidal channels.  相似文献   

12.
Investigations in quarry exposures in the Asheldham Gravel and related deposits of southeast Essex are described. Section logging, mapping and borehole investigations are supported by clast lithological, heavy and clay mineralogical determinations. The sediments are derived from reworking of local Thames basin materials, fine sediment being predominantly from the London Clay. The sequence is shown to represent an aggradation that began as the fluvial infilling of the River Medway valley. The River Thames, diverted into this valley by glaciation further west, overwhelmed the Medway, reworking the deposits. The valley was subsequently drowned and fine laminated lake sediment was initially deposited. This was during a period when the valley was drowned by the glacial lake ponded in the southern North Sea basin by the Anglian/Elsterian ice sheet. Progradation by a braid-delta complex advanced along the valley and subsequently fluvial deposition returned. Valley widening and straightening accompanied the delta progradation. The deposits were dissected by deep fluvial valleys infilled by Hoxnian interglacial sediments. The Asheldham Gravel is therefore placed in the Anglian/Elsterian Stage.  相似文献   

13.
Statigraphic exposures, fluvial archives and borehole data have been allowed to reconstruct the alluvial history of Late Pleistocene to Early Holocene and climate changes in the monsoonal wet–dry region of lower Damodar Basin (West Bengal, India). The facies architectures and climate proxies suggest that five to six climate changes occurred in between ～14 and 6 kiloannum (ka). Supporting evidence from the floodplain of Damodar River demonstrates that the successive phases of aggradation and incision were linked to the south-west monsoonal variability of Late Quaternary period. The onset of semi-arid climate was associated with caliches, pond and backswamp deposits of waning low-energy floods. The relatively warm-humid climate was associated with sandy bedforms, valley fills, slack water deposits and ferruginous nodules. This paper presents a synthesis of the available palaeoclimatic records from the lower Ganga Basin and the rivers of western and central India for the palaeoenvironmental significance of Late Quaternary deposits and discusses the influence of palaeoclimatic controls on the fluvial architectures and archives that developed below the floodplain of Damodar River. We have taken some representative studies from the region to reveal the spatial variability in fluvial successions in response to climate changes during this period.  相似文献   

14.
Organic sediments in a gravel quarry at Block Fen, Cambridgeshire, form a sheet dividing lower from upper gravels. Analyses of pollen, macroscopic plant remains and molluscs from these organic sediments are presented. They indicate the presence of temperate freshwater and slightly brackish fine floodplain sediments, which, on the basis of the palaeobotany, are correlated with the temperate Ipswichian Stage. The freshwater sediments, ascribed to Ipswichian substage IIb, occur at ca. ?3 m OD. Marine-influenced tidal sediments, ascribed to Ipswichian substage III, occur at ca. ?6 m OD. No evidence was found for the presence of more than one temperate stage in the sequence. The lower gravels are then correlated with the cold Wolstonian Stage and the upper gravels with the cold Devensian Stage. In contrast to the woodland environments indicated by the palaeobotany of the Ipswichian organic sediments, post-Ipswichian pollen diagrams and macroscopic plant remains in the upper suite of sands and gravels indicate open tree-less vegetation typical of the cold Devensian Stage. They also contain a typical cold-stage mollusc fauna. The sediments containing these floras and faunas are associated with thermal contraction cracks, indicating the presence of permafrost. The final sand and gravel aggradation in the Devensian forms the Block Fen Terrace, near 0 m OD. The evidence indicates that it is younger than the lacustrine sediments resulting from the blocking of the Fenland at the Wash by Late Devensian ice at ca. 18.5 ka BP. The sequence at Block Fen is related to nearby Ipswichian and Devensian sediments at Chatteris, March, Wimblington and Mepal, and to deposits at Wretton on the east margin of Fenland. The correlation permits an outline reconstruction of the history of the valley carrying the River Great Ouse between the Isle of Ely and the Chatteris and March ‘islands’ from the time of a gravel aggradation before the Ipswichian to the Flandrian. The reconstruction shows the time and level of the Ipswichian marine incursion into the Middle Level of Fenland and the extent of aggradation and erosion in the Devensian.  相似文献   

15.
The grain size of the loess‐like sediment in the Jinsha River Valley is essentially similar to that of typical loess, and it differs from that of the fluvial sediment in the Jinsha River area. We conclude that the loess‐like sediment is of aeolian origin, as is the loess of the Chinese Loess Plateau. The geochemical characteristics of the loess‐like sediment are similar to those of dammed lake and fluvial sediments in the same area, which is significantly different from those of the typical loess in NW China. The geochemical characteristics show that the loess‐like sediment originated from proximal materials. Combined with the grain‐size distribution pattern of the aeolian deposits, we suggest that the loess‐like sediment of the Jinsha River Valley originated from the dammed lake and fluvial sediments that accumulated in the valley. The local mountain‐valley wind circulation (especially the valley wind in winter and spring) provided the transport force for the loess‐like sediment. The presentation of the loess‐like sediment may indicate the appearance of the grassland and forest steppe and the beginning of the dry‐hot valley phenomenon.  相似文献   

16.
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   

17.
Superb surface exposures of a fluvial palaeochannel-belt 2–5 km wide and 13 km long occur in Cretaceous sedimentary rocks of the Cerro Barcino Formation (Las Plumas Member), Chubut Group, Cañadón Asfalto Basin, Argentina. The exceptional plan-view exposures of fluvial sandbodies allowed identification of a large number of WNW–ESE sinuous ridges that represent high-sinuosity, braided and low-sinuosity fluvial palaeochannels, crevasse and chute palaeochannels, and crevasse-splay deposits. Predominance of low-sinuosity palaeochannels and low values of the width/thickness ratio of most them suggest high stability of their margins, probably controlled by the cohesiveness of tuffaceous floodplain deposits. Morphological and sedimentological observations provide evidence of abrupt lithofacies changes in palaeochannel fills, fine-grained intercalations in multi-storey palaeochannels and occurrence of different fluvial styles, implying temporal/spatial variations in palaeodischarge and/or slope conditions. Comparison of the near-identical plan view morphology of the Cretaceous palaeochannel belt with the nearby Chubut River, plus the comparison of palaeohydrological data of the exhumed palaeochannels with hydrological data from this modern analogue, gives evidence of a very similar fluvial behaviour. This provides an integrative tool to be employed in the study of other ancient fluvial successions, including the reconstruction of palaeofluvial hydrological parameters in planetary geology.  相似文献   

18.
Tree-ring studies carried out on subfossil oak trunk deposits within the Holocene valley fills of the River Main can reconstruct phases of increased fluvial activities. These phases have been dated on the base of two absolutely tree-ring dated chronologies and in addition by 11C-datings of eleven floating tree-ring scries of subfossil oaks.
Geological-pedological investigations reveal an alternation between increased and reduced fluvial activity during the Holocene.
Periods of increased gravel redeposition are dated by dendrochronology, and by 14C and cultural findings. Increased fluvial activity becomes more frequent towards Modern Times with culminations in the Middle Atlantic, the Subboreal, the Iron-Roman Age, the Main Middle Ages till earliest Modern Times, and in the last century.
On the sequence of Holocene river deposits there developed specific soil types as indicators for the age of the river deposits since the Last Glacial.
Among other palaeoecological results an important finding is the correlation between tree-ring width, flood-loam sedimentation, and soil development.  相似文献   

19.
This paper records the findings at a temporary exposure at Thorpe St Andrew near Norwich, Norfolk, UK in Early and early Middle Pleistocene Crag deposits. The British Geological Survey (BGS) describes the particular formation exposed as Norwich Crag consisting of Early Pleistocene shallow marine sediments. The section shows a succession of sorted sands and gravels overlain by a sandy diamicton. Based on field evidence and clast analysis, the sands and gravels are interpreted as the product of point bar and overbank sedimentation and represent the product of a river cutting into and aggrading within the more widespread shallow marine deposits. Composition of the sediments indicates derivation, primarily from Wroxham Crag Formation, with a contribution from Norwich Crag. The sandy diamicton is interpreted as late Middle Pleistocene Corton Till that is recorded in the area. A distinct pattern of colour changes at the top of the sands and gravels is interpreted as a soil that developed on the fluvial sediments before being overridden by the glacier that deposited the Corton Till. The existence of the fluvial sediments within the regional shallow marine deposits suggests that a fall of sea-level, possibly due to climate cooling, while the elevation of the sediments and the adjacent Crag implies that the site has been uplifted since sedimentation. This is the first observation of terrestrial sediments within the shallow marine Crag. The paper also makes a contribution to understanding the diagenetic processes that give deposits within this region some distinctive colour and sediment patterns.  相似文献   

20.
The start of deglaciation is recorded in the Minas Basin region of Nova Scotia by the deltaic, glaciofluvial and glaciomarine sediments of the Five Islands Formation. Shell dates on bottomset beds of a delta at Spencers Island range from 14,300 to 12,600, 14C yearsB.P. The time of complete deglaciation of Nova Scotia is still unknown; the uncertainty is at least partially due to evidence for a climatic oscillation at the end of the Late Wisconsinan. Peat beds were deposited during the interval between 12,700 and 10,500 B.P. They overlie previous glacial and fluvial deposits and are overlain by deposits of various origins. Pollen in these peat beds records the migration of spruce into the region indicating climatic warming, and a subsequent deterioration of climate is recorded by the return of tundra-like flora. The peat beds are truncated by a variety of deposits, including fluvial gravel and sand, lacustrine sand, silt and clay, and diamictons. Periglacial landforms and structures have been observed in some of these deposits. At Collins Pond, on the shore of Chedabucto Bay, a diamicton overlying a peat bed is characterized by strong fabrics parallel to the trend of other ice-flow landforms in the region. The evidence suggests that at least some of these deposits are glacigenic, indicating that glaciers were active in Nova Scotia until about 10,000 B.P.  相似文献   

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