Pleistocene Terrace Deposits Research Articles

Accurate determination of the Pleistocene uplift rate of the NE Japan forearc from the buried MIS 5e marine terrace shoreline angle

We used tephra and phytolith stratigraphy to refine Pleistocene marine terrace chronology, with reference to reported eustatic sea levels associated with the dated marine terraces, and estimated uplift rates along the northern part of the northeast (NE) Japan forearc (the overriding plate in the northeast Japan subduction zone) by using elevation measurements of the buried shoreline angle beneath well-dated marine terrace surfaces to derive more accurate paleo-sea levels. On the Kamikita Plain, northernmost Honshu Island, the T4 and T3 marine terraces were correlated to marine isotope stage (MIS) 5e and MIS 7c or 7e, respectively, by the stratigraphic positions of the tephras Toya (MIS 5d) and WP (MIS 7b). The T2 terrace surface, which had previously been assigned to MIS 7, is buried by loess correlated to MIS 8 by its phytolith assemblage; therefore, this terrace can be reasonably re-correlated to MIS 9. The reported optically stimulated luminescence ages for Middle Pleistocene terrace deposits tend to be younger than these refined terrace ages. We used the buried shoreline angle elevation, determined from the reconstructed profile of the marine terrace deposits and paleo-sea cliff, to refine the uplift rate of T4 since MIS 5e. The accurate rate thus determined, 0.18–0.26 m/ky, is slower than the rates initially inferred from the inner edge of T4, but faster than the reported rate (0.14–0.19 m/ky, as recalculated here) inferred from the assumed MIS 5e shoreline elevation. In addition, it is roughly compatible with the rate inferred by using the top of T2 lagoon deposits to determine the shoreline elevation during MIS 9. Therefore, during the last 300 ka, the uplift rate of the Kamikita Plain has been constant at about 0.2 m/ky. This Pleistocene uplift is probably attributable to a combination of moment release on the megathrust, isostatic uplift driven by crustal thickening, and reverse faulting of the upper crust.

Late Middle Pleistocene ecology and climate in Northeastern Thailand inferred from the stable isotope analysis of Khok Sung herbivore tooth enamel and the land mammal cenogram

Paleoecological and paleoclimatic records based on the stable isotopes of mammalian tooth enamel are poorly known in mainland Southeast Asia during the Pleistocene. Khok Sung in Northeastern Thailand is a late Middle Pleistocene terrace deposit, tentatively dated either as 213 ka or 188 ka, yielding 15 described mammalian taxa with especially abundant and complete fossil remains. To investigate paleodiets and habitats of these ancient mammals and to understand the corresponding regional climate, we performed an analysis of stable carbon and oxygen isotopes extracted from tooth enamel carbonate of various mammalian taxa, coupled with the cenogram method. The enamel δ13C values of Khok Sung mammals indicate a variety of diets, ranging from pure C3 to C4 plants, suggesting that C4 grasses were a major component of local Thai ecosystems during the late Middle Pleistocene. The stable isotopic distinction between C3 and C4 plants suggests that the Pleistocene wildlife habitats ranged from closed forests to open grasslands for the Khok Sung area. Moreover, differences within sympatric Pleistocene herbivores such as proboscideans, rhinoceroses, and cervids characterize possible niche partitioning by minimizing interspecific overlap. Paleoclimatic interpretations based on the intra-tooth variability in enamel δ18O values from large mammals and on the cenogram analysis reflect significant seasonal variations in precipitation and temperature, and humid conditions, for the Khok Sung locality. Compared to modern environments in Thailand, it is apparent that C4-dominated grasslands were more widespread at that time when anthropic impacts on the ecosystems were presumably absent or minimal.

LPI Based Earthquake Induced Soil Liquefaction Susceptibility Assessment at Probashi Palli Abasan Project Area, Tongi, Gazipur, Bangladesh

This study aims at evaluation of seismic soil liquefaction hazard potential at Probashi Palli Abasan Project area of Tongi, Gazipur, exploiting standard penetration test (SPT) data of 15 boreholes, following Simplified Procedure. Liquefaction potential index (LPI) of each borehole was determined and then cumulative frequency distribution of clustered LPI values of each surface geology unit was determined assuming cumulative frequency at LPI = 5 as the threshold value for liquefaction initiation. By means of geotechnical investigation two surface geological units—Holocene flood plain deposits, and Pleistocene terrace deposits were identified in the study area. We predicted that 14% and 24% area of zones topped by Pleistocene terrace deposits and zones topped by Holocene flood plain deposits, respectively, would exhibit surface manifestation of liquefaction as a result of 7 magnitude earthquake. The engendered hazard map also depicts site specific liquefaction intensity through LPI values of respective boreholes, and color index, which was delineated by mapping with ArcGIS software. Very low to low, and low to high liquefaction potential, respectively, was found in the areas covered by Pleistocene terrace deposits and Holocene flood plain deposits. LPI values of both units are such that sand boils could be generated where LPI > 5.

Climate-controlled shifts in sediment provenance inferred from detrital zircon ages, western Peruvian Andes

Abstract Provenance analysis of Pleistocene terrace deposits, together with modern sediments from the same streams, from four catchments draining the western margin of the Andes in Peru is used to infer changes in erosion patterns between the past and the present period by matching detrital zircon ages with crystallization ages of source rocks. Age populations suggest major changes in sediment provenance through the past 100 k.y. At present, sediment sources are mainly located along the steep middle reaches of the rivers, whereas during the Pleistocene, sources were additionally located in the low-relief headwaters of these catchments. These shifts in the loci of erosion are interpreted to reflect changes in precipitation patterns, where periods of stronger precipitation on the Altiplano allowed the entrainment of material from the low-relief plateau in the past. In contrast, modern precipitation patterns result in negligible erosion rates on the Altiplano, and the site of material entrainment shifts to the knickzone reaches where steeper slopes and higher stream power promote erosion. In that sense, this work illustrates that terrace aggradation is associated with major shifts in provenance sources.

Log boats, wooden structures, peat and palaeochannels, the challenges and opportunities afforded by decadal monitoring of an active quarry: A case study from Shardlow quarry, Middle Trent Valley, UK

The River Trent, UK, is renowned for a rich palimpsest of alluvial archaeological remains buried within the Holocene sands and gravels of the valley floor. Since the late 1990's extraction of these postglacial deposits at Shardlow quarry in the middle reach of the valley, close to the confluence of the River Trent and River Derwent, has been investigated and monitored on a weekly basis by a project team including geoarchaeologists. Such monitoring of large exposures of floodplain sand and gravel and adjacent Pleistocene terrace deposits, initially by volunteer activity, but latterly, funded by the aggregate company under a formal planning agreement, has revealed significant alluvial archaeological remains including two logboats, a possible brushwood platform, several fish weirs and organic-rich palaeochannel deposits. This paper provides a summary of the wealth of this resource, but also reflects on the challenges of undertaking geoarchaeological studies in complex alluvial environments over such an extended time period. It concludes by providing advice for best practice that could be applied to other long term studies within similar environments.

Occurrences and origins of soft-sediment deformation structures in the late Pleistocene marine terrace deposits of the southeastern coast of Korea

Soft-sediment deformation structures (SSDS) are examined in the late Pleistocene marine terrace deposits of the southeastern coast of the Korean Peninsula. The marine terrace deposits are exposed in thicknesses of more than 10 m, and consist of lagoon, foreshore to backshore, coastal dune, and foreshore to backshore deposits in ascending order. The SSDS are restricted to the coastal dune deposits and the upper part of the underlying foreshore to backshore deposits, and are grouped into ductile and brittle deformation structures. The ductile deformation structures include irregular laminations, compacted laminations in the hinge zone of folds, asymmetric folds of foreset laminae, and water escape structures. The brittle deformation structures include syndepositional faults or deformation bands. The most probable triggering mechanism for the SSDS is liquefaction by moderate-magnitude earthquakes (M = 5–5.5). Likely, the SSDS were generated over time in various stress fields, including those of main shocks, aftershocks, and later seismic events. The evolution of the SSDS-bearing deposits in the study area can be summarised as follows: 1) rising of the groundwater table in the coastal dune deposits as a result of seismic shock, 2) formation of SSDS by liquefaction in the lower part of the dune deposits and upper part of the underlying foreshore to backshore deposits, 3) descending of the groundwater table, and 4) deposition of foreshore to backshore deposits on the SSDS-bearing dune deposits with erosion of the top of the dune deposits.

The Late Paleoindian Occupation of the Western Ouachita Mountains of Southeast Oklahoma: The Archaeology of Component V at the Quince Site (34AT134)

The Quince site (34AT134) is a well-preserved and relatively deeply stratified Ouachita Mountains archaeological site in Atoka County in southeastern Oklahoma. The site’s archaeological deposits are buried in Late Pleistocene and Holocene alluvial terrace deposits of McGee Creek, a tributary to Muddy Boggy Creek, itself a southern-flowing tributary to the Red River, that cuts through the western edge of the mountains. Excavated in 1982 and 1983 prior to the creation of McGee Creek Reservoir by the Bureau of Reclamation, the 3.0 m deep archaeological deposits at the Quince site contained a record of prehistoric occupations spanning most of the Holocene period (from ca. 10,500 B.P to 1000 radiocarbon years B.P., or ca. 12,590 to 927 calibrated years B.P.) Woodland (Component I), Late Archaic (Components II and III), and Middle Archaic (Component IV) period occupational deposits are present in good stratigraphic order within the upper 1 m of McGee Creek alluvium. There are also a series of buried Late Paleoindian occupations (in what is defined as Component V) with features and chipped stone lithic tools recovered in situ that are recognized beginning from about 1.10 m to 3.0 m in depth below the surface. In this article, I discuss the archaeological evidence for use of the Western Ouachita Mountains by Late Paleoindian foragers as seen principally from the micro-scale; that is, from the perspective of this one well-preserved and stratified Late Paleoindian site. Paleoindian occupations with good stratigraphic context are apparently quite rare in the Ouachita Mountains and along the edge of the Southeastern woodlands and the Great Plains in the eastern and eastcentral part of the state of Oklahoma. Much of the archaeological research dealing with Late Paleoindian peoples in this region has dealt primarily with the description and classification of isolated temporally diagnostic projectile points (and the kinds of lithic raw materials employed in projectile point manufacture) found on the surface or in mixed and relatively shallow stratigraphic contexts. The Quince site Late Paleoindian archaeological deposits provide direct and compelling evidence for the long-term and recurrent use of the western Ouachita Mountains by hunter-gatherer groups.

Climatic, geomorphic, and archaeological implications of a late Quaternary alluvial chronology for the lower Salt River, Arizona, USA

Recent archaeological excavations along the lower Salt River, Arizona resulted in the unexpected discovery of buried late Pleistocene soils and cultural features dating 5800–7100cal YBP (Early Archaic), the latter representing the earliest evidence of human activity in the lower Salt River floodplain thus far identified. Because the lower Salt River floodplain has been heavily impacted by recent agriculture and urbanization and contains few stratigraphic exposures, our understanding of the river's geological history is limited. Here we present a late Quaternary alluvial chronology for a segment of the lower Salt River based on 19 accelerator mass spectrometry 14C and four optically stimulated luminescence ages obtained during two previous geoarchaeological investigations. Deposits are organized into allostratigraphic units and reveal a buried late Pleistocene terrace inset into middle-to-late Pleistocene terrace deposits. Holocene terrace fill deposits unconformably cap the late Pleistocene terrace tread in the site area, and the lower portion of this fill contains the Early Archaic archaeological features. Channel entrenchment and widening ~900cal YBP eroded much of the older terrace deposits, leaving only a remnant of fill containing the buried latest Pleistocene and middle-to-late Holocene deposits preserved in the site area. Subsequent overbank deposition and channel filling associated with a braided channel system resulted in the burial of the site by a thin layer of flood sediments. Our study confirms that the lower Salt River is a complex mosaic of late Quaternary alluvium formed through vertical and lateral accretion, with isolated patches of buried soils preserved through channel avulsion. Although channel avulsion is linked to changes in sediment load and discharge and may have climatic linkages, intrinsic geomorphic and local base level controls limit direct correlations of lower Salt River stratigraphy to other large rivers in the North American Southwest.

Palynological analysis of the Late Pleistocene terrace deposits of Lake Van, eastern Turkey: Reconstruction of paleovegetation and paleoclimate

Paleovegetation and paleoclimate reconstruction of a Late Pleistocene terrace of Lake Van (northern part of lake; Erciş Çelebibağı region) was based on pollen analysis from continuous laminated sediments. According to the pollen analysis, NAP pollen values are predominantly abundant. Chenopodiaceae, Artemisia and Poaceae were the prevailing plants, and Chenopodiaceae was the dominant paleoflora element during Late Pleistocene. Pollen data indicate halophyte vegetation. Climate was colder and drier.

Shallow Subsurface Geology of the Ohmi Basin

This study clarified the stratigraphy and sedimentary facies of the shallow subsurface strata of the Ohmi Basin, an inland lake basin in central Japan. Stratigraphic divisions in the basin are based on regional tephra and widely distributed humic layers. The shallow subsurface strata of the basin are divided into two units. Unit II comprises middle to upper Pleistocene terrace deposits. The overlying Unit I comprises uppermost Pleistocene to Holocene postglacial deposits. Although the lithofacies of Unit II vary horizontally and vertically, the uppermost part consistently consists of humic soils containing Aira-Tn tephra (AT). This distinctive tephra is widely distributed throughout the Japanese islands. Humic soils were deposited at ca. 16.5 to 25 ka according to 14C dating. Unit I, which conformably overlies Unit II, and is mainly a repetitive succession of sand, mud, and gravel. Each layer is discontinuous in terrestrial areas, where distribution patterns of lithofacies are controlled by topography. The depth distribution of AT reflects tectonic subsidence induced by reverse faulting in the Biwako-Seigan active fault zone on the western side of Lake Biwa. Thus, tectonic movement was an important factor during sedimentation. Periodic small-scale subsidence (less than several meters per event) due to slips along faults of the Biwako-Seigan system caused discontinuities in late Quaternary fluvial deposits.

Dating of Late Pleistocene terrace deposits of the River Rhine using Uranium series and luminescence methods: Potential and limitations

Uranium-series dating of pedogenic carbonate crusts from fluvial gravels is tested using Optically Stimulated Luminescence (OSL) ages as references. OSL dating yielded ages of 30–15 ka and 13–11 ka, which correlate with the cold periods of the Last Glacial Maximum and the Younger Dryas. These ages are internally coherent and consistent with the geological background and are thus regarded as reliable. Most of the U/Th results scatter widely in the 230Th/ 232Th vs. 234U/ 232Th isochron diagram, making regression unrealistic. Semiquantitative age estimates from the data were found to be mostly older than the OSL ages and the geological context. It is suggested that a heterogeneous initial 230Th input, not relatable to a detrital component, is responsible for the observed discrepancies. This input may be due to bacterial activities and Th transport on organic colloids. It appears necessary to avoid samples where bacteria could have contributed to carbonate precipitation. Further, the relative importance of this problem decreases with sample age, so that U/Th dating of sinters is expected to be more reliable in the >100 ka age range.

Betulaceae from the Pliocene and Pleistocene of Southwest Alabama, Southeastern United States

Recent investigations of mid-Pliocene Citronelle Formation sites and a Pleistocene terrace deposit in southwestern Alabama have yielded fossils of the Betulaceae. Trullate (shield-shaped) leaves with evenly spaced, craspedodromous secondary veins and distinctively serrated margins indicate that Betula nigra was part of the Gulf Coast vegetation for at least the last three million years. This determination is supported by the presence of small, membranous-winged fruits and a tri-lobed catkin bract. Previous reports of a supposed ancestral species, B. prenigra, from the Citronelle Formation are reconsidered in light of the present findings and rejected. Oblong/ovate leaves with craspedodromous secondary veins, serrated margins, and acute/acuminate apices from the Citronelle Formation are assigned to Carpinus caroliniana. A characteristic nutlet bract of Carpinus was previously described from this formation, and here a staminate catkin with typical Carpinus-like bracts and in situ pollen provides additional support. A nutlet bract from the Pleistocene site confirms that C. caroliniana has been consistently present in this region. Some leaves suggestive of Ostrya were found but their identification is inconclusive. All sites produce Alnus pollen but no macrofossils were found. Of the ten species of Betulaceae in the southeastern United States today, only Alnus serrulata, Betula nigra, Carpinus caroliniana, and Ostrya virginiana frequent the Gulf of Mexico Coastal Plain. Our findings confirm that Betula nigra and Carpinus caroliniana were clearly established in the area by the mid-Pliocene and persisted to the recent, probably due to regional climatic stability.

An optically stimulated luminescence dated Middle to Late Pleistocene fluvial sequence from the western Solent Basin, southern England

AbstractThis paper presents numerical dating from a Middle to Late Pleistocene terrace deposit sequence in the Solent Basin, southern England. The sequence from the western part of the former Solent river system is one of the longest in Britain, with 18 mapped terrace aggradations. A set of 23 optically stimulated luminescence (OSL) dates aim to provide dated tie‐points within the lower part of the sequence at five stratotype locations. These dates are replicated at single sites, providing age estimates for fewer members, but increasing the reliability for those members that have been dated. The results provide two reliably dated tie‐points within the sequence and suggest that (i) the lowest six terrace aggradations all postdate ca. 275 kyr (MIS 8), (ii) terraces may have aggraded during cold phases within the penultimate interglacial (MIS 7) and (iii) the interglacial deposits at Stone Point whose age has previously been contested are likely to be of Ipswichian (last interglacial, MIS 5e) age. These findings are compared to previous age models in the western Solent basin, with which they agree in part. They may suggest that fluvial activity in the Solent was particularly dynamic during MIS 7. Copyright © 2006 John Wiley & Sons, Ltd.

Gulf coastal plain evolution in West Louisiana: Heavy mineral provenance and Pleistocene alluvial chronology

High Resolution Heavy Mineral Analysis (HRHMA) of late Pleistocene terrace samples, their Tertiary source rocks, and modern river sediments provided an effective tool for reconstructing sediment provenance and mapping heavy mineral provinces in southwest Louisiana. Each province, linked to a discrete source region, represents Pleistocene fluvial channel belts within which depositional activity was controlled by periods of climate, sediment supply, and sea level changes. Four coastal heavy mineral provinces have been identified. The Northern Province (NP), drained by the lower reaches of the Sabine and Calcasieu Rivers underlies level mid- and late Pleistocene coastal terrace surfaces and is distinguished by high-grade metamorphic assemblages (kyanite, staurolite, sillimanite) and abundant zircon, probably of Ouachita Mts. derivation. Transporting eroded Cretaceous, Tertiary, and Pleistocene coastal plain deposits, the modern Calcasieu and Sabine River sands in west-central and southwest Louisiana and east Texas, display identical heavy mineral composition to that of the NP. Level Late Pleistocene coastal terrace areas in the east represent the Red River Province (RRP) with dominant epidote, tourmaline, garnet, and zircon. Its mineralogy is influenced significantly by Paleozoic–Mesozoic sedimentary units that frame the drainage basin upstream. Modern Red River sands differ in their spectra both from Red River Pleistocene coastal terrace and valley terrace deposits, interpreted by temporal fluctuations in sediment supply initiating a variable contribution of detritus from different sources. Tributaries that drain formations with high concentrations of high-grade metamorphic minerals also affected Red River valley Pleistocene terrace deposits in west-central Louisiana, enriching them in kyanite and staurolite. The Mississippi Province (MP) occupies the eastern-southeastern area of the low, flat, gently seaward-sloping Prairie coastal terrace. Whereas modern Mississippi alluvium is dominated by hornblende, pyroxenes, and epidote, as the result of post-depositional dissolution, pyroxenes are rare in the MP. The Mixed Suite Province (MSP) reflects MP, RRP, and to a lesser degree, NP signatures and forms the Prairie fluvial coastal plain surface closer to the Texas state line. Raw data of the principal heavy minerals were used for statistical analysis. Statistical parameters proved consistent with mineralogy-derived reconstruction of sediment provenance and provinciality of heavy mineral suites, thus providing an independent and objective support to data interpretation. Optical and thermal luminescence dating at other Gulf locations [Otvos, E.G. (2005). Numerical chronology of Pleistocene coastal plain and valley development; extensive aggradation during glacial low sea levels. Quaternary Internat., 135 91–113.] supports the pre-Sangamon ages of the Intermediate Pleistocene terraces in the NP area. Sangamon (135–116 ka), Eowisconsin (114–76 ka), and Wisconsin (74–36 ka) dates characterize the four provinces in the low, level northern Gulf Prairie coastal plain. Refuting earlier assumptions that coastal plain aggradation occurred only during marine highstand phases, thermal and optical luminescence dates indicated that, despite the low Eowisconsin and Wisconsin eustatic sea levels of several preglacial and glacial stages and substages, coastal plain alluviation, paradoxically, recurred between 106 and 35 ka BP. An interesting outcome of our heavy mineral study is the recognition and dating of a previously undocumented, rare ash-fall event that originated in Caribbean andesitic volcanoes. It was identified by the presence of a volcanogenic heavy mineral suite, composed of pristine euhedral clinopyroxene, sphene, zircon, apatite, and hexagonal biotite. Unaffected by fluvial reworking, this suite was recovered from a MP sample, dated ca. 86 ka BP.

The northern segment of the Têt Fault (Pyrenees-Orientales) : Neogene evolution and geomorphic implications

Abstract In intraplate areas, low tectonic deformation frequently resembles denudational processes. Fault scarps are eroded and buried by Quaternary alluvial deposits. The eastern termination of the Pyrenean orogenic belt displays a moderate tectonic and seismic deformation. In the northern segment of the Tet fault (F.T.N.), geomorphic systems are analysed with intent to detect the various response of landforms and drainage pattern to recent tectonics. We used topography, structural data, drainage pattern and sedimentological syntectonic deposits which determine the evolution of the fault scarp since the Pliocene. The F.T.N., trending N080 to 050oE, is about 30 km long. The fault, separating the Pliocene sequences in the hanging wall and granite in the footwall, is emergent along the scarp. The change in fault orientation along strike gives the fault zone a “dog-leg” pattern in plan view (fig. 1 and 2). Structural data indicate that the faults are steeply dipping (> 60o). The stratigraphy of the study area can be divided up into three main depositional units, bounded above and below by sequence boundaries (fig. 6 and 7). The lithofacies of the Pliocene deposits is composed of coarser conglomerate, sandstones and silts. Most of the sediments exposed in the sections were deposited by braided rivers. Palaeocurrent data indicate a dominant SW-NE directed palaeoflow, although there are also a range of lateral flow directions. Proximal breccias provide evidence for the degradation of the fault scarp (fig. 7b). In westward direction, the offset of middle Pliocene level shows a differential uplift from 150 to 300 m. In several places, the fault is covered by middle Pleistocene terrace deposits that are not apparently affected. The activity of the Têt fault and transversal faults is thus probably lower to upper Pliocene age. The geomorphological indices are useful tools in the evaluation of neotectonics. One of the major features of the relief is the fresh and immature aspect of the fault scarp. They are characterized by a sharp contact between sediments and basement, a low sinuosity index and two triangular spurs. Some statistical properties of landscape (relief, hydrographic network geometry, hypsometric integral ...) may be dominated by the influence of tectonic processes [Merrits and Vincent, 1989 ; Lucazeau and Hurtrez, 1997 ; Font, 2002]. These geomorphic parameters can provide quantitative estimates of surface displacements. But the factors other than tectonics (climate, glacioeustatism and lithology) control morphometric properties. In our study, we used topography, drainage pattern and structural data to perform quantitative morphometric analysis on the basis of field investigation and digital elevation model processed with Arcview V.3.1. The geomorphic indices of drainage basins (area, length, basin relief, slope...), physiographic of the drainage network and degree of topographic dissection of the fault scarp provide information to analyse the timing of the landscape development (tables I & II, fig. 12). Hypsometry has been determined both for basins and selected lithologies within these basins. Hypsometric analysis is performed to summarize the form and evolution of drainage pattern (fig. 10). This F.T.N. is the surface expression of vertical movement located along the strike-slip fault with a normal component. The fault scarp is characterized by three segments which have different morphogenic comportements : the western segmented scarp is poorly exhumed and steeped, the central and eastern scarps are highly eroded and present a poorly geomorphic expression. In the western area, steeper topography accompanied by breaks in the slope along transverse profiles seem to correspond to the trace of recent uplift. Triangular shaped analysis, procured by degradation of the fault scarp, is a geomorphic indicator of neotectonics [Delcaillau, 2001]. Lateral propagation of the deformation and rapid valley incision in the Pliocene formation and the granite of the Millas block are the main factors of the geomorphological evolution of the fault scarp. Divergent-oblique stress leads to the development of strike slip main faults, normal faults and transtensional subbasins. The Conflent basin is in a pull-apart that was initiated during the Pliocene. The elements of the basin fill are underlain by local syndepositional relief, such as fault-flank conglomeratic wedges and evidence of syndepositional tectonism including intraformational fault and roll-overs (fig. 6c).

金剛断層系の平均変位速度分布と奈良盆地南西縁地域における地形発達

The Nara basin, located in the central part of the Kinki triangle in central Japan, mainly consists of Plio-Pleistocene sediments (Osaka group), Pleistocene terrace deposits, and Holocene alluvial deposits.The upper most part of the Osaka group extending in this area consist of fluvial deposits, and is correlated with the Ma3, which is includes the Azuki tephra.The terrace surfaces have developed along the eastern foot of the Kongo-katsuragi Range, in the southwestern part of the basin. Based on the distribution of surface heights and stratigraphies, these terraces are classified into the H, Ml, M2, M3, Li, and L2 surfaces in descending order.The Kongo fault system striking in the north-south direction extends along the eastern foot of the Kongo-katsuragi Range. This fault system consists of the Yamaguchi, Kongo, Nakato, and Yamada faults. These faults have displaced fluvial terrace surfaces, and the slip rates of the vertical component are about 0.03-0.3 m/ky.The Median Tectonic Line striking in the west-east direction and extending southward of the Nara basin, separates the Izumi Range and the Kinokawa lowland. The Shobudani fault, one of the fault systems of the Median Tectonic Line, had a tendency of reverse faulting activity in the former half of the Quaternary. On the contrary, right lateral faulting activity of the Gojodani fault started from the middle Pleistocene, and this tectonic movement has continued to the present along the Median Tectonic Line.Based on the stratigraphy of the Osaka group and fault activity around the study area, the fact that the Nara basin was divided from the Kinokawa lowland by reverse faulting of the Shoubudani fault at least the early Pleistocene, was, clarified. This faulting also formed the, present drainage pattern and the watershed located in the southwestern part of the Nara basin.Fault activity of the Kongo fault system started after the middle Pleistocene. The central part of the fault system shows the highest slip rate. On the contrary, the slip rate at the tips of fault system show a small value compared with the slip rate in the central part of the fault system. Both the height distribution of the terraces and that of the Kongo-katsuragi range, extending to the southwestern part of the Nara basin, have same trend in comparison with the distribution of slip rate along the Kongo fault system.In conclusion, tectonic movement with faulting of the Kongo fault system has affected the formation of landforms in the southwestern margin of the Nara basin.

Another Look at the Cuxton Handaxe Assemblage

The well-known Palaeolithic site at Cuxton, Kent (TQ 710 665) is situated on a remnant of Pleistocene terrace deposits of the Medway, which lies on a chalk spur at the junction of the main river and one of its former tributaries (Fig. 1). These deposits have been known as a source of Palaeolithic artefacts since at least 1889 (Payne 1893, cited in Tester 1965), and have been the subject of two controlled excavations, the first by P.J. Tester in 1962–3 (Tester 1965), and the second by John Cruse (on behalf of the Maidstone Area Archaeology Group) in 1984 (Cruse 1987).

Late Quaternary activity of the Feldbiss Fault Zone, Roer Valley Rift System, the Netherlands, based on displaced fluvial terrace fragments

The Meuse River crosses the Feldbiss Fault Zone, one of the main border fault zones of the Roer Valley Graben in the southern part of the Netherlands. Uplift of the area south of the Feldbiss Fault Zone forced the Meuse River to incise and, as a result, a flight of terraces was formed. Faults of the Feldbiss Fault Zone have displaced the Middle and Late Pleistocene terrace deposits. In this study, an extensive geomorphological survey was carried out to locate the faults of the Feldbiss Fault Zone and to determine the displacement history of terrace deposits. The Feldbiss Fault Zone is characterized by an average displacement rate of 0.041–0.047 mm a −1 during the Late Pleistocene. Individual faults show an average displacement rate ranging between 0.010 and 0.034 mm a −1. The spatial variation in displacement rates along the individual faults reveals a system of overstepping faults. These normal faults developed by reactivation of Paleozoic strike-slip faults. As fault displacements at the bases of the younger terrace deposits are apparently similar to the tops of the adjacent older terrace, the age of these horizons is the same within thousands of years. This implies that the model of terrace development by rapid fluvial incision followed by slow aggradation does apply for this area.

Miocene–Pleistocene tectono-sedimentary evolution of Bahı́a Concepción region, Baja California Sur (México)

Bahı́a Concepción is one of the largest fault-bound bays in the Gulf of California. It is one of the area's best examples of an extensional basin, and an accommodation zone related to the Late Miocene extension in the Gulf of California region. Extensional tectonics in the Gulf region initiated from middle to early Late Miocene, in a simple east–west manner. The units within the Comondú Group are tilted between 14 and 45° in opposite directions (E/W), as a direct result of a single main extensional episode. This event produced subsidence that created the depocenters for nearshore marine basins. The oldest sedimentary units present in the region are assigned to the Late Miocene–early Pliocene Tirabuzón Formation. Up-faulted granodiorite basement occurs on the Peninsula Concepción, and at Punta San Antonio as a direct result of the Late Miocene extensional episode. Extension on the Bahı́a Concepción zone was responsible for development of a divided half-graben structure first flooded in Late Pliocene time. The tectono-sedimentary evolution of Bahı́a Concepción is recorded by three stratigraphic stages: (1) pre-rift strata represented by the Comondú Group, (2) a syn-rift unconformity, and (3) a post-rift strata represented by the Late Miocene to Pliocene flat laying sedimentary units. This triad of stratigraphic stages clearly varies from other basins along the margin of the Gulf of California. Upper Pleistocene terrace deposits generally conform to the 6–12 m elevation regionally associated with substage 5e. Their uniformity in elevation inside and outside Bahı́a Concepción indicates that tectonic uplift was locked in step throughout the immediate region at least since that time.

Ground models for the design and construction of a high-speed rail link

Purpose of survey Engineering geomorphological, geological and geotechnical information, pertinent to a long linear engineering project, was required to provide support to a Parliamentary Bill and assist the future design and construction of the Channel Tunnel Rail Link. A wide variety of reports, maps and borehole logs had been collated for locations in the vicinity of the route alignment. These were to be supplemented with Phase I ground investigations for limited locations along the route during the winter of 1993/94. Phase I information was to be incorporated with the desk study information to provide an initial classification of the route geomorphology and ground conditions, and provide a sensible basis from which to design subsequent Phase II ground investigations. The site The Channel Tunnel Rail Link (CTRL) is to be constructed between St Pancras and the Channel Tunnel Railway Terminal at Cheriton, near Folkestone. The CTRL is a high-speed railway, 108 km in length, and its construction will incorporate a variety of engineered structures. The route traverses a wide range of topography, and solid and drift geology, which produce a wide variety of ground conditions to be considered for design and construction purposes. At a macroscale the CTRL is located in three distinct geomorphological areas: the London Basin, the North Downs and the northern limb of the Weald. A wide variety of solid and drift geologies were evident from available British Geological Survey mapping: these included Lower London Tertiary deposits. Pleistocene Terrace deposits and recent alluvium in