Silt Beds Research Articles

Airborne Silts and Dune-Derived Sands in The Permian of the Delaware Basin

ABSTRACT The sandstones and siltstones which dominate the mid-Permian in the Delaware Basin (Texas, New Mexico) are reinterpreted by comparison with the Pleistocene eolo-marine sediments off the Saharan west coast. We suggest that the separation of sands and silts occurred during eolian transport across deserts. Dust was directly contributed to the basin by fallout, yielding topography-mantling, laminated sandy siltstones. Dunes reached the shelf break during a low sea-level stand (peak glaciation) and gave rise to turbidites that deposited the massive channel sands of Brushy Canyon time. Subsequently (Cherry Canyon and Bell Canyon times), dune sands and eolian silts were blended on the platform before aqueous delivery to the shelf break, to yield silty and micaceous channel sands and overbank turbidites interbedded with eolo-marine silt beds. The black-white laminated eolo-marine silstones may record seasonal fluctuations in organic productivity related to the dustborne nutrient supply and to upwelling in a strong seasonal wind regime such as that recorded in the Sahara.

The Coincidence of Macroscopic Paleocurrent Indicators and Magnetic Lineation in Shales from the Precambrian Belt Basin

ABSTRACT Paleocurrent flow direction in shale sequences can be inferred from sedimentary structures of associated lithologies, from orientation of fossils, from alignment of silt and sand-sized particles in shales, from mapping of scalar properties of a shale sequence, and from the orientation of concretions. Not all of these methods relate to shale properties directly, and most of them are very time-consuming and may even require fortuitous circumstances to be applicable. Consequently, even though shales constitute about 60% of all sediments, paleocurrent data from shale sequences are sparse. Thus, in order to improve our understanding of the evolution of sedimentary basins, it would be beneficial to have an accurate and conveniently applicable method of paleocurrent determination for shales. /P> The anisotropy of magnetic susceptibility (AMS) of a number of shale samples from the Precambrian Belt Supergroup carries a fabric-related magnetic lineation that coincides with paleocurrents indicated by cross-laminated silt beds within the shales. Magnetic foliation decreases as dolomite content increases because of diagenetic dolomite growth, but magnetic lineation is only slightly affected. These data indicate that primary flow direction as represented by AMS measurement of these samples is preserved and therefore the AMS method can provide a rapid and accurate way to determine current-flow systems in shale-dominated sedimentary basins.

L'apport des pollens dans le gisement paléolithique moyen de Seclin (Nord)

The excavation at Seclin allowed to organise chronogically different sequences of Prehistoric industries along the Middle Palaeolithic in the silt beds dated from the oldest Weichselian. The pollen analysis of archeological sediments sampled out from four different places in the sites showed numerous gaps in each one of these series, but they also permitted cross-dating. The first phases of the prehistoric industries display practically identical pollinic spectres in the three principal sections, which doubtlessly prove their contemporaneity. The thermoluminescence dates confirm that the Interstadial phase can be dated from the Brôrup period (or 5 c from deap sea cores), a hypothesis which had yet been proposed formely.

Status of Glacial Lake Columbia during the Last Floods from Glacial Lake Missoula

AbstractThe last floods from glacial Lake Missoula, Montana, probably ran into glacial Lake Columbia, in northeastern Washington. In or near Lake Columbia's Sanpoil arm, Lake Missoula floods dating from late in the Fraser glaciation produced normally graded silt beds that become thinner upsection and which alternate with intervals of progressively fewer varves. The highest three interflood intervals each contain only one or two varves, and about 200–400 successive varves conformably overlie the highest flood bed. This sequence suggests that jökulhlaup frequency progressively increased until Lake Missoula ended, and that Lake Columbia outlasted Lake Missoula. The upper Grand Coulee, Lake Columbia's late Fraser-age outlet, contains a section of 13 graded beds, most of them sandy and separated by varves, that may correlate with the highest Missoula-flood beds of the Sanpoil River valley. The upper Grand Coulee also contains probable correlatives of many of the approximately 200–400 succeeding varves, as do nearby parts of the Columbia River valley. This collective evidence casts doubt on a prevailing hypothesis according to which one or more late Fraser-age floods from Lake Missoula descended the Columbia River valley with little or no interference from Lake Columbia's Okanogan-lobe dam.

Geotechnical characteristics of fine-grained turbidite sequences from the Nares Abyssal Plain

Summary Geotechnical property analyses of 21 piston cores obtained from the Nares Abyssal Plain show variations that correspond to facies changes within fine-grained turbidite sequences. Variations in index properties within the turbidite sequences are gradational from the turbidite bases, often containing silt beds or laminae, upwards through the chemically laminated turbiditic clays and into the overlying pelagic and hemipelagic clays. Variations in index properties between sequences can be substantial, with water contents varying by more than 70% over sub-bottom depths of less than a few centimetres. Consolidation test results indicate that most sediments appear to be normally consolidated to over-consolidated. The state of consolidation may vary over short depth intervals within turbidite sequences as a result of the pronounced changes in lithological type. Clay-fabric analyses show significant differences in particle type and degree of sorting between the turbiditic and non-turbiditic clay facies. Particle-to-particle orientations appear quite variable within both clay facies, possibly as a result of modification of the primary fabric by post-depositional changes.

Vertical and Lateral Reservoir Inhomogeneities of a Big-River Bar Deposit, Mississippi River, Missouri: ABSTRACT

The Bryant bar, located on the Mississippi River in southeastern Missouri, is a potential sandstone reservoir that is 18,500 ft long, 3000 ft wide, and 55 ft thick (70,082 ac-ft). A river-meander belt reservoir model was developed from an extensive drilling, coring, trenching, and mapping program. Approximately 2100 horizontal and vertical gas permeability measurements were made of bedding units in trenches, vibracores, and Shelby and splitspoon cores from a variety of depositional environments within this major sand body. Permeability increases with an increase in mean grain size, although the presence of infiltrated mud is an important factor in reducing permeabilities. Avalanche sand and gravel foreset beds in large, laterally continuous, sand waves have permeabilities that range from 91 to 138 darcys. Lower bounding surfaces of foreset laminae are typically not as well sorted, and permeabilities are reduced by 10-50%. Tangential foresets of the laterally restricted, lunate sand dunes have permeabilities that range from 90 to 160 darcys. Permeabilities measured in the interbedded muddy sand, silt, and sandy silt beds from the levee, crevasse, and abandoned channel fill have widely varying permeabilities ranging from 0 to 50 darcys. Mud and silt beds and laminae are very common between and within beddingmore » units in the point-bar and surrounding environments, and are effective permeability barriers to vertical and horizontal fluid migration within point-bar deposits. The distribution patterns of these permeability barriers significantly control effective reservoir continuity. This river-meander belt reservoir model will enhance the understanding of vertical and lateral inhomogeneities in hydrocarbon and water reservoirs.« less

後期更新世における宮崎平野の地形発達

The Miyazaki Plain has the best-developed late Quaternary terraces and deposits in Kyushu. But the landform evolution of this plain has not been investigated in detail in previous works. This study tephrochronologically describes the landform evolution in late Pleistocene.Thick weathered tephra layers overlying the terrace surfaces are subdivided into an older and a younger groups. The younger tephra group, which has been deposited in the last ca. 100, 000 years, contains many marker tephra layers, in ascending order, Ata, K-Tz, FkP and Aso4 of 90, 000-70, 000y.B.P., ; AyP, IwtP, IwP, AwS, HnS II and OtP of 60, 000-30, 000y.B.P.; OsP, ItoPfl, AT and KbP of 22, 000-15, 000y.B.P.; and Ah of 6, 000y.B.P.The older tephra group covers the higher terrace group of middle Pleistocene. The younger group covers the following lower terrace surfaces, in descending order: the Sanzaibaru surface, the Karasebaru surface, the Nyutabaru I, II, III surfaces, the Saitobaru I, II surfaces, the Toyobaru I, II surfaces, the Oyodo surface, the Kunitomi I, II surfaces, the Mikazukibaru I, II surfaces, and the Holocene terrace surface group.Of many terrace surfaces in the Miyazaki Plain, the Sanzaibaru surface is the most extensive one. It is mostly of marine origin, composed of thick transgressive deposits called the Sanzaibaru Formation and lithologically subdivided into three members. The lower member is fluvial gravelous deposit in the regressive stage. The middle member consists of alternating beds of sand and silt with fossils of mollusccs that lived in the embayment of a warm sea in the transgressive stage. The upper member is sandy deposit of deltaic and beach conditions in the maximum stage of the transgression. On the Sanzaibaru surface, the upper member forms sand ridges which are inferred to have been bars, barriers and dunes.The oldest marker tephra layer on the Sanzaibaru surface is the Ata ash which erupted from the Ata caldera ca. 90, 000-80, 000y.B.P.. The Sanzaibaru surface underlying the Ata ash is thought to have emerged ca. 100, 000y.B.P., in the Last Interglacial Stage. It is estimated by subtracting the height of the base of the Sanzaibaru Formation from the height of the shoreline of the surface that sea level rose more than 100m in the Sanzaibaru stage.The Nyutabaru I, II, III surfaces are characterized by gentle gradients and wide distribution. They are of fluvial origin, although the Nyutabaru II and probably III surfaces are partly of marine origin in the northern part of the plain. The Nyutabaru III surface is an accumulation terrace formed during the little transgression. These surfaces are thought to have emerged ca. 90, 000-60, 000y.B.P., when a relatively high sea level was maintained because regression was slow and debris supply from the Kyushu Mountains increased or discharge in rivers decreased.The Saitobaru I and II, Oyodo, and Kunitomi I and II surfaces, which are characterized by steeper and more linear longitudinal profiles, are erosional terraces and are mostly of fluvial origin. Their surfaces came out ca. 50, 000-10, 000y.B.P., in the Last Glacial Stage, when rapid regression occurred and sea level stayed relatively lower. The discharge of the rivers tended to increase gradually.The Karasebaru, Toyobaru I and II and Mikazukibaru I and II surfaces in the northern part of the plain are fluvial fans. They were formed in three regressional stages: the late Last Interglacial Stage, the early Last Glacial Stage and the late last glacial stage. These fans were formed under conditions in which the river bed gradient was steeper than that of the continental shelf when the sea level went down.

Aspectos bio y cronoestratigráficos del Mioceno de Berá (Tarragona)

Se estudian los Moluscos, Foraminíferos, Palinología y Nanoplancton calcáreo de unos nuevos niveles arcilloso-limosos descubiertos en la excavación de un pozo en las proximidades de la Ermita de Berá (Tarragona); la excelente conservación de los restos paleontológicos permite un estudio más exhaustivo. En conjunto, la mayoría de las características indican que se trataría de una sedimentación en condiciones neríticas alrededor de los 30 metros de profundidad con ciertas influencias de carácter estuarino. La presencia de abundantes Orbulina, T. mayeri, junto con G. praemenardii y ausencia de G. fohsi peripheroronda (presente en otras secciones próximas) permite atribuir los niveles a la biozona de G. mayeri, de edad Serravalliense; los datos de Nanoplancton son acordes con dicha edad.

A Pleistocene sandur in western Norway: facies relationships and sedimentological characteristics

At Godøya near Ålesund sequences of unconsolidated fine sand and silt below two till beds are interpreted as remains of a sandur. Two facies sequences dominate: One comprises erosional scours followed by horizontally and current‐ripple laminated fine sand, massive silt and erosional scours. The other sequence differs by planar wedge‐shaped cross‐beds replacing the horizontal lamination. The planar cross‐beds are assumed to represent migrating linguoid or transverse bars, with an orientation partly at a high angle to current ripples in the same beds. The frequent silt beds are interpreted as a result of rapid vertical accretion due to isostatic subsidence during deposition. A Middle Weichselian age is assumed from thermoluminescence, radiocarbon and amino acid dates.

Stratigraphy and Petroleum Potential of the Swift Formation (Upper Jurassic), Southern Alberta and North-Central Montana

ABSTRACT Marine strata of the Upper Jurassic Swift Formation underlie a large area of the Western Interior Plains of the United States and pinch out to an erosional edge in southern Alberta. Two informal members can be distinguished over the study area in southern Alberta and northern Montana: a basal glauconitic shale member, and an upper member, composed of interbedded sandstone, siltstone, and shale, with lithotypes ranging from mudstones with lenticular silt beds to flaser-bedded sandstones. An initial marine transgression resulted in deposition of the basal shale, and was followed by gradual regression and episodic deposition of the ribbon sand member in shallow-marine, bar and interbar facies. Erosion during the latest Jurassic and earliest Cretaceous, particularly valley cutting, determined the distribution of the Swift. Correlation of the Swift with equivalent units throughout the Western Interior of North America provides the basis for a regional reconstruction of Late Jurassic depositional patterns and environments. Insight into erosional patterns and environments during Early Cretaceous time can also be gained. Although potential reservoir strata are widespread in the Swift, poor predictability of sand body distribution and trapping mechanisms make the Swift a low-priority target for hydrocarbon exploration.

Recent Sediment Stratigraphy and Geotechnical Characteristics of Foreset and Bottomset Beds of the Niagara Bar

Forest beds of the Niagara Bar are composed of fine sands and sandy silts. Their thickness is uncertain, but probably 6 to 8 m have accumulated on the upper slope since the last low water stage in Lake Ontario. The maximum thickness of these beds occurs near the foot of the outer slope (water depths 80 to 90 m) where accumulation exceed 20 m north of the present river mouth, and 10 to 12 m to the northwest. The bottomset beds of fine silt and silty clay thin rapidly offshore and decrease to as little as 0.5 m, at about 5 km northwest of the Outer Bar. There is a fining upward lithology in many cores, and this is consistent with continuing deposition under rising water levels. Geotechnical measurements indicate that bottomset and lower foreset beds have low undrained shear strengths (typically less than 4 kPa) and high water contents. Upper foreset beds, of coarser composition, have somewhat higher, undrained shear strengths (20 to 90 kPa, and greater) and much lower water contents. The steepest parts of the Outer Bar lie between 20 and 60 m water depth, where slope angles vary between 2 and 10°; maximum local values reach 14 to 15°. Despite the presence of gas in sediments of the lower foreset beds the slope shows no evidence of slumping.

Stratigraphy and Sedimentology of Ledge Sandstone in Arctic National Wildlife Refuge Northeastern Alaska: ABSTRACT

Data collected from four measured sections of the Ledge Sandstone member of the Ivishak Formation are presented. These sections are located in the Arctic National Wildlife Refuge (ANWR) in northeastern Alaska. The Ledge Sandstone is the time equivalent of the Ivishak sandstones that form the reservoir in the Prudhoe Bay field, east of the study area. The ANWR region is of interest for oil and gas exploration owing to the numerous oil seeps on the coastal plain and surficial expression of possible subsurface antiforms. The Ledge Sandstone in ANWR consists primarily of a massive, thickly bedded, very fine to fine-grained, well-sorted quartz sandstone. Thin beds of silt occur locally. Rare conglomeratic and pebbly zones are found within the unit. Porosity is negligible in the Ledge, owing to siliceous cementation. Bedding planes, where discernible, are predominantly planar with some low-angle cross-bedding. The bases of beds typically contain load features. The thick sandstones are separated by thin siltstone intervals ranging from less than an inch to several feet in thickness. Although the thicker siltstones appear laterally continuous, the thinner beds generally are lenticular over short distances (10 to 20 ft; 3 to 6 m). Cementation of the siltstone appears sporadic, varying laterally and vertically within the unit. Burrowing is extensive in the siltstone intervals. Typically, burrowing cannot be detected in the sandstones because of the obliteration by lithification and diagenetic processes. Fossils are sparse throughout the unit, even in the poorly lithified silts. Some bivalve shells have been preserved intact, but lack any distinct orientation. These data are consistent with a shallow marine environment, within wave base. This contrasts with the nonmarine conglomerates and sandstones of Prudhoe Bay. Time-equivalent units to the south and west consist primarily of cherts and shales of probable deep marine origin, with some arkosic sandstones and dolomites End_Page 439------------------------------ occurring in NPRA. Thus a paleoshoreline is probably located somewhat north of the measured sections. End_of_Article - Last_Page 440------------

MD-QDA characteristics of montane deposits and their confounding of the QDA-MD model for the discrimination of continental environments

The Md-QDa domains of a range of continental deposits originating in a montane environment are derived. They indicate that the Buller-McManus model for environmental discrimination based on Md-QDa analysis lacks generality and is ambiguous to a large degree. This paper's conclusion that alluvial, colluvial and glacial materials are commonly indistinguishable on the basis of their Md-QDa associations cautions against the use of such methodology in the analysis of ancient sediments. Concentrations of the Md-QDa plots for gravel and silt beds about the diagonal of the Md-QDa space are interpreted as resulting from the peculiar nature of source materials for slope deposits in montane environments of the type studied and to the mass movement mode of transportation common to such regions.

A continuous Eemian‐Early Weichselian sequence containing pollen and marine fossils at Fjøsanger, western Norway

A complete interglacial cycle, named the Fjøsangerian and correlated with the Eemian by means of its pollen stratigraphy, is found in marine sediments just above the present day sea level outside Bergen, western Norway. At the base of the section there are two basal tills of assumed Saalian (sensu lato) age in which the mineralogy and geochemistry indicate local provenance. Above occur beds of marine silt, sand and gravel, deposited at water depths of between 10 and 50 m. The terrestrial pollen and the marine foraminifera and molluscs indicate a cold‐warm‐cold sequence with parallel development of the atmospheric and sea surface temperatures. In both environments the flora/fauna indicate an interglacial climatic optimum at least as warm as that during the Holocene. The high relative sea level during the Eemian (at least 30 m above sea level) requires younger neotectonic uplift. The uppermost marine beds are partly glaciomarine silts, as indicated by their mineralogy, drop stones and fauna, and partly interstadial gravels. The pollen indicates an open vegetation throughout these upper beds, and the correlation of the described interstadial with Early Weichselian interstadials elsewhere is essentially unknown. The section is capped by an Early Weichselian basal till containing redeposited fossils, sediments, and weathering products. Several clastic dikes injected from the glacier sole penetrate the till and the interglacial sediments. Radiocarbon dates on wood and shells gave infinite ages. Amino acid epimerization ratios in molluscs support the inferred Eemian age of the deposit. The Fjøsangerian is correlated with the Eemian and deep sea oxygen isotope stage 5e; other possible correlations are also discussed.

Review of the Ecology of Lampreys in Northern Europe

The general distributions of Petromyzon marinus, and Lampetra fluviatilis and L. planeri in Europe are similar and include much of the west and north, whereas Lethenteron japonicum occurs only in the north. The larvae of all four species occupy areas of shaded silt (optimum particle size: 180–380 μm) in parts of streams where current velocities are about 0.4 m/s. The gradients of streams in which they occur range from 1.9 to 5.7 m/km. Though differing in small details, the life cycles have much in common and spawning occurs usually in the spring or early summer. Both males and females spawn only once and die after reproduction. After hatching, the small larvae drift downstream to suitable silt beds. Larval life is variable and may last from 3 to 5 yr or even more. Larval metamorphosis and downstream migration occur during spring and summer and takes place mainly at night. The larvae of all species feed on fine particulate matter — mainly microorganisms and detritus. Adult L. planeri do not feed, but those of the three other species grow and mature in the sea where they are parasitic on a variety of marine and anadromous teleosts. There are considerable differences among the fecundities of the four species — related very much to the size of the adult females. Relatively few data are available on the population dynamics of any of the species.Key words: lampreys, ecology, Europe

MARINE TERRACES AND THEIR TECTONIC DEFORMATION ON THE NORTHEAST COAST OF THE NORTH ISLAND, NEW ZEALAND

The northeastern corner of the North Island, New Zealand, is situated at the southern terminal of the Tonga-Kermadec island arc and trench system, and its east coast runs nearly parallel to the axis of the Kermadec Trench, whereas the trend of its north coast, roughly speaking, is normal to the trench (Fig. 1). Raukumara Range extends approximately parallel to its east coast and terminates close to its north coast, where Matakaoa Range runs from east to west separated from the former by a narrow depression (Fig. 6). The area east of Raukumara Range is hills composed of the Neogene formations and the Taupo Volcanic Zone lies to the west of the range. In this region, marine terraces are developed fairly well on the north coast from East Cape to Cape Runaway and on the southeast coast of the Bay of Plenty as far west as Ohiwa Harbour. Volcanic ash derived from the Taupo Volcanic Zone is extensively distributed in this region and covers the terraces. Its maximum thickness is about 20m in the westernmost part of the region. Volcanic ash beds are grouped into the youngest, the Hamilton and the Tablelands tephra formations (Fig. 2). Fission track ages of the four horizons in the middle and lower members of the Tablelands tephra formation were measured to be 0. 19 to 0. 21m. y. B. P. (Iso et al., to be published). The Ohinewai ash located at the lowest horizon of the Hamilton tephra formation was estimated at about 0.15m, y. B. P.by Vucetich et al. (1978) . A deeply weathered paleosol is developed at the uppermost: horizon of the Hamilton tephra formation and is unconformably overlain by the Rotoehu: ash, which is the lowest horizon of the youngest tephra formation and was dated at 41, 700 14C y. B. P. (Pullar et al., 1973). By tephrochronological and geomorphological means, the marine terraces in this region_ are classified, in descending order, into Matakaoa, Otamaroa, Te Papa and Te Araroa Terraces and can be recognized fairly easily over almost the whole region (Fig. 3 and Fig.. 4 A-F). Matakaoa Terrace is conformably covered with the Tablelands tephra formation.. This terrace is clearly of marine origin, though small in cereal extent, in the northeasternn part of the region, but chiefly forms extensive uplands of fluvial origin, mantled with thick volcanic ash in the southwestern part. Its height ranges from 130 to 20 m. This terrace is capped by the three tephra formations, and is inferred to have been formed in the pe nultimate interglacial age. Otamaroa Terrace is the most extensive terrace in the region, and its initial surface is. preserved fairly well and is conformably overlain by the upper horizon of the Hamilton. tephra formation. Its height ranges from 300 to 10m. Terrace deposits are mainly com. posed of well-sorted rounded gravel and sand 2 to 5m thick, which at several places fill depressions more than 20m deep in the underlying rocks. This suggests that this terrace was formed under a transgressive condition. Fossil mollusca obtained from a silt bed of this terrace in the vicinity of whangaparaoa indicates marine conditions a little warmer than at present (A. G. Beu, personal communication). From its topographical and sedimen tological features, as well as the ages of tephra overlying it, Otamaroa Terrace iss judged to have been formed in the last interglacial age about 0.12m. y. B. P. Te Papa Terrace is mainly distributed in the northeastern part of the region and is less widely developed than Otamaroa Terrace. Its surface is conformably covered by the Rotoehu ash, and its height ranges from 215 to 10m. Terrace deposits consist chiefly of marine gravel and sand 2 to 3m thick, but at a few places they exceed 10m thick. This. terrace, therefore, is inferred to have been formed during a minor transgression.

Lithology and Structures of Quaternary Sediments of Indus Fan: ABSTRACT

The surface sediments of the Indus fan are primarily chalks, marls, and brown clays. Massive terrigenous sediment dilutions occur only in the areas within 100 km from the Indus River confluence. Throughout most of the fan, underlying the sediments, are gray-green muds and turbidites of Pleistocene age. However, the details of lithology and structures of Pleistocene sediments vary from region to region in the fan. The sediments of the upper fan region are primarily fine-grained muds (with several, small silt beds, Td-e), except on the valley floors where coarse-grained turbidites (Ta-e), are commonly present. Two main valley systems, one eastern and the other western, exist on the upper fan. Bioclastic turbidites are common in the eastern valley syste , and are derived from the sediment slumps of the Indian margin. Most of the terrigenous, coarse-grained sediments have bypassed the upper fan and reached the End_Page 734------------------------------ distal areas extending to the Carlsberg Ridge. The percent sand is higher and the number of thick sand beds is more common in the distal areas of the fan; Bouma turbidite sequences, Ta-e, are common. Two main sand lobes are distinguished in the distal fan--an extensive western lobe, derived through channels resulting from the branching of the western valley system, and a restricted, eastern lobe, derived from the eastern valley system. The distributions of these lobes coincide with areas of thick sediments as seen on seismic profile records, implying that sediment dispersal similar to that in the Pleistocene occurred in earlier times. End_of_Article - Last_Page 735------------

Late Pleistocene glacial chronology of the Taylor Valley, Antarctica, and the global climate

Carbonate-rich lacustrine and deltaic deposits, containing thin beds of finely laminated carbonates and thick beds of silt, crop out at several sites in the Taylor Valley and have been encountered in cores obtained by the Dry Valley Drilling Project (DVDP). Fragments of the more indurated carbonate beds have widespread occurrence as part of the desert “lag gravel” which covers much of the valley floor. Analysis of the carbonates suggests that they were deposited as algal limestones from waters derived from the East Antarctic Ice Sheet via the Taylor Glacier at times which correspond to the previous three global interglacial periods, as evidenced by the ice volumes deduced from oxygen-isotopic analysis of oceanic cores. The lacustrine carbonates have been found up to 30 km beyond the present terminus of the Taylor Glacier, and up to 100 m above the level of Lake Bonney, into which the Taylor Glacier at present discharges. It is concluded that the Taylor Glacier has advanced during each of the previous three interglaciations, and it is suggested that this has been caused by a thickening of the East Antarctic Ice Sheet during the interglaciations.

The Geographical Research on the Ancient Grand Canal “Furuichi-ohmizo” in Kawachi Province

There is the historical relic of the grand canal so-called “Furuichi-ohmizo” in Minamikawachi county of Osaka prefecture, where it belongs to the region of the ancient tumuli: Furuichi-Kohun-group. “Furuichi-ohmizo” coexists with these ancient tumuli. It is considered as the big canal which was artificially cut in ancient times. However, the part which “Furuichi-ohmizo” survives is very little, the whole aspect is not yet evident.It is the purpose of this paper to reconstruct the whole canal in detail, and to clear up its character. In this case, the author used the geomorphological and palynological research method in order to investigate the ancient geomorphological and vegetational environment.The results are as follows:1. Ninken-ryo, Minegatsuka-kohun and Seinei-ryo are situated in the vicinity of the mouth of the erosional valleys. (Ryo means the mausoleum of emperor. Kohun means the mausoleum of emperor or powerful family.) They were built in the place of the bad condition. It can be considered that these ancient tumuli were built to bring water of the valley to the moat.2. The sand bed at the upper stratum of the silt bed is accumulated in the flood plain at the junction of the Yamato-gawa River and its branch: the Ishi-kawa River. Such change of sedimentary environment depends on the change of the channel of the Yamato-gawa River. This is an example that the change of the river channel greatly influences the formation of the flood plain.3. By means of the geomorphological investigation and the examination of the placename Koaza in cadastre, the author could reconstruct the canal of the ancient “Furuichi-ohmizo” in the map. As a result, it became clear that “Furuichi-ohmizo” was a big artificial canal from the Ishi-kawa River to the Higashiyoke-gawa River. “Furuichi-ohmizo” formed the one part of the ancient network of canal which was divided into the two main canals and it had some branch canals that linked these main lines. However, it is uncertain whether these canals were built in the same times or not.4. The artificial depression in the west of Shiroyama-kohun exists at the junction of the two main canals. This depression intersects with Ohtsu-michi. The placenames of Koaza as “Kamiohhune”, “Shimoohhune” and “Irimizu” in this place suggest this intersection. Further, it is remarked that the canal crosses the middle terrace. According to these facts, we can infer that the artificial depression is possible to be a port, and the canal was used by way of the water transportation.5. The vegetation in this area changed in the period of early 8th century to early 12th century. The result of the pollen analysis shows it clearly. That is, the forest which was characterized by Abies, Tsuga, Cryptomeria, Sciadopitys, Cyclobalanopsis and Quercus destroyed, changed to the forest of Pinus. And Gramineae increased suddenly before such vegetational destruction. It shows that the clearance of the terrace was faster than the forest destruction of the mountain.The pollen of the large type of Gramineae and Fagopyrum which were the cultivated plant doesn't appear on the lowest pollen zone, it seems that the terrace was not developed at the age of the lowest pollen zone. Therefore, it is assumed that “Furuichi-ohmizo” was used firstly not as the irrigation canal but as the water transportation.

Holocene plant remains from the shores of Lake Manapouri, New Zealand

Abstract Low lake levels at Lake Manapouri expose small plant fragments and logs in beds of silt, deposited on the face of an offshore shelf during a phase of higher lake levels. Radiocarbon dating of wood samples indicates that these beds were laid down between 6 000 and 3 000 yr B.P. Plant fragments are predominantly podocarp, with only a little Nothofagus, which now dominates forests in the area. These results agree with pollen analyses of peats in nearby bogs.