NNW Direction Research Articles

Geophysical and geological constraints on the evolution of the Guadalquivir foreland basin, Spain

Abstract This paper presents a compilation and reinterpretation of available geophysical and geological data recently acquired for the ENE-WSW Guadalquivir foreland basin, located on the northern margin of the Betic orogen in southern Iberia. The data include seismic reflection and refraction profiles, well logs, gravity, geoid, surface heat-flow data and field observations. The deep structure of the southern Iberian margin is characterized by large variations in crustal thickness and high heat-flow values, which result in a very low lithospheric rigidity for the whole area. Geoid and gravity data show that deformation affected the crust and the lithospheric mantle differently, producing anomalous mass distributions that could act as subsurface loads. Seismic sequence analysis of the basin infill has permitted the re-assessment of the depositional sequential arrangement of the sediments deposited from Late Langhian-Early Serravallian to Messinian. They are arranged in six sequences and do not show any E-W progradational pattern indicating that during this period the acting loads moved essentially in a NNW direction. A careful analysis of the southern border of the basin shows that the ‘so-called olistostromes’ correspond to lateral diapirs of squeezed Triassic evaporites and internally imbricated Miocene wedges. We discuss the results obtained in terms of palaeo-geographic environments, time distribution and nature of acting loads, and constraints for future basin modelling approaches.

TRACKING PRODUCED FORMATION WATER DISCHARGE FROM A PETROLEUM PRODUCTION PLATFORM TO THE NORTH WEST SHELF

During September 1995, the Australian Geological Survey Organisation and the Australian Institute of Marine Science took part in a joint survey to monitor the dispersion, fates and effects of Produced Formation Water (PFW) discharged from the Harriet A production platform. Continuous Geochemical Tracer(CGT) analysis of benzene, toluene and C1−C6 hydrocarbons was used to map the spatial distribution of the PFW discharge in near surface waters. Hydrographic parameters were also continuously measured and four hydrocarbon vertical profiles were completed at various distances from the platform.PFW collected at the Harriet A production platform contained 3.75 mg/L of C1−C6 hydrocarbons; 1.59 mg/L of benzene and 1.72 mg/L of toluene. Benzene, toluene and total C1−C6 hydrocarbons are sensitive tracers of PFW, with concentrations of benzene and toluene in the PFW plume about 100 fold higher than typical 'detectable background' levels. Maximum concentrations measured within the PFW discharge plume were 140 ng/L for benzene, 250 ng/L for toluene and 1500 ng/L C1−C6 hydrocarbons. Minimum dilutions of about 2,500 for C1−C6 hydrocarbons and less than 10,000+ for benzene and toluene were measured at distances 1 km from the platform. Thus, close to the platform, benzene and toluene are apparently more 'reactive' than C1−C6 hydrocarbons and disperse more rapidly.The PFW discharge was mapped in a NNW and SSE direction on both the ebb and flood tides to a maximum distance of 10 km from the production platform. A net westerly drift of the plume was evident on both the ebb and flood tides toward the Montebello Islands and Varanus Island, rather than toward the east and the mainland. A one dimensional dispersion model found hydrocarbons are dispersed in seawater, with characteristic half-dispersion distances of about 3.5 km on a spring tide. Vertical profiles of PFW hydrocarbons suggest that within 1 km of the platform the PFW plume is primarily a surface feature but beyond 1 km all hydrocarbons are well mixed.

Paleomagnetism of the Paleoproterozoic Gowganda and Lorrain formations, Ontario: low paleolatitude for Huronian glaciation

To further our understanding of the paleolatitudes of Precambrian glaciations, a paleomagnetic study has been conducted on the glaciomarine Coleman Member of the Gowganda Formation and the conformably overlying deltaic Firstbrook Member and Lorrain Formation (Huronian Supergroup, ∼ 2.4-2.3 Ga) in Ontario, Canada. Many of the rocks, notably the gray and grayish red argillic facies, display unstable magnetization or overprints carried by magnetite and/or hematite that give negative fold tests. Some red sandstones, however, have stable high-temperature (∼ 690°C) components marked by very shallow northerly or southwesterly directions. Five sites in pale red sandstone from the Coleman Member near Elliot Lake give a dip-corrected A direction of D = 216.3°, I = 5.5° ( α 95 = 6.7 °, n = 30), and 17 sites in Lorrain red sandstone near Desbarats give a dip-corrected A direction of D = 5.4°, I = 5.5° ( α 95 = 5.9 °, n = 75). Unfavorable structural attitudes rendered fold tests inconclusive. These very shallow directions may be ascribed to early chemical remanent magnetization (CRM) because (a) some specimens display polarity reversals, (b) such directions are unknown, either as original or as overprint components, in post-Huronian rocks of the region, and (c) a prior site in Coleman red beds gave a high-temperature, shallow NNW direction that is not significantly different from Lorrain A and which a positive conglomerate test suggested is not an overprint. The very shallow directions are near primary directions for the slightly older (2.45 Ga) Matachewan dyke swarm in the region. Lorrain argillic rocks at five sites give a normal component B ( T = 670°C, D = 18.6°, I = 59.6°, α 95 = 6.1 °, n = 16, dip corrected) and a reverse component E ( T = 500°C, D = 190.9°, I = −60.9°, α 95 = 7.3 °, n = 14, in situ), which are close to a prefolding direction carried by magnetite previously identified in Coleman gray argillites (Morris A). However, a primary origin for Morris A is dubious because of the widespread occurrence of overprints carried by magnetite in Coleman gray argillites and because the fold test employed folds formed during the Penokean Orogeny at 1900-1800 Ma. Our results suggest that Morris A/Lorrain B and Lorrain E may data from immediately before and just after Penokean folding, respectively. Hence Coleman-sandstone A and Lorrain A may be better estimates of original directions. Those components and Matachewan paleomagnetic data constrain Huronian paleolatitudes and suggest that Huronian glaciation occurred within 11° and possibly within 4° of the paleoequator.

A detailed study of the active crustal deformation in the Aegean and surrounding area

A detailed study of the active crustal deformation in the Aegean sea and surrounding area is presented. The estimation of the deformation velocities is not performed in broad seismic zones but in seismogenic sources of limited spatial extent, where the seismic energy is practically released, in order to describe the spatial variations of the components of the strain rate tensor. The deformation analysis is based on previous work where the seismicity and the available focal mechanisms are used separately for estimating the rate and shape of the deformation, respectively. The calculations were performed for 63 seismogenic sources identified in the Aegean sea and surrounding area which belong to eight belts with an almost uniform orientation of the stress field. Along the coasts of Albania and northwestern Greece (up to Leukada island) the collision of the Adria plate with Eurasia results in a compressional velocity of about 4 mm/yr in a direction (N49°E) almost normal to the coast line. The dextral movement with almost 3 cm/yr along the Cephalonia transform fault with strike N45°E is expressed as an almost equal extension and compression in N-S and E-W direction, respectively. Along the convex (outer) part of the Hellenic arc a crustal shortening of 1.3 cm/yr is observed in a mean direction N34°E. The direction of this shortening is almost constant from the southern Ionian islands (Zakynthos) up to Rodos while the shortening rate does not significantly change from the outer sources to the inner ones. The Aegean sea and surrounding area is characterised by an extensional deformation. The direction of the maximum extension in the northern part of this area shows an anticlockwise rotation from east to west. Thus, this extension has a NNE direction in northwestern Turkey (N11°E), a NNW direction in central and northern Greece as well as along the southern Aegean volcanic arc and its extension to southwestern Turkey (N12°W) and a WNW direction in the westernmost part of this extensional area (N72°W). The mean value of the extensional velocities in this area is 5 mm/yr. The northern part of Asia Minor and of the Aegean sea is characterised by the dextral strike-slip movement of about 2 cm/yr of the North Anatolian fault and its continuation in the northern Aegean, where this movement gradually decreases to about 6 mm/yr. The vertical crustal (upper 10 km of the crust) thickening is about 2 mm/yr along the convex side of the Hellenic arc and the vertical crustal thinning is about 1 mm/yr in the Aegean sea. These values were obtained from the component U 33 of the velocity tensor.

La faja cataclástica del borde oriental del Sistema de FamatIna, ArgentIna

The cataclastic rocks autcrops are located at the northwestern Pampean Ranges and have a N-S direction. They are limiting the Famatina system to the eastern and carne along the Puna. They have been recognized protomylonites, mylonite gneiss and mylonite schists which may be formed under 10 or 15 km of deep and 275-350° C temperatures of source. The main dominant structure have NNW direction and dips to the eastern. There can be seen compressive movements related to western blocks displacements. During de Ocloyica distrophic phase (Upper Ordovician-Lower Silurian) may be formed these cataclastic rocks, related to the Antofalla Craton collision.

Quaternary tectonic activity in Scotland

Abstract The main features of seven faults inferred to have been active during the Quaternary in Scotland are summarized and their significance in terms of possible tectonic explanations is discussed. One fault in Glen Roy (Central Highlands) is described in detail and evidence is presented for changing stress fields inferred from modes of strain release. Quaternary tectonic activity is interpreted as being dominated by regional effects involving left-lateral simple shear in a NNW direction and some uplift. Stresses associated with ice-load flexure are thought to have played an important role in triggering fault rupture.

Eocene simple shear and plio‐quaternary pure‐shear folding in the Central‐Eastern Algerian Atlas

ABSTRACTTertiary folds of the central and eastern part of the Algerian Atlas were studied in order to assess their kinematics and regimes of deformation. Folds developed following two main phases of deformation during the Eocene and the Pliocene. The NE‐SW trending Eocene folds show a clockwise rotation of fold axis with depth, noncylindrical geometry and a right‐stepping en echelon configuration. Early secondary structures inside each fold are also rotated clockwise with respect to the younger folds. These data are in agreement with progressive ‘simple shear’ deformation. Pliocene folds strike E‐W and display a cylindrical geometry. Associated Plio‐Quaternary brittle structures show no rotational path. These observations are compatible with ‘pure shear’ style of deformation. These results, in combination with focal mechanism solutions, have important implications for the understanding of the kinematic evolution of the western segment of the African‐European plate boundary. For Algeria they imply that transcurrent motion during the Paleogene was followed by coaxial shortening with a NNW direction during Neogene‐Quaternary times. Comparison with published data for Morocco and Tunisia suggests that this transcurrent regime developed from west to east continuing from the Middle Jurassic through to the Miocene.

Rupture complexity of a moderate-sized (mb6.0) earthquake: Broadband body-wave analysis of the North Yemen earthquake of 13 December 1982

AbstractThe occurrence of the North Yemen earthquake of 13 December 1982 provides an important opportunity to study source properties of earthquakes in the southern Arabian Peninsula. Although moderate in size (mb 6.0), this earthquake is the largest to have occurred in the region since the deployment of the Global Digital Seismograph Network. P waves recorded at teleseismic distances can be obtained from stations of this network and of the Graefenberg array that are flat to displacement and velocity in the frequency range from 0.01 to 5.0 Hz. The broad bandwidth of the data is necessary for deriving a dynamic description of the earthquake as well as the static properties of the source. In contrast, inversions using only long-period data provide much less insight into the complexity of rupture. By fitting the displacement pulse shapes with synthetics, we find that the Yemen earthquake was a complex rupture consisting of two events that occurred about 3.0 sec apart. The depth of both hypocenters is estimated to be 7 km. The focal mechanisms of the events each have a nodal plane that strikes 340° and dips 60° to the east. However, the slip directions of the focal mechanisms are in slightly different directions, 230° and 300°, respectively. The total moment of the earthquake is 3.0 ×1025 dyne-cm, with the second event having three times the moment of the initial event. By inverting P-wave arrival time differences at each station, we find the second hypocenter is located 7.5 km from the initial hypocenter in a direction that is nearly colinear with the NNW-striking nodal plane of the focal mechanisms of each event. The trend of extensional ground cracks in the epicentral region and the predominant strike of composite focal mechanisms of locally recorded aftershocks are also in a NNW direction. From the consistency of these observations, we infer that the east-dipping NNW-striking nodal planes are the fault planes. The static stress drop of the first and second events are 44 and 31 bars, respectively. Inverting the energy flux in the velocity waveforms, we find the energy radiated by the earthquake is 4.8 ×1020 dyne-cm. This implies an average apparent stress of 4 bars.At different times during the aftershock sequence, seismicity tended to cluster about one or another of two different planes which, although having roughly the same strike, had conjugate dips. One of these planes, delineated late in the aftershock sequence, coincides with the inferred fault plane for the main shock. The complexity of the main shock and of the aftershock sequence suggests that strain accumulated on a system of strongly interdependent faults. As the region became critically loaded, the effect of a major rupture was to critically stress faults adjacent to the initial nucleation. The second event of the main shock represents the rapid release of stress from the fault system, while the ensuing aftershock sequence represents the gradual release of stress.

Geochemistry and geochronology of the Kibaran granites in Burundi, Central Africa: Implications for the Kibaran orogeny

Recent geological mapping in Burundi defined several generations of granite intrusions in the Burundi Group (middle Proterozoic) according to their structural and geochemical characteristics. Early (Gr 1) and synkinematic (Gr 2) peraluminous granites are related to an extensional tectonic phase D 1 with horizontal deformation and consequent foliation which occurred from ∼ 1400 to ∼ 1260 Ma ago. Peraluminous Gr 3 granites (1185 Ma old) are syntectonic to a compressional phase D 2 which is characterized by upright folds in NNE and NNW directions. Subsequent alkalic Gr 4 granites (∼ 1100 Ma) are associated with transcurrent faults (D′ 2) of lithospheric scale. The Gr 1–3 granitoids display variable 87 Sr 86 Sr initial ratios (0.707–0.735) reflecting the effects of high-level contamination and, to a lesser extent, the composition of their source-region. From isotopic and rare-earth element (REE) data, a large-ion lithophile (LIL)-enriched source of possible Eburnean age, which produced silicic magmas mainly through plagioclase fractionation, is inferred for some granites; however, for most of them the contribution of supracrustal rocks was important. The Gr 4 granites have low Sr initial ratios, suggesting a mantle origin.

Pu isotopes, 241Am and 137Cs in soils from the atomic bombed areas in Nagasaki and Hiroshima.

Plutonium Isotopes, 241Am and 137Cs in soil samples collected from Nagasaki and Hiroshima were measured to evaluate the contribution of residual radioactivity derived from the atomic bombs dropped in 1945. In the soils from Nishiyama area of Nagasaki City, activity ratios different from those of global fallout were found for the 238Pu/239, 240Pu (0.05-0.06), 239, 240Pu/137Cs (0.2-0.3), 241Am/239, 240Pu (0.04-0.05) and 240Pu/239Pu (0.08-0.13), activity ratios indicating that a fair amount of plutonium derived from the atomic bomb had accumulated in this area. On the other hand, in the soils from the “Black-rain” area of Hiroshima, no significant difference from the global fallout was found for the activity ratios among the Pu isotopes, 241Am and 137Cs except for the soils collected at 10 km and 12 km in the NNW direction from the epicenter, where a factor 2 to 3 lower 241Am/239, 240Pu activity ratio was observed. However, no evidence of the contribution of the atomic bomb was found by the measurement of 240Pu/239Pu isotopic ratio.

Precambrian tectonic evolution of eastern India: A model of converging microplates

The Precambrian formations of the Singhbhum and Chotanagpur region of the Indian Peninsular Shield are tectonically classified and their implications in the context of plate tectonics are reviewed on the basis of the stratigraphic, structural, petrologic, geochemical, geophysical and geochronologic data that have accumulated through extensive research in the region in recent years. It is shown that the essential elements in tectonic settings, geological facies and structural and metamorphic characters of the Singhbhum orogenic belt and the reactivated Chotanagpur plateau are elegantly interpretable in terms of interaction of two converging microplates, named here as the Singhbhum and Chotanagpur plates. A detailed correlation of the tectonic evolution with the different stages of a proposed model of plate motions is attempted in the paper. The study reveals three cycles of plate motions with intervening periods of “quiescence”. During the first cycle (2000-1600 Ma), the Singhbhum plate moved northward and collided with the Chotanagpur plate: this led to the tectonic emplacement of the Dalma ophiolite belt and development of the F 1 folds and thrusts and M 1 metamorphism. During the second cycle (1550-1170 Ma), a clockwise rotation of the Singhbhum plate towards the NE generated the F 2 folds and a transcurrent sinistral shear zone. Obduction of the continental lithosphere of this plate occurred during the third cycle (1000-850 Ma) as a result of its continued impingement on the Chotanagpur plate in the NNW direction; this is documented by the evolution of the F 3 folds, M 3 metamorphism and the Singhbhum thrust zone. The “quiescence” periods allowed time for isostatic readjustments, viz., uplifts, intrusions of basic dyke swarms, erosion and paralic sedimentation.

The age of anorthosite events and their geological implications

It is proposed by the authors in the light of isotopie age data available that anorthosite events are advisable to be assigned to two periods, i.e., the Karelian period (1,700–2,00 m.y.) and the Grenville period (1.000–1.300 m.y.), rather than simply to a time span of 1,300±200 m.y. as suggested by N. Herz in 1969. This division is in agreement with the earth history. It is noticed that anorthosites always occur in the mobile zones between plates, indicating a close relationship with deep faults. Anorthosites of the Karelian period are found principally in tectonic zones that strike approximately NWW or NEE in Eurasian (possibly North American) plate. Grenville anorthosites, constituting two (possibly three) belts running roughly in NNE or NNW direction, occur in orogenic zones marginal to the present continents resulting from the breaking up of Pangaca. This suggests that the breaking up of the ancient continent of Pangaea started to operate as early as late Precambrian and was probably responsible for the continental drift along these tectonic belts during late Palaeozoic.

Tectonic model and seismic potential of the eastern Gulf of Alaska and Yakataga Seismic Gap

Based on 13 new fault plane solutions and published seismological, geological, and geophysical data, we interpret the deformation along the Pacific‐North American plate margin in the eastern Gulf of Alaska. Three major tectonic units can be distinguished: (1) the North American plate, (2) the Pacific plate, and (3) a belt of mobile borderland terranes. The Pacific plate moves in a NNW direction at rates of about 6 cm/yr in relation to the North American plate. That motion results in mostly right‐lateral strike slip at the Queen Charlotte‐Fairweather fault system, a well‐known observation. A new finding,however, is that a small component (∼1 cm/yr) of convergence may also be present which results in minor subduction of the oceanic plate beneath portions of the continental margin. Heretofore the Queen Charlotte‐Fairweather fault zone and associated continental margin was interpreted as a classical, pure transform boundary. The Yakutat block, a borderland terrane about 400 km long and 100 to 200 km wide, is carried passively by the Pacific plate except that the block slowly overrides this plate at about 1 cm/yr. This motion is taken up by almost pure thrust faulting in a southwesterly direction along a 400‐km long SE striking shelf edge structure. At its NW edge the Yakutat block is in turn being thrust beneath the North American plate along the Pamplona zone‐Icy Bay lineament. The underthrusting of the Yakutat block results in a major orogeny, crustal shortening and uplift of the Chugach‐St. Elias range. The effects of this collision may extend as far as 500 km inland and cause some deformation at the Denali fault in the central Alaska Range. Subduction of the Pacific plate beneath the colliding margin appears responsible for development of an active volcanic arc up to 300 km inland which trends SE from the Wrangell Mountains to Yukon Territory, Canada, and perhaps to Mt. Edgecumbe volcano in southeast Alaska. The tectonic model proposed implies a high seismic hazard for the Queen Charlotte, Fairweather, and Chugach‐St. Elias fault systems. At these fault zones we estimate recurrence times for great events of about 100 years, but they may vary between 50 and 200 years. A temporarily very high potential for a great earthquake has been determined for the ‘Yakataga seismic gap’ located between Icy Bay and Kayak Island. Large or great thrust earthquakes on the detachment fault underlying the entire Yakutat wedge also appear possible but may only occur infrequently. Their recurrence times are estimated to be several

The nature of deformation within the outer limits of the central appalachian foreland fold and thrust belt in New York state

Residual strain, a self-equilibrating recoverable strain that remains in rocks even after external forces and moments are removed, is found NNW of the folded Appalachian plateau in the Devonian Onondaga limestone and the Silurian Lockport dolomite and Grimsby sandstone of western New York. This residual strain is manifest upon overcoring by a NNW directed maximum expansion of the limestone and sandstone and a random maximum expansion of the dolomite. Strains, recorded with strain gauge rosettes bonded to outcrops, are as high as 200 μϵ (microstrain). Double overcoring of the sandstone and dolomite relieves smaller strains of the same orientation as the initial overcore. X-ray analysis of the Grimsby sandstone shows that the elastic residual strain locked in quartz grains is characterized by a NE principal extension of 60 μϵ and a 10–30 μϵ NW principal compression oriented 30° counterclockwise from the NNW compression indicated by overcoring. Sonic velocity tests on samples in the lab indicate that Grimsby sandstone is anisotropic with a NNW maximum P-wave velocity of 4.05 km/sec. This anisotropy correlates with the residual strain in Grimsby sandstone. Mechanical twinning of calcite within both the Onondaga limestone and Grimsby sandstone indicates that the rock contains a permanent compressive strain of less than 2% in the NNW direction. The permanent strain becomes progressively smaller in a series of samples from Syracuse to Buffalo, New York. The development of solution cleavage in Onondaga limestone also indicates a NNW compression. No evidence of permanent strain was found in the dolomite. The NNW compression of the limestone and sandstone is normal to the fold axes of the Appalachian foreland fold and thrust belt. This geometric relationship indicates that the residual strain well beyond the outermost Appalachian folds was caused by the same tectonic stresses responsible for folding, the Appalachians during the late Paleozoic. Strain within the Appalachian plateau below the Silurian salt horizon suggests either the presence of a second décollement in, perhaps, Ordovician shales or a general NNW shortening of the crust under the Appalachian plateau.

Sediment distribution and transport processes on the outer continental shelf of the Hebridean Sea

The major topographical features of the study area within the Hebridean Sea consist of two submarine banks lying at the edge of the outer continental shelf, an offshore island slope surrounding the Island of Barra-Head, a basin crossing the area in a SSE—NNW direction, and a deep trench. The present investigation suggests that the area was covered with glacial drifts and morainic accumulations during the Pleistocene and that during a subsequent low sea level the drifts were reworked around the topographically high areas. Much of the clay material has been transported to and deposited in regions off the continental slope. Recent conditions are represented by an erosional and depositional environment. The erosional environment is represented by the summit and leeward side of the two banks and the offshore island slope. In these areas tidal-induced currents and south-westerly swells continue to sweep the remaining sand, resulting in the formation of lag gravel deposits. The depositional environment in the basin results in homogeneous sand cover.

Fault-plane solution and tectonic implications of the Pattan, Pakistan earthquake of December 28, 1974

A large destructive earthquake occurred on December 28, 1974 on the western bank of the Indus River near the village of Pattan. The earthquake reportedly killed 5,300 persons, injured 17,000 and left 60,000 people homeless. A seismicity map of the region is presented for the period January, 1963, to March, 1974 on a Mercator projection. Two main linear trends are recognized on the epicenter map. The northwest trend, beginning at 32.3°N, 76.6°E terminates at the southwest alignment of epicenters beginning at 36.0°N, 73.5°E and ending at 33.0°N, 71.0°E. The Pattan earthquake occurred near the junction of the two linear trends. A fault-plane solution for this earthquake has been determined from an analysis of teleseismic P-wave first-motion and S-wave polarization data. The strike and dip of the two nodal planes are N65°E, 68°SE and N50°E, 23°NW, respectively. The solution is compatible with and indicates underthrusting of the Indian plate in this region in the NNW direction along a thrust zone striking northeast.

Geomorphological Development of the Country of Týn nad Vltavou, Southern Bohemia

For this country has been made a geomorphological map in the field scale of 1 : 25000, given here in diminished scale. The geological structure of this peneplenised country is formed by folded and faulted paragneises, migmatitic gneises with smaller veins of different types of granitic vein-rocks. Remnants of the tertiary lake deposits, reduced by denudation, form sands, gravels and clays of miocene and pliocene age. The oldest surface form of this country is south-bohemian peneplain with monadnocks, of the upper-cretaceous age. The surface of the peneplain lies between 450 m a. s. l. in the north and 490 m in the south of the country. Erosion of the rivers Vltava and Lužnice and their brook-affluents with asymetric widely spaced valleys reduced the peneplain into narrow stripes of NNW and NW directions. Parts of the river valleys and most of brook valleys are tectonically predisposed. The widespread form of the country are denudational long gentle slopes (1°-6°) resulting from the denudation of the peneplain. They have isolated cover of tertiary sediments and of pleistocene loess-loams. The penneplain is covered with weathering loams with poor remants of fossil weathering products. Steeper slopes are in the valleys and on the monadnocs crests. On the gentle denudational slopes are from place to place remnants of denudational plains as lowered and reduced remnants of the peneplain. There are also some structural plains on the tertiary deposits. Both great rivers of the country, Vltava and Lužnice, are bordered by erosional and aggradational terraces somewhere preserved only as recuded terraces with residual pebbles. From the level of 51-56 m above river level upwards there are denudated river terraces of pliocene and miocene age. The lower ones, the pleistocene river terraces form a system of 7 main levels, connected with the system of river terraces of the rivers Vltava and Labe in the middle Bohemia. This system of terraces of Vltava and Lužnice in the Týn country is given on the table on the page 324 and on the longitudinal diagramme-section, with the numerical and geometrical representation of the thickness of the terrace aggradational sediments with the bases and surfaces of the terraces, or only with the bases or surfaces of the denudated terrace-remnants.

Winter roost distribution and feeding dispersal of the Grey Starling in Kanto Plain

1. Roost distribution, feeding dispersal and density and behaviour of feeding flocks before roosting flight in the Grey Starling, Sturnus cineraceus, were studied in Kanto Plain from 1953 to 1962. This paper describes the results of some 45 winter observations. The roost distribution will be further iuvestigated.2. In Kanto Plain, extensive feeding range of big Koshigaya roost (about 50, 000 birds) north of Tokyo occupies 30-40km radius circle of the plain. Other smaller roosts are situated outside of this feeding range.3. Daytime (late afternoon observation) feeding flocks usually consisted of several to 30, sometimes 100 birds and each flock was more or less 500m apart. This spacing by small flocks should be a response to the food availability which are minute mud fauna and rather sparcely distributed larger larvae, etc.4. In feeding ground assembly towards evening, up to 300, rarely 500 or exceptionally 1, 000 birds gathered into a flock, the average flock size being 176 birds. Thus an area where a flock of over 150 birds was found could be regarded as a good feeding place. Evening flocks gradually moved always towards the direction of main roost (to which most of the flock members belonged). The distance of this late afternoon movement to final gathering place was usually 1.5-2.0km.5.The density, the economic density, of daytime feeding flocks in the field was 30-500 (average 160) birds per 1km2, therefore 0.3-5.0 (average 1.6) birds per 1 ha, which coincided with previously calculated data. This may suggest that a space of about 1 ha is wanted by one starling.6. Two types of feeding dispersal from a roost were noticed. In type A, the flock size decreased with greater distance along a certain direction and under similar conditions of the feeding environment (see NNW direction in the map). In type B, concentration to a certain feeding area was found. A remarkable concentration was at 40km from the roost which was about the maximum distance of feeding dispersal. On this feeding flight line, the size of feeding flocks decreased with shorter distance from the roost, i. e. greater flock size towards the concentration area. This concentration was possibly due to higher food resources plus good breeding envirnment (old trees with holes).7. The middle area on the B type dispersal line was apparently occupied by a big feeding flock of another roost (confirmed by roosting flight direction). If this were a competitve segregation of feeding grounds by two different roost-flocks, it is a remarkable instance.8. It commonly happens that at the peripheral feeding area, the feeding flocks make a joint flock with birds of other roost or roosts. Thus on starting for roosting flight they take off to different, or to each determined, directions.9. Distribution and observation data at eleven roosts in the study asea (see fig. 1) are described.

Isrecessionen inom Uppsalaområdet

Abstract Ice recession in the Uppsala region. In connection with mapping for the Geological Survey of Sweden in the Uppsala region drillings were carried out at 17 localities (Fig. 1) through the glacial varved clay in order to discover the ice recession in this area. The device used for drilling was a soil sampler with metal foils, constructed by the Swedish Geotechnical Institute (W. Kjellman and co-workers 1950) and able to take undisturbed samples of lengths up to 11 m. Varve measurements were carried out at all localities and used for connections with each other and with earlier measurements from here by Gerard De Geer (1940). The results are given in the graphs of Plate 3 and 4 and the table of Plate 5. Between all localities, situated in the Uppsala plain and the vallies associated with it, it is possible to find varve connections, but it is nearly impossible to do so in the area W of the town, probably owing to topographical conditions influencing the silty bottom streams of melt water from the ice front. Also in about 40 proximal varves, deposited in front of the ice tunnel opening, great irregularities in thickness are observed, owing to the same fact as mentioned above. In the author's opinion it is not possible to make far distant connections of varve series. The map of Plate 2 shows the ice recession in the region with ice margins for every 10 years. During a period of about 90 years — between the years −900—−810 according to the timescale of Gerard de Geer—the ice front retreated from the Uppsala region. From the ice margins it is clear that the ice tunnel, now indicated of the immense glacifluvial deposits of the Uppsala esker, must have debouched into an ice ravine, a fact earlier stated by G. Lundqvist (1955). As it appears from the map the youngest glacial striae W of the esker have a NNW direction, but E of it a NNE direction, indicating an activity of the local ice fronts, formed by the ravine. Glacial striae and end moraines of the region (quoted from G. Lundqvist 1956) correspond very well with the ice margins found in this investigation. In the upper part of the glacial clay of the Uppsala region about 20 to 30 cm above the last discernible microvarve, there is a zone maximally some 10 cm thick — the spotted zone — dotted with sand and gravel particles, mostly calcareous (Fig. 4). The problem of its origin has also been dealt with. According to J. P. Gustafsson (1905) the calcareous material in the spotted zone was once deposited in the sea or lake by ice bergs from the Bay of Gävle, a region where the land ice was rich in such fragments. But the zone is not distributed at random as it would, naturally, be if the material was transported by floating ice, and it is found in every locality where the original strata is preserved, but not in glacial clay, deposited from ice rivers W of the Uppsala region. Its thickness also gradually diminishes with increasing distance from the esker (Table 1), and we never find the spotted zone together with ice floated, large till material which now and then occurs in the glacial clay. The facts above suggest that the spotted zone is a synchronized phenomenon and limited to the sedimentation region of the Uppsala esker. As calculated in Fig. 5, it must have been deposited when the ice front was situated in the southern part of the Bay of Gävle, and the melt water from the ice river carried enormous quantities of calcareous fragments from the Silurian area in the bay. Further investigation of the sediment series N of the Uppsala region will probably provide a definite solution to the problem about the origin of the spotted zone.