Shallow Shelf Seas Research Articles

Role of regional extension and uplift in the Plio-Pleistocene evolution of the Aksu Basin, SW Turkey

The Aksu Basin, within the Isparta Angle area of SW Turkey, documents Plio-Pleistocene crustal processes at the interface between the Tauride Mountains and the Eastern Mediterranean Sea. Basin sedimentation began in the Late Miocene, following an earlier history of emplacement of Mesozoic allochthonous units (Antalya Complex), Miocene basin development and localized Late Miocene compression (Aksu Phase). Late Miocene–Early Pliocene transtension deformed the Aksu Basin, exploiting pre-existing zones of structural weakness. During Early–Mid-Pliocene, muddy sediments accumulated in a shallow shelf sea (<150 m deep), open to the Mediterranean Sea to the south. Regression in the Late Pliocene then resulted in coarse deltaic progradation. Mature erosion surfaces developed on adjacent elevated areas throughout the Pliocene and were accompanied by fanglomerate deposition along the high-relief western margin of the basin. East–west extension then formed the present Aksu Basin as a N–S half graben in the Late Pliocene–early Pleistocene associated with greatly enhanced fluvial downcutting. Accumulation of very extensive (600 km 2 ) and locally thick (up to 250 m) cool-water Antalya tufa deposits then followed, prior to glacial times. Initial localized lacustrine carbonate deposition was followed by development of mainly algal carbonates that are thickest in the west. The terraced nature of the tufa (terraces at 300, 250, 100 m above present sea level) is explained in terms of fluvial processes. Regional comparisons suggest a two-stage history for the Aksu Basin: first, Late Miocene–Early Pliocene transtension and subsidence; secondly, Late Pliocene–Early Pleistocene rifting and marginal uplift. The overall tectonic setting reflects interplay between supra-subduction zone extension and tectonic ‘escape’ of Anatolia westwards towards the Aegean.

Radionuclide activities, geochemistry, and accumulation rates of sediments in the Gulf of Thailand

Downcore concentration profiles of 210Pb, U, and Th isotopes, Al, Fe, Ti, Mn and Sc were measured in sediment box cores collected at 22 stations (16–70 m water depth) covering most of the Thai zone of the Gulf of Thailand. Distributions of excess 210Pb and the detrital elements were used to study spatial variations in sedimentary processes, mineralogy, and geochemistry between different regions of the gulf. Steady-state depositional concentrations and fluxes of excess 210Pb are 3–10 times lower in Gulf of Thailand sediments than in sediments from mid-latitudes in the northern hemisphere, reflecting lower 210Pb inputs from atmospheric fallout at 6–13°N latitude and from lower production of 210Pb from 226Ra in the shallower waters of the Gulf. U and Th concentrations are approximately 2–3 times higher than those in shelf sediments from mid-latitudes of North America, consistent with a higher proportion of granitic source rocks in the Thai environment. Downcore variations in 228Th/232Th activity ratios and in U activities reveal that exchange of interstitial and overlying waters and their dissolved chemicals occurs down to 20 cm in 8 of 10 cores. This benthic exchange may be important in budgets of fluxes of other soluble chemicals in this shallow shelf sea. A net flux of U isotopes from overlying water into Gulf of Thailand sediments occurs, in contrast to their release from sediments of the tropical Amazon shelf. Detectable levels of 137Cs were found only in sediments near the mouth of the largest river, the Chao Phraya. The detrital elements 232Th, 230Th, Al, Ti, and Sc all show relatively uniform downcore concentration profiles. This supports a key assumption in calculations of sediment accumulation rates from downcore profiles of 210Pb activity, that steady-state depositional conditions exist and that basic sediment mineralogy and grain size does not change. 210Pb model derived mass accumulation rates vary between 270 and 490 mg/cm2 per year in the upper Gulf and between 64 and 190 mg/cm2 per year in the central basin. They indicate that suspended sediments and sediment-associated contaminants from the Bangkok area delivered to the upper Gulf are not efficiently transported south into the central Gulf. Al, Ti, Sc, Mn, and Fe sediment concentrations are generally lower than those observed in average shales and crustal materials. This is attributed to greater solubility of these metals during chemical weathering in the hot, humid, organic carbon rich drainage basins of the Gulf. Enrichment factors show that Fe is less and Mn is more efficiently mobilized from the drainage basin than Al, Ti, or Sc. The strong covariance of Al, Ti, and Sc concentrations suggests that they should be equivalently useful normalizing elements to correct for effects of changing grain size and mineralogy on concentrations of other metals with possible anthropogenic inputs. © 1997 Elsevier Science Ltd

The influence of optical properties of shallow shelf seas on temperature structure and acoustic propagation

The penetration of solar radiation below the sea surface is not always taken into account in numerical ocean models, even though its influence on the temperature (and therefore sound speed), structure of the water column can be significant, especially in shallow shelf seas where water turbidity tends to be high. Variations in sound speed structure have a consequent effect on the propagation of sound underwater which, in turn, influences the performance of sonar systems. A double exponential parameterization for the penetration of solar radiation with depth was implemented in an N × 1 D turbulence closure model of the UK shelf seas. The model was run along a section through the Celtic Sea Front, with sets of optical extinction coefficients representing different water clarities, for one month to simulate the generation of the front, and the results were compared with a control model run in which all solar radiation was absorbed in the surface layer. Temperature structure and sound propagation were only affected by changes to the optical parameterization on the stratified side of the front, where consequent variations in acoustic propagation loss of up to 10 dB relative to the control were simulated using an acoustic model. Changes in propagation loss were greatest for acoustic sources placed in the stratified water above the thermocline. Similar changes to the optical parameterization made on the well-mixed side of the front had no discernible effect.

Late glacial sedimentology, foraminifera and stable isotope stratigraphy of the Hebridean Continental Shelf, northwest Scotland

Abstract The detailed stratigraphies of two shallow marine cores from the Hebridean shelf of northwest Scotland are presented. The results provide evidence on the timing of deglaciation from about 15.2 ka BP , with evidence of cold, low salinity water persisting on the shelf until at least 13.5 ka BP . After 13.5 ka BP , probably shortly before 13.0 ka BP , warm shallow shelf seas were established and persisted throughout much of the interstadial. There is some evidence for climatic instability during the interstadial and for a cooling trend from after 11.6 ka BP . Glacial isostatic rebound of the shelf seems to have kept pace with eustatic sea level rise until about 11 ka BP . The fully developed conditions of the Younger Dryas stadial are not observed until 11 ka BP . For the first time from the marine record the constituent tephra peaks of North Atlantic Ash Zone 1 are resolved into a sequence of eruptive events and demonstrate that extensive sea ice transgressed the western UK continental shelf throughout the Younger Dryas. The climatic conditions of the Younger Dryas persist until an initial, precursor warming at 10.2 ka BP , followed by a marked warming of about 8°C and fully established early Holocene temperatures before 10 ka BP . Many of the changes recorded through nearly 5 m of sediments accumulated during the Younger Dryas can be related to changing relative sea levels and source supply.

A survey of the geotechnical properties of some mudrocks of lower liassic age in the Scunthorpe area, Humberside, United Kingdom

During most of the Lower Lias western Europe was covered by a shallow shelf sea in which islands existed. In the English region, deposition was influenced by three tectonic axes which were associated with periodic activity. The succession of the Lower Lias is predominantly argillaceous with subordinate limestones. The clay fraction of the mudrocks usually constitutes more that half the rock with silty material representing between a third and just over 40%. Most of the mudrocks concerned are of intermediate plasticity, the rest being highly plastic. They are inactive and their consistency index indicates that they are either stiff or very stiff. The plasticity tends to decrease with depth, as does the natural moisture content and void ratio. These mudrocks show a general increase in shear strengths with depth. Their shear strength is also influenced by calcium carbonate content, dry density, plasticity, moisture content and prosity. When remoulded, they all displayed a low sensitivity. According to the slake-durability test most mudrocks had a low durability index. The stronger mudrocks were more durable. The compressibility of these mudrocks is very low and is characteristic of heavily overconsolidated very stiff clays. They are impermeable.

Palaeogeography and geodynamic evolution of the Gosau Group of the Northern Calcareous Alps (Late Cretaceous, Eastern Alps, Austria)

The sedimentation of the Late Cretaceous Gosau Group of the Northern Calcareous Alps records the complex geodynamic evolution of the northern part of the Austroalpine microplate. The tectonically controlled sedimentation and facies distribution were mainly governed by the oblique subduction of the Pennic-Ligurian ocean below the Austroalpine margin. Most of the Gosau successions comprise two distinct sedimentary complexes. The Lower Gosau Subgroup (upper Turonian-Campanian) is characterized by terrestrial to shallow-marine facies associations: alluvial fan and fan delta deposits, shallow-marine sandstones and sandy limestones, and storm-influenced nearshore and shelf deposits. During the early Santonian sea-level highstand, a great part of the Northern Calcareous Alps was covered by a shallow shelf sea. Palaeotransport directions point to source areas situated both to the north and to the south of the Northern Calcareous Alps. The Upper Gosau Subgroup (upper Santonian-Eocene) comprises deep-water hemipelagic and turbiditic deposits. Rapid subsidence into bathyal to abyssal depths started diachronously from the northwest (Santonian) to the southeast (Maastrichtian) after a short phase of deformation and erosion. Abyssal deposits in the northern parts of the Northern Calcareus Alps and north-directed palaeotransport indicate a tilting of the slope towards the north. This subsidence pulse is attributed to an event of subcrustal tectonic erosion, probably triggered by the subduction of a topographic high of the South Penninic ocean. The relationships of the Gosau Group of the Austroalpine unit to Late Cretaceous deposits of the Carpathians and Southern Alps are discussed in the framework of a plate tectonic model.

The Oceanographic and Biological Tidal Cycle Succession in Shallow Sea Fronts in the North Sea and the English Channel

Two major discrepancies between existing theories concerning the positioning and development of shallow shelf sea fronts and available data are that these models (1) do not adequately describe the neap-spring adjustment of frontal position and (2) these theories fail to explain the relatively small changes in the location of the front despite the rapid seasonal decay of the stabilizing surface heat flux.In the model presented here, these weaknesses in earlier attempts to describe frontal position are overcome. This is achieved partly by incorporating wind stirring in the heat and mixing balance for the frontal area and partly by allowing for a cross-frontal circulation. This new model defines two types of shallow sea fronts: tidal 'surface' and tidal 'bottom' fronts. Surface fronts are dominated by tidal and bottom fronts by wind stirring. The front type determines the circulation pattern on the stratified side of the front. The circulation pattern, in turn, governs the biological activity. The model describes the persistent but temporally varying redistribution of water from the bottom and surface layers to the thermocline layer which supplies nutrients from the deep (light limited) to the shallow regions where phytoplankton activity is stimulated. This new interpretation of the spring-neap adjustment also implies that, during the heating season, an increasing part of the potential energy to be overcome during a tidal cycle stems from the mixing of nutrient-rich dense bottom water and light surface water imported from offshore. The existence of this mechanism is supported by field observations.

Concentrations, distributions and seasonal variability of dissolved Cd, Co, Cu, Mn, Ni, Pb and Zn in the English Channel

Open ocean studies have shown that dissolved manganese, cobalt and lead exhibit vertical profiles that reflect external sources and short residence times due to scavenging on to particle surfaces. In contrast, dissolved cadmium, copper, nickel and zinc mirror, to different degrees, the profiles of the nutrients. The work reported here for three cruises (November–December 1985, May and July–August 1986) in a shallow shelf sea shows that seasonal variations are shown by metals of the scavenged group, whereas the metals whose cycling in the open ocean parallels those of the nutients, do not show these correlations and, in fact, show no measurable seasonal variability. Concentrations of manganese increased progressively from winter to summer [2.3 ± 0.7(mean± 1σ)to 5.0 ± 3.0 nmol l −1]. A surface enrichment in the upper mixed layer of the western Channel during summer was also observed. Concentrations of cobalt increased from winter to spring (from ≤0.02–0.50 to 0.08–0.71 nmol l −1), paralleling those of manganese, but then decreased into summer (to ≤0.08–0.56 nmol l −1). The regional distribution of lead changed during the spring, possibly reflecting removal by diatoms and decreased river inputs, although overall mean concentrations remained similar throughout the year (0.22 nmol l −1). Concentrations of cadmium (0.20 nmol l −1), copper (3.2 nmol l −1), nickel (3.8 nmol l −1) and zinc (7.6 nmol l −1), and their regional distributions, remained relatively uniform over the period of the observations.

Analysis of the stratification features of the Yellow Sea and the location of its general shelf front in the warm half-year

A stratification parameter\(\bar v\left( {\bar v = \frac{1}{h}\int_{ - h}^0 { \left( {\rho - \bar \rho } \right)gzdz, \bar \rho = \frac{1}{h}\int_{ - h}^0 {} \rho dz} } \right)\), defined as the amount of mechanical energy required to bring about vertical mixing, has been calculated for the Yellow Sea using available data over the past ten years. The monthly distributions of\(Log_{10} \left| {\bar v} \right|\) are obtained to explain the features of the Yellow Sea stratification. Fronts of the shallow shelf sea are often inseparably related with its stratifications. The front of the Yellow Sea in the warm half-year is generated in May and disappears in November. The shelf front moves shoreward and becomes strong in the heating season, but becomes weak in the cooling season upon return.

Sedimentation of riverborne material in a shallow shelf sea: Adige River, Adriatic Sea

Suspended matter and bottom sediments at the Adige River mouth have been investigated with the aim of elucidating the sedimentation pattern of riverine suspended matter in the shallow, low-energy, marginal Adriatic Sea. The grain-size distribution and the mineralogical and geochemical composition of samples collected in two different hydrological situations (low and high river discharge) indicate a similar and consistent sedimentary pattern. Fast sedimentation of fine-grained riverborne suspended matter occurs in the prodelta zone due to deceleration of river flow and spreading into the low-energy environment in front of the river mouth; this is probably associated with flocculation processes in brackish waters. Most of the anthropogenically generated substances associated with the particulate phase accumulate in a restricted area at the Adige River, mouth Knowledge of the area directly influenced by the deposition of riverborne suspended matter is of great interest in assessing the capacity of the Northern Adriatic Sea to assimilate anthropogenically generated material.

Graptolite and conodont faunas in Ordovician Vinini Formation, Roberts Mountains, central Nevada, demonstrate that the Roberts Mountains allochthon is not an exotic terrane

Two very different plate-tectonic models have been proposed to explain the development and emplacement of the Robert Mountains allochthon (RMA) onto the North America craton during the Late Devonian-Early Mississippian Antler Orogeny. In one model, the RMA represents a far-traveled accretionary prism that migrated eastwards over a west-dipping subduction zone. In the other, the eugeoclinal strata of the RMA were deposited on the continental rise of western North America within a closed back-arc basin. Siliciclastic sediments, especially quartz sandstones, compose much of the RMA, yet knowledge of their provenance is poor even though such knowledge is essential for evaluating the two plate-tectonic models.We have recently obtained large collections of graptolites and conodonts from turbiditic quartz sandstones in the Lower Member of the Vinini Formation in the Roberts Mountains. These sandstones of lower Whiterockian age are correlative with the lower Antelope Valley Limestone that deposited on the western shelf of North America. The diverse graptolite fauna represents the oceanic isograptid fauna. However, it also includes pendent didymograptids and rooted dendroids that were restricted to shallow shelf seas. The dendroids (Cactograptus, Dendrograptus, Desmograptus, and Dictyonema) were benthic organisms, could not have lived in a deep marine setting, and are also common in shallow-water carbonate strata of western Utah. All specimens within the turbiditic quartz sandstones of the Vinini were broken before final deposition and burial, but specimens from Utah are generally complete. The diverse conodont fauna is virtually identical to that found in the lower Antelope Valley Limestone, as well as in coeval strata in western Utah. Although it includes a few deep (cold) water, cosmopolitan species, it is dominated by species that are otherwise known only from shallow water strata deposited on the North American craton.We conclude that turbidity currents transported these exotic graptolites and conodonts down from the shelf and onto the rise along with the quartz sands in which they occur. Thus, the Whiterockian quartz sandstones in the Vinini Formation must have a North American provenance just as the fossils do. This is strong evidence that 1) the RMA is not exotic to North America, 2) the eugeoclinal strata of the RMA were deposited on the western continental rise of North America and on the eastern side of a back-arc basin, and 3) the RMA was thrust onto the western shelf of North America by closure of this back-arc basin.

Comparative studies of coastal pelagic fish reproductive habitats: the anchovy (Engraulis anchoita) of the southwestern Atlantic

A framework of comparative climatology of reproductive habitats of coastal pelagic fishes is extended to the anchovy inhabiting the shelf-sea ecosystem off Argentina, Uruguay, and southern Brazil. Maritime weather reports are summarized to yield distributions of wind stress, cloud cover, insolation, sea-surface temperature, wind mixing index, and Ekman transport. These distributions are considered together with other known aspects of the oceanography of the region and with seasonal and geographical aspects of reproductive activity. Over its extensive range, Engruulis anchoita spawns successfully within three different configurations of environmental processes affecting transport, water column stability, and trophic enrichment. One of these, incorporating a coastal indentation downstream from a coastal upwelling center, is very similar to the most common configuration characterizing spawning grounds of eastern ocean anchovy populations. The second, featuring interleaving water masses and upwelling at the continental shelf break, exhibits similarities to the reproductive habitat of the South African anchovy. The third, involving tidal mixing fronts, has been previously noted primarily in connection with herring of higher-latitude, shallow shelf-sea systems. The study adds support to the idea that similar fish populations in different regions must solve similar basic environmental problems and that various experiences of environmental effects in different populations, when viewed from a properly posed conceptual framework, can add up to a useful accumulation of insight.

Cambro-Devonian biogeography of nautiloid cephalopods

Abstract The biogeography of Cambro-Devonian nautiloid cephalopods is documented from their origin during Late Cambrian through to the end of the Devonian. The biogeography developed as the consequence of two related sets of events with different magnitudes. Events controlling the biogeography of first order magnitude were geotectonic, either Gondwana glaciation due to plate movement or contraction in size of oceanic ridges related to decreased rates of sea floor spreading, manifested as first and second order eustatic fall in sea level. These first order events separate nautiloid biogeography into four episodes: (1) Late Cambrian; (2) Ordovician; (3) Silurian through Early Devonian; and (4) Middle through Late Devonian. Each began with an expansion in terms of generic diversity and ended with a crisis of some proportion. Only the end of the Late Cambrian episode cannot be explained by geotectonic events. Events of the second order are both biologic and geotectonic and involve the interaction between the dispersal characteristics of nautiloid cephalopods and plate movements. Due to lack of a planktonic larva and depth restrictions as a function of shell design, the ability of nautiloids to disperse and colonize shallow shelf seas separated by expanses of ocean or depths exceeding shell design limits was minimal. When the width of oceans or depths decreased through some form of geotectonics, nautiloids rapidly radiated and colonized regions as they became available. Thus second order biogeographic episodes tend to evolve from a collection of disjunct patterns with high faunal similarity among faunas of particular landmasses, but with little similarity among separate landmasses, to rapid development of high similarities both among and within faunas of converging landmasses once the physical barrier of distance and water depth is eliminated.

Deep-water hexactinellid sponge mounds from the upper triassic of northern Sichuan (China)

A belt of Upper Triassic (Carnian) sponge mounds was discovered in northern Sichuan in the transition zone between a shallow shelf sea in the SE (Chuan-Dian Shelf) and a deeper marine trough (Ganzi-Aba Trough) in the NW. Individual sponge mounds are up to 60 m high and 150 m wide and interfinger laterally with dark shales. Main frame-builders of the mounds are Lychniscosa and Lyssacinosa, accompanied by (much rarer) Hexactinosa, Lithistida, annelid worms, occasional crinoids and Bryozoa. The reef-dwelling fauna consists of brachiopods, ostracods, foraminifera, pelecypods, gastropods and ammonites. Typical shallow water reef builders (scleractinian corals) and calcareous algae are lacking or extremely rare (coralline sponges). This supports the interpretation of the mounds as buildups in deeper water of several tens up to one hundred meters. The sponge mounds of northern Sichuan are thus an equivalent of similar buildups of late Jurassic age in central and western Europe. They provide the first well-established record of Lychniscosa in the Triassic and their first reported pre-Tertiary occurrence outside of Europe.

Characteristics of Devonian sedimentary facies in the Qinling mountains and their tectono-palaeogeographic significance

Both eastern and western Qinling can be divided into three belts, north, middle and south, based on studies in recent years of the sedimentary facies characteristics, palaeogeographic environments, provenance directions, palaeontologic distributions and geologic event comparisons. Whereas the north belt mainly represents a deep flysch basin on the southern edge of the North China massif, the south belt belongs to the shallow shelf sea on the northern edge of the Yangzi massif. In the middle belt, the Devonian has clear characteristics of a palaeo-island sedimentary system, with a low diversity in coral fauna and some special Upper Devonian geologic events. It represents a micromassif which has been separated from the Yangzi but not yet aggregated to the North China massif. Although the North China and the Yangzi massifs had already had their initial collision during the Caledonian stage, they did not actually converge together to form an unified continent.

Mesozoic and Cenozoic Oceans

Marine sedimentary rocks now exposed on land are mainly deposits of shallow shelf seas, although ancient deep‐sea sediments do occur in the mountains. Thanks largely to the 15‐year effort by the Deep Sea Drilling Project of the Joint Oceanographic Institutions (JOI) Deep Earth Sampling Program, we have made quantum jumps in our understanding of the history of the ocean. Time has been added as the fourth dimension to oceanography, giving birth to a new interdisciplinary science, paleoceanography.The International Lithosphere Program is a successor to the International Geodynamics Program of the 1970s. The program is coordinated by the Inter‐Union Commission on Lithosphere (ICL), a commission of the International Council of Scientific Unions. This volume, Mesozoic and Cenozoic Oceans, is an interim report of Working Group 7 of the International Lithosphere Project.

Vertical distribution, and seasonal and diurnal migration of Calanus helgolandicus in the Celtic Sea

The vertical distribution and migration (seasonal, diel and ontogenetic) of Calanus helgolandicus are described from the shallow (100 m) shelf-seas to the south-west of the British Isles. In 1978 and 1979, the overwintering population of C. helgolandicus consisted primarily of Stage V copepodites and adults. By late winter/early spring the copepodites had moulted to adult females (>90%), which matured and bred the first cohorts of the year, prior to onset of the spring phytoplankton bloom in April/May. C. helgolandicus reached a peak of numerical abundance in August of 20x103 copepodites m-2 (over the depth range sampled -0 to 70 m), which was 200 times the population in winter. The seasonal peak of abundance occurred 4 mo after the peak of the bloom of phytoplankton in spring. The yearly development of the copepod was not always out of phase with the diatom bloom, as seen when the data from 1978 was placed in the context of a longer time-series collected at 10 m over 22 yr (1960–1981, inclusive). Large vertical migrations were observed in the younger copepodites (CI and II) in May from below to above the thermocline. In the remainder of the year, the CI and CII stages behaved differently and were located above the thermocline within the euphotic zone. The largest vertical displacements of biomass were seen in the summer months due to the migrations of the CV stages and adults, which had developed from the spring cohorts. It was contended that the seasonal and vertical migrations of C. helgolandicus are part of a more complex pattern of inherent behavior than has been reported previously and that, however difficult this is to discern in the natural populations, it always expresses itself.

Paleotectonic Controls on Sedimentation in Northern Williston Basin Area, Saskatchewan: ABSTRACT

The Williston basin lies within the so-called stable cratonic interior and would not be expected to have had the same intensity of tectonic activity as is generally considered to be characteristic of cratonic margin sedimentary basins. Local paleotectonic controls on sedimentation are much more subtle, thus sediment distribution patterns are commonly related to major regional structural elements such as the ancestral Williston basin and the Sweetgrass arch. From time to time, however, other structural features appear to have been effective controls on sediment distribution patterns. In southern Saskatchewan, one of the most active of these was the Swift Current platform. This feature appears to have been sufficiently positive during early Paleozoic time to have caused a d stinct thinning of those sediments over it. But it is in early Middle Devonian time that it plays a more prominent role. During the time the Winnipegosis Formation was being deposited, the platform acted as a core for an accreting carbonate wedge that forms the southwestern margin of the Elk Point basin. Progressive inundation of the platform during the remainder of the Devonian made it a part of a broad, shallow shelf sea. However, it was a site of active local salt solution during that time, and may have been as well the locale for repeated accumulations of anhydrite deposits, particularly during the time the Duperow Formation was being laid down. The platform was mildly positive during other periods of sedimentation, as well as during periods of erosion. It was a site of widespread sa t solution during Mesozoic time, which was also its time of major tectonic fluctuation, as well as being the period when it had the most significant influence on sedimentation. Southeastern Saskatchewan is the locale for some significant regional gravity and magnetic anomalies which appear related to exposed structural zones in the Precambrian Shield. A major gravity anomaly on the extreme eastern side of the province is on trend with the Nelson River zone of Manitoba and a magnetic anomaly (Camfield-Gough conductor zone) can be traced to the Wollaston trend in north-central Saskatchewan. The existence of these two trends suggests that the regions proximal to them may have been tectonically active during various geologic periods. The Camfield-Gough zone is particularly significant in that it lies along the axis of the Hummingbird trough, an area affected by basement-controlled early salt solution, and it extends southward into the United States, where it is lanked by a number of local multizone oil-producing structures in North Dakota and Montana. The proximity of these structures to that conductor, which is thought to be a suture between two Proterozoic plates, suggests there is a relationship between them. Isopach and isochron maps have been used to show that these structures have been active during various geologic periods. Similar mapping techniques may show that similar structures are present in southeastern Saskatchewan. End_of_Article - Last_Page 1345------------

Tides and tidal energy

Abstract The present article reviews our understanding of the tides and of the flow of tidal energy through the oceans. The residence time for tidal energy in the oceans is short, and this results in relatively simple relationships between the observed pattern of tides at any port and the motions of the Moon and Sun about the Earth. The first part of the review follows the development of ideas about the tides which led to the harmonic and response function methods of analysing and predicting the tides. The second part of the review is concerned with the energy in the tides, starting from its source in the Earth's rotational kinetic energy, via its transport through the deep ocean, to its eventual dissipation in the shallow continental shelf seas.

Species-diversity patterns in some middle ordovician communities from California - Nevada

Certain fossil communities may be recognized in collections from Early—mid-Middle Ordovician age rock units in the Inyo Mountains, California, and the Bare and Ranger Mountains in adjacent Nevada. These dominantly brachiopod—tribolite communities lived in several different, shallow shelf-sea environments. The communities appear to have maintained their diversity and evenness within relatively narrow limits for as long as the major aspects of the environments in which they lived, remained little changed (periods of about 1–2 m.y.). Some taxa occur in several communities (and are called wide-niched), and some occur in only a single community (and are called narrow-niched). Certain taxa that occur in large numbers in a single community appear to have been far more tolerant of particular environmental conditions than were associated taxa in the same community that are represented by few individuals. Counts of such abundant taxa that are restricted to a single community (and are thus considered narrow-niched) compared with counts of the individuals of those taxa found in several communities (and thus are considered wide-niched) indicate that the taxa highly tolerant of particular environmental conditions may be represented by more individuals than are the wide-niched taxa.