River Rock Research Articles

Morphology and Ecology of Podostemaceae-a Brief Review

Podostemaceae are a specialized group of rheophytes growing only on rocks in torrential rivers mostly in tropical and subtropical regions. Though many species have been described so far, the knowledge on their morphology and ecology is very poor because of the lack of intensive study in most of the species. Now the work on Podostemaceae is urgently needed from the viewpoint of conservation biology as well as the botanical interest in the uniqueness of the plants.

Lithology and Depositional History of Pre-Black River Rocks in the Illinois Basin

Lithology and Depositional History of Pre-Black River Rocks in the Illinois Basin

Early Oligocene paleovalleys in southern and central Wyoming: Evidence of high local relief on the late Eocene unconformity

Local relief in the mountains of southern and central Wyoming at the end of the Eocene was as great as if not greater than it is today. This is indicated by large valleys containing the lower Oligocene White River Formation that extend into the Precambrian cores of the Medicine Bow and Laramie mountains. There has been little deformation of White River rocks in the valleys or on the margins of the mountain ranges, precluding post-Eocene block uplift as a source of modern topographic relief. The regionally widespread low-relief subsummit surface was developed during the Miocene, and is not part of the late Eocene unconformity. Other Oligocene valley fils in the Rocky Mountains indicate that high local relief was widespread during the late Eocene.

Geochemistry of the host rocks of the volcanogenic massive sulfide deposit at Que River, Tasmania

Que River is a moderate-sized, high-grade polymetallic volcanogenic massive sulfide deposit located in the Cambrian Mount Read Volcanics of western Tasmania. Several subvertical lenses of massive sulfide occur in a sequence dominated by variably altered intermediate to silicic volcaniclastic rocks. The sequence was deformed and regionally metamorphosed to prehnite-pumpellyite facies during the Devonian. Approximately 240 host-rock samples have been analyzed in an attempt to determine their primary geochemical affinities and to evaluate the geochemical effects of alteration.On binary variation diagrams, elements such as Zr, Nb, Y, Ti, and Al define linear fields that characteristically project toward the origin. The linear behavior of these elements on such plots is in marked contrast to that of almost all other elements, which show very complex distribution patterns. The linear patterns are interpreted to reflect immobility of the components mentioned, with movement up and down the linear arrays being controlled by concentration or dilution due to subtraction or addition of other components. Thus, primary ratios between immobile components have been preserved and can therefore be used to infer the primary geochemical affinities of the altered rocks. The intersection point of the linear trends defined by the Que River rocks with a low-pressure fractional crystallization trend defined by Cenozoic orogenic lavas probably provides the best estimate of the initial composition of the rocks prior to alteration.In a plot of Zr/TiO 2 vs. Nb/Y the Que River rocks define a restricted area dominantly in the fields defined by modern andesite and dacite-rhyodacite. Basalts and rhyolites are apparently absent. In terms of their primary geochemical affinities, the host rocks of the mineralization are probably best described as a high K, calc-alkaline suite, similar in many ways to modern continental margin andesitic rocks. However, the Que River rocks are by comparison abnormally depleted in Ti and enriched in transition metals such as Ni, Cr, and V.The geochemistry of alteration is complex and not readily amenable to quantitative evaluation. Elements such as Fe, Mg, and Mn have been added to the system whereas Ca and Na have been removed. Both Si and K have been partly remobilized during alteration. Among the major and minor elements, Mn shows the greatest relative enrichment over its inferred primary abundance. However, the Mn anomalies are sporadic and do not define a neat halo. Although most of the observed geochemical alteration appears to have accompanied mineralization, the andesites have been modified from their inferred primary compositions, probably during the regional metamorphism. Hydrothermal alteration is not symmetrical about the ore lenses. Although the presently observed displacement between the massive sulfide lenses and the alteration halo is probably due largely to the Devonian deformation, it is possible that there is also a primary component.The apparent immobility of Al implies that the abundant phyllosilicates, whose development is clearly related to mineralization, do not represent simple chemical precipitates or sediments. Rather, their development would appear to be controlled by the local availability of immobile Al.

Effect of a Caddisfly on Black Fly Density: Interspecific Interactions Limit Black Flies in an Arctic River

In a whole-river fertilization experiment, density of the dominant caddisfly, Brachycentrus americanus, was significantly higher downstream of fertilizer addition, while black fly density was significantly lower. In a caging experiment where Brachycentrus density was manipulated, black flies were significantly less abundant in high-density Brachycentrus cages than in ambient- and low-density Brachycentrus cages. Microcosm experiments and gut analyses showed that Brachycentrus--black fly encounters did not result in predation, but sometimes resulted in black fly drift. Black flies were more abundant on river rocks without conspicuous periphyton cover, but in microcosms they preferred periphyton-covered rocks. In microcosms the presence of periphyton resulted in a shift in black fly distribution from the tops of rocks to the bottoms and sides of rocks, the preferred microhabitat of Brachycentrus. Brachycentrus in microcosms did not affect black fly microhabitat preference. Increased periphyton abundance in ...

The Pontiac problem, Quebec–Ontario, in the light of gravity data

A belt of Archean quartzose metasedimentary gneisses with minor mafic volcanic rocks (the Pontiac Group) lies south of the Blake River and older Archean mafic volcanic rocks of the Abitibi Greenstone Belt, and is separated from them by the Larder Lake – Cadillac Break. To the west of the Pontiac Group, on strike, is the Archean Larder Lake Group of turbidite conglomerate, argillite, limestone, and iron formation with abundant mafic flows and intrusions. These strata also lie south of the Larder Lake – Cadillac Break and south of the Blake River and older Archean mafic volcanic rocks. The western contact between the Pontiac and Larder Lake groups is covered by a narrow north–south strip of Proterozoic Cobalt sedimentary rocks. On the basis of gravity work that compares the Bouguer gravity anomaly gradient across the Cadillac Break with that across the west margin of the Pontiac Group, it is proposed that the Larder Lake and Pontiac groups are separated by a north–south fault and that the Pontiac Group represents a lithologically distinct uplifted block. The Pontiac block may be an Archean terrane.

Diagenesis, Depositional Environments, and Hydrocarbon Potential of the Basal Limestone, Green River Formation, Uinta Basin, Utah: ABSTRACT

The basal limestone of the Eocene Green River Formation is well exposed along the southern margin of the Uinta basin. Surface and subsurface stratigraphy evidence a wide spectrum of mixed siliciclastic-carbonate rocks within a well-defined sequence. Although numerous stratigraphic and petrographic investigations of Green River rocks have been completed, none have dealt specifically with the basal limestone facies in detailed stratigraphic context. Rocks exposed along the southern basin margin reflect deposition in relatively shallow-water, mud-flat conditions. Shallowest conditions are marked by dolomitized ostracod and pellet grainstones. Shoreward of the grainstones in typically fresher water, sandy pelecypod-gastropod grainstones are presented and are commonly interbedded with silty mudstones. Deepest offshore conditions resulted in the deposition of dark-gray, kerogen-rich carbonates. Cores, electric logs, and subsurface mapping indicate rapid facies changes to the north (toward the basin center). Kerogen-rich carbonate potential source beds predominate toward the basin center and interfinger southward with lakeshore and lagoonal deposits, which are composed of ostracod packstone and sandy grainstone reservoirs. Interpretation of the detailed petrography of various environments has evolved a paragenetic sequence. Several authigenic clay and carbonate mineral phases were precipitated in the pore systems.

POST-IMPOUNDMENT TRENDS IN THE FISH POPULATIONS OF THE HENDRIK VERWOERD DAM, SOUTH AFRICA

SUMMARY Fish population changes in the Hendrik Verwoerd Dam are presented as sampled with a series of multifilament gill nets from Spring 1971 to Summer 1977. During this period, species such as Barbus halubi (smallmouth yellowfish), B. kimberleyensis (largemouth yellowfish), Labeo capensis (Orange River labeo), Cyprinus carpio (common carp) and Clarias gariepinus (sharptooth catfish) appeared to favour the newly created dam-environment. L. umbratus (moggel), however, showed a slight decline in abundance, while the Orange River rock catfish, Gephyroglanis sclateri, disappeared entirely from the gill net catches four years after inundation. Low numbers of Labeo umbratus x L. capensis hybrids were sampled, mainly in areas where small streams enter the dam. Rainbow trout (Salmo gairdnerii) and brown trout (S. trutta) were netted annually during the early summer months. Fluctuations in water level and siltation are probably the main factors causing continual changes in food supply and juvenile production and,...

Volcanic rocks of the Blake River Group, Abitibi Greenstone Belt, Ontario, and their sulfur content

Six hundred and ninety samples of volcanic rocks from the Blake River Group of the Abitibi Greenstone Belt have analysed for sulfur on a Leco sulfur analyser. Basaltic rocks have been subdivided into komatiites, Fe-rich tholeiites, Al-rich basalts, and intermediate basalts with more than 1% TiO2 and with less than 1% TiO2. Andesites have been subdivided into Fe-rich types, Al-rich types, and others. All dacites are grouped together as are all rhyolites. Rocks of many of these subdivisions occur at more than one level within the Blake River stratigraphy. Within a given rock subdivision, the sulfur content is distributed log normally. When the geometric mean of the sulfur content of each of the subdivisions outlined above is plotted against the arithmetic mean of the FeO content, a smooth curve is obtained, with sulfur increasing markedly with increase in FeO. The data give no indication of any change in sulfur content of a given rock subdivision with stratigraphic height. The arithmetic mean of the sulfur content of each rock subdivision also increases with the mean FeO content, although less smoothly than the geometric mean. The arithmetic means of sulfur content fall within the scatter of points obtained experimentally for the sulfur content of sulfur saturated basalts, supporting the contention that the Blake River rocks may have been saturated with sulfur at the time of their extrusion.

Palaeoanthropology, chronology, and archeology of the Matjes River Rock Shelter

Palaeoanthropology, chronology, and archeology of the Matjes River Rock Shelter

A Revised Interpretation of the History of the Skeena River Sockeye Salmon (Oncorhynchus nerka)

Three factors are examined as an aid to interpreting the historical sequence of Skeena sockeye catches. One of these (Exploitation Mechanism 1) affects the catch directly, the other two affect catch by way of increasing or decreasing the recruitment produced by a given number of spawners. "Exploitation Mechanism 1" of Ricker (1973) makes the catch taken from any given brood during a time of increasing rate of exploitation greater than when exploitation is steady or decreasing; this is the main reason for excellent catches from 1905 to 1925. "Exploitation Mechanism 2" makes the progeny of any given number of spawners less numerous under conditions of maximum sustainable yield than during the period when rate of utilization is increasing; as a result recruitments observed prior to 1930 overestimate the potential productivity of the system and hence the sustainable yield. Mechanisms 1 and 2 are both operative even if the best rate of exploitation is never exceeded. In fact, however, the rate of exploitation began to exceed the optimum level of 50–55% about 1908, continued to increase until 1928, and then slowly decreased until the optimum level was reached about 1945; during the latter period, and for about 15 yr subsequently, catches were further depressed as spawning stocks were slowly rebuilt. Another factor affecting recruitment is the apparent existence of interaction between neighboring year-classes in respect to survival rate. Although the exact mechanism of this interaction is not yet known, it has produced three sequences of moderately "dominant" year-classes, the most recent being 1959–63–67–71, in spite of the complication of having two important ages of maturity for Skeena sockeye. More important is the fact that during the recent period large spawnings (0.75–1 million) have produced poor returns while moderately small spawnings (0.25–0.5 million) have produced larger year-classes than they did at any earlier period — in spite of the handicap of Mechanism 2. This apparent interaction between broods implies that one or more small spawnings are a necessary prerequisite for unusually successful reproduction by a later large one, and that successful large spawnings depress the reproduction of subsequent smaller ones. When all these factors are considered together, the observed trend of the Skeena catches can be reproduced. Maximum natural sustainable yield from the system would have been achieved about 1960 except for 2 yr of much reduced reproduction caused by the Babine River rock slide of 1951. Currently, the increased numbers of fry produced in artificial spawning channels at Babine Lake have contributed to large smolt runs that are now beginning to appear in the adult catches.

Transparente Schwerminerale aus granitischen Gesteinen und aus Flüssen des Blauen-Massivs (Südwest-Schwarzwald)

Transparente Schwerminerale aus granitischen Gesteinen und aus Flüssen des Blauen-Massivs (Südwest-Schwarzwald)

Prehistory of the Matjes River Rock Shelter

Prehistory of the Matjes River Rock Shelter

Cambrian and Ordovician Rocks in Michigan Basin and Adjoining Areas

Sandstone, limestone, and dolomite of Upper Cambrian and Ordovician age either are exposed at the surface or underlie glacial drift in the Northern Peninsula of Michigan. The outcrop of these rocks extends southward from northern Michigan into Wisconsin and Illinois. Eastward across the Northern Peninsula, Middle Ordovician rocks overlap progressively older rocks, and on Manitoulin and adjacent islands Black River rocks of Middle Ordovician age rest on pre-Cambrian. This same stratigraphic relationship is observed in other outcrop areas in Ontario and in deep wells that have penetrated the full section of sedimentary rocks. Pre-Black River erosion removed most of the older Paleozoic rocks from the underlying pre-Cambrian in southwestern Ontario and in some places only a t in remnant of Upper Cambrian sandstone and some dolomite occurs between Middle Ordovician and pre-Cambrian rocks. Cambrian and Lower Ordovician (sub-Trenton) sandstone and dolomite range in thickness from less than 500 feet to more than 3,500 feet in Michigan. The aggregate thickness of these rocks increases southwestward from Michigan toward Illinois and thins southeastward over the Findlay arch in southeastern Michigan and northwestern Ohio. The rocks increase in thickness eastward into the Appalachian basin from the Findlay arch. The widespread limestones and dolomites of Middle Ordovician age rest on eroded Lower Ordovician and Upper Cambrian rocks in Michigan, northern Indiana, and northwestern Ohio and range in thickness from less than 200 feet in the Northern Peninsula to more than 900 feet in southeastern Michigan. These rocks are thickest a short distance east of the center of the present Michigan basin and are thinner over major anticlinal folds. This indicates that the basin was depressed in an area somewhat similar to its present form as early as Middle Ordovician time. Oil and gas were commercially produced from the sub-Trenton rocks in Ohio on the east flank of the Findlay arch in several small areas. Showings of oil and gas in these rocks have been reported from wells in northeastern Indiana, southeastern Michigan, and southwestern Ontario. The Trenton limestone, which is the producing formation in the Lima-Indiana field, is productive in small areas in southeastern Michigan and southwestern Ontario.

Prehistoric Stock of South Africa

AT a meeting of the Royal Anthropological Institute (Section of Human Biology) on Jan. 8, Sir Arthur Keith exhibited a series of human skulls from the Matje River Rock Shelter, a newly discovered prehistoric site in the Zitzikamma District, on the coast of the Cape Province. The deposits in this rock-shelter, amounting to 21 feet in depth, were excavated by Prof. T. F. Dreyer, of Grey University College, Bloemfontein. The rock-shelter was first inhabited during the age of the ‘Mossel Bay’ culture, which is usually equated with one of the later palaœlithic cultures of Europe, and this culture was richly represented during the formation of the deeper strata, amounting in depth to 14 feet. All the remains from the Mossel Bay strata manifest racial traits, which were first revealed by the discovery of the large-brained Boskop skull in 1913. Three of the skulls from the deepest Mossel Bay strata have peculiar features of the forehead; the frontal bones appear compressed from side to side, with a high median keel. This malformation, known as trigonocephaly, occurs occasionally in modern races. A tendency to trigonism is not uncommon among Bushmen and Hottentots, who may be regarded as descendants of the prehistoric stock of South Africa. Sir Arthur Keith added that South Africa was the home of the most remarkable of all prehistoric peoples known to us, a people or stock tending to produce individuals with brains of remarkable dimensions and with a tendency for infantile and juvenile characters to persist into adult life, a tendency which Prof. M. R. Drennan has termed ‘pedomorphism’. Although remains of Bushmen have been found so far north as Lake Nyassa and Boskop remains in Northern Rho-desia, all the evidence at present points to South Africa as the evolutionary home of this prehistoric pedomorphic race.

... on the Potsdam sandstone and Hudson River rocks in Vermont

... on the Potsdam sandstone and Hudson River rocks in Vermont