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At least 1,585 records · Page 88Linked to original sources
USGS1983

Origin of concretionary Mn-Fe-oxides in stream sediments of Maine, U.S.A.

Studies of stream and sediment-pore waters largely explain the genesis of concretionary Mn-Fe-oxides in Maine. Waters of two small streams near Jackman, Maine, were studied in terms of pH, Eh, dissolved oxygen, dissolved organic carbon, dissolved Mn, total dissolved Fe, and ferrous and ferric Fe. Pyrite Creek has profuse concretions and coatings of Mn-Fe-oxides, whereas West Pyrite Creek has only sparse Mn-Fe-oxide stains. Pyrite Creek drains boggy terrain and West Pyrite Creek drains well-drained terrain. In West Pyrite Creek, stream and subjacent pore waters have chemical characteristics that do not differ greatly. However, dissolved Mn, ferrous Fe, dissolved oxygen, and in situ Eh measurements show that a steep Eh gradient exists between stream and subjacent pore waters of Pyrite Creek. The steep Eh gradient is manifested by the common zonation of coatings and stains on rocks in stream sediment. The bottom zone has no deposition of oxides, the middle zone is red and consists mostly of Fe-oxides, and the upper zone is black or dark-brown and consists of Mn-oxides with varying amounts of Fe-oxides. The zonation agrees with theoretical predictions of oxide stability as one moves from a reducing to an oxidizing environment. At locations where concretionary Mn-Fe-oxides form, pore waters are depleted of oxygen because of abundant decaying organic material in the stream sediment. The pore waters are charged with dissolved Mn and Fe because mechanically deposited Mn-Fe-oxides are remobilized due to the low-Eh conditions. Groundwaters also contribute dissolved Mn and Fe. Stream waters, on the other hand, are oxygenated and the high-Eh conditions result in low concentrations of dissolved Mn and Fe in stream waters because of the insolubility of Mn-Fe-oxides in high-Eh environments. Therefore, concretionary Mn-Fe-oxides form at the interface between pore and stream waters because Mn- and Fe-rich pore waters, which are undersaturated with respect to Mn-Fe-oxides, mix with oxygen-rich stream waters, which are saturated with respect to Mn-Fe-oxides. ?? 1983.

Chemical Geology↗
USGS1984

The occurrence and behavior of radium in saline formation water of the U.S. Gulf Coast region

Radium has been measured in deep saline formation waters produced from a variety of U.S. Gulf Coast subsurface environments, including oil reservoirs, gas reservoirs and water-producing geopressured aquifers. A strong positive correlation has been found between formation-water salinity and Ra activity, resulting from the interaction of formation water with aquifer matrix. Ra isotopes enter the fluid phase after being produced by the decay of parent elements U and Th, which are located at sites on and within the solid matrix. Processes that are belived to be primarily responsible for transferring Ra from matrix to formation water are chemical leaching and alpha-particle recoil. Factors controlling the observed salinity-Ra relationship may be one or a combination of the following factors: (a) ion exchange; (b) increased solubility of matrix silica surrounding Ra atoms, coupled with a salinity-controlled rate of reequilibration of silica between solution and quartz grains; and (c) the equilibration of Ra in solution with detrial barite within the aquifer. No difference was found in the brine-Ra relation in water produced from oil or gas wells and water produced from wells penetrating only water-bearing aquifers, although the relation was more highly correlated for water-bearing aquifers than hydrocarbon-containing reservoirs. ?? 1984.

Chemical Geology↗
USGS1985

Experimental chemical weathering of various bedrock types at different pH-values. 1. Sandstone and granite

Experimental chemical weathering of the so-called Old Rag Granite and Massanutten Sandstone, Virginia, U.S.A., has produced a comparison with the natural environment, and prediction of the effect of acid precipitation. The experimental results of the release of elements, dissolution of minerals, total rock weathered and the degree of weathering as function of volume of leachate were plotted. These data were compared with the natural environment. The use of the plots to predict the effect of high levels of rain acidity on weathering of these rocks is demonstrated. A nonexpandable 14-Å clay was developed from the alteration of biotite during the experimental chemical weathering of the granite at pH 4. This interstratified Al(OH)—mica clay resembles those of the soil developed on the granite and sandstone. Hydroxy-Al may be precipitating between the mica interlayers and producing a 14-Å spacing. Development of this clay by chemical alteration of biotite may change the current hypotheses about its origin in the soils of northeastern U.S.A. While Al-hydroxide seems to regulate Al concentrations in stream waters at the present level of rain acidity, it was found that at lower pH and in the presence of high sulfate concentrations, Al solubility may be controlled by Al-sulfate phase(s).

Virginia↗
USGS1991

A statistical approach to the interpretation of aliphatic hydrocarbon distributions in marine sediments

Q-mode factor analysis was used to quantitate the distribution of the major aliphatic hydrocarbon (n-alkanes, pristane, phytane) systems in sediments from a variety of marine environments. The compositions of the pure end members of the systems were obtained from factor scores and the distribution of the systems within each sample was obtained from factor loadings. All the data, from the diverse environments sampled (estuarine (San Francisco Bay), fresh-water (San Francisco Peninsula), polar-marine (Antarctica) and geothermal-marine (Gorda Ridge) sediments), were reduced to three major systems: a terrestrial system (mostly high molecular weight aliphatics with odd-numbered-carbon predominance), a mature system (mostly low molecular weight aliphatics without predominance) and a system containing mostly high molecular weight aliphatics with even-numbered-carbon predominance. With this statistical approach, it is possible to assign the percentage contribution from various sources to the observed distribution of aliphatic hydrocarbons in each sediment sample. ?? 1991.

Chemical Geology↗
USGS1994

Seawater as the source of minor elements in black shales, phosphorites and other sedimentary rocks

Many of the minor elements in seawater today have a concentration-depth profile similar to that of the biologically essential nutrients, NO-3 and PO3-4. They show a relative depletion in the photic zone and enrichment in the deep ocean. The difference between their surface- and deep-ocean values, normalized to the change in PO3-4, approaches the average of measured minor-element: P ratios in marine plankton, although individual analyses of the latter show extreme scatter for a variety of reasons. Despite this scatter in the minor-element analyses of plankton, agreement between the two sets of data shows unequivocally that an important marine flux of many minor elements through the ocean is in the form of biogenic matter, with a composition approaching that of plankton. This interpretation is further supported by sediment studies, particularly of sediments which accumulate in shelf-slope environments where biological productivity in the photic zone is exceptionally high and organic carbon contents of the underlying sediment elevated. The interelement relations observed for some of these sediments approach the average values of plankton. These same interelement relations are observed in many marine sedimentary rocks such as metalliferous black shales and phosphorites, rocks which have a high content of marine fractions (e.g., organic matter, apatite, biogenic silica and carbonates). Many previous studies of the geochemistry of these rocks have concluded that local hydrothermal activity, and/or seawater with an elemental content different from that of the modern ocean, was required to account for their minor-element contents. However, the similarity in several of the minor-element ratios in many of these formations to minor-element ratios in modern plankton demonstrates that these sedimentary rocks accumulated in environments whose marine chemistry was virtually identical to that seen on continental shelf-slopes, or in marginal seas, of the ocean today. The accumulation of the marine fraction of minor elements on these ancient sea floors was determined largely by the accumulation of organic matter, settling from the photic zone and with a composition of average plankton. A second marine fraction of minor elements in these rocks accumulated through precipitation and adsorption from seawater. The suite of elements in this fraction reflects redox conditions in the bottom water, as determined by bacterial respiration. For example, high Mn, high Cr+V and high Mo concentrations, above those which can be attributed to the accumulation of planktonic matter, characterize accumulation under bottom-water oxidizing, denitrifying and sulfate-reducing conditions, respectively. ?? 1994.

Chemical Geology↗
USGS1987

15N/14N variations in Cretaceous Atlantic sedimentary sequences: Implication for past changes in marine nitrogen biogeochemistry

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds (“black shales”) were found to have significantly lower δ 15 N values (lower 15 N/ 14 N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have ° 15 N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin. The recurring 15 N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15 N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N 2 -fixing blue-green algae, a possible source of this sediment 15 N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment.

Earth and Planetary Science Letters↗
USGS1964

Minor-element composition and organic carbon content of marine and nonmarine shales of Late Cretaceous age in the western interior of the United States

The composition of nonmarine shales of Cretaceous age that contain less than 1 per cent organic carbon is assumed to represent the inherited minor-element composition of clayey sediments delivered to the Cretaceous sea that occupied the western interior region of North America. Differences in minor-element content between these samples and samples of 1. (a) nonmarine carbonaceous shales (1 to 17 per cent organic carbon), 2. (b) nearshore marine shales (less than 1 per cent organic carbon), and 3. (c) offshore marine shales (as much as 8 per cent organic carbon), all of the same age, reveal certain aspects of the role played by clay minerals and organic materials in affecting the minor-element composition of the rocks. The organic carbon in the nonmarine rocks occurs in disseminated coaly plant remains. The organic carbon in the marine rocks occurs predominantly in humic material derived from terrestrial plants. The close similarity in composition between the organic isolates from the marine samples and low-rank coal suggests that the amount of marine organic material in these rocks is small. The minor-element content of the two kinds of nonmarine shales is the same despite the relatively large amount of organic carbon in the carbonaceous shales. The nearshore marine shales, however, contain larger median amounts of arsenic, boron, chromium, vanadium and zinc than do the nonmarine rocks; and the offshore marine shales contain even larger amounts of these elements. Cobalt, molybdenum, lead and zirconium show insignificant differences in median content between the nonmarine and marine rocks, although as much as 25 ppm molybdenum is present in some offshore marine samples. The gallium content is lower in the marine than in the nonmarine samples. Copper and selenium contents of the two kinds of nonmarine rocks and the nearshore marine samples are the same, but those of the offshore samples are larger. In general, arsenic, chromium, copper, molybdenum, selenium, vanadium and zinc are concentrated in those offshore marine samples having the largest amounts of organic carbon, but samples with equal amounts of vanadium, for instance, may differ by a factor of 3 in their amount of organic carbon. Arsenic and molybdenum occur in some samples chiefly in syngenetic pyrite but also are present in relatively large amounts in samples that contain little pyrite. The data on nonmarine carbonaceous shales indicate that organic matter of terrestrial origin in marine shales contributes little to the minor-element content of such rocks. It is possible that marine organic matter, even though seemingly small in amount in marine shales, contributes to the minor-element composition of the shales. In addition to any such contribution, however, the great effectiveness in sorption processes of humic materials in conjunction with clay minerals suggests that such processes must have played an important role as these materials moved from the relatively dilute solutions of the nonmarine environment to the relatively concentrated solution of sea water. The volumes of sea water sufficient to supply for sorption the amounts of most minor elements in the offshore marine samples are insignificant compared to the volumes of water with which the clay and organic matter were in contact during their transportation and sedimentation. Consequently, the chemical characteristics of the environment in which the clay minerals and organic matter accumulated and underwent diagenesis probably were the most important factors in controlling the degree to which sorption processes and the formation of syngenetic minerals affected the final composition of the rocks.

Geochimica et Cosmochimica Acta↗
USGS1984

Stable isotope geochemistry of acid mine drainage: Experimental oxidation of pyrite

Sulfate and water from experiments in which pyrite was oxidized at a pH of 2.0 were analyzed for sulfur and oxygen stable isotopes. Experiments were conducted under both aerobic and anaerobic sterile conditions, as well as under aerobic conditions in the presence of Thiobacillus ferrooxidans, to elucidate the pathways of oxidation. Oxygen isotope fractionation between SO2-4 and H2O varied from +4.0 %. (anaerobic, sterile) to + 18.0 %. (aerobic, with T. ferrooxidans.). The oxygen isotope composition of dissolved oxygen utilized in both chemical and microbially-mediated oxidation was also determined (+11.4 %., by T. ferrooxidans; +18.4 %., chemical). Contributions of water-derived oxygen and dissolved oxygen to the sulfate produced in the oxidation of pyrite could thus be estimated. Water-derived oxygen constituted from 23 to ~ 100 percent of the oxygen in the sulfate produced in the experiments, and this closely approximates the range of contribution in natural acid mine drainage. Oxidation of sulfides in anaerobic, water-saturated environments occurs primarily by chemical oxidation pathways, whereas oxidation of sulfides in well-aerated, unsaturated zone environments occurs dominantly by microbially mediated pathways.

Geochimica et Cosmochimica Acta↗
USGS1985

Germanium geochemistry and mineralogy

Germanium is enriched in the following geologic environments: 1. (1) iron meteorites and terrestrial iron-nickel; 2. (2) sulfide ore deposits, particularly those hosted by sedimentary rocks; 3. (3) iron oxide deposits; 4. (4) oxidized zones of Ge-bearing sulfide deposits; 5. (5) pegmatites, greisens, and skarns; and 6. (6) coal and lignitized wood. In silicate melts, Ge is highly siderophile in the presence of native iron-nickel; otherwise, it is highly lithophile. Among silicate minerals, Ge is concentrated in those having less polymerized silicate tetrahedra such as olivine and topaz. In deposits formed from hydrothermal solutions, Ge tends to be enriched mostly in either sulfides or in fluorine-bearing phases; it is thus concentrated both in some hydrothermal sulfide deposits and in pegmatites, greisens, and skarns. In sulfide deposits that formed from solutions having low to moderate sulfur activity, Ge is concentrated in sphalerite in amounts up to 3000 ppm. Sulfide deposits that formed from solutions having higher sulfur activity allowed Ge to either form its own sulfides, particularly with Cu, or to substitute for As, Sn, or other metals in sulfosalts. The Ge in hydrothermal fluids probably derives from enrichment during the fractional crystallization of igneous fluids, or is due to the incorporation of Ge from the country rocks, particularly from those containing organic material. Germanium bonds to lignin-derivative organic compounds that are found in peat and lignite, accounting for its common concentration in coals and related organic material. Germanium is precipitated from water together with iron hydroxide, accounting for its concentration in some sedimentary and supergene iron oxide deposits. It also is able to substitute for Fe in magnetite in a variety of geologic environments. In the oxidized zone of Ge-bearing sulfide deposits, Ge is concentrated in oxides, hydroxides, and hydroxy-sulfates, sometimes forming its own minerals. It is particularly enriched in some iron- and manganese-bearing oxides and hydroxides, including goethite (up to 5300 ppm) and hematite (up to 7000 ppm).

Geochimica et Cosmochimica Acta↗
USGS1990

Mechanisms controlling Cu, Fe, Mn, and Co profiles in peat of the Filson Creek Fen, northeastern Minnesota

Filson Creek Fen, located in northeastern Minnesota, overlies a Cu-Ni sulfide deposit. A site in the fen was studied to evaluate the hydrogeochemical mechanisms governing the development of Fe, Mn, Co, and Cu profiles in the peat. At the study site, surface peat approximately 1 m thick is separated from the underlying mineralized bedrock by a 6–12 m thickness of lake and glaciofluvial sediments and till. Concentrations of Fe, Mn, Co, and Cu in peat and major elements in pore water delineate a shallow, relatively oxidized, Cu-rich zone overlying a deeper, reduced, Fe-, Mn-, and Co-rich zone within the peat. Sequential metal extractions from peat samples reveal that 40–55% of the Cu in the shallow zone is associated with organic material, whereas the remaining Cu is distributed between iron-oxide, sulfide, and residual fractions. Sixty to seventy percent of the Fe, Mn, and Co concentrated in the deeper zone occur in the residual phase. The metal profiles and associations probably result from non-steady-state input of metals and detritus into the fen during formation of the peat column. The enrichment of organic-associated Cu in the upper, oxidized zone represents a combination of Cu transported into the fen with detrital plant fragments and soluble Cu, derived from weathering of outcrop and subcrop of the mineral deposit, transported into the fen, and fixed onto organic matter in the peat. The variable stratigraphy of the peat indicates that weathering processes and surface vegetation have changed through time in the fen. The Fe, Mn, and Co maxima at the base of the peat are associated with a maximum in detrital matter content of the peat resulting from a transition between the underlying inorganic sedimentary environment to an organic sedimentary environment. The chemistry of sediments and ground water collected beneath the peat indicate that mobilization of metals from sulfide minerals in the buried mineral deposit or glacial deposits is minimal. Therefore, the primary source of Cu to the peat at the study site is outcrops and shallow subcrops of the mineral deposit adjacent to the fen.

Geochimica et Cosmochimica Acta↗
USGS1994

Uranium(VI) adsorption to ferrihydrite: Application of a surface complexation model

A study of U(VI) adsorption by ferrihydrite was conducted over a wide range of U(VI) concentrations, pH, and at two partial pressures of carbon dioxide. A two-site (strong- and weak-affinity sites, Fe s OH and Fe w OH, respectively) surface complexation model was able to describe the experimental data well over a wide range of conditions, with only one species formed with each site type: an inner-sphere, mononuclear, bidentate complex of the type (FeO 2 )UO 2 . The existence of such a surface species was supported by results of uranium EXAFS spectroscopy performed on two samples with U(VI) adsorption density in the upper range observed in this study (10 and 18% occupancy of total surface sites). Adsorption data in the alkaline pH range suggested the existence of a second surface species, modeled as a ternary surface complex with UO 2 CO 3 0 binding to a bidentate surface site. Previous surface complexation models for U(VI) adsorption have proposed surface species that are identical to the predominant aqueous species, e.g., multinuclear hydrolysis complexes or several U(VI)-carbonate complexes. The results demonstrate that the speciation of adsorbed U(VI) may be constrained by the coordination environment at the surface, giving rise to surface speciation for U(VI) that is significantly less complex than aqueous speciation.

Geochimica et Cosmochimica Acta↗
USGS1994

Cyclic variations of sulfur isotopes in Cambrian stratabound Ni-Mo-(PGE-Au) ores of southern China

Cyclic variations of δ 34 S values over a range of at least 48‰ in pyrite nodules from stratabound Ni-Mo-PGE(Au) ores of southern China are attributed to biogenic reduction of seawater sulfate in an anoxic, phosphogenic, and metallogenic basin. Cyclic introduction and mixing of normal seawater into typically stagnant basin waters led to extreme variations in δ 34 S values of aqueous sulfide species present at different times. Intermittent venting of metal-laden hydrothermal fluids into such a bacteriogenic sulfide-rich environment resulted in precipitation of metal sulfides as pseudomorphous replacements of organic debris and as sulfide sediments that record large δ 34 S CDT variations from −26 to +22‰. Apatite and silica dominated the replacement of the organic debris when metals were not being introduced into the basin. The combination of abundant organic debris, localized topographic basins for accumulation of the debris, bacterial production of sulfide species, and introduction of metal-bearing hydrothermal fluids provided the environment necessary to form these unusually rich Ni-Mo ores.

Geochimica et Cosmochimica Acta↗
USGS1963

Applications of geohydrologic concepts in geology

Subsurface water, an active agent in many geologic proceses, must be considered in interpreting geologic phenomena. Principles of the occurrence, distribution, and movement of subsurface waters are well established and readily applicable. In many interpretations in geologic literature, geohydrologic principles have been employed realistically, but in many others these principles have been either ignored or violated. Explanations of genesis of underclays and associated deposits afford some examples wherein principles of movement and activity of vadose and ground water have been ignored and others in which they have been used advantageously. Postulates stating that waters percolate downward from swamp areas do not allow for the usual movement of subsurface water in such environments. The idea that sediments were leached by vadose water after uplift satisfies the geohydrologic requirements. Weathering and solution form porous and permeable zones subjacent to unconformities in dense rocks such as carbonates and granites; this illustrates the geohydrologic and economic significance of unconformities. Examples are Mohawkian carbonate aquifers of northern Illinois and oil-bearing limestones of Mississippian age of eastern Montana. The flushing effects of meteoric water and other hydrodynamic factors active during erosion periods are important elements in the genesis and concentration of brines. Explanation of the origin and occurrence of brines must include consideration of the geohydrologic environments throughout their geologic history.

Journal of Hydrology↗
USGS1973

Karst hydrology: A review

Karst regions of the world are characterized by limestones and other soluble rocks at or near land surface that have been modified by solutional erosion. Such surface features as sinks, long dry valleys, sparse streams, and bare rock and such subsurface features as caverns, arterial solution openings leading to large springs, and a deep water table are typical of karst terranes. These features result in an uneven distribution of permeability in karst systems and surface and subsurface hydrologic conditions that require special hydrogeologic studies. Local high permeability at shallow depth in mature karst regions leads to an ecology associated with a soilless and water-scarce surface environment. Many practical problems result from this high permeability, including: (1) scarcity and poor predictability of groundwater supplies; (2) scarcity of surface-water supplies; (3) instability of the ground; (4) leakage of surface reservoirs; and (5) an unreliable waste-disposal environment. Interest in karst hydrology has increased greatly in the past decade; this interest has resulted in the international exchange of numerous published reports on local areas and on special topical karst problems. Many of these reports have been used by the authors in preparing this paper, which synthesizes results of many workers and focuses attention on: (1) the development of karst features through hydrologic processes; and (2) hydrologic systems of karst terranes.

Journal of Hydrology↗
USGS1980

Neogene sedimentation on the outer continental margin, southern Bering Sea

Neogene sedimentary rocks and sediments from sites on the outer continental margin in the southern Bering Sea and on the Alaska Peninsula are dominated by volcanic components that probably were eroded from an emergent Aleutian Ridge. A mainland continental source is subordinate. Most sediment in the marine environment was transported to the depositional sites by longshore currents, debris flows, and turbidity currents during times when sea level was near the outermost continental shelf. Fluctuations of sea level are ascribed both to worldwide glacio-eustatic effects and to regional vertical tectonics. Large drainage systems, such as the Yukon and Kuskokwim Rivers, had little direct influence on sedimentation along the continental slope and Unmak Plateau in the southern Bering Sea. Sediments from those drainage systems probably were transported to the floor of the Aleutian Basin, to the numerous shelf basins that underlie the outer continental shelf, and to the Arctic Ocean after passing through the Bering Strait. Environments of deposition at the sites along the outer continental margin have not changed significantly since the middle Miocene. The site on the Alaska Peninsula, however, is now emergent following shallow-marine and transitional sedimentation during the Neogene.

Alaska↗
USGS1988

Late Pleistocene drainage systems beneath Delaware Bay

Analyses of an extensive grid of seismic-reflection profiles, along with previously published sedimentary data and geologic information from surrounding coastal areas, outline the ancestral drainage systems of the Delaware River beneath lower Delaware Bay. Major paleovalleys within these systems have southeast trends, relief of 10-35 m, widths of 1-8 km, and axial depths of 31-57 m below present sea level. The oldest drainage system was carved into Miocene sands, probably during the late Illinoian lowstand of sea level. It followed a course under the northern half of the bay, continued beneath the Cape May peninsula, and extended onto the present continental shelf. This system was buried by a transgressive sequence of fluvial, estuarine, and shallow-marine sediments during Sangamonian time. At the height of the Sangamonian sea-level transgression, littoral and nearshore processes built the Cape May peninsula southward over the northern drainage system and formed a contiguous submarine sedimentary ridge that extended partway across the present entrance to the bay. When sea level fell during late Wisconsinan time, a second drainage system was eroded beneath the southern half of the bay in response to the southerly shift of the bay mouth. This system, which continued across the shelf, was cut into Coastal Plain deposits of Miocene and younger age and included not only the trunk valley of the Delaware River but a large tributary valley formed by the convergence of secondary streams that drained the Delaware coastal area. During the Holocene rise of sea level, the southern drainage system was covered by a transgressive sequence of fluvial, estuarine, and paralic deposits that accumulated due to the passage of the estuarine circulation cell and to the landward and upward migration of coastal sedimentary environments. Some Holocene deposits have been scoured subsequently by strong tidal currents. The southward migration of the ancestral drainage systems beneath Delaware Bay is analogous to that found under nearby Chesapeake Bay. In both areas, shifts in the bay mouths and river courses have preserved the morphologies and sedimentary fill of former drainage systems and provided a clear record of major sea-level fluctuations. Data from this study demonstrate that important information concerning ancient estuarine environments can be derived from the locations and characteristics of former fluvial systems. ?? 1988.

Delaware, New Jersey↗
USGS1971

Glacial marine sediments in the precambrian Gowganda formation at Whitefish Falls, Ontario (Canada)

Study of a well-exposed section of the Gowganda Formation at Whitefish Falls, Ontario, suggests criteria for the recognition of glacial marine sediments. Thickness of hundreds of feet, lateral continuity, faint internal stratification, sorted lenses of sandstone and conglomerate, and dropstones characterize much of the tillite. Thickness of hundreds of feet, lateral continuity, and marked development of irregular and lenticular laminae instead of varve structure characterize much of the argillite. These characteristics, together with evidence for a nearshore, marine-to-deltaic environment for the overlying beds, suggest a glacial marine interpretation even though no fossil evidence is available. Massive tillite, tillite containing faint stratification and lenses of sorted conglomerate and sandstone, and dropstone-bearing argillite, all of which interfinger, suggest a glacial marine environment composed of: ( 1 ) a subglacial facies; ( 2 ) a periglacial facies; and ( 3 ) a facies of marine ice rafting, respectively. Separation of the two tillite-bearing members by as much as 700 ft. of argillite containing no dropstones suggests two distinct ice ages during Gowganda time.

Ontario↗
USGS1988

Lacustrine varve formation through time

Studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes. If the bottom waters of a lake are partly or totally anoxic, the seasonally deposited materials are preserved as annual groupings of laminae (varves). Common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin, precipitated carbonate minerals, diatom frustules, iron-rich and manganese-rich flocs, autochthonous organic detritus, and autochthonous and allochthonous materials resuspended from the bottom. The "style" of varving has changed over geologic time, reflecting changes in biologic evolution and types of materials available. Precipitated iron-rich laminations were common in the middle Precambrian. Graded sets of clastic organic laminations persisted through the Precambrian, prior to the evolution of bioturbating benthic organisms. Glaciolacustrine varves appear to have retained their distinctive character through time. Carbonate-rich varves occurred sporadically in the Precambrian and Phanerozoic. With the exception of diatoms, major components of modern lacustrine varves were present through the Paleozoic and Mesozoic, and yet varves are rare in strata of these ages, and may have accumulated in marine to brackish-water environments. Diatoms were introduced into lacustrine systems in Early Tertiary time and are common components of varves from then on. Diatom laminae, combined with a greater chance for geologic preservation of younger lake deposits, have increased the number of geologically young occurrences of varved sediments. However, seasonal associations of modern varve components, and the processes they represent, are present in ancient deposits and provide clues to the interpretation of ancient environments.

Palaeogeography, Palaeoclimatology, Palaeoecology↗