Depositional Textures Research Articles

Electrodeposition of alloys XIII: Electrodeposition of Cu-Ni alloys from solutions containing L-asparagine

Electrodeposits of Cu-Ni alloys containing up to 90% Ni were obtained from aqueous solutions containing copper(II) sulphate, nickel(II) sulphate and L-asparagine. An increase in current density or pH increased the percentage of nickel whereas increasing the temperature of plating increased the amount of copper in the deposit. An increase in the nickel content of the solution increased the nickel in the deposit. Current efficiencies were generally high. Deposits containing more than 10% Ni and obtained at current densities greater than 2.0 A dm -2 were black and powdery and possessed poor adhesion. Thiourea, saccharin, dextrin, resorcinol, β-naphthol and gelatin did not improve the appearance, texture or adhesion of deposits.

Geologic Setting of Polymetallic Sulfide Deposits on East Pacific Rise at 21øN and Juan de Fuca Ridge near 45øN: ABSTRACT

Massive sulfide deposits of zinc, copper, lead, and silver have been recovered from the East Pacific Rise (EPR) in the mouth of the Gulf of California and from the Juan de Fuca Ridge (JFR) west of Oregon. Both of these oceanic spreading centers have a separation rate of about 2.4 in./year (6 cm/year), and the metal composition of their deposits is nearly identical. In both areas, the bulk of the sulfide deposits occur on, or immediately adjacent to, the morphologic axis of spreading in a sediment-free zone underlain by fresh glassy basalt. The axial zone of the EPR at 21°N is nearly 985 ft (300 m) deeper than that of the JFR. An extensive international program at the EPR has photographed and sampled both hydrothermal fluids and mineral deposits. The existence of acti e hydrothermal vents at the JFR is inferred from the form and the absence of weathering of samples recovered during a recent U.S. Geological Survey cruise. The EPR exhibits a moderate degree of morphologic symmetry, and the sulfide deposits are generally situated along a low axial pillow-basalt ridge that is flanked by slightly older crustal zones containing numerous fissures and faults. On the JFR, the massive sulfides occur within a continuous(?) depression along the center of a flat axial-valley floor 0.6 mi (1 km) wide that is underlain by extensive fresh glassy lava sheet flows; overall morphologic symmetry is strikingly developed at the JFR. Although the form and texture of the sulfide deposits are better known from the EPR, it is clear that the deposits and associated faunal communities differ between the two sites. The overall commonality of these deposits and their regional settings suggest that polymetallic sulfide deposits may be fairly common along spreading-center ridges in the East Pacific. To date, sulfide deposits have been discovered at six different widely separated sites. End_of_Article - Last_Page 979------------

Deep-Water Evaporites: Detrital, Authigenic, or Diagenetic?: ABSTRACT

The thought of evaporites commonly conjures images of hypersaline starved basins, chemical precipitation of evaporite minerals in the water column or at the sediment-water interface, and cyclically laminated salts. It is implicit in this model that the evaporite fabrics reflect stagnant, unstirred, abiotic conditions, but deep-water evaporites in the Messinian of the Sicilian basin include evaporite turbidites and resedimented clastic evaporites with wholly different petrographic characteristics and sedimentary structures. Detrital dolomites in the Onondaga Limestone and in the Cretaceous of the western United States reflect clastic depositional histories and yet may have strong diagenetic overprints that obscure the original depositional textures. Diagenetically altered, sandy, anhydritic dolomites from the Bell Canyon Formation in Texas provide examples of deep-water detrital, evaporitic carbonates with a depositional history indicated principally by the included siliciclastics and a diagenetic history indicated first by groundmass versus pore-filling dolomite crystal fabrics and second by nodular versus pore-filling and replacement anhydrite. Comparisons between the Bell Canyon deep-water anhydritic dolomites and other deep-water evaporites is useful in making the distinction between clastic, penecontemporaneous authigenic, and later diagenetic origins. End_of_Article - Last_Page 542------------

Petrology and Reservoir Characteristics of Smackover Formation, Hatter's Pond Field--Implications for Smackover Exploration in Southwestern Alabama: ABSTRACT

ABSTRACT Hatter's Pond Field in northern Mobile County, Alabama has produced 11 million barrels of condensate and 43 Bcf of gas since its discovery in 1974. Production is from multiple pay zones in the Upper Jurassic Norphlet and Smackover Formations. The trapping mechanism in the field is a highly complex, combination structural and stratigraphic trap involving salt movement in association with normal faulting. The Smackover in the Hatter's Pond Field area is enigmatic for the Smackover in Alabama for two principal reasons. One, the Smackover is very thin (less than 200 feet) in comparison to thicknesses to the northwest and southeast. Secondly, the Smackover does not show the characteristic lower Smackover-upper Smackover lithologic subdivision so apparent throughout south Alabama and the Gulf Coast. These unique features are a product of the field's position on the northwest flank of the Wiggins uplift. Smackover deposition was significantly affected by the uplift which maintained the Hatter's Pond area as a subaerial high, while lower Smackover carbonates were being deposited in the deeper areas of the Mississippi Interior Salt Basin and Conecuh embayment. It was not until near maximum transgression that the seas covered the Hatter's Pond area and deposited shallow-water upper Smackover lithologies. These lithologies were later massively dolomitized by mixing-zone dolomitization during the subsequent Buckner regression. This dolomitization almost completely masked depositional textures, but was largely responsible for the development of reservoir grade porosity in the Hatter's Pond area. Six major lithofacies can be identified in the Smackover in the Hatter's Pond Field: anhydritic mudstone, skeletal-pelodial packstone/grainstone, oolitic grainstone, microcrystalline dolomite, finely-crystalline dolomite, and coarsely-crystalline dolomite. The microcrystalline dolomite is commonly associated with bedded and nodular anhydrites and is interpreted to represent early replacement in a sebkha environment. Both the finely- and coarsely-crystalline dolomites are secondary in nature and represent replacement of low energy skeletal-peloidal packstones and high energy oolitic grainstones respectively. The majority of the reservoir porosity in the Smackover is late stage vuggy and/or moldic and is facies selective and preferential to the coarsely-crystalline dolomite. This porosity, which commonly ranges from 4 to 22% with permeabilities of 2 to over 100 millidarcies, is a product of mesogenetic leaching related to migration of CO2-charged fluids during the early stages of hydrocarbon maturation. The porosity is facies selective to the coarsely-crystalline dolomite since this lithology possessed the greatest porosity and permeability at the time of migration of the CO2-charged solutions. Evidence suggests the oolitic grainstones, which were the precursors of the coarsely-crystalline dolomites, were deposited as a series of linear bars along the flanks of the Wiggins uplift. If this is the case, and more study is needed to document this definitively, the coarsely-crystalline dolomite should occur in elongate mappable trends. Hydrocarbon exploration in this area and all along the flanks of the Wiggins uplift should involve location and mapping of these trends with the greatest success occuring in areas where the trends are superimposed over structural highs produced by faulting and/or salt diapirism.

Diffusion of sediment on the lee of dune‐like bedforms: theoretical and numerical analysis

ABSTRACTTheoretical and empirical analyses of flow structure, sediment transport, and sediment size characteristics at the crest of dune‐like bedforms indicate that it is possible to describe, at least semi‐quantitatively, the diffusion and deposition of sediment on the leeside of such structures. A numerical program based on this analysis simulates the grain‐size distribution and deposition rate on the leeside of dunes for specified flow conditions and bed material. Evaluation of flow and sediment variables through the numerical simulation program shows that flow velocity, flow depth and sediment size have a strong influence on the deposition rate and texture of leeside sediment before avalanching. Sorting of the bed material, in particular, appears to exert a strong control on both the grain‐size and the deposition‐rate gradients.

Crystallization and emplacement of the Lac St-Jean anorthosite massif (Quebec, Canada)

The Lac St-Jean anorthosite massif underlies an area of over 20,000 km2 and has been emplaced into migmatitic gneisses of the central granulite terrain of the Grenville Province of the Canadian shield. Field data and petrography in an area straddling the anorthosite-gneiss contact, close to Chicoutimi (Quebec) permits an outline of its tecto-magmatic evolution. Depositional magmatic textures in the massif reveals that it crystallized from a magma in a relatively calm tectonic environment. The absence of fusion in pelitic gneisses at the contact proves that the crystallization did not take place at the level presently exposed. The parallelism of subvertical foliation in the enveloping gneisses and the anorthosite indicates that both were deformed together. It is suggested that the deformation results from a diapiric ascent of the anorthosite massif after its consolidation at depth. The depth of consolidation of the anorthosite is estimated at ∼ 25–30 km from subsolidus reaction between plagioclase and olivine. The diapiric ascent is further substantiated by the fact that three sets of mafic dykes of different ages, intrusive into the anorthosite, have a mineralogy which indicates successively decreasing P, T conditions of emplacement from granulite fades to amphibolite facies. An evolution of the basement gneisses and the anorthosite is proposed as a working hypothesis; it relies on the fact that metabasite dyke swarms in the basement gneisses represent a period of major crustal extension and could be used as a stratigraphic subdivision of the Grenville Province.

Formation and Early Diagenesis of Varved Evaporite Sediments in a Coastal Hypersaline Pool

ABSTRACT This paper reports an occurrence of varved gypsum-organic sediments from a recent shallow-water hypersaline pool in Ras-Mohamad, Southern Sinai. Primary deposition and diagenetic features in this deposit were followed by studying the mineralogy, the depositional textures, the interstitial brine composition, and the concentrations of ions coprecipitated with gypsum. During the summer, when evaporation is intense, gypsum is deposited on the bottom of the pool. During the winter evaporation is milder and the brine became undersaturated with respect to gypsum. At these lower salinities a carpet of blue-green algae floors the pool. The sediments of the pool are composed of alternating layers of gypsum mush and algal mats. The composition of the interstitial brine is essentially that of evaporated sea water, but the concentrations of Ca and SO4 in the upper layers are anomalously high. The calculated degrees of supersaturation with respect to gypsum are as high as about 2. The supersaturation was relieved in the lower layers by early diagenetic growth of gypsum. Some of the diagenetic gypsum has grown by displacement within the algal layers This growth eventually destroyed the fabric of the algal layer, which was ultimately erased. The diagenetic growth of gypsum is reflected also in the concentrations of cations coprecipitated with gypsum. The coprecipitated-ion concentrations decrease with depth, and this is interpreted as due to the decrease in the average growth rate of the crystals.

Pore Networks in Holocene Carbonate Sediments

ABSTRACT Permeabilities of Holocene carbonate sediments from Florida and the Bahamas, determined for 74 samples by water flow rates in a variable-head permeameter, range from 0.6 to 57,000 millidarcies. Porosities range from 40 to 78 percent. These parameters are related to depositional texture as follows: Table The muddiest sediments (i.e., the finest-grained) have the highest porosities but lowest permeabilities; this negative correlation between porosity and permeability is the reverse of the situation found in carbonate rocks, even as young as Pleistocene. High porosity and low permeability in sediments show a strong correlation with percentage of fines (<62 µm). From capillary pressure curves it is inferred that many of the pore throats of muddy carbonate sediments are less than 1 µm in diameter, at least after drying. Measured permeabilities are used to calculate cementation rates for simple models of upper phreatic zone cementation; the calculated rates would require excessive time to produce the degree of cementation seen in Late Pleistocene rocks of Florida and the Bahamas. The amounts of rainfall and evaporation are the most important factors in the degree of cementation.

Reefal Margins of Pliocene-Pleistocene of Great Bahama Bank: ABSTRACT

End_Page 896------------------------------Examination of 16 shallow core borings from the Great Bahama Bank reveals that coral-coralline algal deposits of Pliocene-Pleistocene age line the margins of the bank. These reefal deposits extend up to 5 km bankward from both windward and leeward edges of the platform. Those along leeward margins are framestones and grew in relatively deep water. Those along the windward margins are a mixture of framestone and bafflestone formed in water of various depths probably including low intertidal. A similar assymetric distribution of depositional textures may be indicative of windward versus leeward margins on ancient platforms. The margins of the bank evolved upward through the Pliocene-Pleistocene. This evolution may be divided into three stages. In stage I, the lowermost, discrete depositional units average 8 m in thickness and contain an abundance of species of corals now extinct, including Stylophora affinis. In stage III, depositional units average 3 m in thickness and corals such as S. affinis are rare or absent. Stage III is marked by accumulation of nonskeletal sands (beach and eolian dune deposits) along inner-bankward parts of the margins. The distribution of reefal sediments was reduced to a narrow belt similar to that of the present. The change from stage I to II is of uniform time, apparently coinciding with the initiation of major Northern Hemisphere glaciation at the beginning of the late Plio ene; that from stage II to III is more variable, occurring from the middle to late Pleistocene. End_of_Article - Last_Page 897------------

Petrology of Arbuckle Group, Central Kansas: ABSTRACT

The Arbuckle Group (Late Cambrian and Early Ordovician) in Kansas is mostly crystalline dolomite with abundant chert in the upper part. The Arbuckle is entirely in the subsurface, and there are only scattered cores, mostly from the upper part. Depositional constituents and textures have been reported only from the chert. Study of thin sections from three cores from the Central Kansas uplift reveals abundant evidence of depositional components, as well as diagenetic features of dolomitization and porosity. Despite virtually complete dolomitization, it is often possible to identify primary grain types, fabrics, and textures, and by comparison with better preserved examples, to interpret less well-preserved features. Identifiable grain types include oolites, pellets, intraclasts (of micrite, pellets, and oolites), and skeletal grains, including gastropods, echinoderms, and bivalves. Crenulate, laminated dolomite, interpreted as stromatolites, recurs. Depositional textures range from mudstone to packstone. The dolomite is microcrystalline to coarsely crystalline, with porosity ranging erratically from 1 to 22%. Pore types are: (1) intercrystal (most common), supplemented and interconnected by (2) solution-enlarged fractures, (3) moldic, from solution of depositional grains, (4) fenestral, and (5) primary interparticle. Partly dissolved dolomite crystals have collapsed, compacted, and probably contributed to fracturing. Small, closely spaced fractures may be open or plugged by crystals mobilized from surrounding dolomite, thereby isolating bodies of dolomite with high intercrystal porosity. Laminae of low-porosity dolomite, presumably controlled by depositional texture, contribute also to porosity variability. Most large pores are reduced by dolomite cement. Other scarce cements are anhy rite and sparry calcite, which fills oomolds and fractures. End_of_Article - Last_Page 960------------

The effect of 1,25 (OH)2D3 on bone mineralization: ultrastructural studies in patients with renal osteodystrophy.

The acute effects (15-50 days) of 1,25(OH)2D3 (0.5-2 microgram/day) on the histological, fluorescence-microscopical and ultrastructural appearance of mineralizing osteoid in iliac crest spongiosa were studied in 6 uremic patients on maintenance hemodialysis. While there was a marked decrease on endosteal fibrosis and osteoclast counts, volumetric and surface densities of osteoid continued to stay elevated during the observation period. The number of osteoid seams with tetracycline double label increased in 4/6 patients but no such seams appeared in 2 patients who had shown only nonlabeled seams with diffuse staining of osteoid prior to therapy. In studies with transmission electron microscopy, the interface between non-mineralized osteoid and mineralized bone was irregularly outlined and broad. In contrast to normals, coarse mineral deposits were widely scattered in the nonmineralized osteoid. The mineral deposits had two different appearances, presumable depending on the plane of section relative to the direction of collagen fiber bundles: patches of microcristalline deposits encircling perpendicularly cut non-mineralized collagen bundles and needle- or plate-shaped crystals following the striation pattern of collagen fibers. The findings point to close interaction between the pattern of mineral deposition and collagen texture. The latter was highly irregular (woven) in all uremic patients. Mineral deposits were in part normal and in part highly abnormal in texture, the latter particularly in sites with irregular collagen texture. Upon therapy, no consistent change of the ultrastructure of the mineralizing osteoid/bone interface was observed by transmission or scanning and electron microscopy.

MonDak Mississippian Oil Field, Williston Basin: ABSTRACT

The MonDak Mississippian limestone oil field contains 13.7 million to 68.6 million MT (100 million to 500 million bbl) of recoverable oil. It produces from irregular intervals, both vertically and horizontally, in a 168 m section of fractured Mississippian limestone. Dip in the field is eastward into the Williston basin at 3 to 11 m/km, with some structural flattenings and irregularities. The trap is not structural. The reservoir is limestone with a depositional texture range from mudstone to grainstone, but most of the reservoir rock is wackestone. Normal matrix porosity is 2 to 4% and matrix permeability is less than 0.01 md. Some lentils of fossil End_Page 762------------------------------ fragment grainstone have porosities in the 6 to 15% range and permeabilities of 0.01 to 1.0 md. Production is primarily from vertical microfractures and macrofractures. The reservoir is slightly ovepressured. Oil gravity is 32 to 39° API, gas-oil ratios range from 250 to 650 cu ft/bbl, and produced water range from 10 to 90%. The field is located in the west-central part of the Williston basin in the states of Montana and North Dakota. The discovery well was completed in 1958 as a workover of a test plugged and abandoned in 1954. A diagonal offset to the discovery was completed in 1960. No other completions were made in the Mississippian until 1976. As of June 1, 1980, there will be 182 completed Mississippian wells on a 65-ha. spacing pattern and 10 drilling rigs operating. End_of_Article - Last_Page 763------------

Deposition of Enewetak Atoll Reef, Middle Pleistocene to Holocene: ABSTRACT

Cyclic deposition and diagenesis of a large atoll reef, associated with major eustatic sea-level fluctuation, is documented in six cores from the northeast (windward) reef of Enewetak Atoll. To 250 ft (76 m) depth, the reef section comprises six primary depositional packages that represent periods of reef growth during Pleistocene and Holocene high sea-level stands. These depositional packages are separated by unconformities, former subaerial exposure surfaces, which are demarcated by paleosols. During emergent periods at low sea-level stands, the reef was subjected to meteoric-water diagenesis. However, the depositional textures generally are well preserved. Diagenetic textures, most indicative of meteoric-vadose diagenesis, usually have only partly replaced original tex ures. An oceanward shift of reef environments through time is apparent in a large-scale view of the cores. Reef crests in succeedingly younger depositional packages apparently are offset oceanward. Younger marginal lagoonal deposits unconformably overlie older backreef deposits that unconformably overlie older reef-crest deposits. Within depositional packages, influence of rising sea level on facies development is evident. Subaerial surfaces flooded by rising sea level were rapidly colonized by both solitary corals and patch reefs of diverse composition. Rapid upgrowth of oceanward reef crests led to moderation of wave energy in backreef areas and great increase in deposition of sediment which locally buried and killed patch reefs. Shoaling of backreef areas by sediment aggradation to a tabilized sea level resulted in renewed development of patch reefs and deposition of coarser sediment. End_of_Article - Last_Page 713------------

Storm-Wave Genesis of Bioclastic Carbonates in Upper Jurassic Epicontinental Mudstones, East-central Wyoming

ABSTRACT The offshore mud facies of the Late Jurassic (Callovian-Oxfordian) North American epicontinental seaway is represented in east-central Wyoming by the Redwater Shale Member of the Sundance Formation. This member contains stratigraphically discontinuous concentrations of carbonate skeletal debris and fossiliferous mudstone within an otherwise siliciclastic lithologic association. Individual limestone beds thin and thicken laterally and range in thickness from a few centimeters to several tens of centimeters. Detailed petrographic analysis reveals several distinct carbonate depositional textures; grainstones (containing no mud-sized matrix grains other than remnant grain-sheltered patches), packstones and wackestones. These carbonate textures indicate multiple modes of formation. Fossil rains similar to those from carbonate lithologies occur, in much lower concentration, within surrounding siliciclastic mudstones. Muddy fabrics suggest that original skeletal accumulation took place under non-turbulent conditions. Subsequent winnowing during passage of greater-than-normal magnitude waves resulted in varying degrees of grain-support. Winnowing is attributed to turbulence generated near effective wave base, resulting in entrainment of grains and/or pressure gradients created by the passing wave form, which gently flush mud and interstitial waters from saturated bottom sediments. Wackestone and packstone fabrics are the result of incomplete winnowing of mud-sized matrix grains and form at greater distances from the effects of wave energy. Grainstone fabrics result from wave energies that either entrain bioclasts or cause a thorough flushing of mud from near-surface sediments. Progressively shoaling regressive conditions during upper Redwater Shale deposition facilitated the winnowing and concentrating effects of storm-wave interaction with the fossiliferous mud facies of topographically higher areas in the Late Jurassic sea. It is proposed that a variety of carbonate fabrics result from wave-caused winnowing effects, which vary with water depth and wave magnitude. Such fabrics are present in thin bioclastic carbonate units of the Redwater Shale Member of the Sundance Formation, and it is suggested that their origin is due to storm-wave winnowing of a slightly irregular muddy sea bottom. This mechanism and the depositional textures it produces are significant in the distinction between diastemic skeletal grain accumulations and wave-winnowed grainstones. The storm-wave process may also prove applicable in the re-evaluation of certain epicontinental marine deposits previously interpreted as classical turbidite lithologies. Given the vast expanse of geologic time, it is likely that catastrophic events, suc as intense storms and their related processes, have contributed significantly to the preserved sedimentary record.

Textural and mineralogical variations in the surficial sediments of Chagvan Bay, Alaska: Some stratigraphic implications of a subarctic bay

The surficial sediments of Chagvan Bay consist of: (1) coarse-grained (−3 Φ to −2 Φ) lithic fragments of dunites, diorites and sandstones; (2) fine sands (2—3 Φ) composed of quartz and feldspar; and (3) coarse silts (4—5 Φ) composed mostly of quartz. The lithic fragments primarily result from wave erosion of the coastal bluffs, while the fine sands are transported into the bay by tidal currents and the coarse silts by fluvial currents. During successive ebb tides tidal currents remove most or all of the newly deposited material and tend to maintain a balance between erosion and deposition. The texture and mineralogy of the bay deposits are primarily controlled by provenance. Inasmuch as most of the sedimentary particles are being supplied at present and the dispersal of the surficial sediments reflects the present configuration of distributor processes, the sediments are classified as “neoteric”. Benthic epifauna are present only in relatively low-energy depositional areas, although other parts of the bay offer a similar environment. For this reason, it is postulated that the distribution of benthic organisms is influenced by the scouring activity of currents. Although there is seasonal ice-cover, the sediments rapidly acquire characteristics which reflect the energy regime during the ice-free period and form a hydraulically graded profile. It is concluded from this that the sediments are always at or near an equilibrium state, and that this situation should lead to a diastem or unconformity in the stratigraphic record.

Diagenesis in first-cycle desert alluvium of Cenozoic age, southwestern United States and northwestern Mexico

Petrographic studies of first-cycle desert alluvium of Cenozoic age in the southwestern United States and northwestern Mexico show that the mineralogy, texture, and chemical composition of the deposits have been changed diagenetically. The mineralogy has been changed by addition of mechanically infiltrated clay, partial removal of framework grains of feldspars and ferromagnesian silicates, and precipitation of authigenic potassium feldspar, zeolite, montmorillonite, quartz, hematite, and calcite. The texture has been changed by three processes: (1) infiltration of detrital clay and formation of authigenic montmorillonite, which form interstitial clayey matrix not present in the original sediment, (2) formation of voids where framework grains have been dissolved, and (3) in situ formation of silt and other fine-grained sizes. The chemical composition has been changed by infiltration of clay minerals that are richer in aluminum and lower in alkalis and alkaline earths than the original sediment and by removal in ground water of some of the ions released by dissolution and replacement of framework grains. These changes have significantly increased the mineralogical maturity and decreased the textural maturity of the sediments diagenetically. Four major conclusions are drawn from the studies. (1) Some or all of the diagenetic alterations observed in these deposits probably occurred in many analogous ancient first-cycle alluvial deposits at a comparable time in their history. (2) Prolonged movement of ground water through first-cycle deposits may cause unstable minerals to be removed completely, or nearly so, leaving no direct evidence that they were important original constituents of the deposits. (3) Ancient first-cycle alluvium probably rarely, if ever, has the same mineralogy, texture, or chemical composition that the sediments had when deposited. (4) The present mineralogy, texture, and chemical composition of ancient first-cycle alluvial deposits probably do not accurately reflect lithology and climate in the source area or the nature of depositional currents and other environmental factors in the depositional basin.

Address of the Retiring President, Society of Economic Paleontologists and Mineralogists; The making and unmaking of limestones or the downs and ups of porosity

In modern unconsolidated carbonate sediments the volume of pore space may exceed that of sedimentary particles. During lithification calcium carbonate is introduced from the outside. Surprisingly compaction accounts for only little reduction in pore space. In cementation the waters may be (1) percolating freshwaters on surface or in subsurface, (2) seawaters, and (3) formation waters. Percolating freshwaters may affect carbonate sediments as the generally subsiding sea floor at times rises (yo-yo tectonics) or as sea level falls (yo-yo oscillations) or as freshwaters circulate in the subsurface through carbonate sediments. In the phreatic zone (below the groundwater table), especially in moist climatic belts, the original pore space between particles as well as any secondary moldic pore space fill with cements of various fabrics. As carbonate sediments in the phreatic zone are converted to limestone, they not only lose their pore space and become tight, but they may acquire, as their depositional texture vanishes, a xenotopic and poikilotopic fabric of recrystallization. Phreatic diagenesis, however, may also follow a different sequence: reefs micritize beyond recognition; geologists mistake such reefs for lime mud. Phreatic diagenesis, however, does not always lead to a lack of porosity; carbonates, including reefs, may chalkify into porous micron-size, soft, friable calcite. In the vadose zone, (above the groundwater table) which in arid regions may be thousands of feet thick, the pores remain largely open. In fact secondary pores may develop, and stay open, as the aragonite of ooids or of critters is leached to form oo- or crittermolds. Porous strata as products of vadose diagenesis may occur interbedded, as cyclic sequences, with tight strata of phreatic diagenesis. Cements in limestones may also be derived from the effects of dissolution which stylolitization provides. On the sea bottom cementation may be related to bacterial activity. By such activity organic matter can yield methane or other gases that oxidize on the sea floor and are effective in generating bicarbonate ions which then combine with calcium to deposit a a cemented calcium-carbonate deposit. Sulfate-reducing bacteria use sulfate from seawater as an oxidant for that part of organic matter which they oxidize for energy production. Calcium carbonate as a cement is formed when CO 2 produced in the bacterial oxidation of organic matter combines with calcium ions. In the subsurface this reaction involving formation waters is probably even more important than in seawater and may be the missing link in our explanation of the source of calcite cement. In reefs photosynthesis and respiration of the biomass cause a shift in the bicarbonate buffer system of seawater with the uptake of CO 2 . In this process micro-levels of pH 10 and even 10.5 may be reached and maintained in thin jell-like or monomolecular layers. Such high pH levels trigger the precipitation of carbonate cements. In response to increasing salinities during periods of falling sea level carbonate cements likewise are precipitated.

Production of Phlebotomine Sandflies 1 on the Open Forest Floor in Panama: Hydrologic and Physiographic Relations

Breeding populations of phlebotomine sandflies (Diptera, Psychodidae) on the floor of a rain forest in Panama were studied with soil emergence traps. Supporting studies were made of physiographic and hydrologic features of the breeding habitat. The pattern of distribution of the forest litter and the composition, texture and stability of local deposits are largely determined by physiographic and hydrologic features which are operative in soil transport. The forest litter tends to be removed from steep slopes and valleys and to cumulate on gentle slopes and prominences. On hilltops the forest litter tends to occur in stable, residual deposits, while on hillsides and stream banks relatively unstable, alluvial deposits are more common. Breeding populations of Lutzomyia pessoana (Barretto), L. panamensis (Shannon), L. gomezi (Nitzulescu), and L. insolita (Fairchild and Hertig) are greater in hilltop regions, while those of L. trapidoi (Fairchild and Hertig) are greater in hillside and streamside regions. No comparable effect was noted in the case of L. rorotaensis (Floch and Abonnenc). No effects of physiographic aspect or of non-destructive inundation on breeding populations of sandflies were detected.

Surface‐Catalyzed Anodes for Hydrazine Fuel Cells: I . Preparation of the Substrate

Surface‐catalyzed anodes for the electrochemical oxidation of were prepared by first codepositing a porous layer of Mond Ni powder with Ni on an electroformed Ni sheet substrate and then catalyzing by chemically precipitating nickel boride into the porous Ni layer. The parameters associated with the codeposition step were studied for their effect on (i) the structure and texture of the resultant deposit, and (ii) the electrochemical performance of the subsequently catalyzed electrode. Scanning electron micrographs were made after the Mond Ni was codeposited. The catalyzed electrodes were operated at 2 kA/m2 (200 mA/cm2) and the anode vs. reference potential was monitored. The most influential parameters was the total number of coulombs used during the codeposition process. When 1200 coulombs on 48 cm2 were exceeded, the rough texture of the Mond Ni was destroyed and the catalyst was quickly shed during the electrochemical test.

Buried Strandline Deposits on the Central Florida Inner Continental Shelf

Research Article| January 01, 1974 Buried Strandline Deposits on the Central Florida Inner Continental Shelf MICHAEL E. FIELD MICHAEL E. FIELD 1Geology Branch, U.S. Army Coastal Engineering Research Center, Fort Belvoir, Virginia 22060 Search for other works by this author on: GSW Google Scholar Author and Article Information MICHAEL E. FIELD 1Geology Branch, U.S. Army Coastal Engineering Research Center, Fort Belvoir, Virginia 22060 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1974) 85 (1): 57–60. https://doi.org/10.1130/0016-7606(1974)85<57:BSDOTC>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation MICHAEL E. FIELD; Buried Strandline Deposits on the Central Florida Inner Continental Shelf. GSA Bulletin 1974;; 85 (1): 57–60. doi: https://doi.org/10.1130/0016-7606(1974)85<57:BSDOTC>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Accumulations of the intertidal clam Donax variabilis (Say) have been recovered from the Cape Kennedy inner-shelf subbottom. Depth of the shell deposits correlates with a marked, widespread sonic horizon that underlies the entire central Florida inner shelf. Composition, texture, and radiocarbon ages of the shelf deposits correlate with available data on adjacent onshore beach ridges and with established sea-level curves.The occurrence and location of these deposits are considered significant for four reasons: (1) accumulations of D. variabilis may provide a definitive marker in some areas for relict submerged beach deposits; (2) the restricted depth range of these mollusks makes them suitable for refining portions of the sea-level curve that are based on less well defined criteria; (3) shoals and ridges on the inner shelf have often been interpreted as relict barriers, yet off Cape Kennedy these present-day bottom morphologic features (shoals) appear to be unrelated to the relict beach deposits described herein. This suggests that modern shoal formation must be unrelated to relict strand topography; and (4) the rare occurrence of buried Strandline deposits on the shelf in the vicinity of Canaveral Peninsula, which is an area of well-documented beach-ridge accretion, suggests a large-scale planing or truncating of the surface by the last transgression, which has removed all but trace remnants of the previous Strandline morphology. In other shelf areas where beach ridge accretion has been less dominant, therefore, all traces of former strandlines may have been removed. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.