Micrite Research Articles

Diagenesis and geochemistry of the Aptian dolomite (cretaceous) in the Razzak Oil Field, western Desert, Egypt

Petrographic study of selected thin sections from the Aptian dolomites in the Razzak Oil Field, Egypt reveals three dolomite textures. These textures have been classified based on crystal size, shape, uniformity, and trace element distribution. These textures are as follows: 1) finely crystalline, planar-e dolomite, 2) medium to coarsely crystalline, non-planar dolomite, and 3) very coarsely crystalline, non-planar dolomite (saddle dolomite). Stable isotope analyses indicates that the Aptian dolomites formed in a marine environment and were later subjected to several diagenetic modifications that affected the original sediments. The finely crystalline, planar-e dolomite is penecontemporaneous in origin with d18O that ranges from -7.51 to -8.14%o VPDB and d13C that ranges from +0.39 to -1.27%o VPDB. The medium to coarsely crystalline, non-planar dolomite is a replacement type with a meteoric origin. In this non-planar dolomite, the d18O ranges from -7.99 to -8.82%o VPDB and the d13C ranges from -0.58 to -1.35%o VPDB. The void-filling (saddle dolomite) is the product of chemical compaction and is associated with the thermal sulfate reduction event. This saddle dolomite has d18O that ranges from -7.89 to -8.76%o VPDB and d13C that ranges from +1.41 to +2.42%o VPDB. The diagenetic parasequence of the Aptian Dolomite is recorded by: 1) deposition of the original sediments (lime mud); 2) dolomitization; 3) silicification, 4) pyritization, and 5) precipitation of saddle dolomites (pore-filling dolomite).

Molar tooth structures of the Neoarchean Monteville Formation, Transvaal Supergroup, South Africa. I: Constraints on microcrystalline CaCO3 precipitation

AbstractMolar tooth (MT) structures are enigmatic, contorted millimetre‐ to decimetre‐long veins and spheroids of microcrystalline calcite that formed during very early diagenesis in Precambrian sediments. MT structures in the ca 2·6 Ga Monteville Formation are 600–800 Myr older than previously reported occurrences and establish that conditions necessary for MT genesis were met locally throughout much of the Precambrian. In the Monteville Formation, MT structures were formed shallow subtidally, extending to depths near storm wave base, in shale host sediments intercalated with storm‐generated carbonate sand lenses. They are filled with microcrystalline calcite and rare pyrite. Microcrystalline calcite identical to that in MT structures fills other pore space, including porosity between grains in carbonate sand lenses, moldic porosity in sand grains, sheet cracks in columnar stromatolites, and shallow cracks on sandy bedding planes. Relationships in the Monteville Formation demonstrate that microcrystalline CaCO3 precipitated in fluid‐filled cracks and pores; microcrystalline calcite characteristics, as well as the paucity of carbonate mud in host rocks, are inconsistent with injection of lime mud as the origin of MT structures. Locally, MT cracks were filled by detrital sediment before or during precipitation. Precipitation occurred in stages, and MT CaCO3 evolved from granular cores to a rigid mass of cores with overgrowths – allowing both plastic and brittle deformation of MT structures, as well as reworking of eroded MT structures as rigid clasts and lime mud. Crystal size distributions and morphology suggest that cores precipitated through nucleation, Ostwald ripening and size‐dependent crystal growth, whereas overgrowths formed during size‐independent crystal growth.

Primary versus diagenetic bedding in the limestone-marl/shale alternations of the epeiric seas, an example from the Lower Lias (early Jurassic) of SW Britain

Micritic limestones form part of cyclic alternations of limestones- marls/shales in many offshore facies of epeiric seas and their origin has been, and still is, subject to controversy. As an example from the offshore ramp facies, the origin of Lower Lias micritic limestones of SW Britain has been investigated. The very continuous limestone beds show many petrographic and geochemical similarities to isolated nodules, which occur within the marls and are interpreted as being of diagenetic origin. Displacive growth of the microspar crystals was the most important process that occurred during the near-surface formation of the central part of limestone beds, but their edges formed during later burial. The carbon isotopic values (+1.1‰ to −3.4‰ (PDB)) of the central part of the limestone beds and nodules suggest a predominantly marine source for the carbonate, whereas bacterial sulphate reduction played a minor part in their cementation. The oxygen isotopic values (−1.5‰ to −7.2‰ (PDB)) of the characteristic limestone beds, and nodules suggest their formation (cementation/recrystallization) commenced at shallow depth but continued during progressive burial. The microspar crystals of the matrix of the limestones show rare aragonitic relics or pitted surface. Aragonitic fossil remains are rare in these offshore facies and this is in contrast to their abundance in the laterally equivalent shallow marine facies (Sutton Stone). It is suggested that early submarine dissolution of aragonitic components (lime mud and bioclasts) was important in providing carbonate for cementation of the limestones. Early submarine dissolution may have been a common process in epicontinental epeiric settings with low deposition rates, and as the result long residence time in the early diagenetic zones.

Soil Stabilization of Forest Roads Sub-base Using Lime Mud Waste from the Chemical Recovery Process in Alkaline Pulp Mill

Soil Stabilization of Forest Roads Sub-base Using Lime Mud Waste from the Chemical Recovery Process in Alkaline Pulp Mill

Topographic Controls on Production and Deposition of Tidal Cool-Water Carbonates, Uzes Basin, SE France

We document an example of a cool-water carbonate deposit interpreted as a flood-tidal delta formed during sea-level fall in the Uzes basin (French Miocene foreland basin). In the Miocene it was a peripheral basin connected to the open sea by a narrow, 15-km-long seaway. The studied Uzes Formation is a 50-m-thick tidal bioclastic carbonate body, formed at the junction between the Uzes basin and the seaway. It is composed dominantly of rhodalgal packstones that are interpreted to have been produced inside the basin. However, most of the deposit was built out by bidirectional hydraulic dunes, suggesting that accumulation of carbonate grains was not controlled by production but rather by tidal currents. The deposit is thickest and coarsest grained, and exhibits the larger dunes at the inlet of the seaway, where currents are expected to have been fastest. The deposit is thinner, finer-grained, and more bioturbated away from the inlet toward the basin; that is interpreted as a result of a decrease of current velocity due to flow expansion. The main deposit exhibits a general upward increase in thickness and grain size of cross-beds, together with a decrease of faunal diversity (from bivalve-rich to rhodalgal facies), consistent with progressive tidal flow acceleration in the seaway resulting from sea-level fall. Lime mud is pervasive in the matrix of even the highest-energy facies. This suggests that one cannot draw any average correlation between permeability and architecture of the deposit. Also, this could favor the observed early marine diagenesis of the deposit and give it a high preservation potential in the stratigraphic record.

Development and dismemberment of a Middle Devonian continental-margin submarine fan system in east-central California

A submarine fan system of Middle Devonian age, developed along the middle Paleozoic continental margin in east-central California, apparently is unique for a Paleozoic fan in the exposure of all elements of the system. The fan itself, the main distributary channel, and the lower interchannel slope are represented in pendants (or sedimentary rock septa) in the eastern Sierra Nevada. To the east, in the Inyo Mountains, a middle slope channel, lower and middle to upper interchannel slopes, two upper slope channels, and the shelf are exposed. The quartz sand and lime mud composing the fan were derived from the east or southeast and transported across the shelf during a lowstand of sea level preceding the great Taghanic overlap. This sediment was then swept into the heads of submarine channels in the western Inyo Mountains prior to being transformed episodically into sediment gravity flows that constructed the fan at the base of the slope. Similar successions of Middle Devonian calcareous sandstone and sandy limestone in extreme west-central Nevada and southeastern California, possibly dispersed parts of the Mount Morrison fan, can be utilized to estimate displacements on several major strike-slip faults in this region characterized by long-term tectonic activity.

Bedding and pseudo-bedding in the Early Jurassic of Glamorgan: deposition and diagenesis of the Blue Lias in South Wales

Sedimentary bedding planes in a succession of Lower Jurassic ( Bucklandi Biozone) limestone-shale alternations at Nash Point, South Wales are represented by omission surfaces intermittently developed on the upper surfaces (limestone-shale contacts) of limestone beds. Other lithological contacts (shale-limestone contacts and the majority of limestone-shale contacts) are devoid of positive indications of an associated break in sedimentation. Statistical analysis of (a) limestone-shale contacts and (b) recorded omission surfaces suggests that limestone-shale contacts are regularly spaced and omission surfaces randomly distributed. Limestone-shale contacts and omission surfaces are interpreted as proxies for sedimentary bedding and shale-limestone contacts interpreted as pseudo-bedding planes, with the alternation of limestones and shales arising from the diagenetic differentiation of beds of lime mud. No short- or long-term cyclicities at a scale greater than that of an individual couplet can be detected by the statistical methods employed, and it is therefore unlikely that a Milankovitch-type cyclicity is present. Evidence of strati-graphical environmental succession, exhibited both by ichnotaxa and body fossil assemblages in the biofacies of omission surfaces, suggests that the succession represents part of a third-order shallowing event. It is proposed that beds of lime mud were deposited as a consequence of episodic storm action on a hemipelagic shelf, and diagenetic differentiation was ‘steered’ by this episodicity and not by any orbital control.

Field evaluation of in situ remediation of a heavy metal contaminated soil using lime and red-mud

We evaluated the effectiveness of lime and red mud (by-product of aluminium manufacturing) to reduce metal availability to Festuca rubra and to allow re-vegetation on a highly contaminated brown-field site. Application of both lime and red mud (at 3 or 5%) increased soil pH and decreased metal availability. Festuca rubra failed to establish in the control plots, but grew to a near complete vegetative cover on the amended plots. The most effective treatment in decreasing grass metal concentrations in the first year was 5% red mud, but by year two all amendments were equally effective. In an additional pot experiment, P application in combination with red mud or lime decreased the Pb concentration, but not total uptake of Pb in Festuca rubra compared to red mud alone. The results show that both red mud and lime can be used to remediate a heavily contaminated acid soil to allow re-vegetation.

Use of a Split Microtron for Instrumental Gamma Activation Analysis

The potentials of a split microtron with an electron beam energy of up to 70 MeV for the gamma activation analysis of some natural samples were studied. Certified reference materials of bottom sediments—terrigenous clay (SDO-1), volcanic-terrigenous mud (SDO-2), and lime mud (SDO-3)—were used as model samples. The samples were irradiated with photons generated upon the deceleration of an electronic beam with an energy of 20–50 MeV. The beam was controlled by placing a gold foil before the test sample. Activation products of C, Cl, Na, Mg, Ti, Fe, Ca, Zr, Mn, Rb, Sr, Ni, Co, Y, As, Ba, Zn, Cs, Sc, Cr, and Ce were identified by gamma lines using a high-purity germanium detector.

Sequence stratigraphy and evolution of Middle to Upper Devonian Beaverhill Lake strata, south-central Alberta

Abstract Beaverhill Lake strata of late Givetian to early Frasnian age in the subsurface of south-central Alberta consist of shelfal limestones, dolostones and some anhydrites as well as basinal limestones and shales, and range in thickness from 75 to 240 m. These strata were deposited in the Central Alberta Basin and on banks (platforms) or isolated reefs on both sides of the basin. An integrated physical stratigraphic/sedimentological and conodont biostratigraphic study of these strata reveals that Beaverhill Lake strata form most of one overall (first-order) transgressive-regressive (T-R) cycle of sedimentation that also includes coastal plain and marginal marine deposits of the underlying Watt Mountain Formation (conodont zone of Lower subterminus Fauna) and shallow-marine carbonates of the lower part of the overlying Cooking Lake Formation on the east side of the Central Alberta Basin and the lower part of the overlying Leduc Formation on the west side of the basin. This overall T-R cycle consists of two major (second-order) T-R cycles. The lower, second-order cycle extends from the sub-Watt Mountain subaerial unconformity up to a widespread subaerial unconformity (R4 or Upper C) on banks and isolated reefs on both the east and west sides of the Central Alberta Basin and its equivalent, conformable transgressive surface in the basinal succession and includes Beaverhill Lake strata deposited during conodont zone of Upper subterminus Fauna to upper MN2 Zone. The upper, second-order T-R cycle extends from this subaerial unconformity or its basinal equivalent up to the conformable transgressive surface at the top of the Waterways Formation in the Central Alberta Basin or up to an equivalent position in the lower part of the Cooking Lake and Leduc formations on both sides of the basin. Strata in the upper, second-order cycle were deposited from the upper MN2 to MN4 conodont zones. The Beaverhill Lake portion of each of these second-order cycles includes seven third-order sequences, the basic stratigraphic unit of this study. T-R cycles were produced by the interaction of base-level changes, extrabasinal tectonism and depositional controls. The interaction of these controls resulted in different stacking styles of growth on banks and isolated reefs on the east and west sides of the Central Alberta Basin. Areally widespread progradation of carbonate banks on the east side of the basin was directly related to the delivery of argillaceous sediment to the basin from the northeast. The most likely terrigenous source areas were an uplifted portion of the Caledonian orogenic belt, exposed along the east coast of Greenland, or the eastern part of the Franklinian orogenic belt, exposed in the Canadian Arctic islands. The deposition of basinal argillaceous strata in the study area was episodic. The onset of episodes of argillaceous sediment deposition corresponds to transgressive facies shifts and was triggered by increased rates of base-level rise and not to shelfal incision and sediment bypass during intervals of base-level fall. Clay-rich sediment was carried by either surface, or near-surface, marine currents, or by episodic storm-generated currents or episodic storm-generated sediment-gravity flows. The southwesterly transport of this sediment was due to the southeasterly paleo-trade winds or to storm tracks that moved parallel to these winds. During some intervals, this fine terrigenous sediment appreciably infilled portions of the basin proximal to coeval carbonate banks on the east side of the basin. Westerly, leeside shedding of lime mud from these carbonate banks by storm-induced currents resulted in even further infilling of the basin. As a result, these portions of the basin became sufficiently infilled to promote the westerly, leeside bank progradation during intervals of either slower base-level rise or base-level fall. Banks and most isolated reefs on the west side of the Central Alberta Basin were far removed from the entry of clay-rich sediment into the basin. Therefore, portions of the Central Alberta Basin proximal to these banks and isolated reefs were not significantly infilled by coeval argillaceous successions. Lacking appreciable argillaceous sediment infill of these portions of the basin, banks and most isolated reefs on the west side of the Central Alberta Basin prograded basinward only by building out over their own debris and finer bank- or reef-derived sediment. This severely limited the extent of bank or isolated reef progradation. As a consequence, banks and isolated reefs on the west side of the Central Alberta Basin display an overall retreating or backstepping style of growth. The major episodes of isolated reef growth occur at different times on the east and west sides of the Central Alberta Basin and reflect the difference in the prior evolution of carbonate banks in both areas. Trends, inherent in both stratigraphic cross-sections and in cumulative isopach maps, also suggest that most of the micrite in basinal limestones was shed from upslope portions of carbonate ramps, from areas to the northeast of the sub-Cretaceous subcrop unconformity.

Efficacy of lime mud residues from kraft mills to amend oxidized mine tailings before permanent flooding

Flooding mine tailings that have partially oxidized is a rehabilitation method commonly practiced at sites having a positive hydrologic balance and a suitable topography to limit further oxidation of the remaining sulfide minerals. The purpose of this study was to assess the efficacy of amending oxidized mine tailings with lime mud residue (LMR) before flooding to reduce the release of acidity and heavy metals to the water cover and the pore water. Series of LMR samples from three kraft pulp mills were collected over several weeks and characterized to evaluate their variability in composition and physical characteristics. All LMR samples consisted of silt-sized aggregates of CaCO3 crystals and contained very low concentrations of legislated heavy metals. Flow-through column tests were carried out with the following three configurations: (i) water cover over oxidized tailings; (ii) water cover over LMR layer over oxidized tailings; and (iii) water cover over LMR + oxidized tailings mixtures over oxidized tailings. A permanent water cover was maintained at the top of all the columns to simulate flooded conditions. The LMR amendment was effective for maintaining the pH at neutral or slightly alkaline values and dissolved heavy metal concentrations below regulatory limits in the water cover and in the pore water of the mixed LMR + tailings layer. However, the pH remained acidic and heavy metal concentrations were elevated in the pore water of the underlying oxidized tailings layer, even after hundreds of pore volumes of water had infiltrated through the columns. The behavior of pore water pH in the underlying oxidized tailings was attributed to the low solubility of CaCO3 and the consumption of bicarbonate ions by reaction with Fe-oxyhydroxysulfate minerals. Key words: lime mud residue, recaust, tailings, acid mine drainage, flooding, water cover.

Temperate and semi-arid tufas in the Pleistocene to Recent fluvial barrage system in the Mediterranean area: The Ruidera Lakes Natural Park (Central Spain)

The Ruidera Lakes Natural Park, in Central Spain, contains a well-exposed Pleistocene to Recent freshwater carbonate (tufa) succession dominated by fluvial barrages and lacustrine deposits. The majority of exposed tufas are Holocene to Recent in age. Today, carbonate accumulation is currently manifested as active phytoherm barrage constructions, marginal lacustrine stromatolitic terraces, lacustrine lime muds (all produced mainly by precipitation) and sand-size detrital tufa. The depositional history of the Ruidera Park sites has been interpreted from natural outcrops, rotary drill and percussion auger cores. These reveal a long Quaternary record of microbially dominated barrage framework developments and associated lacustrine carbonates. These alternate with frost weathering deposits and detrital tufa episodes, especially during cooler conditions. U-series dating of several earlier tufa deposits within the park indicates four distinct episodes of tufa development at 190–250 ka B.P., 90–130 ka B.P., 30–40 ka B.P. and 16 ka B.P.–Present. The three oldest episodes appear to be related to cyclic tufa-building events associated with warm periods of Oxygen Isotope Stages (OIS): 7, 5 and 3. Growth under present conditions is slow and several barrages have been damaged by human activity and drought events.

Mixing-Zone Diagenesis in the Subsurface of Florida and the Bahamas

Abstract Three cores from Great Bahama Bank and southern Florida contain examples of mixing-zone diagenesis where typical shallow-water, aragonite-rich sediments were altered to low-Mg calcite. The 40–50 m thick mixing zones are identified on the basis of downcore covariant trends from depleted meteoric (δ18O = -3.2 ± 0.7‰; δ13C = -1.6 ± 1.8‰) to enriched marine isotopic values (δ18O = +1.0 ± 0.3‰; δ13C = +1.9 ± 0.7‰). The age of the mixing zones varies from late Pliocene to Pleistocene, so these cores provide three independent examples of mixing-zone diagenesis. Mixing-zone diagenesis produced a limestone composed of low-Mg calcite with petrographic fabrics including moldic porosity, blocky to dogtooth calcite cementation, and recrystallization of lime mud to micrite and microspar. The mixing-zone diagenetic model predicts alteration in only part of the mixing zone. Because the alteration recorded in these cores shows continuous alteration through the entire mixing zone, we consider the mixing of waters itself to be largely irrelevant. Rather, diagenesis was probably driven by the difference in solubility between aragonite and calcite with some additional dissolution of aragonite driven by the microbial oxidation of buried organic matter. The mixing zone has been proposed as a likely location for dolomitization. With the exception of some clearly sea-floor dolomite in one core (Unda), the mixing zones in these cores lack dolomite despite the sediment clearly having been altered in the mixing zone. The lack of dolomite in these mixing zones, combined with the extensive literature questioning the chemical reasoning for mixing-zone dolomite, supports rejection of the mixing-zone dolomite model.

Recycling of Solid Residues to the Forest: Experimental and Theoretical Study of the Release of Sodium from Lime Mud and Green Liquor Dregs Aggregates

In order to optimize the recycling of solid residues back to the forest, it is necessary to measure and characterize the dissolution rate of the product under well-defined conditions. In this study, inorganic solid residues from a kraft pulp mill were characterized physically and chemically. The effect of pH, as well as physical characteristics and chemical composition, on the leaching rate was investigated. It was shown that the leaching behaviour differed depending on the production method of the aggregates. A model based on mass transfer was fitted to the experimental leaching data. It was shown that the leaching rate for the easily soluble species was reasonably well described using the concentration gradient of these species within the pellet. It was also shown that mass transfer within and from the pellet/granule was the rate-determining step.

Paleogeography of the Matapédia basin in the Gaspé Appalachians: initiation of the Gaspé Belt successor basin

The Matapédia basin consists of the uppermost Ordovician – lowermost Silurian deep-water, fine-grained carbonate–siliciclastic rocks of the Honorat (Garin Formation) and Matapédia groups (Pabos and White Head formations), the lower rock assemblage of the Gaspé Belt in the Gaspé Appalachians. Paleogeographic maps of eight time slices from the Caradocian to the Llandoverian are presented to better understand the tectonosedimentary evolution of the Matapédia basin. Deposition evolved from siliciclastic (Garin Fm.) to argillaceous limestones (Pabos Fm.), to limestones (White Head Fm.). The overall change from terrigenous (Garin Fm.) to limestone facies (White Head Fm.) reflects a change in the source area. Paleocurrent directions and composition of sandstones indicate an orogenic source area to the south for the Garin Formation, which is believed to be the inliers of the Humber and Dunnage zones in the southern Gaspé and New Brunswick Appalachians. Lime muds deposited by turbidity currents coming from the north suggest the Anticosti active carbonate platform as the source area for the White Head Formation. The Matapédia basin was filled from south to north. First deposits, the Garin Formation, occurred south of the Taconian thrust sheets (Humber Zone) and also south of the Grenville basement. This region was the domain of the Ordovician Iapetus Ocean (Dunnage Zone). The northern limit of the basin migrated northward during deposition of the Matapédia Group in Ashgillian–Llandoverian times and reached its actual northern limit at the very end of the Llandoverian (C6), when siliciclastic facies of the lower Chaleurs Group were deposited.

Mixed carbonate–siliciclastic sequence stratigraphy of a Paleogene transition zone continental shelf, southeastern USA

The sequence stratigraphy and facies of the Paleogene in the subsurface of the Albemarle Basin, North Carolina was defined using 1600 thin sections of plastic impregnated well cuttings from 24 wells, wireline logs, biostratigraphic data, and seismic data. The facies formed in the transition zone between warm subtropical and temperate conditions on a swell-wave dominated, open shelf exposed to major boundary current activity. The shelf has a distinctive seismic profile consisting of a shallow inner shelf, inner-shelf break, deep shelf (depths in excess of 200 m), and the continental slope. The inner shelf was characterized by distinctive quartz sand and sandy mollusk facies inshore, passing seaward into a broad, wave-swept abrasional shelf, and then into storm-influenced bryozoan–echinoderm limestones to depths of several tens of meters. Argillaceous lime mud (marl) deposition was widespread across the deep shelf, extending onto the inner-shelf during major highstands. Sediment thickness trends were controlled by greater differential subsidence of crustal blocks within the Albemarle Basin, which considerably modified but did not obliterate the effects of eustatic sea level changes in this passive margin setting. Five supersequences were identified on seismic and in wells, each consisting of multiple regionally identifiable sequences. The Paleocene supersequence is dominated by widespread marl deposition, reflecting shelf flooding into the Late Paleocene thermal maximum. This warming corresponds with widespread inner-shelf skeletal carbonate deposition from the Late Paleocene through the Middle Eocene. The two Eocene supersequences identified are dominated by bryozoan–echinoderm-rich carbonates that formed a seismically definable sediment buildup 50 km wide by 100 m thick across the deepest inner-shelf during the Lower to early Middle Eocene. Middle to Upper Eocene supersequence highstand sequences indicate increased progradation and greater mixing of shelf carbonates with nearshore siliciclastics, likely in response to lowering sea-levels and cooling climate. The two Oligocene supersequences identified are dominated by coarse siliciclastic sand that is heavily admixed with mollusk-foraminifer-dominated carbonates. Rapid flooding, followed by extensive progradation of shallow shelf sediments in Oligocene sequences reflects continued eustatic lowering driven by the onset of icehouse climatic conditions. Increased incision and reworking of deep shelf sediments during Oligocene supersequence highstands resulted from increased ancestral Gulf Stream boundary current activity during icehouse times. Key elements controlling facies distribution through time include significant wave energy, which controls the width and distribution of inner-shelf facies belts through the degree of water bottom abrasion and winnowing. Boundary currents also are capable of large-scale reworking of deep shelf sediment; they also provide a mechanism for widespread inner-shelf hardground development during major transgressions. In addition, boundary currents play a major role in stabilizing local climate by buffering seasonal temperature variations, directly influencing which carbonate grain producers can thrive in this transition zone setting.

Potential Sources of Hydrogel Stabilization of Florida Bay Lime Mud Sediments and Implications for Organic Matter Preservation

Abstract The fine grained carbonate mud sediments of central Florida Bay are resuspended quite easily. However, this disturbance is usually limited to the surficial (‘floc’) layer, as the underlying sediments appear to be stabilized by an hydrogelation involving the bulk organic matter. That gelation has occurred within these sediments is suggested from their physical behavior and an observed mathematical relationship between the percentages of organic carbon (Corg) and water. Specifically, when extruded from a core barrel, the sediment maintains its integrity and has the consistency of a fine spackling compound. However, upon homogenization, as with a stirring rod prior to sieving, these sediments break into two distinct phases, ½–⅔ milky water and ⅓–½ sediment grains, by volume. The relationship observed between Corg and water was modeled as both linear (% water = (0.0777) Corg + 0.2984, R2 = 0.8664) and logarithmic (% water = 0.2489 Ln Corg + 0.2842, R2 = 0.9455) functions. As this relationship tends t...

Tectonic setting of outer trench slope volcanism: pillow basalt and limestone in the Taconian orogen of eastern New York

The only pillow basalt in synorogenic sedimentary rocks at the exterior margin of the Taconic orogen in eastern North America is at Stark's Knob in eastern New York. Earlier reported as extrusive into allochthonous Ordovician slope and rise facies, this small lens (ca. 125+ m long, 39 m thick) is a fault-bounded block in Upper Ordovician melange under the Taconian frontal thrust. Its N-MORB (normal mid-ocean ridge basalt) basalt geochemistry and spinel composition are characteristic of oceanic ridge settings at a water depth of 2 km or more. Abundant limestone lenses on pillows and lava shelves within pillows yielded a middle Late Ordovician gastropod. The limestones are reconciled with this extrusion depth and with limited early Paleozoic pelagic carbonate production by lime mud transport from the Laurentian platform or abiotic carbonate precipitation with sea-water heating during basalt extrusion. A genetic relationship between the parautochthonous Stark's Knob basalts and the allochthonous Jonestown volcanics in slope and rise facies of the Hamburg klippe, eastern Pennsylvania, is likely. Both are Ordovician MORB basalts that reflect volcanism on the subducting outer trench slope prior to the Taconic arc – Laurentia collision. Taconic orogenesis may have led to basalt production on the subducting plate by (1) the setting up of orogen-parallel, predominantly strike-slip motion on the subducting slab with MORB basalt generated at offsets in a setting analogous to the Gulf of California or (2) development of faults in a flexure-induced extensional regime. By either process, mafic volcanism appears to be a rare but tectonically significant process on outer trench slopes as continental margins or oceanic plates enter subduction zones.

Late Quaternary geohistory of Sárrét Basin, based on studies on core Sárrét-2, Hungary

The Sárrét marshland is situated along the northeastern foothills of the Bakony Mountains, along a NE-SW-trending neotectonic zone. Investigation of the marshland and the reconstruction of its evolution are especially interesting to compare to the present and the expected future stage of Lakes Balaton and Velence. Based on the sedimentological characteristics of the core sequence and the geochemical, physical, and mineralogical composition of the layers, three sedimentological cycles could be separated. The three cycles represent the most important evolutionary phases of lake formation: flourishing and progressive aging. First, a nutrient-poor, open-water lake existed, where clastic sediments (sand and silty clay) were deposited. During the second phase, phytoplankton-produced autogenic lime mud was deposited in the progressively more eutrophic water. Peat accumulation during the third stage indicates the marsh phase of the lake.The results suggest that the studied sequence developed from Late Glacial to Middle Holocene. According to radiocarbon dating the accumulation rate in Sárrét (Sümegi, this volume) corresponds to the sedimentation rates in the Tapolca Basin and Lake Balaton.

DIAGENESIS OF SILURIAN REEFAL CARBONATES, KUDIRKA OILFIELD, LITHUANIA

Upper Silurian carbonate reservoir rocks at the Kudirka oilfield, southern Lithuania, have a complex diagenetic history. This consists of the following stages: compaction and dewatering; early lithification; minor fracturing? first generation leaching; precipitation of first‐ and second‐generation inter‐ and intragranular calcite cements; recrystallization of lime mud, sparry calcite cement and bioclastic grains; chemical compaction and the formation of stylolite‐associated fractures; precipitation of dolomite, pyrite and silica; a second phase of leaching, with stylolite surfaces acting as conduits for aggressive fluids; and finally oil emplacement.The Upper Silurian carbonates are interpreted to correspond to a variety of reefal deposits. In all the types of reef rock analysed, late diagenetic leaching has enhanced reservoir quality. However, no clear correlation could be found between rock texture and reservoir quality. This is mainly because the very common crinoid fragments acted as substrates for the growth of pore‐occluding syntaxial calcite cement. The lack of correlation between rock texture and reservoir quality can also be attributed to subordinate localized stylolite‐related dolomitization.