Syndepositional Diagenesis Research Articles

Diagenesis of the Marinoan cap dolostone, Southern Amazon Craton: An unconventional petroleum system in the evolution of the Araras-Alto Paraguai Basin

The post-snowball Earth world favors the development of hydrocarbon source rock intimately linked to periods of post-glacial marine transgression generating important potential petroleum plays. In the Southern Amazon Craton, hydrocarbons occur in one of the most spectacular examples of post-Marinoan cap carbonate, related to the mid-Ediacaran to Early Cambrian (c. Post 635 Ma) interval associated with the early stabilization of the Gondwana Supercontinent. The Puga cap carbonate consists of the basal portion of the Araras Group exposed in the Araras Alto-Paraguai Basin inserted as a reservoir in an unconventional petroleum system. The cap dolostone overlies diamictites and is overlaid by bituminous limestone and shales (source-rock), and dolostone in the top of a 700 m-thick depositional sequence. The cap dolostone has a diachronic relation with the limestone beds typifying as a secondary reservoir characterized by bitumen-filled fenestral and interpeloidal porosity. The upper dolostone has a closed framework and acts as sealing rocks. This study aims to establish paragenesis sequence and decipher its control on the quality of the cap dolostone as a microbialites-dominated reservoir. Drill core and outcrop samples were analyzed using microfacies, scanning electron microscopy, and cathodoluminescence to unravel the diagenetic history. Aftermath, the Marinoan events favored dolomuds precipitation in the shallow platforms, preserving primary porosity and permeability reduced by early gypsum cementation during oversaturation events. Other destructive processes, such as mechanical and chemical compaction (e.g., stylolites) and authigenesis of pyrite and low-Mg ferroan calcite cementation, occurred during burial and mesodiagenesis. The low permeability restricts hydrocarbon migration concentrated in the upper cap dolostone, and the early cementation increases the potential for preserving these carbonate deposits. Hydrocarbon maturation was triggered during the burial and uplift of the Araras-Alto Paraguai basin. The cementation phases described here enhance our understanding of the mechanisms behind syndepositional diagenesis in microbially-induced reservoirs. This study uses proxies associated with diagenetic studies to quantify the quality of microbially induced dolostone reservoir linked to the evolution of the Neoproterozoic unconventional petroleum system. In addition, this conception will promote a guide for future exploration and understanding of petroleum plays and suggests a possible Precambrian source rocks component of traditional Phanerozoic Petroleum systems in the central part of Brazil.

Syndepositional Uptake of Uranium, Molybdenum and Vanadium into Modern Bahamian Carbonate Sediments during Early Diagenesis

Syndepositional diagenesis is a complicating factor when interpreting geochemical proxies in carbonate sedimentary environments. Previous studies have suggested that carbonate deposits may preserve the geochemical and isotopic signatures of seawater that can be used for paleo-redox reconstructions. However, more work is necessary to understand how these trace metals are preserved. The present study examines shallow marine carbonate sediments from the Bahamas to better understand diagenetic effects on trace metal uptake and sequestration. Analysis of diagenetic effects and trace metal uptake follows a multi-method approach, combining sequential extraction, stable isotope analyses, and rare earth elemental analysis. Stable isotopes track bacterial sulfate reduction, denitrification, and organic matter source and provide insight into thresholds and processes for the authigenic trace metal uptake. Importantly, exchangeable phases exhibit authigenic accumulation of molybdenum, uranium and vanadium, and intensified bacterial sulfate reduction is evidenced by most depleted sulfur isotope signatures. In addition, rare earth element values are very indicative proxies that suggest altered primary seawater trace element in carbonates (no cerium or lanthanum anomaly, moderate heavy rare earth element enrichment, decreased y/ho ratios and positive correlations between aluminum, manganese, and iron). Taken together, these results allow the development of a framework to better understand how to apply sedimentary geochemistry of carbonate rocks to paleo-environments as this study shows significant authigenic accumulation of redox-sensitive trace metals by exchangeable phases.

Assessing the reliability of modern marine stromatolites as archives for the uranium isotope paleoredox proxy

Uranium isotopes (238U/235U) are commonly utilised in marine carbonates to reconstruct the redox evolution of ancient oceans and the atmosphere. However, questions remain concerning U isotope fractionation during carbonate precipitation and/or early sedimentary diagenesis. Moreover, the stromatolitic nature of many Precambrian limestones and dolostones brings further questions about U isotope fractionation during stromatolite formation due to microbial activity. Thus, it is unclear whether stromatolites are reliable archives for the U isotope composition of seawater. Here we measure the 238U/235U ratio of modern stromatolites from the hypersaline Shark Bay, Western Australia, a key study area that represents the largest modern example of stromatolite growth globally. A component-specific approach was utilised to analyse the uppermost crusts of modern stromatolites, older material from the deeper stromatolite laminae and the substrate upon which the stromatolites are forming. Our interpretations of δ238U data are aided by δ234U, δ18O, δ13C and trace element measurements, including some mineralogy and total organic carbon determinations for selected samples.Modern aragonitic crusts of stromatolites from the subtidal and intertidal zones around Shark Bay exhibited a narrow range of δ238U (−0.30 to −0.33‰), corresponding to a small offset of ca. +0.07‰ from seawater. This range of δ238U values overlaps with that of other primary carbonate precipitates in shallow marine environments such as corals but with a slightly higher mean δ238U. We investigated if this offset may be associated with the coprecipitation of U with aragonite from hypersaline seawater in Shark Bay, which has a higher proportion of dissolved U present as Ca2UO2(CO3)3 compared to open seawater. However, this measured offset is much smaller than that predicted using a speciation-dependent isotope fractionation model. Sub-recent material in the deeper stromatolite laminae exhibited higher and more variable δ238U (up to −0.15‰) compared to the modern aragonitic crusts of stromatolites. The strong inverse correlation between δ238U and the total organic carbon content (r = −0.83) and positive correlation with Mn concentrations (r = 0.91) suggest that 238U was preferentially reduced in the deeper laminae in association with organic carbon remineralisation under reducing conditions. The average δ238U offset of sub-recent stromatolite laminae from modern seawater was +0.13 ± 0.11‰ (1 s.d.), which is slightly lower than, but within uncertainty of, the offset measured for bulk carbonates from the Bahamas (+0.27 ± 0.14‰; 1 s.d.). These results demonstrate that stromatolites are valuable archives of global seawater δ238U, even in hypersaline restricted basins such as Shark Bay, but an offset to account for syndepositional diagenesis is likely required to accurately reconstruct seawater δ238U using ancient stromatolites.

Is mid-late Paleozoic ocean-water chemistry coupled with epeiric seawater isotope records?

Research Article| September 01, 2009 Is mid-late Paleozoic ocean-water chemistry coupled with epeiric seawater isotope records? Uwe Brand; Uwe Brand 1Department of Earth Sciences, Brock University, St. Catharines, Ontario L2S 3A1, Canada Search for other works by this author on: GSW Google Scholar Jun-ichi Tazawa; Jun-ichi Tazawa 2Department of Geology, Niigata University, Niigata 950-2181, Japan Search for other works by this author on: GSW Google Scholar Hiroyoshi Sano; Hiroyoshi Sano 3Department of Earth & Planetary Sciences, Kyushu University, Fukuoka 812-8581, Japan Search for other works by this author on: GSW Google Scholar Karem Azmy; Karem Azmy 4Department of Earth Sciences, Memorial University, St. John's Newfoundland L A1B 3X5, Canada Search for other works by this author on: GSW Google Scholar Xinqing Lee Xinqing Lee 5Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550002, China Search for other works by this author on: GSW Google Scholar Geology (2009) 37 (9): 823–826. https://doi.org/10.1130/G30038A.1 Article history received: 14 Jan 2009 rev-recd: 07 Apr 2009 accepted: 28 Apr 2009 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Uwe Brand, Jun-ichi Tazawa, Hiroyoshi Sano, Karem Azmy, Xinqing Lee; Is mid-late Paleozoic ocean-water chemistry coupled with epeiric seawater isotope records?. Geology 2009;; 37 (9): 823–826. doi: https://doi.org/10.1130/G30038A.1 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 SocietyGeology Search Advanced Search Abstract Isotopes of epeiric sea carbonates are used to construct seawater records for modeling global changes in Paleozoic ocean chemistry, climate, and for intercontinental correlation. We present for the first time geochemical results of Paleozoic brachiopods (biogenic low-Mg calcite, bLMC) from open-ocean Permian–Carboniferous seamounts of Japan situated in the tropical mid-Panthalassic Ocean. Strontium isotope values of bLMC from the Panthalassic and Paleotethys Oceans are coupled with those of coeval specimens from epeiric seas of North America, Europe, and Russia (p = 0.393), but not with those of epeiric sea whole rocks (matrix aragonite/calcite, mAC; p = 0.029) and conodonts (biogenic apatite, bA; p = 0.031). Oxygen isotope values of bLMC from the Panthalassic and Paleotethys exhibit mixed results with studies of counterparts from epeiric seas (p = 0.596) reflecting overprinting of local environmental conditions on global trends. Carbon isotope values of bLMC and mAC from the Panthalassic and Paleotethys Oceans are generally dissimilar to those of coeval material from epeiric seas of North America, Europe, and Russia (p = 0.001 and 0.002, respectively). Factors such as water mass stratification, evaporation, dilution, depth, temperature, carbon burial and/or oxidation variations, and syndepositional diagenesis within the local environment probably influenced the chemistry of the fauna and accumulating sediments. This decoupling of carbon and oxygen isotope values from the open ocean with those from epeiric seas makes questionable the use of isotope results from epeiric seas for international correlation, constructing global seawater records, determining fluxes in the global carbon cycle, and for modeling climate changes and subsequently atmospheric carbon dioxide levels. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Tertiary non-marine limestone within the strata of the Sullivan Buttes volcanic field, Yavapai County, Arizona: A petrologic and diagenetic investigation

The Oligocene fluvial-volcanic sequence in the Prescott area of central Arizona, USA, contains a thin and laterally limited bed of non-marine limestone. The limestone is characterized by an abundance of opaline diatoms, opalized charophytes, calcified reeds, and cyanobacteria encrustations. Limestone deposition occurred in a small pond of less than a few hundred meters width that formed as the result of damming of a small local stream by a volcanic event. The duration of the pond and limestone deposition was brief and was terminated by burial under volcaniclastic debris. Chemical weathering of coeval volcaniclastic debris was integral both to the formation of the limestone and its syndepositional diagenesis by providing a source for calcium, magnesium, and silica. Biogenicrelated consumption of calcium beyond its rate of re-supply resulted in the elevation of magnesium concentration relative to calcium (Mg/Ca) and the subsequent formation of fibrous calcite cements. Silica concentration seems to be connected to the presence of a series of burrows that provided a pathway from the silica source in the underlying volcaniclastic-rich fluvial sediments to the pond waters. Fluids passing from the sediment through the burrows resulted in the opalization of charophyte internodes and reproductive organs that had collected within the burrow. Silica supplied through the burrows to the pond resulted in diatom growth and their postmortem preservation. Blockage of the burrow system by the growth of cyanobacteria terminated the fluid connection between the sediment and pond water and the subsequent restriction on silica supply resulted in a loss of diatom preservation. The principal depositional phase of the pond was followed by a complex sequence of events that led to the formation of several geopedal fills and isopaceous cements, composed of both calcite and silica.

Sequence Stratigraphic Context of Syndepositional Diagenesis in Cool-Water Shelf Carbonates: Pliocene Limestones, New Zealand

Abstract Pliocene limestones in eastern North Island, New Zealand, are cool-water deposits composed of barnacle–epifaunal bivalve–bryozoan dominated calcitic biota formed in shoal areas about the margins of a tectonically active forearc basin seaway. Vertical changes in the thickness and depositional facies of the limestones, and fundamentally the position and nature of internal bounding discontinuities within them, have enabled identification of high-order (likely 41 ka) transgressive (deepening-upwards) and transgressive–regressive (deepening-then shallowing-upwards) sequences within the formations. Syndepositional (or sea-floor or pre-compaction) diagenesis in the limestones involves a spectrum of destructive to constructive features, including skeletal abrasion, bioerosion, encrustation, dissolution, and cementation. Upward changes in the type and extent of these pre-compaction diagenetic features within the discontinuity-bounded sequences relate closely to the stacking patterns of depositional facies and their associated skeletal and mineralogical composition. Consequently, it has been possible to develop a series of predictive diagenetic models for cool-water shelf carbonates deposited upon and about upthrust antiforms in the forearc that integrate their patterns of syndepositional diagenesis into a sequence stratigraphy based framework driven ultimately by relative sea-level changes. Marine constructive diagenesis, characterized by bioencrustation, turbid cements, and interstratified internal sediments, occurs most commonly in those facies close to the sequence-bounding discontinuities, within the lower levels of transgressive systems tracts (TSTs) and the uppermost levels of regressive systems tracts (RSTs). These sediments equate to the highest-energy facies upon antiform tops, close to the wave abrasion base, where sedimentation rates were low. In contrast, destructive diagenetic processes typically dominate over constructive ones, often exclusively so, in the upper part of TSTs, in highstand systems tracts (HSTs), and in the lower portion of RST carbonates, where the sediments were not so influenced by active fluid circulation or strong reworking for prolonged periods, but were more rapidly buried within accommodation traps below wave abrasion base about the antiforms. The link between the facies motifs and synsedimentary diagenesis in these cool-water Pliocene limestones helps unlock their otherwise often cryptic, high-order sedimentary architecture. Such an interpretive opportunity is not afforded by the subsequent post-compaction diagenetic features in the limestones because these are no longer closely related to the sedimentation realm.

Accurate reservoir characterization to reduce drilling risk in Khuff-C carbonate, Ghawar field, Saudi Arabia

ABSTRACT The Khuff-C reservoir in the Ghawar field is a stratified sequence of cyclic carbonate-evaporite deposits within the Permian Khuff Formation. The reservoir is heterogeneous, complex, and influenced by syndepositional diagenesis. Wells drilled into the Khuff-C in the ‘Uthmaniyah sector of Ghawar are usually prolific producers of non-associated gas but some have intersected poor-quality reservoir intervals with little or no gas production. The Khuff-C reservoir rocks were deposited in a peritidal setting where slight changes in sea level created locally exposed highs. The exposure in an arid climate resulted in outliers of porosity occlusion formed by evaporite cements within the Khuff-C reservoir. The outliers are variably sized and randomly distributed and the challenge is to predict their occurrence in order to avoid them in development drilling. Inverse modeling of the ‘Uthmaniyah 3-D seismic data has identified the tight-porosity outliers as areas of anomalously high acoustic impedance. Integration of 3-D seismic analyses with petrophysical and other well data has improved the reservoir characterization and reduced the drilling risk.

Paleoclimatic and tectonic control on the accumulation of North American cratonic sediment

Variation in accumulation rate as a function of depositional latitude has been determined for North American limestone, dolostone, sand-stone, gray-black shale, red shale, and evaporite rocks from tabulations by Ronov and co-workers, from data in lexicons of United States and Canadian stratigraphy, and from isopach and lithofacies maps published in 1975 by Cook and Bally. Phanerozoic sediment is similar to that on other continents, consisting of 63% terrigenous elastic facies (23% sandstone; 40% shale), 36% carbonate, and 1% chert, evaporite, and other minor rock types. Latitudinal variation in accumulation rate is influenced primarily by past positions of foreland and intracratonic basins. Additional variation related to paleoclimate is recorded as strong dependence of limestone, dolostone, red shale, and evaporite deposition on latitudes of accumulation, a relation reflecting the importance of ambient temperature and meteoric precipitation on the formation of various authigenic phases. Poleward increase in dolostone/total carbonate ratio in both hemispheres implicates the importance of syndepositional diagenesis in the formation of most dolostone sequences. The ratio of sandstone/total terrigenous clastic sediment exhibits little variation with latitude, a constancy indicating that most sand and mud is derived from older sediment rather than from the weathering of crystalline rock. As a result, terrigenous lithofacies record little climatic influence in the proportional delivery of mechanically versus chemically derived weathering products to basins of accumulation.

Syndepositional diagenesis of modern platform carbonates: Evidence from isotopic and minor element data

Physical, elemental, and stable isotopic evidence documents significant syndepositional diagenesis off biogenic carbonate in modern sediment pore water. Halimeda (aragonite) and Neogoniolithon (high-Mg calcite) fragments from sediment cores and experimental substrates were compared with fresh samples to determine the magnitude of minor element (Sr, Mg), and stable isotopic (C and O) compositional shifts. Although no significant shift in bulk sediment mineralogy is apparent, experimental substrates and natural biogenic grains exhibit significant diagenetic changes. These changes include dissolution textures, net loss of mass, changes in minor element composition, and progressive evolution toward carbon and oxygen isotopic equilibrium with p ore water. Our results demonstrate that carbonate sediment can undergo rapid syndepositional dissolution and reprecipitation. Pore waters likely are buffered chemically and isotopically by most abundant carbonate grain types. In turn, compositions of less abundant carbonate grains may shift toward equilibrium with respect to pore water. Therefore, many components of shelf limestone have compositions controlled by chemically evolved pore waters rather than by seawater from which the biotic carbonate originally precipitated.

Sulfate Platform-Basin Transition of the Lower Werra Anhydrite (Zechstein, Upper Permian), Western Poland: Facies and Petrography

ABSTRACT The peripheral evaporite platform of the Zechstein (Upper Permian) Werra Anhydrite of western Poland comprises a series of shoals (with thick sulfate deposits) and lows (with thin sulfate and thick halite deposits). Three cores were selected to examine facies variations from a sulfate platform, slope, and basin. The basal unit of the Lower Werra Anhydrite is represented by different varieties of nodular, bedded-nodular, fluidal-nodular, and brecciated facies. Some nodular fabrics probably originated within sabkha and/or gypsumpond environments, and the deposit was then mechanically redistributed. The absence of nodular structures in units other than the lower one in two of the wells suggests that the origin of these structures cannot be related to deep burial. Other units of the Lower Werra Anhydrite represent subaqueous deposits. The facies in the middle and upper units have no recent analog in coastal salina environments. Turbidity currents displaced sulfates from the platform to the adjacent basin. The origin of lenticular-bedded anhydrite may be related to deformation by compaction or by ravitational instability and slumping, which may have initiated crystallization or recrystallization of anhydrite. The vertical sequence of facies shows a distinct deepening-upward trend starting from the top of the basal nodular units. Deposition in shallow (salina) environments dominated the early history of the Lower Werra Anhydrite basin, although it was probably preceded by transgressive sabkha deposits. Relatively thick nodular anhydrites probably formed by syndepositional diagenesis of probable salina deposits and minor sabkha sediments. Gypsum was the original sedimentary mineral; it was later transformed into anhydrite, during either early or late (burial) diagenesis. We show that in deeply buried evaporites not only some macroscopic primary textures remain but also even microscopic details, which allow reconstruction of depositional environments and primary mineralogy of ancient anhydrites.

Comparison of Sequences Formed in Marine Sabkha (Subaerial) and Salina (Subaqueous) Settings--Modern and Ancient

Marine evaporites occurring in modern subaqueous (salina) settings and subaerial (sabkha) settings are different. Subaqueous Holocene evaporites occur as shoaling-upward lacustrine sequences up to 10 m thick. They are evaporite dominated and are composed primarily of bottom-nucleated crystals that may be deposited as massive, laminated, or rippled units. Each coastal lake is dominated by laminated evaporites with subordinate carbonate sediments. In plan view, they show a well-developed bull's-eye pattern with a sulfate center and a carbonate rim. In contrast, subaerial (sabkha) evaporites occur as part of a laterally prograding, shoaling-upward, peritidal sequence in which the supratidal unit is usually no more than 1 m thick. Sabkha sequences are matrix dominated, not ev porite dominated, with the bulk of the sulfate phase occurring as diagenetic nodules, enteroliths, or diapirlike structures. These sulfates were formed during syndepositional diagenesis by replacement and displacement processes. The various facies of the sequence tend to accumulate in belts parallel with the shoreline. Relative to the sea level or the brine level, sabkhas tend to form over paleotopographic highs whereas salinas tend to occur in paleotopographic lows. Some of the characteristics that distinguish Holocene subaerial and subaqueous evaporite sequences can be used to do the same for similar ancient facies, even when gypsum has been converted to nodular anhydrite. The distinction is important for it can be used by explorationists in the oil industry to define the paleotopography of the associated underlying porous and nonporous carbonates.

Lithification, Micritization and Syndepositional Diagenesis of Biolithites on the Jamaican Island Slope

ABSTRACT Biolithites on the Jamaican Island Slope are undergoing considerable diagenetic alteration. Significant volumes of rock are in the process of being converted to biomicrite and pelmicrite by massive biological erosion and cementation by Mg-calcite micritic cement. Many rocks also display textures similar to some attributed to recrystallization or replacement in ancient limestones. Most neomorphic textures occur in rocks collected from the thermocline layer and especially affect the deeper rocks studied (278 m). Some of these puzzling textures are clearly due to contemporaneous mechanical sedimentation and growth of both Mg-calcite and coarse-grained aragonite crystalline cements, resulting in cement-supported fabrics. Crystalline cements also fill megascopic voids created by the dissolution of aragonite in undersaturated water of the thermocline layer. It is possible that some textures represent true neomorphism.