Significance in the Integration of Facies Analysis, Stable Isotopes and Diagenetical Results for the High-Resolution Sequence Stratigraphy Characterization in the Shallow Platform of Shuaiba Formation, Lower Cretaceous, Abu Dhabi Onshore, UAE

The study presents the sequence stratigraphy of the carbonate platform focused in lower part of Shuaiba Formation, as well as the organization of the arrangement formed by the cyclical sedimentological evolution at high-resolution scale, through the facies analysis, diagenetical imprints and finally, significance of stable carbonate isotope results in the building up of carbonate platform in southeast Abu Dhabi. Interpreted stratigraphic surfaces from integration of depositional facies reviewed in all available cored data within studied area and stable carbon isotope results allowed that four small-scale regression-transgression depositional cycles can be discriminated which are stacked into a medium-scale sequence, that may record a 600 kyr Milankovitch signal. The small-scale sequences were correlated within the studied area using both conventional well logs and stable isotope records. Transgression hemicycles represent the increasing of accommodation space and can be identified in direct evidence, such as 25-40 ft. thickness of lithocodium/bacinella floatstones and skeletal peloidal packstones facies, association of facies interpreted within upper slope sub-environment. Likewise, in δ13C profiles, the rise/fall turnarounds of small-scale sequences are marked by negative δ13C peaks and associated with characteristics patterns: (1) proportion decrease of shallower sub-environments facies is interpreted as an rising relative sea-level and (2) decreasing δ13C trends interpreted to be related to decreasing nutrient supply. The medium/big pores of floatstones poorly connected in packstone matrix are expressed in the medium/high porosity with low permeabilities. In contrast, regressive hemicycles represent the reduction in accommodation space and can be characterized in direct evidence, such as the growing up of persistent 10-20 ft. thickness with thousands of meters of correlation of stromatoporoids and rudist facies, association of facies interpreted within shelf-margin complex sub-environment. In addition, the fall/rise turnarounds are marked by positive δ13C peaks, associated with the stromatoporoids/rudists mounds with characteristic patterns: (1) proportion increase of shallower sub-environments facies is interpreted as falling relative sea-level and increase in proximity and (2) increasing δ13C values interpreted to reflect increasing nutrient supply. Unusually very high permeability is attributed to the present of fractures and dissolution events that is enhanced where proportion of stromatoporoids facies are more pronounced. The described characterization resulted in the identification of genetic cycles that reproduce the sedimentological evolution, which are presented in small-scale sequences. In addition, the δ13C values enabled to understand the internal organization and the development of the carbonate building up in the Shuaiba shallow platform evolution. This study provides update and understanding on sedimentary facies, depositional pattern, and expands on previous published works, using new approach from semi-regional to local scales. Finally, results help to understand the laterally extensive water break-through thin intervals, which are directly related to the regressive hemicycles described previously.

Depositional system and lake-stage control on microbialite morphology, Green River Formation, eastern Uinta Basin, Colorado and Utah, U.S.A.

ABSTRACT Lake-margin lacustrine carbonates of the Green River Formation, in the eastern Uinta basin of Colorado and Utah, occur interbedded with fluvial and shoreline-parallel sandstone and shale. Microbial bindstones were deposited in a saline-alkaline lake during and after the Early Eocene Climate Optimum (EECO) (52–50 million years ago) that is characterized by global hot-house conditions, elevated atmospheric CO2, and highly fluctuating climate conditions. The stratigraphic architecture, chemostratigraphy, and morphology of the microbialites and other associated carbonate beds can be related to these climatic conditions. Three facies associations are recognized in the carbonate units across the lake margin from upper littoral to lower sublittoral environments: facies association 1, delta proximal non-microbial carbonates, characterized by quartzose bioclastic, peloidal, intraclastic packstones and grainstones–rudstones, quartose peloid wackestones and sandy oil shale; facies association 2, microbialite associated non-microbial carbonates, composed of ostracod, ooilitic, peloidal packstones–grainstones and intraclastic packstones, grainstones and rudstones; and facies association 3, microbial carbonates, consisting of diverse forms of stromatolitic and thrombolitic lithofacies. Multiple scales of carbonate cyclicity are suggested by shifts of δ18O and δ13C stable isotopes and deepening-upward microbialite facies. High-frequency cycles, on the order of 1 to 5 m thickness, are characterized by positive shifts in stable isotopes and interpreted deepening trends from littoral to lower sublittoral conditions. Large-scale trends, on the order of tens to hundreds of meters thickness record long-term lake changes, including: 1) sparse microbialite deposition during initial fresh conditions in lake stage 1, with low macro-structure diversity and light δ18O and δ13C isotope values; 2) transitional lake stage 2 corresponding to moderate macro-structural diversity, large meter-scale biostromal and biohermal buildups, and a positive shift in δ18O and δ13C isotope values that suggest increasing saline and alkaline conditions; 3) a highly fluctuating lake stage 3 that contains the highest microbialite macro-structural diversity and marks the interval of heaviest δ18O and δ13C isotope values, suggesting the greatest lake restriction, and the highest salinity and alkalinity conditions; and 4) a rising lake stage 4 that marks the lowest microbialite macro-structure diversity and a reversal in trend of δ18O and δ13C isotope values, that indicate deepening and freshening conditions.

Badenian (middle Miocene) continental paleoenvironment in the Novohrad–Nógrád Basin (Central Paratethys): a volcano-sedimentary record from the Páris-patak Valley in Hungary

Two levels of volcaniclastics, comprising conglomerates, sandstones and mudstones, are interbedded with upper middle Miocene (upper Badenian) andesite pyroclastics near the Hungarian-Slovakian border in the distal region of the Central Slovakian Neogene Volcanic Field. Based on the field sedimentological investigations, the facies of the volcaniclastics (e.g., lateral and vertical grain size changes, sedimentary structures, textures, clast composition), their geometry and field relationships are documented herein with the aim of reconstructing the depositional environment. The silica-cemented volcaniclastics are mostly andesite clasts with only ~ 5% being granitoid, quarzitic, and tuff clasts as well as charred fossil wood fragments. The coarse-grained facies association includes crudely stratified, tabular or lenticular, clast-supported pebble-cobble conglomerates with erosive basal surfaces, b-axis imbrication, alternating with sets of cross-bedding. The fine-grained facies association comprises cross-bedded pebbly to medium-grained sandstone and lenses of tuffaceous clayey siltstone with rare horizontal lamination and water-escape structures. Rip-up mudstone clasts, with diametre up to 1 m, are present in both facies associations, revealing the co-existence of abandoned silty palaeo-channel plugs. Facies associations are arranged in several 0.5-4-m-thick, fining-upwards successions that likely formed in shallow channels as downstream- to laterally accreting longitudinal bars, extensive gravel sheets and bars that migrated in peak flow during floods. Palaeocurrent indicators (i.e., clast imbrication, direction of planar cross-bedding, orientation of petrified wood logs) show bedload transport by traction currents, initially towards ~S, and later towards ~W. Intermittently debris flows also occurred. Cross-bedded sandstones formed as in-channel transverse bars during medium/low discharge. Variation of grain size shows frequent discharge fluctuations during permanently wet conditions in the late Badenian. The 4-5-m-deep, low-sinuosity channels were part of a high-energy, gravel-bed braided-river system on the south-eastern foothills of the Lysec palaeo-volcano. Here, pyroclastics were reworked and redeposited as volcaniclastics during inter-eruption, high-discharge episodes.

DEFINIÇÃO ESTRATIGRÁFICA DA FORMAÇÃO MISSÃO VELHA, BACIA DO ARARIPE

The Missão Velha Formation corresponds to the fluvial deposits through the Jurassic-Cretaceous interval in the Araripe Basin, deposited under the context of the Afro-Brazilian Depression in the West Gondwana Early Rift Stage. The Missão Velha Formation stands out in the Araripe Basin mainly due to the occurrence of an assembly of silicified coniferous trunks. Although the Missão Velha Formation and the Dom João Stage deposits, in general, do not present diagnostic features of tectonism and active magmatism, a series of investigations in the last decade challenged the obviousness, seeking to understand the conditions of the early rift, through new comparative and interpretative methods. Under the sight of these new data and in order to facilitate communication between the authors, the present work proposes an objective delimitation and definition of the unit through the analysis of its state of the art and delimitation, tectonoestratigraphic conditions, and its geological and paleontological settings. The unit presents an internal unconformity and its lower and upper sequences present a distinction in the paleocurrents patterns that change from S-SE to NW, respectively; the facies association change from riverbeds with interdigitated floodplain deposits to high-energy braided channels deposits with the presence of silicified trunks. The assignment of the silicified trunks to the Dadoxylon-Araucarioxylon taxon should be discouraged, since this denomination is outdated accordingly the rules of the International Code of Botanical Nomenclature.

Lithofacies and Environmental Analysis of Reservoir Sandstones in the “ABOM” Oilfield of Eastern Niger Delta, Nigeria

Facies of part of the Coastal swamp depobelt was analyzed using well log. Electrofacies was defined based on well log signatures. The defined facies were inter-related to define a facies association. The facies association were related to deltaic depositional cycles. 10 of such facies association or deltaic cycles were seen in the interval studied. The facies association or deltaic cycles have a different composition of facies related to the level of preservation of the components of the association. The component of the facies association seen include marine clay facies, lower shoreface facies, upper shoreface facies, prograding mouth bar facies and fluvial facies. The marine clay facies underlie each facies association and the channel / prograding mouth bar cap the association where it is preserved. The lower shoreface facies, upper shorefacies, prograding mouth bar and fluvial facies form the Reservoir sandstones. The identified facies association was seen to be repeated in the interval studied though with different composition. This reflects different deltaic depositional cycles with different component of facies due to the prevailing depositional processes occurring at the period of deposition and those affecting the deposit of the cycles after deposition. The arrangements of the different components of the facies within the facies association will help in the prediction of reservoir sand bodies in any deltaic depositional cycle.

Palaeogeographic reconstruction of a fluvio-marine transitional system in Narmada rift basin, India — Implications on Late Cretaceous global sea-level rise

Rising sea-levels in tectonically active epicontinental basins often lead to varied depositional settings and palaeogeography, mostly influenced by the net accommodation resulting from mutual interference of the extent and nature of landward encroachment by the sea and the net sedimentation. The Cenomanian Nimar Sandstone Formation, Bagh Group, Narmada rift basin, uniquely portrays the effect of sea-level rise within an intra-cratonic setting and attributes to the corresponding palaeogeographic changes in west-central India. An integrated sedimentological–sequence-stratigraphic study of the broadly fining-upward Nimar Sandstone Formation (thickness ~ 20–30 m) depicts the actual nature of changeover from a fluvial to a marine-dominated transitional depositional setting. Detailed sedimentological study reveals total seventeen facies, grouped in five facies associations, viz., the channel-fill facies association (FA-1), the overbank facies association (FA-2), the fluvial-dominated fluvio-tidal facies association (FA-3), the tide-dominated fluvio-tidal facies association (FA-4), and the shoreface facies association (FA-5). Overall facies architecture indicates a west-to-eastward marine encroachment, resulting in stacking of three distinct palaeo-depositional conditions: (i) an initial fluvial system with channel and overbank, changing into a tide-influenced fluvial bay-head delta in the inner estuary, followed by (ii) marine encroachment leading to a tide-dominated central estuary with inter- to sub-tidal settings, and finally, (iii) with further intense marine encroachments, a wave-reworked open shore condition in the outer estuary zone. The overall fining-up succession with a systematic change from fluvial to marine-dominated depositional systems points to a landward shift of the shoreline, signifying a major transgressive event correlated to the Cenomanian global sea-level rise. Characteristic stratal stacking patterns point to four coarsening- and fining-up hemicycles, embedded within the major transgressive succession. These high-frequency cycles attest to the varied interplay of sedimentation, tectonics and sea-level changes, and the resultant net accommodations. A palaeogeographic model is proposed based on the high-frequency transgressive–regressive hemicycles, which envisages the evolution of the depositional environments in relation to the Cenomanian eustatic rise in the intra-cratonic riftogenic fluvio-marine transitional basinal setup.

FLUVIO-DELTAIC DEPOSITIONAL COMPLEX OF THE CAMPANO-MAASTRICHTIAN GOMBE FORMATION OF THE GONGOLA SUB-BASIN, NORTHERN BENUE TROUGH, N.E. NIGERIA

Evaluation of the stratigraphic architecture of the Gombe Formation of the Gongola Sub-basin in the Northern Benue Trough indicated a build-up from six facies assemblage that consist of trough crossbedded sandstone, planar crossbedded sandstone, massive bedded sandstone, ripple laminated sandstone, parallel laminated sandstone and mudstones. These units were packaged into three facies association that constitutes of bedded sandstone facies association (FAgI), interbedded sandstone and mudstone facies association (FAgII) and amalgamated trough crossbedded sandstone facies association (FAgIII). These reflects mouth-bars, pro-delta and delta slope deposits and upper delta plain respectively. This deltaic prism is characterized by unidirectional current system devoid of signatures of tide and waves hydrodynamics in the subaqueous delta regions, thus indicating that the delta system of the Gombe Formation is a fluvial dominated delta.

SYN-RIFT FLUVIO-LACUSTRINE DEPOSITIONAL SYSTEM OF THE CRETACEOUS BIMA FORMATION IN THE GONGOLA SUB – BASIN, NORTHERN BENUE TROUGH, NE, NIGERIA

The facies analysis of the syn-rift sequences Bima I Formation in the Gongola Sub-basin of the Northern Benue Trough displayed assemblages of trough crossbedded sandstones facies, planar crossbedded sandstone facies, massive bedded sandstone facies, ripple laminated sandstone facies, parallel bedded sandstone facies and mudstones facies. These arrays of facies form two suites of facies association that consist of the lacustrine-delta complex depicting coarsening upward cycles and fluvial complexes showcasing fining upwards cycle the former accounts for a scenario where the incremental accommodation is lower than the sediment discharge, whereas the latter is reflective of a case where improved subsidence rate induces high accommodation rate that outruns sediment supply. The stratigraphic architecture of the syn-rift Bima I Formation indicated that the lacustrine-delta are restricted to the lower stratigraphic horizons whereas the fluvial complexes essentially defines the upper stratigraphic zones of this formation.

Integrated Sedimentology Characters and Seismic Geomorphology for Reservoir Prediction of Tidal Shelf Ridge: The Upper Cibulakan Formation As A Shallow Marine Reservoir Analogue

The Upper Cibulakan Formation is one of the main reservoirs in the Offshore North West Java Basin. It was deposited in a shallow marine environment with Tidal Shelf Ridge morphology. Sedimentology and seismic approaches are integrated in this study to understand lithofacies, depositional stages and morphological patterns of Tidal Shelf Ridge. The study is restricted to Zone 29, P-Field with available data being 5 wells data that have cores, 64 well data, and 3D seismic data. The lithofacies data of these wells is integrated with log data using a Multi Resolution Graph-based Clustering (MRGC) method to predict the lithofacies and depositional stage of other wells without core. There are 10 different lithofacies and 4 facies association identified from these well cores. Facies associations that were found refer to nomenclature of depositional stage of Tidal Shelf Ridge. The embryonic stage consists of claystone-siltstone or calcareous highly-cemented sandstone (with erosional contact), which is the stage of beginning of deposition of the shelf ridge. The immature accretion stage consists of siltstone and sandstone with an intense heterolithic structure. The mature accretion stage consists of sandstone with little or no appearance of heterollitic structure. The abandonment stage is the final stage of shelf ridge that consist of calcareous highly-cemented sandstone without erosional contact. Stratigraphic pattern based on vertical order of facies association is showing 5 transgressive parasequence tracts bounded by 6 flooding surface markers. Based on seismic attributes, which is an average of amplitude x thickness in parasequence, the pattern and morphology of tidal shelf ridge body is relatively northeast – southwest direction. The results of this study are expected to be a reference in developing more advanced hydrocarbon production by understanding of the morphology of reservoir body.