Carbonate Platform Research Articles

Cenozoic biostratigraphy of larger foraminifera from equatorial carbonate platform of northwestern Brazil

The off-shore Cenozoic succession of the Pará-Maranhão Basin of the Brazilian equatorial margin is studied to investigate skeletal and foraminiferal assemblages during the Oligocene-Miocene interval, one of the fundamental moments in the environmental evolution of our planet. The material from core 1-MAS-16-MA is analyzed using a combination of conventional paleontological analyses, and innovative approaches like micro-CT scan and U/Pb dating on carbonates. The results allowed to clearly constrain the Oligocene – Miocene interval and divide it into four foraminiferal assemblages and seven biofacies useful for both paleoenvironmental reconstructions and stratigraphic correlations. The paleoenvironmental analysis indicates a common pattern of relative sea-level oscillations with the nearby Foz do Amazonas Basin, highlighting a common behavior of this part of the equatorial passive margin during the Oligocene – Miocene interval. The comparison between the succession of skeletal and foraminiferal assemblages of the investigated core and other successions of the Southern and Central American area indicated the presence of stratigraphically relevant foraminiferal assemblages that could be useful for improving the correlation between the various Cenozoic successions of the area (assemblages dominated by nummulitids and lepidocyclinids in the Rupelian; assemblages dominated by Heterostegina (Vlerkina) antillea, lepidocyclinids, and primitive miogypsinids in the Chattian; assemblages dominated by Heterostegina (Vlerkina) antillea, lepidocyclinids, and miogypsinids other than Miogypsinoides and Miogypsinella, in the Aquitanian; assemblages dominated by advanced miogypsinids in the Burdigalian; post Early Miocene assemblages characterized by the lack of abundant lepidocyclinids and miogypsinids). Finally, the overall resilience of most of the large benthic foraminifera taxa to the Oligocene – Miocene transition testifies once more to the adaptability of this group of carbonate producers.

Substantial incorporation of isotopically heavy reduced U species into marine carbonate sediments

The uranium (U) isotope ratio (238U/235U, reported as δ238U) in marine carbonates is an important proxy for reconstructing changes in past oceanic redox conditions, based on the essential assumption that U in carbonates originates from dissolved U(VI) in seawater. However, diagenetic processes may induce the addition of isotopically heavy U(IV) into the carbonates, complicating the application of the U isotope proxy. So far, the valence states of trace amounts of U and its relation with U isotope composition in marine carbonate sediments have not been directly studied. In this study, we have calibrated an ion-exchange chromatographic method to separate U(IV) from U(VI) in geological carbonate samples (e.g., modern and fossil corals, stalagmites, cold seep carbonates) and quantified their contents by mass spectrometry. Our study confirms that modern coral carbonates are faithful archives of U(VI) sourced from seawater. Surprisingly, drill core samples from a modern coral carbonate platform, which bear no sign of alteration inferred from conventional diagenetic proxies (e.g., Mn/Sr), show significant positive correlation between U(IV) fraction and bulk carbonate δ238U, suggesting U(IV) is present in the marine carbonates and drives δ238U toward higher values than that of seawater. We therefore suggest that coupled valence and isotope analyses of U in marine carbonates could provide critical constraints toward reliable reconstruction of marine redox evolution in the Earth’s history.

Sedimentology and Paleoenvironmental Characteristics of Fine‐grained Sediments in Coal‐bearing Strata in the Eastern Ordos Basin: A Case Study of the Exploratory Well in the Zizhou Area

AbstractThe continuously collected cores from the Permo–Carboniferous coal‐bearing strata of the eastern Ordos Basin are essential for studying the hydrocarbon potential in this region. This study adopted sedimentological and geochemical methods to analyze the sedimentary environment, material composition, and geochemical characteristics of the coal‐bearing strata. The differences in depositional and paleoclimatic conditions were compared; and the factors influencing the organic matter content of fine‐grained sediments were explored. The depositional environment of the Benxi and Jinci formations was lagoon to tidal flat with weakly reduced waters with low salinity and dry‐hot paleoclimatic conditions; while that of the Taiyuan Formation was a carbonate platform and shallow water delta front, where the water was highly reductive. The xerothermic climate alternated with the warm and humid climate. The period of maximum transgression in the Permo–Carboniferous has the highest water salinity. The Shanxi Formation was deposited in a shallow water delta front with a brackish and fresh water environment and alternative weak reductiveness. And the paleoclimate condition is dry‐hot. The TOC content in fine‐grained samples was averaging 1.52%. The main controlling mechanism of organic matter in this area was the input conditions according to the analysis on input and preservation of organic matter.

Late Cretaceous‐Recent Tectonostratigraphic Evolution of the Yucatan Back‐Arc Basin, Northern Caribbean Sea

AbstractThe 110,000 km2 Yucatan Basin in the northern Caribbean Sea is critical for understanding the Late Cretaceous to Recent tectonic evolution of the Caribbean‐North American plate boundary. This study integrates gravity, magnetic, and a 5,500 km grid of 2D seismic data to carry out a tectonostratigraphic analysis of the Yucatan Basin. These data provide the first recognition of 38–102 km‐long spreading ridges that constrain a SW‐NE opening direction in the western Yucatan Basin. The age of this oceanic crust is constrained to be late Paleocene‐middle Eocene (57–42 Ma) based on heat flow measurements, depth‐to‐seafloor, and three sedimentary sequences inferred to be Eocene—Recent in age based on stratigraphic correlations to distant wells. We interpret the Yucatan Basin as a back‐arc basin formed during the northeastward movement of the Caribbean volcanic arc that is now exposed in Cuba, evolved during the early Cretaceous to middle Eocene, and was terminated by collision with the Bahama carbonate platform during the late Paleocene to middle Eocene. We identify regional, left‐lateral strike‐slip faults that extend into the Cuban volcanic arc, as observed in other active back‐arc basins. We propose that the Yucatan back‐arc basin once formed the northwestern extension of age‐equivalent back‐arc basins in Hispaniola, where the basin is inverted, topographically elevated, and strongly shortened, and in the Lesser Antilles where the Paleogene back‐arc basin has remained undeformed and submarine. This once‐continuous back‐arc basin was disrupted and left‐laterally offset by ∼500 km during the Late Eocene‐Recent formation of the Cayman trough strike‐slip system.

Middle Triassic (Muschelkalk) transgression in the West Tethys: biostratigraphic evidence from Sardinia (Italy)

Stratigraphic and palaeontological analyses of the Middle Triassic (latest Anisian–Ladinian) in Muschelkalk facies are performed here to further unravel the palaeogeographic evolution of Sardinia in this time-frame. These shallow marine successions reveal a significant palaeontological record comprising facies and marker fossils (ammonoids, bivalves, conodonts, foraminifera etc.) reflecting a regional transgressive episode recorded throughout the West Mediterranean, after the Permian–Triassic biotic crisis. Particularly rich in the Nurra and Sarcidano-Gerrei areas, the facies/fossil record indicates the progressive westward settling of carbonate platforms, and consequently the development of new migration and irradiation routes for Sephardic faunas from the southeast (Palaeotethys) and Alpine faunas (Neotethys) from the northeast. Based on new findings and the revision of palaeontological associations previously reported, comparisons were made with associations of adjacent domains (Balearic Islands, Levantine area), thus refining their palaeoecological distribution and better framing Sardinia as a key area in the palaeogeographic evolution of the West Tethys during the Ladinian.

Salt Tectonics Versus Shortening: Recognizing Pre‐Orogenic Evaporite Deformation in Salt‐Bearing Fold‐And‐Thrust Belts on the Example of the Silica Nappe (Inner Western Carpathians)

AbstractRecognizing salt‐related structures and differentiating them from tectonic shortening‐related anticlines and synclines can be a very challenging task in salt‐bearing fold‐and‐thrust belts, especially in poor outcrop conditions. In this study, we explain several diagnostic structural and sedimentary features that may be used to distinguish pre‐orogenic halokinetic structures from shortening‐related structures on the example of the Silica Nappe (Inner Western Carpathians, Central Europe). Detailed structural mapping in this area resulted in the recognition of several pre‐orogenic salt‐related structures, including linear salt walls and minibasins. Initial evaporite movement started as early as the late Early Triassic, and widespread diapirism occurred during the Middle to Late Triassic, ultimately leading to facies differentiation, with carbonate platform growth in the subsiding minibasins and reduced basinal deposition on top of the diapirs. Later, the inherited salt structures localized the deformation during the Cretaceous Alpine orogeny, and exerted a strong control on the geometry and kinematics of the subsequent deformations. Our new interpretation explains previously unsolved structural problems in the Silica Nappe, like pre‐orogenic thickness variations during the post‐rift phase, frequent young‐on‐older type thrust contacts and multiple folding directions with variable vergencies. The results point out that the Silica Nappe is a fold‐and‐thrust belt, where pre‐orogenic salt tectonics and its effects on the fold‐and‐thrust belt evolution can be studied in detail.

Depositional environment of the Sarmord Formation (Valanginian-Aptian) in selected areas, northeastern Iraq

The current study deals with microfacies and the depositional environment of the Lower Cretaceous Sarmord Formation at selected sections in Sulaimani and Erbil Governorates, northern Iraq. The Sarmord Formation alternates rhythmically between yellowish grey marly limestones and grey black marls. These lithologies are observed in all studied sections of Sarmord Formation in northern Iraq. Petrographic investigation of this study based on 240 thin sections demonstrated that the carbonate constituents are mainly composed of skeletal and non-skeletal grains. The skeletal grains include a variety of foraminiferas (planktonic and benthonic), bioclasts, calcispheres, ostracods, radiolaria, echinoderms, sponge spicules, ammonoids and belemnites. The non-skeletal grains consist of rare intraclasts. Based on field observations, two major lithofacies are recognized in the studied sections, namely marly limestone and marl lithofacies. Depending on the detailed microfacies analysis, two main microfacies, which in turn are divided into four sub-microfacies, were identified. These facies were subdivided upon their environmental interpretation into two types of facies associations: deep shelf and basinal. From the results of petrographic, facies, and textural analyses, it is concluded that Sarmord Formation in the studied sections was deposited at a rimmed carbonate platform. With a gradual shallowing of the basin from basinal sediments at the lower part overlying by deep shelf sediments in the uppermost part of the formation in the studied sections.

Carbonate uranium isotopes across Cretaceous OAE 2 in southern Mexico: New constraints on the global spread of marine anoxia and organic carbon burial

Oceanic anoxic events (OAEs) represent discrete intervals of decreased marine oxygen concentrations often associated with volcanism, enhanced organic carbon burial coupled with positive δ13C excursions, and significant biotic turnover. Cretaceous OAE 2 (ca. 94 Mya) is especially notable for globally-distributed changes in calcareous invertebrate and plankton populations. While the presence of organic-rich facies is consistent with locally anoxic environments in many cases, determining the global extent of anoxia is more problematic. To address this issue, we investigate uranium isotope (δ238U) compositions of upper Cretaceous (Cenomanian-Turonian) open marine platform carbonates from southern Mexico as a proxy for global seawater redox conditions. These data are complementary to previous δ238U studies across OAE 2 in both black shales and pelagic carbonates, which have yielded variable results that reflect both global redox and local depositional processes. In Morelos Formation carbonates, a significant and well-defined negative δ238U excursion down to a nadir of −0.6‰ is recorded over an ∼40 m interval. This is consistent with the expansion of marine anoxia, pointing to an areal extent of anoxic seawater of about 1–10% of the global seafloor (or ∼5 to 50 times the modern value). Importantly, based on biostratigraphically-controlled estimates of sediment accumulation rates, the δ238U anomaly precedes the δ13C excursion by a median of ∼45 to 51 kyr (95th percentile confidence interval, CI) or ∼105 to 120 kyr (95th percentile CI) depending on how the onset of the δ238U anomaly is estimated. These results, along with previously reported thallium isotope and trace metal data, suggest that anoxic expansion preceded carbon cycle perturbation. This observation further increases estimates of the duration of OAE 2, implying that widespread ocean anoxia may have lasted >900 kyr.

Microfacies and paleoenvironment of microbialites of the Cambrian (Stage 4) Qingxudong Formation in the Huayuan area, northwestern Hunan Province, southern China

After the extinction of Archaeocyatha (sponges), microbial bioherms were well developed in the lower Cambrian of the Yangtze cratonic basin, especially in the Qingxudong Formation (Cambrian (Stage 4)) of the Huayuan area, northwestern Hunan Province, southern China. Herein, four sections from this area were chosen for investigating and analyzing their microfacies and depositional environment. Twelve microfacies types were recognized through petrographic analysis of textural attributes and calcimicrobes (including Epiphyton, Renalcis, Girvanella and Kenella), respectively as: laminated calcareous mudstone (MF1), algal wackestone (MF2), intraclastic grainstone (MF3), algal intrasparrudite (MF4), oolitic algal intrasparrudite (MF5), sparry oolitic grainstone (MF6), Epiphyton framestone (MF7), Renalcis bafflestone (MF8), Kenella bafflestone (MF9), Girvanella boundstone (MF10), thrombolitic boundstone (MF11), and dolomite (MF12). These microfacies represent four major depositional environments: carbonate ramp, carbonate platform, slope and tidal flat. Calcimicrobes played an important role in the transition from carbonate ramp to platform, while the evolution from ramp to tidal flat must be ascribed to sea-level fall during the Cambrian Age 4.

Litho- and biostratigraphy of the early Eocenelarger benthic foraminifera-dominated carbonates of the central Tethys domain, Zagros Foreland Basin, SW Iran

The Early Paleogene Tethyan domain saw the development of large platform carbonates rich in large benthic foraminifera (LBF), of which the Taleh Zang Formation in Lurestan Basin, SW Iran, represents an excellent example. The LBF assemblage is dominated by alveolinids, together with a variety of foraminiferal genera such as Nummulites, Rotalia, Sackesaria, Assilina, Operculina, and Glomalveolina. Smaller benthic foraminifera, calcareous algae, gastropods, echinoids, and bivalves constitute minor components of the carbonate. Biostratigraphy analysis of the LBF is conducted on two distinct sections of the Taleh Zang Fm. The sections referred to as TZ-1 and TZ-2 have respective thicknesses of 87 m and 132 m. This analysis has constrained the formation age to the early Ypresian within Shallow Benthic Zones (SBZs) 5–7. Facies analysis supports the major accumulation of these successions in a shallow water environment within the euphotic zone. We recognize 9 distinct facies and microfacies representing four main depositional environments including tidal flat, lagoon, bioclastic shoal, and shallow open marine. These environments are distributed along a low-angle homoclinal ramp and form the foundation of a stratigraphic interpretation characterized by intervals displaying shallowing and deepening trends. Three shallowing-upward intervals have been identified within the Taleh Zang succession. The determined intervals cannot be solely attributed to global sea level fluctuations and support a significant impact of the regional structural context resulting from collision-induced uplift and variable subsidence rates. The identified intervals exhibit local and regional correlation and compatibility on the Arabian Plate, providing robust confirmation of the significant roles played by both tectonics and eustasy at a regional scale.

New Insights into the Platform-to-basin Anatomy of the Urgonian Bas-Vivarais Domain (Lower Cretaceous; SE France)

This paper offers a new contribution to our ongoing harmonization efforts concerning the chronostratigraphic model of the southern France Urgonian-type carbonate platforms, which surrounded the Vocontian Basin during the Early Cretaceous. A multi-stratigraphic approach on the classical sections of the Ardèche River gorges and the Saint-Remèze Plateau have been used for reconstructing the evolution of the Bas-Vivarais Urgonian domain along an inner-to-outer platform profile; the latter being nearly perpendicular to the eastern Vocontian platform margin. In our transect, the installation and first developments of the Urgonian platform domain occured during the early Barremian Taveraidiscus hugii and Kotetishvilia nicklesi ammonite zones. This first platform stage was interrupted at a brief emersion episode that lasted through the Nicklesia pulchella ammonite zone, and resulted in the deposition of a sedimentary wedge with limited gradual downward, basinward shift in inner platform facies. This was followed by the regional deposition of shallow-water communities dominated by corals, echinoids, and orbitolinids, which passes basinward into open-marine, ammonite-bearing marly deposits in the Saint-Remèze Plateau outcrops. This change in facies was previously referred to as the Serre de Tourre Beds (STB), and dated to the Kotetishvilia compressissima and Moutoniceras moutonianum ammonite zones. The STB are further identified to as the local sedimentary expression of the Mid-Barremian Event recording a brief warming climate pulse testified by the presence of Offneria simplex, a caprinid rudist of Caribbean origin. Above, there is a regional recovery of inner platform Urgonian facies during the early late Barremian showing a striking progradational basinward trend. The latter, and its subsequent developments are in need of investigations. Taken together, the general evolution of the Urgonian Bas-Vivarais domain shows strong similarities with the sedimentary context of the nearby Subalpine Urgonian platform during the early Barremian. The finding of common sedimentary signals is more difficult with the Provence platform domain at that time.

Tectonic, eustatic and climate controls on facies architecture during the transition to the Neoproterozoic icehouse in the Adelaide Superbasin, Australia

The Tonian to Cryogenian (ca. 1000–635 Ma) marks a crucial turning point in Earth’s history, where tectonic reorganisation and fluctuating oceanic and atmospheric geochemistry plunged the globe into icehouse conditions. This was followed by a postglacial warming period that delivered large volumes of nutrients to the oceans and stimulated eukaryotic evolution. The Adelaide Superbasin in South Australia hosts a thick repository of Neoproterozoic and lower Cambrian sedimentary successions that preserve the depositional conditions during this unique time. In this study, detailed sedimentological data was collected from over 8,350 m of measured section at seven locations across the northern Flinders Ranges. Tonian deposits reveal a carbonate platform setting, where deposition was controlled by basin geometry and proximity to uplifted source areas. In the early Cryogenian, sedimentary successions were affected by the Sturtian glaciation, characterised by two glacial advance-retreat phases that coincide with climatically driven regression. The end of the Sturtian glaciation was marked by basin subsidence and widespread transgression into a more distal subaqueous environment. Despite the lithostratigraphic and sequence stratigraphic similarity between Tonian–Cryogenian successions globally, their correlation remains contentious. The influence of local tectonic regimes during the Tonian created a potential oceanic restriction between developing basins, which challenges the chemostratigraphic correlation between these deposits. Further, limited geochronological ages and opposing interpretations of glacial cyclicity puts into question the timing and extent of the Sturtian glaciation. Conversely, the post glacial transgression appears to be the most globally consistent as it results from climatically controlled sea level rise that was driven by melting ice sheets.

Calibration of redox thresholds in black shale: Insight from a stratified Mississippian basin with warm saline bottom waters

Depositional models for black shale formation rely on a detailed understanding of redox conditions and how they relate to basin development. Here, we calibrate multiple redox proxies (Fe speciation, U and Mo systematics, and pyrite framboid distributions) in the Bowland Shale, a major hydrocarbon unit in the Mississippian basin of northern England, and develop a depositional model for black shale deposition in basins adjacent to extensive carbonate platforms. The transition from deep ramp carbonates to basinal mudrocks initially occurred under oxic conditions before anoxic conditions began to expand from basin-center locations. By the end of Bowland Shale deposition, ∼10 m.y. later, black shale deposition extended from the basin, where platform-edge carbonates were deposited, into shallow-water settings. By this stage, euxinic conditions were widespread throughout the Bowland Shale. The prolonged persistence of euxinia during younger Bowland Shale deposition, and the sharp transition to fully oxygenated facies at the basin margin, suggest there was a well-developed water-column pycnocline. Black shale development in silled basins is traditionally interpreted to form beneath a halocline with a positive water balance caused by freshwater run-off (estuarine circulation). This model is not considered appropriate in this case. Bowland Shale deposition was terminated by the onset of turbidite deposition supplied by a major deltaic system; but for most of its history, the basin was surrounded by carbonate platforms that are unlikely to have experienced brackish conditions. The encroachment of the clastic system saw the rapid improvement of basinal oxygenation in the uppermost Bowland Shale, and even minor turbidite sandstones within the black shales coincided with a weakening in the intensity of euxinia, which suggests that fresher, sediment-laden waters flushed out and oxygenated the basin. We therefore suggest a warm saline bottom-water model for black shale deposition, with basinal waters generated on the adjacent carbonate platforms due to evaporation. Such a scenario is likely more broadly applicable to basinal black shales that developed adjacent to shallow-water carbonate successions.

New larger benthic foraminifera from Brač Island, Croatia: Further evidence for early–middle Campanian foraminiferan high diversity in the inner platform facies of the Adriatic Carbonate Platform

Four new species of larger benthic foraminifera are described from lower–middle Campanian inner-platform carbonates of the island of Brač, Croatia: Bakhtiarella minima sp. nov. (family Bakhtiarellidae), Biconcava brattiana sp. nov. (family Mayncinidae), Paravanneauina campaniana gen. et sp. nov. and Calveziconus pygmaeus sp. nov. (family Orbitolinidae). The latter two taxa are also reported from time-equivalent strata of the Gavrovo–Tripolitza Platform, southwestern Greece. The new taxa provide further evidence for the pronounced Campanian diversification within the Late Cretaceous Global Maturation Cycle of larger benthic foraminifera in the inner platform facies of the Mediterranean Adriatic Carbonate Platform.

On the occurrence of Carentonosaurus Rage and Néraudeau, 2004 (Squamata, Pythonomorpha) in the Iberian Cretaceous, with description of a new species from the uppermost middle Cenomanian of West Portugal

Several vertebrae were recently collected in paralic facies with fossil assemblages of late middle Cenomanian age, outcropping in the basal carbonate platform sequence of Casais dos Carecos, near Coimbra (West Portugal). These fossil remains are exceptionally well preserved, with fragile elements still present. They correspond to cervical and dorsal vertebrae, including a juvenile cervical vertebra. The general morphology, features and size of the dorsal vertebrae are close to those described and figured for the holotype of Carentonosaurus mineaui Rage and Néraudeau, 2004, but showing distinct lateral and subcentral foramina, neural spine with longitudinal grooves and displaying a sagittal furrow along the ventral surface, which are absent in this genotype. The centrum shows a subtriangular shape in ventral view, with concave borders. These different morphological features of the fossil remains here presented allow the description of Carentonosaurus soaresi sp. nov. This new material improves the knowledge of the representatives of Carentonosaurus and extends the biogeographical distribution of this genus of Pythonomorpha to the western margin of the Iberian Peninsula.

Facies, biostratigraphy and isotope chemostratigraphy of the Tithonian‒Berriasian transition in the easternmost Getic Carbonate Platform (Southern Carpathians, Romania)

The easternmost side of the Getic Carbonate Platform at Postăvaru and Piatra Mare Massifs of Southern Carpathians (Romania) has been studied through eighteen sections using macro and microscopic analyses, micropaleontological studies combined with sedimentological and oxygen and carbon isotope analyses. The studied area is located in central Romania, in the easternmost part of the Southern Carpathians, in the vicinity of the Carpathian Bend. Eight major facies associations are identified defining lower slope, upper slope/reef crest, platform margin and inner platform depositional environments. The microfossil assemblages contain foraminifera, dasycladalean algae, microproblematica and calpionellids characterizing the Tithonian and Berriasian stages. The carbonate succession shares similar characteristics with coeval deposits from the Southern Carpathians and other regions of the Tethys Realm (especially Northern Calcareous Alps, Polish Outer Carpathians, Carpatho-Balkanides, Albanides and Hellenides). The sedimentological and isotope chemostratigraphic analyses provide evidence that subaerial exposure was common in shallow-water and inner platform depositional settings, in a prograding context, under the influence of carbonate sedimentation and eustasy. All the investigations allow deciphering the Tithonian–Berriasian transition in the easternmost Getic Carbonate Platform.

Biomarkers applied to the assessment of organic matter sources, thermal maturation and depositional environment of the Devonian Pimenteiras Formation, Parnaíba Basin (Brazil)

The potential for hydrocarbon generation of Devonian shales from Pimenteiras Formation has been the object of study in many research works. In this study, the focus is to evaluate the organic matter sources, thermal maturation and depositional environments of the Pimenteiras Formation based on aliphatic and aromatics biomarkers. Thereby, a total of 30 samples from three wells were analyzed using gas chromatography and mass spectrometry (GC/MS). The n-alkanes, isoprenoids, and terpanes data revealed that shales from Pimenteiras Formation results of a mixture of marine, transitional and terrestrial organic matter. These findings are consistent with C27, C28 and C29 steranes distribution and abundance of methylphenanthrene and methyldibenzothiophene. The Pr/n-C17 and Ph/n-C18 ratios in the BP-77 well are greater than 1.0 (immature), while the most samples from BP-59 and BP-22 wells, the Pr/n-C17 and Ph/n-C18 ratios are less than 1.0 (mature). Findings are consistent with CPI, M30/H30, S/(S + R) (C29 ααα) and C29 ββ/(αα+ββ ratios. Additionally, the Ts/(Ts + Tm) ratios, MPI-1 versus Ro, 2-MP, 3-MP, MPI-1, MPR-1, dimethylnaphthalenes and dimethyldibenzothiophene indicate that the organic matter varies from immature to mature, and reaches the overmature stage in terms of thermal maturity. The Pr/Ph ratio, Pr/n-C17 vs Ph/n-C18 plot, high H35/H34, C29/C30, C27 Dia/C27 ααα (R + S) ratios and high concentration of dibenzothiophene suggests that the organic matter was deposited under oxic, suboxic and anoxic conditions. On the other hand, the low abundance of gammacerane and low Gam/H30 ratio suggests a low salinity and/or water column stratification. Additionally, the data showed that the organic matter was deposited in marine, marine carbonate platform and terrestrial environments.

Global Geodynamic Control on Phanerozoic Marine Carbonates Sedimentary Systems

AbstractThis pilot study is founded on an exhaustive investigation of representative and well-documented cases (120) of carbonate systems during the Phanerozoic. We investigated the coupling between geodynamic settings and geometry, physiography, and stratigraphic architecture of carbonate platforms. The objective is to identify and quantify the impact of geodynamic controls on carbonate platforms and possible global trends during the Phanerozoic. Carbonate platforms are characterized in terms of geometry, stratigraphic architecture, time duration, preservation rate, progradation and rates of progradation, platform type, and thickness. Geodynamic parameters are characterized in terms of basin physiography, basement depth and type, tectonic setting, and subsidence origin. Relationships between carbonate parameters and geodynamic characteristics are investigated, leading to nine models of Geodynamic Carbonate Platforms. Passive margin is the most favorable geodynamic setting for the development of carbonate platforms in three dimensions. The continental crust hosts most of the carbonate platforms independently of time and geodynamic settings. Carbonate platforms developed above the exhumed mantle or oceanic crust (volcano) are the exception or very small and isolated. Global trends during the Phanerozoic of carbonate platform lateral extend, progradation, or thickness are tentatively interpreted in relation to geodynamic and eustatic parameters. The concept of spatial intersection between geodynamic and climatic windows favorable to carbonate platforms is introduced with its possible retroaction to the global carbon cycle.

Sedimentary characteristics and controlling factors of a Pliocene shelf-edge delta in the Papuan Basin

The Pliocene shelf-edge delta (SED) in the Papuan Basin was formed by deposition of the Pliocene Orubadi Formation. On the basis of a comprehensive analysis of seismic, wireline and mud logging, and paleontological data, the stratigraphic framework, depositional system and controlling factors on the SED development were established. The Orubadi Formation includes a parallel unconformity. Internally, two third-order sequences (SQ1/SQ2) are identified, and system tracts within the sequence layers are determined by the onlaps. By tracing changes in the shoreline trajectories within the sequence, the SED was divided into six phases in the study area, with seaward advances of ∼1543–5400 m during a single phase. The thickness of the foreset is ∼309–887 m, exhibiting sigmoid or sigmoid-tangential seismic reflections. The stratigraphic patterns and sedimentary system evolution of the Orubadi Formation are determined by the interplay between sea-level changes, sediment supply, tectonic evolution and paleogeomorphology. The Coral Sea spreading provided accommodation for the SED. The Miocene–Pliocene uplift and the middle Miocene arc–continent collision in northern PNG, which caused uplift and erosion of mountains in the late Miocene to Pliocene, is the major source of sediments. The large sediment supply and sea-level changes from SQ1–SQ2 indicate an overall relative sea-level fall resulted in rapid shelf margin advancement into the basin, with the Miocene carbonate platform edge providing the necessary slope conditions for material transport. This abundant sediment supply led to the significant development of the SED. This study provides robust insights for deep-water oil and gas exploration in the Papuan Basin. KEY POINTS The Pliocene shelf-edge delta (SED) in the Papuan Basin was formed in a compression setting with arc–continent collision. In the Orubadi Formation, the overall trend of sea-level change is decreasing, and the delta is divided into six stages. The Pliocene SED is controlled by the interplay between sea-level changes, sediment supply, tectonic evolution and paleogeomorphological.

Seismic characterization of Cenomanian–Turonian carbonate platform based on sedimentological and geophysical investigation of onshore analogue outcrop (northern Lebanon)

AbstractOutcrop analogues play a key role in the characterization of subsurface carbonate platforms. The lack of well data and relevant outcrop analogues can result in the misinterpretation of seismic data. To address this issue, we apply an integrated workflow based on sedimentology, geophysics and petrophysics on outcrop analogues present onshore Lebanon, to constrain the carbonate platform's properties on onshore seismic data. A thorough sedimentary description is completed for a 400‐m‐thick Cenomanian–Turonian carbonate platform located in Kfarhelda, northern Lebanon. P‐wave velocity is acquired directly on the outcrop, and the petrophysical properties are measured on 44 samples. A 1D synthetic seismogram is computed with Ricker wavelet 25 Hz resembling seismic resolution. The resulting reflectors are mainly (1) high amplitude reflectors at the limit between two facies with contrasting physical properties enhanced by diagenesis, (2) moderate amplitude reflectors corresponding to stratigraphic limits at the transition between facies and (3) very low amplitude reflectors in karstified units. The integration of outcrop and seismic data is based on the generation of the synthetic seismogram to identify the geological origin of reflectors. The best fit between the synthetic seismic and seismic profile is used to interpret a seismic facies representing bedded limestones of Sannine and Maameltain formations (Cenomanian–Turonian). Two other distinctive reflectors are identified at the boundary of the Marly Limestone Zone, and the Channel facies unit characterized by bioclastic packstone to floatstone. This study highlights the importance of using outcrop analogues to identify the seismic signal of stratigraphic sequences and improve the interpretation of onshore seismic data.