Terms Of Biostratigraphy Research Articles

Planktonic foraminifera from the Aptian section of the Southeastern Brazilian Atlantic margin

Upper Aptian planktonic foraminifera assemblages recorded in the post-salt section of the Santos, Campos and Espírito Santo Brazilian marginal basins are described and interpreted in terms of biostratigraphy and relative ages. The studied section represents the first marine sedimentary rocks deposited above the evaporitic sequence. Material from 26 Petrobras wells, including core, sidewalls and cuttings samples was analyzed. The upper Aptian planktonic foraminifera assemblages are composed mainly of cosmopolitan and chronostratigraphically long-ranging species, among which 22 species have been commonly recorded in the Tethyan Realm and other South Atlantic basins. Considering the biostratigraphic distribution, deposition of the studied section spans from the upper Aptian Globigerinelloides ferreolensis to Paraticinella rohri zones. Hence, the present study allowed the reassessment of the biostratigraphic framework, pointing out to an upper Aptian age for the marine section deposited immediately above the evaporitic sequence in the Santos, Campos and Espírito Santo basins. Indeed, a marine environment was established 5 to 10 Ma earlier than previously proposed. The reevaluation of the age constraints for the section provides new insight to the understanding of early South Atlantic Ocean geological evolution.

Biostratigraphic distribution of orbitolinids in the ammonite biozones (Urgonian platform of southeastern France). Part 2: Barremian p.p.

The biostratigraphic distribution of orbitolinids for the Barremian of SE France proposed hereafter is calibrated on the ammonite biozonation. This work is based on the study of eleven sections with orbitolinids associated to macrofossils (ammonites and/or echinids) significant in terms of biostratigraphy or overlain with levels bearing the above macrofossils.

Age, microfacies and depositional environment of the Middle to Late Paleocene shallow-marine carbonates in the Sirt Basin of Libya (Upper Sabil Formation): \u201cAre Intisar domal structures pinnacle reefs?\u201d

In the central-eastern Sirt Basin, enigmatic Intisar domal structures host significant hydrocarbon accumulations. These structures have been commonly interpreted as pinnacle reefs/bioherms occurring in the open-marine basinal environment. Generally, pinnacle reefs/bioherms are mainly characterized by in situ carbonates. The current study challenges the Intisar pinnacle reef/bioherm model by examining one of the domal structures in terms of biostratigraphy, microfacies and depositional environment. These structures were dated using larger benthic foraminifera, which yielded a Middle to Late Paleocene age (Selandian–Early Thanetian). Thirteen microfacies types representing different carbonate ramp environments ranging from outer ramp to inner ramp, were defined. Outer ramp deposits have been observed adjacent to the domal structure, represented mainly by wackestone with small benthic and planktonic foraminifera. The outer ramp deposits are most likely isochronous to the domal structures. The lower part of the domal structures is composed mainly of foraminiferal–algal–echinodermal packstones. The upper part is characterized by foraminiferal–algal–echinodermal packstones with intercalated microbialite–coral boundstones. The euphotic inner ramp deposits are preserved on the crest of the domal structure, consisting of grainstone and packstone rich in Glomalveolina. As a result of this study, the Intisar domal structures are seen as erosional relics of a carbonate ramp and no evidence for pinnacle reef/bioherm model was found.

Integrated Biostratigraphy, Depositional Setting and Geochemical Analyses for Petroleum Potential Evaluation of the Lower Cretaceous (Barremian – Albian) Strata of the Koppeh‐Dagh Basin, Northeastern Iran

The lower Cretaceous rock units of the Koppeh‐Dagh Basin of northeastern Iran were investigated here in terms of biostratigraphy, depositional setting and geochemical analyses to find out if they, alike other parts of the world, are rich in petroleum. For this purpose, a stratigraphic framework is established using calcareous nannofossil and palynological elements. A nannoplankton zonation based on which subzones of the zones CC7 – CC8 of Sissingh (1977) and their equivalent NC6 – NC8 of Roth (1978) was established indicating a Late Barremian–Albian age. Palynological assemblages led us to establish the local palynozone of Odontochitina operculata. A dominantly marginal basin to a transitional zone between shelf and basin under a dysoxic–anoxic condition with low to moderate sedimentation rates coincided with a gradual sea level rise was introduced as the environment of deposition for the strata via interpretation of the palynological parameters and quantitative palynology. The obtained data from Rock‐Eval pyrolysis in compilation with palynofacies analysis reveals that the studied succession contains mainly gas‐prone type III kerogen. The Spore Coloration Index (SCI) alongside with the Rock‐Eval pyrolysis results (low values of HI and TOC) proves that these rock units locally produced natural gas during the time under consideration.

Dinoflagellate fossils: Geological and biological applications

Dinoflagellates are part of the marine plankton and about 200 species produce a cyst (dinocyst) during their life cycle, these organic-walled sexually-produced cysts being fossilizable in sediments for hundreds of millions of years. Over the past 40–50 years, dinocysts have led to major advances on Mesozoic-Cenozoic research, in terms of biostratigraphy and paleogeogeography. Dinocyst taxonomy has then been continuously revised, with the tabulation being the main morphological link between living dinoflagellates and fossilized cysts. Over the Quaternary, and based on the principle of uniformitarianism (i.e. species ecology did not change through time), relationships between modern assemblages and present-day environmental factors controlling their distribution also allow for dinocyst-based quantitative reconstructions derived from transfer function calculations. This paper presents a non-exhaustive review of the dinocyst literature allowing the reader to get a perspective about how they were discovered and defined, but also how they are applied in (paleo)ecological studies according to the timescale considered allowing then to provide useful insights into the future climate change and its associated ecological repercussions.

Terminal Ordovician stratigraphy of the Siljan district, Sweden

Integration of new isotopic data and earlier biostratigraphic information from eight sections through the terminal Ordovician (Pirgu and Porkuni stages) of the Siljan district, Sweden, allows a more precise correlation of sections in terms of biostratigraphy and carbon isotope dating. Four levels with positive δ13C excursions are identified (from bottom) – the Moe, an unnamed excursion, Paroveja and Hirnantian Carbon Isotope Excursion (HICE). The δ13C values through the Boda Limestone are 1–2‰ higher than usual in Baltica, only the values for the HICE remains within what is expected. Background values increase from 1.5‰ in the bottom of the core of the Boda Limestone up to 3‰ in the top of it. The HICE is identified in five of eight sections and the main peak falls according to inferred correlation within the Metabolograptus persculptus Biozone, at or close to the Hindella beds in the Upper Boda Member. The late Katian (Pirgu) age of Holorhynchus in the Siljan district is clear and its co-occurrence with the chitinozoan Belonechitina gamachiana in Estonia supports a Katian age for this zone. The base of the Ozarkodina hassi Biozone may occur within units B–C of the Upper Boda Member and in the upper part of the Loka Formation and most likely is correlated with the M. persculptus Biozone. The Hirnantia–Dalmanitina faunas reported from the lowermost part of the Loka Formation and units B–D of the Upper Boda Member seem to range through all the Hirnantian, but detailed morphological studies allow to distinguish an older ( = extraordinarius) and a younger ( = persculptus) fauna.

The Toarcian Oceanic Anoxic Event in the Ionian Zone, Greece

The Early Jurassic was characterized by a global disturbance of the carbon cycle known as the Toarcian Oceanic Anoxic Event (T-OAE). This event is recorded worldwide by a negative excursion in marine and terrestrial carbon-isotope ratios, typically interrupting an overarching positive trend attributed to large-scale burial of marine organic matter under oxygen-depleted conditions. The negative excursion is attributed to introduction of isotopically light carbon into the ocean–atmosphere system. Three sections from the Ionian Zone in Greece have been analysed in terms of biostratigraphy, Total Organic Carbon (TOC), CaCO3, δ13Ccarb, δ18Ocarb and δ13Corg. On the basis of bio- and chemostratigraphy, the age of Pliensbachian–Toarcian formations from the Ionian Zone in Greece has been refined and the geochemical signature of the T-OAE recognized. All sections illustrate the characteristic negative excursion in carbon isotopes from both carbonates and organic matter and, in only one locality, a positive excursion has also been recorded. The recognition of the T-OAE in this part of the Tethyan continental margin offers additional information on the global impact and amplitude of this important Jurassic palaeoceanographic event.

Biocronoestratigrafia da Bacia de Pelotas: estado atual e aplicação na geologia do petróleo

The biostratigraphic studies of the Brazilian sedimentary basins have providing a support for the exploratory research of energetic and mineral resources, in particular at the continental margin. From new discoveries of hydrocarbon accumulations at the Santos and Campos basins, the south portion of the Brazilian continental margin were converted in an important target of the exploration. Therefore, the biostratigraphic refinement is necessary to detect gaps and to promote an increment on the precision of the lateral correlations in the delimitation and spatial analysis of the potential reservoirs. The actual stage of the bio-chronostratigraphic framework of the Pelotas Basin is presented herein, focusing on its application to the reservoir prospection. The main questions and lacunae on the knowledge are also discussed. In terms of biostratigraphy, the Pelotas Basin remains poorly evaluated, despite publication of important works on the biostratigraphy are known since the 1960’s. A comparison of biostratigraphic schemes proposed for the Tertiary section of the basin allows the inference of diverse hiatuses, identified by the absences of biozones. Hiatuses identified in the 87Sr/86Sr curve, suggest their relationship with discontinuities in the deposition. Discrepancies between the proposed schemes can be attributed to the particular resolution of the different groups used, the variations in the biostratigraphic criteria and the sampling interval, influencing the biostratigraphic resolution and therefore its potential as a correlation tool.

Biocronoestratigrafia da Bacia de Pelotas: estado atual e aplicação na geologia do petróleo

The biostratigraphic studies of the Brazilian sedimentary basins have providing a support for the exploratory research of energetic and mineral resources, in particular at the continental margin. From new discoveries of hydrocarbon accumulations at the Santos and Campos basins, the south portion of the Brazilian continental margin were converted in an important target of the exploration. Therefore, the biostratigraphic refinement is necessary to detect gaps and to promote an increment on the precision of the lateral correlations in the delimitation and spatial analysis of the potential reservoirs. The actual stage of the bio-chronostratigraphic framework of the Pelotas Basin is presented herein, focusing on its application to the reservoir prospection. The main questions and lacunae on the knowledge are also discussed. In terms of biostratigraphy, the Pelotas Basin remains poorly evaluated, despite publication of important works on the biostratigraphy are known since the 1960’s. A comparison of biostratigraphic schemes proposed for the Tertiary section of the basin allows the inference of diverse hiatuses, identified by the absences of biozones. Hiatuses identified in the 87 Sr/ 86 Sr curve, suggest their relationship with discontinuities in the deposition. Discrepancies between the proposed schemes can be attributed to the particular resolution of the different groups used, the variations in the biostratigraphic criteria and the sampling interval, influencing the biostratigraphic resolution and therefore its potential as a correlation tool.

An integrated chemostratigraphic study of the Campanian-Early Maastrichtian deposits of the Offshore Miskar Field in southeastern Tunisia: SIS, d13C and d18O isotopes, and elemental geochemistry

Chalk deposition characterizes the Late Cretaceous period in many areas of the world. In Tunisia it occurred predominantly during Campanian - Maastrichtian time, resulting mainly in Abiod Chalk Formation deposits that show high potential as a petroleum reservoir. Cored intervals of the uppermost Aleg and Abiod formations (around 100 m) have been logged and sampled in detail from three wells (Miskar W1, W2, W4) in the Miskar Gas Field, Gulf of Gabes, offshore eastern Tunisia. The uppermost Abiod and the base of the overlying El Haria Formation have been logged and sampled in one additional well (Miskar W3). In this area, the Abiod Formation mainly consists of homogenous chalk successions that, while adequately constrained in terms of biostratigraphy, are inadequately correlated between wells, so that the need remains for additional integrated studies that combine geochemical and isotopic methods. Such studies would further confirm the validity of chemostratigraphy as a reliable correlation tool. The Abiod Formation is subdivided lithologically into two units in Miskar W3, three units in Miskar W4, and four units in the Miskar W1 and W2 wells. The Aleg and El Haria formations are designated as separate lithostratigraphic intervals. A low-resolution biostratigraphic study was carried out in which comparisons to previous studies (Moody et al. 1995; Bailey et al. 2000a, 2000b) indicated an Early Campanian-earliest Maastrichtian age for the Abiod Formation, a probable Late Turonian-Coniacian age for the uppermost Aleg Formation, and an Early Maastrichtian age for the base of the El Haria Formation. Strontium isotope (87Sr/86Sr) stratigraphy (SIS) supports the biostratigraphic dating. Geochemical determinations of nineteen elements in the Miskar wells at high stratigraphic resolution show significant vertical variation. Five geochemical curves (Ca, Al, Mn, Ti, Zr) appear to be suitable for correlation. Based on these elements, the uppermost part of the Aleg (in Miskar W1, W2, and W4), and the lower part of the El Haria Formation (Miskar W3) can be geochemically characterized. The Abiod Formation is subdivided into eight geochemical units in Miskar W1, six in Miskar W2, four in W4 and three in W3. The proposed geochemical correlation agrees with the biostratigraphic interpretation, and in addition, some of the lithological boundaries lie close to the geochemical unit boundaries. However, the established geochemical correlation between wells suggests that detailed geochemical subdivisions of the formation can be established and laterally correlated without being entirely related to specific lithological variation. Study of the carbon and oxygen isotope profiles in the Miskar wells confirms the existence of an unconformity between the Aleg and Abiod formations that is indicated by biostratigraphic and SIS studies. Isotopic correlation of the Abiod Formation between Miskar W1 and W4 is based on the definition of eleven isotope units in W1, which appear to be suitable for correlation elsewhere. A good agreement exists between the isotopic units and the identified geochemical unit boundaries. In sum, the integrated chemostratigraphic study in this paper identifies correlatable geochemical discontinuities and recognizes stratigraphically significant surfaces and marker beds, as well as small-scale chemostratigraphic events in a presumed homogenous chalk succession.This study offers comparative data for the hemostratigraphic correlation and characterization of the Upper Cretaceous successions elsewhere in the southern Tethys.

Integrated biostratigraphy of the Campanian–Maastrichtian transition in the Nile Valley, Southern Egypt

Rocks of the Campanian/Maastrichtian transition form the main bulk of the Duwi Formation, exposed in the Nile Valley, Southern Egypt. In terms of biostratigraphy, the concerned transition has been subdivided into three planktic foraminiferal zones coeval with two ammonite and three bivalve zones. The proposed zones have been integrated and correlated with other zonal schemes. The Campanian/Maastrichtian boundary has been located at the contact between the Campanian Bostrychoceras polyplocum and the Maastrichtian Pachydiscus neubergicus Ammonite Zones, corresponding with the contact between the Campanian Globotruncana aegyptiaca and the Maastrichtian Rugoglobigerina hexacamerata planktic foraminiferal zones, as well as the contact between the Campanian Cameleolopha tissoti–Plicatula pausicostata and the Maastrichtian Abruptalopha abrupta bivalve zones.

Towards a new time scale for the Upper Miocene continental series of the Pannonian basin (Central Paratethys)

In this study we assert that most of the "Pontian" stratigraphic succession of western Hungary is much older than Pontian stage (older than 7 Ma). In fact, these strata form a clearly distinct chronostratigraphic unit between the Pontian strata (as they are defined in the type area of the Black Sea basin) and the Pannonian strata (as they are de- fined in the type area of the Vienna basin). To denote such a problematic chronostratigraphic interval we propose the in- troduction of a new stage (or substage) named Transdanubian between the Pannonian sensu stricto (s.s.) and Pontian s.s. stages of the Upper Miocene series of the Central Paratethys System (ca. 9.0-7.4 Ma in the chronology adopted in this study). The Transdanubian stage has been defined in terms of biostratigraphy, lithostratigraphy, magnetostratigraphy and allostratigraphy. The location of a suitable stratotype has also been proposed. As a first approach, we tried to avoid the in- troduction of new terms in the already complex chronostrati- graphic nomenclature of the Pannonian basin. However, we arrived to the conclusion that the introduction of the Trans- danubian as a new stage (or substage) is a necessary break- through, to avoid further confusion and circular reasoning in- volving facies associations versus chronostratigraphic units. Transdanubian strata represent a distinct anticipation of the Pontian facies within the intra-Carpathian area. The fact that these strata have been reported for decades as "Pontian" in the literature has been the source of much terminological confusion and chronostratigraphic miscorrelation.