Browsing by Author "Clayton, Geoff"
Now showing 1 - 10 of 11
Results Per Page
Sort Options
- Assessing thermal maturity through a multi-proxy approach: a case study from the Permian Faraghan Formation (Zagros Basin, Southwest Iran)Publication . Spina, Amalia; Cirilli, Simonetta; Sorci, Andrea; Schito, Andrea; Clayton, Geoff; Corrado, Sveva; Fernandes, Paulo; Galasso, Francesca; Montesi, Giovanni; Pereira, Zelia; Rashidi, Mehrab; Rettori, RobertoThis study focuses on the thermal maturity of Permian deposits from the Zagros Basin, Southwest Iran, employing both optical methods (Thermal Alteration Index, Palynomorph Darkness Index, Vitrinite Reflectance, UV Fluorescence) and geochemical analyses of organic matter (Rock Eval Pyrolysis and MicroRaman spectroscopy) applied to the Faraghan Formation along two investigated Darreh Yas and Kuh e Faraghan surface sections. Furthermore, an integrated palynofacies and lithofacies analysis was carried out in order to integrate the few studies on the depositional environment. The Faraghan Formation, which is widely distributed in the Zagros area, generally consists of shale intercalated with sandstones and pebble conglomerates in the lower part, followed by a succession of sandstone, siltstone and shaly intercalations and with carbonate levels at the top. The integrated palynofacies and lithofacies data confirm a coastal depositional setting evolving upwards to a shallow marine carbonate environment upwards. Rock Eval Pyrolysis and Vitrinite Reflectance analysis showed that the organic matter from samples of the Darreh Yas and Kuh e Faraghan sections fall in the mature to postmature range with respect to the oil to gas generation window, restricting the thermal maturity range proposed by previous authors. Similar results were obtained with MicroRaman spectroscopy and optical analysis such as Thermal Alteration Index and UV Fluorescence. Palynomorph Darkness Index values were compared with Rock Eval Pyrolysis and vitrinite reflectance values and discussed for the first time in the late stage of oil generation.
- Maturação Orgânica da Bacia Mesozóica Algarvia (Sul de Portugal): implicações para a exploração de hidrocarbonetosPublication . Fernandes, Paulo; Matos, Vasco; Rodrigues, Bruno; Borges, Marisa; Clayton, GeoffA Bacia Algarvia (BA) situa-se no sul de Portugale apresenta uma direção principal E - O estando a sua parte emersa representada ao longo da costa, desde o Cabo de São Vicente até ao rio Guadiana, estendendo-se também para o offshore.
- New evidence concerning the thermal history of Devonian and Carboniferous rocks in the South Portuguese ZonePublication . Fernandes, Paulo; Musgrave, J. A.; Clayton, Geoff; Pereira, Zélia; Oliveira, José Tomás; Goodhue, R.; Rodrigues, B.The Late Palaeozoic rocks of southern Portugal have a complex thermal history. Vitrinite reflectance determinations from 90 samples confirm that the organic maturity of Late Palaeozoic rocks in SW Portugal is very high, mainly corresponding to meta-anthracite coal rank. The optic fabric of vitrinite in oriented coal samples from the Brejeira Formation suggests maturation under simple, non-tectonic, burial conditions with peak temperatures being attained prior to Variscan deformation. The lack of any increase in vitrinite reflectance with depth through c. 1 km of section in borehole AC-1 is not consistent with conductive heat transfer and is interpreted as the result of late synorogenic to post-orogenic advective heating. This heating episode generated temperatures sufficiently high to produce levels of maturity corresponding to metaanthracite coal rank through much of the terrane now exposed, but not high enough to result in overprinting of the pre-deformation optic fabric of vitrinite in the thin coals. The slightly lower maturity of older, platformfacies rocks in the Aljezur–Bordeira area may reflect either deposition on a basement high followed by less burial than adjacent parts of the basin, or the area being the site of a sink for descending relatively cool fluids.
- Organic maturation levels and thermal history of the Carboniferous rocks of the Dublin BasinPublication . Fernandes, Paulo; Clayton, GeoffThe Dublin Basin sucession comprises sediments in age from Mississippian (Courceyan) to Pennsylvanian (Langsettian). The Viséan part of. the succession is dominated by turbiditic calcarenites interbedded with grey-black shales. Namurian and earliest Westphalian rocks preserved in the Kingscourt Outlier in the north of the basin are dominated by sandstones interbedded with silstones and shales.
- Organic maturation of the Algarve Basin (southern Portugal) and its bearing on thermal history and hydrocarbon explorationPublication . Fernandes, Paulo; Rodrigues, Bruno; Borges, Marisa; Matos, Vasco; Clayton, GeoffThe Algarve Basin, southern Portugal is under-explored in terms of petroleum geology. Organic maturation levels and the thermal history of this basin have been ascertained, together with their implications for future exploration. Maturity was determined using vitrinite reflectance and spore fluorescence/colour. The succession was extensively sampled (158 onshore samples and 20 samples from two offshore wells). Thermal history was modelled using 1D PetroMod®. A palynostratigraphic study of two offshore wells was also completed, showing thick marl–limestone sequences of Middle and Upper Jurassic age. Hiatuses were identified in the offshore wells within the Jurassic section and between the Jurassic and the Miocene sections. The Mesozoic rocks of the Algarve Basin lie within the oil window. Vitrinite reflectance ranges from 0.52–0.7%Rr in the Lower Cretaceous to 1–1.1%Rr in the Upper Triassic–Hettangian. Miocene rocks that unconformably overlie the Mesozoic strata are immature (0.42–0.47%Rr). Maturation levels increase with increasing age of the strata, indicating that burial was the main process controlling maturation. Thick marl–limestone sequences of the Middle Jurassic (Callovian) and the Upper Jurassic (Oxfordian) are the main source rock intervals. The Miocene successions of both offshore wells contains reworked vitrinite and palynomorphs with maturation levels similar to the Mesozoic rocks of the basin, suggesting exposure and erosion of these rocks during Miocene times. Palaeogeothermal gradients in the onshore Algarve Basin range from 52 °C/km to 24.7 °C/km with pre-Miocene exhumation estimated at 2000–2500 m. The probable age for the removed cover is Upper Cretaceous to Lower Palaeocene(?) and peak temperatures in the Mesozoic rocks were attained during latest Cretaceous–Early Palaeocene times. Modelled palaeotemperatures suggest that the Jurassic entered the oil-window at the beginning of the Cretaceous with peak oil generation in late Cretaceous time.
- Palynology of the kingscourt outlier (Ireland)Publication . Fernandes, Paulo; Clayton, GeoffThe Kingscourt Outlier occupies a roughly triangular area on the southern part of the Lower Palaeozoic Longford–Down Massif in eastern Ireland. It comprises a condensed succession of sedimentary rocks that record the onset of fluvio‐deltaic sedimentation across eastern Ireland during Late Viséan to Late Bashkirian (Jackson, 1955, 1965). The outlier forms a syncline structure with an axis orientated approximately north‐south and parallel with the normal Kingscourt Fault that downthrows beds of Carboniferous and Permo‐Triassic age against the Lower Palaeozoic rocks.
- Palynostratigraphic reassessment of the Late Devonian of Bjørnøya, SvalbardPublication . Lopes, Gilda; Mangerud, Gunn; Clayton, Geoff; Vigran, Jorunn OsA comprehensive study of the Late Devonian palynostratigraphy of Bjørnøya, Svalbard Archipelago is presented.A total of 61 samples collected from 10 outcrops located along the eastern coast of the island were analyzed forpalynology yielding a mid- to latest Famennian age. A reassessment of the existing palynostratigraphy of the UrsaSandstone Unit of the Røedvika Formation was undertaken. As no independent age control exists for this succes-sion, the palynological assemblages were correlated to well-calibrated palynological zonations from the Easternand Western Europe. The middle to upper part of the Vesalstranda Member and the Kapp Levin Member wereassigned a mid- to late Famennian age (CVa to VF biozones), and the middle to lower-upper part of the TunheimMember was dated as latest Famennian in age (LL to LN biozones). For thefirst time, a palynological age wasassignedto the upperpart ofthe KappLevin Member. Correlation with other Arctic areas show close resemblanceto Late Devonian assemblages from Europe and the Arctic region. However, differences in the stratigraphicalranges of several taxa were identified. In terms of Late Devonian paleophytogeographic provinces the miosporeassemblages are assigned to the Northern EuroamericanCornispora varicornataRealm for the mid-Famennian. Amore cosmopolitan trend was recognized for the latest Famennian (Strunian), with assemblages including abun-dantRetispora lepidophyta. The paleobotanical affinities of the palynomorphs reveal aflora of lycopods andprogymnosperms occupying this area during the Late Devonian, withRetispora lepidophytabecoming a commonelement in the latest Famennian.
- Poder reflector da vitrinite, mineralogia das argilas e cristalinidade da ilite na Zona Sul PortuguesaPublication . McCormack, Niall; Clayton, Geoff; Fernandes, PauloO Poder Reflector Aleatório da Vitrinite (PRAV) na Zona Sul Portuguesa (ZST) varia entre 2,1% e 5,3%. O PRAV não aumenta com o aumento da idade estratigráfica e o processo de maturação é portanto, considerado como pós-deformação (pós-Vestefaliano D inferior). Amostras do Triásico e do Jurássico do Outlier da Carrapateira têm PRAV de 1,1% e 0,9% respectivamente. Isto implica que temperaturas máximas relacionadas com a maturação da ZSP foram alcançadas entre o Vestefaliano D inferior e o Triásico médio. A caulinite é o mineral das argilas dominante nas regiões ocidentais da ZSP, enquanto que as regiões localizadas a este e norte são dominadas pela clorite.
- The thermal history and hydrocarbon source rock potential of the mid Carboniferous Quebradas Formation in SW Portugal and its correlatives in western Atlantic offshore basinsPublication . Clayton, Geoff; Fernandes, Paulo; Goodhue, R.; McCormack, Niall; Musgrave, J. A.; O'Donoghue, E. P.The mid Carboniferous Quebradas Formation of the ‘South Portuguese Zone’ (SPZ) comprises 80m of post-mature black mudrocks with a mean TOC of 2.5%. Lithostratigraphic units of similar facies and age such as the Holywell Shale, the Edale Shale and the Bowland Shale are important HC source rocks in the UK, having sourced a considerable proportion of the hydrocarbons in the East Irish Sea, East Midlands and Formby oilfields respectively. The kerogen content of the Quebradas Formation is mixed but slightly more oil-prone in its lower part. At outcrop, it is strongly post-mature with vitrinite reflectance (Rr) ca. 4%. Illite crystallinity results from the Quebradas Formation and associated units suggest lower maturity than vitrinite reflectance. Analysis of the optic fabric of very thin coal lenses within the Brejeira Formation which overlies the Quebradas Formation suggests that peak temperatures were attained before the Variscan (late Carboniferous – early Permian) deformation. Triassic rocks unconformably overlying the Carboniferous sequence are much less mature, with Rr ca. 1.2%. Although the the Quebradas Fm has no HC source potential onshore due to its high maturity, Carboniferous rocks offshore may not have experienced the same extreme thermal history as the SPZ.
- The thermal history of the Mesozoic Algarve Basin (South Portugal) and its implications for hydrocarbon explorationPublication . Rodrigues, Bruno; Fernandes, Paulo; Matos, Vasco; Borges, Marisa; Clayton, GeoffThe Algarve Basin is the southernmost geological province of mainland Portugal, outcropping along the entire south coast area and extending offshore, where it is recognised on seismic lines and in hydrocarbon exploration wells. It mainly comprises Jurassic and Lower Cretaceous limestones and marls making a succession over 3 km thick. This sedimentary basin belongs to a series of basins that were initiated by rifting associated with the opening of the North and Central Atlantic Ocean, following the breakup of Pangaea.