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- Organic Maturation and Source-Rock Potential of the Mesozoic Algarve Basin: southern PortugalPublication . Fernandes, Paulo; Borges, Marisa; Rodrigues, B.; Matos, VascoThe Algarve Basin is an important Mesozoic depocentre in southern Portugal.
- Middle-Upper Jurassic palynology of the Sagres region and the Carrapateira outlier: southern PortugalPublication . Borges, Marisa; Fernandes, Paulo; Pereira, Zélia; Riding, JimThe palynology of the Middle-Upper Jurassic fill of the Sagres region (Algarve Basin) and the Carrapateira outlier, southern Portugal was investigated. Samples were collected from Mareta beach, Cilheta beach and the Carrapateira outlier. Dinoflagellate cysts are confined to the Upper Bajocian to Upper Callovian sedimentary rocks exposed at Mareta and Cilheta beaches and the Lower Kimmeridgian strata of the Carrapateira outlier. The palynostratigraphical study of the Jurassic successions has yielded new biostratigraphical data based on dinoflagellate cysts and miospores. The results confirm, and in some cases refine, the existing macrofaunal age determinations of these successions.
- Callovian (Middle Jurassic) dinoflagellate cysts from the Algarve Basin, southern PortugalPublication . Borges, Marisa; Riding, James B.; Fernandes, Paulo; Matos, Vasco; Pereira, ZéliaThe palynology of three Callovian (Middle Jurassic) limestone-marl successions from the Algarve Basin in southern Portugal was studied. These localities are Baleeira Harbour, Mareta Beach and Telheiro Quarry; they provide a composite. succession, tied to ammonite zones, through the Lower, Middle and Upper Callovian from the western and eastern subbasins of the Algarve Basin. The three sections generally yielded relatively abundant marine and continental palynofloras. Diversity is low to moderate and the dinoflagellate cyst associations are dominated by Ctenidodinium spp., the Ellipsoidictyum/Valensiella group, Gonyaulacysta jurassica subsp. adecta, Korystocysta spp., Meiourogonyaulax spp., Pareodinia ceratophora, Sentusidinium spp., Surculosphaeridium? vestitum and Systematophora spp. Some intra-Callovian marker bioevents were recorded; these include the range bases of Ctenidodinium ornatum, Gonyaulacysta eisenackii, Korystocysta pachyderma, Mendicodinium groenlandicum, Rigaudella spp. and Surculosphaeridium? vestitum. The occurrences of Endoscrinium acroferum and Impletosphaeridium varispinosum in the Early to Middle Callovian of Mareta Beach and Telheiro Quarry are also characteristic of this interval. At Baleeira Harbour, the presence of Ctenidodinium continuum and Gonyaulacysta centriconnata in the Peltoceras athleta Zone confirms the Late Callovian age of this section. The successions studied were deposited in restricted infralittoral neritic marine environments which lack deep water circulation, and possibly represent restricted embayments. The relatively low diversity nature of the dinoflagellate cyst assemblages appears to be largely due to the highly enclosed nature of this depocentre. Many Callovian index dinoflagellate cyst taxa which are found in northwest Europe are absent in the Algarve Basin. These forms may have been intolerant of enclosed palaeoenvironments which have restricted or no deep circulation. The Callovian marine palynofloras from the Algarve Basin compare well to the few other published records from the Iberian Peninsula of this age. However they are significantly less diverse than coeval floras from elsewhere in the extensive Mid Latitude Callovian phytoprovince. Many typically Callovian dinoflagellate cysts are cosmopolitan, however some provincialism is clearly manifested. The Arctic and Austral Callovian phytoprovinces are characterised by key endemic taxa such as Paragonyaulacysta retiphragmata and Ternia balmei, which are not present in the Algarve Basin and are assumed to have been polar forms.
- 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.
- Miocene dinoflagellate cyst assemblages: preliminary correlation between the Lower Tagus and Algarve Basins (Portugal)Publication . Castro, Lígia; Borges, Marisa; Pereira, Zélia; Fernandes, Paulo; Pais, JoãoBiostratigraphic studies of several sections and a borehole (Belverde) of the Lower Tagus Basin, based on Miocene dinoflagellate cyst assemblages, have allowed a detailed stratigraphic investigation to be conducted. Assemblages are very diverse and abundant and can be used as important biostratigraphic guides. Recently, a palynostratigraphic study based on dinoflagellate cysts was conducted in two offshore wells, Ruivo-1 and Corvina, located in the Algarve Basin (southern Portugal). The recovered dinoflagellate assemblages are less abundant and diverse than those obtained in the Lower Tagus Basin. New inferences are made regarding the correlation between the dinoflagellate cysts known from the Lower Tagus Basin with the assemblages recently recovered from the Algarve Basin. Species of selected dinoflagellate cyst assemblages recovered are similar in both basins. Continuing progress with these new palynological studies and biostratigraphic data will help to refine knowledge of and correlations between Portuguese Miocene deposits.
- Jurassic palynostratigraphy of the Algarve Basin and the Carrapateira Outlier, Southern PortugalPublication . Borges, Marisa; Riding, James B.; Fernandes, Paulo; Pereira, ZéliaThe Mesozoic Algarve Basin (AB) corresponds to the southernmost geological province of mainland Portugal. The Carrapateira Outlier (CO) is a small outcrop of Mesozoic rocks located 20 km north of the AB. In this study we investigated the palynology of the Jurassic (Upper Bajocian to Lower Kimmeridgian) of the AB and CO.
- Carbon isotope record (d13Ccarbonate) of the Middle to Late Jurassic (Callovian - Oxfordian) from the Algarve Basin, PortugalPublication . Borges, Marisa; Fernandes, Paulo; Rodrigues, Bruno; Goodhue, R.The Algarve Basin is an important Mesozoic depocentre located in southern Portugal which formed during the succesive phases of the North Atlantic rifting following the break-up of Pangea [1]. Several unconformities related to compressive episodes are observed in the stratigraphic record of the Algarve Basin. One of these episodes ocurred in the transition from Middle to Upper Jurassic times and is marked by an important tectonic episode, observed throughout Iberia [1], that caused the tilting and folding of the Middle Jurassic strata. This situation can be observed at Benaçoitão, where Oxfordian limestones rest unconformably over tilted Middle Callovian marly limestones. In this work we present !13Ccarbonate data across the Middle and Upper Jurassic rocks from the Algarve Basin at Benaçoitão.
- d13Ccarbonate chemostratigraphy of the Carrapateira Outlier (Lower Kimmeridgian), Southern PortugalPublication . Borges, Marisa; Goodhue, R.; Fernandes, Paulo; Pereira, Zélia; Matos, Vasco; Rodrigues, B.The Carrapateira Outlier (CO) located 20 km north of Sagres is formed by Upper Triassic to Kimmeridgian sediments. The studied section is located at Três Angras bay and consists of approximately 50 m of limestones interbedded with marls, assigned to the Early Kimmeridgian based on corals, foraminifera and dinoflagellate cysts. The uppermost limestone beds are rich in macrofossils with well-preserved corals in life position. To compile 13C chemostratigraphy for this section, sixty five bulk carbonate samples were studied.
- Jurassic Palynostratigraphy of the Sagres Region (Algarve Basin) and the Carrapateira Outlier: preliminary resultsPublication . Borges, Marisa; Fernandes, Paulo; Pereira, Zélia; Riding, James B.The Algarve Basin (AB) corresponds to the southernmost geological province of mainland Portugal. More than 3000m of essentially marine sediments accumulated during Mesozoic-Cenozoic times in the AB.
- Palinoestratigrafia do Jurássico da região de Sagres (Bacia Algarvia) e da Carrapateira: resultados preliminariesPublication . Borges, Marisa; Fernandes, Paulo; Pereira, Zélia; Riding, JimA análise palinoestratigráfica das sucessões jurássicas da região de Sagres (Bacia Algarvia) e do afloramento Mesozóico da Carrapateira permitiu a obtenção de novos dados bioestratigráficos, com base em dinoflagelados e mioesporos. Os novos resultados confirmam, e em alguns casos refinam, as idades atribuídas a estas sucessões com base em macrofaunas.