Browsing by Author "Riding, James B."
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- 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.
- 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.
- 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.
- New palynological data from the Ruivo-1 and Corvina wells, offshore Algarve Basin, Portugal: implications for future hydrocarbon explorationPublication . Borges, Marisa; Riding, James B.; Fernandes, Paulo; Pereira, Zélia; Matos, VascoThe Algarve Basin is an important Mesozoic sedimentary basin located in southern Portugal. Its onshore part consists largely of marine carbonate sediments with more than 2000 m in thickness. The basin extends offshore where its geology is recognized seismically and a few hydrocarbon exploration wells were drilled in the mid 70’s and early 80’s. The palynostratigraphical study of two of these wells, Ruivo- 1 and Corvina, has yielded new biostratigraphical data based on dinoflagellate cysts. The Ruivo-1 well has a total depth of 2100 m and drilled a thick Callovian succession between 1800 and 2030 m. The samples from this interval yielded abundant organic residues that comprise well-preserved palynomorphs together with plant fragments. The dinoflagellate cysts assemblage include Batiacasphaera spp., Ctenidodinium sp., Ctenidodinium sellwoodii group, Ellipsoidictyum gochtii, Ellipsoidictyum/Valensiella group, Gonyaulacysta jurassica subsp. adecta, Impletosphaeridium spp., Korystocysta gochtii, Meiourogonyaulax caytonensis group, Pareodinia ceratophora, Sentusidinium spp., Systematophora areolata, Systematophora penicillata, Systematophora spp. and Tubotuberella dangeardii. This association is indicative of the Middle-Late Callovian. However, the presence in this interval of Nannoceratopsis deflandrei subsp. deflandrei, a Toarcian-Aalenian marker, suggesting reworking. The Corvina well cored a 2700 m thick succession of Miocene to Upper Jurassic sediments. Samples collected between 1595 and 2680 m yielded relatively abundant organic residues dominated by dinoflagellate cysts. The pollen associations are of low diversity and include bisaccate pollen, Callialasporites dampieri, Callialasporites turbatus, Callialasporites spp., Classopollis classoides and Perinopollenites elatoides. The dinoflagellate cyst floras from these samples are indicative of the ?Early-Middle Oxfordian due principally to the occurrence of Ctenidodinium ornatum, Compositosphaeridium polonicum, Hystrichosphaerina orbifera, Endoscrinium luridum, Gonyaulacysta jurassica subsp. jurassica, Rigaudella aemula, Surculosphaeridium vestitum, Stephanelytron redcliffense, Systematophora spp. and Wanaea acollaris. The dinoflagellate cyst assemblages from the two wells are less diverse than typical Callovian-Oxfordian associations from further north in Europe. The results are also consistent with the onshore Algarve Basin and could be explained by the partially enclosed nature of the Algarve Basin during Jurassic times. This new biostratigraphical data will help to refine the time calibration of the available seismic lines and help in future hydrocarbon exploration work.
- The Jurassic (Pliensbachian to Kimmeridgian) palynology of the Algarve Basin and the Carrapateira outlier, southern PortugalPublication . Borges, Marisa; Riding, James B.; Fernandes, Paulo; Pereira, ZéliaThe palynology of the Jurassic (Upper Pliensbachian to Lower Kimmeridgian) fill of the Algarve Basin and the Carrapateira outlier, southern Portugal was investigated. Samples were collected from Armação Nova Bay, Mareta Beach, Cilheta Beach and the Carrapateira outlier. At Armação Nova Bay the Upper Pliensbachian–Lower Toarcian succession proved barren, or yielded sparse, non age-diagnostic palynomorphs. 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. At Mareta Beach, the Upper Bajocian, Bathonian and Callovian produced relatively low to moderate diversity dinoflagellate cyst assemblages. Several key bioevents confirm the Bathonian and Callovian ages of the succession; no age-significant Late Bajocian bioevents were noted. The Upper Callovian of Cilheta Beach yielded moderately diverse dinoflagellate cyst associations dominated by Ctenidodinium spp. Key Late Callovian bioevents confirm the age of this succession. Many familiar marker forms known from northwest Europe were not encountered. No typically Arctic forms were recovered throughout the Upper Bajocian to Callovian of this part of the Algarve Basin. It is clear that there was no significant Late Bajocian to Late Callovian dinoflagellate cyst provincialism within southern and northern Europe and adjacent regions. The Carrapateira outlier yielded a moderately diverse Early Kimmeridgian dinoflagellate cyst flora. The Early Kimmeridgian age assessment based on corals and foraminifera is confirmed. Amphorula and Histiophora are present; these are typical of the Late Jurassic of the Tethyan Realm, and their presence is consistent with Late Jurassic provincialism within Europe. The relatively low diversity nature of these Late Bajocian to Early Kimmeridgian dinoflagellate cyst floras is probably mainly due to the relatively deep water, partially enclosed depositional setting. The partially enclosed nature of this part of the Algarve Basin and the Carrapateira outlier seems to have prevented the free migration of dinoflagellates between southern Portugal and elsewhere in Europe.
- The palynological response to the Toarcian Oceanic Anoxic Event (Early Jurassic) at Peniche, Lusitanian Basin, western PortugalPublication . Correia, Mariana F.; Riding, James B.; Duarte, Luis V.; Fernandes, Paulo; Pereira, ZeliaThe uppermost Pliensbachian and lower Toarcian (Lower Jurassic) succession exposed at Peniche in the central part of the Lusitanian Basin, western Portugal, was examined for palynomorphs. The 45 samples span the Emaciaticeras emaciatum, Dactylioceras polyrnorphum and Hildaites levisoni ammonite biozones (ABs), and the succession includes the Global boundary Stratotype Section and Point (GSSP) for the Toarcian Stage and the Toarcian Oceanic Anoxic Event (T-OAE). A low diversity dinoflagellate cyst flora, typical of the Sub-Boreal Realm, was recovered from the Emaciaticeras emaciatum and Dactylioceras polymotphum ABs. The dominant element is the cold water species Luehndea spinosa, which is an index for the Pliensbachian to earliest Toarcian, and is thought to have migrated from the more northerly Boreal Realm. Prior to the T-OAE, dinoflagellates thrived in the Lusitanian Basin, except during a brief warm period in the earliest Toarcian. Despite the latter, the recovery from this event was relatively rapid and was characterised by a return to relatively cool temperatures. The Hildaites levisoni AB at Peniche represents the T-OAE and the overlying strata, and is characterised by a profound reduction in dinoflagellate cyst relative abundances. This dinoflagellate cyst 'blackout', and the associated rise of prasinophytes, reflects significant environmental stress, such as marine anoxia, elevated temperatures and reduced salinity, with the former two probably being most important. The low proportions of dinoflagellate cysts following the T-OAE indicates a protracted recovery phase from the bottom and water column anoxia developed throughout the Lusitanian Basin.
- The palynology of the lower and middle Toarcian (Lower Jurassic) in the northern Lusitanian Basin, western PortugalPublication . Correia, Vania F.; Riding, James B.; Fernandes, Paulo; Duarte, Luis V.; Pereira, ZeliaThe lower and middle Toarcian (Lower Jurassic) successions of the northern Lusitanian Basin in western Portugal were examined for palynomorphs. Two localities, the Maria Pares and the Vale das Fontes sections, were sam-pled. The sections span the Dactylioceras polymorphum, Hildaites leyisoni and Hildoceras bifrons ammonite biozones. The samples produced relatively low diversity dinoflagellate cyst floras which are typical of those from coeval European successions; the most abundant species is Luehndea spinosa. The other forms encountered were Mancodinium semitabulatum, Mendicodinium microscabratum, M. spinosum subsp. spinosum, Mendicodinium sp., Nannoceratopsis ambonis, N. gracilis and N. senex. Dinoflagellate cysts typically dominate throughout the Dactylioceras polymorphum ammonite biozone; their abundance significantly decreased in the overlying Hildaites levisoni and Hildoceras bifrons ammonite biozones. The low diversity Luehndea-Nannoceratopsis dinoflagellate cyst flora of the northern Lusitanian Basin is characteristic of the Sub-Boreal region of Europe. This is a transitional region, intercalated between the Boreal and Tethyan realms. The Toarcian Oceanic Anoxic Event (T-OAE) in the northern Lusitanian Basin is characterised by a sudden decline in palynomorph abundance and diversity, including the virtual absence of acritarchs and dinoflagellate cysts. Following the T-OAE, Mancodinium semitabulatum and Mendicodinium spp. were the only dinoflagellate cysts recorded. This 'blackout' of dinoflagellate cysts during the T-OAE, and their partial recovery following the event, shows that dinoflagellate populations were responding to a major palaeoenvironmental change. (C) 2016 Elsevier B.V. All rights reserved.