Jorge Dinis

Timing of Early Cretaceous angiosperm diversification and possible links to major paleoenvironmental change

Palynological records from the Western Portuguese and Algarve basins (Portugal) provide new insights on the timing and pattern of the early diversification of angiosperms (flowering plants) and its relationship to global environmental perturbations during the late Early Cretaceous. Angiosperm pollen displays a stepwise increase in both diversity and relative abundance during the late Barremian to middle Albian interval (ca. 124–104 Ma), reflecting the incipient radiation of flowering plants in lower midlatitude floras. Our results provide new evidence for the age interpretation of the previously described angiosperm mesofossil floras and associated in situ pollen assemblages from the Western Portuguese basin, until now interpreted as Barremian or possibly Aptian in age. Biostratigraphic and sedimentologic evidence indicates a post-Aptian age for these assemblages, hence demonstrating a major radiation phase of angiosperms during the early Albian. Correlation of the angiosperm pollen record with data on global paleoenvironmental changes suggests a link between the rapid adaptive radiation of flowering plants and major climatic and oceanographic perturbations during the late Early Cretaceous.

Le Bassin lusitanien (Portugal) à l'Aptien supérieur–Albien : organisation séquentielle, proposition de corrélations, évolution

The Lusitanian Basin (Portugal) during the late Aptian-Albian: sequential arrangement, proposal of correlations, evolution. Three transgressive-regressive 2nd-order cycles were identified in the Upper Aptian-Albian fluvial and marine deposits of the Lusitanian Basin. Its widespread nature, probably including eustatic origin, allows correlation between the southern package, with precise stratigraphic positioning, and the northern series with a poorly constrained age. The main unconformities can be related to the onset of an oceanic crust, in the western margin of Galicia during the Late Aptian, in the bay of Biscay during the Early Albian, and, to the northwest of the Galicia triple point, during the Middle to Late Albian transition, and, at the Albian-Cenomanian boundary, to a probable compressive event with Africa due to the

Climate and vegetation history of western Portugal inferred from Albian near-shore deposits (Galé Formation, Lusitanian Basin)

The late Early Cretaceous greenhouse climate has been studied intensively based on proxy data derived essentially from open marine archives. In contrast, information on continental climatic conditions and on the accompanying response of vegetation is relatively scarce, most notably owing to the stratigraphic uncertainties associated with many Lower Cretaceous terrestrial deposits. Here, we present a palynological record from Albian near-shore deposits of the Lusitanian Basin of W Portugal, which have been independently dated using Sr-isotope signals derived from low-Mg oyster shell calcite. 87 Sr/ 86 Sr values fluctuate between 0.707373 ± 0.00002 and 0.707456 ± 0.00003; absolute values and the overall stratigraphic trend match well with the global open marine seawater signature during Albian times. Based on the new Sr-isotope data, existing biostratigraphic assignments of the succession are corroborated and partly revised. Spore-pollen data provide information on the vegetation community structure and are flanked by sedimentological and clay mineralogical data used to infer the overall climatic conditions prevailing on the adjacent continent. Variations in the distribution of climate-sensitive pollen and spores indicate distinct changes in moisture availability across the studied succession with a pronounced increase in hygrophilous spores in late Early Albian times. Comparison with time-equivalent palynofloras from the Algarve Basin of southern Portugal shows pronounced differences in the xerophyte/hygrophyte ratio, interpreted to reflect the effect of a broad arid climate belt covering southern and southeastern Iberia during Early Albian times.

Integrated stratigraphy of shallow marine Albian strata from the southern Lusitanian Basin of Portugal

Stratigraphic age assignment of Cretaceous shoal-water deposits is notoriously difficult and often hampered by the lack of typical index fossils and the prevalence of sedimentary gaps. Here, we present new bioand chemostratigraphic data for three sections located in the Lusitanian Basin, Portugal, composed of Albian strata. Sections are correlated and dated using dinoflagellate cyst biostratigraphy, strontium-isotope stratigraphy based on oyster and rudist shells and carbon-isotope stratigraphy. The measured Sr-isotope values from pristine shells are in line with global open marine 87Sr/86Sr values from the Albian. Correlation of the Portuguese C-isotope curve with hemipelagic Albian reference records and the presence of typical Albian dinoflagellate cysts further constrain the age of the different sections. The proximal-marine and thick (~ 190 m) Sao Juliao section serves hereby as reference curve. Correlation with the independently well-dated and more distal Guincho section in the Lusitanian Basin slightly revise the age of the Sao Juliao and Magoito sections compared to previously published results. Furthermore, our findings demonstrate the time-transgressive nature of marine deposition in the southern Lusitanian Basin. The onset of marine conditions in the Agua Doce Member and the deposition of rudist bearing carbonates of the Ponta da Gale Member are diachronous and started significantly earlier in the southernmost part of the basin compared to the north. In summary, the combined geochemical and biostratigraphic results provide an enhanced time control and slightly revise the age of the sections in comparison to previously published studies while providing lithological descriptions, Sr-isotope derived ages and carbon-isotope records. Furthermore, the carbon-isotope record of Sao Juliao can be correlated with Italian (Umbria-Marche Basin) and French (Vocontian Trough) sections and highlights the applicability of shallow marine deposits as chemostratigraphic archives.

Palaeoenvironmental significance of clay minerals in Upper Cenomanian–Turonian sediments of the Western High Atlas Basin (Morocco)

Abstract Upper Cenomanian-Turonian clay mineral assemblages of sediments cropping out in the Western High Atlas basin are studied in four sections. Smectite and mixed-layer illite-smectite (I-S) have been identified as major constituents of the deposits. The composition of clay associations in black shales and associated sediments varies considerably according to age, but usually depends either on the general lithology, the abundance of organic matter, or the depth of burial. A distinct correlation is evident between clay mineral distribution and sea-level. Smectite and mixed-layer I-S with greater percentages of smectite layers increase in sediments deposited during transgressive periods, whereas they decrease progressively in the shallower facies deposited during regression in favouij of illite and mixed-layer I-S with a greater percentage of illite. The vertical evolution and lateral distribution of clay assemblages and their relationships with sea-level as well as the palaeogeographic conditions prevailing during the Late Cenomanian-Turonian period (flattened topography and arid climate), indicate a detrital origin of the smectite minerals and a distribution pattern controlled by differential settling processes.

A erosão nas praias do Cabo Mondego à Figueira da Foz (Portugal centro-oeste), de 1995 a 1998

EnglishA winter storm followed by unusual wave characteristics during 1996-1998 caused intense erosion of the Cape Mondego-Figueira da Foz beaches. This coast located southwards of an important natural headland, showed widespread beach erosion in a negative sedimentary budget (sand starvation) caused by an unusual mean direction of the waves (reduction of the NW and increase of the SW). The main effect on the coastal morphology was a large erosion of the beach sand which progressively lead to the destruction of a roadway seawall built on the beach sand. Planning and management of this coast should include higher restrictions to human activities on the coast (constructions, sand mining, etc.) and rivers, but als orequest monitoring studies to understand rapid sedimentary evolutions and to improve the knowledge of the sedimentary dynamics which can optimise coastal antrophic interventions in order to avoid risks, expensive repairs and negative impacts to adjacent beaches. portuguesDescreve-se a intensa erosao que desde finais de 1995 afectou o litoral entre o Cabo Mondego e a Figueira da Foz, focando em particular o recuo da linha de costa verificado com a progressiva perda de areia da praia, seguida do desmoronamento do enrocamento da marginal oceânica a norte de Buarcos e, posteriormente, da erosao na faixa arenosa entre Buarcos e Figueira da Foz. Alem de uma periodica monitorizacao foi feita analise de dados da ondulacao, mares, caracteristicas dos sedimentos e volumes de extraccao de areia na praia. Tendo em conta a influencia relativa de parâmetros tais como o fornecimento sedimentar, deriva litoral e caracteristicas da agitacao maritima, compara-se a evolucao deste sector litoral com a dos adjacentes e apresenta-se um modelo explicativo para este intenso fenomeno erosivo local. Concluiu-se que a continua erosao destas praias verificada apos o temporal de Janeiro de 1996, foi essencialmente devida uma alteracao das caracteristicas habituais da ondulacao; os rumos medios mais rodados para W reduziram a transposicao de areia para sul do Cabo Mondego, induzindo um defice sedimentar no seguinte troco costeiro.

Preliminary Magnetostratigraphy for the Jurassic–Cretaceous Transition in Porto da Calada, Portugal

We present a stratigraphic log supporting a preliminary magnetostra- tigraphy of a Tithonian-Berriasian section in Porto da Calada (Portugal). Based on biostratigraphy and reversed and normal magnetostratigraphy, the location of the Tithonian-Berriasian boundary is tentatively located at ca. 52 m, not in dis- agreement with former proposals. Due to the occurrence of later remagnetization (diagenesis), the magnetostratigraphic definition of the Tithonian-Berriasian sec- tion at the Cabo Espichel (Portugal) location was not able to be established.

Clastic Cave Sediments and Speleogenesis of the Buraca Escura Archaeological Site (Western-Central Portugal)

A new geomorphological and structural cave survey, as well as a sedimentological and stratigraphic analysis of clastic cave sediments and local post-Jurassic siliciclastic covers, was performed at the Buraca Escura archaeological site (Poio Novo valley, Sico Massif, western–central Portugal). Provenance and endokarstic transport were investigated by examining clastic cave sediments and making comparisons with new and published data on the siliciclastic regional covers. A framework for speleogenesis, beginning during the Late Cretaceous–Miocene, is established.

Clays and Vegetation: Comparing Palaeoclimatic Signatures in the Portuguese Lower Cretaceous

We collected a set of 120 clay samples with precise stratigraphic locations from the Lower Cretaceous coastal outcrops of the Ericeira area (western Portugal). The kaolinite versus illite dominance can be considered as revealing wet or dry climates, respectively, prevailing in the watershed. Swelling clays are associated with seasonally dry climates. However, since hydrodynamics and rejuvenation events also control clay associations, the relative role of climate versus depositional setting is still to be fully deciphered. As the onshore Lower Cretaceous of western Portugal is a key area for studying the Early Cretaceous initial diversification of angiosperms, several well-studied floras are summarized and their environmental interpretations presented.

Lower Cretaceous Pollen-Spore and Mesofossil Associations of the Bombarral Formation (Lusitanian Basin, Western Portugal)

The Lower Cretaceous of the Lusitanian Basin (western Portugal) contains rich assemblages of plant remains. The study of the palynological and mesofossil flora of the Berriasian Bombarral Formation in Vale Painho, near Juncal, contributes to ascertaining the environmental conditions during deposition, the vegetation diversity, and the unit’s age. The fossil site is just below the base of the Figueira da Foz Formation, a basin-wide breakup paraconformity. Regional correlation with biostratigraphically dated units (Lourinha p.p., Farta Pao, Porto da Calada, and Serreira) points to a Berriasian age for the top of the Bombarral Formation. The Vale Painho palynological assemblage is clearly dominated by fern spores and gymnosperm pollen. The mesofossil flora is characterized by seeds of conifers or taxa related to the Bennettitales– Erdtmanithecales–Gnetales (BEG) group, in agreement with palynomorphs. No angiosperm remains were recognized. The assemblage is very similar to the Berriasian to Valanginian Bornholm flora (Denmark). Plant features and sedimentary proxies indicate a hot climate with marked seasonality in precipitation.