The parallel run of Angiosperms and OAEs: Coincidence or causal effects? Current research projects in Portugal

The Portuguese Cretaceous is worldwide known since the late 19th century, and namely the studies on plant macroremains become classics in palaeobotany. Over the past twenty-five years, the discovery of well preserved angiosperm mesofossil floras with flowers, fruits and seeds, coupled with pollen, have provided an extremely fast progress on the understanding of angiosperms systematics and diversity. Despite that fact, little attention was dedicated to correlate the palaeoenvironmental aspects to the angiosperm radiation record. Recently, some studies proved that the Portuguese Cretaceous palaeofloral record is well suited for studies aiming to enlighten the relationships between environmental – global and or regional - and phylogenetic changes. We admit as initial premise that the global biosphere-atmosphere-ocean cycle is a fundamental control on the evolution of the vegetation, but also receiving its feed-back. This cycle and its main transfers are currently addressed by 13C chemostratigraphy. Accordingly, two projects were funded by the Portuguese Science Agency (FCT – Fundação para a Ciência e a Tecnologia): ANGIOGAL – “The emergence of angiosperms and the Cretaceous ecosystem changes in Portugal”, started in 2010; CretaCarbo – “The record of coupled oceanic-atmospheric changes analyzed by carbon isotopes and palaeobotany in the Portuguese mid-Cretaceous: chemostratigraphy and palaeoecology”, to start in 2011. Both projects are developed in the Estremadura and Beira Litoral regions of West Central Portugal, between Arrábida and North of Aveiro, focusing the stratigraphic record of the Barremian-Turonian interval. These deposits were selected due to a set of favourable conditions:- positioned in the transition between the Tethyan and the Atlantic Boreal realms; - located between the warm-humid and the hot-arid mid-latitude belts; - several good and continuous exposures; - a significant number of previous studies on stratigraphy, sedimentology and palaeontology; - proved existence of angiosperms (palyno, meso and macroremains); - well-established lithostratigraphic framework; - field and age correlation of continental, transitional and nearshore deposits; - nearshore to continental siliciclastic successions rich in plant debris suitable for C-isotopic studies; - nearshore to transitional carbonates suitable for Ccarb-isotopic studies; - an excellent knowledge of the focused units and regional geology by the team. This twin projects will use several methods: - I. Palaeobotanical studies of macroremains, mesoremains and palynomorphs. - a. Systematics - the description and phylogenetic analyses of new taxa; - b. Palaeoenvironmental analysis based on community composition and significance of physiological/morphological features. - II. Geological studies of palaeobotanical sites and reference sections. - a. Lithostratigraphic and chronostratigraphic setting; - b. Lithofacies, depositional architecture and palaeosoils/palaeoweathering; - III. Environmental proxies. - a. Bulk and clay mineralogy, and heavy mineral analysis; - b. 13C chemostratigraphy based on terrestrial organic matter and marine carbonates. We will test or find new hypotheses on the ecological-adaptative evolution of angiosperms, against: - the fossil record of angiosperms and other plant fossils from the Portuguese Early and mid- Cretaceous sequence; - the hypothesis of a relationship with the break-up of Gondwana, when regional climate changed from continental to more humid conditions; - the swing of the analyzed area between the Northern Mid-Latitude Warm Humid Belt and the Northern Hot Arid Belt; - the establishment of new topographies, due to tectonic movements; - global coupled oceanic-atmospheric changes, in particular the record ofOceanic Anoxic Events (OAEs) as recorded in the 13C signature. Other main targets of the projects are based in 13C chemostratigraphy, addressing the following questions: - Are the 13C records of shallow marine carbonates and terrestrial vegetation in phase, reflecting global carbon cycle perturbations of the entire ocean-atmosphere system? - How global and how local are the identified carbon isotope shifts and what factors drive local/regional variations? - Can the obtained 13C curves be used as a regional chemostratigraphic references for correlation despite various sedimentary gaps, and contribute to global standard curves? - The completeness of continental vs. marginal marine vs. deep marine record.

In this communication we will present the above questions and methods, as well as the state-of-the-art of stratigraphy, sedimentology and palaeontology. In particular, the chrono and lithostratigraphic settings, the significant biostratigraphy, the sections logs, the palaeoenvironmental interpretations (depositional systems and climate), the 2nd and 3rd order sequences, the sampling strategy, and the 13C curves published so far.