Lateglacial and Holocene environmental changes in Portuguese coastal lagoons 1: the sedimentological and geochemical records of the Santo André coastal area

Abstract

The sedimentological and geochemical study of a core corresponding to sedimentation in the Santo André lowland since 14 000 BP allowed the reconstruction of environmental changes of this area and discussion of the relative importance of local versus global forcing factors responsible for its evolution. The pre-Holocene section of the core represents terrestrial sedimentation in a fluviatile environment, contemporaneous of a low sea level and a distal shoreline. Sediment inputs were terrestrial and resulting from intensive weathering and high erosion rate in the adjacent watershed. During the Early Holocene ( c. 10 020 to 5380 BP) the sea invaded this lowland and defined an open marine shallow environment corresponding to a wide gulf which has been disturbed by multiple terrestrial inputs that might have been induced by massive episodes of fluvial discharge. The first symptoms of confinement were noticed close to 5400 BP, and c. 5380 BP a major environmental threshold occurred (possibly reflecting the marked deceleration of the sea-level rise rate) corresponding to the establishment of an efficient detrital barrier that completely isolated the bay and changed this lowland into a closed coastal lagoon. After 5380 BP, the lagoonal environment evolved as a function of local forcing factors, among which the frequency and efficiency of exchanges with the ocean predominate: until c. 3570 BP the lagoon was restricted, fed by fresh water and terrestrial sediment inputs; a second episode of lagoonal sedimentation lasts until c. 1620 BP, reflecting brackish conditions and increase in marine influence due to a reduced efficiency of the barrier. The upper section of the core represents the final stages of filling of the lagoonal margin by fluvial activity. Human settling and intervention in the barrier are possible causes of a short-lived return to brackish conditions recorded in the uppermost sediment unit of the core and of the dramatic increase of the sedimentation rates

Eucera bees (Hymenoptera, Apidae, Eucerini) preserved in their brood cells from late Holocene (middle Neoglacial) palaeosols of southwest Portugal

“…2003, 2007; Freitas et al . 2003; Ramos Pereira & Angelucci 2004; Neto de Carvalho 2009; Monge Soares et al . 2012; Figueiredo et al .…”

Integrated MASW and ERT Imaging for Geological Definition of an Unconfined Alluvial Aquifer Sustaining a Coastal Groundwater-Dependent Ecosystem in Southwest Portugal

“…The study area (Figure 1b) belongs to the western Mesozoic extensional margin of the Iberian Plate, which has had a long distensive tectonic and magmatic history from the Late Triassic up to the present [44,45]. Locally, the CSB includes the following synthetic succession from bottom to top [40,[46][47][48][49]: (1) Variscan crystalline bedrock includes (i) Devonian low-grade metapelites and quartzites, and (ii) Carboniferous low-grade metapelites, vulcano-sediments, and tuffites underlying to metapelites, greywakes, and conglomerates; (2) Mesozoic sedimentary cover includes (i) Triassic continental sandstones intruded by basaltic and doleritic dikes, and (ii) Lower Jurassic platform dolomites, carbonates, and marls; and (3) Upper Miocene to present sedimentary filling includes (i) Pliocene marine sandstones, biocalcarenites, and marls, (ii) Pleistocene continental fluvial terraces and clay-rich colluvials underlying to coastal sand dunes, and (iii) Holocene alluvial, lagoon, and beach sands sediments.…”

Late Pleistocene Landscape and Settlement Dynamics of Portuguese Estremadura

“…The PRC wetland (PC5) formed in a paleovalley connected to the Óbidos estuary, one of several structurally-controlled valleys on the margins of the Caldas da Rainha diapir subject to fluctuating water levels during late Quaternary climatic and sea-level change (Dinis et al 2006;Freitas et al 2003).…”