Postglacial sea-level rise and sedimentary response in the Guadiana Estuary, Portugal/Spain border

Abstract

The study of sedimentological features, foraminifera and molluscan fauna in samples recovered from four rotary boreholes permitted, after 14C dating, the first assessment of the post-glacial transgression in Guadiana River Estuary. The Holocene sequence is underlain by coarse sediments from delta fan enclosing continental swamp deposits dated 16 980 year BP. The Holocene sedimentary sequence was deposited either directly on this delta fan gravels or on top of fluvial sands deposited probably between 11 000 and 10 000 yr BP. An accelerated phase of the estuary infilling by clayey sediments containing the salt marsh foraminifer Trochammina, began ca. 9800 year BP, when sea level was about 39 m below present. Between 7500 and 7000 year BP, the central part of the estuary started to accommodate coarser sediments, partially introduced from the continental shelf. The first phase of Holocene sea-level rise at a rate of 0.85 m/century terminated ca. 6500 year BP. Since then, lagoonal sediments in the vicinity of the estuary have been enclosed behind sand spits and predominantly sandy sedimentation was initiated within the estuary. After a second phase of slower rise at the rate of 0.3 m/century, which lasted until ca. 5000 year BP, the sea approached the present level.

Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast, Southern Portugal

“…when the local continental sources of sand such as the sandy cliffs of the Western Algarve (Granja et al, 1984) could supply the eastward longshore current with clastic material. The present annual volume of sand transported eastwards along the Algarve coast and accumulated at the Guadiana Estuary is estimated to be 1.7 Â 10 5 m 3 (Boski et al, 2002). As may be deduced from the sequence of three dated points (at 2, 5.8 and 7.5 m), the bar sediments have been accumulated in several pulses of accretion with sandy material transported through the tidal inlet of the lagoon.…”

Taxonomy, ecology and biogeographical trends of dominant benthic foraminifera species from an Atlantic-Mediterranean estuary (the Guadiana, southeast Portugal)

“…; 4-dorsal view; 5-ventral view; 6-7-Helenina anderseni (Warren, 1957); 6-dorsal view; 7-ventral view; 8-Haynesina depressula (Walker and Jacob, 1798) side view; 9-Haynesina germanica (Ehrenberg, 1840) side view; 10-Elphidium advenum (Cushman, 1922) side view; 11-Elphidium excavatum (Terquem, 1875) Jones (1994) and the Ellis andMessina (1942-2012) online catalogue. The foraminiferal collection gathered during the study of Guadiana River paleoenvironments (Boski et al, 2002(Boski et al, , 2008 was the main reference for taxonomic identification.…”

“…With 35 taxa so far described, the genus Ammonia exhibits a significant range of morphological variants, making species-level identification particularly difficult morphologically (Holzmann et al, 1998;Langer and Leppig, 2000;Hayward et al, 2004). A variety of specific epithets for Ammonia morphotypes are in current use along the Guadiana Estuary and adjacent shelf (see Ruiz et al, 1996Ruiz et al, , 2005Boski et al, 2002Boski et al, , 2008Mendes et al, 2004Mendes et al, , 2012Delgado et al, 2012). Aiming to better understand Ammonia genetic affinities and clarify some of these taxonomic problems, we subjected three morphological variants to genetic analysis.…”

Morphological features and processes in the central Algarve rocky coast (South Portugal)

“…In their model, Inman et al (2003) used a 2% continental shelf slope (similar to the slope in sectors II and III) with a rapid rise in sea level interrupted by a still-stand, and obtained a shelf slope recedence of 15 m during the rapid rise of sea level and a wave-cut terrace 100 m wide during a simulated 1000-year duration still-stand. In the Algarve, sea level rose about 80 cm/1000 yrs between 8000 and 6000 yr BP, reducing to 30 cm/1000 yrs until around 3000 yr BP when it was very close to the present level (Pereira et al, 1993;Boski et al, 2002;Teixeira and Pinto, 2002a). Therefore, comparing these values with those obtained by Inman et al (2003), P0 platform (up to 150 m wide) could be scraped and smoothed mainly by wave erosion during the last ca.…”