AJF Silva(1)

A BoOom Sediment Distribu*on Map for the Portuguese Con*nental Shelf in ArcGIS Format
A. J. F. Silva(1), M. R. Azevedo(1), R. Martins(2), R. Mamede(2), F. Ricardo(2), L. Magalhães(2),
P. Monteiro(3), L. Bentes(3), J. M. S. Gonçalves(3), V. Quintino (2), A. M. Rodrigues(2) & R. Freitas(2)
(1) Departamento de Geociências, GeoBioTec, Universidade de Aveiro, Portugal
(2) Departamento de Biologia, CESAM, Universidade de Aveiro, Portugal
(3) Centro de Ciências do Mar CCMAR/CIMAR, Universidade do Algarve, Portugal
1. BACKGROUND AND OBJECTIVES
This work presents a simplified map of the spa4al distribu4on of surficial sediments and rock outcrops along the Portuguese con4nental shelf in ArcGIS format (Fig. 1). Grain size data for nearly 500 samples of soG boHom shelf sediments collected in the scope of the MeshAtlan4c, RENSUB and ACOSHELF projects were classified according to a modified version of the FOLK classifica4on system and used to create a new sediment distribu4on map and develop an easy-­‐
to-­‐use GIS interface. The GIS interface will be available in the MeshAtlan4c website (hHp://
www.meshatlan4c.eu/), as part of a global broad scale habitat map for the Atlan4c Area. Preliminary map prepara4on involved scanning, georeferencing and digi4zing of pre-­‐exis4ng base maps from the Portuguese Hydrographic Ins4tute (INSTITUTO HIDROGRÁFICO, 1985, 1986, 2005, 2010 a,b,c) and harmoniza4on with other published and non-­‐published cartographic informa4on (e.g. DIAS & NITTROUER, 1984; POMBO, 2004; PINTO, 2006; OLIVEIRA et al., 2007; GONÇALVES et al., 2010; MARTINS et al., 2012). The new sediment distribu4on map shown in Figure 1 results from the combina4on and harmoniza4on of the exis4ng cartographic informa4on with the textural domains (coarse sediment, mixed sediment, sand, muddy sand, sandy mud and mud) defined by the samples analysed during the present inves4ga4on. 2. GRAIN SIZE ANALYSIS AND SAMPLE CLASSIFICATION
Grain-­‐size analysis was performed using dry and wet sieving following the procedure described by QUINTINO et al. (1989). The procedure includes chemical destruc4on of organic maHer with H2O2, chemical dispersion with tetra-­‐sodium pyrophosphate, separa4on of the mud frac4on by wet sieving and dry sieving of both sand and gravel frac4ons. Raw grain-­‐size data were expressed as weight percentages and classified according to a modified version of the Folk classifica4on system (Figs. 2 and 3). GRAVEL
0
0.1
0.2
Figura 2: FOLK CLASSIFICATION SYSTEM
(simplified version)
0.3
0.4
0.5
MIXED SEDIMENTS
0.6
0.7
Figure 1. Preliminary map of the spa*al distribu*on of surficial sediments and rock outcrops along the Portuguese Con*nental Shelf. Spa*al Reference: UTM, WGS 1984 (modified from published maps from the Portuguese Hydrographic Ins*tute – IH) 0.8
0.9
MUD 1
SAND
MUDS
SANDY MUDS
MUDDY SANDS
GRAVEL
GRAVEL
0
(a)
(b)
0.1
0.2
that: 0.2
0.3
0.4
0.7
MIXED SEDIMENTS
represented in the southern shelf; S
S
0.6
NT
ME
0.5
NT
ME
MIXED SEDIMENTS
the Portuguese shelf, to the south of the Nazaré and Setúbal canyons, and are sparsely I
ED
I
ED
0.5
• the coarser deposits occur mainly in the inner and mid-­‐shelf of the northwestern sector of ES
RS
ES
RS
0.4
A
CO
A
CO
0.3
0.7
0.8
• sand banks dominate the near shore shelf; 0.8
0.9
0.9
MUD 1
MUDS
Overall, the boHom sediment distribu4on paHerns for the Portuguese Con4nental Shelf show 0
0.1
0.6
3. CONCLUSIONS
SANDS
SANDY MUDS
MUDDY SANDS
SAND MUD 1
MUDS
SANDS
SAND
SANDY MUDS
MUDDY SANDS
SANDS
GRAVEL
• muddy sands characterize the deeper shelf; • patches of sandy mud and mud reflec4ng a less energe4c hydrodynamic regime cover a 0
large sector of the southern shelf and areas located off the major rivers mouths in the 0.1
(c)
0.2
A
CO
0.3
ES
RS
0.4
MIXED SEDIMENTS
• rock outcrops are unevenly distributed throughout the en4re shelf.
NT
ME
0.5
S
0.6
• mixed sediments are residual; I
ED
Figure 3: (a) Coarse and
mixed sediments; (b) sands
and muddy sands; (c) muds
and sandy muds
western shelf; 0.7
0.8
0.9
SAND
MUD 1
MUDS
SANDY MUDS
MUDDY SANDS
SANDS
ACKNOWLEDGMENTS
This work was supported by the following research projects: MeshAtlan4c (Atlan4c Area Program 2009-­‐1/110 MeshAtlan4c), ACOSHELF (POCI/MAR/56441/2004–PPCDT/MAR/56441/2004) and RENSUB (ARH Algarve -­‐ POVT/QREN). A.J.F. Silva and F. Ricardo benefited from MeshAtlan4c research grants. R. Mar4ns and R. Mamede benefited from PhD grants (SFRH/BD/
44231/2008 and SFRH/BD/74312/2010, respec4vely) awarded by the Portuguese Founda4on for Science and Technology (FCT). European Union
European Regional
Development Fund
REFERENCES
DIAS, J. M. A. & NITTROUER, C. A. (1984) – Con4nental shelf sediments of northern Portugal. Con*nental Shelf Research, vol. 3, p. 147-­‐165. FOLK, R.L. (1965). Petrology of Sedimentary Rocks, Hemphill. GONÇALVES, J.M.S., MONTEIRO, P., AFONSO, C., OLIVEIRA, F., RANGEL, M., MACHADO, M., VEIGA, P., LEITE, L., SOUSA, I., BENTES, L., FONSECA, L. & ERZINI, K. (2010) – Cartografia e caracterização das biocenoses marinhas da Reserva Ecológica Nacional Submarina entre a foz do Rio Arade e a Ponta da Piedade. Relatório Final. ARH Algarve. CCMAR, Faro, 122 pp. + Anexos. INSTITUTO HIDROGRÁFICO (1985; 1986; 2005; 2010 a, b e c) – Carta de Sedimentos Superficiais da Plataforma Con4nental, Escala 1:150.000: Folha SED 1 (Caminha -­‐ Espinho), Folha SED 2 (Espinho -­‐ Cabo Mondego), Folha SED 4 (Cabo Carvoeiro -­‐ Cabo da Roca), Folha SED 5 (Cabo da Roca -­‐ Cabo de Sines), Folha SED 6 (Cabo de Sines -­‐ Cabo de São Vicente), Folha s SED 7 e 8 (Cabo de São Vicente -­‐ Rio Guadiana). MARTINS, R., AZEVEDO, M. R., MAMEDE, R., SOUSA, B., FREITAS, R., ROCHA, F., QUINTINO, V. & RODRIGUES, A. M. (2012) – Sedimentary and geochemical characteriza4on and provenance of the Portuguese con4nental shelf soG-­‐boHom sediments. Journal of Marine Systems, 91, 41–52. OLIVEIRA, A., SANTOS, A. I., RODRIGUES, A. & VITORINO, J. (2007) – Sedimentary par4cle distribu4on and dynamics on the Nazaré canyon system and adjacent shelf (Portugal). Marine Geology, vol. 246, p. 105-­‐122. PINTO, C. (2006). Cartografia geológica da reserva ecológica nacional submarina do Algarve central. Faro, Universidade do Algarve, Centro de Ciências do Mar, 110 pp. POMBO, J. (2004) – Sedimentos Superficiais da Plataforma Con4nental Portuguesa entre o Cabo Mondego e S. Mar4nho do Porto. MSc Thesis, Universidade de Coimbra, 185 pp. QUINTINO, V., RODRIGUES, A. M. & GENTIL, F. (1989) – Assessment of macrozoobenthic communi4es in the lagoon of Óbidos, western coast of Portugal. Scien*a Marina, 53, 645–654.