The NW Iberian river Miño terraces in a new perspective: tectonic implications

W. Viveen, R.T. van Balen, J.M. Schoorl, A. Veldkamp, D. Fernandez-Mosquera, J. Sanjurjo-Sanchez

Research output: Chapter in Book/Report/Conference proceedingAbstract

Abstract

The fluvial terrace staircase in the Galician/Portuguese Lower Miño region has been studied for a long time. Already in 1945 the first systematic study was made by Lautensach, followed in later years by e.g. Teixeira (1952), Nonn (1967) and Alves (2004). Those studies focused on either the Portuguese or Galician side of the river, or covered only a small area in the region. Investigation tended to be focused on either terrace height mapping or sedimentology. Due to the unfavorable conditions for fossil preservation, absolute ages for the Miño terraces are not known. Because of these restrictions, a coherent framework in which to place terrace formation is lacking. We re-mapped all terrace levels of the Lower Miño using a 5 m DEM, aerial photographs and field studies. Our analysis reveals that terrace distribution is strongly controlled by both small and large scale lineaments. Small lineaments are probably fractures in the granites underlying the terraces. The larger lineaments however, may represent faults. Their principal directions, N-S, NE-SW and E-W, coincide with known fault directions in the area (Pliego-Dones et al., 1972). Throughout the area these faults intersect, forming small rhomboidical structures in which conglomerates and clays are found. The termination of these structures usually marks a step in the landscape towards a new terrace level. Some terrace levels are unusually wide, sometimes up to 1 km. Inspection of the many outcrops and gravel mines in the region shows that the terraces are made up of predominantly homogeneous course-grained conglomerates and clay banks. Up to 30 m of deposits have been found in some mines, without the base of the terraces being visible. In the upper part of most outcrops, sediments with fluvial characteristics are found. These include clast imbrication, paleao-channels and channel leg deposits. Deposits in the lower part of the outcrops seem to lack these characteristics, especially in one of the larger mines. Preliminary results of quartz-OSL dating of a geomorphologically young terrace yields minimum ages of >100 ka. These results suggest that in the Lower Miño river basin, a large number of tectonic sub-basins are present, which are controlled by potentially active faults. The sediments found in these basins might therefore be much older basin infill than previously assumed. Correlation with other tectonic basins in NW Iberia points towards a possible Tertiary age. These sediments in turn, may be overlain by more recent alluvial deposits which form the current river Miño terrace staircase. References Alves, M.I.C. 2004. A sedimentação fluvial cenozoica na região do entre-douro-e-minho (NW de Portugal). p. 93-115, In M. A. Araujo and A. A. Gomes, eds. Geomorfologia do Noroeste da Peninsula Iberica. Faculdade de letras da universidade do Porto, Porto. Lautensach, H. 1945. Formação dos terraços interglaciarios do norte de Portugal e suas relaçoes com os problemas da epoca glaciaria. Publ. Soc. Geol. Portugal:5-44. Nonn, H. 1967. Les terrasses du rio Mino inferieur. Localisation et etude sedimentologique. Revue de geomorphologie dynamique 17:97-108. Pliego-Dones, D., J. Rubio-Navas, and J. Abril-Hurtado. 1972. Hoja 261 Tuy, In I.G.M.E., (ed.) Mapa geologica de España 1:50.000. Servicio de publicaciones del ministerio de industria y energia, Madrid. Teixeira, C. 1952. Os terraços da parte Portugesa do rio Minho Comunicações dos servicios geologicos de Portugal 33.
Original languageEnglish
Title of host publicationLong term River evolution and fluvial dynamics, Abstracts, Fluvial Archives Group (FLAG) Biennial Meeting, Vila Velha de Rodao, Castelo Branco, Portugal, 5-10 September 2010
EditorsM. Stokes, A. Gomes, P. Cunha
PublisherFluvial Archives Group (FLAG)
Pages12
Publication statusPublished - 2010
EventLong term River evolution and fluvial dynamics -
Duration: 5 Sep 201010 Sep 2010

Conference

ConferenceLong term River evolution and fluvial dynamics
Period5/09/1010/09/10

Fingerprint Dive into the research topics of 'The NW Iberian river Miño terraces in a new perspective: tectonic implications'. Together they form a unique fingerprint.

Cite this