María José Machado

River response to Quaternary subsidence due to evaporite solution (Gállego River, Ebro Basin, Spain)

Abstract The stream terrace evolution of the Gallego river during the Quaternary was controlled by both climatic change and subsidence. Quaternary terrace deposits, overlying Tertiary clay and limestone, are between 2 and 5 m thick, whereas above evaporite formations the alluvial deposits may be as much as 110 m thick. Chronologically, the first period of alluvial thickening involved the stream terraces T2 (+ 105 m above the present thalweg), T3 (+ 95 m) and T4 (+ 85 m), which have been dated by paleomagnetic reversals as Matuyama (pre-780,000). The second subsidence period affected the deposits of the stream terrace T9 (+30), dated as Brunhes (post-780,000). In both thickening periods, the subsidence was due to solution of the underlying evaporite formations (halite and gypsum), presumably, during intervals of high water flow. In the proposed model, the valley subsidence was balanced by stream aggradation maintaining the river equilibrium profile. The subsidence recorded in the alluvial deposits shows a complex spatial and temporal evolutionary pattern and total subsidence was assumed to be equal to the alluvial thickening for each subsidence period, reaching up to 165 and 25 m, respectively.

Sandstone weathering processes damaging prehistoric rock paintings at the Albarracin Cultural Park, NE Spain

The rock paintings in cliff-foot caves of the Albarracin Cultural Park are known as some of the most important evidences of the Levantine prehistoric art of Spain (8000–3000 BP). The paintings are on sandstone (Buntsandstein facies) of Triasic age, which may develop intense weathering. The analysis of the variables controlling the weathering indicate that salt and wetting-drying weathering are responsible for granular disintegration and flaking, which lead to rock painting deterioration.

Investigating population structure of Sea Lamprey (Petromyzon marinus, L.) in Western Iberian Peninsula using morphological characters and heart fatty acid signature analyses.

This study hypothesizes the existence of three groups of sea lamprey Petromyzon marinus L. in Portugal (North/Central group, Tagus group, and Guadiana group), possibly promoted by seabed topography isolation during the oceanic phase of the life cycle. Within this context, our purpose was to analyze the existence of a stock structure on sea lamprey populations sampled in the major Portuguese river basins using both morphological characters and heart tissue fatty acid signature. In both cases, the multiple discriminant analysis revealed statistically significant differences among groups, and the overall corrected classification rate estimated from cross-validation procedure was particularly high for the cardiac muscle fatty acid profiles (i.e. 83.8%). Morphometric characters were much more useful than meristic ones to discriminate stocks, and the most important variables for group differentiation were eye length, second dorsal fin length and branchial length. Fatty acid analysis showed that all lampreys from the southern Guadiana group were correctly classified and not mixing with individuals from any other group, reflecting a typical heart fatty acid signature. Our results revealed that 89.5% and 72.2% of the individuals from the Tagus and North/Central groups, respectively, were also correctly classified, despite some degree of overlap between individuals from these groups. The fatty acids that contributed to the observed segregation were C16:0; C17:0; C18:1ω9; C20:3ω6 and C22:2ω6. Detected differences are probably related with environmental variables to which lampreys may have been exposed, which leaded to different patterns of gene expression. These results suggest the existence of three different sea lamprey stocks in Portugal, with implication in terms of management and conservation.

Geomorphology of the Adwa District

This chapter describes the geologic and geomorphic characteristics of the Adwa district and provides a reconstruction of the major phases of the long-term landscape evolution from the Late Proterozoic to the Quaternary. Two landscape features of the Adwa district exemplify the control of tectonic uplift and erosion, often in a feedback loop: the plateau landscape and river incision. The plateau landscape developed upon metamorphic, sedimentary and volcanic materials, with major contacts marked by planation surfaces correlative with major regional- and sometimes continental-scale unconformities. In the southern Adwa district, the most prominent landscape feature is a regionally extensive erosion surface bevelled across the Precambrian basement and later buried by Palaeozoic and Mesozoic sedimentary rocks. In the northern district, the flat-top horizontal structural plateaux are formed by the Mid-Cenozoic upper basaltic Trap sequence, intruded by trachyte and phonolite plugs originated during the Miocene and Pliocene volcanic activity, and a lower plateau developed over the laterised Adigrat Sandstone Formation. The post-Pliocene landscape evolution has led to exhumation of the former erosion surfaces and dissection of the drainage network. These stream channels have cut large amphitheatre headwaters and flow southwards to join the regional base level of the Weri River, a contributor to the Nile basin. The Quaternary sedimentary record in the Adwa area is composed by consolidated carbonate Late Pleistocene rocks (travertines), unconsolidated Pleistocene/Holocene alluvial fan deposits, Holocene fluvial deposits (river terraces and valley fill deposits) and historical to present-day colluvial deposits.