FLUVIAL LIMESTONE TUFFS FROM THE S. PORTUGAL (LOULE-TAVIRA) AND N. MOROCCO (TETUAN): COMPARISON AND ENVIRONMENTAL IMPLICATIONS

Limestone tuff deposits precipitated in fluvial environments are widespread in the northern Morocco and the S Portugal. These deposits represent environmental conditions prone for the carbonate precipitation mainly in areas of Mesozoic limestone substratum with active water seepage from the aquifers. The mesoscopic and microscopic characteristics of tuff deposits from Tetouan (Morocco) and Loule and Tavira (Portugal) are very alike; namely on deposit types (e.g. phytoherm barriers; banded limestones with abundant vegetation macro-remains; carbonates precipitation as cement of some early alluvial conglomerates or interbedded alluvial deposits). The common textural features and macro-facies (e.g. banded calcite in regular layers ; moldic porosity; textures resulting from carbonate precipitation mediated by bacteriological activity) point to a similar origin of these limestone tuffs on both sides of Gibraltar Strait despite their slightly different climatic conditions that are influenced by the active inflow of surface Atlantic water towards the Mediterranean (for the Tetouan region) and by the Azores anticyclone (for the Loulé-Tavira region). The field observations show that the limestone tuffs precipitation is nowadays residual and radiocarbon dating of Portuguese deposits points to a chronological framework for their formation starting in the beginning of the post-Younger Dryas climatic recovery and ending around 2.5 ky BP. The oxygen stable isotopes data show a gradual change in the tuffs isotopic signature through the time interval during which the system remained active, without any particular record of climate events such as the 8.2 ka. The available data and those from monitored modern pluvial characteristics allow the speculation on the parameters controlling the limestone tuffs deposition on both northern and southern sides of the Gibraltar Strait during the Holocene. The carbonate deposition on fluvial systems, such as the studied ones, probably depends on the precipitation / evaporation balance leading to the availability and turbulence of the flowing water along the streams. Acknowledgments: This works was done with the financial support of the FCT Proc. 441.00 CNRST- MARROCOS and PTDC/CTE-GIX/117608/2010 projects and the SFRH/BD/62323/2009 grant

Indicadores del nivel del mar durante el MIS 5 y elevación tectónica en el Estrecho de Gibraltar (Norte de Marruecos)

This study investigates the morpho-sedimentary evidence of two highstands registered and dated during MIS 5 stage by U-series dating in the North of Morocco (Strait of Gibraltar). Bioerosive notch and mixed siliciclastic and carbonate deposits, high energy beaches with algal bioherms, were formed in coastal environments during MIS 5a. A sea-level altitude of +10 m asl was inferred for this substage. The record of MIS 5e-2 substage is less complete, consisting in upper foreshore and storm deposits located some meters above the sea-level (+13-15 m asl). A tectonic uplift rate of ~0.1 mm/yr has been estimated for the last 130 ky. This data is consistent with models of coastal uplifts elaborated for the Gibraltar Strait.Este trabajo analiza las evidencias morfosedimentarias de dos altas paradas del nivel marino datadas en el MIS 5 mediante series de U en el Norte de Marruecos. Durante el MIS 5a se formaron socaves bioerosivos (notches) y facies de playas de alta energía constituidas por depósitos mixtos siliciclástico-carbonatados. Una altura de 10 m snm ha sido estimada para esta etapa. El registro del MIS 5e-2 es menos completo, constituidos por depósitos de foreshore y de tormenta formados varios metros sobre el nivel del mar (+13-15 m snm). Se ha deducido una tasa de elevación tectónica de 0.1 mm/año para los últimos 130 ka. Estos datos son consistentes con los modelos previos de levantamiento tectónico elaborados para el Estrecho de Gibraltar.Ministerio de Ciencia, Innovación y Universidades CGL2010-15810/BT

Sedimentary evolution of Quaternary tufas and travertines (Tetouan-Northern Morocco): implications for earth processes and depositional systems.

The continental carbonates, such as travertine and tufa, are among the sediments recording climate change manly during Quaternary times. Their lithofacies and petrofacies are useful for understanding the related hydrologic, geomorphologic and climatic processes as well as the depositional palaeoenvironments. Thus, the present work deal with the analysis and interpretation of the main facies association of Tetouan city travertine cliffs and terraces. According to morphologic, sedimentologic and petrographic investigations coupled with 1/5000 scale mapping, four main facies associations were recognized and show from the top to bottom: i) barrage and cascade limestones, ii) base of the cascade limestone breccias and blocks, iii) lacustrine detrital deposits and iv) carbonate pedogenic crusts. The barrage facies associationis characterized by carbonate deposits with a wide textural features: a) massive micritic limestone, b) brecciated limestone with remnants of calcified leaves, stems of macrophytes and fresh-water gastropods, c) thin-layered calcite sheets (probably corresponding to ancient algal mats) or calcite layers to remnants of herbaceous plants, d) soft black pocket marls with remnants of calcified leaves, stems and mollusks (i.e. terrestrial and fresh-water gastropods). The base of the cascade facies association, located at the east and the central part of the escarpment, is made of fallen blocks detached from the carbonate build-up that constitutes the dam that are embedded in multi-colored crystalline travertine bands. The third facies association is constituted by detrital sediment strata with an obvious contribution from barrage and cascade limestones mainly supplied from the Dorsal calcaire relieves mainly made of calcacareous plateform deposits The fourth facies association correspond mainly to pedogenic carbonate crusts usually topping outcrops of lacustrine sediments, but also present in erosive surfaces or within cascade limestones. Vertical NNE-SSW fracture sets are found in the Oued Martil slope, fulfilled by carbonate crust-like material. Tetouan travertine petrofacies are mainly represented by: i) rolled crusts made of different morphological types: cylindrical, oncholites, flat and corrugated crystallized around various nucleus. ii) detrital fine to medium grained calcareous sands, iii) homogenous micritic facies with primary precipitation of micrite during periods of low flow velocities and calm waters and probably in relation to microbial activities, iv) micrite-coarse banded crystalline sheets consist of palisade calcite crystals related to cyclic changes in chemical, physical and/or environmental conditions or even diurnal cycles of microbial activity. In addition, this study has highlighted that Tetouan travertines may have formed under strong hydrodynamic environments within rapid water flow waterfalls intercalated with slower flow and calm waters periods. These travertines may also record the occurrence of seasonal climatic variations related to microclimatic fluctuation during part of the Holocene. In Southern Portugal the same type of Holocene terrestrial carbonate deposits, exhibit similarities in the petrofacies observed and in the facies association. A smaller urban coverage allows a detailed observation of the outcrops showing the existence of active and fossil incrusting systems fed by the Jurassic aquifers

Geomorphology, sedimentology and petrography of Quaternary travertines (Tetouan-Northern Morocco): implications for depositional paleoenvironments and climatic context.

The continental carbonates, such as travertine, are among the sediments recording climate change manly during quaternary times. Their lithofacies and petrofacies are useful for reading related hydrologic, geomorphologic, climatic processes and depositional palaeoenvironments. Thus, the present work deal with analysis and interpretation of the main facies association of Tetouan city travertine cliffs and terraces. According to morphologic, sedimentologic and petrographic investigations coupled with 1/5000 to scale mapping, four main facies associations were recognized and show from the top to bottom: i) barrage and cascade limestones, ii) base of the cascade limestone breccias and blocks, iii) lacustrine detrital deposits and iv) carbonate pedogenic crusts. The first facies association of barrage is characterized by travertinous limestones with a wide textural features: i) massive micritic limestone, ii) brecciated limestone with remnants of calcified leaves, stems of macrophytes and mollusks, iii) thin-layered parallel calcite sheets (probably algal mats) or calcite layers to remnants of herbaceous plants, iv) soft black pocket marls with remnants of calcified leaves, stems and mollusks (i.e. terrestrial and fresh water gasteropods). The second facies association of base of the cascade, located at the east and the central part of the escarpment, is made of fallen blocks embedded in multi-colored crystalline travertine bands. The third facies association is constituted by detrital sediment strata with an obvious contribution from barrage and cascade limestones. The fourth facies association show mainly crusts usually topping outcrops of lacustrine sediments, erosive surfaces on or within cascade limestones. Vertical NNE-SSW fracture sets are found in the Oued Martil slope, fulfilled by carbonate crust-like. Tetouan travertine petrofacies are mainly represented by: i) rolled crusts made of different morphological types: cylindrical, oncholites, flat and corrugated crystallized around various nucleus. ii) detrital fine to medium grained calcareous sands, iii) homogenous micritic facies with primary micrite precipitation occurred during lower flow and calmer waters probably in relation to microbial activities iv) Micrite-coarse banded crystalline sheets consist of palisade calcite crystals related to cyclic changes in chemical, physical and/or environmental conditions or even diurnal cycles of microbial activities. In addition, this study has highlighted that Tetouan travertines may have formed under strong hydrodynamic environments within rapid water flow waterfalls intercalated with lower flow and calmer waters periods. These travertines may also record occurrence of seasonal climatic variations related to microclimatic fluctuation during a part of the Holocene

Evidence of MIS 5 sea-level highstands in Gebel Mousa coast (Strait of Gibraltar, North of Africa)

The Last Interglacial is considered the most suitable episode from which to infer patterns of rapid sea-level change since its climatic conditions were similar to those of the present interglacial. However, specifying the true position of its sea level with high accuracy is very troublesome in the absence of sedimentological, erosional or even palaeontological markers. This study investigates the morphosedimentary evidence (beach deposits, cliff, notch and shore platform) of two highstands registered and dated during MIS 5 stage by U-series dating in the North of Morocco (Strait of Gibraltar). Bioerosive notches and mixed siliciclastic and carbonate deposits, high energy beaches with algal bioherms, were formed in coastal environments during MIS 5a. A sea-level height of +10 m asl can be inferred for this substage. The record of MIS 5e substage is less defined in the geomorphological record, consisting of backshore/foreshore deposits located at +13 to +15 m asl. A tectonic uplift rate of ~0.1 mm/yr has been estimated for the last 130 kyr. These data are consistent with models of coastal uplifting calculated for the Strait of Gibraltar.Ministerio de Ciencia e Innovación CGL2010-15810/BT