37 macla nº 13. septiembre ‘10 revista de la sociedad española de mineralogía sONT Mineralogy of Methane- Related Sediments of the Atlantic Moroccan Shelf / NARJISSE ALAOUI MHAMMEDI (1), RUBÉN MARTOS VILLA (1,*), CARMEN FALAGÁN (1), M.PILAR MATA (2), LUIS SOMOZA (2), NIEVES LÓPEZ-GONZÁLEZ (3), DAVID CASAS (2), ANGEL SÁNCHEZ-BELLÓN (1) INTRODUCTION. The Gulf of Cadiz is one of the most important areas to study mud volcanoes and fluid venting related structures. Most of them are clustered in vast fields in the Spanish, Portuguese and Moroccan margins and are located at different depths. The occurrence of these features is linked to the very complex geological evolution of this area and the presence of the Olistostrome Unit (Medialdea et al., 2009 among others). Although most of the studies have focused on the microbiological activity on these environments, the study of the mineralogical composition of mud volcanoes can provide us valuable information as it is related to the nature and origin of the parent layers feeding these structures, the interactions with deep fluids and with diapiric structures. The published mineralogical data of the mud volcanoes situated in the Moroccan fields are still rare (Mhammedi et al., 2008). Thus, the aim of this work is to present the preliminary results of bulk mineralogy of Meknes mud volcano and of a possible near gas-related structure, and to compare them with the mineralogical results of other gas- related sediments of the gulf of Cadiz, of the Iberian margin, in order to determine if there is any resemblance or any connection between the source units of the mud volcanoes of different areas of the Gulf of Cádiz (Fig. 1). MATERIALS AND METHODS. The Meknes mud volcano was first discovered during the TTR 14 survey in 2004 on board O/V Pr Logachev. It presents one central pear shaped crater at 650 m water depth, and a width/mwd of 1 km. Tg 3 Tg 4 fig 1. Geological setting of the area showing the location of the studied cores (blue arrows) (From Medialdea et al, 2009). The two gravity cores (TG3 and TG4) studied in this work were collected during the oceanographic mission MVSEIS/08 on board of R/V Hespérides. TG4 was taken on the top of the mud volcano Meknes (650 mwd) and is constituted by two units: a mud breccia and a foraminifera-rich hemipelagic unit at top. TG3 was taken on a possible diapiric structure at 600 m mwd, and is essentially made of brownish mud. Both cores were sampled on board every 10 cm. The bulk mineralogical analysis, X- Ray Powder diffraction (XRD) was performed with a Bruker instrument of the University of Cádiz. A microscopic study of smear slides were made in order to determine the different biogenic, clastic and authigenic components of the sediments. Total organic carbon (TOC) and organic matter palabras clave: volcanes de fango, mineralogía, Golfo de Cádiz key words: mud volcanoes, mineralogy, gulf of Cadiz resumen SEM 2010 * corresponding author: ruben.martos@uca.es (1) Departamento de Ciencias de la Tierra, Fac. Ciencias del Mar y Ambientales. Univ. Cádiz. Campus Rio San Pedro. 11510, Cádiz (España) (2) Instituto Geológico y Minero. C/ La Calera, 1, Tres Cantos. 28760, Madrid (España) (3) Instituto Español de Oceanografía, Centro Oceanográfico de Málaga, Puerto Pesquero s/n, Fuengirola. 29640, Málaga (España) fig 2. Vertical profiles of bulk mineralogy of TG4 (Meknes mud volcano). Total sulfur (S, %), Organic Matter content (OM, %) and Total organic Carbon / Total Nitrogen (TOC/N) are also shown.