Séquence de dépôts binaire et discontinuités associées Binary Sequence of Deposits and Associated Discontinuities

Une séquence de dépôts binaire a été élaborée à partir d’observations de terrain. Elle s’applique à différentes échelles et à différents milieux de dépôts. La séquence binaire est composée de deux séquences. Chacune d’elles est subdivisée en deux cycles. Les cycles inférieurs représentent les 3/5e en durée et les cycles supérieurs les 2/5e. Au total, cela fait quatre cycles. Dans le détail, cette séquence binaire comprend dix termes de faciès délimités par dix discontinuités dont quatre sont importantes. Ces dernières délimitent les quatre cycles. On distingue deux « maximum flooding surface » (m.f.s.) au centre des deux cycles supérieurs. <br> A binary sequence of deposits was elaborate starting from the observations of ground. It applies to various scales and various of deposits media. The binary sequence is made up of two sequences. Each sequence is subdivided in two cycles. The lower cycles account for the three fifths in duration and the higher cycles the remaining two fifths. On the whole, that made four cycles. In detail, this binary sequence includes ten terms of facies delimited by ten discontinuities of which four among they are significant. These last delimit the four cycles. One distinguishes two m.f.s. or maximum flooding surface in the center from the two higher cycles

Gypsum resources of Spain: Temporal and spatial distribution

Spain is one of the main gypsum producers in the world. Spanish gypsum reserves are large and a good knowledge of the location of the ore reserves permits to establish better exploitation strategies. Plotting the Spanish major gypsum outcrops, using a GIS base, helps to classify them by age, establish the main depositional character and determine the factors controlling their origin. Evaporitic deposits from Cambrian to Quaternary are preserved throughout Spain. The evaporites are formed by chemical precipitation of natural brines, either of marine or continental origin. The oldest evaporite vestiges in the Spanish geological record have been described in carbonate materials, as gypsum and anhydrite pseudomorphs, in Cambrian deposits of the Cantabro–Iberian basin (northern Spain). The first properly identified evaporite formation in Spain is located in the Triassic deposits that characterize central and northern Europe. In Spain, evaporites of this age appear well represented in 4394.5 km2 of outcrop area in the eastern part of the Iberian Peninsula. The Lower Jurassic (covering 1068 km2 of outcrop area) and the Cretaceous (covering 706.9 km2 of outcrop area) are periods of intense evaporitic sedimentation, and outcrops appear concentrated towards central and eastern parts of the Peninsula. More recently, in the Cenozoic, numerous continental and marine basins resulted from the tectonic activity produced by the Alpine Orogeny. Here, a combination of different factors produced thick and wide evaporite accumulations (outcrop surface is 13592.7 km2). In the Quaternary, evaporitic conditions are common in Spain, including various saline lakes (covering 1092.1 km2 of outcrop area) mainly in the Ebro basin and La Mancha zone. In addition, there are many artificial marine salinas. The evaporitic conditions in a basin strongly depend on factors such as climate, tectonics and brine composition. A study of the spatial distribution and age of the gypsum-bearing units in Spain suggests a wide variation in factors controlling the origin of gypsum deposits. The Spanish evaporite precipitation from Permian to Jurassic times was controlled by global conditions such as climate. They were formed during a global warming period. On the other hand, evaporites formed from late Cretaceous to Neogene were more influenced by regional factors that were related to the tectonic activity produced by the Alpine Orogeny. At present evaporite precipitation occurs due to the endorheic character of lakes in some parts of Spain