A mineralogical and geochemical approach to establishing a sedimentary model in a passive continental margin (Subbetic Zone, Betic Cordilleras, SE Spain)

Abstract

A B S T R A C T:The spatial and vertical distributions of six clay mineral assemblages were identified in the pelagic marls and marly limestones and in the Ammonitico Rosso of the Lower Jurassic in the Betic Cordilleras (SE Spain). The six assemblages contain varying proportions of illite, kaolinite, chlorite, smectite and mixed-layer illite-smectite. The clay mineralogy and the geochemical data, particularly for the rare earth elements, indicate that the sediments were deposited in a pelagic environment influenced by a nearby continent. The source areas were many and lithologically varied. Clay mineralogy and geochemistry are shown to be most useful in the reconstruction of the palaeogeography of a basin in a passive continental margin.At the beginning of the Jurassic a considerable marine transgression took place in the Betic Cordilleras and a shallow carbonate platform developed with episodes of tidal-flat and, locally, open-sea facies. The environment is interpreted as being that of a very shallow carbonate platform, the varying textures of which reflect different energy regimes according to their position relative to the tidal level (Garcia Hern~indez et al., 1980). The deposition of sequences of the Ammonitico Rosso facies and thick marine series of marls and marly limestones show that pelagic conditions were established in the Subbetic Zone from the Domerian onwards.In this paper we study the mineralogy and geochemistry of these facies with a view to understanding the palaeogeographic conditions that controlled their sedimentation, and also to locating the source-areas of these sediments.

First Data on Clay Mineral Assemblages and Geochemical Characteristics of Toarcian Sedimentation in the umbriamarche basin (central italy)

“…This can be seen by the high values for the detrital index (D) and the high concentration of REE (Table 3), both of whose values are much greater than those found in equivalent sediments from other correlative geological environments (Ortega Huertas et al, 1991b). As a parameter indicative of the degree of detrital influence in a basin, the data provided by the Ce/Ce* ratio agree with the foregoing.…”

“…Jenkyns, 1980;Vera, 1981). From a mineralogical and geochemical point of view, knowledge of Early Jurassic facies in the Betic Cordilleras is exhaustive (Palomo, 1987;Ortega Huertas et al, 1991b). This paper presents the first data on identical lithofacies in the Apennines.…”

Clay minerals in recent sediments of the continental shelf and the Bay of Cádiz (SW Spain)

“…The <2 ~tm fraction was separated by a standard sedimentation method (Tucker, 1988) and the mineralogical composition determined by X-ray diffraction analysis, using a Philips PW-1710 diffractometer with Cu-KQt radiation, automatic slit and graphite monochromator. Semiquantitative clay mineralogical composition was calculated using data from Schultz (1964), Biscaye (1965) and Ortega-Huertas et al (1991).…”

Utility of clay Minerals in the Determination of Sedimentary Transport Patterns in the Bay of Cadiz and the Adjoining Continental Shelf (SW-Spain)

“…Quantitative clay mineralogical composition was calculated by the classic method of area measurement of peaks, considering the different reflection capacities of the minerals [46,58,49]. The factor analysis (Principal Components Analysis) was used to establish the relation between different clay minerals and their associations [54].…”