The Upper Neoproterozoic±Lower Cambrian sedimentary succession in the central areas of the Central Iberian Zone has been subdivided into 12 mostly siliciclastic lithostratigraphic units, ranging in thickness between 1800 and 3900 m. The lithology and facies of each unit are described and the facies associations are interpreted. The facies resulted mainly from turbidity currents and debris flows and, to a lesser extent, from submarine slides and traction flows. The facies associations suggest that sedimentation took place in slope and base-of-slope environments. Two depositional sequences are recognized, separated by a type-1 unconformity. The lower sequence is of Late Neoproterozoic age (units I±IV) and exhibits lowstand, transgressive, and highstand systems tracts. Most of the upper sequence is probably of Early Cambrian age (units V±XII). It begins at the base of unit V and possibly ends with the Tamames Limestone Formation. The upper sequence records a lowstand systems tract and minor-order sea-level oscillations. In the Cambrian units there are higher amounts of feldspar and smaller quantities of intrabasinal clasts than in the Neoproterozoic units. The modal data plot close to the Q±L and Qm±Lt sides of Q±F±L and Qm±F±Lt triangular diagrams, suggesting a provenance from a recycled orogen evolving into a provenance from a craton interior towards the top of the succession. The chemical results, based mainly on Al 2 O 3 , TiO 2 , Zr, and Nb abundances in shales from all the units, strongly suggest a gradual compositional change within this sedimentary succession. Together with the petrological data, the chemical results do not reveal any obvious coeval volcanic contribution to the sed-iments. On the basis of the chemical data, a comparison is made with other European zones containing detrital sediments composed of reworked crustal components.

No abstract

No abstract

No abstract

Sandstones and shales from the Upper Neoproterozoic (UN) succession in the Central Iberian Zone (CIZ) show parallel REE patterns and relatively restricted and similar ranges and average values of some element ratios such as Al 2 O 3 /TiO 2 , Ti/Nb, Eu/Eu*, (La/Yb)n, (Gd/ Yb)n and Th/U. This remarkable geochemical homogeneity for related medium-and fine-grained rocks is unusual, and strongly suggests a recycled source area. However, the Lower Cambrian (LC) equivalent rocks are, in general terms, geochemically less mature, more heterogeneous and more fractionated. Their average REE patterns are practically coincident, probably as a consequence of REE redistribution related to the reworking of sediments during a stage of sea level fall in Lower Cambrian times. Ti and Zr abundances, chemical index of alteration (CIA) values and element ratios such as Al 2 O 3 / TiO 2 , K/Rb, Ti/Nb and Rb/Zr can be used for discriminating purposes between the UN and LC siliciclastic rocks. Detrital zircons from a UN and a LC sandstone display morphological differences. However, U-Pb data are discordant and cannot be interpreted in a straightforward manner. Nevertheless, age data are compatible with a model in which the continent of Gondwana would have supplied zircons, showing a bimodal age distribution, in variable proportions to the respective sandstone units.

No abstract

No abstract

No abstract