Análisis sedimentológico de las discontinuidades y depósitos asociados del Calloviense superior-Oxfordiense medio en la Cordillera Ibérica Noroccidental.

Abstract

irregular sedimentation during the upper Callovtm-middle Oxfordian in tbe Iberian basin resulted in a condensed level , which ineludes a set of unconformities and assoeiated stratigrapliic gaps. This condensed level has been studied in the Ricla-Vera del Moncayo area (NW Iberian Chain, Spain). Dur analysis is favoured by both excellent outcrop conditions, and time control based on aminonite biostratigraphy. Three unconformities related to subaerial exposure of the carbonate platform Lave been recognized. `[`hese exposure eventis resulted in the formation of both irregular karstic surfaces and scarce continental deposits (i.e.. meteorie cements>. During subsequent transgressive episodes, these surfaces were bioeroded and locally covered hy strornatolitcs. Thrce discontinuous levels of marine facies (np to 20 cm tIlick> are rccorded between these unconformities. Tliev consist of condensed scdiments coritaining fossil rernains of nectonie and planktonic groups as arii monites (generally, reworked internal moulds infilhng the erosional cavities>, belemnites and planktonic forams, lithoclasts and authigenic grains (berthierine, glauconite, chamosite>. Tlie larger interval of subaerial exposition corresponds to the CallovianOxfordian boundary (Laniberti and Mariae biozones>. Two further exposure events are recognized tit the late Early Oxfordian (upper pan of thc tordatum biozone> and early Middle Oxfordian (Upper part of the Plicatiis biozonc pp.>. Open marine sedimentation and fuli coionization by benthic marine fauna (rnainly siliceous sponges) was restore(l at the onset of the Transversarium bio-?one.