No abstract

This paper develops a tectono -stratigraphic model for the evolution and drowning of Early Jurassic carbonate platforms.The model arises from outcrop analysis and Sr isotope dating of successions exposed in the Betic Cordillera in southeastern Spain. Here, an extensive Early Jurassic (Sinemurian) carbonate platform developed on the rifted Tethyan margin of the Iberian Plate.The platform was dissected by extensional faults in early jamesoni times (ca. 191 Ma) and again in late ibex times (ca.188 Ma) during the Pliensbachian stage. Extensional faults and fault block rotation are shown to control the formation of three sequence boundaries that divide the platform stratigraphy (the Gavilan Formation) into three depositional sequences.The last sequence boundary marks localised drowning of the platform and deposition of the deeper water Zegri Formation, whereas adjacent platforms remain exposed or continue as the site of shallow-marine sediment accumulation.This study is based on mapping, facies analysis and dating of platform carbonates exposed in three tectonic units within the zone: Gabar, Ponce and Canteras. Facies analysis leads to the recognition of facies associations deposited in carbonate ramp environments and adjacent to synsedimentary, marine, fault scarps. Sr isotope dating enables us to correlate platform-top carbonates from the di¡erent tectonic units at a precision equivalent to ammonite zones. A sequence stratigraphic analysis of sections from the three tectonic units is carried out using the facies models together with the Sr isotope dates.This analysis indicates a clear tectonic control on the development of the stratigraphy: depositional sequences vary in thickness, have wedge-shaped geometries and vary in facies, internal geometries and systems tracts from one tectonic unit to another. Criteria characterising depositional sequences and sequence boundaries from the Gabar and Ponce units are used to establish a tectono -stratigraphic model for carbonate platform depositional sequences and sequence boundaries in maritime rifts, which can be applied to other less well-exposed or subsurface successions from other sedimentary basins. Onlapping transgressive and progradational highstand systems tracts are recognised on dip slope ramps. Falling stage and lowstand systems tracts are developed as thick breccia units in hangingwall areas adjacent to extensional faults. Sequence boundaries vary in character, amplitude and/or duration of sea-level fall and persistence across the area. Some boundaries coalesce onto the Canteras unit, which remained as a relatively positive area throughout the early Pliensbachian (Carixian).The carbonate platform on the Ponce tectonic unit drowned in the latest Carixian (davoei biozone). However, the adjacent tectonic units remained emergent and developed a long-lived sequence boundary, indicating tectonic subsidence as the major cause for platform drowning.The stratigraphic evolution of this area on the rifted southern Iberian margin indicates that a widespread restricted shallow...

No abstract

No abstract

The middle and upper members of the GavilSn Formation near Velez-Rubio (Almerfa Province, southeast Spain) are interpreted as carbonate platform deposits. The studied outcrops form geologically part of the External Zones of the Betic Cordillera (South Iberian Palaeomargin). A genetic unit limited by intra-Sinemurian and intra-Upper-Carixian sedimentary breaks is defined. The evolution of the parasequence sets in the area, and the development of deeper sedimentation in its northern outcrops, suggest that this platform was isolated with regard to the South Iberian Margin. Three distinct parasequence sets are proposed: progradational parasequence set (only locally present), retrogradational parasequence set (middle member of the GavilSn Formation) and aggradational parasequence set (basically composed of the upper member of the GavilSn Formation). Sedimentary features (such as neptunian dykes, sharp lithological changes, thickness variations), the presence of palaeofaults and the subsidence history all lead to the conclusion of a significant regional tectonic influence in the genetic unit evolution. Normal extensional faulting has been proposed as a major control on sedimentation on this isolated platform. This regional factor has completely distorted the effect of the eustatic fluctuations for this period of time.Diagram of Monte del Marrajo shows details of metre-scale cycles in the middle member and coral biolitite.

No abstract

No abstract

No abstract