Synsedimentary deformation structures are recognized in Upper Miocene deposits of the eastern Betic Cordillera (SE Spain). A singular stratigraphic section in these deposits shows several levels with soft-sediment deformation structures (load casts, ball-and-pillows and pipes) induced by liquidization (liquefaction and/or fluidization) of sandy sediments. The morphologic analysis of these structures reveals a liquidized sediment thickness ranging from 0.1 to 1.5 m. Although they have been previously interpreted as a result of seismic shocks, their origin was most likely related to the action of storm waves as the structures are always associated with tempestites. Facies analysis, geometrical features of the deformed beds and appraisal of geotechnical properties for shelf and coastal sediments allow the soft-sediment deformation structures to be interpreted as a result of the cyclic effect of storm waves on unconsolidated sediments, and excludes other processes such as overloading, tsunamis or the impact of breaking waves.

The identification of triggering agents for soft‐sedimentation structures is an enigmatic geological problem. Mainly seismic‐induced soft‐sediment structures have been recognized in ancient sediments, rather than those resulting from storm waves. We analyse soft‐sediment deformation structures in Upper Miocene calcarenitic tempestites of the Guadalquivir Basin (Southern Spain). The most common structures are load‐casts which vary in height and width from 10 centimetres to several metres. The structures are always restricted to a small part of the stratigraphic sections, in exclusive association with tempestites. The analysed soft‐deformation structures are interpreted to be the result of liquidization processes. Chiefly from their inferred depositional environment, and subordinately from the deformation style, we have devised basic criteria to identify the trigger mechanism. In these soft‐sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves.

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

During the middle Jurassic on the Southern Iberian Continental Margin (at the westernmost end of the northern Tethys) isolated carbonate platforms developed over volcanic edifices, forming guyots. The volcanic edifices were composed of K‐rich pillow‐lavas and pyroclastic rocks with a radiometric age ≈ 170 Myr. Such phenomena have not been described until now in this continental margin nor in other passive continental margins of Alpine domains. The presence of a shallowing‐upward megasequence (Bajocian–Bathonian) with hummocky cross‐ stratification strata below oolitic shoals, shows that very shallow isolated carbonate platforms developed above the volcanic edifices, with similar facies to those recognized in other guyots, but with a different age and geodynamic context.

No abstract

No abstract