Uno de los rasgos de mayor interés de las rocas del Triásico, desde el punto de vista sedimentario, es la presencia frecuente de depósitos relacionados con las tormentas. Entre las estructuras sedimentarias más significativas aparecen los gutter casts y los pot casts. Se trata de los rellenos de estructuras erosivas producidas por el descenso de la energía, de las corrientes sobre una zona somera con cierta pendiente, normalmente al cesar una tormenta.
Sedimentology, 48, 1371-1388 (2001)
Significance of pot and gutter casts in a Middle Triassic carbonate platform, Betic Cordillera, southern Spain
A. Pérez-López
ABSTRACT
Pot casts and gutter casts are described for the first time in the lower part of the Majanillos Formation, a Middle Triassic carbonate unit, located in the External Zones of the Betic Cordillera (southern Spain). Their identification, as well as their relation to tempestites, enable the better interpretation of the depositional environments and the shoreline-to-offshore facies transition on the Anisian muddy carbonate ramp of the southern Iberian Massif. The Majanillos Formation contain three members, which become progressively more marly towards the top. Well-preserved pot and gutter casts and thin intercalations of calcarenite beds, which are interpreted as tempestites, are abundant in the lowest member. Above the pot and gutter casts, thicker calcarenite beds which locally contain hummocky cross-stratification, predominate. Bioturbated nodular limestones are prevalent at the top of the member. The remaining succession, which records a long-term Triassic transgressive cycle, consists mostly of fine-grained limestones deposited in very shallow marine environments. Calcarenitic sediment only accumulated within potholes and gutters in the nearshore. They developed during storms when strong currents transported sediment towards the outer shelf, where it was deposited as tempestite beds. Pot and gutter casts characterise sedimentation in the bypass-zone. It is concluded that storm deposits provide important constraints for the interpretation of environment palaeobathymetry; it is proposed that gutter casts display a trend of increasing width/thickness ratios towards the outer shelf. The identification of these structures in marine elsewhere successions should prove useful in the interpretation of depositional environments.
Sedimentology, 59, 646-678 (2012)
Tempestite facies models for the epicontinental Triassic carbonates of the Betic Cordillera (southern Spain)
A. Pérez-López and F. Pérez-Valera
ABSTRACT
This study focuses on storm deposits in the Muschelkalk facies of the Betic Cordillera (southern Spain) and interprets their deposition mechanisms. Three types of storm deposit are distinguished: (i) pot/gutter casts; (ii) tempestite beds; and (iii) storm-winnowed deposits. Each deposit provides information about the carbonate platform environment in which it was deposited. The tempestite models proposed are: (i) the bypass-zone tempestite model, occurring in a muddy ramp at the epicontinental basin margin. This model is characterized by potholes and gutters that form in a shoreline bypass-zone during storms; (ii) the gradient-current tempestite model in which frequent tempestite beds are related to storm gradient currents. Thickness and grain size decrease towards the deep distal ramp; and (iii) the winnowed deposit tempestite model whereby storm deposits are winnowed and deposited in the same environment with only short lateral transport having occurred. This model evokes more restricted and shallower conditions, lagoons or inland seas. The distribution of all these deposits in the stratigraphic sections studied corroborate the eustatic third-order cycle identified, although the different features of the storm deposits and their positions in each section indicate a subsidence varying in time and space. In the transgressive stage, the margins of the epicontinental basin were a well-developed ramp with potholes and gutters. In contrast, during the high sea-level stage, storm deposits generated tempestite beds or storm-winnowed deposits in the different areas. The epicontinental carbonate platform with ramp edges evolved into a complex depositional system of coastal and shallow-marine environments with lagoons and restricted inland seas. Thus, the epicontinental platform underwent substantial change from the Late Anisian to the Late Ladinian and this is reflected in its storm deposits.