Re-interpretation of a Lower-Middle Cambrian WestGondwanan ramp depositional system: a case studyfrom the Cantabrian Zone (NW Spain)

摘要

Detailed litho- and biofacies investigations of theLower–Middle Cambrian carbonate Lancara Formationresulted in its subdivision into nine lithofacies types: (1) clay-stone, (2) recrystallized mudstone, (3) laminated mudstonewith laminoid-fenestral fabrics, (4) stromatolite, (5) lami-nated aggregate grainstone, (6) non-laminated aggregategrainstone, (7) oolitic-bioclastic floatstone, (8) echinodermalpackstone, and (9) bioclastic grainstone. The thicknesses oflithofacies 1-7 (lower member of the Lancara Formation)decrease from south to north. Lithofacies types 8-9 (uppermember of the Lancara Formation) are characterized by sim-ilar thicknesses and low facies and faunal gradients and arethus indicative of deposition on a carbonate ramp. From pal-aeoecological, palaeo(bio)geographical, palaeomagnetic, andtectonic considerations, the depositional environment of theLancara Formation is re-interpreted as an eastwardorth-eastward sloping, low morphology carbonate ramp. The Can-tabrian Zone, with a primary lateral extension of about300 km, is further construed to be an element of a wide-spread and connected, discontinuous drowned Perigondwa-nan depositional system.