Lower Cambrian paleosols from the Cantabrian Mountains (Northern Spain):: A comparison with neogene-quaternary estuarine analogues

The Lower Cambrian Barrios Beds (Cantabrian Mountains) consist of a siliciclastic succession deposited in deltaic environments punctuated by intertidal and fluvial systems. In the 'Barrios de Luna' area, this succession displays a progradational depositional systems tract that contains linkages between upper offshore, tidal sand bars, fluvial channels, and floodplain environments. The uppermost fluvial channels are encased within floodplain or interfluvial deposits, some of which develop muddy paleosols. The detailed micromorphological, scanning electron microscopy (SEM), geochemical, and mineralogical studies of their pedogenic profiles indicate the presence of three well-differentiated horizons: fragmentation and shrinking of the upper horizons originated a network of channel-like-to-vuggy porosity occluded by microlaminated clays, cyclically emplaced by tidal floods and seasonal oxidation; the middle horizons have concretionary to vermicular textures associated with microbioturbation and bacterial colonization; and the lower ones are mottled, containing numerous preserved lithorelics. The Barrios (sulfidic) Ustifluvent paleosols represent short-time pedogenic events under semiarid subtropical conditions, and support previous studies of Cambrian microbial life on subaerially exposed microenvironments. (C) 2003 Elsevier B.V. All rights reserved.