Formation, exposure, and evolution of a high-latitude beachrock in the intertidal zone of the Corrubedo complex (Ria de Arousa, Galicia, NW Spain)

摘要

The presence of beachrocks is noted on the Galician shoreline at 41 °N, a latitude at which this phenomenon is rarely found. The present study focuses on the petrological characterization and sedimentological evolution of a beachrock that was exhumed during an exceptional storm in the winter of 2001 in the intertidal zone of a high-energy beach. The cemented material comprises medium-to-coarse mixed siliciclastic-carbonate sands. Unlike tropical beachrocks, the cement consists of epitaxial low-Mg calcite presenting varied morphologies and textures: acicular and bladed coatings and pore linings, pore fillings of sparitic calcite, and meniscus-style cements. Seawater, dominantly wave action, plus marine and meteoric mixed waters are invoked as the main generative fluids. Beachrock formation and evolution are approached from a morphodynamic viewpoint, considering four progressive stages: 1. initial cementation in the intertidal zone; 2. exposure and modelling by wave action; 3. colonization and hardening; and 4. disintegration/preservation and burial. Finally, the morphodynamic significance, climatic implications, and occurrence of this type of cementation along the north and northwest shoreline of Spain are discussed.