Depósitos eocenos de transporte en masa en Getxo (Bizkaia)deducciones sobre bulldozing y transformación de flujos en masa

Resumen

Subaqueous mass flow evolution is the progressive transformation from slide to slump, then to debris flow, terminating in turbidity currents. However, recent studies have shown that other processes, including substrate entrainment (bulldozing), can interfere with this standard progression. This work supports these findings using as reference Eocene mass transport deposits (MTDs) from the Basque Basin (Pujalte et al., 1997; Payros and Pujalte, 2020). Here, Eocene mass wasting proces- ses destabilized shelfal and slope deposits, creating sediment gravity flows that moved downslope towards the SE. The indi- vidual thickness of the MTDs ranges from 10 to 33 m, with an estimated minimum extent of 1.5x106 m 2 and average volume of 24x106 m 3. Four different types of MTDs were identified, which allowed a facies model to be conceived showing that the sediment gravity flows switched from slides to slumps, which in turn became debris flows. However, the transformations did not occur en masse and were not linear: bulldozing processes interfered by contributing to maintaining flow heterogeneity and actually produced retrograde mass flow transformation. The potential effects of bulldozing should be taken into account when determining the proximal or distal nature of other MTDs.