Taphonomy of Middle Cambrian Trilobites: Distinguishing tsunamis from storms in La Laja Formation of Western Argentina

PRATT, B.R. Y BORDONARO, O.L.

Toledo, España

Congreso; 4º International Trilobite Conference; 2008

Institito Geologico y Minero de España

Coarse-grained strata deposited on continental shelves and epeiric seas in some tens of metres’ water depth are conventionally ascribed simply to storms of varying intensity which interrupted the settling out of suspended mud. Storms eroded the sea bottom, concentrated and winnowed coarser particles, and delivered sediment from shallower water. Surprisingly, the possibility of tsunamis is virtually never evaluated even though they might, indeed should, have been common in many regions. Portions of the Middle Cambrian La Laja Formation of the Argentine Precordillera formed in such a submerged epeiric platform or shelf. The taphonomy of trilobites in this unit provides the key that enables tsunami deposits (tsunamites) to be distinguished from storm deposits (tempestites).