Limonao and the Cañadón Las Minas (Figure 2).
The succession of the geological sequence containing
the fish beds is equivalent in all of the localities,
though the thickness of the different layers
may vary, probably due to deposition on an existing
paleorelief of rocks of the Lonco Trapial Group. In
places where the contact with the underlying unit is
exposed, such as in a small canyon west of Puesto
Almada and at the entrance of the Cañadón Los
Chivos, the sequence starts with a coarse conglomerate
that unconformably overlies the Lonco
Trapial Group. The conglomerate is an orthoconglomerate
composed of angular to well-rounded
clasts of reworked Lonco Trapial Group and varies
considerably in thickness. The lower part of the
sequence above the conglomerate is dominated by
lacustrine shales and mudstones, with intercalations
of sandstones and tuffites. The fish beds are