  We consider the stochastic propagation of high-energy protons and nuclei in
the cosmological microwave and infrared backgrounds, using revised photonuclear
cross-sections and following primary and secondary nuclei in the full 2D
nuclear chart. We confirm earlier results showing that the high-energy data can
be fit with a pure proton extragalactic cosmic ray (EGCR) component if the
source spectrum is $\propto E^{-2.6}$. In this case the ankle in the cosmic ray
(CR) spectrum may be interpreted as a pair-production dip associated with the
propagation. We show that when heavier nuclei are included in the source with a
composition similar to that of Galactic cosmic-rays (GCRs), the pair-production
dip is not present unless the proton fraction is higher than 85%. In the mixed
composition case, the ankle recovers the past interpretation as the transition
from GCRs to EGCRs and the highest energy data can be explained by a harder
source spectrum $\propto E^{-2.2}$-- $E^{-2.3}$, reminiscent of relativistic
shock acceleration predictions, and in good agreement with the GCR data at
low-energy and holistic scenarios. While the expected cosmogenic neutrino
fluxes at high energy are very similar for pure proton and mixed composition
hypothesis, the two scenarii predict very different elongation rates from
$10^{17.5}$ to $10^{20}$ eV.
