  Numerous geological features that could be evaporitic in origin have been
identified on the surface of Titan. Although they seem to be water-ice poor,
their main properties -chemical composition, thickness, stratification- are
essentially unknown. In this paper, which follows on a previous one focusing on
the surface composition (Cordier et al., 2013), we provide some answers to
these questions derived from a new model. This model, based on the up-to-date
thermodynamic theory known as "PC-SAFT", has been validated with available
laboratory measurements and specifically developed for our purpose. 1-D models
confirm the possibility of an acetylene and/or butane enriched central layer of
evaporitic deposit. The estimated thickness of this acetylene-butane layer
could explain the strong RADAR brightness of the evaporites. The 2-D
computations indicate an accumulation of poorly soluble species at the
deposit's margin. Among these species, HCN or aerosols similar to tholins could
play a dominant role. Our model predicts the existence of chemically trimodal
"bathtub rings" which is consistent with what it is observed at the south polar
lake Ontario Lacus. This work also provides plausible explanations to the lack
of evaporites in the south polar region and to the high radar reflectivity of
dry lakebeds.
