In the snowball Earth hypothesis, the position of the continents near the equator in the Neoproterozoic pre-glacial episodes, resulted in an increase in Earth's albedo, and in combination with the increase in silicate weathering in the tropics due to the location of the continents, caused cooling of the Earth and expansion of the polar ice caps. Positive feedback resulting from further increase in planetary albedo resulted in ice reaching the equator, glaciated continents, and a shutdown of the global hydrological cycle: the 'snowball earth'. Volcanic outgassing of CO2 gradually warmed the atmosphere, and eventually resulted in catastrophic meltdown of the global ice cover. Mixing of cold biocarbonate-rich deep waters with warm shallow waters, in addition to increased silicate weathering producing more HCO3-, resulted in global deposition of a 'cap carbonate'.
Whatever the formation mechanism, ie: Snowball Earth or not, the 'cap carbonate' sequences are depositional sequences associated with post glacial sea level rise. The transgressive systems tracts of these depositional sequences is often a thin 'cap dolostone', which grades into a deeper water limestone or shale, which in turn gradually shoals upward through carbonate and siliciclastic lutites and arenites. Because cap dolostones are transgressive, they typically extend far beyond their antecedent glacial deposits, and unconformably overlie preglacial rocks.