Cap carbonates, which are inferred to have formed in warm waters, overlie some glacial deposits from snowball earth events. why do these cap carbonates support, rather than contradict, the leading hypotheses for how snowball earth events progress?

Explanation:

Cap carbonates overlie Neoproterozoic glacial rocks with or without having a sharp contact in between them. These cap carbonate rocks characterized by typical ripple like sedimentary structures are thought to be the result of the post glacial aftermath. It signifies a sharp transition of glacial deposits into meters or tens of meters thick. Most reliable hypothesis about its origin states that due to melting of a snow-ball earth a significant amount of carbon-di-oxide gets dissolved into water and forms carbonic acid that might have led to acid rain which might have attacked exposed silicates and carbonates and subsequently released calcium ( that might led to textured layers of carbonates i.e. so called carbonate caps when come in contact to the ocean). A school of scientists think that in a snowball earth condition a distinctive boundary might have been created between the oceanic and atmospheric Carbon dioxide reservoirs and sudden increase in carbon dioxide  content in atmospheric reservoir led to deglaciation and melting and this made a pathway of the transportation of carbon dioxide from atmosphere to the ocean and resulted in carbonate precipitation. Again post-glacial up welling might bring out physical stratification and carbonate accumulation in the continental setting.  

answer; (d) melting of sea ice;

the answer would be b).