The Collaborative International Dictionary
Superstratum
Superstratum \Su`per*stra"tum\, n.; pl. Superstrata. [NL.: cf. L. supersternere, superstratum, to spread upon. See Super-, and Stratum.] A stratum, or layer, above another.
Wiktionary
superstratum
n. 1 (context geology English) A stratum that is on top of another 2 (context linguistics English) A language imposed upon a population that previously spoke another language