German to English Science Geology

This is describing various Albian Age geological strata. I also see Wechselfolge, which I assume to be analogous. Is it something like "shifting stratification" or "transitional layer?"

Here is a sample sentence:

Um Pule Khumri und Nahrin greift eine Wechsellagerung aus Kalk, Mergel, Ton und Sandstein transgressiv über die kontinentalen Bildungen des Valendis-Apt-Komplexes."

Any help would be greatly appreciated. Thanks!