Complex sentence: Unlike the Avalon terrane, the Meguma terrane has not been definitely associated with territory on the other side of the Atlantic; it may be represented in the Galicia-Tras-Os-Montes Zone in Spain and Portugal.
Split into simpler sentences: Unlike the Avalon terrane, the Meguma terrane has not been definitively associated with territory on the other side of the Atlantic. It may be represented in the Galicia-Tras-Os-Montes Zone in Spain and Portugal.