The Devonian sedimentary record of the Ossa-Morena Zone is scarce. In its southwestern domains, the Odivelas Limestone and correlatable units represent the single evidence of latest Early Devonian to Middle Devonia n (possibly into Frasnian) sedimentation in this area. Reefal and perireefa l sediments are frequently, but not always, associated to coeval volcanic rocks that probably supported atoll-like systems on the top of volcanic edifices. The northernmost occurrences are spatially associated with mississippian volcani c-sedimentary complexes. Their geometrical relation is still unclear, the limestones are possibly embedded as olitoliths, but can also be tectonically imbricated or simply reflecting draping of younger sediments around and above older (Devonian) sea-bed topography
