From the introduction: "The nasalization of vowels in Sharanahua can be explained on the basis of consonants present in the underlying form of the morphemes, but the underlying consonants are not always nasal consonants. The explanation proposed here for oral consonants producing nasal vowels exploits the notion of sequential constraint rules ordered among or after other phonological rules."
Loos, Eugene E.
"Nasalization in Sharanahua,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 19, Article 3.
Available at: https://commons.und.edu/sil-work-papers/vol19/iss1/3