Complex sentence: Only the largest and geologically youngest tektite deposit in Southeast Asia, called the Australasian strewnfield, has not been definitively linked to an impact site, probably because even very large impact structures are often not easy to detect.
Split into simpler sentences: Only the largest, geologically youngest tektite deposit in Southeast Asia, called the Australasian strewnfield, has thus far had no known impact crater associated with it. This is probably due to the fact that even very large impact structures are often not easy to detect.