Matsya Purana — The Attendant Hosts of the Sun and Moon: Monthly Gaṇas
पीत्वार्धमासं गच्छन्ति अमावास्यां सुराश्च ते पितरश्चोपतिष्ठन्ति अमावास्यां निशाकरम् //
pītvārdhamāsaṃ gacchanti amāvāsyāṃ surāśca te pitaraścopatiṣṭhanti amāvāsyāṃ niśākaram //
Having drunk, they depart for the span of half a month; on Amāvāsyā (the new-moon day), those very gods—and the Pitṛs (ancestral fathers) as well—attend upon Niśākara, the Moon, on Amāvāsyā.
It does not describe Pralaya directly; it explains the ritual-cosmic rhythm of Amāvāsyā, when Devas and Pitṛs are said to be present in relation to the Moon, emphasizing sacred time (tithi) rather than dissolution.
It supports the householder’s (and by extension the king’s) duty to honor ancestors through properly timed śrāddha/tarpaṇa: offerings are linked to the lunar fortnight, with Amāvāsyā singled out as a key moment for Pitṛ-related rites.
The significance is ritual (not architectural): Amāvāsyā is highlighted as a powerful tithi for Pitṛ offerings, implying that śrāddha/tarpaṇa performed on new-moon day aligns with the presence/attention of Pitṛs and Devas in the lunar order.