05080nas a2200193 4500008004100000245012700041210006900168490000700237520445000244100001804694700001604712700001904728700001604747700002204763700001604785700001404801700001604815856005504831 2024 eng d00aSpongy-looking microfabrics in the earliest named stromatolite represent deep burial alteration and incipient metamorphism0 aSpongylooking microfabrics in the earliest named stromatolite re0 v143 a
The earliest named stromatolite Cryptozoon Hall, 1884 (Late Cambrian, ca. 490 Ma, eastern New York State), was recently re-interpreted as an interlayered microbial mat and non-spiculate (keratosan) sponge deposit. This “classic stromatolite” is prominent in a fundamental debate concerning the significance or even existence of non-spiculate sponges in carbonate rocks from the Neoproterozoic (Tonian) onwards. Cryptozoon has three types of microbially-induced carbonate layers: clotted-pelletoidal micrite with microbial filaments, clotted-pelletoidal micrite with vesicular structure, and dense microcrystalline laminae. A fourth, stratiform to patchy fabric comprises suspect sponges. Using contextual fabric analysis, elemental mapping, cathodoluminescence, fluid inclusions, electron backscatter diffraction, U–Pb dating, and burial history, the sponge interpretation is denied. Neither a distinct sponge body outline nor a canal system is identifiable. Instead, the suspect fabric is secondary in origin, and best explained as a product of Carboniferous (Mississippian) deep burial alteration associated with basement reactivation. Key petrographic observations include heterogenous recrystallization via aggrading Ostwald ripening with interfingering reaction fronts typical for partially miscible fluids, a granoblastic calcite texture (incipient metamorphism), and subsequent hypidioblastic white mica (arguably Carboniferous/Permian, Alleghenian orogeny). Topotype Cryptozoon is a stromatolite altered to sub-greenschist metacarbonate. The published Tonian to Phanerozoic record of interpreted non-s​p​i​c​u​l​a​t​e​
1 aNeuweiler, F.1 aMueller, M.1 aWalter, B., F.1 aLanding, E.1 aBeranoaguirre, A.1 aSendino, C.1 aAmati, L.1 aKershaw, S. uhttps://www.nature.com/articles/s41598-024-83359-7