Lithostratigraphic characterization of Well ZK002 identifies three major units within the Gufeng Formation: (a) Lower-middle unit (24 m thick): Dark-gray to gray argillaceous limestone transitioning upward into bioclastic and micritic limestone, with intermittent black mudstone interbeds and thin siliceous bands; (b) Middle-upper unit (25 m thick): Rhythmic alternations of dark-gray limestone and mudstone, with occasional nodular limestone layers); (c) Uppermost unit (12.5 m thick): Dark-gray mudstone intercalated with marly and bioclastic limestone, including a distinctive 1-m-thick Mn-enriched bioclastic limestone horizon. The Mn-ore in Well ZK002 is petrographically similar to that in Well ZK5903, exhibiting comparable color and sedimentary structures to its enclosing limestone. Its relatively low Mn concentration results in negligible density contrast, rendering it macroscopically indistinguishable at the core scale.

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