GEOCHEMISTRY AND PALEOSEDIMENTOLOGY OF IRON SULFIDE-RICH CARBONACEOUS MUDSTONES IN DRILL CORE DDKS-010: A TIDALLY RESEDIMENTED ESTUARINE MUDFLAT ORIGIN FOR SURFICIALLY NI-ZN-CU-CO –ENRICHED PALEOPROTEROZOIC TALVIVAARA FORMATION (2.1–2.0 GA), FINLAND
The exact depositional age is not tightly constrained, but the TV fm is correlated with the voluminous accumulation of Corg-rich sediments (the "Shunga event") immediately following the Lomagundi–Jatuli -isotopic excursion. Also, the regional post-Jatulian basin-margin iron formations of the Kainuu Belt display in several localities laminated sulfide-facies units that likely correspond closely in time with the C-S-Fe –rich TV fm.
We document rhythmic, mainly tidally pulsed to massive fluid-mud deposition combined with river-plume sedimentation for the majority of the metalliferous organic-rich mudstones–siltstones of the TV fm. Thicker, graded mass-flow interbeds of fine to coarse sands are common, also material from nearby siliciclastic intertidal flat is positively identified. The highest "primary" Ni-Zn-Cu –concentrations (Ni up to 5226–5740 ppm) occur in most undiluted graded-laminated fine clay- and organic-rich pyrrhotitic mudstones. A classification scheme was established for the various sulfidic mudstone and claystone lithofacies.
Our results indicate a mud-dominated, near-estuarine subtidal environment in a narrow unrestricted craton-margin seaway. All element behavior and ratios feature paleomarine hydrogenous trends, and the organic productivity is attributed to riverine P and nutrient loading. High Ni-Zn-Cu levels correlate with interpreted Fe-Ti –rich smectitic protolith clay component, likely sourced from weathered continental basalts and hydrodynamically sorted to proximal offshore zone with deeper ferruginous watermass, euxinic chemocline and shore-sourced replenishment of oxic, sulfatic water.