EROSIONAL INDICATORS IN LATE HOLOCENE BEACH-DUNE COMPLEXES OF SOUTHWESTERN UKRAINE

The non-tidal Black Sea coast of Odessa region, Ukraine, contains a diverse suite of coastal landforms that bear enduring signs of erosion, flooding, and retreat. Modern and recent erosional indicators include: 1) sub-vertical to overhanging berm scarps; 2) beachface and upper berm/dune heavy-mineral concentrations (HMCs); 3) fresh and partially vegetated dune scarps, and 4) healed overwash and breach (“prorva”) channels. Berm scarps on S-SE-facing open-coast beaches expose paleo-storm event horizons, with exposes scarp morphology retained upon burial. Recent erosion at Dolphin Beach (Odessa Bay) uncovered at least four shell-rich layers, with the oldest dating to AD 713-890. Prograded beach-ridge complexes, fronting either high mainland bluffs or fresh-to-hypersaline paleo-river valleys (“limans”) retain diagnostic signatures of erosion within their wave-generated lithosomes capped by aeolian deposits. Occasional surges inside the limans variously affect the elevation and continuity of low NE- and SE-SW-facing cuspate and swash-aligned barriers. Modern and relict HMCs (detected by shore-normal surveys) have swash and aeolian genesis. Their bulk magnetic susceptibility ranges from 40-115 μSI (grain-thick HMC on aeolian ripple crests), to >500 μSI (upper beachface), and >1,500 μSI (3-cm-thick HMC in a paleo-scarp), in contrast to MS<30 μSI in background sediments. In addition to mineralogical (magnetite, garnet) density lag of the HMCs, mollusk accumulations produced by storms may be further concentrated into a shell pavement by a combination of persistent swash winnowing and aeolian deflation. As a result, carbonate fraction (primarily shell fragments) may comprise from 5% to more than 90% of beach sediments. Today, overprinting of primary sedimentary structures by foot traffic and other biogenic activity must be taken into account, even when examining shallow subsurface records. Our research demonstrates that beach and dune complexes contain morphological and compositional indicators of extreme events that have equivalents in historical (~3,000 years) and geological archives of coastal accumulation forms along the northwestern Black Sea coast.