TEXTURAL AND COMPOSITIONAL TRENDS WITHIN LATE HOLOCENE OLD-GENERATION COASTAL RIDGES, SLITERE, LATVIA

Most coastal strandplains are characterized by sets of (sub)parallel ridges, often with substantial component of aeolian aggradation. Once vegetated, weathering and pedogenesis may impart varying degrees of granulometric and compositional variation to otherwise sedimentologically mature aeolian lithosomes. To investigate the degree of weathering on millennial scales, two forested early-stage ridges (relief: 5-6-m) were investigated at Slitere National Park, Kurzeme region, Latvia. Georadar imaging revealed a contrasting internal structure, with the older terrace-like ridge and fronting swale showing signal attenuation below 2 m depth. This deep horizon resulted in core refusal and corresponded to sand coated with up to 20% red mud (mostly silt), likely derived from the Devonian bedrock. The overlying mud-free sand exhibits a fining-upward sequence ranging from 1.4-2.1 φ to 2.1-2.3 φ above 0.6 m. Skewness was positively correlated with both mean grain size and sorting (good to poor), suggesting retention of finest fraction independent of depth. Leptokurtic (mean kurtosis: 1.4) is consistent with aeolian origin of the ridge superstructure penetrated by cores. The quartz-dominated sand showed varying degrees of oxidation, as reflected in their bulk low-field magnetic susceptibility (MS) ranging from <100 μSI (unoxidized) to >400 μSI (highly oxidized). Unaltered heavy-minerals (especially magnetite) also contributed to MS increase. Optical ages of ridge-top samples indicate a Late Subboreal aeolian deposition, but sample from ridge interiors are needed to confirm the timing of their original deposition. Our study demonstrates the potential for using gross weathering characteristics for estimating the relative age of coastal accumulation forms, similar to those in nearby Lithuania and Poland (Gray Dunes, etc.). Furthermore, correlation of sedimentological parameters to georadar signal response patterns will improve subsurface characterization of the remaining ridges within the 3-10-km-wide strandplain.