Depositional environment of the tidally-dominated transgressive succession: Rezekne and Pärnu Regional Stages, Baltic Devonian basin

Devonian deposits are widespread in the territory of Baltic States and adjacent regions. The Lower, Middle and lowermost Upper Devonian succession consist mainly of siliciclastic rocks such as sandstones, siltstones and clays with a minor role of dolostones and gypsum (Kurshs, 1975; 1992). It forms more than 500 m thick tidally influenced complex that contains both transgressive and regressive tidally influenced and tidally dominated deposits (Plink -Björklund, Björklund, 1999). This study focuses on R zekne and Pärnu Regional Stages (RS) of the Baltic Devonian Basin (BDB) that represents a complex transgressive succession of fluvial and tidal transition zone to outer estuarine deposits in tide-dominated estuaries associated with adjacent tidal flat complex that developed in a shallow, epicontinental sea. The implications of tidal control to the deposition of Middle and lowermost Upper Devonian siliciclastic succession in general have been discussed by Plink-Björklund and Björklund (1999). The most recent studies by Pontén and Plink-Björklund (2007), Tänavsuu-Milkeviciene et al. (2009), Tänavsuu-Milkeviciene, Plink-Björklund (2009) and Pontén, Plink-Björklund (2009) discuss the depositional environment of the BDB in mid and early Late Devonian. The authors describe tide-influenced retrograding shallow marine sedimentary environment and prograding delta complex of the Narva Formation (Tänavsuu-Milkeviciene et al., 2009), delta plain and delta front deposits associated with a large southward prograding delta comple x of the Aruküla Formation (Tänavsuu-Milkeviciene, Plink-Björklund, 2009) and Gauja Formation (Pontén, Plink-Björklund, 2007), as well as compare barforms from deltaic succession of the Gauja Formation with bars of estuaries in the Amata Formation (Pontén, Plink-Björklund, 2009). The results of this study complement the results given by the above-mentioned authors on the overall development of the BDB in the Middle and early Late Devonian, which contributes to reconstruction of the sedimentary environments at different evolutionary stages of the BDB: from transgressive to regressive settings.