Sedimentology and vertebrate fossils of the Frasnian Ogre Formation, Gurova outcrops, eastern Latvia

Abstract

Combined sedimentological and palaeontological study of the siliciclastic sequence of the Ogre Formation in the easternmost area of its distribution in Latvia was aimed at the facies analysis of the deposits and at detailed observation of the taxonomical and taphonomical peculiarities of the fossil vertebrate assemblage. Two facies associations, tidally-influenced fluvial channels and lateral tidal bars, have been identified in exposures along the Gurova River. Sedimentological evidences suggest that the studied deposits were formed in the fluvial environment with strong tidal influence. The sedimentary concentrations of vertebrate remains, dominated by the antiarch Bothriolepis maxima, porolepiform Holoptychius cf. nobilissimus and psammosteid heterostracans, have been formed under the influence of fluvial and tidal processes in the shallow-water environment, deltaic or estuarine settings. The finding of the psammosteid Obruchevia heckeri has confirmed the distribution of this species outside the type area.

Keywords

• facies analysis
• tidal processes
• vertebrate assemblage
• taphonomy.