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.
Allen, J. R. L. 1968. The nature and origin of bed-form hierarchies. Sedimentology, 10, 161–182.
https://doi.org/10.1111/j.1365-3091.1968.tb01110.x
Allen, J. R. L. 1983. Studies in fluviatile sedimentation: bars, bar complexes and sandstone sheets (low-sinuosity braided streams) in the Brownstones (L. Devonian), Welsh Borders. Sedimentary Geology, 33, 237–293.
https://doi.org/10.1016/0037-0738(83)90076-3
Brangulis, A. J., Kuršs, V., Misāns, J. & Stinkulis, Ģ. 1998. Latvijas ģeoloģija [Geology of Latvia] (Misāns, J., ed.). State Geological Survey, Riga, 70 pp. [in Latvian].
Brugger, J., Hofmann, M., Petri, S. & Feulner, G. 2019. On the sensitivity of the Devonian climate to continental configuration, vegetation cover, orbital configuration, CO2 concentration, and insolation. Paleoceanography and Paleoclimatology, 34, 1375–1398.
https://doi.org/10.1029/2019PA003562
Dalrymple, R. W. & Choi, K. 2007. Morphologic and facies trends through the fluvial–marine transition in tide-dominated depositional systems: a schematic framework for environmental and sequence-stratigraphic interpretation. Earth-Science Reviews, 81, 135–174.
https://doi.org/10.1016/j.earscirev.2006.10.002
Denison, R. H. 1978. Placodermi. In Handbook of Paleoichthyology, Part 2 (Schultze, H.-P., ed.), pp. 1–128. Gustav Fischer Verlag, Stuttgart and New York.
De Vleeschouwer, D., Crucifix, M., Bounceur, N. & Claeys, P. 2014. The impact of astronomical forcing on the Late Devonian greenhouse climate. Global Planet Change, 120, 65–80.
https://doi.org/10.1016/j.gloplacha.2014.06.002
Elliott, D. K., Mark-Kurik, E. & Daeschler, E. 2004. A revision of Obruchevia (Psammosteida: Heterostraci) and a description of a new obrucheviid from the Late Devonian of the Canadian Arctic. Acta Universitatis Latviensis, 679, 22–45.
Esin, D., Ginter, M., Ivanov, A., Lebedev, O., Luksevics, E., Avkhimovich, V., Golubtsov, V. & Petukhova, L. 2000. Vertebrate correlation of the Upper Devonian and Lower Carboniferous on the East European Platform. Courier Forschungsinstitut Senckenberg, 223, 341–359.
Gibling, M. R. 2006. Width and thickness of fluvial channel bodies and valley fills in the geological record: a literature compilation and classification. Journal of Sedimentary Research, 76, 731–770.
https://doi.org/10.2110/jsr.2006.060
Glinskiy, V. 2018. Phylogenetic relationships of psammosteid heterostracans (Pteraspidiformes), Devonian jawless vertebrates. Biological Communications, 62, 219–243.
https://doi.org/10.21638/11701/spbu03.2017.402
Gross, W. 1933. Die Fisches des baltischen Devons. Palaeontographica, A 79, 1–74.
Gross, W. 1942. Die Fischfaunen des baltischen Devons. Korrespondenzblatt des Naturforscher Vereins zu Riga, 64, 373–436.
Joachimski, M., Breisig, S., Buggisch, W., Talent, J., Mawson, R., Gereke, M., Morrow, J., Day, J. & Weddige, K. 2009. Devonian climate and reef evolution: Insights from oxygen isotopes in apatite. Earth and Planetary Science Letters, 284, 599–609.
https://doi.org/10.1016/j.epsl.2009.05.028
Kuršs, V. 1975. Litologiya i poleznye iskopaemye terrigennogo devona Glavnogo polya [Lithology and Mineral Resources of the Terrigenous Devonian of the Main Field]. Zinātne, Rīga, 216 pp. [in Russian].
Kuršs, V. 1992. Devonskoe terrigennoe osadkonakoplenie na Glavnom devonskom pole [Devonian Terrigenous Deposition on the Main Devonian Field]. Zinātne, Rīga, 208 pp. [in Russian].
Lanier, W. P. & Tessier, B. 1998. Climbing-ripple bedding in the fluvio-estuarine transition: a common feature associated with tidal dynamics (modern and ancient analogues). In Tidalites: Processes and Products (Alexander, C. R., Davies, R. A. & Henry, V. J., eds), SEPM Special Publication, 61, 109–118.
https://doi.org/10.2110/pec.98.61.0109
Leclair, S. F. & Bridge, J. S. 2001. Quantitative interpretation of sedimentary structures formed by river dunes. Journal of Sedimentary Research, 71, 713–716.
https://doi.org/10.1306/2DC40962-0E47-11D7-8643000102C1865D
Longhitano, S. G., Mellere, D., Steel, R. J. & Ainsworth, R. B. 2012. Tidal depositional systems in the rock record: A review and new insights. Sedimentary Geology, 279, 2–22.
https://doi.org/10.1016/j.sedgeo.2012.03.024
Lukševičs, E. 2001. Bothriolepid antiarchs (Vertebrata, Placodermi) from the Devonian of the north-western part of the East European Platform. Geodiversitas, 23, 489–609.
Lukševičs, E. (in press). Revision of asterolepidoid antiarch remains from the Ogre Formation (Upper Devonian) of Latvia. Estonian Journal of Earth Sciences [accepted].
Lukševičs, E. & Zupiņš, I. 2004. Sedimentology, fauna, and taphonomy of the Pavāri site, Late Devonian of Latvia. Acta Universitatis Latviensis, 679, 99–119.
Lukševičs, E., Ahlberg, P. E., Stinkulis, Ģ., Vasiļkova, J. & Zupiņš, I. 2011. Frasnian vertebrate taphonomy and sedimentology of macrofossil concentrations from the Langsēde Cliff, Latvia. Lethaia, 45, 356–370.
https://doi.org/10.1111/j.1502-3931.2011.00288.x
Lyarskaya, L. 1981. Baltic Devonian Placodermi. Asterolepididae. Zinatne, Riga, 152 pp. [in Russian, with English summary].
Lyarskaya, L. & Lukševičs, E. 1992. Sostav i rasprostranenie beschelyustnykh i ryb v silurijskikh i devonskikh otlozheniyakh Latvii [Composition and distribution of agnathan and vertebrate assemblages in the Silurian and Devonian deposits of Latvia]. In Paleontologiya i stratigrafiya fanerozoya Latvii i Baltijskogo morya [Palaeontology and Stratigraphy of the Phanerozoic of Latvia and the Baltic Sea] (Sorokin, V. S., ed.), pp. 46–62. Zinātne, Riga [in Russian].
Miall, A. D. 2014. Fluvial Depositional Systems. Springer, 316 pp.
https://doi.org/10.1007/978-3-319-00666-6
Nichols, G. 2009. Sedimentology and Stratigraphy. Wiley-Blackwell, 419 pp.
Pontén, A. & Plink-Björklund, P. 2007. Depositional environments in an extensive tide-influenced delta plain, Middle Devonian Gauja Formation, Devonian Baltic Basin. Sedimentology, 54, 969–1006.
https://doi.org/10.1111/j.1365-3091.2007.00869.x
Pontén, A. & Plink-Björklund, P. 2009. Regressive to transgressive transits reflected in tidal bars, Middle Devonian Baltic Basin. Sedimentary Geology, 218, 48–60.
https://doi.org/10.1016/j.sedgeo.2009.04.003
Reineck, H. E. & Singh, I. B. 1980. Depositional Sedimentary Environments. Springer-Verlag, New York, 549 pp.
https://doi.org/10.1007/978-3-642-81498-3
Scotese, C. R. 2014. Atlas of Devonian Paleogeographic Maps, PALEOMAP Atlas for ArcGIS, Volume 4, The Late Paleozoic, Maps 65–72 (Mollweide Projection). Evanston, IL: PALEOMAP Project.
Sorokin, V. S. 1978. Verkhnefranskij pod´yarus Glavnogo devonskogo pol´ya [Upper Frasnian Substage of the Main Devonian Field]. In Stratigrafiya fanerozoya Pribaltiki [Stratigraphy of the Phanerozoic of the Peribaltics] (Sorokin, V. S., ed.), pp. 44–111. Zinatne, Riga [in Russian].
Sorokin, V. S. 1981. Ogrskaya svita [Ogre Formation]. In Devon i karbon Pribaltiki [Devonian and Carboniferous of the Peribaltics] (Sorokin, V. S., ed.), pp. 275–281. Zinatne, Riga [in Russian].
Sorokins, V. 1997. Ogres svīta [Ogre Formation]. In Latvijas Daba, IV (Kavacs, G., ed.), pp. 52–53. Preses Nams, Rīga [in Latvian].
Takcidi, E. 1999. Data base: “Drillings”. State Geological Survey of Latvia, Riga. Data summarised within the ESF project “Establishment of interdisciplinary scientist group and modelling system for groundwater research”, contract No. 2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060.
Tänavsuu-Milkeviciene, K. & Plink-Björklund, P. 2009. Recognizing tide-dominated versus tide-influenced deltas: Middle Devonian strata of the Baltic Basin. Journal of Sedimentary Research, 79, 887–905.
https://doi.org/10.2110/jsr.2009.096
Tänavsuu-Milkeviciene, K., Plink-Björklund, P., Kirsimäe, K. & Ainsaar, L. 2009. Coeval versus reciprocal mixed carbonate–siliciclastic deposition, Middle Devonian Baltic Basin, Eastern Europe: implications from the regional tectonic development. Sedimentology, 56, 1250–1274.
https://doi.org/10.1111/j.1365-3091.2008.01032.x
Tovmasjana, K. 2013. Depositional Environment of the Tidally-Dominated Transgressive Succession: Rēzekne and Pärnu Regional Stages, Baltic Devonian Basin. Summary of doctoral thesis. University of Latvia, Riga, 88 pp.
Van den Berg, J. H., Boersma, J. R. & Van Gelder, A. 2007. Diagnostic sedimentary structures of the fluvial-tidal transition zone – evidence from deposits of the Rhine and Meuse. Netherlands Journal of Geosciences – Geologie en Mijnbouw, 86, 287–306.
https://doi.org/10.1017/S0016774600077866
Vasiļkova, J., Lukševičs, E., Stinkulis, Ģ. & Zupiņš, I. 2012. Taphonomy of the vertebrate bone beds from the Klūnas fossil site, Upper Devonian Tērvete Formation of Latvia. Estonian Journal of Earth Sciences, 61, 105–119.
https://doi.org/10.3176/earth.2012.2.03
