Depositional environments within Middle Jurassic oyster-dominated lagoons: an integrated litho-, bio- and palynofacies study of the Duntulm Formation (Great Estuarine Group, Inner Hebrides)
ABSTRACT The Duntulm Formation of the Bathonian (Middle Jurassic) Great Estuarine Group represents a marine-brackish lagoonal complex which was transgressively established on the drowned delta of the underlying Valtos Sandstone Formation. Duntulm Formation sediments accumulated in adjacent basins, the Sea of the Hebrides-and Inner Hebrides-basins. Litho-, bio-, and palynofacies analysis of these rocks show that the most distinctive lithologies, monotypic shell banks of the oyster Praeexogyra hebridica (Lithofacies 1), accumulated under variable, but distinctly marine conditions. Argillaceous carbonate muds (Lithofacies 2), probably accumulated in the lee of the oyster banks under variably marine-freshwater conditions, while the supralittoral lagoon shores were fringed by algal marshes (Lithofacies 3). The palynology of Lithofacies 3 shows that some marshes accumulated close to the lagoon (dominated by marine dinocysts), while others formed further inland (dominated by terrestrial pollen and spores). In the N of the Sea of the Hebrides Basin, small deltas continued to prograde into the lagoons (Lithofacies 4), and toward the end of Duntulm Formation times, muds and sands colonised by freshwater molluscs ( Unio and Neomiodon ), the planktonic alga Botryococcus , and dominated by terrestrial pollen and spores (Lithofacies 5), accumulated in this area, representing a basin-wide change from marine to freshwater conditions. The structural high which divided the basins exerted a strong control on lithofacies evolution, effectively preventing any material coarser than silt grade entering the Inner Hebrides Basin. Thickness variation in the Formation is similarly structurally/facies linked, with thick sequences accumulating where sandstones (Lithofacies 4) predominate, and thin sequences occurring close to the structural high.
- 원문이 없습니다.
유료 다운로드의 경우 해당 사이트의 정책에 따라 신규 회원가입, 로그인, 유료 구매 등이 필요할 수 있습니다. 해당 사이트에서 발생하는 귀하의 모든 정보활동은 NDSL의 서비스 정책과 무관합니다.
원문복사신청을 하시면, 일부 해외 인쇄학술지의 경우 외국학술지지원센터(FRIC)에서
무료 원문복사 서비스를 제공합니다.
NDSL에서는 해당 원문을 복사서비스하고 있습니다. 위의 원문복사신청 또는 장바구니 담기를 통하여 원문복사서비스 이용이 가능합니다.
- 이 논문과 함께 출판된 논문 + 더보기