English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

This study is devoted to the lower series (Barremian-lower Albian) of Hole 549, just west of the continental shelf of northwestern Europe (Leg 80 of DSDP-IPOD). The lithological analysis is correlated with downhole logging, X-ray mineralogy, foraminiferal assemblages, and biological content. Biosedimentary environments and general pattern of distribution are interpreted and compared with Cretaceous exposures of northern Spain. Two successive paleogeographic phases are identified: a short transgressive episode giving a shallow environment (Barremian), and the opening (lower Albian) of a long period of pelagic sedimentation in a bathyal environment. They were separated by a gap in deposition, so that the record of intervening events is lost. The lower series begins with a record of marine transgression. The sporadic occurrences of oysters indicate a lowering of salinity. As the transgression became more extensive, the sediments became more calcareous, forming part of a carbonate platform. Trocholina species are associated with encrusting and other benthic foraminifers, bryozoans, corals, and algae. Subsequent deposition could not keep pace with subsidence, and the water deepened, as indicated by the presence of the planktonic foraminifer Hedbergella in association with small benthic foraminifers in a clayey-silty sediment interpreted as a quiet muddy seafloor. Clastic material is very mature, implying provenance in a very weathered area. In the lower part of the column kaolinite was the main mineral in the fraction smaller than 2 μm. In the carbonate sediments, kaolinite has been replaced by smectite. The second phase is characterized by planktonic foraminifers of the genus Hedbergella and by radiolarians, reflecting increased subsidence and bathyal conditions. The general trend of this evolution is chronologically in accordance with that known from the southern margin (Spain margin) of Biscay Bay. INTRODUCTION Four sites were drilled during Leg 80. Material from the lower part of Hole 549 was studied by our team. Hole 549 is located at 49°05.28'N, 13°05.88'W. Drilling was initiated at 2533 m below sea level and penetrated 965 m of sediment ranging in age from Barremian to Quaternary before Hercynian basement was reached. (Fig. 1). The post-Hercynian series begins with marine formations dated by study of their foraminifers as Barremian (Magniez and Sigal, this vol.). These formations are the main object of this study. A sediment gap (very likely including part of the upper Barremian, the Aptian, and part of the lower Albian) separates these marine formations from the next formation upsection (Albian), which has also been examined, more briefly, in order to follow the evolution of the sedimentary pattern from Lower to middle Cretaceous until a pelagic facies appears. The aim of this work is essentially to discover the environments and sedimentary pattern by a threefold approach of sedimentology, mineralogy, and paleoecology, then to go further in their interpretation with the help of comparable data from the Cretaceous outcrops in northern Spain. 1 Graciansky, P. C. de, Poag, C. W., et al., Init. Repts. DSDP, 80: Washington (U.S. Govt. Printing Office). Address: Institut des Sciences de la Terre, Laboratoire associé au CNRS no. 157, Université de Dijon, 6 Bd. Gabriel, 21100 Dijon, France. LITHOLOGIC SUCCESSION The lithologic succession is shown in Figures 2, 3, and 4 (Fig. 4 back pocket). All the material studied contains a terrigenous fraction, sometimes inconspicuous, and a carbonate phase of sedimentary or diagenetic origin. The clastic terrigenous part is mainly silt-size particles (quartz and a few feldspars and micas). The carbonate phase is composed of bioclasts, in places extremely varied, and a microsparitic, micritic, or sparitic matrix visible in the most calcareous beds. The terrigenous-to-carbonate ratio, the biological content, the arrangement in well-defined beds or lack of such arrangement, and the grain size of the terrigenous clastic material allow division of the succession into five formations, dated according to their microfauna (Magniez and Sigal, this vol.). These formations are described from the bottom of the hole upward. Unit E: Transgressive Terrigenous Formation This unit is dominantly terrigenous, with generally well sorted clastic particles: siltstones, claystones, sandstones with carbonate cement, and bioclastic siltstone lying in well-defined, approximately 1-m-thick beds. Very calcareous beds rarely occur, and always contain terrigenous material. A further division can be made into four members according to the frequency of calcareous interbeds and some additional criteria. Terrigenous arrivals are coarser at the bottom (Subunit E4), gradually become finer

Paleoenvironmental Study of Barremian-Albian Sediments at Deep Sea Drilling Project Site 549 in the Eastern North Atlantic