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Geologische Rundschau

, Volume 78, Issue 1, pp 81–104 | Cite as

Seismic and sedimentologic features of Oxfordian-Kimmeridgian syn-rift sediments on the eastern margin of the Lusitanian Basin

  • R. R. Leinfelder
  • R. C. L. Wilson
Integration of Geologic Data

Abstract

Following deposition of widespread middle Oxfordian lacustrine carbonates and evaporites, the Lusitanian Basin was differentiated into a number of sub-basins. The Arruda sub-basin is a half graben basin situated some 30 km north of Lisbon. It accumulated over 2.5 km of Kimmeridgian siliciclastic sediments, and is bounded to the east by the Vila Franca de Xira fault zone. Carbonate deposition persisted over horsts along the fault zone from the Oxfordian to the early Kimmeridgian, and in places to the late Kimmeridgian, and shows a pronounced west-east facies zonation, with higher energy framestones and grainstones accumulating along the exposed western margins. Seismic data indicate a major gap between the horst blocks that acted as a conduit through which basement derived siliciclastics were fed westwards into the sub-basin to form a submarine fan system. The presence of large blocks of framestone carbonates encased in siliciclastics indicates that carbonate sedimentation occurred in abandoned parts of the fan system. The rapid changes of sediment thicknesses and facies types along the eastern margin of the Arruda sub-basin are indicative of contemporaneous strike-slip movements.

Keywords

Fault Zone Evaporite Grainstones Eastern Margin Oxfordian 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Zusammenfassung

Nach der weitverbreiteten Ablagerung mitteloxfordischer Seenkarbonate und Evaporite differenzierte sich das Lusitanische Becken in verschiedene Sub-Becken. Das Arruda Sub-Becken befindet sich ca. 30 km nördlich Lissabon und entspricht einem Halbgraben, in dem über 2.5 km mächtige Siliziklastika des Kimmeridgium zur Ablagerung kamen. Das Sub-Becken wird durch die Störungszone von Vila Franca de Xira nach Osten begrenzt. Auf Horststrukturen entlang der Störungszone wurden im Oxfordium und Unterkimmeridgium, z. T. auch bis ins Oberkimmeridgium Karbonate sedimentiert. Diese Karbonatschelfe weisen eine ausgeprägte Fazieszonierung von West nach Ost auf. Die westlichen Schelfränder sind durch höherenergetische Riffkalke (framestones) und Karbonatsande (grainstones) charakterisiert. Seismische Profile lassen eine große Lücke zwischen den Horstblöcken erkennen, durch welche Siliziklastika aus dem Hinterland ins Sub-Becken gelangten, wo sie einen submarinen Fächer aufbauten. Große Riffkalkblöcke innerhalb der Siliziklastika weisen auf Karbonatsedimentation in verlassenen Fächerbereichen hin. Die schnellen Mächtigkeits- und Fazieswechsel entlang des Ostrandes des Arruda Sub-Beckens sind durch synsedimentäre tektonische Bewegungen zu erklären, welche oftmals eine Dominanz der Lateralkomponente aufweisen.

Resumo

Depois da sedimentação dos calcários lacustres e depósitos evaporíticos da idade Oxfordiano médio, a Bacia Lusitánica diferenciou-se em várias sub-bacias. A sub-bacia de Arruda está situada ca. de 30 km ao norte de Lisboa e corresponde a uma estrutura «half-graben» em que mais do que 2.5 km de sedimentos foram acumulados. Para leste, a sub-bacia é limitada pela zona das falhas de Vila Franca de Xira. Entre o Oxfordiano e o Kimeridgiano, calcários desenvolveram-se em cima dos blocos elevados (“horsts”) ao longo da zona de falhas. Estes calcários de tipo plataforma exibem uma distincta zonação de facies de oeste a leste. As margens occidentals das plataformas pequenas são caracterisadas por sedimentos recifais e areníticos. Cortes sísmicos indicam uma abertura grande entre os blocos elevados, pelo quai sedimentos siliciclásticos passaram de “hinterland” à sub-bacia formando um “fan” submarino. Grandes blocos recifais situados dentro dos depósitos siliciclásticos são evidências para sedimentação carbonática em várias áreas abandonadas dentro do “fan”. Mudanças rápidas das espessuras e das fácies dos sedimentos ao longo da margem oriental da sub-bacia de Arruda podiam ser explicadas por uma tectónica sinsedimentária dominada por movimentos horizontais.

Краткое содержание

Лузитанский бассейн / стратиграфический я рус верхней юры, залегающ ий выше оксфордского и ниже киммериджского / подразделяют по широ ко распространенным от ложениям среднеоксф ордских карбонатов и эвапори тов на более мелкие ба ссейны. Один из них, бассейн Ар руда, находится приме рно на 30 км севернее Лиссабон а и соответствует пол уграбену, в котором отложились силикокластиты кимм ериджского века мощностью свыше 2,5 км. Этот небольшой бассейн ограничен на востоке у Vila Franca de Xira зоной сбросов. На стр уктурах горста вдоль этой зоны сбросов в оксфор дском и нижнекиммери джском веках, частично и до ве рхне-киммериджского века, откладывались в осно вном карбонаты. Эти ме лководные отложения карбонато в проявляют явное раз деление на фации при простира нии с запада на восток. Западные края их хара ктеризуются известн яками рифов / framestones /и карбонатны ми песками / grainstones /. С помощью сейсмическ их методов удается выделить большой про бел между броками гор стов, по которым силикатная к ластика приносилась из тыла в эту часть бассейна, г де она отлагалась под водой веероподобно. Больши е блоки известняка ри фов среди кластичессого материала силикатов указывают на отложение карбона тов в основном в впади нах этого «веера». Быструю смен у мощностей и фация вд оль восточного края арру дского бассейна объя сняют синседиментными тек тоническими движени ями, которые часто преобладают на боковых отрезках так их отложений.

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Copyright information

© Ferdinand Enke Verlag Stuttgart 1989

Authors and Affiliations

  • R. R. Leinfelder
    • 1
  • R. C. L. Wilson
    • 2
  1. 1.Institut für GeowissenschaftenUniversität MainzMainzFRG
  2. 2.Department of Earth SciencesOpen UniversityMilton KeynesUK

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