Geologische Rundschau

, Volume 70, Issue 1, pp 327–343 | Cite as

Mineralogy of sedimentary formations in the western North Atlantic Ocean: Preliminary results

  • Peter Rothe
  • Brian E. Tucholke
Aufsätze

Abstract

Six sedimentary formations, and two separate members recently were described byJansa, et al. (1979) from the western North Atlantic Ocean basin. We have investigated the mineralogical composition of these lithostratigraphic units by qualitative X-ray diffraction analyses of about five hundred samples from DSDP Sites 105, 106, 386, 387, and 391. The sedimentary section studied, from bottom to top, consists of: argillaceous limestones (Cat Gap Formation); limestones (Blake-Bahama Formation); claystones and shales (Hatteras Formation); zeolitic claystones (Plantagenet Formation); nannofossil marls (Crescent Peaks Member); siliceous oozes, clays, and cherts (Bermuda Rise Formation), and hemipelagic muds (Blake Ridge Formation) that locally contain redeposited shallow-water carbonates (Great Abaco Member). The section ranges in age from Oxfordian at the base to Quaternary at the sea-floor.

Most of the formations and members described byJansa, et al. (1979) have a characteristic mineralogical composition. Thus it is possible to recognize boundaries between formations and members by changes in mineral components, although these changes range from sharp to transitional. Within the same formation local differences in mineral spectra between sites can be explained by changing distance from terrigenous sources, lateral changes in surface paleoproductivity, and varying diagenetic conditions.

Keywords

Shale Ooze Oxfordian Sedimentary Formation DSDP 

Zusammenfassung

Sechs sedimentäre „Formations“ und zwei dazugehörige „Members“ wurden vor kurzem durchJansa, et al. (1979) aus dem Ozeanboden des westlichen Nordatlantik beschrieben. Wir haben die Mineralzusammensetzung dieser lithostratigraphischen Einheiten anhand von etwa 500 qualitativen röntgenographischen Analysen untersucht; die Proben dazu entstammen den DSDP-Bohrungen 105, 106, 386, 387 und 391. Vom Liegenden zum Hangenden lassen sich folgende Einheiten unterscheiden: Tonige Kalksteine (Cat Gap Formation); Kalksteine (Blake-Bahama Formation); Tonsteine und shales (Hatteras Formation); Zeolithische Tonsteine (Plantagenet Formation); Nannofossil-Mergel (Crescent Peaks Member); Kieselige Schlamme, Tone und Hornsteine (Bermuda Rise Formation) und Hemipelagische Schlamme (Blake Ridge Formation), die lokal umgelagerte Flachwasser-Karbonate (Great Abaco Member) enthalten. Das Gesamtprofil reicht altersmäßig von Oxfordium an der Basis bis zum Quartär.

Die meisten der vonJansa, et al. (1979) beschriebenen „Formations“ und „Members“ haben eine charakteristische Mineralzusammensetzung; es ist daher möglich, Grenzen sowohl zwischen „Formations“ als auch zwischen „Formations“ und „Members“ anhand ihrer Mineralkomponenten zu erkennen; der entsprechende Wechsel kann scharf sein oder fließende Übergänge aufweisen. Lokale Unterschiede in den Mineralspektren einer „Formation“ zwischen einzelnen Bohrpunkten lassen sich auf wechselnde Entfernungen vom Liefergebiet bzw. unterschiedliche Liefergebiete selbst, auf laterale Wechsel in der oberflächennahen Paläo-Produktivität und/oder auf unterschiedliche diagenetische Bedingungen zurückführen.

Résumé

Six »formations« sédimentaires ainsi que deux »members« séparés ont été ré cemment décrits parJansa, et al. (1979) dans la partie nordouest du bassin de l'océan Atlantique. Nous avons étudié, d'un point de vue qualitatif, la composition minéralogique de ces unités lithostratigraphiques à partir de l'analyse diffractométrique d'environ 500 échantillons provenant des sites DSDP 105, 106, 386, 387 et 391. Les sections sédimentaires examinées comprennent de bas en haut: Des calcaires argileux (Cat Gap Formation); des calcaires (Blake-Bahama Formation); des argilites et des argiles schisteuses (Hatteras Formation); des argilites zéolitiques (Plantagenet Formation); de la marne aux nannofossiles (Crescent Peaks Member); des boues silicieuses, des argiles et du silex (Bermuda Rise Formation), ainsi que des boues hémipélagiques (Blake Ridge Formation) qui contiennent par endroits des carbonates resédimentaires provenant d'un milieu peu profond (Great Abaco Member). Leur âge s'échelonne de l'Oxfordien à la base jusqu'au Quaternaire au fond océanique.

La plupart des »formations« et des »members« décrits parJansa, et al. (1979) ont une composition minéralogique caractéristique. Il est donc possible de reconnaître les limites entre des »formations« et des »members« à partir des changements de la composition minéralogique, bien que ces changements varient du net au transitoire. Dans une même formation on peut expliquer les différences locales des spectres minéraux entre les sites, par la variation de distance des sources terrigènes, des changements latéraux de la paléoproductivité de surface et des conditions diagénétiques variables.

Краткое содержание

Jansa и др. (1979) описали 6 осадоч ных формаций и 2 принадлежащие к ним пачки осадков дна океана северной Атла нтики. Авторы данного опубл икования исследовали минерал огический состав эти х литографических еди ниц на основании 500 количес твенных рентгеногра фических анализов. Пробы принадлежали буровы м скважинам 105, 106, 386, 387, и 391. От по дошвы к кровле эти единицы ра сполагаются в следую щем порядке: глинистые известняк и — формация Cat Gap —, известн яки — формация Blake-Bahama —, глины и сланцы — форма ция Hatteras'a —, цеолитовые гл ины — формация Plantagenet —, мергели с нано-фос силиями — пачка Crescent Peaks —, и силикатный ил, глины и роговая обманка — фор мация Bermuda Rise — и полупелагические ил ы — формация Blake Ridge —, локал ьно перераспределенные известняками мелков одья — пачка Great Abaco. Общий п рофиль по возрасту охватыва ет период от Оксфордс кого яруса на основании до четвертичного перио да включительно. Боль шенство описанных Jansa формаций и пачек имеет характе рный минералогическ ий состав; на основании их состава устанавли ваются границы между ними, причем переход может быть, как резким, так и с глаженным. Локальные различия в спектре минералов формации между отдел ьными буровыми скваж ивами можно объяснить различием в отдалени и от области сноса, или различиями этих областей сноса по их составу., боковым и изменениями палеопродуктивност и в слоях, близких к поверхности и/или ра зличиями условий диагенетических про цессов.

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Copyright information

© Ferdinand Enke Verlag Stuttgart 1981

Authors and Affiliations

  • Peter Rothe
    • 1
  • Brian E. Tucholke
    • 2
  1. 1.Abteilung für GeologieGeographisches Institut der UniversitätMannheimFGR
  2. 2.Department of Geology and GeophysicsWoods Hole Oceanographic InstitutionWoods HoleUSA

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