Die Deltaphasen der Unterkreide am Basko-kantabrischen Kontinentalrand, Nordspanien
Zeitschrift: Neues Jahrbuch für Geologie und Paläontologie, 1982165, 1: 60 - 76
Reitner, Joachim; Wiedmann, J., 1982: Die Deltaphasen der Unterkreide am Basko-kantabrischen Kontinentalrand, Nordspanien. In: Reitner, Joachim; Wiedmann, J. (1982): Die Deltaphasen der Unterkreide am Basko-kantabrischen Kontinentalrand, Nordspanien - Neues Jahrbuch für Geologie und Paläontologie; Vol. 165, 1, p. 60-76, DOI: 10.23689/fidgeo-2571.
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Excellent onshore outcrops, DSDP cores and dredge sampies facilitate
recognition and definition of successive stages in the evolution of the subsiding
southern Biscay margin. Here the Lower Cretaceous episodes of this subsidence
are treated. In contrast to the central North;Atlantic, rifting in trus area decreased
du ring the Jurassic and later renewed in Late Jurassic time.
"Wealden" sediments of extreme thidmesses were deposited in the first stage
of pronounced subsidence (Oxfmdian to Barremian?). It is to be considered as
the first deltaic episode of the second and final rifting stage of the Biscay
Ocean. Late Jurassic ("Late Cimmerian") distension tectonics are the major
factor controlling the sedimentary environments. Distribution of continental,
limnic and brackish facies exhibit arelief of torted blocks wruch persisted
through the entire Lower Cretaceous. The predominance of NW-SE directed
faults at that time and the maximum of Wealden thicknesses in the N Celtiberic
Ranges point to the possihility that the Bay of Biscay originally intented to
open this way. The Valanginian transgression was found to be of minor importance
with regard to subsidence, but is used as datum level.
The second phase in the Lower Cretaceous history of the southern Biscay
margin is the development of Urgonian carbonate platforms (Ap~ian to Lower
Albian). These island platforms used the previous relief as far as the subrecifal
carbonates were restricted to previous horst structures, while marine pelitic
«Parahoplites shales" were accumulated in the channel-like grabens Decreasing
subsidence may be the only difference to the previous evolutionary stage;
sedimentation is, however, still able to compensate subsidence. At this time, the
actual E-W directed tectonic structures became predominant.
l1lis platform evolution is followed and simultaneously closed up by a second
deltaic phase (Middle Albian to Lower Cenomanian in the N , Albian in the S).A new inerease of subsidenee may be eorrelated with "Austrian" distension
teetonies and eonsiderable terrigenous input from the Sand W. This is a time
of extreme fa eies diversity: 1) turbiditie sedimentation at the subsiding eontinental
margin, 2) deltaie fans in the northern baseo-eantabrie trough, 3) eontinental
and fluviatile sands in the S, 4) final persistenee of restrieted island
platforms and diapirie atolls on loeal highs, 5) oceanie erust in the eentral
basin, and 6) alkaline magmatism in the onshore Biseay syncline. In eorrelation
with the distension teetonies this is the first period of pronouneed diapirism.
The next abrupt change in sedimentary environment, i.e. co an uniform pelagie
sedimentation ' (Middle Cenomanian), is due to the "global" Cenomanian transgression
and integrates the whole area into a widespread pelagie faeies realm.
At this time, sedimentation is unable co eompensate subsidenee. There is no doubt,
that late "Cimmerian" and "Austrian" distension teetonies and the related Val anginian
and Cenomanian transgressiom, altogether widespread at the North Atlantie
margins, have their origin in the episodie aetivity of the mid-oceanie ridge and
eompensating erustal processes.
An attempt is made to eorrelate similar stages in the history of subsiding
passive margins in various time-per iods.
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