Aptian-Albian Carbonate Episode of Basque-Cantabrian Basin, Northern Spain

Joaquin Garcia-Mondejar

The Aptian-Albian episode of the Basque-Cantabrian basin in northern Spain contains up to 4,000 m of rudistid limestones, changing laterally into marls and other terrigenous materials. Ten deposystems with environments ranging from alluvial fan to carbonate intraplatform basin and three deposequences corresponding to late Aptian, upper Aptian-early late Albian and late late Albian-middle Albian, respectively, have been distinguished within it. Wide patch reefs with ramp-like margins appeared in the late Aptian. Thick platform or bank limestones bearing big reef-mounds in the margins and megabreccias in the slopes built up in the upper Aptian and, particularly, in the Albian. A general terrigenous arrival in the upper Albian finally put an end to most of the carbonate depo ition.

Several controls determined the appearance and characteristics of the carbonate episode. Block-faulting in the basement created differential subsidence, inducing limestones to deposit in highs and terrigenous materials in troughs, and bringing about halokinesis and tectonic pulses. Four relatively short-lived lowstands of sea level (in pre-Aptian, middle Aptian, late Albian, and middle Albian) and their intervening highstands have been established which can be correlated interregionally and so attributed to eustatism, besides tectonism. Sedimentary dynamics--specially terrigenous arrivals--also controlled carbonate sedimentation, as did warm, wet climate, which induced reef and coal formation.

Finally, the general extensional tectonic pattern deduced from the northwest-southeast and southwest-northeast oriented troughs and highs can be better explained through the synsedimentary action of several major and sinistral strike-slip faults. These took advantage of former basement lineaments as a result of the counterclockwise drift of Iberia with respect to Eurasia.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.