Facies analysis and correlation of high-order sequences in middle-outer ramp successions : variations in exported carbonate on basin-wide δ13Ccarb (Kimmeridgian, NE Spain).

Abstract

Carbonate mud that accumulated in the deep parts of a late Kimmeridgian carbonate ramp (Iberian Basin, NE Spain) was partly derived by resedimentation from shallow water production areas. High-frequency sea-level changes, probably driven by climatic changes in tune with precession and short-eccentricity cycles, affected carbonate production and the amount of exported sediment. Facies analysis and correlation of three outcrops located in middle and outer ramp settings allows a comparison of high-order sequences (bundles of beds and sets of bundles) across a ramp transect and an assessment of the carbonate factory. Analysis of the storm deposits found in middle ramp settings identifies deepening to shallowing high-frequency cycles based on the level of exported carbonate. In outer ramp areas, many of the bundles exhibit a thinning trend, indicating a progressive decrease of carbonate production and hence, carbonate export during periods of high-frequency sea-level rise. δ13Ccarb values show a gradual increase through the studied long-term transgressive interval ranging from 1·5‰ to 2·8‰. Within this long-term evolutionary trend, short-term δ13Ccarb fluctuations occur that correspond with some of the high-order cycles defined from sedimentary facies analysis. These short-term δ13Ccarb shifts are interpreted as shifts in carbonate export from shallow reef regions to the outer ramp. A consequence of this study is that variation in δ13Ccarb can be used for correlation in outer ramp successions, at least on a basin-wide scale.