Proximal–distal facies relationships and sedimentary processes in a storm dominated carbonate ramp (Kimmeridgian, northwest of the Iberian Ranges, Spain)

Abstract

Facies analysis of the upper Kimmeridgian rocks in the outcrops located near Ricla (Zaragoza province, northeast Spain) and the integration of the resultant data in a broader context (the northern part of the Iberian Basin), has produced two general models showing the facies distribution and the processes that controlled the sedimentation in the Kimmeridgian carbonate ramp. Using these two models the transition from shallow to relatively deep environments of the carbonate ramp is examined in detail. Model 1 corresponds to the development of a mixed carbonate-siliciclastic ramp during a slow rise and stillstand of sea level (Sequence 1-HST), whereas Model 2 represents the growth of a pure carbonate ramp during a rapid rise of sea level (Sequence 2-TST).Carbonate production was higher in the shallow ramp domains (coral reefs and oolitic shoals in Model 1 and reefs in Model 2) than in deeper domains, where there is no indication of signi®cant pelagic or benthic production. The activity of unidirectional return¯ows induced by winter storms and hurricanes, played an important role in the redistribution of the sediment across the ramp, generating different coarse-grained deposits. In the inner and mid-ramp settings dunes, lower scale bedforms and tempestites occur in Model 1, and storm lobes, bars and tempestites in Model 2. Moreover, a signi®cant bulk of the carbonate mud produced in shallow areas would eventually be resedimented in the outer ramp as suspended load in the density currents. Stillstand of sea level in Model 1 involved a rapid progradation of the inner and proximal mid-ramp carbonate and siliciclastic facies. The rapid relative sea level rise of Model 2 is determined by the dominance of the carbonate facies and by the presence of aggradational geometries in the transitional area between shallow and deep-ramp domains. The presence of relatively thick sections in the outer-ramp settings (instead of condensed sections, as observed in Model 1) during times of sea level rise (Model 2) can mainly be explained by the increase of the shallow production in the reef dominated areas. q

Sequence stratigraphy and bedding rhythms of an outer ramp limestone succession (Late Kimmeridgian, Northeast Spain)

“…In Aguilón, the transgressive event at the onset of the studied sequence is indicated by a sharp decrease of the terrigenous silty grains (quartz, micas) and marly intervals, recognised between the mixed carbonate -siliciclastic muds of the lower Loriguilla Formation and the pure carbonate muds of the upper Loriguilla Formation. This discontinuity is located around the acanthicumeudoxus zones boundary (Bádenas and Aurell, 2001b), and is likely to correspond to the Kim 4 boundary reported by Hardenbol et al (1998) in the Tethyan domain.…”

“…The TST is characterised by an agradational growth of coralgal reefs that grade offshore into lime mudstones with proximal tempestites. The HST corresponds to the progradation of inner ramp silty lime mudstones and skeletal packstones (Bádenas and Aurell, 2001b). The presence of the trangressive and highstand deposits of the studied depositional sequence in the outer ramp succession of Aguilón can be tested from the obtained facies data.…”

“…The bioclastic patches may also be interpreted as distal tempestites, later disrupted by the effects of bioturbation. Bádenas and Aurell (2001b) have described proximal tempestites in mid-ramp settings (Ricla outcrops, see Fig. 1).…”

“…The distal mid-ramp area represented the inclined morphological segment and was characterised by the deposition of lime mudstones and coarsegrained tempestites. Grains mainly derived from the shallow oolitic shoals and reefs compose these storm deposits (Bádenas and Aurell, 2001b). The erosion and resedimentation by storm-generated density currents from the shallow ramp areas were favoured by the windward orientation of the Iberian basin margin.…”

From platform to basin to swell: orbital control on sedimentary sequences in the Oxfordian, Spain

“…Around maximum flooding and during sealevel highstand, the carbonate factory on the platform is active and carbonate mud is exported to the basin (Schlager et al, 1994;Pittet and Strasser, 1998b), creating limestone beds in the basin. For the Kimmeridgian of the same area, Ba´denas and Aurell (2002) have demonstrated the causal relationship between shallow carbonate production areas, export by storms, and accumulation on the ramp. When sea level drops, the platform is subaerially exposed and the climate less humid.…”