Continuity and facies heterogeneities of shallow carbonate ramp cycles (Sinemurian, Lower Jurassic, North-east Spain)

Abstract

The lateral continuity and facies heterogeneities of metre-scale cycles in a greenhouse Lower Jurassic (Sinemurian) carbonate ramp from the northern Iberian Basin (Spain) was evaluated from extensive field analysis carried out on a well-exposed 12 km long outcrop. Eleven high-frequency continuous cycles and their bounding surfaces are traceable laterally through the entire outcrop. However, three of these cycles are found to split laterally into discontinuous cycles of more limited distribution (up to 3 to 5 km of lateral extent). The continuous and discontinuous cycles have a similar field expression in one-dimensional logs. As a consequence, the number of cycles that can be differentiated is variable along the logged sections (i.e. from 11 to 16). Cycles have variable facies heterogeneities and sedimentary trends depending on the environment of formation: shallowing-upward and symmetrical cycles occur in protected lagoon-tidal flat areas and in the open-marine, high-energy domain. These cycles show significant facies heterogeneities, which were controlled mainly by lateral migration of a mosaic of facies over an irregular topography. Deepening-upward and aggradational cycles are generated in low-energy, sub wave-base, openmarine areas. Facies are laterally homogeneous, reflecting low potential for carbonate accumulation and inability to fill the created accommodation space in this low-relief and relatively deep area. Cycle boundaries are generated by stages of rapid accommodation gain, involving the flooding of the carbonate ramp; they are more likely to originate from regional tectonic pulses (related to the extensional tectonics operating in the northern Iberian Basin) rather than greenhouse low-amplitude eustacy. Discontinuous cycles tend to occur in thickened areas and are interpreted as originating from the infill of wedgeshaped accommodation space resulting from differential subsidence (i.e. local tectonic pulses). In conclusion, where thickness variations occur in extensional settings lateral continuity of cycles should not be expected. In less well-exposed, or in one-dimensional sections and in wells, it would not be possible to distinguish continuous from discontinuous cycles, or to understand such two-dimensional heterogeneities. Identification of unique cycle-forming mechanisms or attempting cyclostratigraphic long-distance correlation of cycles is unrealistic without a detailed analysis of the architecture of cycles in laterally continuous outcrops.

Peritidal cyclic sedimentation from La Manga Formation (Oxfordian), Neuquén Basin, Mendoza, Argentina

“…The finning up-ward facies indicate that these lags probably correspond to washover expanding into the protected lagoon and intertidal set-tings (cf. Bádenas et al, 2010). Moreover, during the storms, shell debris of marine organisms would be transported and washed from the shallow subtidal to the intertidal-lower supratidal environments.…”

“…Adams and Grotzinger, 1996) even though a local subsidence can not rule out (Hamon and Merzeraud, 2008). As Bádenas et al (2010) suggest, the lateral continuity of cycles can be controlled by depositional topography or by local subsi-dence, where facies distribution results from production rate and accumulation. Evidence of sea level fall was reported by Palma et al(2010Palma et al( , 2011 because of the presence of paleokarstic breccias facies.…”

Lateral facies variations in the Triassic Dachstein platform: A challenge for cyclostratigraphy

“…Many workers have described laterally persistent platform cycles (Demicco, 1985;Goldhammer et al, 1987;Goldhammer, Dunn, & Hardie, 1990;Goodwin & Anderson, 1985;Grotzinger, 1986;Koerschner & Read, 1989;Osleger & Read, 1991), although lithofacies within individual cycles can vary laterally (Adams & Grotzinger, 1996;Bádenas, Aurell, & Bosence, 2010;Cloyd, Demicco, & Spencer, 1990;Cowan & James, 1996;Egenhoff, Peterhänsel, Bechstädt, Zühlke, & Grötsch, 1999;Laporte, 1967;Obermaier, Ritzmann, & Aigner, 2015;Pratt & James, 1986;Samankassou, Strasser, Di Gioia, Rauber, & Dupraz, 2003). Lateral facies variations have also been reported from modern sites (Bosence, 2008;Eberli, 2013;Enos & Perkins, 1979;Harris, Purkis, & Ellis, 2011;Purkis & Harris, 2016;Wilkinson & Drummond, 2004) and from the Triassic Dachstein platform in the Northern Calcareous Alps (Enos & Samankassou, 2002;Piller, 1976Piller, , 1981Satterley, 1996b;Zankl, 1967).…”

Allogenic and autogenic processes combined in the formation of shallow-water carbonate sequences (Middle Berriasian, Swiss and French Jura Mountains)

“…It is therefore the combination of autogenic/autocyclic and allogenic/allocyclic processes that is responsible for sediment deposition and the formation of the final sedimentary record. Many case studies have already shown and discussed the coexistence of autocyclic and allocyclic processes, for example: Sami and James (1994) in the Proterozoic of northwest Canada; Jiang et al (2003) in the Proterozoic of the Lesser Himalaya; Adams and Grotzinger (1996) in the Middle Cambrian of California; Cowan and James (1993) in the Late Cambrian of Newfoundland; Smith and Read (2001) in the Mississippian of Illinois; Yang et al (1998) in the Late Pennsylvanian and Early Permian of Texas; Bádenas et al (2010) in the Sinemurian of Spain; Carpentier et al (2010) in the Oxfordian of France; Sattler et al (2005) in the Barremian and Aptian of Oman; Lehmann et al (1998) in the Barremian to Albian of northeastern Mexico; Rankey (2002) in the Holocene of the Bahamas.…”