Jurassic guyots on the Southern Iberian Continental Margin: a model of isolated carbonate platforms on volcanic submarine edifices

Abstract

During the middle Jurassic on the Southern Iberian Continental Margin (at the westernmost end of the northern Tethys) isolated carbonate platforms developed over volcanic edifices, forming guyots. The volcanic edifices were composed of K‐rich pillow‐lavas and pyroclastic rocks with a radiometric age ≈ 170 Myr. Such phenomena have not been described until now in this continental margin nor in other passive continental margins of Alpine domains. The presence of a shallowing‐upward megasequence (Bajocian–Bathonian) with hummocky cross‐ stratification strata below oolitic shoals, shows that very shallow isolated carbonate platforms developed above the volcanic edifices, with similar facies to those recognized in other guyots, but with a different age and geodynamic context.

Glauconitic laminated crusts from hydrothermal alteration of Jurassic pillow-lavas (Betic Cordillera, S Spain): a microbial influence case

“…Basaltic pillow-lava flows dominate, interbedded with pyroclastic rocks and pelagic sediments. The maximum thickness of these volcanic rocks, described in the literature, is over 300 m (Vera et al, 1997). The Lower Jurassic submarine volcanic rocks of the Median Subbetic are considered as transitional alkaline, originated in an extensional process of crustal thinning (Portugal et al, 1995;Vera et al, 1997).…”

“…Jurassic pillow-lavas, intercalated between pelagic sediments, have been studied by numerous authors in the Median Subbetic domain of the External Zones of the Betic Cordillera (Southern Spain) (Comas et al, 1986;Puga et al, 1988Puga et al, , 1989Portugal et al, 1995;Morata et al, 1996;Vera et al, 1997). These submarine volcanic rocks are held to be related to an extensional process of crustal thinning.…”

“…Fe was mobilised by a breakdown of volcanic glass or hydrothermal fluids (in that case Fe 2+ ), while sea-water had to be an additional supplier of K (Clayton and Pearce, 2000; D'Antonio and Kristensen, 2005;Renac et al, 2010;Baker et al, 2012). The volcanic edifices of the Median Subbetic are composed of K-rich pillow-lavas (Vera et al, 1997) and they are potential sources of K. Thus, Fe and K had to be added to the oxidation zone and fixed in the precipitation of Fe-rich dioctahedral micas (glauconite and celadonite).…”

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“…1). La Formación han descrito intercalaciones de rocas carbonatadas pelágicas dentro de las rocas volcánicas (Comas et al, 1981;Vera et al, 1997). En otros se han datado con precisión las coladas a partir de los ammonites de los materiales infrayacentes y suprayacentes (García-Yebra et al, 1972) o a partir de dataciones radiométricas (Puga et al, 1988;Portugal et al, 1995).…”

“…En otros se han datado con precisión las coladas a partir de los ammonites de los materiales infrayacentes y suprayacentes (García-Yebra et al, 1972) o a partir de dataciones radiométricas (Puga et al, 1988;Portugal et al, 1995). En un trabajo reciente (Vera et al, 1997) han descrito, en este mismo sector, depósitos carbonatados marinos someros (incluyendo calizas oolíticas y superficies de karstificación), sobre edificios volcá-nicos, que corresponderían a guyots jurásicos.…”