Ichnological analysis in high-resolution sequence stratigraphy: The Glossifungites ichnofacies in Triassic successions from the Betic Cordillera (southern Spain)

Abstract

This study integrates ichnological and sedimentological data in order to refine sequence stratigraphy and interpretations of sealevel dynamics for the Ladinian (Middle Triassic), Muschelkalk succession (Siles Formation) in the Betic Cordillera (southern Spain). Facies analysis was integrated with a detailed ichnological study, focused on the middle part of the lower member of the Muschelkalk succession (transgressive systems tract), which is characterized by an abundant and conspicuous trace fossil assemblage. Seven lithofacies were recognized, recording sediment accumulation in tidal flat, and inner to outer marine carbonate ramp, depositional environments. Thin-bedded marly limestones with bioclastic shelly beds (Facies E: middle ramp, with storm influence), are characterized by Diplocraterion and Rhizocorallium. Diplocraterion is protrusive, usually eroded on top, and mainly recorded in the marly limestone intervals. Rhizocorallium preserves well defined scratch-marks, and is commonly emplaced in bioclastic, shelly beds. The assemblage represents the Glossifungites ichnofacies. Sedimentological and ichnological data are interpreted to record a complex transgressive context, associated with high-frequency sea-level dynamics that allowed formation of transgressive surfaces of erosion (TSE, i.e., ravinement surfaces) of different orders. Major TSE, associated with continuous bioclastic shelly beds, delimit parasequences; the absence of the Glossifungites suite reveals that there was little time between erosion and deposition. Intermediate TSE, associated with discontinuous shell beds, are related to comparatively less significant sea-level rises and occur within parasequences. The Glossifungites suite reveals colonization of firmgrounds during relatively prolonged times between erosion and deposition related to intermediate TSE. Minor order TSE, recorded between the intermediate TSE, are related to punctuated, highest frequency sea-level changes; phases of colonization by the Diplocraterion tracemaker and protrusive, capped structures reveal more or less stillstand phases (TSE/stillstand phases), and minor order erosional phases.