Accumulations of ferganites (fusulinacea) in shallow turbidite deposits from the carboniferous of Spain

Abstract

As occurs commonly in upper Kasimovian and lower Gzhelian strata from several parts of Eurasia, the lower part of the Puentellés Formation (Cantabrian Zone, NW Spain) contains high concentrations of reworked Ferganites tests. No other large fusulinacean taxa are recorded in these beds, which are interpreted as shallow turbidite deposits derived from flood-dominated fan-delta and river-delta systems. These alluvial to shelfal lobes developed in a tectonically active setting and were located in the proximal sectors of a marine carbonate ramp, with hyposaline water conditions. In contrast, the upper member of the Puentellés Formation contains more varied fusulinacean assemblages, including Ferganites and other large fusulinaceans. This upper part is characterized by diverse biota, skeletal wackestone deposits with abundant boundstone intervals (algal bafflestones and mud mounds), and represents the gradual backstepping from detrital lobes and re-establishment of normal marine conditions, lacking clastic influx from the hinterland. The Ferganites species occurring in the lower member seem to have lived in near-shore, high-energy environments in which their durable morphology was advantageous. These forms seemingly were well adapted to relatively low salinity conditions, which otherwise greatly restricted faunal diversity. Four Ferganites forms from the lower member of the Puentellés Formation (including a new species, Ferganites martinezi) are described.