Coralgal buildup in a mixed carbonate-siliciclastic succession of the upper Eocene Sant Martí Xic Formation (Orís, Vic, SE Ebro Basin, Spain)

Abstract

Coralgal buildups from the mixed carbonate siliciclastic succession of the upper Eocene Sant Martí Xic Formation (Orís, Vic, SE Ebro Basin, Spain) were studied. During the upper Eocene, the sedimentation in the Orís area was strongly influenced by global and local factors associated with the evolution of the Ebro Basin. The stratigraphic series in Orís shows first a transgressive sedimentary sequence characterized by floatstone to rudstone limestone with Discocyclina and Nummulites, which developed in a deeper and oligophotic environment and in a general context of humid climate conditions. The second sequence is formed by progradational deltaic deposits rich in Nummulites and developed under more arid climate conditions. Coralgal buildups occur interdigitated with these deltaic deposits forming two different lens-shaped bioherms that resulted in a coalescent buildup, with coral colonies sparse in a skeletal matrix of different grain-size. Corals grew in the mesophotic zone of the deltaic system affected by light fluctuations during periods of low siliciclastic input. The coralgal buildups of Sant Martí Xic Formation were thus influenced both by climatic changes and by the local detrital input from a deltaic system, associated with the uplift of the Catalan Coastal Range, highlighting the resilience of Eocene corals to environmental change.