Bivalves in the upper Miocene reef complex of Mallorca, Spain

Resum

Bivalves are common components in all the palaeoenvironments recognised in the Llucmajor Platform, the best-known outcrop of the Upper Miocene Mallorca Reef Complex. Shell concentrations of autochthonous elements with a low degree of taphonomical modification accumulated on the deep, quiet water bottoms from the basin to proximal reef slope. Low sedimentation presumably enhanced shell concentration as well as the development of clusters of superimposed slow-growing organisms, such as Neopycnodonte oysters that are typical of the basin and distal slope settings. Debris-flow beds of mostly disarticulated, fragmented and reoriented moulds of valves intercalate with the autochthonous shell concentrations in the basin and slope deposits as the result of downslope transport of bioclasts from shallower reef areas. Bivalve assemblages in the shallower-water reef palaeonvironments mainly con.sist of moulds of reworked fragments of disarticulated valves. Some crevice-dwellers, cemented and epibyssate forms were preserved in life position in the shelters created by coral colonies and blocks. The percentage of unbroken and articulated shallow endosedimentary bivalves is higher towards the protected inner-lagoon settings, in which Tellina specimens are the most characteristic components. We have identified 52 bivalve species belonging to 38 genera and recorded 19 additional species only identifiable at the generic level in all the sampled reef palaeonvironments.