OCCURRENCE AND TAPHONOMY OF BIVALVES FROM THE NIJAR REEF (MESSINIAN, LATE MIOCENE, SE SPAIN)

Bivalves are conspicuous and important components in the Messinian Nij ar reef, a fringing reef which developed on the northern margin of the Almeria-Nijar Neogene basin in southeastern Spain. Bivalves appear in four distinct taphofacies that coincide with the facies and subfacies belts in which the reef has previously been divided: (1) In the reef core (Taphofacies 1) well-preserved, crevice-inhabitants occur. Sand- to gravel-sized bivalve fragments are included in the matrix that fill s the framework voids. (2) Bivalve bioclasts appear in gravels surroun ding reef-framework blocks in Taphofacies 2. Sheltering among blocks d iminished breakage of shells, pointing to a hydraulic origin of shell reworking and fragmentation in this upper part of the slope. The recog nisable fragments belong to bissally-attached, cemented, and endobenth ic forms. Endolithic, and some cemented and endosedimentary bivalves r emain in life position. (3) Bivalves are found in Taphofacies 3 as cla sts in debris-flow breccias and constitute allochthonous assemblages c oming downslope from the reef-talus. They a so appear as sand- to grav el-sized particles in the calcarenites intercalating the breccias and only a few unbroken and sometimes articulated examples are considered to be autochthonous/parautochthonous in this environment. (4) Scarce, not fragmented, deep-water oysters are dispersed in the fine-grained s ediments of the distal slope. The number of bivalve species is very lo w compared with the species richness of modern coral reefs, and most o f the recorded taxa have a present-day temperate distribution. All thi s supports the hypothesis of the marginal biogeographical character of the western Mediterranean Messinian reefs.