Rhodolith assemblages from the lower Tortonian carbonate ramp of Menorca (Spain): Environmental and paleoclimatic implications

Lower Tortonian distally steepened carbonate ramp of Menorca mostly consists of foramol and rhodalgal facies deposited in inner-middle ramp, ramp slope and outer ramp settings. Red algae are abundant from the middle ramp to the lower part of the slope and their taxonomic assemblages are clearly related to the bathymetric position. Melobesioids percentage increases basinward, passing from 55.8% in the middle ramp to 97% in the toe of slope. Mastophoroids are more abundant in the middle ramp (43.1%) and decrease toward deeper paleoenvironments (1.2%). Lithophylloids and sporolithaceans appear as accessory components from the middle ramp to slope settings. The percentage of melobesioids and mastophoroids observed in the middle ramp suggest that growth of the rhodoliths started in a water depth below 10-20 m. The deepest occurrence of the rhodoliths is in the ramp slope environment, where the dominance of melobesioids and the low percentage of shallower-water subfamily suggests a water depth range of 70 to 100 m. Shape and structure of rhodoliths are indicative of high-energy conditions in all ramp settings and they do not reflect a decrease in hydrodynamic energy related to water depth increase. These conditions are related to the presence of unidirectional currents that produced cross-bedded grainstones existing in the middle ramp, ramp slope and at the toe of the ramp slope settings. The high percentage of mastophoroids in the shallowest environments and the presence of Lithoporella and Sporolithon in the coralline assemblages suggests that carbonate production took place in tropical waters.