SR-87 SR-86 CHRONOSTRATIGRAPHY AND DOLOMITIZATION HISTORY OF THE SEROE-DOMI FORMATION, CURACAO (NETHERLANDS-ANTILLES)/

The Seroe Domi Formation is a 350 m-thick sequence of Neogene marine l imestones and silicilastic sandstones cropping out on the leeward coas t of Curacao, Netherlands Antilles. Integrated analyses of lithofacies , biostratigraphy, geochemistry and Sr isotope model age analyses indi cate that Seroe Domi Formation has experienced three major episodes of limestone diagenesis and dolomitization (Dolomites I, I', and II) tha t have taken place after successive Mio-Plio-Pleistocene depositional and subaerial exposure events (Subunits 1, 2, and 3). Subunit 1, the l owermost 30 to 100 m of the Seroe Domi Formation, is composed of inter bedded coralgal grainstone gravity flows,pelagic wackestones; and allo chthonous blocks deposited in Middle Miocene deep-water (>500 m) fore- reef and carbonate slope environments. Subunit 2, the uppermost 250 m of the Seroe Domi Formation, consists of coralgal packstones with base ment-derived siliciclastic sands that were deposited in shallowing for e-reef to reef-front environments during the Late Miocene to Pliocene. Subunit 3 siliciclastic sandstones were deposited during the Early Pl eistocene within erosional cavities in the Subunit 2 limestones, and a re overlain by Late Pleistocene Quaternary Limestone Terraces. The pet rography, distribution and geochemistry of Dolomites I, I' and II indi cate that they were precipitated from seawater-freshwater mixing zone fluid environments. Dolomite rhombs and meteoric calcite cements withi n biomolds illustrate that the host Seroe Domi Formation limestones we re subaerially exposed prior to each dolomitization event. Dolomite I (delta(18)O = +1.04 to +2.46 parts per thousand PDB; delta(13)C = -2.5 5 to -6.79 PDB; Sr-87/Sr-86 = 0.708866 to 0.708915; Zn = 0 ppm; Cu = O ppm) was precipitated from mixtures of seawater with isotopically-dep leted freshwater during the late Middle Miocene. Dolomite I' (delta(18 )O = +2.08 to +3.55 PDB, delta(13)C = -1.53 to +1.69 PDB, Sr-87/Sr-86 = 0.708981 - 0.709030; Zn = 0 ppm; Cu = 0 ppm) was also precipitated f rom mixtures of seawater with isotopically-depleted freshwater, but du ring late Late Miocene. In contrast, Dolomite II (delta(18)O = +2.69 t o +3.51 PDB; delta(13)C = -0.34 to +1.53 PDB; Sr-87/Sr-86 = 0.708954 t o 0.709088; Zn = 20 ppm; Cu = 20 ppm) precipitated from late Early Pli ocene mixtures of seawater with isotopically-depleted freshwater that had derived Zn, Cu, and less-radiogenic Sr from basalts comprising the Curacao basement.