Provenance and Diagenesis of Heavy Minerals, Cenozoic Units of the Northwestern Gulf of Mexico Sedimentary Basin
Heavy mineral studies in the post-Mesozoic units of the Gulf of Mexico (GOM) passive margin basin include numerous classic applications for deciphering sediment provenance and for stratigraphic correlation. Because of the well-documented provenance and simple burial history, this basin has also served as a natural laboratory for research into the nature of processes by which provenance information is ‘erased’ and otherwise complicated by diagenesis.
Based on observations in the GOM, a generalized model for basinal diagenesis of heavy minerals is proposed. From the surface to depths corresponding to around 80 to 100 ˚C, diagenesis of the heavy mineral assemblage is dominated by dissolution that is best characterized as an acid hydrolysis or weathering process. At depths that overlap the ultimate completion of the subsurface weathering process, precipitates, including a number of high-density phases, form by reactions that can be described as acid-releasing or reverse weathering. At depths near the limit of coring (> 5 km), the surviving ultrastable detrital heavy mineral assemblage (mostly zircon, tourmaline, and rutile) is accompanied by an intriguing variety of high-density authigenic minerals (including anatase and sphene). The provenance interpretation of heavy mineral extracts from rocks that have had a protracted history of burial must be evaluated cautiously and with an emphasis on the use of ultrastable species.