Oil and gas reside in reservoirs within peritidal and shallow subtidal lagoonal carbonate sediments across the globe. This is a zone of facies heterogeneity, controlled by changes in depositional energy, water depth, clastic influx, and evapotranspiration. Close proximity to evaporitic brine pools means that it is also an environment with the potential for dolomitization during shallow burial. As a result, the original pore system of carbonate sediment can become drastically altered prior to burial, such that reservoir properties may not be predictable from facies models alone. The Miocene Santanyí Limestone Formation, Mallorca, Spain, is well exposed and has undergone minimal burial and therefore presents an excellent opportunity to integrate sedimentology, facies architecture, and diagenesis to determine how porosity evolves within individual facies in the shallow subsurface. From here, the impact on pore type, pore volume, pore connectivity, and petrophysical anisotropy can be assessed. The Santanyí Limestone consists of pale mudstones and wackestones, rooted wacke-packstones, stratiform laminites, and skeletal and oolitic, cross-bedded grainstone. Thin-section analysis reveals a paragenetic pathway of grain micritization, followed by dissolution of aragonite, possibly by meteoric fluids associated with karstification. Subsequently, the unit underwent fracturing, compaction, recrystallization, cementation, dolomitization, and matrix dissolution to form vugs. Petrophysical analyses of 2.54-cm-diameter plugs indicate that these complex diagenetic pathways created petrophysical anisotropy [mean horizontal permeability (Kh)/vertical permeability (Kv) of whole formation = 3.4] and that measured parameters cannot be related directly to either geological facies or pore type. Instead, petrophysical data can be grouped according to the diagenetic pathways that were followed after deposition. The best reservoir quality (i.e., typical porosity 15 to >40% and permeability >100 mD) is associated with pale mudstones, stratiform laminites, and skeletal and oolitic grainstone that have undergone pervasive recrystallization or dolomitization. These rocks have the some of the lowest formation resistivity factor (FRF) values (<200) and thus the simplest pore system. The poorest reservoir properties ( k <10 mD) occur in mudstones and wackestones that have not been recrystallized and, hence, are dominated by a simple network of micropores (FRF <101). Skeletal and oolitic grainstones and rooted and brecciated wacke-packstones that have undergone some cementation and partial recrystallization have moderate reservoir properties and a high FRF (>>1000), reflecting a complex pore system of biomolds, vugs, and microporosity. Consequently, reservoir properties can be predicted based on their primary rock properties and the diagenetic pathway that they followed after deposition.

Abstract Inorganic whole rock geochemical and magnetic susceptibility (χ) data have been gathered from seven sections through the Upper Miocene reef complexes of the Llucmajor Platform, Mallorca. The aim of acquiring these data is to determine what chronostratigraphic information a combination of magnetic susceptibility stratigraphy (MSS) and chemostratigraphy can provide in reef complexes of a carbonate platform with no nearby source of terrigenous material. Chi values display short-term cyclical fluctuations, maximum values commonly being associated with the upper bounding surfaces of sigmoids and sigmoid sets, the building blocks of the Llucmajor reef complexes. Values of χ are low at the bases of the sigmoids; they reach a maximum at the top of the sigmoids, and then fall rapidly to the base of the next sigmoid, indicating a base-level control on χ values. No longer term variation in the χ values have been identified that would enable differentiation of an old reef complex from one that is demonstrably younger in the cliff sections, and there is no apparent facies control on χ values. While the elemental data do not vary in response to base-level fluctuations and therefore do not define stratigraphic surfaces, they do show long-term variations, enabling reef complexes of differing ages to be geochemically characterized: the key to defining chemostratigraphic schemes. The elements used to characterize different age reef complexes are Cr, Zr, Al 2 O 3 , TiO 2 , Ga, and Rb, which are controlled by changes in the amount and composition of wind-blown terrigenous material and tuffaceous material. As such, the changes are chronostratigraphic events on the scale of the study intervals here. Although the two datasets used are both ultimately controlled by the mineral composition of the sediments, it has proved impossible to find a direct link between the elemental data and χ values. Despite the lack of an understanding of the relationship between whole rock geochemistry and χ values for this dataset, they clearly provide a means to (1) define stratal surfaces that relate to base-level fluctuation and (2) recognize reef complexes deposited at different times. Therefore, the combined approach adopted here for the Llucmajor reef complex has the potential to provide cross-facies chronostratigraphic correlations in detached platform carbonate settings, and since both methods can be applied to core and cuttings samples, the approach could work in subsurface settings where samples would be from well bores.