Quantitative analysis of stylolite networks in different platform carbonate facies

Abstract

Stylolites are rough surfaces that form by pressure solution, and present variable geometries and spatial distributions. Despite being ubiquitous in carbonate rocks and potentially influencing fluid flow, it is not yet clear how the type and distribution of stylolite networks relate to lithofacies. This study investigates Lower Cretaceous platform carbonates in the Benicàssim area (Maestrat Basin, Spain) to statistically characterize stylolite morphology and stylolite network distributions in a selection of typical shallow-marine carbonate lithofacies, from mudstones to grainstones. Bedding-parallel stylolite networks were sampled in the field to quantify stylolite spacing, wavelength, amplitude, intersection morphology and connectivity. Grain size, sorting and composition were found to be the key lithological variables responsible for the development of rough anastomosing stylolite networks. Poorlyconnected stylolites with large vertical spacings were found to be dominant in grainsupported lithofacies, where grains are fine and well sorted. Anastomosing stylolite networks appear well developed in mud-supported lithofacies with poorly-sorted clasts that are both heterogenous in size and composition. Mud-supported facies feature stylolites that are closely spaced, have high amplitudes and intersection densities, and predominantly present suture and sharp-peak type morphologies. Larger grains and poor sorting favour the formation of stylolites with small vertical spacings, low wavelengths and high amplitudes. This statistical analysis approach requires only limited information, such as that from drill core, and can be used to characterise stylolite morphology and distributions in subsurface carbonate reservoirs.

Stylolites and stylolite networks as primary controls on the geometry and distribution of carbonate diagenetic alterations

“…Expanding upon extensive research at the Benicàssim area, we have carefully mapped and examined diagenetic replacement fronts at variable scales, ranging from the km-to the μmscale, away from large-scale faults and within the stratigraphic and structural context. We have re-examined more than 300 thin sections analyzed in previous studies (e.g., Martín-Martín et al, 2013;2015;Gomez-Rivas et al, 2014;Humphrey et al, 2020. Moreover, 20 additional samples of selected reaction fronts were collected for a detailed characterization of such surfaces.…”

“…2b). Humphrey et al (2020) investigated the prevalence of the different stylolite types in the most representative carbonate depositional facies of the Benassal Fm, using the classification of Koehn et al (2016). Suture-and-sharp peak and wave-like stylolites are ubiquitous in all the facies analyzed, with grainstones also featuring rectangular layer-type stylolites (Fig.…”

“…Beddingparallel stylolites, also called diagenetic or sedimentary stylolites, form during burial and compaction as a response to layer-normal compression associated with the weight of the overburden sediments. Stylolites are ubiquitous in most carbonate formations, present variable distributions depending on the host rocks (Ehrenberg et al, 2016) and often form complex anastomosing networks (Ben-Itzhak et al, 2014;Humphrey et al, 2020). These structures have historically been considered barriers to fluid flow because they can collect insoluble material (e.g., clays, mica, oxides, sulphides, organic matter) while they grow (e.g., Nelson, 1981;Finkel and Wilkinson, 1990;Alsharhan and Sadd, 2000).…”

“…These scenarios assume that the diagenetic fluid can transport enough solutes to the reaction site, by advection-diffusion, and that the reaction will occur if the fluid reactivity and environmental conditions are appropriate. Finally, another hitherto not considered key aspect is that stylolites in nature often appear arranged in networks rather than in isolation (e.g., Ben-Itzhak et al, 2014;Humphrey et al, 2019;Humphrey et al, 2020). Therefore, one should collectively evaluate how individual stylolites may impact fluid flow, transport and reactions, and what the role of networks of stylolites is on these processes.…”

“…We examine at multiple scales mineral replacement reactions (dolomitization and calcitization), dolomite recrystallization, corrosion, and precipitation of saddle dolomite, calcite and iron oxide cements. Building upon the extensive previous knowledge of the area (Martín-Martín et al, 2013;2015;Gomez-Rivas et al, 2014;Humphrey et al, 2020;Yao et al, 2020) we provide new observations and analyses of outcrops and samples, paying special attention to cases in which individual stylolites act as baffles/inhibitors or enhancers of different types of diagenetic reactions, whether the same structures can exhibit different transport behaviour and, finally, to what extent large-scale (i.e., metre to kilometre-scale) diagenetic alterations can be controlled by stylolite networks. The findings of this study have implications beyond the study of diagenesis in carbonate formations because the same principles of stylolite and fluid flow interactions apply to the circulation of geofluids (hydrocarbons,brines,groundwater,injected CO2,etc.…”