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A dolomitized Upper Miocene carbonate system in southeast Spain contains extensive upper and lower zones of calcite cementation that cut across the stratigraphy. Cement textures including isopachous and circumgranular, which are consistent with phreatic-zone cementation. Cements in the upper cemented zone are non-luminescent, whereas those in the lower cemented zone exhibit multiple bands of luminescent and non-luminescent cements. In the upper cemented zone, isotopic data show two meteoric calcite lines (MCL) with mean δ 18 O at − 5.1‰ and − 5.8‰ VPDB, whereas no clear MCL is defined in the lower cemented zone where mean δ 18 O for calcite cement is at − 6.7‰ VPDB. δ 13 C values in both cement zones are predominantly negative, ranging from − 10 to + 2‰ VPDB, suggestive of carbon from soil gas or decayed organics. Measurements of Tm ice in primary fluid inclusions yield a mode of 0.0 °C in both zones, indicating calcite cementation from fresh water. These two zones define the positions of two different paleo-water tables that formed during a relative sea-level fall and erosional downcutting during the Plio-Pleistocene. The upper cemented zone pre-dated the lower cemented zone on the basis of known relative sea-level history. Meteoric calcite cementation reduced porosity and permeability, but measured values are inconsistent with simple filling of open pore space. Each texture, boundstone, grainstone, packstone, wackestone, produces a different relationship between percent calcite cement and porosity/permeability. Distribution of cements may be predictable on the basis of known sea-level history, and the effect of the cementation can be incorporated into subsurface geomodels by defining surfaces of rock boundaries that separate cemented zones from uncemented zones, and applying texture-specific relationships among cementation, porosity and permeability. [ABSTRACT FROM AUTHOR]

Previous research has explored the linkage between bioturbation, porosity, and permeability in carbonate reservoir rocks. The impact of bioturbation on natural fractures in such rocks remains relatively unexplored, however, but is crucial for effective subsurface resource management. This study focuses on the relationship between bioturbation and fracture characteristics in a well-exposed outcrop, the upper Cretaceous Khanasir Member of the Aruma Formation, central Saudi Arabia. The approach includes field investigation, petrography, imaging analysis, and CT scanning to quantify the relationship between burrows and fracture characteristics at scales from thin section to outcrop scale. At the outcrop scale, the Khanasir Member comprises three distinct units based on their fracture and burrow characteristics. These units reveal two primary categories of fractures: (1) burrow-related fractures, influenced and controlled by bioturbation; and (2) non-burrow-related fractures, unaffected by bioturbation. The characteristics of fractures within these units are influenced by multiple factors including: if burrows are filled; composition of the burrow fillings; mineralogy of host rock matrix; texture of the host rock matrix; and burrow percentage. The interplay of these factors affects fracture attributes such as density, length, and spacing, all of which have a direct impact on fluid flow behavior within subsurface reservoirs. • Bioturbated strata in the Aruma Formation display extensive burrowing and fractures. • Fractures are influenced by burrow attributes, composition and diagenesis. • Two fractures categories are identified: burrow and non-burrow-related fractures. • The burrows, fractures, and the host rock matrix forms a triple-porosity system. [ABSTRACT FROM AUTHOR]

The upper Cretaceous Aruma Formation in Central Saudi Arabia exhibits Thalassinoides -bearing strata resembling a bioturbated carbonate reservoir with large burrows. These burrows possess distinct stratigraphic characteristics. Certain intervals within the formation feature open or partially filled Thalassinoides , creating three-dimensional permeability pathways, while others contain Thalassinoides filled with low-permeability sediments. This comprehensive study investigates the paleoenvironment, ichnological features, bulk permeability influence, and stratigraphic variations of these bioturbated intervals. Incorporating field observations, laboratory analyses (including petrography, geochemical assessments, petrophysical measurements, and computed tomography scanning [CT]), we present the division of the studied interval into three biogenically influenced fluid flow media (BIFM 1–3). BIFM 1 comprises solution-enlarged open Thalassinoides (average shaft diameter: 5 cm) hosted within a mud-dominated matrix. BIFM 2 consists of Thalassinoides with mud-dominated infills (average shaft diameter: 3 cm) embedded in a dolomite matrix. BIFM 3 exhibits compacted open Thalassinoides. These BIFM units demonstrate burrow percentages ranging from 10% to 45%, featuring interconnected networks. The identified units reflect diverse depositional settings, ranging from open marine to restricted lagoon, and distinct stratigraphic positions. By highlighting the sedimentological and stratigraphic controls on the petrophysical properties of carbonate strata containing Thalassinoides with large burrows, this research contributes to the prediction of super-permeability zones in analogous settings. • Bioturbated strata in the upper Cretaceous Aruma Formation resemble a carbonate reservoir with distinct large burrows. • Thalassinoides -bearing intervals exhibit both permeability pathways and low-permeability infills. • The study investigates the paleoenvironment, ichnological, and stratigraphic variations of the bioturbated intervals. • Three biogenically influenced fluid flow media (BIFM 1–3) are identified via field observations and laboratory analyses. • Sedimentological and stratigraphic controls on petrophysical properties provide insights for predicting super-K zones. [ABSTRACT FROM AUTHOR]