## 1 Introduction  
In many parts of the world, Jurassic strata contain extensive bioturbated intervals that encompass significant hydrocarbon reservoirs such as the Fulmar Formation and Brent Group, North Sea, UK [1, 2]; the Ile Formation, Norway [3]; the Shaqra Group and the Ghawar Field, Saudi Arabia [4, 5, 6]; and the Vaca Muerta Formation, Argentina [7]. Bioturbation is defined as the biogenic (by benthic infauna) transport of sediment particles and pore water which destroys the sediment stratigraphy. These processes also impact the physical properties of the sediment such as grain size spectrum, porosity, and permeability [8]. Benthic infauna can significantly modify the original sediments while generating new structures through sediment mixing and redistribution of the grains. Such modification may include sediment removal (bioerosion), sorting (biotransformation), emplacement (biode-position), and compaction [9]. Moreover, geochemical signatures of sediments may also be modified by burrowing organisms through a combination of organic matter produced by these organisms [6,10]. Bioturbation can have a significant influence on the petrophysical properties of hydrocarbon reservoirs. Several studies were carried out that demonstrated the impact of bioturbation on improving and decreasing of petrophysical properties of siliciclastics [11, 12, 13, 14, 15], as well as of carbonates [5, 6, 7, 8]. Some studies demonstrated that bioturbation can enhance the reservoir quality, mainly in permeability, to variable degrees [5, 6, 12, 15, 16, 17, 18, 19]. All the aforementioned studies have demonstrated that the impact of bioturbation on reservoir quality is dependent on the bioturbation style and burrow attributes [20,21]. The acoustic velocity is the main controlling factor on seismic reflectivity of different rock units. Seismic reflectivity is the basis for seismic reflection behavior, one of the most important principles in hydrocarbon exploration. The acoustic velocity of carbonate sedimentary strata is largely controlled by (i) the mineralogy, (ii) petrophysical properties, i.e., amount of porosity, pore type, pore distribution, and (iii) diagenetic processes modifying the sediments [22, 23, 24, 25, 26, 27, 28, 29, 30, 31]. Bioturbated strata are characterized by a complex distribution of porosity and permeability, as the trace fossils can alter the pore-throat distribution and the bioturbation traces may act as loci for dissolution and cementation processes during early and late diagenesis [32]. These processes consequently influence the acoustic wave propagation through these bioturbated units. Bioturbation is common throughout the carbonate strata of the Middle-Upper Jurassic of Saudi Arabia (Tuwaiq Mountain, Hanifa, Jubaila, and Arab formations), and they show a significant control on fluid flow properties of these strata [4, 5, 6, 33]. These studies have shown that _Thalassinoides_ burrows have enhanced flow properties of the dolomitic and mud-dominated units of the strata of these formations, and contributed significantly to the fluid flow properties of the Super-K Zone in the Ghawar field of Saudi Arabia [6]. The previous studies aimed at understanding the impact of bioturbation and ichnofabrics on reservoir quality, and specifically, permeability. However, the impact of bioturbation on carbonate acoustic velocities was not reported in the literature so far. This study aims to determine the main factors that control the reservoir quality (porosity and permeability) and acoustic velocities of the Upper Jurassic bioturbated strata of the Hanifa Formation in Central Saudi Arabia. To determine the factors influencing the petrophysical properties and acoustic velocities of bioturbated strata, a series of outcrops along the Riyadh-Mecca road in the Darma quadrangle (Figure 1) in Central Saudi Arabia were studied, sampled, and analyzed in detail. Analyses include the characterization of all intrinsic and extrinsic features such as mineralogical composition, texture, porosity and pore types, and permeability.