## 5 Discussion
As a result, a dense and elongated structure forms [27], with the layers of clay stacked in domains but without coming into contact with each other and leaving a significant intra-aggregated porosity (Figure 6F), which differs from the most common flocculated structures in MOCs, in which an inter-aggregated porosity is usually much more significant. This structure partially explains the low Cc values measured for the DC when compared with other references of similar materials. Concerning the clays of marine origin (MOCs), the Vallerica Clay reports values between 0.37 and 0.40 [8], and in the Pappadia Clay this index ranges from 0.2 to 0.4 [53]. More similar results have been reported in the Corinth Marl, with Cc = 0.2 [12]. Moreover, considering the COCs, Pietrafitta Clay shows a greater compressibility, with Cc of 0.81 [12], which is smaller than in the Avezatto Clays [13], and quite similar to those from the Viso Clays (Cc = 0.18-0.32) [54]. The common feature of all the clays mentioned is the significant presence of carbonates--of fossiliferous origin--in the MOC and without being part of a cement. With respect to the differences between the DC and the other two COCs, the Pietrafitta Clay and the Avezatto Clay, with the current data, two different circumstances can explain this. First, the type of carbonate, with at least two overimposed processes in the case of the DC; and second, the geological history behind the overconsolidated character of these clays, which is the lithostatic load in the case of the DC and the lowering of the piezometric level for those studied in [13]. * Preconsolidation pressure  
The oedometer compression curves for intact samples show the effect of the geological history, reducing compressibility when compared with the reconstituted samples. The bending in the compression curve is sometimes interpreted due to the maximum lithostatic pressure, which is called the preconsolidation pressure (\(\sigma^{\prime}_{\text{vc}}\)). However, this point can also be affected by other postdepositional processes that usually correspond to pressures higher than those established by geological means. For these cases, [29] introduced the term \"vertical yield stress\" (\(\sigma^{\prime}_{\text{vy}}\)). In lacustrine normally consolidated clay, [13] found that yield stress was greater than the in situ stress, and therefore they interpreted this reinforcement caused by the cementation. Assuming that the vertical effective stress is given with sufficient accuracy by the multiple of depth and effective unit weight, \(\gamma^{\prime}\) = 10 m kN/m\({}^{3}\), the \(\sigma^{\prime}_{\text{vc}}\) of 2000 kPa obtained for the DC would represent an erosion of approximately 200 m above the study area. This value is incompatible with the geological history of the surrounding area, where the location of the Calizas del Paramo Formation at 850 m.a.s.l. is representing an estimation for the infill of the basin [55; 56]; compared with the elevation in the sampled area, 730 m.a.s.l., such sediment thickness would have caused a pressure of 1200 kPa, lower than the 2000 kPa obtained in the oedometer. From this perspective, the reinforcement effect of cementation, already described in [13], and in agreement with [57], may explain this mismatch. However, considering the geological interpretation of other authors [58; 59], the preconsolidation pressure would agree with the maximum overburden pressure. For these authors, the Calizas del Paramo can be divided into Paramo I and Paramo II, each having a different age and a different position, with the highest located only in the east of the Duero Basin (200 km from the outcrop studied) and the lowest in the center, where the study outcrop is located. According to this interpretation, the gap between these two Paramos would represent additional erosion of 50 to 70 m and, therefore, the preconsolidation pressure agrees with the geological history. * Intrinsic versus natural compression curves--the sensitivity framework The intrinsic consolidation curves are shown in Figure 6D.