## 5 Discussion  
Throughout the discussion, it is assumed that the geological processes of sediments deposited in marine and continental (lacustrine) basins are different and, therefore, their mechanical behaviors could not be the same. The alternation of layers of different competence, observed even in the outcrop, imbues the Duenas Clay formation with an unquestionable heterogeneity, a characteristic that also exists in other formations of the same continental context within the Duero [40, 41] and the Tajo Cenozoic basins (Spain) [42, 43]. In other types of basins, some differences exist: in the Guadalquivir Basin (Spain), with marine and continental episodes and where the over-consolidated Blue Clay of the Guadalquivir is located, even though rock levels exist (mainly sandstones), they are infrequent [3]. In other marine basins including overconsolidated clay materials, such as the London Clay [44] or the Boston Clay [9], the lithology is more homogeneous and only the variation in the granular fraction gives rise to the identification of singular levels [6, 7]. Although each basin has its own unique characteristics, in general, it can be stated that marine basins present more stable conditions compared to continental basins, in addition to marked differences in salinity, greater depth of water, and a higher rate of sedimentation, which is also more continuous [45]. Indeed, the vertical heterogene  
Figure 6: Results of uniaxial compression, direct shear, and oedometer tests. (**A**) Uniaxial compression tests. (**B**) Direct shear tests. (**C**) Normal stress and peak shear stress obtained from the shear tests. (**D**) Oedometer tests with natural and reconstituted samples. ity of the studied outcrop is reinforced by the position attributed to the area, at the edge of the center of the basin, where the transition between the alluvial and the lacustrine facies is framed [38]. Therefore, overconsolidated clay formations from continental origin can be considered more heterogeneous than the marine clay formations, and the coexistence of soil and rock behavior materials is a consequence of that. From the mineralogical composition and microscopic observations, several carbonate cementation episodes have been detected, which are more intense at the upper levels and decrease downwards. On the clay levels at the bottom, inherited palygorskite exists. This mineral provides an idea about the conditions of the sediments--it is considered a mineral indicator of high Si and Mg activity, and a hyper salt medium with high pH (8-10) [37; 46], deposited in a more basic environment than those at the marine basins. At the same time, and even in small amounts, smectites caused swelling pressures up to 100 kPa. It must not be ruled out that these pressures may be even higher in more central areas within the basin, where higher contents may exist. Concerning the clay levels, all the processes indicate a post-sedimentation structure for the DC. * The role of the carbonate content  
As a first approximation, the higher carbonate content in each level, the higher strength, and therefore the results of the Lutton tests, can be explained easily. This is partially correct, as the rock samples are those with a carbonate content above 69 (levels 1, 2, and 3), but the highest carbonate content is not associated with the highest point load strength index. A significant difference in strength was measured between levels 2 and 3, both with a 76% carbonate content. It was observed that the carbonate cement does not always shows the same texture, which in some cases is an eminently micritic cement, and in others is mainly microspharitic, with the rock behavior prevailing. Even for a much lower carbonate content, as in the case of level 5 (42%), the microspharitic cement can govern the rock behavior of the material, in contrast with level 4 (44% of carbonate), in which only micritic carbonate was described.