科研之友
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摘要
Cores from 190 mechanic boreholes that cut through the Miocene deposits of Montjuic mountain (Barcelona) were studied. Part of these deposits are well lithified (sandstone, conglomerate) while other parts are not (marl, sand and gravel). There is a significant lateral and vertical gradation between the lithified and non-lithified parts. In the eastern sector of Montjuic, these deposits form a 100 m thick sequence made up of 7 coarsening-upward cycles of progradant deltaic origin. Below these cycles there is a massive alluvial unit that extends downward until it reaches a Paleozoic basement made up of metamorphic rocks identified in the subsoil of the Barcelona harbour. In the western sector of Montjuic, the boreholes cut through a 80 m thick sequence made up of 4 fining-upward cycles of retrogradant alluvial origin with minor marine deposits at the top. This sequence is developed over the continental deposits of the Early Miocene (Burdigalian) found in the subsoil of the western edge of Montjuic. The deltaic sequence of the eastern sector corresponds to a higher stratigraphic position than the alluvial sequence of the western sector. Both sectors are bounded by a listric fault of NE-SO strike, which may have caused the sinking of the eastern sector and its tilting toward the NW. This fault would be related to the extensional fault system that formed the coastal Catalan margin during the Neogene period. The entire Miocene unit of Montjuic was also folded and form a gentle anticline of NO-SE strike. This fold would have originated before the faulting and can be interpreted as a syn-edimentary structure originated by a differential compaction between the early cemented alluvial and deltaic sediments that form the fold core and the unconsolidated sediments that form its limbs. Both the anticline and the fault were subsequently unconformably covered by the Quaternary deposits that cover the mountain of Montjuic.
- 出版日期2013
