The Middle Miocene Son Verdera Lacustrine-Palustrine System (Santa Margalida Basin, Mallorca)

• Autores: Emilio Ramos Guerrero, Igone Berrio, Joan Josep Fornós Astó, Lluís Moragues
• Localización: Lake basins through space and time / coord. por Elizabeth H. Gierlowski-Kordesch, K. Kelts, 2000, ISBN 0891810528, págs. 441-448
• Idioma: inglés
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• Resumen

  • The island of Mallorca forms part of the Balearic promontory, which, in turn, forms part of the alpine Betic Range extending from the southern Iberian Península as a northeast ward submarine prolongation into the western Mediterranean. The Betic orogen underwent its phase of maximum deformation in Mallorca during the early-middle Miocene (Burdigalian-Langhian), when the area developed a series ofimbricate thrust sheets transported in a northwest direction (Fallot, 1922; Alvaro, 1987; Sabat et al., 1988).After this compressive stage, post-Langhian extension resulted in a series of horsts and grabens bounded by northeast-southwest and northwest-southeast oriented faults. The Santa Margalida Basin is one of these small grabens filled by marine, as well as continental,postorogenic sediments, ranging from Serravallian to Quaternary in age (Figure 1).

    The postorogenic sedimentary record in Mallorca issplit into 11 sequences (Figure 2). The thickness of these successions is highly variable due to the strong fault activity, which generated several grabens andhalf-grabens. From borehole and geophysical data, Benedicto et al. (1993) estimated a post orogenic fill thickness of 1500 m for the Inca Basin, which lies a few 441kilometers to the west, whereas the Santa Margalida Basin, one of the smallest grabens, is filled by up to 300mof postorogenic sediments. Approximately 150 m of this infill belongs to Sequence V (Figure 2).The lowermost unit of this postorogenic filling (Sequence V according to Forn6s et al., 1991) consists of 150 m of clastic nonmarine carbonates (Figure 2).Three informal lithostratigraphic units can be identified in this nonmarine sequence. Two of these units(the Pina Marls unit and the Son Verdera Limestone unit (Pomar et al., 1983); units 1 and 2 respectively in Figure 2) consist mainly of lacustrine and palustrine carbonate rocks that interfinger laterally into the third terrigenous unit (marginal terrigenous complex),which extends along the basin edges (Manacor Silt unit; Pomar et al., 1983).

    The lowermost Pina Marls unit lies unconformablyover the folded and thrusted pre- and syn-orogenic substratum (Figure 2). The unit is composed of greymarls with interbedded gypsum and sandy layers,and contains abundant resedimented marine micro foraminifera attributed to the Burdigalian (Celom,1967). The Son Verdera Limestone unit conformably overlies the Pina Marls and is composed of limestones and fine-grained siliciclastic rocks with variable amounts of organic matter.