Late Miocene evaporite geochemistry of Lorca and Fortuna basins (Eastern Betics, SE Spain): Evidence of restriction and continentalization

Abstract

The Lorca and Fortuna basins are two intramontane Neogene basins located in the eastern Betic Cordillera (SE Spain). During the Late Tortonian-Early Messinian, marine and continental evaporites precipitated in these basins as a consequence of increased marine restriction and isolation. Here we show a stratigraphic correlation between the evaporite records of these basins based on geochemical indicators. We use SO 4 isotope compositions and Sr isotopic ratios in gypsum, and halite Br contents to characterize these units and to identify the marine or continental source of the waters feeding the evaporite basins. In addition, we review the available chronological information used to date these evaporites in Lorca (La Serrata Fm), including a thick saline deposit, that we correlate with the First Evaporitic Group in Fortuna (Los Baños Fm). This correlation is also supported by micropalaeontological data, giving a Late Tortonian age for this sequence. The Second Evaporitic Group, (Chicamo Fm), and the Third Evaporitic Group (Rambla Salada Fm) developed only in Fortuna during the Messinian. According to the palaeogeographical scheme presented here, the evaporites of the Lorca and Fortuna basins were formed during the Late Tortonian-Early Messinian, close to the Betic Seaway closure. Sulphate isotope compositions and Sr isotopic ratios of the Ribera Gypsum Mb, at the base of the Rambla Salada Fm (Fortuna basin), match those of the Late Messinian selenite gypsum beds in San Miguel de Salinas, in the near Bajo Segura basin (40 km to the East), and other Messinian Salinity Crisis gypsum deposits in the Mediterranean. According to these geochemical indicators and the uncertainty of the chronology of this unit, the assignment of the Rambla Salada Fm to the MSC cannot be ruled out.

Ages and stratigraphical architecture of late Miocene deposits in the Lorca Basin (Betics, SE Spain): New insights for the salinity crisis in marginal basins

“…The overlying pink marls and sandstones correspond to the Post-evaporitic unit attributed to the Messinian by Wrobel and Michalzik (1999). However, Rouchy et al (1998) and Garcia-Veigas et al (2019) only found reworked foraminifera and non-marine biostratigraphical markers, which did not allow them to determine the age of the formation.…”

“…All these authors proposed a Messinian age for these evaporites, while Krijgsman et al (2000) considered a Tortonian age. A Tortonian age was also proposed by Garcia-Veigas et al (2019) on the basis of ages proposed by Corbi et al (2012) themselves based on ages proposed by Krijgsman et al (2000). The overlying pink marls and sandstones correspond to the Post-evaporitic unit attributed to the Messinian by Wrobel and Michalzik (1999).…”

“…In addition to the biostratigraphical dating based on the absence of foraminifera or nannofossils species in diatomites rather than on the occurrence of biostratigraphical markers, the age was mainly constrained on the basis of magnetostratigraphy. Corbi et al (2012) and Garcia-Veigas et al (2019) also considered a Tortonian age for the diatom-bearing deposits and overlying evaporites but did not provide new direct biostratigraphical evidences.…”

“…The overlying alternation of laminated grey marls and evaporites constitutes the Upper Gypsum Fm and grades vertically to pink laminated marls devoid of evaporites of the Cañada Honda Fm. Both formations are the equivalent of the Post-evaporitic unit of Rouchy et al (1998) and Wrobel and Michalzik (1999) and the Laminated Pelite Mbr of Garcia-Veigas et al (2019).…”

“…Krijgsman et al (2000Krijgsman et al ( , 2006 and Tent-Manclus et al (2008) challenged this dating and proposed a Tortonian age for evaporites of these two basins. More recently, this Tortonian age for evaporites of the Lorca Basin was also considered by Corbi et al (2012) and Garcia-Veigas et al (2019). Consequently, the concept of "Tortonian Salinity Crisis" has been widely adopted and geodynamic models involving differential uplift and subsidence rates between basins along trans-Alboran strike-slip faults were produced to explain diachronous confinements of Neogene basins (Garces et al, 2001;Krijgsman et al, 2006;Rodriguez-Fernandez et al, 2012).…”