Nodular anhydrite growth controlled by pedogenic structures in evaporite lake formations

Several nodular gypsum beds exhibiting a remarkable vertical arrangement of individual nodules are present in the Miocene continental evaporite formations of the Calatayud Basin, northeastern Spain. The growth of the gypsum nodules, initially anhydrite, took place within magnesitic carbonate deposits which display incipient pedogenic features such as rhizoliths and clotted to peloidal textures. Simultaneous and after the pedogenic modification of the carbonate substratum, displacing nodules started to grow, their arrangement being closely conditioned by the development of vertical fissuring related to root penetration. The transformation of anhydrite to gypsum was probably realized early after little burial of the sulphate–carbonate deposits. The occurrence of vertically oriented gypsum nodules can be seen as a diagnostic feature for palustrine conditions developed in evaporitic lake settings, this peculiar morphology of the sulphate nodules having been strongly controlled by the internal structure of the palustrine palaeosols

Calcitization of Mg±Ca carbonate and Ca sulphate deposits in a continental Tertiary basin (Calatayud Basin, NE Spain)

Diagenetic carbonates formed through early calcitization of evaporite (gypsum, anhydrite) and/or magnesium carbonate (dolomite, magnesite) deposits have been identified throughout the Tertiary Calatayud Basin (NE Spain). The diagenetic carbonates consist in all cases of low magnesian calcite and are related to main sedimentary discontinuities, which record episodes of significant subaerial exposure in the basin. Early calcite replacements predominate in sediments of the Intermediate Unit in central areas of the basin. Two types of diagenetic carbonates have been distinguished: (1) laminated diagenetic carbonates in which the original structure of sequences formed of laminated magnesite, dolomite and primary gypsum is preserved, though transformed in calcite; (2) brecciated diagenetic carbonates, which resulted from extensive dissolution of lenticular gypsum macrocrystals accompanied by dedolomitization processes of dolomite host rock. The replacement by calcite resulted from rapid transformation of evaporite deposits either at the contact of these deposits with overlying freshwaters or by percolating freshwater at very shallow burial depth. Stable isotope (carbon and oxygen) analyses of the diagenetic carbonates support influence of meteoric-derived carbonate-rich groundwater for their formation. The meteoric isotope signature is supported by its comparison with the stable isotope values determined from diagenetic calcites formed after magnesite in evaporite sequences during the Late Pleistocene and Holocene. The diagenetic carbonate bodies formed as a result of a progressive change from highly to moderately concentrated saline lake waters. This gradual evolution was related to a climatic shift from dry and hot to cooler and more humid conditions throughout the Miocene, a trend that has been also recognized in other large Tertiary basins of the Iberian Peninsula in this period

Unusual twinning features in large primary gypsum crystals formed in salt lake conditions, Middle Miocene, Madrid Basin, Spain: palaeoenvironmental implications reply

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Síntesis de la cronoestratigrafía y evolución sedimentaria de los sistemas lacustres evaporíticos y carbonatados neógenos de la Cuenca de Calatayud-Montalbán.

La Cuenca terciaria de Calatayud-Montalbán consta de dos subcuencas diferentes separadas por el umbral de Daroca (Cuenca de Calatayud en el sector septentrional y Cuenca de Montalbán en el sector meridional). Estas cuencas presentan una evolución sedimentaria muy similar de los sistemas lacustres neógenos evaporíticos y carbonáticos, que generalmente ocupan los sectores centrales de ambas depresiones. En la Cuenca de Calatayud, se reconocen tradicionalmente en el Neógeno tres unidades sedimentarias mayores denominadas Unidad Inferior, Intermedia y Superior separadas por dos rupturas sedimentarias principales. Las dos primeras tienen carácter evaporítico, mientras que la última tiene un carácter fluviolacustre. En los sectores centrales de la Cuenca de Montalbán, el sondeo Barrachina-l y las secciones estratigráficas complementarias han permitido apreciar una evolución sedimentaria muy similar para las unidades neógenas, con facies evaporíticas y carbonáticas muy parecidas, aunque con una cronoestratigrafía diferente y la ausencia del registro sedimentario del Mioceno medio a Plioceno. En este trabajo también se describe por vez primera la presencia de un nivel volcanoclástico intercalado entre las facies evaporíticas del Mioceno inferior de la Cuenca de Montalbán. Las asociaciones minerales identificadas en los depósitos lacustres del Mioceno inferiormedio de ambos sectores de la cuenca, muestran una secuencia que evoluciona desde facies lacustres evaporíticas de alto grado de hipersalinidad, hacia facies lacustres evaporíticas de baja-moderada salinidad. Solamente, el registro sedimentario de la Cuenca de Calatayud permite asegurar que esta evolución sedimentaria se completa con la presencia de facies carbonáticas fluviolacustres características de aguas dulces en el Mioceno superior. Esta secuencia de precipitación salina responde a un cambio progresivo en la hidroquímica de los sistemas lacustres relacionado con un cambio gradual de las condiciones climáticas que comenzaría en el Rambliense y se extendería, al menos, durante todo el Mioceno medio. Las diferencias cronoestratigráficas entre los dos sectores de la misma depresión deben estar relacionados con los diferentes condicionantes tectónicos y/o geomorfológicos a los que se han visto sometidas ambas cuencas durante el Mioceno. [ABSTRACT] The Tertiary Calatayud-Montalbán Basin consists of two distinct sub-basins separated by the Daroca High (Calatayud Basin in the northern sector and Montalbán Basin in the southern sector). These basins present a quite similar sedimentary evolution of the Neogene evaporitic and carbonatic lacustrine systems, that generally occupy central locations in both basins. Three main sedimentary units (Lower, Intermediate and Upper units) divided by two main sedimentary breaks are traditionally described in the Calatayud Basin. The Lower and Intermediate units have evaporitic sedimentation, whilst the Upper Unit is tipically freshwater fluviolacustrine sedimentation. In the central areas of the Montalbán basin, the Barrachina-l drill hole and complementary stratigraphic sections showed a very similar sedimentary evolution of the Neogene units, with similar evaporitic and carbonatic facies, but different chronostratigraphy. The Upper MiocenePliocene sedimentary record of the Montalbán Basin is absent. In addition, this work presents the first occurrence of a volcanoclastic layer interbedded in the Lower Miocene evaporitic facies of the Montalbán Basin. The identified mineral assemblages of the lacustrine deposits of both sectors of the basin, show an evolutionary sequence during the Lower-Middle Miocene from hypersaline to lower moderated salinity lacustrine facies. This evolutionary trend is only complete in the sedimentary record of the Calatayud Basin, where freshwater carbonatic fluviolacustrine facies are described in the Upper Miocene. This precipitation sequence is the result of a progressive hydrochemical change of the lacustrine systems related to a climatic change from the Ramblian to the Middle Miocene. Differences in the chronostratigraphy of both basins should be related to distinct tectonic scenarios and/or geomorphologic features during the Miocene

The late Messinian \u201cLago-Mare\u201d event and the Zanclean Reflooding in the Mediterranean Sea: New insights from the Cuevas del Almanzora section (Vera Basin, South-Eastern Spain)

The return to normal marine conditions in the Mediterranean Sea after the end of the Messinian Salinity Crisis (MSC), that led to the deposition of thick evaporitic succession followed by settlement of brackish to freshwater conditions of the \u201cLago-Mare\u201d, is still subject to extensive debate between two opposite scenarios. One scenario implies an abrupt reflooding through the Gibraltar gateway of the Mediterranean Sea previously disconnected from the world ocean and partly desiccated. The second scenario postulates that the Mediterranean Sea kept a high-water level throughout the Messinian Salinity Crisis and was connected continuously to the Atlantic Ocean and to the Paratethys. The stratigraphic record of the classical Cuevas del Almanzora section (Vera Basin) is of a crucial importance as the Vera Basin is located on the eastern margin of the Alboran Sea close to the Gibraltar gateway where Atlantic waters reflooded the Mediterranean Sea after the MSC. The present new study completes previous investigations (Pierre et al., 2006) and is mostly focused on detailed sedimentological observations, analysis of ostracod and foraminifer assemblages and on stable isotopes study of three species of planktonic foraminifers (Globigerina bulloides, Globigerinoides obliquus s.l. and Sphaeroidinellopsis spp.) from the lower Pliocene deposits. Biostratigraphical correlations with the reference deep-sea section from ODP Site 975 (Balearic Basin) and the onshore succession of Eraclea Minoa (Sicily) provide an accurate chronostratigraphy and paleoclimatic reconstruction during the Zanclean. During the late Messinian, the Vera Basin was characterized by very unstable lacustrine to brackish environments with significant water depth variations and the deposits display evidences of subaerial exposure. The ostracod content is dominated by Loxocorniculina djafarovi and Cyprideis gr. agrigentina associated to reworked planktonic foraminifera from older sediments. The Messinian/Zanclean contact is well marked by a clear erosional surface that grades laterally into a megabreccia with reworked gypsum blocks and to the large incision of the Palomares canyon in the offshore domain. The marine reflooding occurred abruptly with a sea level rise by more than 250 m, an important value for a marginal basin. In this western part of the Mediterranean Sea, the marine invasion began with the onset of the lowermost biozone MPl 1 at the base of the Zanclean. The fluctuations of the planktonic foraminifer assemblages and of their stable isotopes allowed to identify five lithological cycles forced by Milankovitch\u2019 precession periodicity, as well as paleoclimatic variations through the lower part of the Zanclean. Thus, these new data allow us to reaffirm that the Messinian/Zanclean boundary corresponds to a major change, characterized by an \u201cinstantaneous\u201d restoration of marine conditions at the onset of the Pliocene, related to the abrupt re-flooding of the Mediterranean Sea from the Atlantic Ocean

Architecture and corals ecology of Tortonian-Messinian shallow-water bioherms (Las Negras basin, SE Spain).

International audienc

Evaporite control on mixed carbonated-clastic platform architecture and carbonate production: A Late Messinian case study (Sorbas Basin, SE Spain).

International audienc