I. Zamarreño

Messinian pre-evaporite sapropels and precession-induced oscillations in western Mediterranean climate

Abstract Cyclical fluctuations in planktic foraminiferal assemblages have been recognized in the pre-evaporitic Messinian in a marginal basin of the western Mediterranean. The fluctuations coincide with a dominantly precession-controlled sedimentary cyclicity (sapropels). During sapropel deposition, high planktic foraminiferal diversities are indicative of relatively stable marine conditions, while during homogeneous marl deposition low diversities seem to indicate the presence of unfavourable, more saline surface water conditions. The dominance of a precession-related signal indicates that regional climate oscillations rather than (obliquity-related) glacio-eustatically controlled influxes of Atlantic and/or Mediterranean waters are responsible for the faunal fluctuations and sedimentary cyclicity. Our scenario links the persistence of normal marine conditions during sapropel formation with increased rainfall and run-off along the western Mediterranean at times that perihelion occurred in Northern Hemisphere summer. Less favourable, highly saline surface water conditions prevailed during periods of drier climate induced by opposite precessional extremes. The cyclical oceanographic fluctuations could also have governed periodic reef growth along the margins.

Orbitally-controlled oscillations in planktic communities and cyclic changes in western Mediterranean hydrography during the Messinian

We use quantitative analyses of the planktic foraminiferal assemblages and stable isotope analyses of the Sorbas section in the western Mediterranean to reconstruct the cyclical changes in surface and deep water hydrographic conditions during the Late Miocene prior to the Messinian salinity crisis. Oscillations in winter and summer temperatures linked to cyclical fluctuations in the hydrographic conditions and nutrient availability were the main mechanisms driving the cyclical changes in the planktic foraminiferal assemblages during the Messinian. The winter intensification and southward expansion of the northern cool and dry winds during precession maxima lowered sea surface temperatures (below≃14–15°C), favoring water convection and the upward mixing of nutrients with the consequent increase in the proportion of cold, eutrophic water foraminifera. The low summer temperatures (below 24°C) inhibited the growth of warm, oligotrophic water foraminifera, as occurs today in the Mediterranean. By contrast, at times of precession minima the low influence of the high latitude air masses caused winter temperatures to remain relatively high which, combined with the lower surface salinities, led to the formation of a permanent pycnocline. Winter conditions prevented the growth of cold, eutrophic water foraminifera, while high summer temperatures and the formation of a permanent pycnocline stimulated the growth of warm, oligotrophic water foraminifera. The prevalence of stable water stratification during winter due to the large density gradient between the surface and intermediate waters prevented deep water formation and slowed down the rates of oxygen supply to the bottom, resulting in the formation of the sapropels. A sharp decrease in δ13C of benthic and planktic foraminifera that occurred between 6.8 and 6.7 Myr is related to an increase in the residence time of Mediterranean waters. Because similar changes have been observed in other regions of the Mediterranean, we conclude that this change records a significant reduction in the Atlantic–Mediterranean water exchange at that time. Mediterranean climatic amplification increased throughout the Messinian as the Atlantic–Mediterranean water exchange was progressively more limited and oscillations in the ratio of planktic/benthic foraminifera and of warm-oligotrophic/cold-eutrophic species are good records of this increasing amplification, which culminated at 5.95 Myr with the deposition of gypsum–pelitic layers that mark the onset of the Messinian salinity crisis.

Palaeogene lacustrine record in Mallorca (NW Mediterranean, Spain): depositional, palaeogeographic and palaeoclimatic implications for the ancient southeastern Iberian margin

Abstract Middle Bartonian (Middl1e Eocene) and Chattian (Upper Oligocene) lacustrine and alluvial-lacustrine successions exist in Mallorca (northwestern Mediterranean). They yield a significant palaeobiological record comprising fossil land plants and vertebrates and constitute the best available depositional record for a preliminary palaeogeographic and palaeoclimatic analysis of the northeastern part of the Palaeogene southern Iberian Margin (western Tethys). Both lacustrine systems developed under similar warm and humid climatic conditions, increasingly affected by seasonal and/or pluriannual rhythms marked by changing precipitation patterns. These climatic conditions were mainly caused by the low palaeolatitude where the lacustrine systems evolved, the still probable although decreasing influence of Indo-Pacific warm surface currents, and the occurrence of very extensive marine water masses adjacent to wide, emerged continental zones. The Palaeogene lacustrine systems were shallow, and characterised by low gradient depositional conditions. They were perennial, open freshwater-oligosaline carbonate lakes where eutrophy, thermal meromixis and anoxic bottom conditions could develop, allowing the accumulation and preservation of macrophytic plant remains of the circum-lacustrine marginal belt and neighbouring terrestrial mesophytic zones. The higher plant/algal-bacterial organic contribution balance favoured the generation of mineable huminitic coal seams, carbominerites and of gas-prone, kerogene type III and IIb source rocks. The hydrogen-bicarbonate-rich waters led to high biogenic and inorganic bio-induced carbonate sediment production. Biogenic muds, cyanobacterial incrustations and travertine and tufa precipitation constituted the major carbonate products. Moreover, the high pH conditions in the lacustrine water bodies and in the lacustrine sediment pore waters favoured bacterial sulphate reduction, contributing to organic sulphur enrichment in coals. These highly alkaline conditions also resulted, in some cases, in the exceptionally good preservation of chlorophyllinite, a rare liptinite maceral recorded in the Eocene coal deposits. The Middle Eocene lacustrine system did not evolve in a very well defined tectonic setting, characterised by the generation of low uplifts and gently subsiding basins. Terrigenous contributions from the source areas and clastic sedimentation were restricted to river mouths. High autochthonous carbonate production and accumulation characterised most of the remaining lacustrine zones. A significant spring recharge of the lacustrine zones is suggested by the well developed spring-related travertine deposits. By contrast, the Oligocene lacustrine zones developed both in fluvial-related floodplains and in the distal zones of a major alluvial system, which was fed from tectonically active source areas located to the NW of the island. A more significant water runoff contribution is suggested for this system although underground recharge could also be substantial.

Late Quaternary climatic changes on the southwestern Balearic slope (Western Mediterranean): isotopic, faunal, and mineralogical relationships

Abstract We report the results of a research on the carbonate mineralogy, planktonic foraminifera distribution, and oxygen and carbon isotope composition of G. bulloides in hemipelagic carbonate oozes of the Southwestern-Balearic Slope (Western Mediterranean) to contribute to the understanding of climatic and ecological variations during the last Quaternary interglacial/glacial cycle and their influences on the carbonate sedimentary processes of the Western Mediterranean. Oxygen isotope stages 1, 2 and 3 have been identified and correlated to those established in Tyrrhenian cores. The carbon isotope records display several anomalies which are explained by productivity variations and diagenetic processes. Pelagic carbbonates (low Mg-calcite and aragonite) and detrital minerals (quartz, high Mg-calcite and dolomite display variations that are climate related. Pelagic carbonates increase during warm intervals, while intense low Mg-calcite dissolution and greater quantities of detrital minerals are found in colder intervals. Our results suggest that the carbonate distribution of the Western Mediterranean correlates to the reported from the Atlantic Ocean. Nevertheless, the molar MgCO3 content in low Mg-calcite disagree to the established temperature relationship in other oceans.

Late Quaternary hemipelagic carbonate oozes on the southwestern Balearic slope (western Mediterranean)

Abstract Carbonate sediments on continental slopes in temperate areas have not received as much attention as their tropical counterparts. This study documents the sedimentology and main early diagenetic features of hemipelagic carbonate oozes from two piston cores from the continental slope of the south Balearic margin (western Mediterranean) between 38° and 39°N. The two cores contain hemipelagic carbonate oozes consisting of a mixture of clay minerals and several carbonate phases, which settled on the flanks of the Balearic carbonate platform during the last full Quaternary glacial-interglacial cycle. Textural, faunal and mineralogical data suggest that the Balearic sedimentary record is closely related to changes in productivity, dissolution and dilution, all of which are related to δ18O and δ13C signals during the Late Quaternary. The dominant carbonate phase is low-magnesian calcite, whereas aragonite and high-magnesian calcite are present as minor components. The incorporation of low-magnesian calcite in the sediment is due to planktonic pelagic rain. The high-magnesian calcite is incorporated via resuspension of particles originating from the degradation of molluscan and red algal carbonate skeletons from the adjacent carbonate-rich Balearic shelves. Aragonite derives from pteropods and presumably shallow-water aragonite organisms, as the red algae Peyssonelia. The main differences between tropical carbonate slope sediments and Balearic temperate hemipelagic oozes are the lesser amounts of carbonate minerals, mainly aragonite and high-magnesian calcite, and the greater quantity of quartz and clay minerals. Our results suggest that the hemipelagic carbonate oozes of the Balearic slope are an intermediate type of carbonate oozes between the low-magnesian calcite deep-pelagic oozes with low diagenetic potential and the multiphasal carbonate tropical periplatform sediments with high diagenetic potential.

The shell microstructure, mineralogy and isotopic composition of Amussiopecten baranensis (Pectinidae, Bivalvia) from the Miocene of Spain : A valuable paleoenvironmental tool

Abstract Amussiopecten baranensis ( Almera & Bofill , 1896 ), of the Family Pectinidae, is widespread in Miocenemarine sediments from northeastern and southeastern Spain, ranging in age from Early Langhian to Middle Messinian. The shell consists of an outer homogeneous and foliated layer composed of low-magnesium calcite, a middle layer aragonitic, and an inner foliated layer of low-magnesium calcite. Both left and right valves have, in general, the same microstructure and mineralogy except for an outermost thin polygonal layer in the earliest-formed dissoconch of the right valve. The homogeneous structure (dense and granular sublaminae) up to 50 μm thick overlies the sublayer of foliated calcite (regular, irregular and crossed foliated) that extends throughout the whole shell, being thinnest in the dorsal margin and thickening toward the ventral margin. The regular foliated inner layer extends from the beak, where it attains its maximum thickness, to near the adductor muscle scar. The middle layer is the most complex in structure and distribution, being composed of three sublayers which from exterior to interior are: 1) aragonitic simple crossed lamellar, 2) aragonitic prismatic (myostracal), and 3) aragonitic complex crossed lamellar. The latter sublayer in the internal shell surface extends to the area interior to the pallial line. Prominent features of the middle layer are the asymmetrical distribution of the prismatic structure (absent in the anterior margin), and the thinning of the three sublayers both in radial and antero-posterior directions. The divaricate microsculpture extending on the umbonal area and auricles in both valves originates from the granular calcite of the homogeneous structure. δ180 values of the outer foliated layer from the ventral margin suggest that A. baranensis segregates its calcite in isotopic equilibrium with ambient sea-water, and thus affords a valuable tool in paleoenvironmental studies.