Messinian benthic foraminifera from the Mediterranean

Abstrac

Precessional variability of 87 Sr/86 Sr in the late Miocene Sorbas Basin: An interdisciplinary study of drivers of interbasin exchange

We present the first subprecessional record of seawater 87Sr/86Sr isotope ratios for a marginal Mediterranean subbasin. The sediments contained in this interval (three precessional cycles between 6.60 and 6.55 Ma) are important because they record conditions during the transition to the Messinian Salinity Crisis (MSC; 5.97 to 5.33 Ma), an event for which many details are still poorly understood. The record, derived from planktic foraminifera of the late Miocene Sorbas Basin (SE Spain), shows brief excursions with precessional cyclicity to 87Sr/86Sr ratios higher than coeval ocean 87Sr/86Sr. The hydrologic conditions required to generate the observed record are investigated using box modeling, constrained using a new paleodepth estimate (150 to 250 m) based on benthic foraminiferal assemblages. The box model results highlight the role of climate‐driven interbasin density contrast as a significant driver of, or impediment to, exchange. The results are particularly significant in the context of the MSC, where 87Sr/86Sr excursions have been interpreted purely as a consequence of physical restriction. To replicate the observed temporal patterns of lithological variations and 87Sr/86Sr isotope excursions, the Sorbas Basin “box” must have a mainly positive hydrologic budget, in contrast with the Mediterranean's negative budget during the late Miocene. This result has implications for the assumption of synchronous deposition of specific sedimentary layers (sapropels) between marginal and open Mediterranean settings at subprecessional resolution. A net positive hydrologic budget in marginal Mediterranean subbasins may reconcile observations of freshwater inclusions in gypsum deposits

Prism Adaptation in Rehabilitation? No Additional Effects of Prism Adaptation on Neglect Recovery in the Subacute Phase Poststroke

Background. Patients with neglect ignore or respond slower to contralesional stimuli. Neglect negatively influences independence in activities of daily living (ADL). Prism adaptation (PA) is one of the most frequently studied treatments, yet there is little evidence regarding positive effects on neglect behavior in ADL. Objective. To assess whether PA in the subacute phase ameliorates neglect in situations of varying complexity. Methods. A total of 70 neglect patients admitted for inpatient stroke rehabilitation received either PA or sham adaptation (SA) for 2 weeks, with full access to standard treatment. There were 7 time-dependent measurements (baseline and 1-4, 6, and 14 weeks after start of treatment). The primary outcome was change of neglect as observed during basic ADL with the Catherine Bergego Scale (CBS). Secondary outcomes were changes in performance on a dynamic multitask (ie, the Mobility Assessment Course [MAC]) and a static paper-and-pencil task (ie, a shape cancellation task [SC]). Results. In all, 34 patients received PA and 35 SA. There were significant time-dependent improvements in performance as measured with the CBS, MAC, and SC (all F > 15.57; P <.001). There was no significant difference in magnitude of improvement between groups on the CBS, MAC, and SC (all F < 2.54; P >.113]. Conclusions. No beneficial effects of PA over SA in the subacute phase poststroke were observed, which was comparable for situations of varying complexity. Heterogeneity of the syndrome, time post–stroke onset, and the content of treatment as usual are discussed. Basic knowledge on subtypes and recovery patterns would aid the development of tailored treatment

The Gibraltar Corridor:Watergate of the Messinian Salinity Crisis

The existence and evolution of a Messinian salt giant in the Mediterranean Sea has caused much debate in the marine science community. Especially the suggestion that the Mediterranean was a deep desiccated basin during the Messinian Salinity Crisis (MSC, 5.97–5.33 Ma), triggered by a temporal disconnection from the global ocean, made it a well-known crisis beyond the scientific boundaries. Approximately ~50 years after this provocative statement, it remained unknown which Mediterranean–Atlantic seaway delivered the 5–6% of the global ocean's salt into the Mediterranean basin. Here, we review the changes in Mediterranean-Atlantic connectivity throughout the late Miocene in order to locate, date and quantify the missing Messinian gateway that provided the salt water inflow during the MSC. We conclude that all the known pre-MSC gateways through southern Spain and northern Morocco were closed, leaving the “Gibraltar Corridor” at its Messinian configuration as the sole candidate. We consider the possibility of longer and narrower straits existing at depth below the present Gibraltar region, and using strait dynamic theory we calculate its dimensions during the Messinian based on the salinity changes in the Mediterranean. A marine Messinian gateway through the Gibraltar Corridor is in agreement with growing evidence that Atlantic waters reached the Mediterranean Sea during all three stages of the MSC

Paleobathymetric evolution of the Miocene deposits of the Gombe sector of the Lycian Foreland and Aksu basins in Antalya, Turkey

The evolution of the Lycian Foreland and Aksu basins are associated with the Africa-Eurasia convergence and collision of intervening continental blocks. Both basins developed around the Beydaglari, a Mesozoic carbonate platform, which constitutes the main component and western limb of the Isparta Angle. The Gombe Basin is an integral part of the Lycian Foreland Basin that comprises mainly Eocene to Late Miocene turbidites, onto which the allochthonous Lycian and Antalya nappes thrust over. The Aksu Basin, however, developed in the inner part of the Isparta Angle and is bounded by the Aksu Thrust in the east. During their evolution, these basins experienced significant bathymetric changes, possibly due to vertical motions and variations in the sediment supply. This study provides a detailed analysis of the paleobathymetric evolution of these basins. This conducted paleobathymetric study was based on the determination of the depositional depth by the abundance ratio of planktonic versus benthic foraminifera, which is the function of the water depth. The percentage of planktonic foraminifera relative to the total foraminifer population (%P) increases from shallow to deep water. However, some benthic foraminifera species are directly affected by the oxygen level of the bottom water, rather than by paleobathymetry, i.e. stress markers, and were discarded in the calculation. Additionally, the dissolution of the foraminifera has the potential for miscalculations, since planktonic foraminifera are more prone to dissolution than benthic ones. Nevertheless, the obtained quantitative results were verified and validated qualitatively by specific benthic depth markers that lived at specific depth ranges. Aksu Basin had a shallowing trend, and the sedimentation rate exceeded the subsidence in the middle of the section. Calculated depths for the Gombe Basin indicated depths around 1000 m, which was contrary to the high sedimentation rates indicated by the turbiditic facies of the basin infills

ELMALI-GÖMBE VE AKSU HAVZALARININ MİYOSENYAŞLI ÇÖKELLERİNİN PALEOBATİMETRİK EVRİMİ(TÜRKİYE)

Geç Senozoyik Antalya Havzası, Isparta Büklümü içerisindeki Batı Toroslar Mesozoyik otokton karbonat platformunun üzerinde uyumsuz olarak gelişmiştir. Elmalı-Gömbe Havzası, Isparta Büklümü’nün batı kanadında yer alır ve Beydağları Platformu üstünde, Likya Napları’nın doğusunda bir ön ülke havzası olarak gelişmiştir. Bununla birlikte, Aksu Havzası Isparta Büklümü’nün iç kısmında gelişmiş olup doğuda Aksu Fayı ile sınırlanmıştır. Bu havzalar evrimleri sırasında düşey hareketler ve çökelme miktarındaki değişime bağlı olarak önemli batimetrik değişiklikler gösterir. Bu çalışma, bu havzaların paleobatimetrik evriminin detaylı bir incelemesini kapsar. Yapılan paleobatimetrik çalışma, foraminifer faunasını kullanarak bu havzaların çökelme derinliğinin belirlenmesini içerir. Uygulanan yöntem, su derinliği ile ilişkili olan bentik foraminifer miktarı ile planktonik foraminifer miktarının oranlanmasına dayanır. Planktonik foraminiferlerin toplam foraminifer popülasyonuna oranı (%P) sığdan derine doğru artar. Bununla birlikte, bazı bentik foraminiferler, oksijen seviyesinden doğrudan etkilenir ve stres belirteçleri olarak kabul edilirler ve bu nedenle popülasyon oranı hesaplamasına dahil edilmezler. Buna ek olarak, karbonat kabuk çözünmesi planktonik foraminiferlerde bentik olanlara göre daha yaygındır. Bu durum yanlış hesaplamalara neden olabilir. Fakat yine de, bentik türlerin belirlenmesi ve tanınması bile bu komplikasyonun üstesinden gelmek için yeterlidir. Ayrıca, elde edilen niceliksel verileri, derinlik belirteçleri olan bentik foraminifer türleri kullanarak, nitel olarak doğrulamak mümkündür. Aksu havzasının depolanma derinliğindeki genel eğilime bakıldığında sığlaştığı görülmektedir ve kesitin orta seviyelerinde sedimantasyon oranı çökme oranını geçmektedir. Gömbe havzasının türbiditik fasiyeslerinin işaret ettiği hızlı depolanmaya rağmen, birçok seviyede hesaplanan sonuçlar çökelmenin bin metre kadar derinlikte gerçekleştiğini göstermektedir

Paleobathymetric evolution of the miocene deposits of the gömbe sector of the lycian foreland and aksu basins in antalya, Turkey

The evolution of the Lycian Foreland and Aksu basins are associated with the Africa-Eurasia convergence and collision of intervening continental blocks. Both basins developed around the Beydağları, a Mesozoic carbonate platform, which constitutes the main component and western limb of the Isparta Angle. The Gömbe Basin is an integral part of the Lycian Foreland Basin that comprises mainly Eocene to Late Miocene turbidites, onto which the allochthonous Lycian and Antalya nappes thrust over. The Aksu Basin, however, developed in the inner part of the Isparta Angle and is bounded by the Aksu Thrust in the east. During their evolution, these basins experienced significant bathymetric changes, possibly due to vertical motions and variations in the sediment supply. This study provides a detailed analysis of the paleobathymetric evolution of these basins. This conducted paleobathymetric study was based on the determination of the depositional depth by the abundance ratio of planktonic versus benthic foraminifera, which is the function of the water depth. The percentage of planktonic foraminifera relative to the total foraminifer population (%P) increases from shallow to deep water. However, some benthic foraminifera species are directly affected by the oxygen level of the bottom water, rather than by paleobathymetry, i.e. stress markers, and were discarded in the calculation. Additionally, the dissolution of the foraminifera has the potential for miscalculations, since planktonic foraminifera are more prone to dissolution than benthic ones. Nevertheless, the obtained quantitative results were verified and validated qualitatively by specific benthic depth markers that lived at specific depth ranges. Aksu Basin had a shallowing trend, and the sedimentation rate exceeded the subsidence in the middle of the section. Calculated depths for the Gömbe Basin indicated depths around 1000 m, which was contrary to the high sedimentation rates indicated by the turbiditic facies of the basin infills

Foraminifera of the Faneromeni section (Crete, Greece) reflect the palaeoenvironmental development towards the Messinian salinity crisis

A severe phase of disturbance around 7.17 Ma initiated an ongoing development towards the Messinian salinity crisis (MSC) of the Mediterranean. We present foraminiferal data from the Faneromeni section on Crete to understand how the astronomical cyclicity and the restriction phase starting at 7.17 Ma were reflected in a succession that was deposited on the continental shelf and characterized by a precession-dominated alternation of organic-enriched grey marls and sapropels and light-coloured homogeneous marls. Benthic and planktic abundance data show that the foraminifera are closely associated with precessional cyclicity. Similar as in other Mediterranean sections, the 7.17 Ma shift in benthic assemblages is sedimentologically expressed by the occurrence of the first distinct sapropel (Faneromeni cycle F18). At this level, throughout the Mediterranean a group of open marine benthic species intolerant to oxygen stress abruptly decreased in abundance with several species disappearing at or shortly after 7.17 Ma. These species were replaced by species indicating increasing stress, implying decreasing oxygen content of the bottom waters after 7.17 Ma. The data further suggests that sapropelic sediments dominated by Bolivina dilatata/spathulata were deposited under hypoxic conditions, rather than under continuous organic flux. Our data reflects a second step in the restriction of the Mediterranean between 6.8 and 6.7 Ma, indicated by decreasing benthic diversity and increasing abundances of planktic and benthic taxa considered tolerant of hypersalinity. An increase in water salinity has been suggested before, and if true, appears to have affected the bottom waters and the surface waters around the same time