Within the Gulf of Mexico (GOM), the Bryant Canyon is exceptional in that rapid sedimentation sustained by high rates of terrigenous sediment delivery and surface marine productivity make this basin ...an excellent recorder of paleoenvironmental and paleoclimatic conditions. We present a new 21-kyr record of sea surface temperature (SST) and local salinity changes from the NW GOM (core JPC-26) approximated from combined Globigerinoides ruber morphotype-specific δ18O and Mg/Ca, as well as Ba/Ca, which reflect the subtropical GOM hydrographic dynamics and their relationship to both Mississippi River discharges and climate evolution during the last deglaciation. Overall, the reconstructed SST and SSS-related patterns reveal notable variations in amplitude between the analyzed morphotypes, adding valuable insights to previously published G. ruber (w, mixed) GOM records. Especially during the deglaciation, Bryant Canyon meltwater flooding events (BCDFs) and associated sea surface freshening seem to be more pronounced than the SST reduction. Our Mg/Ca-derived SST records of both morphotypes (G. ruber sensu stricto (s.s.) and G. ruber sensu lato (s.l.)) show comparable general trends, but with important SST differences (ΔT). We interpret down-core ΔT as a record of changing upper water column hydrography, with particular influence from the deglacial meltwater (BCDFs) or Holocene (BCHFs) flooding events. During the warm intervals, the deeper, thicker and probably more seasonally persistent mixed layer led to more uniform thermal conditions for both G. ruber morphotypes and therefore to a minimum ΔT. On the contrary, during the cold and low salinity periods, the shallower mixed layer favored more habitat divergence, and caused a maximum thermal gradient in the well-stratified upper water column. Overall, this supports the notion that G. ruber s.s. is consistently calcifying in warmer waters than G. ruber s.l., either due to a shallower depth habitat or to a more summer-weighted seasonal distribution. Moreover, intra-specific paired δ13C and Ba/Ca differences show that G. ruber s.l. is more sensitive to river water influence than G. ruber s.s., due to its ability to change its depth habitat and therefore exploit optimal (temperature, salinity, productivity, stratification) conditions during the low-salinity events. Overall, our observations support the current practice of treating the two G. ruber morphotypes separately and further illustrate the necessity to map both their spatial and temporal distribution.
One of the most enigmatic features of long-term Cenozoic climatic evolution, with some analog potential for present/future global climate change, is the last sustained warm and high-atmospheric CO2 ...interval in Earth's history, which started after the end of the Messinian Salinity Crisis (5.971–5.332Ma) in the Mediterranean Sea. We present high-resolution, astronomically-tuned climate (Mg/Ca, δ18O) and productivity (Ba/Ca, δ13C) proxy records from the planktonic foraminifera Globigerinoides obliquus in the Kalamaki section (Zakynthos Island, Greece), which sheds new light on the early Pliocene Mediterranean hydrographic dynamics, and the associated climatic transition from 5.33 to 5.11Ma. We recognized four distinct climatic phases with variable amplitude changes: (1) very warm climate interval prior to 5.28Ma characterized by minimum ice volume, large salinity fluctuations, enhanced productivity, and intense river runoff, (2) stable paleoceanographic conditions from 5.28 to 5.23Ma, which reflect a relatively warm and mesotrophic to eutrophic open-marine environment with improved ventilation, (3) a brief interval (20ky) characterized by the most pronounced ice growth and intense cooling (∼5°C) coupled with the abrupt decrease of ventilation and primary productivity, and (4) reinstatement of relatively stable conditions (warm and well-ventilated mesotrophic upper water column) in conjunction with relatively stable sea-level after 5.21Ma. Overall, the succession of these phases provides an explanation for the more variable Mediterranean climate and stronger hydrographic variability with respect to other regions during the early Pliocene.
•Early Pliocene climate variability and hydrographic history is inferred.•We present a combination of lithostratigraphy with climate-sensitive records.•We discuss diagenesis and Mg/Casw variability effects on Mg/Ca-paleothermometry.•We compare western, central and eastern Mediterranean basins in the early Pliocene.•We outline a warm and variable (4-fold evolution) early Pliocene.
Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine ...terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (40Ar/39Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60–100°C/Ma between 22.5 and 19Ma, then cooled to temperatures around 40°C between 19 and 18Ma. They were re-heated at around 110°C between 18 and 15Ma then rapidly cooled and exhumed to reach the surface temperature at around 13Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13Ma the cooling resumed at a rate of 50°C/Ma indicating an exhumation rate of 0.8mm/y considering an average 40°C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events and vertical movements. Pliocene deposits of the Rifian coast represent the passive infilling of palaeo-rias between 5.33 and 3.8Ma. The whole coastal area was uplifted at slow average rates (0.01–0.03mm/y) in relation with a northeastward tilting of 0.2–0.3° since the Lower-Pliocene. A late Pliocene to present extensional tectonics associated to uplift has been identified all along the coastal ranges of the Internal Zone of the Rif chain. This extension was coeval with the major late Pliocene to Pleistocene extensional episode of the Alboran Sea and appears to be still active nowadays. No significant late Messinian uplift was evidenced, thus calling into question the geodynamic models relating the closure of the marine gateways and the MSC to slab roll back.
Planktonic foraminiferal geochemistry presents a valuable archive for paleoceanographic reconstructions. However in high salinity and carbonate super-saturated settings, precipitation of inorganic ...calcite onto foraminiferal tests can potentially alter the primary geochemical signal, biasing Mg/Ca ratios and ensuing paleoceanographic reconstructions. Here we utilize test biometrics (specifically related to the compression and elongation of the last chambers) to identify four distinct morphotypes (labelled A-D) of the paleoceanographically important planktonic foraminifer species Globigerinoides ruber, and further evaluate their susceptibility to diagenetic alteration from a suite of surface sediments in the eastern Mediterranean Sea. The three distinguished morphotypes (A–C) correspond to previously recognized morphotypes (“Normal”, “Platys”, “Elongate” respectively) in the Mediterranean Sea, while the remaining (D or “Twin”) was designated for the first time. We also compare Scanning Electron Microscopy (SEM) observations performed on four distinguished morphotypes, indicative of potential diagenetic alteration influence. We identified 3 different overgrowth stages (OGA1–OGA3), as a function of geography in the study area. The early diagenesis degrees (involving all the morphotypes) are only geographically distinct along the eastern Mediterranean (increasing to the south), since the morphology does not play a role in the likelihood of diagenetic alteration. Particularly, in the north Aegean Sea, SEM analyses reveal the absence or limited presence of an overgrowth imprint in all recognized morphotypes, while in the central-south Aegean and Levantine Seas they show higher amplitudes of diagenetic overprint supporting the general trend to advanced diagenetic alteration. The semi-enclosed oligotrophic nature and high salinity of this setting, in combination with the different degree of carbonate precipitation and calcite super-saturation between the sub-basins, could be the most plausible explanation for the observed diagenetic stages. The ecological divergence between the morphotypes, determined by different controlling factors (depth habitats, growth optimum/stressed conditions, productivity, stratification, near-/offshore-conditions), in combination with their different test morphologies (related to shell porosity), control directly their distribution pattern. Regardless of the exact mechanism of early diagenetic processes, our results remove one potential source of uncertainty in Mg/Ca-T reconstructions in such highly evaporitive basins of the (sub)tropics, and potentially open the door to the calculation of a multivariate calibration with greater accuracy. However, further investigations should extend this approach to test the robustness of our findings in a number of similar oceanic settings.
•Four distinct G. ruber morphotypes are defined based on morphometric criteria.•All G. ruber morphotypes present the same vulnerability to the overgrowth effect.•Diagenetic alteration presents a strong geographic signal in a N-S direction.•We identified 3 diagenetic stages with different overgrowth/dissolution signals.•Diagenesis ecophenotypically correlates to habitat with different biotic features.
Marine environmental status can be assessed through the study of bio-indicator species. Here, we monitor natural environmental stress by the occurrence of morphologically abnormal planktonic ...foraminiferal specimens from a suite of surface sediments in the eastern Mediterranean Sea. We also compare Scanning Electron Microscopy (SEM) abnormality observations from sapropel S1-derived sediments in the Aegean, Libyan and Levantine basins, since they provide a direct record of a natural stress experiment that took place over past time scales. At initial sapropel deposition levels, we observe increased growth asymmetry in Globigerinoides ruber twinned and twisted individuals, possibly associated with eutrophication and anoxia. In modern material, a range of malformations and aberrant morphologies from slight deformity with smaller or overdeveloped chambers to more severe deformity with abnormally protruding or misplaced chambers, distorted spirals, and double tests is also observed, as a result of the hypersaline, oligotrophic and oxygen-depleted nature of the Mediterranean Sea water column. Overall, we highlight the current use of the relative abundance of abnormal tests as a bio-indicator for monitoring natural stress, especially the occurrence of twin specimens as indicative of high-salinity stress conditions, and further illustrate the necessity to map both their spatial and temporal distribution for accurate paleoenvironmental reconstructions. Such an approach presents the advantage to rapidly provide information over wide spatial and temporal scales, extending our ability to monitor a wide variety of environments (from coastal to the open-sea). However, further investigations should extend this approach to test the robustness of our findings in a number of similar oceanic settings.
•We assess the degree of potential natural stressors (T, S, P, hydrodynamics).•Morphological abnormalities comparison through time (core-tops vs sapropel S1)•Double test formation (G. ruber twin) as bio-indicator of stressful conditions•A new cost-effective biomonitoring approach in coastal and open-marine settings•Salinity fluctuations positively correlate to the angle of twinned chambers.
New sedimentological, micropaleontological and geochemical data from the Upper Miocene pre-evaporitic sedimentary sequence of the Faneromeni section (Crete Island, eastern Mediterranean) revealed a ...stepwise restriction of the Mediterranean Sea preceding the Messinian Salinity Crisis (MSC), which was modulated by a sedimentary cyclicity responding to orbital parameters. This cyclicity is manifested by lithological alternations from laminated to indurated homogeneous marls and clayey limestones, and covers the Tortonian-Messinian Transition (TMT; 7.6–6.7 Ma). This time window covers the successive closure of the marine Mediterranean-Atlantic gateways, which culminated in the onset of the MSC. In the present study, we present the first evidence for changes in the upper water column reflected by sea surface temperature (SST) and salinity (SSS) variations that correlate with pronounced paleoclimatic fluctuations. Planktonic foraminiferal isotopes, in combination with paired mixed layer Sr/Ca-derived SST data, reveal that the very warm late Tortonian interval has been followed by a strong long-term cooling (~10 °C) and desalination (~10‰) trend during the earliest Messinian, attributed to the paroxysmal phase of the so-called “siphon” event. In particular, the climate shift that occurred at the end of a global carbon isotope (δ13C) decrease suggests that changes in the carbon cycle were instrumental in driving late Miocene climate dynamics (cooling and aridity) in the progressively isolated eastern Mediterranean Sea. The observed salinity variability during this time interval also provides further insights about seasonal freshwater inputs and gives new support to the much-debated hydrologic regime (linear salinity increase vs step-function evolution with strong salinity fluctuations) preceding the deposition of evaporites. The novel methodology of foraminiferal Sr/Ca paleothermometry and results of this study could have numerous potential applications to other regions and relevant extreme geological events. Therefore, in the near future we expect this approach to add important new information to our understanding of Neogene climates.
•A strong cooling (10 °C) and desalination (10‰) trend was observed during the TMT.•The S variability supports the concept of stepwise evolution prior the MSC onset.•Application of foraminiferal Sr/Ca paleothermometry in Late Miocene Mediterranean•Step-by-step development of the late Miocene cooling (siphon event)•Progressive restriction of the Mediterranean basin in response to paleoclimate
The Apostoli Basin, in the central-west part of Crete, was formed as a fore-arc type basin related to the convergent plate boundary between the African and the Eurasian plates. Most of the Neogene ...sediments filling the basin were deposited in a terrestrial to shallow marine environment. The succession is a transgressive cycle, which culminates in the alternation of Rethymnon bioclastic limestones with marls, documenting the important Tortonian marine transgression.
The Rethymnon limestones are classified as a typical non-tropical carbonate lithofacies. Two particular lithofacies have been recognized: (a) a
rhodalgal-type lithofacies, characterized by predominance of encrusting coralline algae and bryozoans, and (b) an
echinofor-type lithofacies, characterized by predominance of echinoderms and/or benthic foraminifera. The coralline algae occur mostly as in situ spheroidal or branched rhodoliths, whereas benthic foraminifera are mainly represented by larger foraminifera. In both lithofacies, typical tropical carbonate elements are lacking. Skeletal elements consisted of low- and high-Mg calcite. Although the observed lithofacies possess many similarities with facies of non-tropical carbonates, the presence of large benthic foraminifera suggests development in a warm temperate biogeographic province.
The depositional environment corresponds to a shallow ramp, the sediments being deposited in a nearshore environment and under conditions analogous to those prevailing in the present-day circalittoral bottoms of the Mediterranean Sea. The main carbonate accumulation area is located at the factory area itself (rhodalgal-type sediments), and downslope from the factory area (echinofor-type sediments). In the classic zonation of Mediterranean benthic assemblages of Peres and Picard Rec. Trav. Stn. Mar. (1964), the rhodalgal-type sediments of the Rethymnon Fm correspond to the “Facies a Pralines”, developed in areas strongly controlled by currents (e.g., tops of plateaus), and the echinofor-type sediments to the “Detritique Cotier” bioclastic deposits, derived mostly by bioerosion and fragmentation of local and adjacent calcareous benthic communities.
Changes in benthic foraminiferal and mollusk assemblages from the lower part of the Upper Pliocene of the Atsipades Section (Iraklion Basin, central Crete) were studied. The Atsipades Section ...represents a shallowing-upward sequence from outer shelf blue–gray clays at the bottom of the sequence, deposited below the storm wave base, to shallow inner shelf deposits affected by storm waves at the top. The foraminiferal assemblage at the bottom of the sequence is dominated by
Bolivina spathulata,
Bolivina dilatata and Uvigerinidae, a microfossil assemblage corresponding to the deepest deposits formed under dysoxic sea-floor conditions. Foraminiferal assemblages of the middle part of the section are highly diversified, predominantly
Haynesina depressula,
Cassidulina carinata and
Reusella spinulosa. The top of the section is mainly characterised by
Asterigerinata planorbis,
Bolivina pseudoplicata,
Cibicides lobatulus and
Elphidium sp., a typically epiphytic foraminiferal assemblage which can be correlated with the presence of an algal covered sea-bottom. Within this general environmental trend, a minor shallowing cycle can be differentiated. The boundaries of this cycle can be inferred, based on a substantial microfossil assemblage change and on the coincidence of species diversity maximum and a planktonic/benthic (P/P + B) ratio peak. Nonetheless, upwelling currents and/or over-abundance of nutrients due to continental outflow could also contribute to increased diversity and P/P + B ratio. The character of the mollusk assemblages is in accordance with these trends. Moreover, the increase in diversity and in sculpture constitutes a clear indication of an increase in hydrodynamic energy related to a shallowing-upward trend.
L'évolution des assemblages de foraminifères benthiques et de mollusques de la base du Pliocène supérieur de la Section Atsipades (Bassin d'Iraklion, Crête centrale) est étudiée. De la base au sommet, la Section Atsipades présente des niveaux de moins en moins profonds, partant d'argiles bleu–grises de la plate-forme externe, déposées sous la profondeur limite d'action des vagues de tempêtes, jusqu'à des dépôts de plate-forme interne affectés par les vagues de tempêtes. En base de la séquence, les foraminifères dominants sont
Bolivina spathulata,
Bolivina dilatata et les Uvigerinidae, un assemblage micro fossile correspondant à des dépôts profonds formés en conditions disoxiques. Les assemblages de foraminifères de la partie médiane de la section sont très diversifiés, dominés par
Haynesina depressula,
Cassidulina carinata et
Reusella spinulosa. Le sommet de la section est principalement caractérisé par
Asterigerinata planorbis,
Bolivina pseudoplicata,
Cibicides lobatulus et
Eplhidium sp., un assemblage épiphyte typique qui peut être corrélé à l'existence d'un fond marin couvert d'algue. Au sein de cette séquence, un cycle mineur de diminution de la profondeur peut être isolé. Les limites de ce cycle peuvent être inférées sur la base d'un changement substantiel de l'assemblage microfossile ainsi que de la coïncidence du maximum de richesse spécifique avec un pic du rapport d'espèces planctoniques (P/P + B). Les caractéristiques des assemblages de mollusques sont en accord avec cette séquence environnementale. De plus, l'augmentation de diversité et d'ornementation constitue une indication claire de l'accroissement de l'énergie hydrodynamique reliée à la diminution de profondeur.
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