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Trophism, climate and paleoweathering conditions across the Eocene-Oligocene transition in the Massignano section (northern Apennines, Italy)
No full textThe Eocene-Oligocene transition represents the latest greenhouse-icehouse shift faced by Earth, a major global climate change associated with carbon cycle perturbation. In this paper, we investigate the Massignano stratigraphic section (northern Apennines, Italy), GSSP of the Eocene-Oligocene boundary, by X-ray diffraction analysis of clay minerals and carbon and oxygen stable isotopes to explore the link among climate, paleoweathering and runoff, and carbon cycle in the Neotethys across this major climatic transition. We examine the interplay between global climate forcing and orogen evolution controlling the Massignano hemipelagic sedimentation. The late Eocene clay mineral assemblages indicate that the Neotethys was sensitive to global eustatic changes as well as changes in composition and rates of weathered sediments accumulating into the basin. The carbon isotope record matches with the global signal, showing productivity pulses linked to cooling phases and sea-level drops before 34.8 Ma. Subsequently, a constant negative trend is recorded, which is consistent with the global carbon isotope curve, and attests for a decrease of primary productivity linked to decreasing atmospheric CO2. This negative trend ends at the Eocene-Oligocene boundary, when the onset of the global carbon isotope positive excursion is recorded also within the Massignano hemipelagic succession. On the contrary, the clay mineral assemblage is quite constant across the Eocene-Oligocene boundary reflecting the complex interplay among fluvial discharge, sea level changes and orogen dynamics which clouded the global climate shift. In this context, the enhanced fluvial discharge likely contributed to sustain high trophic conditions in the Adriatic waters and, in turn, the Oligocene positive carbon isotope shift. These results highlight how clay minerals proved to be a useful proxy to identify the interplay between global and regional controlling factors on hemipelagic sedimentation and, their integration with the carbon isotope record, provides insights into carbon cycle dynamics
Miocene paleoceanographic evolution of the Mediterranean area and carbonate production changes. A review
Full text linkMiocene is a key interval in the global climate evolution as well as in the geodynamic evolution of the Mediterranean basin. Therefore, global and regional factors controlled Miocene Mediterranean oceanography, which, in turn, affected carbonate production. In this work, we review the Miocene paleocenographic evolution of the Mediterranean starting from its Sr and Nd isotope records. Secondly, we discuss Mediterranean shallow-water carbonate production changes to identify the role of oceanographic conditions in controlling carbonate systems' evolution. During Aquitanian, Sr and Nd isotope records attest an open Mediterranean, mainly fed by the Indian Ocean. From the late Burdigalian, the intermittent connection with the Indian Ocean changed the overall circulation in the basin, leading to higher residence time of waters and smaller water exchanges with the adjacent oceans. In this newly established paleoceanographic framework, regional factors such as volcanism, significantly affected Mediterranean seawater chemistry. Local tectonics led to the development of small sub-basins in the Eastern Mediterranean, characterized by restricted water exchanges from the Tortonian in the easternmost part, to the early Messinian, as attested by the deviation of the Sr isotope record of the proto-Adriatic basin. Larger Benthic Foraminifera (LBF) assemblages dominated carbonate production in the Aquitanian, while they were the most affected by the Indo-Pacific closure, showing a demise after the Burdigalian. With the LBF demise, red algae and bryozoans dominated carbonate ramps from the middle Miocene to the Tortonian. Bryozoans in particular spread during the Monterey Event, favoured by global and regional factors. During early to middle Miocene, corals formed mounds in the oligophotic zone or coral carpets controlled by local conditions. Conversely, in the late Tortonian-early Messinian, they developed as huge reef complexes in the Western and Central Mediterranean, with the exception of small restricted sub-basins, such as the proto-Adriatic basin, where red algae and small benthic foraminifera persisted
The Monterey Event in the Mediterranean platform to basin transition. The Guadagnolo Formation (Miocene, Prenestini Mountains, Central Apennines)
No full textThe stratigraphic evolution of the Guadagnolo Fm, developed on the transition between the Latium-Abruzzi Platform and the Umbria Sabina Basin (central Apennines), was studied through facies and stable isotope analysis. Calcareous nannofossil biostratigraphy allows to identify the Burdigalian-Langhian boundary, constraining the sections to the lower to middle Miocene. This interval consists of marly deposits forming the intermediate member of the formation dominated by sponge spicules, molluscs, bryozoans, benthic and planktonic foraminifers. This member is deposited in a distal outer ramp where the abundance of siliceous sponges has been attributed to the high seawater fertility coinciding with the Monterey event, enhanced by regional nutrient flux due to continental runoff and volcanism. The upper member is Serravallian and consists of bryozoan-dominated cross-bedded calcarenites deposited in a shallower environment of the outer ramp. A positive carbon isotope excursion was correlated with the Monterey event recorded in the Central Apennines carbonate ramps and from ODP sites. Five carbon maxima belonging to the Monterey Carbon Isotope Excursion have been identified. Four carbon isotope peaks fall in the spongolitic member, one in the upper member. The Carbon Maxima recorded within the spongolitic member show an attenuate isotope excursion compared with the pelagic and the carbonate platforms record. The weaker signal is due to the fractionation effect of primary producers of the photic zone and to the sponge release of 12C-enriched CO2 deriving from the oxidation of organic matter. Conversely, the largest positive carbon isotope excursion is recorded in the upper member, representative of a shallower environment, and it is due to the absence of sponges and the increased contribution of photosynthetic biota. The shoaling of the depositional environment is related to the global cooling recorded after 14 Ma, as evident also from the δ18O positive shift at the base of the upper member of the Guadagnolo Fm
The stratigraphic architecture of Bolognano Fm in the eastern Majella: implication for environmental and climatic evolution of the central paleo-Adriatic domain.
No full textThe Bolognano Fm in the south-eastern sectors of Majella and correlation with the north-western domain
No full textThis work investigated the evolution of the Bolognano Fm in the southern
portion of the Majella Mountain and correlated it with the northwestern sector.
Here the Bolognano Fm overlies unconformably the Eocene deposits of the S.
Spirito Fm. The first unit is the Burdigalian Bryozoan Calcarenite, overlain by the
Hemipelagic limestone to calcareous marls Burdigalian to Langhian in age. Lastly,
the Tortonian to early Messinian interval is represented by different units. The
first unit, which unconformably overlies the hemipelagic limestone to calcareous
marls, is the Bioclastic calcarenites unit, which is fed by sediments produced
within a euphotic inner ramp and accumulated in a deep environment. Upwards,
the Marly limestones and laminated calcareous marls unit shows a mixing of
deep water and shallow skeletal components deposited in an outer ramp. Moving
southward, the Coralline algal limestone crops out, identifying a productive
middle ramp environment. Lastly, a coral limestone unit was identified, where
coral bioconstructions interfinger with seagrass meadows and ooidal shoals, in
the euphotic zone. The Marly limestone and laminated calcareous marls testify
for a deterioration of environmental conditions due to both global climate change
as well as the approaching of the Apennines accretionary wedge, which triggered
an increase of terrigenous runoff
Neodymium isotopes of central Mediterranean phosphatic hardgrounds reveal Miocene paleoceanography
Full text linkUnderstanding the causes of the formation of hardgrounds provides insights on the oceanographic evolution of a basin. Phosphate-rich hardground formation interrupted carbonate ramp deposition in the Mediterranean during the Miocene. We analyzed the epsilon(Nd) record of three central Mediterranean hardgrounds to identify the origin of the phosphate-rich waters that formed them within the frame of Mediterranean Miocene paleoceanographic evolution. The Nd isotopes suggest that eastern Mediterranean deep waters were controlled by runoff, in contrast to Atlantic and Indian Ocean waters. This Nd isotope record attests to the weakening of Mediterranean circulation during the Miocene due to closure of the Indian Gateway. Limited exchange with Atlantic shallow seawater led to long residence times for deep waters in the basin. This record indicates the role of upwelling in formation of phosphate hardgrounds and shows the influence of global climate change and local paleoceanographic conditions
The potential of carbonate ramps to record C-isotope shifts: insights from the upper Miocene of the Central Mediterranean area
No full textThe late Miocene is a crucial interval for global climate evolution as well as for the regional geodynamic evolution of the Central Mediterranean area. It spans the transition from the warm Mid Miocene Climatic Optimum, associated with the major Monterey Carbon Isotope Excursion, to the cooler Pliocene, characterized by a bipolar glaciation. Within this climatic transition, during the early Tortonian, a positive carbon isotope excursion related to a global carbon cycle perturbation is recorded, named Carbon Maximum 7 (CM7). In this study, two upper Serravallian–lower Tortonian carbonate ramps of the Central Mediterranean have been analysed: the Latium-Abruzzi and the Apula ramps (Central Apennines, Central Italy). Carbon isotope ratios have been coupled with facies and microfacies analyses with the aims: (1) to identify the CM7 in the Central Mediterranean carbonate ramp successions; (2) to evaluate potential carbonate factory changes or demises related to the CM7; and (3) to discriminate the role of global vs regional factors in affecting the Mediterranean carbonate ramps. The two studied ramps show different evolutions due to regional geodynamics causes. The Latium-Abruzzi ramp drowns in the Tortonian, while the Apula shows a regressive trend, with upper Tortonian middle ramp facies overlying the lower Tortonian outer ramp. Despite the complex geodynamic setting, a positive carbon isotope shift has been identified in both ramps and correlated with the CM7. This positive carbon isotope shift may be linked to the strengthening of the global ocean circulation during the late Miocene cooling. This strengthening of the circulation enhanced the coastal upwelling, bringing nutrient-rich waters to the surface and triggering an enhanced primary productivity consistent with the CM7
Continuous attractors for dynamic memories
Full text linkEpisodic memory has a dynamic nature: when we recall past episodes, we retrieve not only their content, but also their temporal structure. The phenomenon of replay, in the hippocampus of mammals, offers a remarkable example of this temporal dynamics. However, most quantitative models of memory treat memories as static configurations, neglecting the temporal unfolding of the retrieval process. Here, we introduce a continuous attractor network model with a memory-dependent asymmetric component in the synaptic connectivity, which spontaneously breaks the equilibrium of the memory configurations and produces dynamic retrieval. The detailed analysis of the model with analytical calculations and numerical simulations shows that it can robustly retrieve multiple dynamical memories, and that this feature is largely independent of the details of its implementation. By calculating the storage capacity, we show that the dynamic component does not impair memory capacity, and can even enhance it in certain regimes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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