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The project OLCAPP was aimed at exploring the response of a natural, eutrophic system to ocean liming by slaked lime (calcium hydroxide) dispersal in the wake of ships. The main objectives were:- to monitor and model the slaked lime dissolution kinetics and the carbonate equilibrium (alkalinity, pH spikes/alteration, Dissolved Inorganic Carbon);- to assess Dissolved Organic Matter changes in quantity and composition;- to assess possible changes in primary production, photosynthetic efficiency and phytoplankton abundance and associations;- to assess the short and medium-term response of planktonic and benthic calcareous primary producers (calcareous red algae = maerl) to alkalinization and potential precipitation of carbonate crystals induced by the treatments.In the framework of the Transnational Access provided by AQUACOSM-plus, at the ECIMAT-UVIGO facility (Vigo, Spain) we had the opportunity to test ocean liming in nine mesocosm tanks. A sediment trap and a basket of calcareous algae (maerl) were positioned at the bottom of each tank. Mearl was previously collected in the Ria de Vigo at 7m depth and prepared for the experiment. Successively, each tank was filled with natural coastal seawater (~1m3).Out of the nine mesocosms, three tanks were treated with calcium hydroxide 0.02g/L (High) and three tanks with 0.006g/L (Low) per treatment, repeated on days 1, 3 and 5 (multiple exposure). The remaining three tanks were kept as control. A record of pH, O2, salinity, temperature and PAR was performed in the mesocosms during the experiment with a ten-minutes frequency.Nutrient concentration is monitored on a long-term basis in the Ria de Vigo, and was also tested on days 1, 3 and 5 for all treatments and controls. Seawater samples were collected from the mesocosms before (pre-treatment), and after 1h, 4h, and 24h from each treatment, with a 5L Niskin bottle. Dissolved Organic Matter as Dissolved Organic Carbon (DOC) and Chromophoric Dissolved Organic Matter (CDOM) were analysed, along with the Dissolved Inorganic Carbon (DIC). Moreover, samples collected after 1h from treatments were used for assessing also the bacterial association, the size-fractionated Chl-a concentration and the plankton primary production and photosynthetic efficiency. Gross primary production, community respiration and net community production were measured by changes in oxygen concentrations after 24 h light-dark bottle incubations. Dissolved oxygen was measured by Winkler titration. A total of 165 samples were obtained from filtering 2L of mesocosm water from pre-treatments, 4h and 24h samples, for the collection of the phytoplankton community, to be analysed under optical and scanning electron microscope.Preliminary observations during the experiment and the first data on the plankton community suggest that the High treatment leads to important flocculation and sedimentation affecting both the transparency of the water and the bottom environment, with significant and stable pH increase and decrease in phytoplankton production and efficiency. The mineralogical nature of the flocculation, the response of benthic calcareous algae and phytoplankton community, in term of composition and abundance of the major components, is here discussed.

The detailed study of diatom laminations conducted by means of backscattered electron imaging serves as tool to unravel details of past ocean dynamics. In this paper we apply this method to the analysis of the diatomites of Cerro Los Quesos, Upper Miocene Pisco Fm, Peru. Numerous studies have been conducted on the Pisco Fm; however, a focus on its paleoceanographic significance is still lacking. In this work, we provide information on the oceanographic setting in the area at the time of diatomites deposition. The high abundance of deep-living Coscinodiscus laminae, proceeded by either a mixed lamina or a terrigenous one, let us hypothesize a deep position of the thermocline during the deposition of the Pisco diatomites; together with the scarcity of Chaetoceros Hyalochaete spp. resting spores, this evidence confutes the belief that equals high biogenic silica content in marine sediments with enhanced upwelling. Conversely, the depositional setting of the Pisco Fm diatomites is more similar to what is known as “permanent El Niño” (or “El Padre”) state, meaning a constant weakened upwelling (or upwelling of nutrients-poor waters). Climate modeling warns that an increase in atmospheric CO2 may lead to this mean state in the near future. Thanks to this study we also obtained refined information on the diatomites sedimentations rates. The comparison of the Pisco diatomites sedimentation rates with those of Quaternary diatomites gave strength to the hypothesis that the formation of the vertebrate Lagerstätte may have been enhanced, among others, by the so-called “impact-burial” mechanism.

Along the Peruvian coast, the sedimentary succession of the East Pisco Basin is exposed in the Ica Desert. At Cerro Los Quesos, laterally continuous dolomite layers characterise the diatomaceous sediments of the P2 sequence of the Miocene Pisco Formation, where a large number of marine vertebrates are exceptionally preserved, many enclosed in dolomite nodules. In this work, cemented layers from this sequence were described and sampled for petrographic, chemical, microscopic and isotopic analyses. Dolomite occurs in continuous 10–50 cm thick well cemented layers, formed by sediment of different nature: biogenic, terrigenous, volcanoclastic, and phosphatic. The underlying sediments exhibit a yellow layer with sparse dolomite crystals, a black layer with abundant Mn-oxides, and a reddish layer rich in Fe-oxides, indicating redox-related fronts. Two generations of dolomite can be recognised: an early diagenetic microcrystalline one, and a sparry one, filling the large cavities. As observed in both thin sections and on broken surfaces, microcrystalline dolomite also fills the inner spaces of the diatom areolae replicating their finest ultrastructure, such as foramina and cribra and replace calcite shells of foraminifera. δ18O and δ13C values from the microcrystalline dolomite of two layers, selected based on the absence of other carbonate phases (e.g. calcite) and the lack of sparry cement, are in agreement with those reported for the Peru margin and fall in the fields of either sulphate-reduction or methanogenesis. All the data point to dolomite precipitation associated with low-temperature early diagenesis that typically occurs in upwelling settings, where high surface water productivity is responsible for high rates of organic carbon flux to the sea bottom and for the cyclical oxygen depletion at the bottom. Such conditions also promote high abundances of marine vertebrates and the exceptional preservation of their skeletons in the sediments.

Strata of Chilcatay and Pisco formations exposed in the Ica Desert (East Pisco Basin, southern Peru) preserve one of the most complete and rich records of Miocene marine vertebrates of the world. Despite its exceptional importance, the chronostratigraphy of these fossil-bearing deposits has been only sporadically studied in the literature until recently. This work presents a detailed reconstruction of the chronostratigraphic framework, achieved by mapping and measuring of seven sections (totaling a height of almost 1000 m) of the Miocene Chilcatay and Pisco formations along the western side of the Ica River. The Chilcatay Formation consists of two allomembers, namely Ct1 and Ct2, bounded at the base by unconformities CE0.1 and CE0.2, respectively. Similarly, the immediately overlying Pisco Formation is divided into allomembers P0, P1, and P2, bounded at the base by unconformities PE0.0, PE0.1 and PE0.2, respectively. The new 39Ar–40Ar results presented here, combined with ages of previous work, provide precise constraints on the age of several stratigraphically referenced volcanic ash layers intercalated in the studied fossil-bearing succession, placing its vertebrate fossil fauna within a refined temporal framework and laying the solid ground for its detailed regional and global comparison. The ages of the allomembers, and thus their associated faunas, can be reliably estimated by the combination of 39Ar–40Ar dating on tephra layers with diatom biostratigraphy. In the study area, two methods are mutually consistent and constrain the deposition of the Chilcatay Formation between 19.2 and 18.0 Ma, that of P1 between 9.5 and 8.6 Ma, and that of P2 between 8.4 and 6.7 Ma. In the absence of direct dating of the P0 allomember, which lacks both preserved tephra suitable for 39Ar–40Ar dating and microfossils, its age can be constrained to the temporal gap between the youngest age available from the underlying Chilcatay strata (18.0 Ma) and the oldest age available from the overlying P1 strata (9.5 Ma).

International audience; Based on mapping of laterally traceable stratigraphic discontinuities, we propose a high-resolution allostratigraphic scheme for one of the world's foremost fossil marine vertebrate Lagerstätten: the lower Miocene strata of the Chilcatay Formation exposed along the Ica River near Zamaca, southern Peru. Measured sections combined with 1:10,000 scale mapping of a 24 km 2 area provide an overview of the stratal architecture, as well as a general facies framework and interpretation of the various depositional settings. As a whole, the Chilcatay alloformation is bounded by the CE0.1 unconformity at the base and the PE0.0 unconformity at the top. An internal Chilcatay surface, termed CE0.2, splits the alloformation into two distinct allomembers (Ct1 and Ct2). The Ct1 allomember comprises three facies associations recording deposition in shoreface, offshore, and subaqueous delta settings. The Ct2 allomember comprises two facies associations, recording deposition in shoreface and offshore settings. Using these data, we place the rich marine vertebrate assemblage in a precise spatial and stratigraphic framework. The well-diversified vertebrate assemblage is dominated by cetaceans (mostly odontocetes) and sharks (mostly lamniforms and carcharhiniforms); rays, bony fish, and turtles are also present. Taxonomic novelties include the first records of baleen whales, platanistids, and eurhinodelphinids from the Chilcatay Formation. ARTICLE HISTORY

The Eocene sediment successions of the East Pisco Basin (southern Peru) host an exceptionally rich and well-preserved assemblage of vertebrate fossils. However, due to the dearth of geochronological and biostratigraphic controls as well as of stratigraphic correlations, our understanding of these rocks and their fossil content remains elusive. This paper provides a comprehensive calcareous nannofossil, diatom, and silicoflagellate biostratigraphic framework for the Eocene strata exposed at four localities along the Ica River Valley, permitting a robust chronological calibration of the marine vertebrate fauna entombed therein and a better definition of important appearance/ extinction events. The Paracas Formation, deposited directly on top of the Proterozoic and Paleozoic rocks of the crystalline basement, is formed by a siliciclastic-bioclastic sand-sized deposit (Los Choros member) and calcareous-terrigenous siltstone (Yumaque member) that was deposited from the Lutetian (47.8–41.2 Ma) through the Bartonian (41.2–37.7 Ma) to the early Priabonian (37.7–33.9 Ma). The unconformably overlying Otuma Formation consists of a basal sandstone, followed by calcareous siltstone intercalated by diatomite layers towards the top. In the study area, the Otuma Formation is Priabonian in age and is truncated at the top by an unconformity at the base of the overlying Miocene Chilcatay Formation. Due to the angular nature of the unconformity, the upper Otuma strata reach the Oligocene elsewhere. Average sedimentation rates range from 17 to 24 m/My in the Yumaque member of the Paracas Formation and increase to 147–170 m/My in the Otuma Formation. The microfossil assemblages witness a coastal setting with warm-temperate conditions for the Paracas Formation that become slightly cooler (though still temperate) in the upper Otuma Formation. Diatomaceous layers in the upper Otuma Formation indicate an overall increase in nutrient availability, which could reflect the global reorganization of ocean currents at the Eocene-Oligocene transition. However, the taxonomic composition of the diatom assemblage suggests seasonal rather than persistent upwelling conditions.

The northward-flowing Humboldt Current hosts perpetually high levels of productivity along the western coast of South America. Here, we aim to elucidate the deep-time history of this globally important ecosystem based on a detailed palaeoecological analysis of the exceptionally preserved middle–upper Miocene vertebrate assemblages of the Pisco Formation of the East Pisco Basin, southern Peru. We summarise observations on hundreds of fossil whales, dolphins, seals, seabirds, turtles, crocodiles, sharks, rays, and bony fishes to reconstruct ecological relationships in the wake of the Middle Miocene Climatic Optimum, and the marked cooling that followed it. The lowermost, middle Miocene Pisco sequence (P0) and its vertebrate assemblage testify to a warm, semi-enclosed, near-shore palaeoenvironment. During the first part of the Tortonian (P1), high productivity within a prominent upwelling system supported a diverse assemblage of mesopredators, at least some of which permanently resided in the Pisco embayment and used it as a nursery or breeding/calving area. Younger portions of the Pisco Formation (P2) reveal a more open setting, with wide-ranging species like rorquals increasingly dominating the vertebrate assemblage, but also local differences reflecting distance from the coast. Like today, these ancient precursors of the modern Humboldt Current Ecosystem were based on sardines, but notably differed from their present-day equivalent in being dominated by extremely large-bodied apex predators like Livyatan melvillei and Carcharocles megalodon.

Tephra layers are a unique tool for stratigraphy. Their geologically instantaneous deposition together with their dispersion on wide areas make them a powerful instrument for dating and correlating simultaneous events at different localities. In this paper, we present and discuss the application of tephra fingerprinting in the upper Miocene portion of the Pisco Formation. The Pisco Formation is an important marine vertebrate Fossil-Lagerstätte that crops out in the Ica Desert, on the Peruvian Coast. The paleontological relevance of this formation has entailed the necessity of reconstructing a chronostratigraphic framework, using 40Ar/39Ar dating and correlations on volcanic ashes. Tephra layers from the volcanic activity of the Peruvian Andes are very frequent in the Pisco Formation and many represent a primary air-fall deposition on the sea floor. Therefore, many samples from tephra layers within measured stratigraphic sections at different sites in the study area were fingerprinted with a combined approach, using petrographic and chemical analyses on phenocrysts and volcanic glasses, as well as glass shard morphology and granulometric analyses, performed on 53 selected samples, collected from different localities. Based on the results obtained, we correlate some tephra layers in two localities at several km distance, where the correlation between the measured sections was previously only hypothetical. Major element chemistry of biotite proved a valuable tool to discriminate different tephra in the upper Miocene portion of the Pisco Formation, due to the presence of peraluminous as well as metaluminous compositions. This work shows that it is possible to apply tephra fingerprinting and tephrostratigraphy in a complex situation such as that represented by the Pisco Formation, where a high number of apparently similar volcanic ash layers were deposited in a shallow marine environment. The application of this correlation method allows us to increase the chronostratigraphic detail in the studied interval of the Pisco Formation, providing an accurate framework in which fossil marine vertebrates are stratigraphically located. The obtained high-resolution chronostratigraphy will greatly clarify the evolutionary history of Cetaceans.

The late Miocene Pisco Formation of Peru is an outstanding example of richness and high-quality preservation of fossil marine vertebrates. In order to reconstruct the fossilization path, we present new textural, mineralogical and Sr-isotope data of diagenetic minerals formed in correspondence of fossil specimens such as marine vertebrates and mollusks. These fossil specimens were found at Cerro los Quesos, in the Ica Desert, within the diatomaceous strata of the Pisco Formation. Dolomite, gypsum, anhydrite and Mn minerals are the main phases found, while the calcium carbonate originally forming the mollusk valves is replaced by gypsum. An early formation of dolomite and of Mn minerals, triggered by the modifications of the geochemical environment due to organic matter degradation, is suggested by the textural relationships and is confirmed by the Sr isotopic ratio of dolomite, which agrees with that of seawater at the time of sedimentation. Instead, gypsum Sr isotopic ratios indicate a pre-Miocene seawater-derived brine circulating within the sedimentary sequence as a source for Sr. Oxidation of diagenetic sulfide causing a lowering of the pH of porewater is proposed as an explanation for Ca-carbonate dissolution. The diagenetic chemical environment was, nevertheless, favorable to bone preservation.

Time-series analyses of satellite images reveal that sea ice extent in the Ross Sea has experienced significant changes over the last 40 years, likely triggered by large-scale atmospheric anomalies. However, resolving how sea ice in the Ross Sea has changed over longer timeframes has until now remained more elusive. Here we used a laminated sediment piston core (14.6 m) collected from the Edisto inlet (Western Ross Sea) to reconstruct fast ice dynamics over the last 2.6 ka. Our goal was to first understand the climate expression of selected well-defined sediment laminae and then use these characteristics for reconstructing past sea ice behaviour across the whole sedimentary sequence. We used the recently established sea ice diatom biomarker proxy IPSO25 in combination with diatom census counts and bulk analyses. Analyses performed on a suite of discrete laminae revealed statistically significant differences between dark and light laminae reflecting different depositional conditions. Based on their respective biogeochemical fingerprints, we infer that dark laminae accumulated during sea ice thaws in early summer. Under these conditions, laminae contain relatively high concentrations of IPSO25 and display an enriched delta C-13 composition for the bulk organic matter (OM). While diatom assemblages in dark laminae are relatively homogenous, as the thaw continues later in the summer, Corethron pennatum becomes the dominant diatom species, resulting in the formation of light laminae characterized by low IPSO25 concentrations. Since C. pennatum can migrate vertically through the water column to uptake nutrients and avoid competition in oligotrophic waters, its high concentration likely reflects stratified and ice-free surface waters typical of late summer. Down-core trends show that the correlation between sediment brightness and geochemical fingerprint (i.e., IPSO25 and delta C-13) holds throughout the record. Based on the knowledge gained at lamina level, our down-core high-resolution reconstruction shows that the summer fast ice coverage changed dramatically during the late Holocene. Specifically, we conclude that the Edisto inlet experienced regular early summer opening between 2.6 ka, and ca. 0.7 ka, after which, coastal fast ice persisted during summer months and ice-free conditions became less frequent. Comparison with previous regional ice core data suggests that the sudden cooling recorded over the Victoria Land Coast region since 0.7 ka might potentially explain our observation of persistent summer fast ice in the Western Ross Sea. Our study has shown that multi-proxy data derived from laminated sediments can provide hitherto unknown detail regarding past summer sea ice dynamics in coastal Antarctic regions. (C) 2020 Elsevier Ltd. All rights reserved.

Exceptionally preserved delicate baleen microstructures have been found in association with the skeleton of a late Miocene balaenopteroid whale in a dolomite concretion of the Pisco Formation, Peru. Microanalytical data (scanning electron microscopy, electron probe microanalysis, X-ray diffraction) on fossil baleen are provided and the results are discussed in terms of their taphonomic and paleoecological implications. Baleen fossilization modes at this site include molding of plates and tubules, and phosphatization. A rapid formation of the concretion was fundamental for fossilization. We suggest that the whale foundered in a soft sediment chemically favorable to rapid dolomite precipitation, allowing the preservation of delicate structures. Morphometric considerations on the baleen plates and bristles coupled with the reconstructed calcification of the latter permit speculation on the trophic preferences of this balaenopteroid whale: the densely spaced plates and the fine and calcified bristles provide evidence for feeding on small-sized plankton, as does the modern sei whale.

With the aim of preparing the ground for a comprehensive stratigraphic work on the Mio-Pliocene Pisco Formation, Peru, diatom marker species from the upper Miocene sites of Cerro Colorado (CC) and Cerro Los Quesos (CLQ) were investigated. Samples were collected along two composite stratigraphic sections and prepared for microscope analysis. Marker species are listed and described; their ranges and taxonomy are discussed in the light of recent works on Pacific diatom biostratigraphy and compared to findings in previous works from the 1980s on the Pisco Formation. Subsequently, marker species ranges and taxonomy have been significantly revised, suggesting that age-attributions based on sediments of the Pisco Formation should also be corrected. Examples are: (1) Koizumia tatsunokuchiensis, which was known as a Pliocene marker, but is now known to first appear in the late Miocene; (2) Thalassiosira cf. flexuosa, which was reported in early works on the Pisco Formation biostratigraphy as Coscinodiscus plicatus...

Fossil bones, together with teeth, are the most common remains of vertebrates that could manage to get preserved over geological times, providing information on the diagenetic and fossilization processes that occurred in the depositional paleoenvironment. Fossil bones from the marine vertebrate Konservat-Lagerstatte in the East Pisco Basin and Sacaco area (Peru) show a high variety of different textural and chemical features, suggestive of different processes variably contributing to the fossilization path. At the macroscopic scale, bone samples can be grouped into six different categories on the basis of the color (red to gray to white) and hardness (which relates to the mineralization degree); a variety of case studies can be found between these categories. Microscopically, the original microstructure of the bone tissue, both compact and cancellous, is well preserved in all the studied samples, with differences in cavity fillings, distribution of microcracks, and presence of Fe oxides in the diverse bone types. The bone composition and mineralogy correspond to fluorapatite. Differences in color, mineralization degree and geochemistry can be interpreted in terms of different fossilization paths, from burial at the seafloor to exposure in the present-day desert environment. The fossilization paths are strongly conditioned by the factors controlling the interplay of the mechanisms of apatite dissolution-recrystallization and dolomite precipitation (formation of carbonate concretions) as well as the fixation of iron in finely disseminated sulfides in the very early stages of fossilization.

International audience; The taphonomy and palaeoecology of the early Miocene (Burdigalian) vertebrate assemblage of Ullujaya (East Pisco Basin, Peru) is here described. Vertebrate remains are concentrated in marine facies (Ct1a association) of the exposed Chilcatay Formation (dated 19-18 Ma) deposited within a 30-40 m deep, semi-enclosed, offshore environment. Coupled with ichnological observations, the size distribution of pyrite framboid relics reveals fluctuation of euxinic and oxic-dysoxic conditions at the seafloor. The assemblage is dominated by toothed cetaceans (kentriodontids, squalodelphinids, physeteroids, and the eurhinodelphinid-like Chilcacetus), together with a large dermochelyid turtle, some bony fish, and diverse elasmobranchs, mostly juveniles of Carcharhinus brachyurus and Cosmopolitodus hastalis. The vertebrate assemblage comprises a coastal community, dominated by mesopredators, representative of a warm-temperate, sheltered embayment connected with riverine and open-ocean environments. Vertebrate skeletons are typically disarticulated and incomplete, and some bone elements display shark bite marks. Microborings are observed at the bone surface. Bones exhibit a good degree of apatite mineralisation and bone cavities are locally filled by Ca-Mg carbonates. Our taphonomic observations suggest prolonged flotation of carcasses during which they were subject to biogenic and physical processes of partial destruction (including scavenging by sharks), before final deposition on a soft compact substrate. Preservation was favoured by the oxygen-deficient bottom conditions that inhibited the action of benthic macro-scavengers.

International audience; This paper is the first integrated account of the sedimentology, stratigraphy, and vertebrate paleontology for the marine strata of the Chilcatay Formation exposed at Ullujaya, Pisco basin (southern Peru). An allostratigraphic framework for the investigated strata was established using geological mapping (1:4000 scale) and conventional sedimentary facies analysis and resulted in recognition of two unconformity-bounded allomembers (designated Ct1 and Ct2 in ascending order). The chronostratigraphic framework is well constrained by integration of micropaleontological data and isotope geochronology and indicates deposition during the early Miocene. The marine vertebrate fossil assemblage is largely dominated by cetaceans (odontocetes), whereas isolated teeth and spines indicate a well-diversified elasmobranch assemblage. Our field surveys, conducted to evaluate the paleontological sensitivity of the investigated strata, indicate that vertebrate remains only came from a rather restricted stratigraphic interval of the Ct1 allomember and reveal the high potential for these sediments to yield abundant and scientifically significant fossil assemblages. ARTICLE HISTORY

Paleoclimatic and paleoenvironmental reconstruction during the last 2ka using geochemical and biological proxies in marine sediments from western Ross Sea (Antarctica)

Field mapping and sedimentological study of outcrop sections exposed along the Ica River valley permitted the establishment of a regional allostratigraphic framework for the upper Miocene portion of the Pisco Formation. The stratigraphy of the studied interval is illustrated using a new 1:20,000-scale geological map which reveals that this formation is a cyclical sedimentary succession composed of three fining-upward allomembers. The bounding surfaces defining each allomember are transgressively modified subaerial unconformities. They converge and merge landward into a single composite surface representing the time-transgressive lower boundary of the Pisco Formation. Accordingly, the extent of the stratigraphic gap associated with the basal unconformity varies significantly throughout the basin and increases toward the basin margins. The timing of allomember-bounding surfaces coincides with that of major oxygen-isotope maxima in the deep-sea oxygen isotopic record and matches the ages of eustatic sequence boundaries identified elsewhere, indicating glacio-eustatic falls due to the growth of Antarctica ice sheets as a viable mechanism for their development.

The upper Neogene Pisco Formation of Peru is known worldwide as one of the most significant Cenozoic\ud marine vertebrate Konservatt-Lagerstätten, even featuring cetacean specimens that retain remains of soft tissues or\ud stomach contents. Previous works showed that biomediated precipitation of dolomite concretions around large-sized\ud decaying carcasses was one of the most relevant processes responsible for exceptional fossil preservation. In turn, little is\ud known about the modes of fossilization of well-preserved small-sized vertebrates, which are rather common in the Pisco\ud Formation, but mostly do not exhibit dolomite concretions. We report on a cetacean specimen, identified as belonging\ud to the extinct short-snouted, small dolphin species Brachydelphis mazeasi (Pontoporiidae), preserved within a late\ud Miocene sandy deposit at the site of Pampa Corre Viento. This specimen consists of a moderately disarticulated partial\ud skeleton exhibiting well-mineralized bones; it is not enclosed within a dolomite concretion, being however delimited\ud by an evident dark boundary in the host sediment. Scanning electron microscopy and microanalytical investigations\ud identify Mn-oxides and apatite as early diagenetic minerals around the skeleton. We argue that a rapid burial of the\ud specimen was pivotal for the preservation of the bones, and allowed the early establishment of anoxic processes for\ud degradation of organic matter. Coupled with availability of P in porewater, the reducing conditions and the lowered\ud pH allowed precipitation of Ca-phosphate while increasing Mn solubility close to the pontoporiid carcass. Mn-oxides\ud precipitated at the redox boundary, the latter defining the outer edge of the volume of sediment affected by altered\ud chemical conditions due to the decaying processes. The permeability of the sediment and the small size of the carcass\ud were possible factors unfavorable to extensive sulfate reduction, thus preventing the formation of a dolomite concretion\ud and allowing bone phosphatization. This record emphasizes the role of conditions favorable to bone mineralization in\ud absence of an isolating carbonate concretion, in cases of high quality preservation of small-sized vertebrates observed\ud in the Pisco Formation. The observation of patterns in the distribution of diagenetic minerals in the sediment enclosing\ud vertebrate remains without, or with limited carbonate concretions provides insights into early taphonomic processes.

We present the combined abundance of all extant fossilizable planktonic groups (Dinoflagellates, Coccolithophores, Silicoflagellates, Diatoms, Parmales, Archaeomonads and micro-zooplankton) from surface waters collected along a latitudinal transect in the western Pacific sector of the Southern Ocean, ranging from ~ 48°S, offshore New Zealand, to ~ 70°S in the Ross Sea, Antarctica. Latitudinal shifts in species' distribution correspond with the Antarctic Circumpolar Current fronts and with the seasonal position of the ice-edge. Distinct bioprovinces are defined by clustering samples with a high degree of similarity. Our data confirm the importance of previously-defined taxa as palaeoceanographic proxies but also reveal some differences: the shift in dominance between the silicoflagellates genera Dictyocha and Stephanocha, used as a proxy of palaeo sea-surface temperatures, occurs slightly north of the Southern Sub-Antarctic Front rather than at the Polar Front; the shifts in abundance between the open-ocean diatom species Fragilariopsis kerguelensis and sea-ice related F. curta and F. cylindrus, as well as the drop in the coccolithophore Emiliania huxleyi, occur at the southern Antarctic Circumpolar Front rather than at the Polar Front. Finally, we introduce the Corona-index, based on the ratio of the coronatid to non-coronatid silicoflagellates species Stephanocha speculum, as a new proxy for sea-ice and we confirm the occurrence of abundant Archaeomonads and Parmales (Triparma laevis subsp. ramispina) in the marginal ice-edge zone.

This paper describes a ∼200 m-thick section of the Pisco Formation exposed at Cerro Colorado, an important fossiliferous site in the Ica desert. In order to properly place the fauna in its correct relative position, this study establishes the stratigraphic framework within which the different fossil-bearing intervals of this site can be compared and may prove invaluable in future high-resolution studies on the faunal change. Most of the Pisco Formation deposits exposed at Cerro Colorado consist of gently dipping fine-grained sandstones, diatomaceous siltstones and diatomites with minor ash layers and dolomites deposited within nearshore and offshore settings. To facilitate detailed stratigraphic correlations within the Pisco strata for a 30 km2 area, eight marker beds have been defined and large-scale (1:10,000 scale) geological mapping conducted to determine fault positions, styles and offsets. The geological map shows that there are two important angular unconformities in the study area. The first one is the interformational basal unconformity of the Pisco Formation against folded, faulted, and planated Oligo-Miocene rocks of the Chilcatay Formation. The second is a low-angle intraformational erosional discontinuity of up to 4° angular discordance that allows the subdivision of the Pisco stratigraphy exposed in the study area into two informal allomembers. Dating of the exposed succession by diatom biostratigraphy suggests that the age of the lower allomember is late Miocene, whereas the upper allomember is late Miocene or younger.

The enormous concentration of marine vertebrates documented within the Pisco Formation is unique for Peru and South America and places this unit among the prime fossil Lagerstätten for Miocene to Pliocene marine mammals worldwide. In order to provide a robust stratigraphic framework for the fossil-bearing locality of Cerro Los Quesos, this study presents a 1:10,000 scale geological map covering an area of about 21 km2, a detailed measured section spanning 290 m of strata, and a refined chronostratigraphy for the studied succession well constrained by diatom biostratigraphy and high-resolution 40Ar/39Ar isotopic dating of three interbedded ash layers. Within the apparently monotonous, diatomite-dominated sedimentary section, the Pisco Formation has been subdivided into six local members, with stratigraphic control over the different outcrops facilitated by the establishment of a detailed marker bed stratigraphy based on 15 readily distinguishable sediment layers of different nature.

International Ocean Discovery Program (IODP) Expedition 353 (29 November 2014–29 January 2015) drilled six sites in the Bay of Bengal, recovering 4280 m of sediments during 32.9 days of on-site drilling. Recovery averaged 97%, including coring with the advanced piston corer, half-length advanced piston corer, and extended core barrel systems. The primary objective of Expedition 353 is to reconstruct changes in Indian monsoon circulation since the Miocene at tectonic to centennial timescales. Analysis of the sediment sections recovered will improve our understanding of how monsoonal climates respond to changes in forcing external to the Earth’s climate system (i.e., insolation) and changes in forcing internal to the Earth’s climate system, including changes in continental ice volume, greenhouse gases, sea level, and the ocean-atmosphere exchange of energy and moisture. All of these mechanisms play critical roles in current and future climate change in monsoonal regions. The primary signal targeted is the exceptionally low salinity surface waters that result, in roughly equal measure, from both direct summer monsoon precipitation to the Bay of Bengal and runoff from the numerous large river basins that drain into the Bay of Bengal. Changes in rainfall and surface ocean salinity are captured and preserved in a number of chemical, physical, isotopic, and biological components of sediments deposited in the Bay of Bengal. Expedition 353 sites are strategically located in key regions where these signals are the strongest and best preserved. Salinity changes at IODP Sites U1445 and U1446 (northeast Indian margin) result from direct precipitation as well as runoff from the Ganges-Brahmaputra river complex and the many river basins of peninsular India. Salinity changes at IODP Sites U1447 and U1448 (Andaman Sea) result from direct precipitation and runoff from the Irrawaddy and Salween river basins. IODP Site U1443 (Ninetyeast Ridge) is an open-ocean site with a modern surface water salinity very near the global mean but is documented to have recorded changes in monsoonal circulation over orbital to tectonic timescales. This site serves as an anchor for establishing the extent to which the north to south (19°N to 5°N) salinity gradient changes over time.

The Mio-Pliocene Pisco Formation (Peru) is a world-famous marine vertebrate Lagerstatte. Several fossil specimens are wrapped up in dolomitic nodules. Some others lie in the sediment displaying dolomite only in bone cavities (e.g., mesorostral canal and endocranium). With the aim to understand whether the precipitation of the dolomitic nodules influenced the formation of the Lagerstatte, we collected field data on a high number of fossil vertebrates and conducted petrographic and mineralogical analyses on samples representative of the variable development of concretions. Our results revealed positive relationships between size, completeness and articulation of skeletons and the presence of an external nodule. Clear evidence of chemoautotrophic communities that thrived on the carcasses is scarce. Microborings are often found in the cortical bone tissues together with iron oxides; the former are left by microorganisms feeding on the carcass, the latter are traces of former Fe sulphides, a product of organic matter degradation. We suggest that an early burial of the skeletons was a determinant factor in the development of dolomite concretions, since it allowed methanogenesis and anaerobic sulphate reduction exploiting the lipids in the bones and the organic matter dispersed in the sediments. Dolomite precipitation was driven by the same bacteria operating during the suphophilic stage of whale-fall communities. Textural observations imply that dolomite precipitated shortly after the burial of carcasses. The increase of alkalinity generated by sulphate reduction and methanogenesis caused a rapid precipitation of the dolomite within skeletal cavities and prevented the degradation of the bones and diagenetic compression of skeletons; the nodules themselves prevented erosion of fossils after exhumation. Therefore, nodule formation had a crucial role in the development of the Pisco Lagerstatte.