Elisa Malinverno

Stratified prokaryote network in the oxic-anoxic transition of a deep-sea halocline

The chemical composition of the Bannock basin has been studied in some detail. We recently showed that unusual microbial populations, including a new division of Archaea (MSBL1), inhabit the NaCl-rich hypersaline brine. High salinities tend to reduce biodiversity, but when brines come into contact with fresher water the natural haloclines formed frequently contain gradients of other chemicals, including permutations of electron donors and acceptors, that may enhance microbial diversity, activity and biogeochemical cycling. Here we report a 2.5-m-thick chemocline with a steep NaCl gradient at 3.3 km within the water column betweeen Bannock anoxic hypersaline brine and overlying sea water. The chemocline supports some of the most biomass-rich and active microbial communities in the deep sea, dominated by Bacteria rather than Archaea, and including four major new divisions of Bacteria. Significantly higher metabolic activities were measured in the chemocline than in the overlying sea water and underlying brine; functional analyses indicate that a range of biological processes is likely to occur in the chemocline. Many prokaryotic taxa, including the phylogenetically new groups, were confined to defined salinities, and collectively formed a diverse, sharply stratified, deep-sea ecosystem with sufficient biomass to potentially contribute to organic geological deposits.

Sulfur cycling and methanogenesis primarily drive microbial colonization of the highly sulfidic Urania deep hypersaline basin

Urania basin in the deep Mediterranean Sea houses a lake that is >100 m deep, devoid of oxygen, 6 times more saline than seawater, and has very high levels of methane and particularly sulfide (up to 16 mM), making it among the most sulfidic water bodies on Earth. Along the depth profile there are 2 chemoclines, a steep one with the overlying oxic seawater, and another between anoxic brines of different density, where gradients of salinity, electron donors and acceptors occur. To identify and differentiate the microbes and processes contributing to the turnover of organic matter and sulfide along the water column, these chemoclines were sampled at a high resolution. Bacterial cell numbers increased up to a hundredfold in the chemoclines as a consequence of elevated nutrient availability, with higher numbers in the upper interface where redox gradient was steeper. Bacterial and archaeal communities, analyzed by DNA fingerprinting, 16S rRNA gene libraries, activity measurements, and cultivation, were highly stratified and metabolically more active along the chemoclines compared with seawater or the uniformly hypersaline brines. Detailed analysis of 16S rRNA gene sequences revealed that in both chemoclines δ- and ε-Proteobacteria, predominantly sulfate reducers and sulfur oxidizers, respectively, were the dominant bacteria. In the deepest layers of the basin MSBL1, putatively responsible for methanogenesis, dominated among archaea. The data suggest that the complex microbial community is adapted to the basins extreme chemistry, and the elevated biomass is driven largely by sulfur cycling and methanogenesis.

Distribution of fossil marine vertebrates in Cerro Colorado, the type locality of the giant raptorial sperm whale Livyatan melvillei (Miocene, Pisco Formation, Peru)

Hundreds of fossil marine vertebrates cropping out at Cerro Colorado (Pisco Basin, Peru) are identified and reported on a 1:6500 scale geological map and in a joined stratigraphic section. All the fossils are from the lower strata of the Pisco Formation, dated in this area to the late middle or early late Miocene. They are particularly concentrated (88%) in the stratigraphic interval from 40 to 75 m above the unconformity with the underlying Chilcatay Formation. The impressive fossil assemblage includes more than 300 specimens preserved as bone elements belonging mostly to cetaceans (81%), represented by mysticetes (cetotheriids and balaenopteroids) and odontocetes (kentriodontid-like delphinidans, pontoporiids, ziphiids, and physeteroids, including the giant raptorial sperm whale Livyatan melvillei). Seals, crocodiles, sea turtles, seabirds, bony fish, and sharks are also reported. Isolated large teeth of Carcharocles and Cosmopolitodus are common throughout the investigated stratigraphical interval, whereas other shark teeth, mostly of carcharinids, are concentrated in one sandy interval. This work represents a first detailed census of the extraordinary paleontological heritage of the Pisco Basin and the basis for future taphonomic, paleoecological, and systematic studies, as well as a much needed conservation effort for this extremely rich paleontological site.

Stratigraphic framework of the late Miocene to Pliocene Pisco Formation at Cerro Colorado (Ica Desert, Peru)

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.

Fossil marine vertebrates of Cerro Los Quesos: Distribution of cetaceans, seals, crocodiles, seabirds, sharks, and bony fish in a late Miocene locality of the Pisco Basin, Peru

ABSTRACT One-hundred and ninety-two fossil marine vertebrate specimens, preserved as bone elements cropping out at Cerro Los Quesos (Pisco Basin, Peru), are identified and reported on a 1:4,000 scale geological map and in the corresponding stratigraphic section. All the fossils originate from the Pisco Formation, which is dated in this area to the late Miocene (from 7.55 Ma to ≥6.71 Ma, based on 40Ar/39Ar analyses of three volcanic ash layers along the section). Specimens are particularly concentrated near the top of the two main hills, where the geologically youngest portion of the examined section crops out. The impressive fossil assemblage includes cetaceans (91.6%), represented by mysticetes (balaenopteroids and cetotheriids) and odontocetes (phocoenids, physeteroids, and ziphiids, including the holotype of Nazcacetus urbinai). Seals, a crocodile, a seabird, bony fish, and sharks are also reported. Isolated large teeth of Carcharocles and Cosmopolitodus are common and, in several instances, associated to mysticete skeletons. Together with a similar work recently published for the other late Miocene locality of Cerro Colorado, this work represents a case study for the detailed inventory of the extraordinary paleontological heritage of the Pisco Basin. As such, it constitutes the basis for future taphonomic, paleoecological, and systematic studies, as well as for a much-needed conservation effort.

Stratigraphic framework of the late Miocene Pisco Formation at Cerro Los Quesos (Ica Desert, Peru)

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.

Exploring preserved fossil dinoflagellate and haptophyte DNA signatures to infer ecological and environmental changes during deposition of sapropel S1 in the eastern Mediterranean

phylotypes, which were previously only detected in anoxic Black Sea sediments. In the same section of the core, the most abundant haptophyte sequence showed highest similarity with uncultivated haptophytes that were previously shown to grow mixotrophically as predators of picocyanobacteria, an adaptation that promotes growth in oligotrophic marine waters. Sequences with highest similarities to clones found in marine surface waters predominated in the S1 after ∼8 14 C kyr B.P. We discuss whether the shifts in haptophyte and dinoflagellate populations inferred from the preserved DNA reflect known environmental changes that occurred during the formation of sapropel S1.

SEQUENCE STRATIGRAPHY AND PALEONTOLOGY OF THE UPPER MIOCENE PISCO FORMATION ALONG THE WESTERN SIDE OF THE LOWER ICA VALLEY (ICA DESERT, PERU)

The sequence stratigraphic framework and a summary of the fossil fauna of the upper Miocene portion of the Pisco Formation exposed along the western side of the Ica River (southern Peru) is presented through a new geological map encompassing an area of about 200 km 2 and detailed chronostratigraphic analyses. Extensive field mapping and sedimentological study of outcrop sections have shown that the Pisco Formation is a cyclical sediment unit composed of at least three fining-upward, unconformity-bounded depositional sequences, designated P0, P1, and P2 from oldest to youngest. In the study area, these sequences progressively onlap a composite basal unconformity from southwest to northeast. Integration of biostratigraphic and tephrochronologic age determinations constrains the ages of the three Pisco sequences within the study area. Based on the age of surrounding sediments, a conservative estimate of the age of P0 suggests deposition of these strata between 17.99 ± 0.10 Ma and 9.00 ± 0.02 Ma, whereas diatom biostratigraphy and calculated 40 Ar/ 39 Ar ages converge to indicate that strata of the P1 sequence were deposited sometime between 9.5 Ma and 8.9 Ma and that those of the P2 sequence are younger than 8.5 Ma and older than 6.71 ± 0.02 Ma. Our survey for both vertebrate and macro-invertebrate remains in the three sequences confirms the outstanding paleontological value of the Pisco Formation and contributes to depict regional faunal shifts in the fossil assemblage.

A new odontocete (toothed cetacean) from the Early Miocene of Peru expands the morphological disparity of extinct heterodont dolphins

A key step in the evolutionary history of Odontoceti (echolocating toothed cetaceans) is the transition from the ancestral heterodont condition – characterized by the presence of double-rooted cheek teeth bearing accessory denticles – to the homodont dentition displayed by most extant odontocete species. During the last few decades, new finds and the reassessment of specimens in collections revealed an increased morphological disparity amongst the Oligo–Miocene heterodont odontocetes. Based on a partly articulated skeleton from late Early Miocene (Burdigalian, 18.8–18.0 Ma) beds of the Chilcatay Formation (Pisco Basin, Peru), we describe a new genus and species of heterodont odontocete, Inticetus vertizi, in the new family Inticetidae. This large dolphin is characterized by, amongst other things, a long and robust rostrum bearing at least 18 teeth per quadrant; the absence of procumbent anterior teeth; many large, broad-based accessory denticles in double-rooted posterior cheek teeth; a reduced ornament of dental crowns; the styliform process of the jugal being markedly robust; a large fovea epitubaria on the periotic, with a correspondingly voluminous accessory ossicle of the tympanic bulla; and a shortened tuberculum of the malleus. Phylogenetic analyses (with and without molecular constraint; with and without down-weighting of homoplastic characters) yielded contrasting results, with Inticetus falling either as a stem Odontoceti or as an early branching member of a large Platanistoidea clade. With its large size, robust rostrum and unusual dental morphology, and the absence of conspicuous tooth wear, Inticetus increases the morphological and ecological disparity of Late Oligocene–Early Miocene heterodont odontocetes. Finally, this new taxon calls for caution when attempting to identify isolated cetacean cheek teeth, even at the suborder level. http://zoobank.org/urn:lsid:zoobank.org:pub:5B306B49-EB1B-42F9-B755-B0B05B4F938F

Facies analysis, stratigraphy and marine vertebrate assemblage of the lower Miocene Chilcatay Formation at Ullujaya (Pisco basin, Peru)

ABSTRACT 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.