86 research outputs found
"Excess Ar" by laboratory alteration of biotite
Many biotite phenocrysts from marine tephra layers have substoichiometric potassium concentrations and alkali occupation << 2.0 atoms per formula unit. Diagenetic alteration is an expected effect of exposure of fresh magmatic minerals to interstitial water and brine intrusions after the deposition and burial of sediments. To test the effect of diagenetic alteration on potassium-argon ages, we irradiated and step heated untreated Fish Canyon biotite (t = 28.2 Ma) and several aliquots leached to various extents in strong and weak acids. Laboratory alteration caused loss of K, age spectrum discordance, high step ages and total gas ages, Ar release at lower furnace temperature, higher Cl/K and Ca/K, and a slight decrease in 36Ar concentration. Potassium loss was always higher than 40Ar* loss. Electron microprobe element maps document that acids preferentially penetrate in phyllosilicate interlayers, removing K (and Na). Because Ar* is removed to a lesser extent than K, we propose that natural 40K decay partly implants radiogenic Ar* into the tetrahedral-octahedral-tetrahedral (T-O-T) phyllosilicate layer, where Ar is shielded from interlayer leaching. The recoiled 39Ar, which was produced by irradiation after the leaching, also partitioned between T-O-T and the interlayer; age spectrum discordance was probably enhanced by the heterogeneous partition of 39Ar and 40Ar* in leached samples
LOWER PLIOCENE BARNACLE FACIES OF WESTERN LIGURIA (NW ITALY): A PEEK INTO A WARM PAST AND A GLIMPSE OF OUR INCOMING FUTURE
The lower Pliocene deposits of Pairola (Liguria, Italy) display the otherwise rare occurrence of rock-forming amounts of barnacles (mostly belonging to the extinct Euromediterranean species Concavus concavus). Three main facies are recognised in the investigated succession: a barnacle-dominated facies, which formed along a shallow (<15 m deep) nearshore environment, a foraminifera-dominated facies from relatively deeper waters (40-100 m), and an intermediate facies forming at the boundary of the other two. These facies and their relationships suggest deposition in a flooded valley – a kind of setting that was common in the Mediterranean after the Messinian Salinity Crisis. Differing from other rias, the Pairola basin was exposed to strong waves, resulting in conditions favourable to barnacles. Sedimentological and stratigraphic observations indicate that the Pairola succession formed within a timespan covering both cold and warm phases. This is relevant because the sub-tropical foraminifer Amphistegina is ubiquitous throughout the succession. Amphistegina occurs in the Pliocene and lower Pleistocene (Gelasian) of Northern Italy, but not in the remainder of the Pleistocene, not even its warm portions. This genus is currently recolonizing the Mediterranean and is projected to reach the northern coast of the basin soon, foretelling that Anthropocene temperatures are going to overcome those of the late Pleistocene warm periods and reach those of the Pliocene
A new large squalodelphinid (Cetacea, Odontoceti) from Peru sheds light on the early miocene platanistoid disparity and ecology
The South Asian river dolphin (Platanista gangetica) is the only extant survivor of the large clade Platanistoidea, having a well-diversified fossil record from the Late Oligocene to the Middle Miocene. Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay Fm; southern coast of Peru), we report here a new squalodelphinid genus and species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled near the fossil, yielded the 40Ar/39Ar age of 18.78±0.08Ma (Burdigalian, EarlyMiocene). The phylogenetic analysis places Macrosqualodelphis as the earliest branching squalodelphinid. Combined with several cranial and dental features, the large body size (estimated body length of 3.5 m) of this odontocete suggests that it consumed larger prey than the other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid further demonstrates the peculiar local diversity of the family along the southeastern Pacific coast, possibly related to their partition into different dietary niches. At a wider geographical scale, the morphological and ecological diversity of squalodelphinids confirms the major role played by platanistoids during the EarlyMiocene radiation of crown odontocetes
Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
The upper Neogene Pisco Formation of Peru is known worldwide as one of the most significant Cenozoic
marine vertebrate Konservatt-Lagerstätten, even featuring cetacean specimens that retain remains of soft tissues or
stomach contents. Previous works showed that biomediated precipitation of dolomite concretions around large-sized
decaying carcasses was one of the most relevant processes responsible for exceptional fossil preservation. In turn, little is
known about the modes of fossilization of well-preserved small-sized vertebrates, which are rather common in the Pisco
Formation, but mostly do not exhibit dolomite concretions. We report on a cetacean specimen, identified as belonging
to the extinct short-snouted, small dolphin species Brachydelphis mazeasi (Pontoporiidae), preserved within a late
Miocene sandy deposit at the site of Pampa Corre Viento. This specimen consists of a moderately disarticulated partial
skeleton exhibiting well-mineralized bones; it is not enclosed within a dolomite concretion, being however delimited
by an evident dark boundary in the host sediment. Scanning electron microscopy and microanalytical investigations
identify Mn-oxides and apatite as early diagenetic minerals around the skeleton. We argue that a rapid burial of the
specimen was pivotal for the preservation of the bones, and allowed the early establishment of anoxic processes for
degradation of organic matter. Coupled with availability of P in porewater, the reducing conditions and the lowered
pH allowed precipitation of Ca-phosphate while increasing Mn solubility close to the pontoporiid carcass. Mn-oxides
precipitated at the redox boundary, the latter defining the outer edge of the volume of sediment affected by altered
chemical conditions due to the decaying processes. The permeability of the sediment and the small size of the carcass
were possible factors unfavorable to extensive sulfate reduction, thus preventing the formation of a dolomite concretion
and allowing bone phosphatization. This record emphasizes the role of conditions favorable to bone mineralization in
absence of an isolating carbonate concretion, in cases of high quality preservation of small-sized vertebrates observed
in the Pisco Formation. The observation of patterns in the distribution of diagenetic minerals in the sediment enclosing
vertebrate remains without, or with limited carbonate concretions provides insights into early taphonomic processes
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 48 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
Insights into the diagenetic environment of fossil marine vertebrates of the Pisco Formation (late Miocene, Peru) from mineralogical and Sr-isotope data
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 Cacarbonate
dissolution. The diagenetic chemical environment was, nevertheless, favorable to bone
preservation
VID22 counteracts G-quadruplex-induced genome instability
Genome instability is a condition characterized by the accumulation of genetic alterations and is a hallmark of cancer cells. To uncover new genes and cellular pathways affecting endogenous DNA damage and genome integrity, we exploited a Synthetic Genetic Array (SGA)-based screen in yeast. Among the positive genes, we identified VID22, reported to be involved in DNA double-strand break repair. vid22Δ cells exhibit increased levels of endogenous DNA damage, chronic DNA damage response activation and accumulate DNA aberrations in sequences displaying high probabilities of forming G-quadruplexes (G4-DNA). If not resolved, these DNA secondary structures can block the progression of both DNA and RNA polymerases and correlate with chromosome fragile sites. Vid22 binds to and protects DNA at G4-containing regions both in vitro and in vivo. Loss of VID22 causes an increase in gross chromosomal rearrangement (GCR) events dependent on G-quadruplex forming sequences. Moreover, the absence of Vid22 causes defects in the correct maintenance of G4-DNA rich elements, such as telomeres and mtDNA, and hypersensitivity to the G4-stabilizing ligand TMPyP4. We thus propose that Vid22 is directly involved in genome integrity maintenance as a novel regulator of G4 metabolism.Associazione Italiana per la Ricerca sul Cancro (AIRC) 15631, 21806MIUR PRIN 2015- 2015SJLMB9, PRIN 2017-2017KSZZJW, PRIN2017-2017Z55KCMinisterio de Economía y Competitividad BFU2016- 75058-PCanadian Institutes of Health Research FDN-15991
- …