Classifying vertebrate assemblages preserved in Quaternary tank deposits: Implications for vertebrate taphonomy and paleoecology (original) (raw)
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Palaios, 2009
Biostratinomic and bone-diagenesis parameters are used to evaluate the effects of abiotic and biotic processes on the final composition of two late Eocene vertebrate assemblages preserved in a swampy circum-lake environment from the Zambrana site (Basque-Cantabrian Region, northern Iberian Peninsula). No significant transport or bone sorting by fluvial action is observed, and complete and fragmentary bones in the assemblages (Z4 and Z6 beds) show the same biostratinomic features. The attritional bone accumulation in both excavated beds was caused mostly by biotic factors related to routine ecological deaths of population members, probably with some input from predators on the most vulnerable ungulate individuals (autochthonous), although a weak input of small remains by superficial water currents from nearby areas (parautochthonous) cannot be rejected. The vegetation and wet conditions of the swampy environment, together with possible predator and scavenger activity, could have caused the disarticulation and dispersion of some vertebrate remains, mainly those of ungulates. The bones were buried relatively quickly in the phreatic zone under reducing conditions and suffered considerable crushing and fragmentation because of lithostratigraphic compaction. Mineralogic similarities between sedimentary fillings in the fossils and the host sediment, as well as the homogeneous rare earth element (REE) trends of the fossils, are indicative of a uniform and unique diagenetic history and the absence of reworked elements. The fossil bone mineral is well-crystallized francolite (carbonate fluorapatite). The REE enrichment of bones and their calcite and pyrite crusts and fillings were formed during early diagenetic phases. The black coloration of the bones may be explained by their high hydrocarbon (n-alkane components) contents.
Curimatãs Paleontological Site (CPS) preserved one of the most iconic fossil assemblages of Late Pleistocene vertebrates of Brazil. Fossils were collected in a tank deposit,a singular type of Quaternary vertebrate-bearing deposit of South America. In this work, a detailed taphonomic study of the tank assemblage of CPS is presented. This analysis also provides taphonomic and paleoecological data obtained through the application of common multivariate techniques and provides estimates of time-and spatial resolution for tank deposits. The results show that, although the CPS assemblage has experienced an array of taphonomic processes, the long-distance transport was the main process controlling the taphonomic pathway of the thanatocoenosis during the biostratinomic phase, and was responsible for the co-occurrence of other processes, such as abrasion, fragmentation and bioclastic sorting. The origin of the taphonomic modes of vertebrates in the tank deposit of CPS may have been controlled by three major taphonomic phenomena: (i) a taphonomic bias towards the large-bodied size; (ii) long time span of transportation towards the final burial environment; and (iii) some degree of reworking. Furthermore, the analysis of these taphonomic modes supports a previous hypothesis: although taphonomic biases affect the origin of tank assemblages, paleoecological patterns can be preserved with considerable fidelity. The time resolution in tank accumulations is of the order of 10 -3 to 10 4 years and their spatial resolution seems to be from local to regional.
Conulariid taphonomy as a tool in paleoenvironmental analysis
Revista Brasileira de Geociências, 2000
In the Devonian sequence of the Parana Basin conulariids (Cnidaria) are conspicuous elements in sediments of the basal portion of the Ponta Grossa Formation (Lochkovian-Frasnian). Their preservation seems to be associated to unusual preservational circumstances. In fact, the fossiliferous sediments rich in conulariids were deposited under platformal or shallow water conditions in a muddy epeiric sea, punctuated by storm events. The exam of 28 oriented blocks (-5400 cm3) of siltstone or mudstones, including 29 specimens of conulariids, indicates that they are preserved according to the following preservational modes: Vertically oriented conulariids (1) with aperture-up, 90°-70° to the bedding plane, in massive or less bioturbated siltstones, inclined (2) or horizontally oriented conulariids (3) in a completely bioturbated siltstone or mudstones, rich in Zoophycos. Vertically oriented specimens are interpreted as autochthonous elements, indicating the abrupt burial of living invertebrates. Thus, an attached epifaunal mode of life is inferred for these specimens. Horizontally oriented specimens correspond to disrupted elements, particularly by the biological activity within the substrate, during and after the rapid sediment deposition, associated to storm events. Specimens vertically preserved directly adjacent to horizontally oriented conulariids in zones of intense sediment bioturbation support this idea. In this case, even the horizontally oriented specimens are reliable indicators of changes in siliciclastic accumulation rates, in tempestite proximality, and postmortem alteration by biological agents, specially when the inorganic primary sedimentary structures are lacking or were completely destroyed or obliterated by the biological activity in the substrate. The sediments rich in conulariids are interpreted here as tempestite beds.
New data towards the development of a comprehensive taphonomic framework for the Cleveland-Lloyd Dinosaur Quarry, 2016
The Cleveland-Lloyd Dinosaur Quarry (CLDQ) is the densest deposit of Jurassic theropod dinosaurs discovered to date. Unlike typical Jurassic bone deposits, it is dominated by the presence of Allosaurus fragilis. Since excavation began in the 1920’s numerous hypotheses have been put forward to explain the taphonomy of CLDQ, including a predator trap, a drought assemblage, and a poison spring. In an effort to reconcile the various interpretations of the quarry and reach a consensus on the depositional history of CLDQ, new data is required to develop a robust taphonomic framework congruent with all available data. Here we present two new data sets which aid in the development of such a robust taphonomic framework for CLDQ. First, x- ray fluorescence of CLDQ sediments indicate elevated barite and sulfide minerals relative to other sediments from the Morrison Formation, suggesting an ephemeral environment dominated by periods of hypereutrophic conditions during bone accumulation. Second, the degree of weathering and hydraulic equivalency of small bone fragments dispersed throughout the matrix were analyzed from CLDQ. Results of these analyses suggest that bone fragments are autochthonous or parautochthonous and are derived from bones deposited in the assemblage. The variability in abrasion exhibited by the fragments is most parsimoniously explained by periodic reworking and redeposition during seasonal fluctuations throughout the duration of the quarry assemblage. Collectively, these data support some previous interpretations that the CLDQ represents an attritional assemblage in a poorly-drained overbank deposit where vertebrate remains were introduced post-mortem to an ephemeral pond during flood conditions. Furthermore, elevated heavy metals and rare earth elements detected at the quarry are likely a diagenetic signal, potentially produced in part from an abundance of vertebrate remains, and not the primary driver for the accumulation of carcasses. These new data help to explain the specific depositional environment of the quarry, and represent a significant step in understanding the taphonomy of the bone bed and late Jurassic paleoecology.
Origin of bonebeds in Quaternary tank deposits
Tank deposits are an exceptional type of fossiliferous deposit and bear a remarkably fossil record of the Pleistocene megafauna of South America, particularly of Brazil. The taphonomy of vertebrate remains preserved in this type of environmental context was clearly driven by climate, similarly to most of the Quaternary continental fossil record. The formation of the vertebrates fossil record in tank deposits was influenced by the climate seasonality typical of arid climate. The taphonomic history of most tank deposits is a consequence of this seasonality and, as a result, the paleoecological data preserved in their fossil assemblages is reliable with respect to paleobiological and paleoenvironmental settings of the Quaternary ecosystems of the Brazilian Intertropical Region (BIR). Other tank deposits experienced an unusual taphonomic history that, besides climate, was affected by recurrent events of reworking produced by the depositional agents dominant in the surrounding alluvial plains. The conclusions obtained here concerning the main taphonomic settings and formative processes that characterize fossil vertebrate assemblages of tank deposits will help further studies aimed to recover information on the paleoecology of Quaternary fauna collected in such deposits by allowing a better understanding of their time and spatial resolutions and other potential biases.
The importance of taphonomic studies on biochronology: examples from the european middle Jurassic
1997
Biochronology deals with the organisifis of te past and is used to subdivide geological time on the basis of biological evolution that is a continuous and irreversible process. Given the importance of biochronological scales, one cannot just assume the contemporaneity offossils and enclosing sediments: the stratigraphic record and the paleontological one do not necessarily coincide and must be considered separately. In the same way, also the chronological relationships among fossils cannot be simply derived from Iheir relative stratigraphical position: the first occurenee of two taxa in a bed, tbr example, may not correspond to a real contemporaneous appearanee. The possibility exists, in fact, of reelaboration i.e. of exhumation after a tirst pbase of burial. Reelaborared fossils are, by definition, non contemporaneous with the host sediment and the other fossils not affected by reelaboration present in tbe same bed. Therefore tapbonomic analys¡s is an absolute prerequisite to biochronological reconstructions. Two examples of ammonite-bearing calcareotis successions from the Middle Jurassic of Northern Europe (Poiton, France and IDorset, England) are discussed. In the first case an increase of information results from taphonomie studies: a correct chronostratigraphy may be reconstructed, [he Cuadernos de Geología Ibérica, n. The importance of taphonomiú studies oit biochronology 155 como referencia para la identificación de límites y duraciones de los intervalos biocronológicos.