Developing a radiometrically-dated chronologic sequence for Neogene biotic change in Australia, from the Riversleigh World Heritage Area of Queensland
Authors:
Woodhead et al
Abstract:
Radiometric U-Pb ages are presented for the Riversleigh World Heritage fossil mammal site in northwestern Queensland, Australia. The ages are determined on speleothems which are generally found in intimate or well-documented association with fossil remains and thus can be assumed to record the age of the latter with a high degree of confidence. The new ages encompass the early (18.2-16.5 Ma) and middle Miocene (15.1-13.5 Ma) deposits at Riversleigh in addition to the younger Rackham’s Roost site which returns early Pleistocene ages. Together, these provide a robust chronological framework for the interpretation of Neogene biotic change in Australia that has, until now, relied almost entirely upon biocorrelative techniques. In particular they permit closer investigation of links between other regions/faunas and allow comparison with other records of climatic and environmental change. This is the first documented example of a methodology that has widespread potential application across many continents and throughout much of Earth history.
Persistence and Change in Community Composition of Reef Corals through Present, Past, and Future Climates
Authors:
Edmunds et al
Abstract:
The reduction in coral cover on many contemporary tropical reefs suggests a different set of coral community assemblages will dominate future reefs. To evaluate the capacity of reef corals to persist over various time scales, we examined coral community dynamics in contemporary, fossil, and simulated future coral reef ecosystems. Based on studies between 1987 and 2012 at two locations in the Caribbean, and between 1981 and 2013 at five locations in the Indo-Pacific, we show that many coral genera declined in abundance, some showed no change in abundance, and a few coral genera increased in abundance. Whether the abundance of a genus declined, increased, or was conserved, was independent of coral family. An analysis of fossil-reef communities in the Caribbean revealed changes in numerical dominance and relative abundances of coral genera, and demonstrated that neither dominance nor taxon was associated with persistence. As coral family was a poor predictor of performance on contemporary reefs, a trait-based, dynamic, multi-patch model was developed to explore the phenotypic basis of ecological performance in a warmer future. Sensitivity analyses revealed that upon exposure to thermal stress, thermal tolerance, growth rate, and longevity were the most important predictors of coral persistence. Together, our results underscore the high variation in the rates and direction of change in coral abundances on contemporary and fossil reefs. Given this variation, it remains possible that coral reefs will be populated by a subset of the present coral fauna in a future that is warmer than the recent past.
Stratigraphic significance of rapid faunal change across the Cenomanian–Turonian boundary in the Eastern Desert, Egypt
Author:
Nagm
Abstract:
A significant and rapid faunal change across the Cenomanian–Turonian boundary in the Eastern Desert of Egypt has been recognized by reconstructing the stratigraphic ranges of macroinvertebrates within the upper Cenomanian–lower Turonian Galala and Abu Qada formations. The faunal change initiated with a considerable loss of taxa during the late Cenomanian at the top of the Neolobites vibrayeanus ammonite zone, coinciding with sequence boundary SB Ce 5, ∼400 ka before the Cenomanian–Turonian boundary (93.9 Ma). Only 10% of the taxa that existed during the late Cenomanian have been recorded from lower Turonian strata. The changes in the macroinvertebrate faunas continued across the Cenomanian–Turonian boundary and new faunal associations evolved after the earliest Turonian Vascoceras proprium ammonite zone of (∼200 ka after the Cenomanian–Turonian boundary). Therefore, the crisis that caused this faunal change around the Cenomanian–Turonian boundary over approximately 600 ka. The timing of the macrofaunal change recognized in the study area completely overlaps with the well-known Oceanic Anoxic Event (OAE) 2 and most probably it is one of the effects of the major environmental perturbations (critical warming, high atmospheric CO2 concentration, and ocean water acidification) associated with this event. In addition, the sequence-stratigraphic analysis shows strong correlation exists between pattern of first and last occurrences of macroinvertebrate faunas and sea-level changes. Therefore, the oceanographic changes (rapid sea-level rise) may have also contributed to the Cenomanian–Turonian faunal change in the study area.
The site of Shuitangba (Yunnan, China) preserves a unique, terminal Miocene fauna
Authors:
Jablonski et al
Abstract:
The late Miocene was an important interval in mammalian evolution because of the concatenated tectonic, climatic, and environmental changes that led to increased seasonality and heterogeneity of most terrestrial ecosystems (Ruddiman and Kutzbach, 1989; An et al., 2001; Guo et al., 2002). These phenomena had profound influences on mammalian habitats and on the anatomies and fates of many mammalian lineages (Fortelius et al., 2002; Jablonski, 2005). In Eurasia, this period was marked by the decline in diversity and abundance of obligate forest dwellers and the rise of species able to survive in more open and seasonal habitats. Southeastern Asia did not escape the effects of changing global climatic conditions of the Late Neogene, but appears to have, in part, played a role as a refugium for some mammals. The few known fossil sites of southern China are beginning to reveal the architecture of faunal change in the region. The terminal Miocene site of Shuitangba, Yunnan Province, China, provides a snapshot of this critical transition.
Quantifying the process and abruptness of the end-Permian mass extinction
Authors:
Wang et al
Abstract:
Studies of the end-Permian mass extinction have suggested a variety of patterns from a single catastrophic event to multiple phases. But most of these analyses have been based on fossil distributions from single localities. Although single sections may simplify the interpretation of species diversity, they are susceptible to bias from stratigraphic incompleteness and facies control of preservation. Here we use a data set of 1450 species from 18 fossiliferous sections in different paleoenvironmental settings across South China and the northern peri-Gondwanan region, and integrate it with high-precision geochronologic data to evaluate the rapidity of the largest Phanerozoic mass extinction. To reduce the Signor-Lipps effect, we applied constrained optimization (CONOP) to search for an optimal sequence of first and last occurrence datums for all species and generate a composite biodiversity pattern based on multiple sections. This analysis indicates that an abrupt extinction of 62% of species took place within 200 Kyr. The onset of the sudden extinction is around 252.3 Ma, just below Bed 25 at the Meishan section. Taxon turnover and diversification rates suggest a deterioration of the living conditions nearly 1.2 Myr before the sudden extinction. The magnitude of the extinction was such that there was no immediate biotic recovery. Prior suggestions of highly variable, multi-phased extinction patterns reflect the impact of the Signor-Lipps effect and facies-dependent occurrences, and are not supported following appropriate statistical treatment of this larger data set.
High-precision U–Pb geochronology and a new chronostratigraphy for the Cañadón Asfalto Basin, Chubut, central Patagonia: Implications for terrestrial faunal and floral evolution in Jurassic
Authors:
1. Rubén Cúneo (a, e)
2. Jahandar Ramezani (b)
3. Roberto Scasso (c, e)
4. Diego Pol (a, e)
5. Ignacio Escapa (a, e)
6. Ana M. Zavattieri (d, e)
7. Samuel A. Bowring (b)
Affiliations:
a. Museo Paleontológico Egidio Feruglio, Ave. Fontana 140, 9100 Trelew, Argentina
b. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
c. Departamento de Ciencias Geológicas, Universidad de Buenos Aires, Ciudad Universitaria Pab. II, 1428 Buenos Aires, Argentina
d. Laboratorio de Paleopalinología, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), Casilla de Correo 131, 5500 Mendoza, Argentina
e. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
Abstract:
The fluvial, lacustrine and tuffaceous sedimentary succession of the Cañadón Asfalto continental basin exposed in the Argentinean Chubut Province of central Patagonia preserves an extraordinary record of Jurassic fauna and flora that marks key events in the evolution of Dinosauria, early mammals and major South American plant groups. However, basin-wide correlation of the fossiliferous units is complicated by fault displacements, unconformities and repetitive lithofacies. New U–Pb analyses of zircon (CA-TIMS method) from five primary tuff beds interstratified with the lacustrine strata establish a new chronostratigraphic framework for the sedimentary and volcanic units of Cañadón Asfalto Basin, constraining ca. 33 m.y. of depositional history and biotic evolution that spans nearly all three epochs of the Jurassic. Five major vertebrate- and plant-rich stratigraphic intervals have been identified, and are being actively investigated, that range in age from Pliensbachian to Kimmeridgian (or younger). Our combined biostratigraphic and high-precision geochronologic results indicate that the major faunal turnover of the sauropodomorph dinosaurs which led to the rise of the eusauropods took place in the Early Jurassic, earlier than previously recognized. Similarly, the first successful radiation of the ornithischian dinosaurs (heterodontosaurids), as well as the evolutionary diversifications of the araucarian conifers and the osmundaceous ferns, all occurred before the end of the Early Jurassic. The diverse palynofloral assemblage of the Cañadón Calcáreo Formation that was once considered to be early Cretaceous in age, is now entirely constrained to the Late Jurassic.
