查看更多>>摘要：Profound environmental changes punctuated the Early Jurassic period, as recorded by marked carbon and oxygen isotope anomalies and major biotic crises. The response of low-latitude regions of Northern Gondwana to such intense changes is not documented as well as that of other Tethys areas. We present new calcareous nannofossil assemblages from three sections located in NW Algeria, in the Sahara and Tlemcen Basins, respectively. New stable carbon and nitrogen isotope data are provided from the Tlemcen Basin to reconstruct local environmental conditions in the wider context of a Toarcian greenhouse climate. We first established a solid chemoand biostratigraphic framework by integrating stable carbon isotope data and calcareous nannofossil events. Calcareous nannofossil assemblages show common trends in the two basins, such as the occurrence in high proportions of the deep-dweller species Mitrolithus jansae, likely indicating stratification of the water column with a deep nutricline. This taxon dominated the assemblage during the negative carbon isotope excursion (CIE) interval, often used to delineate the base of the Toarcian anoxic event (T-OAE). Such a nannofossil record is unique in the Western Tethys domain, as M. jansae is known to drastically decrease in abundance during the TOAE until its disappearance in the aftermath of the event. The NW Algeria nannofossil record indicates prolonged thermal stratification of water-masses, finally triggering hyper-oligotrophy and low productivity in shallow waters during the Toarcian CIE. Such peculiar conditions are likely related to the combined effects of a warm and arid climate dominating along the northern Gondwana margin and the presence of a strong clockwise gyre over the epicontinental shelf, which brought warm equatorial waters from the Tethys Ocean to the NW Algeria shelf.
Gasca, Jose ManuelCastanera, DiegoBadenas, BeatrizAurell, Marcos...
13页
查看更多>>摘要：Dinosaur tracks have been identified in several Upper Jurassic-Lower Cretaceous sedimentary units across the Maestrazgo Basin in eastern Iberia, which are preserved in a variety of transitional and continental paleoenvironments. Here, we described the lower Barremian San Ben ' on tracksite with the first occurrence of clear dinosaur tracks in the El Castellar Formation within the Galve subbasin. This palustrine-lacustrine formation has yielded a rich osteological record although dinosaur tracks are notably scarce. The new footprints represent an uncommon case of dinosaur track preservation since the site has yielded several non contemporary tracks (part of different ichnoassemblages) preserved as carbonate casts at the base of a limestone bed forming a composite ichnofabric. The tracksite shows a complex history of sedimentation, track production and preservation linked to the lake level variations. The ornithopod tracks are identified to belong to the ornithopod ichnogenus Caririchnium, concretely to the ichnospecies C. magnificum. The studied tracks represent the oldest occurrence of this ichnotaxa in the Maestrazgo Basin and are coherent with other coeval (or almost coeval) occurrences in the Iberian Peninsula. The presence of C. magnificum in the El Castellar Formation fills a gap between the oldest (Tithonian-early Valanginian?) and younger (Barremian) occurrences of ornithopod tracks within the Maestrazgo Basin, being one of the most complete successions of ornithopod tracks in Europe. Interestingly, the underlaying formations have ichnoassemblages with Dinehichnus-like and Iguanodontipus-like tracks, whereas Caririchnium is mainly found in El Castellar Formation and other Barremian units. These changes in the ichnoassemblages reflect the ornithopod faunal changes shown by osteological data in the Iberian Peninsula recording a Late Jurassic-earliest Cretaceous stage dominated by basal iguanodontians followed by an Early Cretaceous stage with abundance of more derived and large-sized iguanodontians.
查看更多>>摘要：In this study, two new climofunctions based on major elements are proposed from the study of 28 modern al-luvial soils with pedogenic carbonate from NE Spain. The first climofunction relates a base ratio (CaO, K2O) to the mean annual temperature (MAT), and the second one the clayeness ratio (Al2O3/SiO2) to the mean annual precipitation (MAP). In both climofunctions, the use of the parent material ratio as normalizer gave the best results, taking into account the natural variability of alluvial deposits. Application of these climofunctions to 86 paleosols from Oligo-Miocene alluvial successions in southern France and central Spain was performed, and combined with morphological functions previously proposed, with the aim to build detailed paleoclimatic data for this key period of climate history. This work provides a high frequency record (range of 10s to 100 s kyr) of paleoclimate fluctuations, with estimated MAP from both methods very comparable (mean similar to 550 mm/yr). Estimated MAT and MARP (mean annual range of precipitations) mainly exhibit the same trends: 1) high values followed by a rapid decrease during the early Aquitanian (from 18.8 to 13.5 degrees C; from 80 to 20 mm), 2) a warming trend towards the middle Aquitanian (up to 16.6 degrees C, 90 mm), 3) a cooling (down to 13.4 degrees C, 40 mm) during the late Aquitanian - early Burdigalian. Comparisons with paleoclimate data from paleontological remains indicate similar MAT and two times lower MAP estimated from paleosols. However, consistency between estimated MAP from this study to previous paleopedological investigations in NE Spain suggests a regional climate pattern (southern France and central Spain) precursor of the Mediterranean conditions that developed during middle Neogene whereas humid conditions prevailed in the western coastal basins of Europe. Periods of large amplitude fluctuations in MARP and MAT are interpreted as reflecting the interrelation between the lower Miocene climate instability (Mi1, Mi1a events) and continental climate.
Mantilla, Gregory P. WilsonSamant, BandanaMohabey, Dhananjay M.Dhobale, Anup...
28页
查看更多>>摘要：The first Cretaceous mammals described from India were recovered from the Naskal locality, on the southeastern edge of the Deccan Traps Volcanic Province (DTVP), where it is preserved between two basalt flows. Because the DTVP eruptions spanned the Cretaceous-Paleogene boundary (KPB), it is often unknown whether trap-associated fossil sites are latest Cretaceous (Maastrichtian) or early Paleocene in age. The Naskal locality accounts for nearly half of published mammal records from DTVP-associated sediments as well as a host of other vertebrate microfossils. Its age takes on singular importance in the context of mammalian evolution in India and the effects of the end-Cretaceous mass extinction and subsequent evolutionary radiation of placentals. Here we describe two new mammal species, Indoclemensia naskalensis gen. et sp. nov. and I. magnus sp. nov., from Naskal and present evidence from Ar-40/Ar-39 geochronology, magnetostratigraphy, and chemostratigraphy of the over- and underlying basalt flows to refine the age of the Naskal locality and nearby Rangapur locality. In conjunction with palynostratigraphy and vertebrate biostratigraphy, these sites can be confidently restricted to a < 100 kyr interval spanning the KPB. The most probable Ar-40/Ar-39 age is latest Cretaceous (66.136-66.056 Ma), but an earliest Paleogene age cannot be ruled out. We explore the implications of this age assignment for Deccan chemostratigraphy and Deccan volcanism, Cretaceous-Paleogene (K/Pg) mass extinction, Indian mammalian faunal evolution, and the timing of the origin of placental mammals.
查看更多>>摘要：The Aksu Basin, near Antalya, is an important area from many aspects of the geology as it hosts the youngest marine deposits of the western Taurides in southwestern Turkey. These marine deposits play an important role in revealing the response of the Eastern Mediterranean coasts to the post-Zanclean transgression following the Messinian Salinity Crisis and provide a chronological record for detailing the late Cenozoic regional tectonic and sedimentary features. Therefore, biostratigraphic reconstruction of this basin is essential to enhance our understanding of the late Cenozoic evolution of the region and the response of the Eastern Mediterranean realm to climatic shifts. Here, we present an updated foraminifer biostratigraphy of the topmost part of the Eskiko center dot y Formation in the Aksu Basin, a member of the Neogene Antalya basins. The studied Kargi section, located in the northern part of the Aksu Basin, contains planktic foraminifer species such as Neogloboquadrina pachyderma, Globigerinoides tenellus, Globigerinoides obliquus obliquus, and Globoturborotalita rubescens, and benthic foraminifers Bulimina marginata and Saidovina karreriana. These species are important bioevent markers in the Mediterranean Region. Accordingly, we update the stratigraphic range of the Eskiko center dot y Formation found in southwestern Turkey extending it to the Pleistocene falling in MPle1a Neogloboquadrina spp. sx Interval Subzone, more specifically between 1.54 and 1.36 Ma, which previously was considered to be of Pliocene age. This age interval is also in agreement with the previous studies that reported Calabrian-Chibanian aged marine deposits in the Mut Basin, southern Turkey.
查看更多>>摘要：Material properties of the diet of extant species is reflected by the microwear texture recorded on the enamel tooth surface, a signal that can be useful for estimating the diets of extinct species. Intra-specific dietary vari-ations can occur between sexes or depend on seasonal vegetation cover changes in their habitat. However, these factors cannot, or very rarely, be incorporated within a paleontological context, especially if the fossil record of an extinct species is mainly composed of isolated teeth. In order to assess the effects of these factors on microwear texture features, we studied 42 wild-caught specimens of two sympatric extant species of caviomorph rodents, Proechimys cuvieri and Proechimys guyannensis (Echimyidae, Octodontoidea) from the Cacao area located in French Guiana. Animals were captured between 2007 and 2012, in July and October, along a 1.5 km transect ranging from an old secondary forest to a disturbed forest. We applied a Scale Sensitive Fractal Analysis (SSFA) to the first upper molars of these specimens. Differences of dental microwear textures were found between sexes, between months, and between habitat, leading to one species overlapping in microwear texture parameter space with the other in some cases. The results obtained help identifying which factors might drive intra-population variations in dental microwear texture. Its understanding is indeed a key-step to better interpret the disper-sion observed within a given fossil sample set to obtain refined dietary reconstructions.
查看更多>>摘要：Multiproxy records of benthic foraminifera, pteropods, and total organic carbon (TOC) are reported from the late Pleistocene-Holocene interval of Core SK291/GC17, located off the coast of Goa (water depth 182 m), eastern Arabian Sea. Findings help unravel significant shifts in monsoon behavior and associated changes in the Oxygen Minimum Zone (OMZ). During the Younger Dryas (11900-11,600 cal yr BP) and ~ 11,600 to 9400 cal yr BP, the coast was closer to the studied core location because of the low eustatic sea level. This interval shows a higher abundance of benthic foraminifera preferring oxic bottom water condition over the suboxic group. At ~& nbsp;8000 cal yr BP, the decreased abundance of pteropod species Limacina trochiformis as well as lower values of TOC suggest the presence of a dry phase of the monsoon. The interval from ~& nbsp;7800 to 6400 cal yr BP was deposited under favorable bottom water conditions, as documented by a higher number of species (S), Information Function (Hs) and species richness of the benthic foraminiferal assemblage. The middle Holocene (~& nbsp; 6200 to 4200 cal yr BP) interval is marked by a significant increase in the number of epipelagic pteropods caused by higher surface productivity and by a decreasing abundance of mesopelagic pteropods caused by the shoaling and intensification of the OMZ. The oxic group decreased drastically while the dysoxic group of benthic foraminifera increased during this interval due to the intensified OMZ. After ~4200 cal yr BP, the oxic assemblages of benthic foraminifera and pteropods suggest low productivity coinciding with the 4.2 ka dry event observed in the Indian monsoon records. The intervals with oxic assemblages of benthic foraminifera align with Bond events. Further the oxic assemblages show high frequency cycles centered at 692, 440 and 358 yr driven by solar variability, while Uvigerina peregrina, a benthic foraminifer sensitive to OMZ variability, shows high frequency cycles of 403 and 745 yr.& nbsp;
Roberts, Eric M.Titus, Alan L.Beveridge, Tegan L.Eaton, Jeffrey G....
22页
查看更多>>摘要：The Western Interior of North America preserves one of the most complete successions of Upper Cretaceous marine and non-marine strata in the world; among these, the Cenomanian-Campanian units of the Kaiparowits Plateau in southern Utah are a critical archive of terrestrial environments and biotas. Here we present new radioisotopic ages for the Campanian Wahweap Formation, along with lithostratigraphic revision, to improve the geological context of its fossil biota. The widely accepted informal stratigraphic subdivisions of the Wahweap Formation on the Kaiparowits Plateau are herein formalized and named the Last Chance Creek Member, Reynolds Point Member, Coyote Point Member, and Pardner Canyon Member (formerly the lower, middle, upper, and capping sandstone members respectively). Two high-precision U-Pb zircon ages were obtained from bentonites using CA-ID-TIMS, supported by five additional bentonite and detrital zircon LA-ICP-MS ages. Improved geochronology of the Star Seep bentonite from the base of the Reynolds Point Member via CA-ID-TIMS demonstrates that this important marker horizon is over a million years older than previously thought. A Bayesian age-stratigraphic model was constructed for the Wahweap Formation using the new geochronologic data, yielding statistically robust ages and associated uncertainties that quantifiably account for potential variations in sediment accumulation rate. The new chronostratigraphic framework places the lower and upper formation boundaries at 82.17 +1.47/-10.63 Ma and 77.29 +0.72/-0.62 Ma, respectively, thus constraining its age to the first half of the Campanian. Additionally, a holistic review of known vertebrate fossil localities from the Wahweap Formation was conducted to better understand their spatio-temporal distribution including revised ages for early members of iconic dinosaur lineages such as Tyrannosauridae, Hadrosauridae, and Centrosaurinae. Chronoand lithostratigraphic refinement of the Wahweap Formation and its constituent biotic assemblages establishes an important reference for addressing questions of Campanian terrestrial paleoecology and macroevolution, including dinosaur endemism and diversification throughout western North America.
Bicknell, Russell D. C.Holmes, James D.Pates, StephenGarcia-Bellido, Diego C....
20页
查看更多>>摘要：The Cambrian explosion represents the rapid emergence of complex marine ecosystems on Earth. The propagation of predator-prey interactions within these systems was almost certainly one of the major drivers of this evolutionary event, sparking an arms race that promoted the proliferation of biomineralised exoskeletons and shells, and the evolution of the first durophagous (shell-crushing) predators. The most commonly documented evidence of Cambrian durophagous predation comes from injured trilobites. However, quantitative analysis based on multiple specimens from single localities is lacking. Such studies are required to reveal the dynamics of ancient predator-prey systems at fine ecological scales (e.g. at the population or community level). This study documents injured specimens of two trilobite species, Redlichia takooensis and Redlichia rex, from the Emu Bay Shale Konservat-Lagersta center dot tte (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia. A total of 38 injured specimens exhibiting various healed cephalic and thoracic injuries are documented, in addition to the mangled remains of two individuals that probably resulted from the activities of a durophagous predator or scavenger. Specimens of both species show that most injuries are located on the posterior portion of the thorax, indicating that predators preferentially attacked from behind and/or prey individuals presented the posterior of the trunk towards the predator when threatened or fleeing. The larger sample of injured R. takooensis shows that while unilateral injuries are more common than bilateral ones, there is no evidence for a left-or right-side bias, contrasting with previous suggestions that Cambrian trilobites exhibit right-sided injury stereotypy. Comparing the position of injured and non-injured R. takooensis and R. rex in bivariate space, we illustrate that injured specimens of both species typically represent some of the largest individuals of these taxa. This suggests that smaller individuals were completely consumed during an attack and/or larger individuals were more likely to survive an attack and thus record a healed injury. We argue that R. rex, rather than radiodonts, was likely the chief producer of exoskeletal injuries and large shelly coprolites in the Emu Bay Shale biota, and represents one of the earliest cannibalistic trilobites.
查看更多>>摘要：We synthesise records of stable carbon isotopes (delta C-13 values), TOC/TN, magnetic susceptibility (xlf), palynology, and phytoliths for a late Quaternary lacustrine archive from the northern Gangetic Plain, India to determine the primary driver(s) of past C-3/C-4 plant variability. The study reveals nine climate-driven shifts in vegetation over the last 15.2 ka and provides a comprehensive picture of the evolution of the lake sequence. During 15.2-14.5 ka, lower delta C-13 values, relatively higher TOC/TN ratios and xlf values suggest increasing contribution of C(3 )plant-derived organic matter into the lake and enhanced hydroclimatic conditions in the northern Gangetic Plain. Subsequently, a warm and humid phase corresponding to the B phi lling-Aller phi d interstadial is inferred during 14.5-12.8 ka, followed by evidence of a waning of the Indian Summer Monsoon (ISM) during the Younger Dryas from 12.8-11.7 ka. Despite a strong ISM regime during the early-Greenlandian (11.7-11.0 ka), vegetation shifted from a mixed C-3 -C-4 to a C-4 dominated composition as inferred from higher delta C-13 values, TOC/TN ratios and xlf values. However, a weakened ISM phase is noted between 11.0 and 10.2 ka. On return of warm and humid climatic conditions during 10.2-8.3 ka, tall C-4 Panicoideae grasses flourished around the lake. Two weaker hydroclimatic phases between 8.3 and 6.5 ka and 4.2-2.5 ka favoured C-4-short Chloridoideae grasses over C-4-tall Panicoideae members. Moderate hydroclimatic conditions after 0.6 ka favoured C-4-tall moist-loving grasses. This study shows that before shifting to a C-4-dominated vegetation during the early-Greenlandian to early-Northgrippian, C-3 plants used to dominate the northern Gangetic Plain throughout the late-Pleistocene period. We infer that temperature and rainfall jointly influenced the diversity and distribution of C-4 plants in the northern Gangetic Plain.
NSTL
Elsevier