A new Late Miocene chondrichthyan assemblage from the Chagres Formation,Panama

The lLate Miocene Chagres Formation from northern Panama contains the youngest outcrops of the Panama Canal Basin. Here we report two chondrichthyan assemblages that include 30 taxa from both the Rio Indio and Chagres Sandstone Members of the Chagres Formation. We report 18 new fossil records for Panama and four for tropical America, constituting the most diverse chondrichthyan association for the Cenozoic of Panama. We performed a paleobathymetry analysis based on the modern water depth preference of extant chondrichthyan taxa. The assemblage from the Rio Indio Member is characterized by taxa with neritic affinities, suggesting depths <100 m, whereas the assemblage from the Chagres Sandstone Member is dominated by taxa with oceanic affinities, suggesting 200–300 m water depths. The Chagres Sandstone Member could have accumulated at the edge of a platform–upper slope, bordered by a deep oceanic margin.     

Quantitative paleotemperature estimates from δ18O of chironomid head capsules preserved in arctic lake sediments

A paleoenvironmental perspective of temperature change is paramount to understanding the significance of recent warming in the Arctic. Late Quaternary sediments from many arctic lakes provide environmental archives with decadal resolution, but reconstructions are hampered by the relative insensitivity of many traditional proxies to temperature. Here, we show that the δ¹⁸O of head capsules of chironomid larvae are equilibrated with the δ¹⁸O of lakewaters in which they live. In suitable lakes, lakewater δ¹⁸O is controlled by the δ¹⁸O of local precipitation, which is strongly correlated to mean annual air temperature (MAT). From this correlation, chironomid δ¹⁸O can be used to examine past changes in MAT. We illustrate the potential of this novel approach to paleothermometry with examples from two arctic lakes that reveal strong regional paleoclimatic gradients in the early Holocene.     

Late Mesozoic bivalve faunas from the Tetori Group,Japan

The Tetori Group of Japan ranks amongst the more important Upper Mesozoic strata in East Asia, with common animal and plant fossils throughout and is well suited for analyses of the links between environmental changes and the various animal and plant fossil assemblages. Three marine transgressions (i. e., Bathonian–Oxfordian, Tithonian–Berriasian and Hauterivian–Barremian in age) have been recognized in the Tetori Group, based on ammonite index taxa. These pulses are also reflected in bivalve faunas which comprise, 81 species in 65 genera (marine taxa) and 16 species in 13 genera (non-marine taxa). Many of these are considered as endemic species to the Tetori Group. In view of the fact that the occurrence of non-marine taxa was primarily controlled by environmental conditions, these do not constitute chronological indices. The faunal composition of the first marine transgressive phase is similar to that found elsewhere in southeast Asia, while that of the second one resembles both that of southeast Asia and of northeast China and Far East Russia. Assemblages of the third phase are similar to those of Heilongjiang, northeast China. Currents from the equator and high-latitudes explain these similarities.     

Use of CART analysis to differentiate pollen of red pine (Pinus resinosa) and jack pine (P. banksiana) in New England

The identification of fossil pollen at the generic rather than species level is hampering progress in understanding the biogeography and dynamics of paleo-vegetation. We used CART analysis to facilitate the differentiation of fossil pollen of Pinus banksiana and Pinusresinosa, which are morphologically similar and nearly always combined in paleoecological studies. The CART model, using four of the ten morphological traits measured, exhibited a high level of correct identification for pollen of each of the species and shows promise as a tool for increasing the detail of paleoecological records and inferences.     

Paleoecology of Inoceramus amakusensis Nagao et Matsumoto, 1940 (Bivalvia) in a Late Cretaceous shallow clastic sea: The Himenoura Group, Kyushu, Japan

The taphonomic features and paleoecology of this species were investigated focused on vertically embedded individuals of articulated Inoceramus amakusensis Nagao et Matsumoto. In the Hinoshima Formation, Himenoura Group of Kyushu, Japan, this Santonian (Late Cretaceous) inoceramid bivalve characteristically occurs in incised-valley fill siliciclastic marine deposits. Modes of I. amakusensis occurrence and preservation, from in situ (= occurrence in life position) to allochthonous shell fragments, are strongly affected by its paleoecology and depositional environments. Several I. amakusensis (up to 25 cm in shell height) were recovered from bioturbated sandstones associated with storm-influenced deposits. Their commissural planes are almost perpendicular to the bedding plane, with the anterior face oriented downward and the posteroventral portion extending upward. Furthermore, I. amakusensis is morphologically comparable to endobyssate mytilid bivalves today. These results suggest that this Cretaceous species was an orthothetic sand sticker at least during mid-ontogeny that preferentially inhabited a well-oxygenated, nearshore seafloor. I. amakusensis was distributed in various depositional environments and has been regarded as a recliner in offshore muddy substrate. However, the present discovery suggests that it was also well adapted, with an upright life position, to high-energy shallow clastic environments characterized by high sediment supply.     

Linderochelys rinconensis (Testudines: Pan-Chelidae) from the Upper Cretaceous of northern Patagonia: New insights from shell bone histology,morphology and diagenetic implications

The panchelid turtle Linderochelys rinconensis de la Fuente, Calvo and González Riga, 2007 was described on the basis of several postcranial elements from the Rio Neuquén Subgroup of Loma del Lindero site, near Rincon de los Sauces (Neuquén, Argentina). New preparation of the type material revealed new parts of the animal, including cervical vertebrae, parts of the carapace and a right tibia. The study of the newly recovered material herein improves our knowledge of the macroanatomy of this taxon. The first costal shows an axillary buttress similar to Australasian chelids and the cervical vertebrae morphology suggests a short-necked chelid condition. The re-examination of the type material of Linderochelys and the discovery of new material allowed new studies on microanatomy, osteohistology and diagenesis. Osteohistology suggests some similarities with Patagonian Cretaceous and Palaeocene Yaminuechelys, based on the presence of parallel-fibred bone in the external cortex and a much thinner internal cortex. Paleoecological studies on the proportions of forelimbs and microanatomy point towards aquatic or semi-aquatic habits, closely related to the condition seen in some extant South American chelids, such as Phrynops hilarii, Phrynops geoffroanus, and Mesoclemmys gibba. The fossil-diagenetic processes inferred substitution, fracturing, plastic deformation and permineralization events. Combined analyses through scanning electron microscopy with energy-dispersive X-ray spectrometry and petrographic studies revealed the substitution of hydroxyapatite by francolite. Permineralization stages include infilling of vascular canals, trabeculae and fractures with iron oxides and carbonate minerals during their burial history.     

Epibiosis across the Late Devonian biotic crisis: a review

Across the Late Devonian biotic crisis, sclerobionts declined in diversity and abundance and the proportions of brachiopod shell textures changed radically. Most of the major sclerobiont clades were common to Givetian through Mississippian ecosystems. Microconchids, most abundant sclerobiont in most Devonian assemblages, were replaced by bryozoans in the Mississippian. Diversity and abundance of Mississippian sclerobionts were lower than Frasnian–Famennian assemblages.     

土壤次生碳酸盐碳氧稳定同位素古环境意义及应用

土壤次生碳酸盐碳氧稳定同位素特征是反映古气候与古环境的重要代用指标,其碳氧稳定同位素组成分别受土壤CO2中C同位素组成和大气水的O同位素控制。在一定深度的土壤中,土壤次生碳酸盐δ^13C就主要受当地植物类型(C3植物和C4植物等)控制。土壤次生碳酸盐样预处理中剔除土壤中原生碳酸盐以及有机物污染尤为重要。土壤中次生碳酸盐C、O稳定同位素地球化学在土壤发生学、古气候恢复、古生态重建以及全球变化研究中应用日益广泛,但解译时可能受应用年代范围、成岩作用、原生和次生碳酸盐混杂、土壤碳酸盐多元发生等因素影响,其应用机理和范围还需进一步探讨。     

Late Holocene forest dynamics, volcanism, and climate change at Whitewing Mountain and San Joaquin Ridge, Mono County, Sierra Nevada, CA, USA

Deadwood tree stems scattered above treeline on tephra-covered slopes of Whitewing Mtn (3051 m) and San Joaquin Ridge (3122 m) show evidence of being killed in an eruption from adjacent Glass Creek Vent, Inyo Craters. Using tree-ring methods, we dated deadwood to AD 815-1350 and infer from death dates that the eruption occurred in late summer AD 1350. Based on wood anatomy, we identified deadwood species as Pinus albicaulis, P. monticola, P. lambertiana, P. contorta, P. jeffreyi, and Tsuga mertensiana. Only P. albicaulis grows at these elevations currently; P. lambertiana is not locally native. Using contemporary distributions of the species, we modeled paleoclimate during the time of sympatry to be significantly warmer (+3.2°C annual minimum temperature) and slightly drier (−24 mm annual precipitation) than present, resembling values projected for California in the next 70-100 yr.     

Late Barremian to early Aptian calcareous nannofossil paleoceanography and paleoecology from the Ocean Drilling Program Hole 641C (Galicia Margin)

Calcareous nannofossil assemblages at Site 641C (Galicia Margin, North Atlantic) were investigated in order to determine changes in fertility and temperature of surface waters. Taxa such as Zeughrabdotus spp. <3.5 μm, Biscutum constans, Discorhabdus rotatorius and Diazomatolithus lehmanii, which thrived in higher fertility conditions, are particularly abundant across the CM0 interval as opposed to those with oligotrophic affinities such as Watznaueria spp. and Nannoconus spp., which are generally reduced in abundance. The abundances of nannoconids are much lower than those observed in Tethyan sections, indicating higher fertility conditions. Slumpings and low recovery prevent the identification of the onset of the “nannoconid crisis”, but a sharp drop in nannoconid abundances, observed prior to the CM0 interval, correlates with the “nannoconid decline” observed in several Tethys sections.The normalized ratio between low and high fertility taxa (Fertility Index) was used to characterize the nannofossil assemblages in terms of productivity changes. The highest values of the Fertility Index were observed across magnetic chron CM0. The paucity of cold water taxa such as Seribiscutum spp. and Repagulum parvidentatum suggests warm water conditions throughout the deposition of upper Barremian–lower Aptian sediments on the Galicia Margin.