Search

Your search keyword '"Leanne Stepchinski"' showing total 2 results
Start Over Author "Leanne Stepchinski"
2 results on '"Leanne Stepchinski"'

1. Guano stable isotopic evidence of Anthropocene climate change influence on aridity and vegetation dynamics

Author

Daniel M. Cleary, Leanne Stepchinski, F. Paul Bertetti, Rebecca Nunu, Ronald T. Green, and Bogdan P. Onac

Subjects
δ13C, δ15N, Cave, Bat, Drought, Texas, Ecology, QH540-549.5
Abstract

A 2.8 m-long core of cave bat guano was obtained from an excavated pit within Bracken Cave (Texas, USA) and analyzed for δ13C and δ15N. Radiocarbon dating of the core indicated that guano deposition occurred between 1974–1989 and 1998–2016 CE. The hiatus between 1989 and 1998 CE was interpreted to be related to documented mining activities during this interval. The average Suess-corrected δ13C values for the entire series (–19.7 ± 1.0 ‰) suggest that insects ingested by the bats had a diet incorporating both C3 and C4 plants. The proportion of each appeared to be dependent on the sensitivity of vegetation to prolonged and frequent droughts. Two documented La Niña events centered around 2008 and 2011 CE occurred contemporaneously with intervals of higher δ13C values. The drought recorded in 2006 may have corresponded with foraging of insects located over C3 vegetation, which resulted in lower δ13C (–22.0 ‰). δ15N values agree well with records of drought and precipitation in Texas, suggesting an aridity control on the local nitrogen cycle. The highest δ15N values occurred during periods of a weaker North American Monsoon (1977 and 1982 CE). Higher δ15N values also occur at 2006, 2009, and 2012 CE, corresponding with years of reduced precipitation locally and throughout the region. This study further demonstrates that guano δ13C and δ15N records can provide paleo-information with respect to climatic influence on the environment in semi-arid regions.

Published
2022
Full Text
View/download PDF

2. An integrated biostratigraphy (conodonts and foraminifers) and chronostratigraphy (paleomagnetic reversals, magnetic susceptibility, elemental chemistry, carbon isotopes and geochronology) for the Permian–Upper Triassic strata of Guandao section, Nanpanjiang Basin, south China

Author

Daniel J. Lehrmann, Leanne Stepchinski, Demir Altiner, Michael J. Orchard, Paul Montgomery, Paul Enos, Brooks B. Ellwood, Samuel A. Bowring, Jahandar Ramezani, Hongmei Wang, Jiayong Wei, Meiyi Yu, James D. Griffiths, Marcello Minzoni, Ellen K. Schaal, Xiaowei Li, Katja M. Meyer, and Jonathan L. Payne

Subjects
Hindeodus, Paleomagnetism, biology, Permian, Early Triassic, Geology, Biostratigraphy, biology.organism_classification, Paleontology, Stage (stratigraphy), Geochronology, Chronostratigraphy, Earth-Surface Processes
Abstract

The chronostratigraphy of Guandao section has served as the foundation for numerous studies of the end-Permian extinction and biotic recovery in south China. Guandao section is continuous from the Permian–Triassic boundary to the Upper Triassic. Conodonts enable broad delineation of stage and substage boundaries and calibration of foraminifer biostratigraphy as follows. Changhsingian–Griesbachian: first Hindeodus parvus, and first appearance of foraminifers Postcladella kalhori and Earlandia sp. Griesbachian–Dienerian: first Neospathodus dieneri, and last appearance of foraminifer P. grandis. Dienerian–Smithian: first Novispathodus waageni and late Dienerian first appearance of foraminifer Hoyenella ex gr. sinensis. Smithian–Spathian: first Nv? crassatus and last appearance of foraminifers Arenovidalina n. sp. and Glomospirella cf. vulgaris. Spathian–Aegean: first Chiosella timorensis and first appearance of foraminifer Meandrospira dinarica. Aegean–Bithynian: first Nicoraella germanica and first appearance of foraminifer Pilammina densa. Bithynian–Pelsonian: after last Neogondolella regalis, prior to first Paragondolella bulgarica and first appearance of foraminifer Aulotortus eotriasicus. Pelsonian–Illyrian: first Pg. excelsa and last appearance of foraminifers Meandrospira? deformata and Pilamminella grandis. Illyrian–Fassanian: first Budurovignathus truempyi, and first appearance of foraminifers Abriolina mediterranea and Paleolituonella meridionalis. Fassanian–Longobardian: first Bv. mungoensis and last appearance of foraminifer A. mediterranea. Longobardian–Cordevolian: first Quadralella polygnathiformis and last appearance of foraminifers Turriglomina mesotriasica and Endotriadella wirzi. The section contains primary magnetic signature with frequent reversals occurring around the Permian–Triassic, Olenekian–Anisian, and Anisian–Ladinian boundaries. Predominantly normal polarity occurs in the lower Smithian, Bithynian, and Longobardian–Cordevolian. Predominantly reversed polarity occurs in the upper Griesbachian, Induan–Olenekian, Pelsonian and lower Illyrian. Reversals match well with the GPTS. Large amplitude carbon isotope excursions, attaining values as low as −2.9‰ δ13C and high as +5.7‰ δ13C, characterize the Lower Triassic and basal Anisian. Values stabilize around +2‰ δ13C through the Anisian to Carnian. Similar signatures have been reported globally. Magnetic susceptibility and synthetic gamma ray logs show large fluctuations in the Lower Triassic and an overall decline in magnitude of fluctuation through the Middle and Upper Triassic. The largest spikes in magnetic susceptibility and gamma ray, indicating greater terrestrial lithogenic flux, correspond to positive δ13C excursions. High precision U–Pb analysis of zircons from volcanic ash beds provide a robust age of 247.28 ± 0.12 Ma for the Olenekian–Anisian boundary at Guandao and an age of 251.985 ± 0.097 Ma for the Permian–Triassic boundary at Taiping. Together, the new U–Pb geochronology from the Guandao and Taiping sections suggest an estimated duration of 4.71 ± 0.15 Ma for the Early Triassic Epoch.

Published
2015
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results