John L Isbell

John L Isbell
University of Wisconsin - Milwaukee | UWM · Department of Geosciences

Ph.D.
Clastic Sedimentology and Stratigraphy

About

165
Publications
55,274
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
4,493
Citations
Additional affiliations
September 1992 - present
University of Wisconsin - Milwaukee
Position
  • Professor
December 1990 - August 1992
The Ohio State University
Position
  • Research Scientists
Education
September 1984 - December 1990
The Ohio State University
Field of study
  • Geology (Sedimentology, Stratigraphy, and Basin Analysis)
September 1981 - August 1985
Northern Illinois University
Field of study
  • Geology (Sedimentology, Stratigraphy, Basin Analysis and Palynology)
September 1978 - June 1981
Augustana College
Field of study
  • Geology

Publications

Publications (165)
Chapter
A long-term global cooling driven by supercontinental reconfiguration and colonization of land by vascular plants culminated in the Phanerozoic's longest, most severe and widespread icehouse epoch. The Late Paleozoic Ice Age spanned approximately a 106-Myr interval from the latest Devonian, throughout the Carboniferous, to its demise in the late Pe...
Article
Despite a lack of detailed sedimentologic analyses, diamictites in the Middle Permian Atkan Formation were previously interpreted as glaciomarine and glacially-influenced marine deposits. This interpretation allowed this unit to play a prominent role in paleoclimatic and biogeographical reconstructions associated with presumed bipolar glaciation du...
Article
Full-text available
The middle Sakmarian Basal Beds on Maria Island were deposited during the initial decline of the Late Palaeozoic Ice Age following Late Pennsylvanian–Early Sakmarian maximum glaciation. At that time, Tasmania was located within the South Polar Circle between an apparent ice-free pole (Antarctica) and the mid- to high-latitude Sydney-Bowen-Gunnedah...
Article
Full-text available
The location, longevity, and geographic extent of late Paleozoic ice centers in west-central Gondwana remain ambiguous. Paleovalleys on the Rio Grande do Sul Shield of southernmost Brazil have previously been interpreted as fjords carved by outlet glaciers that originated in Africa and emptied into the Paraná Basin (Brazil). In this study, the sedi...
Conference Paper
Full-text available
Highly complex glacial dynamics produced an intricate mosaic of glacial strata and erosional landforms throughout Gondwana during the late Paleozoic Ice Age (LPIA; 362-256 Ma), the Phanerozoic's longest and most severe icehouse interval. An extensive gap in understanding the extension of ice masses in western Gondwana remains due to glacial success...
Conference Paper
Full-text available
The stratigraphic architecture of fjords is complex as it is controlled by ice dynamics, sediment supply, relative sea-level fluctuations, and topography. Glacially-transported debris are prone to failure and to be carried downslope to the fjord floor through the entire spectrum of mass movements and density flows, as the submarine landscape moves...
Conference Paper
Full-text available
Determining the ice dynamics of deep-time glaciations is limited by the scarcity of well-preserved subglacial erosional features and their irregular distribution. In particular, small-scale erosional features known as s-forms that are subglacially sculpted in bedrock by water and/or ice are rarely preserved from the pre-Cenozoic record. A detailed...
Article
Full-text available
We propose that a “local first” approach should be applied to the interpretation of provenance indicators in glacigenic sediments of all depositional ages, especially where the glacier flow path is poorly constrained and the records of potential source lithologies are incomplete. Provenance proxies, specifically U-Pb detrital zircon geochronology,...
Article
The late Paleozoic ice age (LPIA) was the longest-lived glaciation of the Phanerozoic, and the demise of LPIA is the Earth's only recorded transition from an icehouse to a greenhouse state. In order to explore the records of chemical weathering and volcanism linked to paleoclimate, an integrated multi-proxy study from the Pennsylvanian to the earli...
Article
Full-text available
A Era Glacial Neopaleozoica (LPIA – Late Paleozoic Ice Age) é representada na Bacia do Paraná pelo Grupo Itararé, cujos estratos fornecem um registro glacial dominado por sucessões glácio-marinhas e raros intervalos deformados por geleiras. Depósitos glaciotectonizados possuem macroestruturas como dobras, falhas e zonas de cisalhamento geradas sub...
Article
Full-text available
The Late Paleozoic Ice Age (LPIA; 362 to 256 Ma) left a record in the Gondwanan sedimentary basins as glacial successions and ice-carved features. In the Paraná Basin the glaciation is recorded in the Itararé Group and on its basal unconformity that contains micro to mega scale erosive features. Diamictites and glacial erosive landforms such as str...
Article
The late Paleozoic Ice Age (LPIA) was one of Earth's most important Phanerozoic climatic events lasting for over 100 Mys. Despite its importance, its history is controversial with two hypotheses that portray glaciation differently (Fig. 1). Traditional views characterize the LPIA as a continuous glacial event that lasted from the Middle Mississippi...
Article
Full-text available
The currently favored hypothesis for Late Paleozoic Ice Age glaciations is that multiple ice centers were distributed across Gondwana and that these ice centers grew and shank asynchronously. Recent work has suggested that the Transantarctic Basin has glaciogenic deposits and erosional features from two different ice centers, one centered on the An...
Article
The Permian Mackellar Formation in the central Transantarctic Mountains is a fine-grained siliciclastic succession, which was deposited in a marine to brackish inland sea (Mackellar Sea) along the hinterland of the Gondwana margin. The Mackellar strata were deposited in an elongate, trough-shaped basin oriented subparallel to the present trend of t...
Article
The southwestern margin of South America offers a complete record of the Late Paleozoic Ice Age (LPAI) that affected the Gondwana supercontinent. The tripartite division of LPIA glacial episodes has been refined with the help of new radiometric dates and biostratigraphic (flora and fauna) zonations in recent years to five shorter-lived discrete eve...
Article
Full-text available
The Paraná Basin, Brazil and the Chaco-Paraná Basin, Uruguay both contain sedimentary records that are critical to reconstructing late Paleozoic ice centers in central Gondwana. The orientations of subglacial landforms and glaciotectonic structures suggest that late Paleozoic glacial deposits in the eastern Chaco-Paraná Basin and the southernmost P...
Article
The western margin of Gondwana records evidence of mid-Carboniferous glaciation (Visean- Bashkirian) in the strata of the Paganzo Basin and adjacent areas. Previous studies focused on constraining the orientations of ice flow and generalizing the extent and occurrence of glacial ice in the basin. However, there is uncertainty occurs concerning the...
Article
The provenance of sandstones deposited in the late Paleozoic Tepuel-Genoa Basin is analyzed in this paper. Five sections were sampled in Esquel, Sierra de Tepuel, Sierra de Tecka, El Molle, and Río Genoa areas for petrographic and geochemical studies. The sandstones in the Tepuel-Genoa Basin are dominated by feldspathic litharenites and litharenite...
Conference Paper
Full-text available
The Itararé Group and time equivalent Aquidauana Formation represent the Late Paleozoic Ice Age in the Paraná Basin. These sedimentary rocks provide an extensive glacial record which contains deformed intervals interpreted as glaciotectonites, with features such as folds, thrusts and subhorizontal shear zones, which could be produced sub-or proglac...
Conference Paper
The Late Paleozoic Ice Age spanned approximately a 106-million-year interval from the latest Devonian, throughout the Carboniferous, to its demise in the late Permian. Asynchronous ice centers waxed and waned across Gondwana sculpturing landforms and leaving a sedimentary record within the late Paleozoic sedimentary basins. In the Kaokoveld region,...
Article
Full-text available
The demise of the Late Paleozoic Ice Age has been hypothesized as diachronous, occurring first in western South America and progressing eastward across Africa and culminating in Australia over an ~60 m.y. period, suggesting tectonic forcing mechanisms that operate on time scales of 106 yr or longer. We test this diachronous deglaciation hypothesis...
Article
Full-text available
Carboniferous glaciogenic strata (Itararé Gp.) in the southernmost Paraná Basin, Brazil exhibit soft-sediment deformation features previously interpreted as glaciotectonism. These sediments were studied in detail to confirm that they were deformed by ice and to assess the nature of the glaciation, depositional environments, and paleoclimate in this...
Conference Paper
Full-text available
El análisis de las modas detríticas de areniscas pertenecientes a la Formación Valle Chico y al Grupo Tepuel (formaciones Pampa de Tepuel, Mojón de Hierro y Río Genoa) permite establecer las probables áreas de proveniencia para la cuenca neopaleozoica. Desde el punto de vista composicional, las areniscas corresponden a litoarenitas y litoarenitas f...
Article
Full-text available
Most ice-age diamictites were emplaced in basinal settings by non-subglacial processes. Nonetheless, the occurrence of diamictite in rock successions is widely employed to estimate ice extent and delimit glacial growth-decay cycles that serve as background for paleoclimate modeling. We report a cyclic diamictite-mudstone succession from the Bashkir...
Article
The timing and geographic distribution of glaciers in high-latitude southern Gondwana during the Late Paleozoic Ice Age remain poorly constrained, ultimately precluding our ability to estimate ice volume and associated climate teleconnections and feedbacks during Earth's penultimate icehouse. Current aerial extents of glaciers, constrained by sedim...
Conference Paper
Full-text available
The reconstruction of geological events and processes in deep time depends on the availability of a robust chronos-tratigraphic framework. Generating such a framework depends on the occurrence of dateable material throughout the sedimentary successions of interest, and on the accuracy and precision of the obtained radioisotopic ages. Reconstructing...
Conference Paper
Full-text available
Mediante el análisis de las modas detríticas de areniscas pertenecientes a las formaciones Pampa de Tepuel, Mojón de Hierro y Río Genoa fueron investigadas las áreas de proveniencia del Grupo Tepuel (Carbonífero Tardío-Pérmico), Cuenca Tepuel-Genoa, Chubut. Desde el punto de vista composicional las areniscas corresponden a litoarenitas y litoarenit...
Article
Full-text available
The timing of the late Paleozoic glaciation and its terminal deglaciation in the Paraná Basin, Brazil, is unconstrained and prohibits correlation of the Paraná Basin ice record with other high-latitude Gondwanan and low-latitude contemporaneous records. Here, we reexamine the existing U-Pb framework for the Carboniferous-Permian Paraná succession t...
Article
Full-text available
Euthycarcinoid arthropods (Cambrian–Triassic) were likely the first animals to transition from oceanic to freshwater and emergent environments. Although their basic bauplan is well known, they have a poor fossil record because their non-sclerotized exoskeleton was rarely preserved. Euthycarcinoids’ unusual morphology (varying numbers of body segmen...
Conference Paper
Full-text available
In this contribution we explore recent advances from ongoing research on the interplay between tectonics and climate in the evolution of the Paraná Basin from the mid-late Carboniferous to the earliest Permian, a time characterized by intense climatic and tectonic instabilities in SW Gondwana. Latest Devonian to Pennsylvanian uplifting on the easte...
Article
Full-text available
The most complete Permian-Triassic Gondwana succession in Antarctica crops out in the central Transantarctic Mountains. The lower Permian strata were deposited in an intracratonic basin that evolved into a foreland basin in late Permian time. Sedimentary petrology and paleocurrent data have been interpreted as indicating a granitic (craton) provena...
Conference Paper
Ambientes de sedimentação situados sob e na frente de geleiras (subglaciais e glácio-marginais) estão entre os sítios deposicionais mais complexos conhecidos devido aos impactos das flutuações da margem da geleira no acúmulo, erosão e deformação da pilha sedimentar. Embora depósitos formados nesses ambientes sejam escassos e pouco preservados no re...
Conference Paper
As global climate transitioned from the icehouse of the Late Paleozoic Ice Age (LPIA) to greenhouse conditions of the Late Permian, glaciers vanished across Gondwana; however, not all ice centers responded synchronously. The Paganzo Basin, northwestern Argentina, was geographically adjacent to significant mid-Carboniferous ice centers that disappea...
Conference Paper
Full-text available
High-Resolution Zircon U-Pb CA-TIMS Dating of the Carboniferous—Permian Successions, Paraná Basin, Brazil Abstract The late Paleozoic Ice Age (LPIA) is Earth’s only record of a CO2-forced climatic transition from an icehouse to greenhouse state in a vegetated world. Despite a refined framework of Gondwanan ice distribution, questions remain about...
Article
Full-text available
The Atkan Formation in the Ayan-Yuryakh anticlinorium, Magadan province, northeastern Russia, is of great interest because of the occurrence of deposits of apparent "dropstones" and "ice rafted debris" that have been previously interpreted as glacial. Two high-precision U-Pb zircon ages, one for an intercalated volcanic tuff (262.5. ±. 0.2. Ma) and...
Conference Paper
Full-text available
The late Paleozoic Ice Age (LPIA) was the most significant icehouse of the Phanerozoic, as this interval marks the only complete transition from an icehouse to a hothouse state for a biologically complex Earth. Because of similarities between the LPIA and the Cenozoic Ice Age (i.e., long duration glaciation interspersed with nonglacial epochs, low...
Conference Paper
The Paraná Basin of southern Brazil contains one of the most complete and detailed glacial and post-glacial records of the late Paleozoic ice age (LPIA; 346-259 Ma) during the Carboniferous and Permian. Despite this, there is little consensus on the character and timing of the glacial intervals. One hypothesis describes numerous small ice sheets ex...
Article
Full-text available
The leaf longevity of trees, deciduous or evergreen, plays an important role in climate feedbacks and plant ecology. In modern forests of the high latitudes, evergreen trees dominate; however, the fossil record indicates that deciduous vegetation dominated during some previous warm intervals. We show, through an integration of palaeobotanical techn...