Late Pennsylvanian Through Early Permian Alluvial Paleosols (north-central Texas) PDF Download

Author: Neil John Tabor
Publisher:
ISBN:
Category :
Languages : en
Pages : 316

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Author: Sharane Simon
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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The Lower Permian Clear Fork Formation of north-central Texas is a ~350 m thick redbed deposit with extensive paleosols and well-preserved plant and vertebrate fossils. Deposited on the western equatorial margin of Pangea under (semi)arid conditions on the stable Eastern Shelf of the Midland Basin, the formation experienced shallow burial, which minimized diagenetic effects and allowed the preservation of paleoclimatic indicators. This study investigates the spatial and stratigraphic variations of the alluvial systems and provides a parallel assessment of Early Permian paleoclimatic trends established from previous studies. Four fluvial styles were identified, representing fine-grained meandering and coarser ephemeral sandbed channels. The meandering channels exposed in cliff sections and as exhumed point bars represent a continuum between sustained lateral accretion of bedload composed of quartzose sediments and reworked pedogenic mud aggregates, and oblique accretion of suspended sediments. Swept ripples were formed as water levels declined rapidly to near-dryness and as overbank floodwaters re-entered the channels downstream. Mud aggregates are unusually well-preserved in some channel bodies due to rigid surrounding grains and cements, rapid burial within the migrating point bar, and shallow long-term burial. Abandoned channel fills contain variegated laminated mudstone with well-preserved plant leaves derived from the vegetated riparian zone. The ephemeral channels are represented by tabular sandstones that cut across the landscape and show evidence for strong but fluctuating flow. In the formation, cements and nodules change upward from mainly calcite and ankerite in the lower unit to dolomite and gypsum with minor celestine in the middle and upper units, implying increasingly saline groundwater and supporting progressive regional aridification, which is also evident in other Late Paleozoic studies. In the meandering channel bodies, upper flow regime bedforms are confined to the lower unit, and the occurrence of plant and animal fossils decreases upsection. However, tabular sandstones and avulsive meandering bodies in the middle unit imply more humid periods with higher discharge. Many features of the Clear Fork Formation are similar to the Channel Country of central Australia, making it an appropriate modern analogue.

Author: Spencer G. Lucas
Publisher: New Mexico Museum of Natural History and Science
ISBN:
Category : Animals, Fossil
Languages : en
Pages : 371

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Author: Michael Montenari
Publisher: Academic Press
ISBN: 0128209925
Category : Science
Languages : en
Pages : 780

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Carbon Isotope Stratigraphy, Volume Five in the Advances in Sequence Stratigraphy series, covers research in stratigraphic disciplines, including the most recent developments in the geosciences. This fully commissioned review publication aims to foster and convey progress in stratigraphy with its inclusion of a variety of topics, including Carbon isotope stratigraphy - principles and applications, Interpreting Phanerozoic d13C patterns as periodic glacio-eustatic sequences, Stable carbon isotopes in archaeological plant remains, Review of the Upper Ediacaran-Lower Cambrian Detrital Series in Central and North Iberia: NE Africa as possible Source Area, Calibrating d13C and d18O chemostratigraphic correlations across Cambrian strata of SW, and much more. Contains contributions from leading authorities in the field Informs and updates on all the latest developments in the field Aims to foster and convey progress in stratigraphy, including geochronology, magnetostratigraphy, lithostratigraphy, event-stratigraphy, and more

Author: Geological Survey (U.S.)
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 488

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Author: Mark McKinzie
Publisher: Lulu.com
ISBN: 1105682145
Category :
Languages : en
Pages : 156

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Author: Christopher R. Fielding
Publisher: Geological Society of America
ISBN: 0813724414
Category : Science
Languages : en
Pages : 366

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"This volume summarizes new developments in understanding the longest-lived icehouse period in Phanerozoic Earth history, the late Paleozoic ice age. Resolving the Late Paleozoic Ice Age in Time and Space provides summaries of existing and new data from the various Gondwanan continental relics, and also reviews stratigraphic successions from the paleotropical and temperate regions of Laurussia that preserve an indirect record of glaciation. It addresses the extent to which records of glaciation indicate protracted, long-term climatic austerity, as opposed to fluctuating, more dynamic climate, and provides new constraints on the timing of glaciation. Additionally, it tackles questions of synchroneity of glaciation across the various Gondwanan continental relics, and timing relationships between near-field and far-field records at greater levels of resolution than has been possible previously. Results point toward a dynamic icehouse regime that is comparable to the Cenozoic icehouse, and away from traditional interpretations of the late Paleozoic ice age as a single, protracted event that involved stable, long-lived ice centers."--Publisher's website.

Author: Dallas Geological Society
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 69

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Author: Margaret Ann Molineux
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 1206

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Certain horizons in Late Missourian-Early Virgilian shales of north-central Texas contain an unusual mixture of marine invertebrates, terrestrial plant fragments, and phosphate nodules. These dark shales form part of the cyclothemic series of limestones, shales, and sandstones that result from the interplay of marine transgressions and regressions, uplift and erosion, deltaic development, and climatic variations. Classic models for phosphate genesis place these deposits near the oxygen minimum zone in a slope or off-shelf location, in relatively deep-water. Such an interpretation, however, suffers from: (1) the need for off-shelf transport of terrestrial material, (2) the repetition of this dark shale facies, often with obviously shallow-water algal limestones or deltaic deposits, and (3) the inferred deeper habitat for shallow-water invertebrates producing isolated patches of the mollusc-dominated Modern Evolutionary Fauna far offshore, a fauna that otherwise dominates nearer-shore habitats in the late Paleozoic. This study seeks a more viable explanation for these particular dark shales. Sixty-three sites were characterized for both fossils and enclosing sediment. Conventional paleontological procedures are supplemented with statistical cluster analysis and various analytical techniques (XRD, SEM, microprobe, INAA/ICP, rock-eval pyrolysis, stable & radiogenic isotopes) to suggest that the shales were intermittently deposited in a proximal shelf or nearshore environment. Encrustation and boring of fossils and nodules indicate that reworking, fluctuation of redox levels, and variations of sedimentation rates were all characteristics of the phosphate-bearing shale horizons of the Wayland Shale and Finis Shale. Shelly layers in the Placid and Finis shales record event horizons. Both plant roots and taxonomic congruence of miospore and plant fragments in the Bluff Creek/Necessity Shale are indicative of proximal shelf deposition. Phosphate middle rare earth element enrichment and radiogenic 87Sr/86Sr signatures do not support a deep water hypothesis. The proposed dysaerobic, shallow-shelf, depositional model resolves the sedimentary and other incongruities in the earlier deep-water depositional model by eliminating the need to explain the offshore transport of terrestrial material and the interbedding of shallow- and deep-water deposits. In particular, it clarifies the anomalous late Paleozoic occurrences of the Modern Evolutionary Fauna by assigning them to a more appropriate shallow-water setting.

Author: Stephen F. Greb
Publisher: Geological Society of America
ISBN: 081372399X
Category : Science
Languages : en
Pages : 344

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