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Tandis S Bidgoli - One of the best experts on this subject based on the ideXlab platform.
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Conodont thermochronology of exhumed footwalls of low angle normal faults a pilot study in the mormon mountains tule springs hills and beaver dam mountains southeastern nevada and southwestern utah
Chemical Geology, 2018Co-Authors: Tandis S Bidgoli, James P Tyrrell, Andreas Moller, Douglas J Walker, Daniel F StockliAbstract:Abstract (U-Th)/He thermochronology is a well-established dating technique used to understand the temperature-time histories of rocks in a wide range of geologic settings. The technique is presently restricted to rocks that contain specific accessory minerals, such as apatite or zircon. Marine carbonates and shales typically lack these accessory phases in quantities and sizes practical for (U-Th)/He dating and thus present a challenge for application of the method. Here, we explore the utility of biogenic apatite from Conodonts as a (U-Th)/He thermochronometer at a well-studied calibration site located in eastern Nevada and southwestern Utah. We performed (U-Th)/He thermochronometry, laser ablation inductively coupled plasma mass spectrometry, X-ray micro-computed tomography, and scanning electron microscopy (SEM) on specimens with Conodont color alteration indices (CAI) of 1.5–3, extracted from carbonate rocks in the footwalls of low-angle normal faults in the Mormon Mountains, Tule Spring Hills, and Beaver Dam Mountains. Conodont (U-Th)/He (CHe) dates have high scatter; dates are commonly reproducible to 20% of sample means but can deviate up to 150%. All CAI 1.5–2.5 Conodonts produce CHe dates younger than 240 Ma, consistent with thermal resetting of samples; however, most CAI 3 Conodonts give ages 2–6× older than Mississippian and Permian deposition. Average U, Th, and rare earth element (REE) concentrations depend on porosity and permeability differences between albid and hyaline Conodont tissue and range from We propose that microstructural changes associated with increasing CAI influence CHe dates. Parent isotope loss occurs during the post-cooling stage, either in the outcrop or in the laboratory. Our hypothesis is that the double-buffered formic acid procedure for dissolving dolomitized carbonates may accelerate this loss in thermally altered, higher CAI Conodonts.
Daniel F Stockli - One of the best experts on this subject based on the ideXlab platform.
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Conodont thermochronology of exhumed footwalls of low angle normal faults a pilot study in the mormon mountains tule springs hills and beaver dam mountains southeastern nevada and southwestern utah
Chemical Geology, 2018Co-Authors: Tandis S Bidgoli, James P Tyrrell, Andreas Moller, Douglas J Walker, Daniel F StockliAbstract:Abstract (U-Th)/He thermochronology is a well-established dating technique used to understand the temperature-time histories of rocks in a wide range of geologic settings. The technique is presently restricted to rocks that contain specific accessory minerals, such as apatite or zircon. Marine carbonates and shales typically lack these accessory phases in quantities and sizes practical for (U-Th)/He dating and thus present a challenge for application of the method. Here, we explore the utility of biogenic apatite from Conodonts as a (U-Th)/He thermochronometer at a well-studied calibration site located in eastern Nevada and southwestern Utah. We performed (U-Th)/He thermochronometry, laser ablation inductively coupled plasma mass spectrometry, X-ray micro-computed tomography, and scanning electron microscopy (SEM) on specimens with Conodont color alteration indices (CAI) of 1.5–3, extracted from carbonate rocks in the footwalls of low-angle normal faults in the Mormon Mountains, Tule Spring Hills, and Beaver Dam Mountains. Conodont (U-Th)/He (CHe) dates have high scatter; dates are commonly reproducible to 20% of sample means but can deviate up to 150%. All CAI 1.5–2.5 Conodonts produce CHe dates younger than 240 Ma, consistent with thermal resetting of samples; however, most CAI 3 Conodonts give ages 2–6× older than Mississippian and Permian deposition. Average U, Th, and rare earth element (REE) concentrations depend on porosity and permeability differences between albid and hyaline Conodont tissue and range from We propose that microstructural changes associated with increasing CAI influence CHe dates. Parent isotope loss occurs during the post-cooling stage, either in the outcrop or in the laboratory. Our hypothesis is that the double-buffered formic acid procedure for dissolving dolomitized carbonates may accelerate this loss in thermally altered, higher CAI Conodonts.
Christopher R. Barnes - One of the best experts on this subject based on the ideXlab platform.
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hirnantian ordovician through wenlock silurian Conodont biostratigraphy bioevents and integration with graptolite biozones cape phillips formation slope facies cornwallis island canadian arctic islands
Canadian Journal of Earth Sciences, 2017Co-Authors: Shunxin Zhang, David Martyn Stuart Jowett, Christopher R. BarnesAbstract:Cornwallis Island in the Canadian Arctic Archipelago provides one of the world’s best areas for establishing an integrated graptolite–Conodont biozonation for the Late Ordovician – Silurian given the well-exposed interfingering relationship of the basinal shale and carbonate platform facies. Building on earlier graptolite work, 180 samples were collected from nine sections of the Cape Phillips Formation, of which 118 yielded approximately 7600 Conodont elements representing 54 species in 25 genera, including one new genus and species, Mayrodus melchini ; the Conodonts are well preserved, with minimal thermal alteration (colour alteration index, CAI 1). Nine Conodont zones are recognized and defined for this region, namely the Amorphognathus ordovicicus , Distomodus kentuckyensis , Aspelundia expansa , As. fluegeli , and Pterospathodus celloni Interval zones, Pt. a. amorphognathoides Taxon-range Zone, Pt. pennatus procerus and Kockelella ranuliformis Highest-occurrence zones, and K. ortus absidata Taxon-range Zone. An integration of graptolite and Conodont zones is documented. Earlier paleontological and isotope geochemical studies have demonstrated the dynamic nature of the Silurian ocean–climate system and identified major faunal turnovers or events. Five of these are recognized in the Cornwallis fauna and related to oceanographic and climate changes, in part referring to recent oxygen isotope data from Conodonts from the Cornwallis collections: Hirnantian extinction event, Sandvika Event (late Aeronian, Llandovery), Snipklint Primo Episode (early Telychian, Llandovery), Ireviken Event (late Telychian, Llandovery–Sheinwoodian, Wenlock), and Mulde Event (early Homerian, Wenlock).
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Conodonts from the Kechika Formation and Road River Group (Lower to Upper Ordovician) of the
2015Co-Authors: Cassiar Terrane, Northern British Columbia, Leanne J. Pyle, Christopher R. BarnesAbstract:Abstract: This study examines the lower Paleozoic stratigraphy of the Cassiar Terrane from three key sections com-prising an east–west transect across the terrane. The Cassiar Terrane, west of the Northern Rocky Mountain Trench, consists of a Neoproterozoic to Triassic succession and is a fragment of the Cordilleran Miogeocline that has been dis-placed northward. The amount of displacement from its original position remains controversial. Conodonts from the Cassiar Terrane have been previously reported from only a few reconnaissance studies. More than 3000 m of strata have been measured and examined in detail and 85 Conodont samples collected. A total of 926 identifiable Conodont elements are assigned to 31 species representing 21 genera. The Conodonts are mainly representative of the Midcontinent Faunal Realm, but some also represent the Atlantic Realm. Conodonts from the upper Kechika Formation and base of the Road River Group are Early Ordovician (Tremadocian) in age, and those from the upper Road River Group range into the Upper Ordovician (Caradocian). The detailed Ordovician stratigraphy and temporal constraints es-tablished by Conodont biostratigraphy provide for correlation to coeval facies of ancestral North America. The onset of Road River sedimentation in the mid-Tremadocian is, however, older than that in the Macdonald Platform to the east (early Arenigian). This onset timing may help link the Cassiar Terrane to a specific part of the miogeocline from which it was transported. Résumé: Cette étude examine la stratigraphie du Paléozoïque inférieur du terrane de Cassiar à partir de trois section
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Paleoecology of Llandovery Conodonts, Anticosti Island, Québec
Palaeogeography Palaeoclimatology Palaeoecology, 2002Co-Authors: Shunxin Zhang, Christopher R. BarnesAbstract:Abstract Anticosti Island, Quebec, has perhaps the most fossiliferous and complete Llandovery (Early Silurian) sequence in the world. The undeformed limestones are well exposed and yield extremely well preserved Conodonts whose taxonomy and biostratigraphy has been studied in detail. In addition to documenting the general temporal and spatial distribution of Llandovery Conodonts, a set of 107 Conodont samples was taken from four cliff sections in the lower and upper Becscie, lower Gun River, and upper Jupiter formations. These samples were used to examine the relationship of Conodont elements and communities with microfacies, and explore their change through time. Over 9300 Conodonts elements were identified and subjected to cluster analysis. The sections comprise mainly the background sedimentation of lime mudstones, deposited in 30–100 m of water on a gentle ramp. These mudstones are variably affected by interbeds or channel fill deposits interpreted as tempestites. A pattern of evolving Conodont communities is documented for the lime mudstone facies through time. Different communities are found in the tempestite deposits that do not suggest a reworking of the mudstones, but rather the importation of deeper offshore faunas during periods of storm surge onto the ramp. The tempestites contain the highest species diversity and show no evidence of reduced diversity through post-mortem selective sorting by the storms.
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A major Conodont extinction event during the Early Ordovician within the Midcontinent Realm
Palaeogeography Palaeoclimatology Palaeoecology, 1993Co-Authors: Christopher R. BarnesAbstract:Ji, Z. and Barnes, C.R., 1993. A major Conodont extinction event during the Early Ordovician within the Midcontinent Realm. Palaeogeogr., Palaeoclimatol., Pataeoecol., 104: 37-47. The major change in the Lower Ordovician Conodont faunas of the Midcontinent Realm was recognized by earlier workers. Our recent intense study of Midcontinent Conodonts from the St. George Group, Port au Port Peninsula, western Newfoundland, has shown that seven major Conodont lineages, involving some 33 multielement species, completely terminate in the late Tremadoc Series, within an interval of a few metres, at a level between the Lower Ordovician Conodont Fauna C and Fauna D. The extinction event occurs during the peak of a regressive phase within the deposition of the St. George Group and at a time of apparent global eustatic fall at or slightly below the Tremadoc-Arenig series boundary. This important extinction bioevent has been recognized throughout the Midcontinent Realm in North America.
Charles M Henderson - One of the best experts on this subject based on the ideXlab platform.
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revised wuchiapingian Conodont taxonomy and succession of south china
Journal of Paleontology, 2017Co-Authors: Shuzhong Shen, Dongxun Yuan, Charles M HendersonAbstract:Abstract. South China has become the most important area to establish a global stratigraphic framework of the Wuchiapingian Stage because complete Wuchiapingian sequences include the GSSPs for the base and top of the stage. As the markers of the Wuchiapingian GSSP, Conodonts are the most important fossil group to establish the Wuchiapingian biostratigraphic framework. However, few documents have investigated in detail the Conodont biostratigraphic succession through the entire Wuchiapingian Stage. Furthermore, the Conodont taxonomy of several Wuchiapingian Clarkina species is still debated. Therefore, we here review all Wuchiapingian Clarkina species from South China and figure ontogenetic growth series from juvenile to adult individuals for each valid and important species in order to revise both Wuchiapingian Conodont taxonomy and the biostratigraphic succession. Based on the Penglaitan, Dukou, and Nanjiang sections, seven Conodont zones (Clarkina postbitteri postbitteri, C. dukouensis, C. asymmetrica, ...
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stratigraphic versus environmental significance of permian serrated Conodonts around the cisuralian guadalupian boundary new evidence from oman
Palaeogeography Palaeoclimatology Palaeoecology, 2003Co-Authors: Charles M HendersonAbstract:Abstract Conodonts from the cephalopod limestones of Rustaq and Ba’ad, Oman, have for many years been dated as Wordian because of the presence of the ammonoid, Waagenoceras. Revised definitions for Guadalupian stages and major differences of Conodont morphology among apparently coeval faunas necessitate a review of this age assignment. The lack of serration within the Oman Conodont faunas as well as from Waagenoceras-bearing limestone blocks in Sicily differs markedly from Conodonts in the Guadalupian stratotype sections of West Texas. These differences have previously been interpreted to be the result of upwelling ‘cold bottom-water’ that may have restricted the distribution of serrated, warm-water Jinogondolella species. However, our samples from Oman are dominated by species with a carinal configuration that is comparable to gondolellids from the Equatorial Warm Water Province (EWWP). Abundant species include Mesogondolella siciliensis in the lower ammonoid beds and Mesogondolella idahoensis lamberti in the upper ammonoid beds. If cold bottom-water currents were present at Oman then these taxa must have been pelagic, living in warm surficial water. In contrast, the North Cool Water Province (NCWP) includes coeval Conodonts that have a different carinal configuration and are dominated by long-ranging Mesogondolella idahoensis idahoensis. These taxa and their morphologic variations represent a geographic cline between the EWWP and NCWP. In addition, Early Roadian serrated gondolellids have been recognized in temperate cool-water settings in the Jilin Province, NE China, the Phosphoria Basin, Idaho, USA, and the Sverdrup Basin, Arctic Canada. These serrated forms extend above the Lower Roadian in only the Phosphoria Basin, indicating a distribution into temperatures cooler than previously thought, at least during the Early Guadalupian. Other Conodonts from the deep-water cephalopod limestones of Oman include rare, shallow warm-water sweetognathids, suggesting that these too must have been pelagic; if true, then cold bottom-waters probably played little role in Conodont distribution. The identified Conodont taxa at Oman best correlate with the uppermost Kungurian at the Luodian section of South China and in the Guadalupe Mountains of West Texas, suggesting that the lack of serration is not a result of cold water but rather of a stratigraphic position prior to the evolution and expansion of serrated gondolellids in the Roadian. It is possible that other paleoecologic controls affected distribution, and an alternative age assignment of Early Roadian is considered for these Conodonts. The ammonoids, including advanced species of Waagenoceras, suggest that the best correlation is with the third limestone of the Word Formation (Willis Ranch Member), which correlates with the Upper Roadian according to ratified global stage definitions. There is still an apparent discrepancy between Conodont and ammonoid ages, but discounting previous Wordian ages has considerably reduced this. Associated fusulinaceans cannot resolve this argument because of profound provincialism, but they can contribute to correlation of the global stages with Tethyan stages. It is here suggested that the Kungurian correlates with the Upper Bolorian to Upper Murgabian and that the Roadian correlates with the Lower Midian or Upper Murgabian and Lower Midian.
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evolution of permian Conodont provincialism and its significance in global correlation and paleoclimate implication
Palaeogeography Palaeoclimatology Palaeoecology, 2001Co-Authors: Charles M HendersonAbstract:Abstract The main components of Asselian through Artinskian Conodont faunas found around the world are basically the same, and the provincialism is indicated only by less common endemic elements such as Gondolelloides and New Genus A Henderson in North Pangea, Sweetognathus bucaramangus around the equator and Vjalovognathus in eastern Gondwana. Provincialism is marked by differences at the species level of Mesogondolella, Neostreptognathodus and Sweetognathus during the Kungurian, and becomes very distinct with differences at the genus level during the Guadalupian and Lopingian. Three provinces of Permian Conodonts, referred to as the North Cool Water Province (NCWP), the Equatorial Warm Water Province (EWWP) and the peri-Gondwana Cool Water Province (GCWP), are recognized. The NCWP is marked by Gondolelloides in the early Cisuralian, dominance of Neostreptognathodus and no or rare Sweetognathus in the late Cisuralian, dominance of Merrillina and Mesogondolella and absence of Sweetognathus in the Guadalupian, and dominance of Merrillina and Mesogondolella and absence of Iranognathus in the Lopingian. The EWWP is characterized by the absence of Gondolelloides and Vjalovognathus in the Cisuralian, abundance of Sweetognathus and Pseudosweetognathus in the Kungurian (late Cisuralian), Jinogondolella and Sweetognathus in the Guadalupian, and Clarkina and Iranognathus in the Lopingian. The GCWP is marked by Vjalovognathus, Merrillina in the Cisuralian, Vjalovognathus, Merrillina and Mesogondolella in the Guadalupian, and Vjalovognathus and Merrillina in the Lopingian. Mixed faunas are recognized in regions bordering between the EWWP and GCWP including Western Timor during the Artinskian, Pamirs during the Kungurian and the Salt Range during the Guadalupian and Lopingian. Three different Conodont zonations are proposed, one for each of the three Conodont provinces. Four potential horizons for inter-provincial correlation of Permian Conodonts are recognized. They are in ascending order: (1) the first appearance of Sweetognathus whitei, which is closely related to the last occurrence of Carboniferous-type Conodonts such as Streptognathodus and Adetognathus; (2) the first appearance of Neostreptognathodus pequopensis; (3) the base of the Jinogondolella nankingensis Zone; and (4) the base of the Clarkina postbitteri–Iranognathus erwini Zone. The spatial and temporal distribution pattern of Permian Conodonts suggests that temperature is the primary controlling factor. Evolution of Permian Conodont provincialism reveals a glaciation during the Asselian and Sakmarian, a global warming during the Artinskian, a climate cooling in North Pangea during the Kungurian, a continuation of Kungurian climate trends in the Guadalupian, a relatively minor warming during the Wuchiapingian, a returned cooling in the Changhsingian and Lower and Middle Griesbachian, and a global warming in the Late Griesbachian, which ended the Permian Conodont lineage.
Sylvain Richoz - One of the best experts on this subject based on the ideXlab platform.
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allometry in anisian middle triassic segminiplanate Conodonts and its implications for Conodont taxonomy
Palaeontology, 2016Co-Authors: Yanlong Chen, Thomas A Neubauer, Leopold Krystyn, Sylvain RichozAbstract:Conodonts are a clade of chordates and are valuable indicator fossils for biostratigraphy. The segminiplanate (neogondolelliform) Conodonts represent a major morphological group ranging from upper Carboniferous to Upper Triassic marine sediments. However, the morphological similarity of segminiplanate P 1 elements generates problems for taxonomy, especially in the Permian and Triassic clades. This paper represents the first study of morphological variation in Triassic segminiplanate Conodonts using a geometric morphometric approach. The laminar microstructures observed in Conodont cross-sections indicate that, within our analysed specimens, smaller Conodonts with fewer laminae are generally from an earlier ontogenetic stage while larger Conodonts with more laminae are from a later stage of ontogeny. Using linear regressions between relative warp scores from both upper and lateral views and Conodont length, we demonstrate strongly allometric growth patterns for the species Paragondolella bifurcata Budurov & Stefanov. Our results indicate that the species-group taxon Pg. praeszaboi bystrickyi (Kovacs et al.) is an early growth stage of Pg. bifurcata and thus synonymous. We suggest that the allometry of Conodonts should be considered seriously, especially when there are numerous transitional morphologies between large- and small-sized Conodonts. Reconstructing the ontogenetic series and using larger-sized Conodonts within the numerous transitional morphologies in the population of a rock sample for the definition of new species are suggested for future studies.
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Early Triassic Conodonts of Jiarong, Nanpanjiang Basin, southern Guizhou Province, South China
Journal of Asian Earth Sciences, 2015Co-Authors: Yanlong Chen, Sylvain Richoz, Chunbo Yan, Haishui Jiang, Xulong Lai, Xiaodan Liu, Lina WangAbstract:Abstract Jiarong (Huishui County, Guizhou Province, South China) is a key locality for the study of the Early Triassic recovery after the end-Permian mass extinction. The size reduction of Conodonts at the Smithian/Spathian transition was first documented in Jiarong, and it is also a locality that contributes to the documentation of the Early Triassic paleo-seawater temperatures. In the Jiarong sections, thirteen Conodont zones were identified for the Early Triassic; in ascending order, they are Hindeodus parvus Zone, Hindeodus sosioensis Zone, Clarkina krystyni Zone, Neoclarkina discreta Zone, Neospathodus cristagalli–Eurygnathodus costatus assemblage zone, Novispathodus waageni eowaageni Zone, Novispathodus waageni waageni Zone, Discretella discreta Zone, Pachycladina–Parachirognathus assemblage zone, Novispathodus pingdingshanensis Zone, Icriospathodus collinsoni Zone, Triassospathodus homeri Zone, Triassospathodus triangularis Zone. These Conodont zones in the Jiarong sections improve the global correlation of Early Triassic sections and also provide better regional age constraints in an area that is important for studies of recovery from the extinction. Based on the first appearance of Nv. waageni eowaageni, the Induan/Olenekian boundary is recognized at 3.6 m above the base of the Jiarong III Section. The dominance of blade-shaped (segminate) Conodonts was replaced by gondola-shaped (segminiplanate) Conodonts twice; the first time was in the late Griesbachian, and the second time was in the early Spathian. The dominance of segminiplanate Conodonts probably indicates that the deeper seawater environment became more oxygenated during the late Griesbachian and early Spathian for short time intervals, as it is believed that the Griesbachian segminiplanate Conodonts favored deeper oxygenated water habitats. A new genus, Spathogondolella gen. nov., and a new species, Spathogondolella jiarongensis sp. nov., have been recognized.