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Smithian ammonoid faunas from northeastern Nevada: Implications for Early Triassic biostratigraphy and correlation within the western USA basin
Abstract
Intensive sampling of the lower portion of the Thaynes Group within the Palomino Ridge area (northeastern Nevada) yielded abundant and well-preserved Smithian (Early Triassic) ammonoid faunas. Ammonoid taxonomy and a detailed biostratigraphy for this locality are reported herein. One new genus (Palominoceras) and one new species (?Pseudosageceras bullatum) are described. Additionally, based on new data from Palomino Ridge and previous data from neighboring localities in Utah, we porvide here the first quantitative Smithian ammonoid biochronological scheme for the western US basin. This new zonation is based on the Unitary Associations (UA) method. The biochronical sequence comprises five unitary association zones that can be correlated with other localities from the Northern Indian Margin (Salt Range, Pakistan, Spiti, northern India and Tulong, South Tibet). Three unitary association zone (UAZ1, UAZ2 and UAZ3) are defined for the early Smithian, one (UAZ4) spans the entire middle Smithian and one (UAZ5) signifies the first part of the late Smithian. Finally, a hypothetical UAZ6 would represent the second part of the late Smithian.
... The Smithian substage was also proposed by Tozer (1965Tozer ( , 1967 and initially comprised two ammonoid zones in Arctic Canada, Euflemingites romunderi Zone and Wasatchites tardus Zone. In recent decades, Smithian ammonoids have been intensively sampled and studied in the western USA basin Jattiot et al., 2017;Jenks and Brayard, 2018;Brayard et al., 2020Brayard et al., , 2021, the Salt Range (Brühwiler et al., , 2012c, Spiti (Brühwiler et al., 2010c(Brühwiler et al., , 2012b, North Vietnam (Shigeta et al., 2014), South Primorye (Shigeta et al., 2009;Zakharov et al., 2013;Zakharov et al., 2021), and South China Dai et al., 2021). Among these sites, the Salt Range and Spiti show the most complete Smithian ammonoid successions so far, comprising 14 UAZs (Brühwiler et al., 2010a. ...
... Compared with classical interval zones, which are based on the first and last occurrences of specific taxa, the UA method utilizes the associations and superpositions of a set of taxa and provides more robust discrete biozones with a higher lateral reproducibility (Guex et al., 2016). The UA method has therefore been used in many regional and global biostratigraphic works (Brühwiler et al., 2010a;Ware et al., 2015;Klein and Korn, 2016;Jattiot et al., 2017;Xiao et al., 2018;Wu et al., 2020). The UA method implemented in PAST 3.0 (Hammer et al., 2001) was used in this study. ...
... The western USA basin is one of the key regions for Smithian ammonoids. It has been studied since the beginning of the last century (Hyatt and Smith, 1905;Smith, 1932;Kummel and Steele, 1962) and recently provided new ammonoid findings Brayard et al., 2013;Jattiot et al., 2017;Jenks and Brayard, 2018;Brayard et al., 2020Brayard et al., , 2021. Middle and late Smithian ammonoid faunas are well documented, while early Smithian assemblages are less well-known owing to the lack of well-preserved specimens (Fig. 22). ...
Ammonoids are key fossil indexes for Triassic biochronology, as all Triassic stages and substages were initially defined on ammonoid faunas. In recent decades, the temporal resolution of ammonoid biostratigraphical scales for the Early Triassic has been greatly improved. However, many uncertainties in zones correlation and superpositions remain, mainly due to sampling heterogeneities, preservation biases, and faunal endemicity. In this work, we present the first comprehensive Early Triassic ammonoid zonation from South Tibet, China, a previously poorly investigated region. Ammonoids were sampled from the Kangshare Formation at four sections (Selong, Paizi, Qubu and Xialong), representing a total of 140 species, ranging from the Griesbachian to the Smithian. These new robust data allow the construction of a high-resolution biostratigraphy using the Unitary Association (UA) method. A total of 22 Unitary Association zones (UAZs) were recognized, including two UAZs for the Griesbachian, nine for the Dienerian, and 11 for the Smithian. Then, we integrated data from neighboring basins, i.e., Spiti (India) and the Salt Range (Pakistan), and the new data from South Tibet to construct synthetic, laterally reproducible Dienerian-Smithian ammonoid UAZs, which include 12 UAZs for the Dienerian and 16 UAZs for the Smithian. Based on the newly obtained data and high-resolution biostratigraphic scales, we revised global correlations known for the ammonoid biostratigraphy in the Griesbachian, Dienerian and Smithian. Finally, the high-resolution ammonoid zones are generally in agreement with conodont zones in defining stage/substage boundaries. They also provide a robust and accurate time calibration for Early Triassic carbon isotope trends and temperature changes.
... Early Triassic biostratigraphical scales based on ammonoids (Smith, 1932;Spath, 1934) and produced prior to the beginning of the 2010s (Tozer, 1994;Ermakova, 2002;Brayard and Bucher, 2008) have often treated the late Smithian as a unique biostratigraphic entity with numerous genera of the family Prionitidae, such as Anasibirites and Wasatchites, considered as typical of this time interval. However, in the last decade, many works have shown that the late Smithian can be subdivided into at least two parts (Brühwiler et al., 2010a(Brühwiler et al., , 2011(Brühwiler et al., , 2012aBrayard et al., 2013;Jattiot et al., 2017;Jenks and Brayard 2018;see Jenks et al., 2015 for a summary of late Smithian global correlations). The lower part corresponds to a marked worldwide dominance of prionitids, a species-rich family (Jattiot et al., 2016), associated with a few xenoceltitid species (e.g., Xenoceltites subevolutus) and rare occurrences of surviving arctoceratids, inyoitids, galfettitids and palaeophyllitids in some places (Brühwiler et al., 2012a, b;Shigeta and Kumagae, 2015;Smyshlyaeva et al., 2018;Jattiot et al., 2020;questionably in Tozer, 1994, andPiazza et al., 2017). ...
... The lower part corresponds to a marked worldwide dominance of prionitids, a species-rich family (Jattiot et al., 2016), associated with a few xenoceltitid species (e.g., Xenoceltites subevolutus) and rare occurrences of surviving arctoceratids, inyoitids, galfettitids and palaeophyllitids in some places (Brühwiler et al., 2012a, b;Shigeta and Kumagae, 2015;Smyshlyaeva et al., 2018;Jattiot et al., 2020;questionably in Tozer, 1994, andPiazza et al., 2017). In most regions (see Zakharov et al., 2013Zakharov et al., , 2021, for a putative exception regarding late Smithian ammonoid assemblages from deep-water facies of South Primorye, which enigmatically appear relatively dissimilar and more diverse than elsewhere), the Prionitidae abruptly disappeared prior to the onset of the upper part that is characterized by the occurrence of assemblages, in which latest Smithian representatives of xenoceltitids (Glyptophiceras, Xenoceltites, Condensoceras) and hedenstroemiids (e.g., Pseudosageceras augustum, P. plicatum, ?P. bullatum) coexist (Brühwiler et al., 2012a;Jattiot et al., 2017;Jenks and Brayard, 2018). Very few of these taxa survived the SSB, but at least two other families (the proptychitids and palaeophyllitids) virtually persisted into the Spathian (Brayard and Bucher, 2015; see also Zakharov et al., 2021, for another surviving scheme based on a different phylogenetic conception). ...
... Based on these restricted basinal occurrences, and especially on the presence of P. augustum, Jattiot et al. (2017) postulated the existence of a regional Unitary Association Zone (their UAZ6) representing the second part of the late Smithian. To corroborate the existence of this zone throughout the western USA basin, representatives of P. augustum, Condensoceras or Glyptophiceras must therefore be reported from outside Nevada. ...
The late Smithian extinction represents a major event within the Early Triassic. This event generally corresponds to a succession of two, possibly three successively less diverse, cosmopolitan ammonoid assemblages, which when present, provide a robust biostratigraphic framework and precise correlations at different spatial scales. In the western USA basin, known occurrences of latest Smithian taxa are rare and until now, have only been documented from northeastern Nevada. Based on these restricted basinal occurrences, a regional zone representing the latest Smithian was postulated but not corroborated, as representative taxa had not yet been reported from outside Nevada. Here we document two new ammonoid assemblages from distant localities in northern Utah, overlying the late Smithian Anasibirites beds and characterized by the unambiguous co-occurrence of Xenoceltites subevolutus and Pseudosageceras augustum. The existence of a latest Smithian zone in the western USA basin is therefore validated, facilitating the identification of the Smithian/Spathian boundary and intra-basin correlation. This zone also correlates with the latest Smithian zone recognized from southern Tethyan basins. Additionally, these new data support other observed occurrences of Xenoceltites subevolutus throughout most of the late Smithian.
... The Smithian ammonoid biostratigraphy is presently the most wellconstrained one among the four substages of the Early Triassic, benefiting from several recent extensive bed-by-bed fieldworks and detailed taxonomic revisions in the last decade Shigeta et al., 2009Shigeta et al., , 2014Brühwiler et al., 2010bBrühwiler et al., , 2010cBrühwiler et al., , 2011Brühwiler et al., , 2012aBrühwiler et al., , 2012bBrühwiler et al., , 2012cBrayard et al., 2013;Jattiot et al., 2016Jattiot et al., , 2017Jattiot et al., , 2020Jenks and Brayard, 2018). Based on these works, the Smithian can be further subdivided into three parts: early, middle and late (Brühwiler et al., 2010a). ...
... Two zones correspond to the middle Smithian: the Flemingites rursiradiatus and Owenites koeneni zones, and the other two are late Smithian: the Anasibirites kingianus and Xenoceltites variocostatus zones, in ascending order (Fig. 3). This succession is nearly identical to the one proposed by Brayard and Bucher (2008), except their initial A. multiformis beds, which are here further subdivided into two distinct zones, i.e., the lower A. kingianus Zone and the upper X. variocostatus Zone, which can be correlated worldwide (e.g., Jenks et al., 2015;Jattiot et al., 2017). ...
... The Xenoceltites variocostatus Zone corresponds to the second zone of the late Smithian and is characterized by the association of X. variocostatus, Pseudosageceras augustum, and Condensoceras youngi. These taxa are also rather cosmopolitan and the X. variocostatus Zone can therefore be correlated worldwide Shigeta et al., 2014;Jattiot et al., 2017;Jenks and Brayard, 2018). The Xenoceltites variocostatus Zone correlates with the conodont UAZ5 at Shanggang (Widmann et al., 2020). ...
The biotic recovery following the Permian/Triassic boundary mass extinction was influenced by several secondary extinctions during the Early Triassic, of which the late Smithian crisis is the most severe known for some nekto-pelagic organisms such as ammonoids. The Smithian-Spathian transition is characterized by successive global biotic and environmental changes, including a dramatic positive carbon isotopic excursion, oceanic anoxia and a cooling event beginning in the late Smithian. However, the tempo, modalities and the causal relationships among these various events remain poorly constrained. Here we synthesized paleontological, sedimentological, and geochemical data from three sections (Motianling, Nafang, and Shanggang) within the Nanpanjiang Basin, representing platform slop to basinal deposits spanning the Smithian/Spathian boundary. High-resolution analyses of thin sections show a sudden decrease in richness and abundance of fossil grains at the middle/upper Smithian boundary in all three sections, coinciding with the onset of a positive shift in δ¹³Ccarb. It also slightly precedes the beginning of the late Smithian cooling. At Shanggang, a change in dominance from bivalve-rich to ostracod-rich strata is also recorded at the middle/upper Smithian boundary. Overall, our results therefore indicate that a first major biotic crisis and turnover happened during the beginning of the late Smithian in the Nanpanjiang Basin, rather than around the Smithian/Spathian boundary. Complementary analyses on pyrite framboid size indicate that these observed biotic changes are concurrent with oxygen depletion in the studied sections, supporting the hypothesis that oceanic anoxia also played an important role in the late Smithian crisis in combination with climate cooling and oceanic acidification.
... Conodonts also indicate a late Smithian age for these beds (Lucas et al., 2007b;Olivier et al., 2014). Typical latest Smithian ammonoid assemblages in which e.g., Pseudosageceras augustum, Xenoceltites and Glyptophiceras can co-occur (Brayard et al., 2013;Jattiot et al., 2017Jattiot et al., , 2018Jenks and Brayard, 2018) have not yet been found in southwestern-most Utah, suggesting that a rapid regressive phase was probably already occurring at that time in this area. Age constraints for the base of the Sinbad Fm., i.e. the microbially-dominated part, are much vaguer due to, e.g., the paucity and poor preservation of conodonts (Paull and Paull, 1993). ...
... A total of eight ammonoid taxa were identified from the four studied localities. These are attributed to specific ammonoid zones permitting high-resolution correlation at a local to global scale (Brayard et al., 2009a(Brayard et al., , 2013Jenks et al., 2010Jenks et al., , 2015Jattiot et al., 2017;Jenks and Brayard, 2018). ...
... It co-occurs with Guodunites hooveri, which is abundant throughout the studied area. This taxon is restricted to the Inyoites horizon and is thus characteristic of the late middle Smithian in the southern part of the basin (Brayard et al., 2009a(Brayard et al., , 2013Stephen et al., 2010) and the top of the regional middle Smithian UAZ4 as defined by Jattiot et al. (2017). Although rare, Guodunites also occurs in late middle Smithian assemblages of the Owenites beds at Crittenden Springs, NE Nevada . ...
New Smithian (Early Triassic) ammonoid assemblages were sampled near the Utah/Arizona border. They provide several spatiotemporal constraints on the regional Sinbad Formation showing that the extent of the Smithian sea in the southwestern-most part of the western USA basin is larger than previously expected, reaching northern Arizona and an area just east of Kanab in Kane County, Utah. This southwestern-most excursion of the sea in the western USA basin is part of the third order Smithian transgression-regression cycle, which is well-documented worldwide. These new spatiotemporal constraints also indicate that the Sinbad Formation spans the late middle to early late Smithian time interval in the studied area. The observed transgressive trend corresponds to the warm temperatures of the middle-early late Smithian and the regressive trend to the cooling phase spanning the Smithian-Spathian transition. Thus, the Sinbad Formation and its marine deposits are the direct result of global climatic fluctuations and related sea-level changes that occurred from the late middle Smithian to the Smithian-Spathian transition. This highlights the importance of the Sinbad Formation in untangling local and global changes occurring around the late Smithian, and thus in overcoming a major obstacle to the understanding of the biotic recovery after the Permian/Triassic boundary mass extinction. This also indirectly confirms that the western USA basin is a key area containing essential information for the understanding of the Early Triassic events. The taxonomic richness of late middle Smithian assemblages is much lower in the studied area than in the more northern localities. However, the occurring taxa confirm the known regional to global distribution of Smithian ammonoids, witnessing the major global environmental changes from the middle Smithian to the early Spathian.
... Moreover, these authors showed that the rediversification and spatiotemporal distribution of ammonoids during the Early Triassic were likely constrained by successive, marked environmental fluctuations, particularly changes in oceanic temperatures. After Brayard et al.'s (2006Brayard et al.'s ( , 2007 work, which analyzed 181 Early Triassic ammonoid genera, there were 67 new genera erected for the Early Triassic Brühwiler et al. 2008Brühwiler et al. , 2010bBrühwiler et al. , 2012aShigeta et al. 2009;Guex et al. 2010;Ware et al. 2011;Brayard et al. 2013;Smyshlyaeva and Zakharov 2013;Jattiot et al. 2017;Jenks and Brayard 2018;Ware et al. 2018a,b). These recent advances largely improved our knowledge about Early Triassic ammonoid taxonomy and biostratigraphy. ...
... S1, S2). To reveal the impact of the late Smithian crisis on the biogeographic structure of the ammonoid, we adopted the subdivisions (early, middle, and late) proposed by Brühwiler et al. (2010a) for the Smithian and consequently used in many recent ammonoid studies (e.g., Brayard et al. 2013;Jattiot et al. 2017). The duration of each Smithian subunit was estimated by the mean of the estimated time duration of ammonoid unitary association zones (Brühwiler et al. 2010a), owing to the current absence of a radiometric age date for the middle/late Smithian boundary. ...
Cosmopolitanism occurred recurrently during the geologic past, especially after mass extinctions, but the underlying mechanisms remain poorly known. Three theoretical models, not mutually exclusive, can lead to cosmopolitanism: (1) selective extinction in endemic taxa, (2) endemic taxa becoming cosmopolitan after the extinction and (3) an increase in the number of newly originated cosmopolitan taxa after extinction. We analyzed an updated occurrence dataset including 831 middle Permian to Middle Triassic ammonoid genera and used two network methods to distinguish major episodes of ammonoid cosmopolitanism during this time interval. Then, we tested the three proposed models in these case studies. Our results confirm that at least two remarkable cosmopolitanism events occurred after the Permian–Triassic and late Smithian (Early Triassic) extinctions, respectively. Partitioned analyses of survivors and newcomers revealed that the immediate cosmopolitanism event (Griesbachian) after the Permian–Triassic event can be attributed to endemic genera becoming cosmopolitan (model 2) and an increase in the number of newly originated cosmopolitan genera after the extinction (model 3). Late Smithian cosmopolitanism is caused by selective extinction in endemic taxa (model 1) and an increase in the number of newly originated cosmopolitan genera (model 3). We found that the survivors of the Permian–Triassic mass extinction did not show a wider geographic range, suggesting that this mass extinction is nonselective among the biogeographic ranges, while late Smithian survivors exhibit a wide geographic range, indicating selective survivorship among cosmopolitan genera. These successive cosmopolitanism events during severe extinctions are associated with marked environmental upheavals such as rapid climate changes and oceanic anoxic events, suggesting that environmental fluctuations play a significant role in cosmopolitanism.
... Mullen (1985) reported the occurrence of Griesbachian (early Induan, Early Triassic) conodonts in the Dinwoody Formation and middle-late Spathian-aged (late Olenekian, Early Triassic) conodonts in the unnamed siltstone unit and Thaynes Group, meaning that part of the Dienerian, the entire Smithian and part of the lower Spathian were locally removed by thrust faulting and erosion. For instance, the iconic middle Smithian (lower Olenekian, Lower Triassic) regional marker beds, the Meekoceras beds (e.g., Jattiot et al. 2017;Jenks and Brayard 2018), are consistently absent from the studied area. Our recent field investigations agree with Mullen's (1985) conclusions and the discovery of successive ammonoid faunas in the Thaynes Group of Immigrant Canyon confirms a middle-late Spathian age (late Olenekian, Early Triassic) for the lower part of this unit (see Smith et al. 2021 for a schematic preliminary biostratigraphic zonation of the area). ...
Knowledge of the early evolution of post-Palaeozoic crinoids mainly relies on the well-preserved and abundant material
sampled in Triassic Konservat-Lagerstätten such as those from the Anisian Muschelkalk (Middle Triassic) of the
Germanic Basin. These crinoid-bearing Lagerstätten have been central to understanding the rapid evolution and diversification
of crinoids after the dramatic Permian/Triassic Boundary biological crisis that led the class to near-extinction.
The Encrinida are the emblematic crinoids of the Triassic. They are mainly known from rich fossil deposits where their
abundant ossicles are at the origin of the extensive crinoidal limestone beds of the German Upper Muschelkalk. So far,
they were first represented in the Middle Triassic by the family Dadocrinidae and genus Dadocrinus. In the present work,
a new species Dadocrinus montellonis sp. nov., is described based on a well-preserved, almost complete articulated specimen
from the Spathian (Lower Triassic) of Nevada (USA). The new species differs from other species of Dadocrinus by
its palaeobiogeographic position but also by its earlier stratigraphic occurrence and ancestral morphology. It represents
the first reported occurrence of Dadocrinus outside the Germanic Basin prior to the Middle Triassic and also the oldest
firm evidence of its presence in the Early Triassic (middle–late Spathian). This discovery sheds new light on the origin
of post-Palaeozoic crinoids. It suggests a much wider distribution than commonly assumed for the genus Dadocrinus
and implies that the first dadocrinids originated either in the Panthalassa or Tethys oceans, and then dispersed over long
distances in a relative short period of time.
... Usually, faint ribs are associated with compressed apertures and involute coiling, while strong ribs are associated with depressed apertures and evolute coiling. These patterns of intraspecific variation have been observed in Triassic [68][69][70][71][72][73][74][75][76][77], in Jurassic [66] and in Cretaceous [78] ammonoids. As these patterns of covariation have been observed in phylogenetically distant ammonoids at several different time periods, they represent evolutionary convergences that stem from the developmental constraints imposed by accretionary growth [19,[79][80][81][82][83]. ...
Background:
Many pathologies that modify the shell geometry and ornamentation of ammonoids are known from the fossil record. Since they may reflect the developmental response of the organism to a perturbation (usually a sublethal injury), their study is essential for exploring the developmental mechanisms of these extinct animals. Ammonoid pathologies are also useful to assess the value of some morphological characters used in taxonomy, as well as to improve phylogenetic reconstructions and evolutionary scenarios.
Results:
We report on the discovery of an enigmatic pathological middle Toarcian (Lower Jurassic) ammonoid specimen from southern France, characterized by a pronounced left-right asymmetry in both ornamentation and suture lines. For each side independently, the taxonomic interpretations of ornamentation and suture lines are congruent, suggesting a Hildoceras semipolitum species assignment for the left side and a Brodieia primaria species assignment for the right side. The former exhibits a lateral groove whereas the second displays sinuous ribs. This specimen, together with the few analogous cases reported in the literature, lead us to erect a new forma-type pathology herein called "forma janusa" for specimens displaying a left-right asymmetry in the absence of any clear evidence of injury or parasitism, whereby the two sides match with the regular morphology of two distinct, known species.
Conclusions:
Since "forma janusa" specimens reflect the underlying developmental plasticity of the ammonoid taxa, we hypothesize that such specimens may also indicate unsuspected phylogenetic closeness between the two displayed taxa and may even reveal a direct ancestor-descendant relationship. This hypothesis is not, as yet, contradicted by the stratigraphical data at hand: in all studied cases the two distinct taxa correspond to contemporaneous or sub-contemporaneous taxa. More generally, the newly described specimen suggests that a hitherto unidentified developmental link may exist between sinuous ribs and lateral grooves. Overall, we recommend an integrative approach for revisiting aberrant individuals that illustrate the intricate links among shell morphogenesis, developmental plasticity and phylogeny.
The ammonoid genus Arctoceras (Hyatt) occurs across all palaeolatitudes, and is a key genus for middle Smithian biostratigraphical correlations globally. In this study, intraspecific variations in conch morphology, ornamentation and allometry are examined in relation to stratigraphic position. Arctoceras is the most abundant ammonoid genus in the middle Smithian of Svalbard. Originally, seven Arctoceras species were described from Svalbard. Later, as the importance of intraspecific variation was recognized, six of the Arctoceras species from Svalbard were treated as junior synonyms of Arctoceras blomstrandi (Lindström). Yet, the variations in A. blomstrandi conch morphology remain poorly quantified and the dependence on stratigraphic position, unknown. We quantify the intraspecific variation in conch morphology, ornamentation and allometry in relation to stratigraphy of the Svalbard Arctoceras. The results support the assignment of all Arctoceras morphotypes from Svalbard to a single species A. blomstrandi. The new data allow for an updated species description and open the way for the use in biostratigraphy of the endmember morphology A. blomstrandi var. costatus. We document consistent changes in conch morphology and ornamentation in the studied stratigraphic interval, with a distinct shift towards more evolute and ornate conchs in the top of the interval. The trends in the strength of ornamentation are partly explained by covariation with conch morphology (Buckman's law). The most marked shift in the conch morphology and allometric development of A. blomstrandi coincides with the onset of the positive carbon isotope excursion at the end of the middle Smithian, but pre‐dates the mid–late Smithian cooling of the sea surface.
In the wake of the Mesozoic, the Early Triassic (~251.95 Ma) corresponds to the aftermath of the most severe mass extinction of the Phanerozoic: the end-Permian crisis, when life was nearly obliterated (e.g., 90% of marine species disappeared). Consequences of this mass extinction are thought to have prevailed for several millions of years, implying a delayed recovery lasting the whole Early Triassic, if not more.Several paradigms have been established and associated to a delayed biotic recovery scenario expected to have resulted from harsh and deleterious paleoenvironments. These paradigms include a global anoxia in the marine realm, a “Lilliput” effect, and the presence of “disaster” taxa and “anachronistic” facies. However, recent works have shown a more complex global scheme for the Early Triassic recovery, and that a reevaluation of these paradigms was needed. Especially, new data from the western USA basin were critical in re-addressing these paradigms.The western USA basin is the result of a long tectono-sedimentary history that started 2 Gyr ago by the amalgamation of different lithospheric terranes forming its basement. A succession of orogenies and quiescence phases led to the formation of several successive basins in the studied area, and traces of this important geodynamical activity are still present today. The Sonoma orogeny occurred about 252 Ma in response to the eastward migration of drifting arcs toward the Laurentian craton. As a result, compressive constrains lead to the obduction of the Golconda Allochthon above the west-Pangea margin in present-day Nevada. Emplacement of this topographic load provoked the lithosphere flexuration beneath present-day Utah and Idaho to form the Sonoma Foreland Basin (SFB) studied in this work.The SFB record an excellent fossil and sedimentary record of the Early Triassic. A relatively high and complex biotic diversity has been observed there leading to describe a rapid and explosive recovery for some groups (e.g., ammonoids) in this basin after the end-Permian crisis. The sedimentary record is also well developed and has been studied extensively for a long time. Overall, these studies notably documented a marked difference between the northern and southern sedimentary succession within the basin, whose origin was poorly understood.This work therefore aims to characterize the various depositional settings in the Early Triassic SFB, as well as their paleogeographical distribution. Their controlling factors are also studied based on an original integrated method using sedimentological, paleontological, geochemical, geodynamical, structural and cartographic analyses. Aside the fossil and sedimentary discrepancy between the northern and the southern parts of the SFB, geochemical analyses provide new insights supporting this N/S dichotomy. This study also questions the validity of the geochemical signal as a tool for global correlation, as it appears to mainly reflect local forcing parameters.The geodynamical framework of the SFB was also investigated along with a numerical modelling of the rheological behavior of the basin. This work distinguishes the northern and southern parts of the basin based on markedly distinct tectonic subsidence rates during the Early Triassic: ~500 m/Myr in the northern part vs ~100m/Myr in the southern part. Origin of this remarkable difference is found in inherited properties of the basin basement itself. Indeed, different ages and therefore, rheological behaviors (i.e., rigidity to deformation and flexuration) of the basement lithospheric terranes act as a major controlling factor over the spatial distribution of the subsidence, and therefore of the sedimentary deposition. The lithosphere heritage is thus of paramount importance in the formation, development and spatio-temporal evolution of the SFB.This work leads to a new paleogeographical representation of the Sonoma Foreland Basin and its multi-parameter controlling factors (...).
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