Detrital zircon U-Pb geochronology of the Sierra de Santa Rosa Formation, Sonora, Mexico, and implications for an Early Jurassic retroarc basin

Abstract

A succession of Triassic to Jurassic strata occurs in the vicinity of Caborca, Mexico, where the Antimonio, Río Asunción, and Sierra de Santa Rosa Formations contain a nearly continuous marine section deposited in previously reported shallow basin environments. The Sierra de Santa Rosa Formation is known to be Early Jurassic, but with an 18 m.y. uncertainty in age. Here we establish the ages of the three members of the Sierra de Santa Rosa Formation as early Sinemurian to middle Toarcian. Detrital zircon U-Pb geochronology from a set of 2334 grains along with ammonite zonation is used to establish depositional ages and to support the interpretation of the formation as being deposited in a retroarc basin. We find 2 zircon populations of 199 Ma and 192 Ma that mark the onset of Early Jurassic magmatic activity in the formation. Older Neoproterozoic and Early Devonian populations not attributable to local sources imply a robust Early Jurassic exchange with southwestern Laurentian eolianites. Here we also establish the ages of three fossiliferous units containing solitary and colonial corals in the Sierra de Santa Rosa Formation. The end-Triassic mass extinction decimated coral reefs worldwide and reports of Early Jurassic corals have been particularly rare in North America. The ages indicate an earlier regional recovery for North American corals than previously proposed; this has implications for understanding postextinction reef recovery.

Quantifying the Link Between the Detrital Zircon Record and Tectonic Settings

“…Of these, 1,201 samples were modern sediment (e.g., Campbell & Allen, 2008; Garzanti et al., 2016, 2018; Ibañez‐Mejia et al., 2018; Jacobs et al., 2017; MacDonald et al., 2013; Parra‐Avila et al., 2016; Pepper et al., 2016; Zhong et al., 2017) such that their depositional ages are clearly defined. EDAs in other 4,860 samples were obtained based on various pieces of evidence, including micropaleontology, paleontology, biostratigraphy (e.g., Blum et al., 2018; Bootes et al., 2019; Clift et al., 2019; Hodges et al., 2017; Jaeger et al., 2014; Leary et al., 2020; Zhang et al., 2018), U‐Pb or 40 Ar/ 39 Ar dating of tuffs or volcanic ash deposits (e.g., Abdullayev et al., 2018; Amidon et al., 2017; Kimbrough et al., 2015; Viglietti et al., 2018; Zhang et al., 2019), magnetostratigraphy (e.g., Abdullayev et al., 2018; Amidon et al., 2017; Clift et al., 2019; Kimbrough et al., 2015; Koshnaw et al., 2020; Zhang et al., 2018), depositional facies analysis and stratigraphy (Olierook et al., 2019), and geologic maps (e.g., Hart et al., 2016). EDAs of 2,468 samples in the data set obtained by estimated age intervals (e.g., Abdullayev et al., 2018; Amato et al., 2013; Bootes et al., 2019; Koshnaw et al., 2020) or the stratigraphy of deposition (e.g., to stage stratigraphy) (e.g., Andersen et al., 2016; Craddock et al., 2021; Leary et al., 2020; Lundmark et al., 2014), which were converted to absolute ages as EDAs using the middle of the age intervals and the ICS International Chronostratigraphic Chart (Cohen et al., 2013) in the data set of Puetz & Condie.…”

Ammonoid biostratigraphy and paleobiogeography of Lower Jurassic sections from Sonora (northwest Mexico) and their tectonic implications

“…Consequently, the tectonic setting of the El Antimonio basin of Sonora has been interpreted as a fore-arc basin (Stanley and González-León, 1995;González-León, 1997;González-León et al, 2005). Alternatively, a retroarc setting was proposed to better explain the presence of old detrital zircon populations derived from the North American craton (Hodges et al, 2017). Terranes, defined as distinct tectonostratigraphic units, are key elements of modern Cordilleran tectonic models (Coney et al, 1980) and numerous terranes have been accreted to the western Laurentian continental margin since the late Paleozoic (Colpron et al, 2007).…”

“…Apart from biostratigraphy, U-Pb dating of detrital zircons from sandstone beds in the Sierra de Santa Rosa Formation has been used to obtain independent numeric age constraints on 10 samples (González-León et al 2005;2009;Hodges et al, 2017). Clearly useful to identify provenance of the sediments, the youngest age group in volcanically derived zircons was also interpreted as the depositional age of the sandstone beds, assuming coeval arc volcanic activity nearby (Hodges et al, 2017).…”

“…Apart from biostratigraphy, U-Pb dating of detrital zircons from sandstone beds in the Sierra de Santa Rosa Formation has been used to obtain independent numeric age constraints on 10 samples (González-León et al 2005;2009;Hodges et al, 2017). Clearly useful to identify provenance of the sediments, the youngest age group in volcanically derived zircons was also interpreted as the depositional age of the sandstone beds, assuming coeval arc volcanic activity nearby (Hodges et al, 2017). However, this approach can only be followed with caution, as evidenced by one sample from the oldest Jurassic part of the Sierra del Álamo section that only yielded pre-Jurassic detrital zircons (González-León et al, 2009), suggesting that a conservative interpretation would permit determination of a maximum depositional age.…”

“…4), as an improvement over the lithologic correlation of the sections (Hardy, 1981), partly by emphasizing that the youngest detrital grains provide only maximum age constraints rather than true depositional ages, as demonstrated by the oldest Jurassic sample from Sierra del Álamo. All three samples yielding a 180 Ma cluster of youngest detrital zircons (Hodges et al, 2017) originate from the upper member in the area northeast of Rancho San Carlos, several km away from the measured sections and separated from them by a thrust fault (Hardy, 1981). The uppermost part of the formation here also differs in thickbedded, shallow marine limestone facies with abundant reef-forming corals but lacking ammonoids.…”