Making the Southern Margin of Laurentia themed issue Stratigraphy and age of Upper Jurassic strata in north-central Sonora, Mexico: Southwestern Laurentian record of crustal extension and tectonic transition David J. Mauel1,*, Timothy F. Lawton1, Carlos González-León2, Alexander Iriondo3, and Jeffrey M. Amato1 1Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA 2Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de México, Apartado Postal 1039, Hermosillo , Sonora, 83000, México 3Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla Querétaro, 76230, México ABSTRACT derived from Middle Jurassic arc rocks region, refi ne temporal limits of Upper Jurassic and exhumed Caborcan basement, Paleo- strata and the unconformities bounding them, Stratigraphy, sedimentology, and geo- zoic–Lower Jurassic sedimentary cover, and and shed light on the stratigraphic relationships chronology of the Upper Jurassic Cucurpe Lower Cretaceous intermediate volcanic of the Glance Conglomerate, a synorogenic unit Formation in north-central Sonora, Mexico, rocks. Revised stratigraphy of the Cucurpe- inferred to establish the locations and timing of provide new insights into Late Jurassic rift- Tuape region indicates that several con- extensional basins in the region. This study was ing along the southwestern margin of Lau- glomeratic units, formerly interpreted as carried out within a main study area and within rentia. The Cucurpe Formation is the fi ll of Late Jurassic pull-apart basin deposits, are a broader general study area (Fig. 1) where the Altar-Cucurpe Basin. This basin devel- not of Late Jurassic age. comparative reconnaissance geology was com- oped upon attenuated crust of the Triassic– pleted. The main study area is located ~13 km Middle Jurassic continental arc and was INTRODUCTION northwest of the village of Cucurpe along the part of the Arivechi-Cucurpe seaway; a nar- eastern fl ank of Sierra de Cucurpe, where an row marine embayment oriented parallel to extensive Lower Jurassic to Lower Cretaceous The Late Jurassic marked changing interplate and located west of the Chihuahua trough. section is exposed. Although structurally dis- dynamics in the Cordillera of the southwestern The Cucurpe Formation unconformably turbed, this section is intact and contains a com- U.S. and northwestern Mexico. Incipient open- overlies Middle Jurassic arc assemblages plete section of the Cucurpe Formation. ing of the Gulf of Mexico during the breakup and represents upward-coarsening marine of Pangaea was coincident with Late Jurassic prodeltaic deposits. New U-Pb zircon geo- METHODS continental rifting and marine incursion in chronology and a Kimmeridgian ammonite north-central Sonora. Opinions vary as to the Research in the main study area included (Idoceras cf. I. densicostatum) constrain its dominant tectonic mechanisms that initiated geologic mapping at a scale of 1:25,000, strati- age to between ca. 158 and 149 Ma. Detrital this rifting. Some workers infer that exten- graphic measurement, U-Pb zircon geochronol- zircon ages from the unconformably over- sion resulted from rollback of the subduct- ogy, and petrography of the Cucurpe Formation lying Lower Cretaceous Bisbee Group indi- ing oceanic slab (e.g., Lawton and McMillan, and basal strata of the overlying Bisbee Group. cate a maximum depositional age of 139 ± 1999; Dickinson and Lawton, 2001b), whereas In the general study area, local mapping and 2 Ma (2σ error), demonstrating a hiatus of others infer transtensional extension associated comparative stratigraphy were accompanied by at least 10 m.y. between Jurassic and Cre- with the Mojave-Sonora megashear (MSM; compilation of previous mapping (Plate 2) to taceous strata. Detrital zircon ages and e.g., Anderson and Nourse, 2005; Busby et al., unify the stratigraphic nomenclature and iden- petrographic data indicate the provenance 2005). Mesozoic sedimentary successions tify problem areas. of Cucurpe Formation and lowermost Bis- exposed in the Cucurpe-Tuape region of north- Sandstone thin sections for point counts bee strata. The lower part of the Cucurpe central Sonora (Fig. 1, Plates 1–2) provide were selected on the basis of quality, minimal was derived dominantly from Middle Juras- details con cerning volcanic activity, basin sub- alteration, and grain size. Each thin section was sic volcano-sedimentary successions. The sidence, and basement uplift during this criti- stained with sodium cobaltinitrate. The Gazzi- upper part of the Cucurpe Formation was cal period of transition. Dickinson method was utilized for point count largely derived from syneruptive volcanic We present new data on the stratigraphy, sedi- analysis (Ingersoll et al., 1984; Zuffa, 1980). A material equivalent to the Ko Vaya vol- mentology, and age of Upper Jurassic strata of single operator performed all point counts with canic suite of southern Arizona and north- the Cucurpe Formation and review stratigraphi- a node spacing of 0.66 mm for medium-grained ern Sonora. Lowermost Bisbee strata were cally adjacent units of Middle Jurassic and Early sandstones and a node spacing of 0.99 mm for Cretaceous age. Upper Jurassic strata are signif- coarse-grained sandstones. Point count param- *Present address: Alaska Division of Geological icant because they record onset of major exten- eters, raw count data, and normalized modal & Geophysical Surveys, 3354 College Road, Fair- banks, Alaska 99709, USA; email: david.mauel@ sion and marine incursion into northern Sonora. percentages of framework grains are presented alaska.gov. Our data improve the lithostratigraphy of the in Supplemental Table 11. Geosphere; April 2011; v. 7; no. 2; p. 390–414; doi: 10.1130/GES00600.1; 13 fi gures; 2 tables; 2 plates; 2 supplemental tables. 390 For permission to copy, contact [email protected] © 2011 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/2/390/3714949/390.pdf by guest on 25 September 2021 Stratigraphy and age of Upper Jurassic strata in north-central Sonora, Mexico 113°W 8 10 111°W 0 50 100 km 2 Tucson 32°N MSM United States 10 32°N 19 Mexico Explanation Glance Conglomerate Nogales Ko Vaya suite upper Altar Cananea High Formation Cucurpe (Nourse, 2001) ? Formation SB Imuris A CA Papago domain Caborca Magdalenaa general 2 study area Mojave-Sonora MSM main SM and MSM megashear study approximate Gulf area Cucurpe area of Plate 2 of 30°N N EV California LC LT 30°N 113°W 111°WTuape Figure 1. Outcrops of strata known or inferred to be of Late Jurassic age in southern Arizona and northern Sonora (adapted from Tosdal et al., 1989). Rectangles indicate general and main study areas. Localities: A—Altar; CA—Cerros El Amol; EV—El Venado; LC—Rancho La Colgada; LT—Rancho La Tesota; SB—Sierra El Batamote; SM—Rancho San Martin. U-Pb geochronology was performed for 1σ level, and errors on igneous crystallization means of these groups were calculated using detrital zircons using the laser ablation multi- ages are reported at the 2σ level. Analytical Isoplot 3.0 (Ludwig, 2003). We employ the collector induced-coupled-plasma mass spec- results, age data, and global positioning system time scale of Walker and Geissman (2009). trometer (LA-MC-ICPMS) at the University (GPS) coordinates for each sample are included of Arizona. Geochronology on tuffs was com- in Supplemental Table 22. GPS coordinates use GEOLOGIC SETTING AND pleted at the Stanford/U.S. Geological Survey the 1927 North American Datum for Mexico. TECTONIC MODELS (USGS) facility using the sensitive high- Only detrital zircons in coherent age groups of resolution ion microprobe (SHRIMP). Sample three or more were considered representative Mesozoic tectonic events proposed for the preparation used standard mineral crushing and for obtaining maximum depositional ages due southwestern margin of Laurentia include large- separation techniques. Analytical errors asso- to problems that can arise from discordance scale sinistral truncation and translation (MSM), ciated with the LA-MC-ICPMS facility at the (e.g., Dickinson and Gehrels, 2009b). The continental arc magmatism, arc extension and University of Arizona are detailed elsewhere youngest coherent age groups from detrital zir- rifting, exotic arc or fringing arc accretion, post- (Gehrels et al., 2008). Errors on ages of indi- con analysis were determined using the Detrital rift thermal subsidence, and Late Cretaceous vidual detrital zircon grains are reported at the Age Pick program of Gehrels (2006). Weighted metamorphism and magmatism. The evidence for and existence of several of these events 1Supplemental Table 1. PDF file of Sandstone 2Supplemental Table 2. Excel fi le of SHRIMP data remain controversial (Molina-Garza and Iriondo, point count parameters. If you are viewing the PDF and LA-ICPMS data. If you are viewing the PDF of this paper or reading it offl ine, please visit http:// of this paper or reading it offl ine, please visit http:// 2005). The following summarizes some of the dx.doi.org/10.1130/GES00600.S1 or the full-text article dx.doi.org/10.1130/GES00600.S2 or the full-text article hypotheses concerning the Mesozoic tectonic on www.gsapubs.org to view Supplemental Table 1. on www.gsapubs.org to view Supplemental Table 2. evolution of southwestern Laurentia. 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