East-central Sonora Research Articles

Distribution and habitat of Ocelot (Leopardus pardalis) in Sonora, México

The ocelot (Leopardus pardalis) ranges from northeastern Argentina to southern Texas and southeastern Arizona. It is listed as Endangered in Mexico and the United States. Previous works on ocelots in Sonora, found them occupying different habitats, including tropical deciduous forest, thornscrub, desert grassland, oak woodland, and pine-oak forest, avoiding the driest areas of the Sonoran Desert. The majority of our records are from camera traps, with indirect records from tracks. We analyzed images and videos of more than 100 camera traps used to monitor wildlife in ranches and natural protected areas of Sonora. Cameras were set at an altitude of 70 to 100 cm above ground, some were baited with a sardine-tomato mixture, others were not, the majority were set in areas where other species were the main objective. We obtained 147 recent records from 2015 to 2021 and 28 previous records of ocelots in Sonora. Ocelots occur in the eastern half of Sonora, avoiding areas with less than 400 mm of annual rainfall in the eastern and northwestern Sonoran Desert. Ocelots have been recorded from 53 to 2,151 m elevation (av. 996 m). 21 images in nine localities show females with kittens, indicating breeding populations. In southern and east-central Sonora, ocelots live in tropical deciduous forest, and foothills thornscrub. At Maycoba east of Yécora, in Sierra Huachinera and in the Sky Islands Mountain ranges in northeastern Sonora, ocelots live in temperate vegetation, including desert grassland, oak woodland, and pine-oak forest. Ocelots have been recorded in riparian habitats, transecting other vegetation types in the principal rivers of the state: Ríos Bavispe-Yaqui, Mayo, and Sonora, which drain the Sierra Madre Occidental, the Sky Island Region and southeastern Arizona to the Gulf of California, providing dispersal corridors. Other medium sized rivers provide corridors for the dispersal of ocelots, such as Río Mátape in central Sonora, and Ríos Cocóspera, San Pedro, and Santa Cruz in the north. The nearest Sonoran populations to Arizona are in the Sierra El Alacrán and Río Cocóspera on Rancho El Aribabi.

Late Pleistocene Mammuthus and Cuvieronius (proboscidea) from Térapa, Sonora, Mexico

What is currently known about México paleontology and specifically the proboscideans has centered in the central and southern states, with much of the north largely unknown. Here we report on Cuvieronius (Gomphotheriidae) and Mammuthus (Elephantidae) recovered from Térapa, a Late Pleistocene site in east-central Sonora. The local fauna reflects a badlands environment along the Río Moctezuma, 183 km (114 mi) south of the Arizona border. The recovery of Bison places the locality within the Rancholabrean Land Mammal Age. Chronological analyses confirm that impounding basalt and fossiliferous sediments were deposited 43,000 to 40,000 years ago (MIS 3). Cuvieronius and Mammuthus are found throughout the stratigraphic profile. A review of Late Pleistocene collections indicates that Mammuthus, Cuvieronius, and one location of Mammut are known from Sonora. The Late Pleistocene along the Térapa river valley is reconstructed as cooler, with a more equable, less seasonal environment than today. The corridor was wetter, more tropical and included a riparian forest, ponding water, marsh, and savanna grassland. The area west of Térapa in western Sonora had a cooler summer climate, more winter rains and less summer rains. Woodlands and shrub communities occupied the upper bajadas and rocky hills, areas possibly where Mammut ranged more commonly. Valleys contained more grasslands than they do today. The environments and climates of valleys permitted Cynomys, Mammuthus, and Cuvieronius to exist over most of western Sonora where they are extinct today.

Chemical and isotopic signatures of hot springs from east-central Sonora State, Mexico: a new prospection survey of promissory low-to-medium temperature geothermal systems

A promissory low-to-medium temperature geothermal system located in Sonora (Mexico) has been studied. In the present work, a detailed geochemical survey was carried out to understand the hydrogeochemical signatures of hot spring waters. A field work campaign was conducted for collecting water samples from twelve hot springs placed in four major zones (NW, NE, C, and S). The collected samples were analysed by chemical and isotopic methods for determining their chemical (major and trace elements) and isotopic (18O/16O and D/H) compositions. Using geochemometric analyses of the fluid composition and fractionation, depletion and enrichment processes exhibited by major and trace elements were analysed.
 Hydrogeochemical classification was used to indicate the presence of sodium-sulphate (Na-SO4) waters in the North (NW and NE) and South hydrothermal zones; whereas calcium-magnesium-bicarbonate (Ca-Mg-HCO3) waters were identified for the Central zone. Some hot spring waters located in the NE zone were also typified as sodium-bicarbonate (Na-HCO3). In relation to the isotopic signatures of 18O/16O and D/H, four water samples from NE and C zones lie near to the global meteoric water line; whereas the remaining eight samples showed a shift for both oxygen and deuterium isotopes. A mixing line with a small shift of δ18O was identified and used as a proxy to discriminate waters with different isotopic signatures.
 After applying a geochemometric outliers detection/rejection and an iterative ANOVA statistical test, the mean temperature inferred from the most reliable solute geothermometers was 149±40 °C, which suggests to be considered as the minimum value of the reservoir temperature. As most of the hot spring waters fall outside of the full equilibrium curve, the original reservoir conditions were corrected by using a mixing conductive model, which predicted a deep equilibrium temperature of 210±11 °C. As this temperature is considerably higher than the mean temperature inferred from the geothermometers, it was suggested as an optimistic maximum reservoir temperature of the Sonora geothermal system.
 Using 150 °C and 200 °C as rounded-off reservoir temperatures (or min-max estimates), geochemical equilibria modelling based on fluid-mineral stability diagrams was carried out. An equilibrium process among local hydrothermal waters and albite-potassium feldespar and muscovite-prehnite-laumontite mineral assemblages was found. These minerals were proposed as representative mineral assemblages of low-grade metamorphism, which seems to indicate that the geothermal fluid equilibria were probably reached within the intermediate to acidic volcanic rocks from the Tarahumara Formation.

Geology and geochemistry of the Suaqui Verde deposit: A contribution to the knowledge of the Laramide porphyry copper mineralization in south central Sonora, Mexico

The Suaqui Verde porphyry copper deposit is a small ore body of about 20milliontons of oxide ore grading 0.29% copper, located ~8km E-NE of the town of Suaqui Grande in east-central Sonora, northwestern Mexico. The largest and better-known deposits occur in northern Sonora, whereas those from central and southern Sonora are smaller and poorly studied. This paper contributes with new geological and geochemical data to characterize the Suaqui Verde porphyry copper prospect, which may help to understand the porphyry copper mineralization in central Sonora. The Cu mineralization is centered on a 57±0.3Ma old quartz-feldspar porphyry stock, intruding co-magmatic Laramide volcanic and plutonic rocks. The Suaqui Verde porphyry copper system is characterized by widespread phyllic alteration dominated by quartz-sericite, propylitic and local potassic alteration, with Cu, Mo, and Fe sulfide mineralization emplaced in quartz veinlets filling stockwork zones. Quartz-tourmaline breccias, presumably pre-dating the copper sulfide mineralization, occur in the southern part of the deposit, apparently forming the apical parts of the equigranular plutons. Geochemical data of plutonic and volcanic rocks indicate derivation from subduction related calc-alkaline and metaluminous to slightly peraluminous magmas. Light REE enriched normalized patterns, with negative Eu anomalies resemble typical composition of Laramide magmatic rocks in northwestern Mexico. However, positive Eu anomalies in three of the samples indicate that some magmatic stages underwent a process that increased the Eu+2/Eu+3 ratios in the liquid, possibly associated with changes in the oxidation-reduction conditions. Chondrite-normalized multi-elemental diagrams show negative Nb-Ta, P and Ti anomalies, coupled with positive Rb, Th, U, Sr and Pb anomalies, strongly suggesting a subduction-related magmatic arc affinity. The mineralized system was segmented and tilted during the Cenozoic Basin and Range extension, which exhumed the hypogene sulfide zone, promoting supergene enrichment processes and subsequent transport of copper solutions that developed weak exotic copper mineralization.

Late Cretaceous to early Eocene magmatic evolution of the Laramide arc in the Nacozari quadrangle, northeastern Sonora, Mexico and its regional implications

Late Cretaceous to early Eocene volcanic and plutonic rocks that crop out in the Nacozari quadrangle compose the Laramide magmatic arc in northeastern Sonora, northwestern Mexico. The purpose of this work is to characterize the arc rocks based on new cartography, stratigraphy, U-Pb and K-Ar geochronology, and major, trace and isotope geochemical data and interpret them in the regional context of evolution of the arc. The study area lies within the Proterozoic Mazatzal crustal block which is limited to the south by the Caborca block. The volcanic rocks regionally correlate with the Tarahumara Formation and consist of volcanic flows, breccias, tuffs and volcaniclastic sandstones with an estimated thickness of 4km. They range in composition from andesite to rhyolite and have isotopic ages from 76.8±0.4 to 57.1±0.4Ma. The granitic plutons and rhyolitic domes that intrude them yielded ages from 59.3±0.8 to 53.3±1.6Ma. Initial 87Sr/86Sr and epsilon Nd values for these rocks vary from 0.70553 to 0.70841 and −3.7 to −8.5, respectively, and have 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb isotope ratios that range from 18.05 to 19.05, 15.52 to 15.63, and 38.25 to 39.07, respectively. Regional integration of our U-Pb ages suggests that the volcanic activity lasted between ca. 81 and 57Ma, with two main peaks of activity at 74.5 and 61Ma. Similarly, regional magmatic activity indicated by dated plutons initiated at ca.91 and ended by 50Ma, after main peaks of activity at 71 and 60–55Ma. The plutonism between 91 and 80Ma was subordinate and regionally restricted to coastal and central Sonora and might represent an older event unrelated to the Laramide arc. Two K-Ar cooling ages of 55.4±0.7 and 48.5±0.7Ma obtained from La Púrica granite dated at ca. 59Ma (U-Pb) in the study area, correlate regionally with a possible event of rapid uplift between 68 and 50Ma. The geochemical composition of the studied rocks indicate high-K, calc-alkaline, metaluminous to weakly peraluminous compositions, typical of subduction arc-related magmas which characterize the Laramide magmatic belt in northwestern Mexico. The Nd, Sr and Pb isotope compositions of these and other samples documented for northeastern Sonora, closely correlate with isotope signatures of the Mazatzal crustal block in southeastern Arizona and differ from those in the Caborca block, which display affinity with the Mojave-Yavapai province. The data also allow to best constrain the location of the boundary between the Mazatzal and Caborca crustal blocks in east-central Sonora.

Erpetogomphus molossus, a new species from Sonora, Mexico (Odonata: Anisoptera: Gomphidae).

Erpetogomphus molossus is described from 3 male and 3 female specimens (holotype and allotype in collection of Instituto Biologico de la Universidad Nacional Autónoma de México) from the intermittent pine-oak woodland of the Yécora municipio in east-central Sonora, Mexico. Diagnostic features of the new species include the seemingly bulbous tip (in lateral view) and prominent baso-ventral process of the male cerci and the notched and denticled posteromesal corners of the female subgenital plate.

Primer registro del murciélago bigotón <i>Pteronotus parnelli</i> (Chiroptera: Mormoopidae) al Este de Sonora

AbstractParnell’s mustached bat, Pteronotus parnellii, is found from southern Sonora and Tamaulipas to Chiapas in Mexico. On October 3, 2012, at 18:30 hr, six and nine-meter nets were placed above water ponds in the Babisal creek located in the “Northern Jaguar Reserve” near the town of Sahuaripa. At 19:50 hrs the six-meter net was checked, and an adult male, without scrotum, of the species Pteronotus parnellii was found at a height of 70cm above ground level. The Sahuaripa region in east-central Sonora, is outside the known distribution range of this species extending it by at least 220 km north of the Sierra de Alamos. The “Northern Jaguar Reserve” where Pteronotus parnellii was found, is a protected area and an important wilderness area for the protection of the northernmost breeding population of jaguars. Key words: Pteronotus parnellii, Reserva Jaguar del Norte, Sonora, october. Palabras clave: Pteronotus parnellii, Reserva Jaguar del Norte, Sonora, octubre.

Late pleistocene passerine birds from Sonora, Mexico

Songbirds (Passeriformes) have a very limited fossil record in spite of making up more than one-half of the world's 10,000 living species of birds. From the late Pleistocene fossil site of Térapa in east-central Sonora, Mexico, the identifiable fossils of songbirds consist exclusively of species of Icteridae. The seven extant species (Red-winged Blackbird Agelaius phoeniceus, Yellow-headed Blackbird Xanthocephalus xanthocephalus, Brewer's Blackbird Euphagus cyanocephalus, Great-tailed Grackle Quiscalus mexicanus, Bronzed Cowbird Molothrus aeneus, Brown-headed Cowbird M. ater, and Orchard Oriole Icterus spurius) still occur in Sonora, either as residents or migrants. The eighth fossil icterid from Térapa is an extinct genus and species of cowbird, Pandanaris convexa. The genus Pandanaris was known formerly only from late Pleistocene sites in southern California ( P. convexa A. H. Miller) and Florida ( P. floridana Brodkorb). We synonymize P. floridana with P. convexa because their supposed differences either cannot be substantiated or can be attributed to sexual dimorphism in size within a single species. Among the few Pleistocene sites from Mexico or the United States with well-studied and substantial assemblages of fossil passerines, Térapa is unique in its dominance of icterids (which may be common elsewhere but not dominant) and in its absence of corvids. Today, tropical “foothills thornscrub” is the vegetation type at Térapa except for riparian forest along the río Moctezuma. The icterid fossils are compatible with previous evidence (from plant, invertebrate, and other vertebrate fossils) that tropical/subtropical marsh, savanna, and riparian forest existed at Térapa during the late Pleistocene. Just as the two extant species of cowbirds associate today with large grazing mammals, the extinct Pandanaris convexa may have foraged in association with Pleistocene mammals whose extinction led to the demise of P. convexa as well.

Dire Wolf, Canis dirus (Mammalia; Carnivora; Canidae), from the Late Pleistocene (Rancholabrean) of East-Central Sonora, Mexico

Abstract We describe the first occurrence of the extinct dire wolf, Canis dirus, from the late Pleistocene deposits of east-central Sonora, Mexico. Remains include a partially complete left mandible and a left distal fragment of humerus collected from the deposits at Terapa. Local environments are interpreted to have been a tropical marsh with thorn-scrub to deciduous forest including some component of a nearby grassland. Although the mandible is nearer to the size of other large species of Canis known to occur in Mexico, the deep and robust mandible, presence of an accessory cuspid on the p2, an enlarged and robust p4, and accessory cuspids on the posterior margin of the trigonid ally the Canis from Terapa with C. dirus. Length of p4 suggests a possible closer affiliation to C. d. guildayi than to C. d. dirus.

La Formación Los Picachos en la Sierra de Los Chinos, Sonora, México

The Sierra Los Chinos is located in east-central Sonora, where three stratigraphic sequences whose ages that vary from Lower Cretaceous to Tertiary are exposed. The Lower Cretaceous succession is composed of the Agua Salada, Lampazos and Los Picachos Formations. A second sequence of Upper Cretaceous strata is constituted by volcanosedimentary rocks; while a third sequence of the Tertiary rocks is comprised by volcanic and intrusive rocks and by the sedimentary Baucarit Formation. The Lower Cretaceous rocks are strongly folded and faulted, the outstanding structures are the anticlines and synclines oriented NW-SE, with vergencies either to the northeast or to the southwest faulting in the area is mainly normal and trust faults. The Alamo section is separated into 5 informal units (A, B, C, and D), which correspond to the Los Picachos Formation.The Los Picachos Formation exposed in The Alamo range has a thickness of 560 m. and is constituted by 4 lithics packages, the presence of rudist inside the clasts that constitute a package of conglomerates near the base, as well as the rudist Coalcomana sp. in the unit A and of orbitolinids and calcispheres (Pithonella ovalis) near the top, allow us to assigne it to the middle to upper Albian. The textural characteristics of the limestone beds, as well as its faunal content indicate that these sediments were deposited in a shallow water outer-neritic marine environment with local development of ooidal banks and rudist bioherms.

Temporal constraints on the eastward migration of the Late Cretaceous–early Tertiary magmatic arc of NW Mexico based on new 40Ar/ 39Ar hornblende geochronology of granitic rocks

Hornblende step-heating 40Ar/ 39Ar dating for granitic plutons along an E–W transect of central Sonora was carried out to constrain the Late Cretaceous–early Tertiary migration of the cordilleran magmatic arc across northwestern Mexico. Geochronological data from previous studies offer a good estimate of the overall process, but because they come from different dating schemes performed on a variety of rocks and/or minerals with a wide range of closure temperatures, the ages largely overlap when plotted on a map. Previous data suggest that the Cordilleran magmatic arc was nearly static in the western portion of the Peninsular Ranges batholith in Baja California (140–105 Ma), then the axis of magmatism migrated east at approximately 10 km/Ma and reached coastal Sonora approximately 90 Ma ago. The locus of the plutonic emplacement continued to migrate inland during the Laramide magmatic pulse (80–40 Ma), penetrating up to central Chihuahua. New argon data indicate that granitic plutons intruded the region northeast of Bahía Kino, in coastal Sonora, approximately 77 Ma ago. Magmatism subsequently moved east to the area surrounding the city of Hermosillo approximately 69 Ma ago and continued its easterly migration, reaching the Sonora–Chihuahua state boundary 59 Ma ago. However, the granitic rocks of east-central Sonora yield ages in a relatively wide range of 62–56 Ma. Synchronic plutons reported farther east in central Chihuahua suggest an unusually broad magmatic arc, which appears difficult to explain on the basis of the traditional subduction model assumed for southwestern North America during this time and may reflect particular – and little understood – tectonic conditions derived from the relatively flat subduction regime prior to the extinction of the Laramide magmatic arc. Moreover, volcanic rocks exposed in east-central Sonora yield fairly old U–Pb zircon dates of 90–70 Ma, which have no known contemporaneous plutons, and complicate the scenario for the Laramide event in Sonora, perhaps requiring the existence of a second volcanic arc. Considering solely the evidence from granitic plutons, the data provide a systematic way to evaluate the shift of magmatic activity across Sonora. It needs a proper restitution for the conspicuous Cenozoic extension affecting the region. After restoring the cumulative extension of 90% estimated for east-central Sonora, a rate of approximately 8.5 km/Ma of eastward migration can be roughly estimated for the Laramide arc across Sonora.

Duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora, Mexico

Research Article| April 01, 2001 Duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora, Mexico Fred W. McDowell; Fred W. McDowell 1Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Jaime Roldán-Quintana; Jaime Roldán-Quintana 2Instituto de Geología, Universidad Nacional Autónoma de México, Estación Regional del Noroeste, Apartado Postal 1039, Hermosillo, 83000 Sonora, Mexico Search for other works by this author on: GSW Google Scholar James N. Connelly James N. Connelly 3Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Fred W. McDowell 1Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Jaime Roldán-Quintana 2Instituto de Geología, Universidad Nacional Autónoma de México, Estación Regional del Noroeste, Apartado Postal 1039, Hermosillo, 83000 Sonora, Mexico James N. Connelly 3Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Publisher: Geological Society of America Received: 21 Apr 1999 Revision Received: 04 May 2000 Accepted: 05 May 2000 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2001) 113 (4): 521–531. https://doi.org/10.1130/0016-7606(2001)113<0521:DOLCET>2.0.CO;2 Article history Received: 21 Apr 1999 Revision Received: 04 May 2000 Accepted: 05 May 2000 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Fred W. McDowell, Jaime Roldán-Quintana, James N. Connelly; Duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora, Mexico. GSA Bulletin 2001;; 113 (4): 521–531. doi: https://doi.org/10.1130/0016-7606(2001)113<0521:DOLCET>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Late Cretaceous–early Tertiary arc magmatism in east-central Sonora includes the Sonoran batholith and the volcanic rocks of the Tarahumara Formation. The Tarahumara Formation consists predominantly of propylitically altered andesitic to dacitic lava, agglomerate, and volcanic breccia, all of local derivation, along with subordinate felsic pyroclastic components. Relatively thin volcaniclastic intervals with intercalated freshwater limestone that contains Late Cretaceous plant fossils occur within the upper third of the formation. Six new U-Pb zircon ages from the Tarahumara Formation extend the known duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora. Four of the samples yield ages between 73 and 70 Ma, and the other two are 90 and 89 Ma (errors are generally <1 m.y.). All of these ages are older than 65 to 55 Ma K-Ar and U-Pb ages for plutons of the Sonoran batholith in east- central Sonora determined in other studies. Combined, the ages indicate arc magmatism over at least 35 m.y. Initiation of magmatism in eastern Sonora by 90 Ma is much earlier than predicted by regional trends, which are largely based on geochronology of plutons. It appears that a full history of the regional evolution of this magmatic arc will require substantial age information from its volcanic rocks.A component of inherited zircon was detected in five of the six dated samples from the Tarahumara Formation. Although ages calculated from upper concordia intercepts are mostly imprecise, all are consistent with the presence of one or more Proterozoic components. In one sample, a persistent inherited component provided a precise upper-intercept age of 1448 Ma. These small cores surrounded by new zircon growth must represent material incorporated into the magma chamber prior to eruption. The results record the presence of Laurentian basement 200 km south and east of known outcrops in Sonora. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Lower Cretaceous rocks of Sierra Los Chinos, east-central Sonora, Mexico

La gran mayoría de las rocas del Cretácico Inferior de Sonora son parte del Grupo Bisbee del sur de Arizona, depositadas a lo largo de la Cuenca Bisbee, una extensión del Golfo de México a Texas, Nuevo México, Arizona y Sonora. Sin embargo, las rocas del Cretácico Inferior de la Sierra Los Chinos están relacionadas con las rocas del área de Lampazos del este de Sonora, y consecuentemente con la estratigrafía de Chihuahua. En el área de Los Chinos, las unidades del Cretácico Inferior son las Formaciones Agua Salada, Lampazos y Los Picachos; unidades tomadas del área de Lampazos. El Cretácico Superior está constituido por rocas volcanosedimentarias, sobreyacidas por rocas terciarias intrusivas, volcánicas y sedimentarias. Las rocas del Cretácico Inferior en la Sierra Los Chinos están fuertemente plegadas y falladas, siendo las estructuras kilométricas (pliegues volcados y fallas de cabalgadura) las más visibles. Además el área fue afectada por al menos dos episodios de fallas normales. El Cretácico Inferior de la Sierra Los Chinos está paleogeográfica y tectónicamente relacionado con el Cinturón Tectónico de Chihuahua y no con el Grupo Bisbee de Sonora. Además el conglomerado marino en la base de la Formación Los Picachos representa un episodio tectónico activo al final del Albiano, y que aunque localmente importante, puede ser evidencia de reactivación de fallas de desplazamiento horizontal, relacionadas con transpresión tectónica. Las estructuras de compresión en Los Chinos es muy similar a la deformación de rocas de la misma edad en Chihuahua, Coahuila y Nuevo León.

Stratigraphy and structure of the Lower Cretaceous of Lampazos, Sonora, (northwest Mexico) and its relationship to the Gulf Coast succession

The stratigraphy and structure of the Lower Cretaceous (Aptian-Albian) rocks exposed in the area of Lampazos, Sonora, are redefined and correlated to well-known stratigraphic successions of Chihuahua and northeast Mexico (Coahuila and Nuevo Leon). Originally, seven stratigraphic units were proposed for the Cretaceous rocks exposed in the Lampazos area, but in this article only five units (El Aliso, Agua Salada, Lampazos, Espinazo del Diablo, and Los Picachos formations) have been used, and we propose herein to discontinue usage of the other two (Nogal and La Mesa formations). This Aptian-Albian succession of east-central Sonora yields facies and fossil content remarkably similar to coeval sequences in the Gulf of Mexico realm (Chihuahua, Coahuila, and Nuevo Leon). These sections contain abundant microfossils (benthic and planktonic foraminifera, colomiellids, nannoconids, and radiolarians) that permit detailed biostratigraphic determinations. A complete Aptian-lower Albian section (base of K-6 through top of K-15 of the biochronologic scheme of Longoria, 1984) was identified. Abrupt lithic changes through the Aptian-Albian section of Lampazos revealed three major paleoceanographic events having an overall regional marine transgression, including an early Aptian (K-6 to K-7) event, a late Aptian (K-10 to K-11) event, and an early Albian (K-13 to K-14) maximum flooding phase. We used physical and biochronologic data to tie the aforementioned events to geochemically constrained Aptian-Albian oceanic anoxic events (OAEs) in Santa Rosa Canyon of Nuevo Leon. The close correlation between the oceanic events in east Sonora (northwest Mexico) and central Nuevo Leon (northeast Mexico) invokes the closer paleogeographic development of the two regions and undoubtedly links the area of Lampazos to a rapid encroachment of the paleo-Gulf of Mexico through north-central Mexico (the Mexican Sea) into northwestern Mexico (Chihuahua trough and Sonoran basin). The early Aptian (biozones K-6 to K-7) transgression has its maximum extension during the early Albian (biozones K-13 to K-14), culminating with the drowning of the carbonate platforms. The Lower Cretaceous rocks exposed in the Lampazos area are complexly folded and faulted. The more conspicuous structures are isoclinal and box-shaped folds and thrust faults, mostly oriented north-south and northwest-southeast, having vergences to both the northeast and southwest. A very conspicuous feature is the opposite vergence of thrust faults, either converging or diverging. Two dextral strike-slip faults (northeast-southwest and east-west) separate the area into three large blocks that have different patterns of folds and thrust faults. Also, it is evident that the area was affected by at least two episodes of normal faulting. Furthermore, the structural style of deformation present in the Lampazos succession is remarkably similar to the style of deformation of coeval rocks in northeastern Mexico, especially to the structure of the Chihuahua tectonic belt. The Lampazos succession is paleogeographically and tectonically related to the Chihuahua tectonic belt, and it is considered to be the westernmost extension of the ancestral Gulf of Mexico. The fact that the Lampazos succession can be lithocorrelated to known sequences in northeastern Chihuahua (Lucero, Ahumada, and Loma Plata formations) and northeast Mexico (Cupido, San Angel, La Pena, and Tamaulipas formations), which are know to be source rocks in exploration wells in Nuevo Leon and Coahuila, makes the Lampazos area of Sonora potentially attractive as an exploration target.

Croton yecorensis (Euphorbiaceae), a New Species from Northwestern Mexico

Croton yecorensis, a new species in the section Medea, is described and illustrated. This species appears taxonomically isolated, and its exact affinities are not obvious. It is endemic to a narrow zone in the Sierra Madre Occidental of extreme east-central Sonora between the vicinities of