NE Mexico Research Articles

Fungi associated with the Asian citrus psyllid, Diaphorina citri Kuwayama, in northeastern Mexico

ABSTRACT Diaphorina citri Kuwayama (Asian citrus psyllid, ACP) is a devastating pest due to transmission of Liberibacter spp. to citrus plants. We identified presumed entomopathogenic fungi (EF) naturally associated with field-collected adult ACP, both killed (mycosed) and alive, at 14 field sites in the Gulf Coastal Plain of NE Mexico. On dead ACP, five species of EF (Hypocreales) were observed: Hirsutella citriformis Speare (Ophiocordycipitaceae), Cordyceps javanica (Frieder. & Bally) Kepler, Shrestha & Spatafora, Beauveria cf. bassiana (Bals.) Vuill., and Akanthomyces cf. lecanii (Cordycipitaceae); also, Niveomyces J.P.M. Araújo & C. de Bekker (Cordycipitaceae), a hyperparasite of Ophiocordycipitaceae, in this case H. citriformis. The most prevalent fungi on field ACP were H. citriformis and C. javanica, on dead and on live, incubated insects, respectively. In laboratory bioassays, C. javanica and H. citriformis conidia from cultures killed >60% of ACP adults. H. citriformis, C. javanica, and A. lecanii killed >60% nymphs. Niveomyces was observed only growing on H. citriformis fructifications on field-killed ACP; it was absent from live incubated insects, indicating Niveomyces is a mycoparasite on H. citriformis. Niveomyces cultures (ARSEF 10230) on agar grew as a Pleurodesmospora synanamorph; its LSU rRNA region D1–D2 sequences (Genbank OM780101) were 99.81% identical to Niveomyces sequences. Conidia from Niveomyces cultures were entomopathogenic on ACP nymphs and adults. These are the first reports of Niveomyces associated with H. citriformis; of the in vitro dimorphic growth (synanamorphs) Niveomyces/Pleurodesmospora; and of experimental verification of entomopathogenicity of Niveomyces. Understanding the interactions of these fungi will support sustainable ACP management.

Upper Cretaceous Crustacea from Central Cuba

We report new occurrences and additions to previously described species of decapod crustaceans from the Late Cretaceous (Campanian-Maastrichtian) of Cuba. Three of the eight species herein described and illustrated were published previously: Vegaranina rivasi Arano-Ruiz et al.2018; Graptocarcinus collinsi Vega et al., 2020; and Icriobranchiocarcinus rodas Vega et al., 2021; however additional specimens are included. New records include one indeterminate lobster, two new genera and three new species of raninoids, and the first report of Ophthalmoplax cf. O. brasiliana Maury 1930 from Cuba. The most numerous specimens correspond to raninoids, which although not complete, can be described based on complementary pieces of the dorsal carapace and front, and they are assigned as follows: Aguadites hexagranula Vega, Garassino, Nyborg, and Pasini n. gen. sp.; Rodanina monosensis Vega, Garassino, Nyborg, and Pasini n. gen et sp., and Raninoides granulofrons Vega, Garassino, Nyborg, and Pasini n. sp., which represents the oldest record for the genus. Vegaranina rivasi is compared to V. precocia (Feldmann, Vega, Tucker, García-Barrera and Avendaño, 1996) from the Maastrichtian of Chiapas, Mexico, confirming different characters to keep both species as representatives of Vegaranina Van Bakel, Guinot, Artal, Fraaije and Jagt 2012a. The astacid lobster is represented by one isolated carapace (part and counterpart), preserved in a concretion. Two complete dorsal carapaces (one preserving the right cheliped) of Graptocarcinus collinsi represent additional information on the morphology of this species. An incomplete specimen of Ophtalmoplax cf. O. brasiliana, confirms the extensive distribution of this species during Maastrichtian times in the Atlantic shallow marine environments, from Brazil to North Carolina, USA, representing the missing link of the distribution to be found in the Caribbean province. A dorsal carapace is assigned to Icriobranchiocarcinus rodas , since it shows the typical transverse ridges of the species. This report represents an important addition to the knowledge of the Cretaceous crustaceans from Cuba and the Caribbean, confirming that this paleobiogeographic province was composed by a quite different assemblage from those reported from the same age (Campanian-Maastrichtian) of nearby regions such as NE Mexico, SE USA and NE South America.

Geochronology and geochemistry of the El Salvador plutonic complex (Sierra de Tamaulipas, NE Mexico): cenozoic tectonic implications of the eastern Mexican alkaline province

ABSTRACT The El Salvador plutonic complex is a 9.2 km2 circular body within the Sierra de Tamaulipas, part of the Eastern Mexican Alkaline Province (EMAP). Three alkaline magmatic suites were identified from El Salvador from the geochemical analysis of 20 samples. Suite A (SiO2 = 58.3–65.3 wt.%) is ferroan (Fe* = 0.761–0.873) and alkalic (MALI = 4.83–9.89). In contrast, Suites B (SiO2 = 52.5–60.8 wt.%; Fe* = 0.680–0.756) and C (SiO2 = 50.5–67.1 wt.%; Fe* = 0.616–0.749) are magnesian. Suite B is alkali-calcic (MALI = -2.18–4.64), while Suite C is alkalic (MALI = 4.48–8.59). All suites display arc-related signatures. U-Pb and fission-track geochronology data reveal two uplift episodes during the cooling history of Suite A. One in the Late Eocene was based on U-Pb zircon (38.42 ± 0.21 Ma) and titanite ages (35.54 ± 3.77 Ma). The other was during the Oligocene from U-Pb apatite (29.9 ± 6.54 Ma) and fission-track titanite (30.2 ± 5.53 Ma) and apatite ages (32.7 ± 7.06 Ma). Integrating the arc-related signatures of El Salvador rocks with the well-documented Palaeogene arc magmatism of the Sierra Madre del Sur, we propose that the mantle beneath the EMAP experienced metasomatism during the Early Permian (and possibly the Early Jurassic) but not after the Late Cretaceous, ruling out Cenozoic slab subduction in eastern Mexico. In the absence of a slab to explain the El Salvador magmatism, we suggest a long-lasting, widespread mantle upwelling beneath Mexico’s northern half in response to the Farallon slab’s break-up. Under this context, the westward drift of the North American plate led to the Mexican Foreland Basin lithosphere reaching this massive mantle upwelling in late Eocene times to produce the EMAP magmatism.

The role of the Serranía del Burro range in the distribution and hydrochemical behavior of water resources in Coahuila, NE Mexico

Highlands form one of the essential links ensuring the good performance of the hydrological cycle on Earth, and significant amounts of good-quality water are concentrated in these areas and distributed to lowlands. These resources are indispensable for arid/semi-arid regions such as NE Mexico, where water is scarce and sometimes lacks good quality. In the state of Coahuila, the Serranía del Burro is one of the most important hydrogeological systems, and at least seven aquifers show some type of relationship with this system or benefit from its recharging. In this paper, data from 50 well and spring samples are presented with the goal of identifying the effect of the range on the chemical composition of the surrounding aquifers and the mechanism of recharging. The results show that in this area, the waters are mostly of the type Ca2+-Mg2+-HCO3-, with minor contributions from more saline and mixed waters. The main processes responsible for the chemistry of the waters are water-rock interactions, mixing and, cationic exchange, in which, the weathering of silicates and, the dissolution of carbonates through karst processes predominates. Recharging is characterized as fresh and deep, due to the influence of karst and tectonic phenomena throughout the geology of the Serranía del Burro and the adjacent areas. Limited shallow meteoric percolation occurs in the NO of the Serranía del Burro due to the presence of conglomerates and caliche sequences, resulting in low permeability. This study highlights the need to take care of good-quality water resources located in the mountains; adequate exploration work must be carried out in these areas, since waters of questionable quality prevail throughout the state, mainly due to natural salinization processes in lowland areas.

Berriasian–Valanginian calpionellid biostratigraphy and associated microfossils from the upper Pimienta and lower Tamaulipas formations (Hidalgo state, Mexico): paleoenvironmental and paleobiogeographic significance

A section measured from the upper part of the Pimienta Formation and the lowest part of the Tamaulipas Formation located in the central-eastern part of the state of Hidalgo, NE Mexico was studied. The lower part of the succession consists of an argillaceous and laminated dark gray limestone, black shale, black calcareous shale, siltstone and bentonite; the Pimienta–Lower Tamaulipas transition is marked by the sporadic appearance of light-colored limestone in the upper part of the Pimienta and the shift to a succession dominated by thicker beds of yellowish and bioturbated limestone. The microfossil assemblage consists of calpionellids, radiolarians, and planktonic and benthic foraminifers. The biostratigraphic study of the calpionellids enabled three zones to be identified: Calpionella, Calpionellopsis and Calpionellites as well as five subzones, Elliptica, Oblonga, Murgeanui, Darderi and Major, ranging from early late Berriasian to early Valanginian. This allows a chronostratigraphic correlation to be drawn between the Tethys and the Southeastern Pacific provinces. In addition, we report the occurrence of abundant radiolarians and planktonic and benthic foraminifers. The paleoenvironmental inferences in the studied section are documented from the predominant wackestone texture and microfossil association, indicating a pelagic basin environment. The abundant occurrence of radiolarians mostly in the Elliptica and Oblonga subzones could suggest an increase in the input of nutrients.

New frog crabs (Brachyura, Raninoidea) from the early Maastrichtian of Paredón (Coahuila, NE Mexico)

We report several raninoid specimens collected from the lower Maastrichtian Lower Siltstone Member of the Potrerillos Formation (Difunta Group), NE Mexico. These specimens were collected from fine-grained sandstones that crop out at the NE edge of the Parras Basin, Coahuila. This outcrop is very close to a structural feature that has been active since Late Jurassic times (San Marcos Fault) and has affected depositional lithostratigraphic units from the Upper Jurassic to Upper Cretaceous. The studied specimens are assigned to Bournelyreidus paredonensis n. sp. (Lyreididae Guinot, 1993) and Coahuilanina difuntaensis n. gen., n. sp. (Raninidae de haan, 1839). A new subfamily, Coahuilanininae is described to accommodate the new genus and species, Coahuilanina difuntaensis. The new frog crabs represent the first formally described raninoids from the lower Maastrichtian portion of Difunta Group, adding to an already diverse assemblage of raninoids from Mexico.

Cretaceous echinoids in Paleocene reworked tsunamite from Coahuila, NE Mexico

The Maastrictian echinoid species Hardouninia mortonis (Michelin, 1850) typical from Upper Cretaceous deposits along the Gulf and Atlantic Coastal plains of USA and Canada, is here reported for the first time for Mexico into a peculiar matrix, which consists of a K/Pg reworked tsunamite deposited during an early Paleocene storm event in the NW portion of the Parras Basin, Difunta Group, NE Mexico. Our specimens have a peculiar small size compared with those reported for Maastrichtian localities in Mississippi amd North Carolina. Small-sized specimens are abundant in late Maastrichtian Las Encinas Formation of the Parras Basin, and are identical to the more than 50 specimens found included in reworked K/Pg tsunamite at Arroyo Amargos, Coahuila. Our interpretation is that the tsunamite was reworked during an early Paleocene storm, forming a channel-like structure of microconglomeratic sandstone, which includes ammonites (Sphenodiscus pleurisepta), the small Hardouinia mortonis, and delicate early Paleocene ostreoids. Other localities with reworked K/Pg tsunamite deposits are found in the adjacent La Popa Basin, interpreted also as deposited by early Paleocene storms in this area of NE Mexico, in Coahuila and Nuevo León states, but mix of Maastrichtian and Paleocene invertebrates has only been observed in Amargos.

Constraints on the origin of the cenozoic intraplate aldama volcanic field, tamaulipas, NE México

The Cenozoic Aldama Volcanic Field (8–0.24 Ma) is located on the southeastern margin of the Sierra de Tamaulipas and is the largest field of the Eastern Mexican Alkaline Province. It contains cinder cones, tuff rings, maars, and simple cones, as well as widespread lava flows. The volcanic rocks are geochemically characterized as alkali basalts, subalkaline basalts, trachybasalts (potassic and hawaiites), latites to trachytes, and grouped in six rock types according to their Mg-content and normative composition: (a) Alkaline near-primary rocks, (b) Alkaline basic rocks, (c) Alkaline intermediate rocks, (d) Subalkaline near-primary rocks, (e) Subalkaline basic rocks, and (f) Subalkaline intermediate rocks.Trace elements and isotopic ratios show that the source of the basaltic melts displays asthenospheric characteristics and stability conditions, indicating that the partial melting (<5%) occurred in lithospheric levels within the spinel stability depth. The coexistence in time and space of alkaline and subalkaline rocks could be explained by selective alkali metasomatism of a regional HFSE and REE-enriched OIB-like source. The magma generation occurred in a typical continental intraplate setting, associated with mantle disturbances produced by the eclogitization and detachment of the Hess conjugate subducted under NE Mexico. Some alkaline and subalkaline melts evolved to intermediate members by fractional crystallization.

Taphonomy of the teleost Tselfatia formosa Arambourg, 1943 from Vallecillo, NE Mexico.

The platy limestone deposit of Vallecillo in northeastern Mexico is dated to the early-middle Turonian (Late Cretaceous) and known to contain a variety of well-preserved vertebrate fossils. One of the most common fish species is the teleost Tselfatia formosa. A review of 149 individuals reveals the presence of two types of body shapes (diamond-shaped and torpedo-shaped individuals) which is interpreted as sexual shape dimorphism (SSD). A unimodal size distribution illustrates a dominance of diamond-shaped specimens, but both body shape types are present in small (young) and big sized (old) individuals. The abundance of well-articulated and complete specimens suggests that T. formosa populated deep levels of the water column, which excluded buoyancy and flotation as well as carcass disintegration near the surface. The reconstruction of the dorsal and anal fins suggests the presence of a membrane between each fin ray and allows for ecological comparison of T. formosa with modern fan fishes.

The Global Boundary Stratotype Section and Point (GSSP) for the base of the Coniacian Stage (Salzgitter-Salder, Germany) and its auxiliary sections (Słupia Nadbrzeżna, central Poland; Střeleč, Czech Republic; and El Rosario, NE Mexico)

Ireneusz Walaszczyk, Stanislav Čech, James S. Crampton, Zofia Dubicka, Christina Ifrim, Ian Jarvis, William J. Kennedy, Jackie A. Lees, Damian Lodowski, Martin Pearce, Danuta Peryt, Bradley B. Sageman, Poul Schiøler, Jordan Todes, David Uličný, Silke Voigt, Frank Wiese, With contributions by Christian Linnert, Tobias Püttmann, Seiichi Toshimitsu. Episodes 2022;45:181-220. https://doi.org/10.18814/epiiugs/2021/021022

San Felipe and Caracol tuffaceous sandstones, NE Mexico – Late Cretaceous continental arc petrogenetic link: Petrographic, geochemical, and geochronological evidence

Sedimentological and provenance (petrography, whole-rock geochemistry, zircon geochemistry, and ages documented by other authors) analysis carried out in San Felipe Formation and provenance (petrography and zircon geochemistry) analysis established for this unit and the Caracol Formation have allowed inferring the depositional environment for the San Felipe Formation, source area composition, and a possible relationship with the Laramide continental arc system during the Late Cretaceous in Northeast Mexico for both units. San Felipe Formation is constituted by two facies that are characterized by (a) intercalations of shales, tuffaceous sandstones that have Bouma sequence-like structures, ash tuffs and lapilli that develop supercritical and critical flow regime structures (e.g., low-angle parallel lamination), and (b) limestones with mudstone, wackestone, and packstone texture, that show Cruziana and Zoophycos ichnofacies. These features can be interpreted as a mixed ramp system in open sea conditions developed in the foredeep, forebulge, and back-bulge depozones. The San Felipe tuffaceous sandstones are lithic-feldspatho-quartzose to feldspatho-lithic-quartzose rocks (Q54F22L24; n = 13; mean value), rich in microlithic and lathwork tuffaceous volcanic fragments (Lvf40LvMic + Lvlt15LvTob45; felsitic volcanic grains-microlithic volcanic fragments + lathwork lithic fragment-tuffaceous fragments), with abundant volcanic glass. Tuffaceous sandstones from the Caracol Formation, a facial variant of the San Felipe unit, are lithic feldspatho-quartzose to feldspatho-lithic-quartzose rocks (Q46F26L28; n = 12; mean value) rich in felsitic (Lvf79LvMic + Lvlt4LvTob17) and plutonic lithics with subordinate metamorphic fragments and abundant volcanic glass. A predominance of felsitic tuffaceous volcanic lithics and plutonic fragments with low weathering degree (CIA = 41 ± 7; PIA = 38 ± 9) in the San Felipe volcaniclastic strata and magmatic zircons with chemistry linked mostly from continental arcs (log of U/Yb and Nb/Yb ratios) in both formations suggest that the volcaniclastic rocks of the San Felipe and the Caracol Formations have an origin related to the Cretaceous-Eocene Mexican Magmatic Arc. After a relatively fast transport, the volcanic tuffs were deposited in the foredeep, forebulge, and back-bulge depocenters distributed in Northeast Mexico.

Digging deeper into colonial palaeontological practices in modern day Mexico and Brazil.

Scientific practices stemming from colonialism, whereby middle- and low-income countries supply data for high-income countries and the contributions of local expertise are devalued, are still prevalent today in the field of palaeontology. In response to these unjust practices, countries such as Mexico and Brazil adopted protective laws and regulations during the twentieth century to preserve their palaeontological heritage. However, scientific colonialism is still reflected in many publications describing fossil specimens recovered from these countries. Here, we present examples of ‘palaeontological colonialism’ from publications on Jurassic–Cretaceous fossils from NE Mexico and NE Brazil spanning the last three decades. Common issues that we identified in these publications are the absence of both fieldwork and export permit declarations and the lack of local experts among authorships. In Mexico, access to many fossil specimens is restricted on account of these specimens being housed in private collections, whereas a high number of studies on Brazilian fossils are based on specimens illegally reposited in foreign collections, particularly in Germany and Japan. Finally, we outline and discuss the wider academic and social impacts of these research practices, and propose exhaustive recommendations to scientists, journals, museums, research institutions and government and funding agencies in order to overcome these practices.

Carbon cycle perturbation and mercury anomalies in terrestrial Oceanic Anoxic Event 1b from Jiuquan Basin, NW China

Abstract Oceanic Anoxic Event (OAE) 1b is well documented in western Tethys; however, records in Eurasia are still lacking. Here, we carried out high-resolution organic carbon isotope (δ 13 C org ), total organic carbon (TOC) content and mercury (Hg) concentration analysis of the lacustrine sediments from the Xiagou and Zhonggou formations in the Hanxiagou section of the Jiuquan Basin, NW China. The lacustrine δ 13 C org curve presents three stages of negative excursions above the basalt layer dated at 112.4 ± 0.3 Ma in the lowermost Zhonggou Formation. The three negative δ 13 C org excursions correspond well with the three sub-events (Kilian, Paquier and Leenhardt) of the OAE 1b in the Poggio le Guaine (central Italy), Vocontian Basin (SE France) and St Rosa Canyon (NE Mexico) sections, supporting the record of the terrestrial OAE 1b in the Jiuquan Basin. Five mercury enrichment intervals in Hg/TOC ratios were recognized, indicating that the pulsed volcanism from the Southern Kerguelen Plateau likely triggered OAE 1b. However, the decoupling between negative isotopic excursion shifts and mercury enrichments, signifying another carbon reservoir (with no link to mercury), probably contributed to the global carbon cycle perturbation during the OAE 1b period. Our results provide direct evidence to link OAE 1b and the terrestrial ecosystem in Eurasia.

New insights on the avian trace fossil record from NE Mexico: Evidences on the diversity of latest Maastrichtian web-footed bird tracks

In this study we describe three new web-footed bird tracks found in uppermost Maastrichtian strata of Las Encinas Formation, southeast Coahuila, NE Mexico. The described materials were collected at Rancho San Francisco locality, Ramos Arizpe County. These bird tracks can be ecomorphologically compared with those of modern members of the Order Anseriformes and the Family Ardeidae (Order Pelecaniformes). Associated invertebrate ichnotaxa include Cochlichnus and Skolithos. The co-occurrence of Leptoptilostipus isp., morphotype A and morphotype B with several invertebrate traces at Rancho San Francisco suggests that this area could represent a feeding site with abundant food sources during the latest Maastrichtian. These new bird footprints add to the previous reports of avian trace fossils for the Upper Cretaceous of the state of Coahuila and suggest that the Rancho San Francisco tracksite can be considered up to now, as the richest locality of web-footed bird tracks worldwide.

Early Mississippian precollisional, peri-Gondwanan volcanic arc in NE-Mexico: Aserradero Rhyolite from Ciudad Victoria, Tamaulipas

The study of the pre-Mesozoic geological history of NE Mexico offers the opportunity to reconstruct the processes that occurred at the NW margin of Gondwana. The Huizachal–Peregrina Anticlinorium, which is located west of Ciudad Victoria (Tamaulipas) is a regional structure produced during the Cretaceous–Palaeogene Laramide Orogeny. Its eroded core exposes Precambrian and Palaeozoic units that together comprise the Sierra Madre Oriental basement. These units are the Neoproterozoic metamorphic Novillo Complex, the Ordovician Peregrina Tonalite, the metamorphic Pennsylvanian Granjeno Complex, and the sedimentary Silurian–Permian Tamatan Group. Aserradero Rhyolite belongs to the Tamatan Group, occurring between the siliciclastic deposits of the Early Mississippian Vicente Guerrero and the Pennsylvanian Del Monte Formations. The studied rhyolites display geochemical characteristics corresponding to high-K, low-Sr, and S-type granitoid rocks that may have been produced by upper-crustal anatexis from a source similar to that of the Novillo Complex. New LA-ICP-MS U–Pb geochronological analysis on zircons separated from the Aserradero Rhyolite yielded Early to Middle Mississippian crystallisation ages of 347.8 ± 2.7 Ma and 340.7 ± 3.6 Ma, confirming that this acidic unit is in its original stratigraphic position despite the pervasive deformation of the Tamatan Group. Based on the correlation with other Carboniferous–Early Permian magmatic complexes in Mexico and Central America, it is suggested that the Aserradero Rhyolite represents an early stage of a precollisional Carboniferous–Permian peri-Gondwanan arc, occurring also in the Las Delicias, Oaxaquia, the Acatlan Complex, the Maya Block, as well as in the buried crystalline basement along the Western Gulf of Mexico. The assembly of the Precambrian and Palaeozoic basement units from the Huizachal–Peregrina Anticlinorium were integrated with the Ciudad Victoria Block, which was dismembered from Oaxaquia and their peripheral units during the Upper-Jurassic Gulf of Mexico opening.

Provenance and tectonic setting of the Paleozoic Tamatán Group, NE Mexico: Implications for the closure of the Rheic Ocean

The Huizachal–Peregrina Anticlinorium in northeastern Mexico comprises a wide variety of Precambrian and Paleozoic basement units. In this work, Silurian-to-Permian unmetamorphosed siliciclastic successions (i.e., Cañón de Caballeros, Vicente Guerrero, Del Monte, and Guacamaya formations) forming the Tamatán Group is described; the group overlies the Novillo metamorphic complex, which is the northernmost exposed region of the Oaxaquia microcontinent. In this paper, a provenance model for the Tamatán Group is proposed based on new petrological data, whole-rock geochemical data, and U–Pb LA-ICP-MS detrital zircon age data from these marine fossiliferous strata. The results show a shallow-marine to deep-water clastic succession classified as feldspatho-lithic-quartzose and litho-feldspatho-quartzose (Cañón de Caballeros and Vicente Guerrero formations) and feldspatho-quartzo-lithic and litho-quartzo-feldspathic (Del Monte and Guacamaya formations). The petrological and geochemical data indicate a derivation from felsitic, intermediate, and basic rocks, intense to moderate weathering, and high to moderate recycling of the source area. The geochronological data can be organized into three main detrital zircon U–Pb age groups: (1) a Meso-Neoproterozoic group, likely derived from Oaxaquia and the Maya block, which is also the probable source of 1.5–1.6 Ga zircon grains; (2) an Ordovician–Silurian group that is likely sourced by igneous Maya Block intrusions or from local units such as the Ordovician Peregrina Tonalite; and (3) Pennsylvanian and Permian zircon that can be derived from magmatic arc-related intrusions from the diachronous Rheic closure. Additionally, major, trace, and rare earth element concentrations and ratios from the Tamatán Group indicate a passive margin that evolved into magmatic arc sources within the upper continental crust. The integration of our data indicates that the Tamatán Group was deposited in an unreported back-arc basin from the northernmost part of Oaxaquia near the Maya Block along the northwestern Gondwanan margin during the closure of the Rheic Ocean priori to complete Pangea.

Neoproterozoic extension and the Central Iapetus Magmatic Province in southern Mexico – New U-Pb ages, Hf-O isotopes and trace element data of zircon from the Chiapas Massif Complex

Final fragmentation of Rodinia occurred during the Ediacaran Period as Amazonia, Baltica and Laurentia drifted apart to form the Iapetus Ocean. Accompanying rift-related mafic dyke swarms of the Central Iapetus Magmatic Province (CIMP) were emplaced between 0.62 and 0.55 Ga, which are preserved in Laurentia and Baltica, whereas no coeval mafic rocks are known from Amazonia. First evidence for the CIMP extending into Oaxaquia (Rodinia-type basement of Mexico) was reported as tholeiitic dykes that intruded the Novillo gneiss, NE Mexico, at 619 ± 9 Ma. In Chiapas, SE Mexico, amphibolite dykes that are chemically similar to the Novillo dykes intruded anorthosite and gneiss. In this paper, a new dating approach to obtain mafic dyke intrusion ages is presented by targeting contact metamorphic zircon with the UPb method, employing Secondary Ion Mass Spectrometry. Zircon that crystallized in anorthosite at intrusive contacts to mafic dykes and at temperatures exceeding 700 °C (Ti-in-zircon thermometry) yields ages between 615 ± 7 Ma and 608 ± 12 Ma, reflecting the time of dyke intrusion. Zircon chemical and isotopic (Hf, O) characteristics suggest a diachronous sequence of metamorphic processes involving Zr release from FeTi oxides, breakdown and recrystallization of other phases, and fluid-mitigated reactions during Ordovician metamorphism. Zircon δ18O values of granulites from Oaxaquia range from +6.2‰ to +9.8‰, whereas Tonian (~0.92 Ga) metamorphic zircon from SE Chiapas yielded low δ18O values from +2.0‰ to +2.8‰ that are explained by the reactivation of major tectonic boundaries during Tonian gravitational collapse. The observations increase the known extent of the CIMP in Mexico, suggesting that a Neoproterozoic superplume was still active during the Early Ediacaran producing a Large Igneous Province that extended over Amazonia, Baltica and Laurentia. The results further suggest that Oaxaquia at the northern edge of Amazonia formed the conjugate margin of Baltica during rifting.

In situ magnetic susceptibility and gamma radiation data in the Candela-Monclova intrusive belt, Northeast Mexico: case studies of the Cerro Colorado and Cerro Marcelinos plutons

The Cerro Marcelinos (CM) and Cerro Colorado (CC) plutons are part of the Candela-Monclova intrusive belt (NE Mexico), which is mid-Eocene in age (43-35 Ma). It intrudes into the Sabinas Basin, primarily made up of limestones, of Lower and Upper Cretaceous age. Around several intrusions, including the CM and CC plutons, mineralizations are known. However, how much hidden mineralizations would occur is not known. Trends within the plutons and in contact aureoles are also poorly described at present. Therefore, we provide here in situ magnetic susceptibility (MS) and gamma ray spectrometry (GS) data along two composite transects, one in each pluton, to delineate such potential trends. The data show variations of 0.003 × 10-3 SI and 104 × 10-3 in MS and of 7.1 nGy/h and 196 nGy/h in GS with a clear relation to rock type and amount of metasomatism. The radioactive contents in the outcrops of contact metamorphic rocks indicate a contact metasomatism with differing degrees of alteration during emplacement of the plutons. The host limestones have magnetic minerals incorporated during the intrusion process. MS and GS indicate an increase in the degree of acidity towards the center of both plutons, possibly associated with the later stages of the magmatic differentiation process. The MS could divide the igneous rocks into two groups, weakly magnetic (group 1 with MS ≤ 3 × 10-3 SI) and strongly magnetic (group 2 with MS > 3 × 10-3 SI), associated with the magnetite and ilmenite series, respectively. These classes provide useful information regarding the internal magnetic zoning in the plutons, which can be associated with mineralizations of mainly Au and Cu. Mainly, the magnetite series (group 2) delimited more perspective zones for mineral exploration. This zoning in MS could guide future mineral exploration in both plutons.

Response of the western proto-North Atlantic margin to the early Aptian oceanic anoxic event (OAE) 1a: an example from the Cupido platform margin-Gulf of Mexico, NE Mexico

Integrated microfacies and geochemical analyses conducted on five stratigraphic sections in northeastern Mexico (ancentral western margin of the proto-North Atlantic) reveal major paleoenvironmental changes in shallow water and pelagic environments in the prelude and run-up of the early Aptian oceanic anoxic event (OAE) 1a. During the Barremian–Aptian transition, the replacement of photozoan rudist-coral by mesotrophic/eutrophic orbitolinid-miliolid communities in the Cupido platform occurred in association with increased nutrient input. Thereafter, oligotrophic, photozoan, green algal communities repopulated briefly the carbonate ramp. Microbial-dominated ecosystems and peloidal carbonates with scarce fossils flourished before and during the onset of the OAE 1a, attesting carbonate crisis and highly stressed conditions. Organic-rich sediments deposited under weak reducing conditions in some parts of the platform. Carbonate sedimentation at the end of OAE 1a was characterized by photozoan ooid-dominated facies documenting a recovery phase of marine alkalinity. The studied carbonate platform shows a response mode to OAE 1a marked by continuous carbonate production, presumably protected by the “kettle effect”, but accompanied by significant ecological perturbations and incipient drowning. The documented change shares attributes of both central/southern and northern Tethyan platforms response modes. The OAE 1a deposits in the pelagic setting are characterized by organic-rich, radiolarian-dominated carbonates accumulated under oxygen-restricted bottom water conditions and during enhanced nutrient input linked to intense chemical weathering. The intensity of the trace metal anomalies suggests that volcanic-hydrothermal activity associated with the construction phases of the Ontong Java LIP also influenced the elemental abundance in the proto-Atlantic water mass.

Modeling rainfall interception components of forests: Extending drip equations

Assessment of forest interception, I, and its components; the average evaporation rate during the storm, E¯, and canopy storage, S, are essential for simulating the contribution of forests to the water cycle and the climate system. The objectives of this study were to: (i) propose a new model to predict I, E¯, and S, as well as rainfall duration, RD and rainfall intensity, R¯ ; (ii) correlate E¯, RD, and R¯ assessments; and (iii) quantify the role plant surfaces play on the generation of interception from four forests in Mexico. Based on extended drip equations, the model was calibrated using field measurements from forty-five forest interception case studies (N = case studies, n = number of rains) in tropical dry, TDF (N = 21, n = 347), arid/semi-arid, A&SF (N = 15, n = 659), temperate, TF (N = 4, n = 258), and tropical montane cloud, TMCF, forests (N = 6, n = 658) and validated using field measurements from sprinkling experiments in ne Mexico. The model performed very good in predicting both individual and cumulative I values, with average errors, ME%, as a function of precipitation, P, smaller than 4% and Nash-Sutcliffe, NSE, values > 0.33 for three out of four forests. E¯ assessments accounted for between 65% and 93% of I in these forests. Higher E¯ and I figures were found in individual trees (3.78A mm h−1, 27%) in contrast to forest plots (2.24B mm h−1, 14%). E¯ assessments decreased as a function of RD but increased as a function of R¯ for all forests (p ≤ 0.05). Leaf area index, LAI, significantly explained part of the I variance in complex non-linear fashions (p ≤ 0.05). The novel independent assessments of I, E¯, S, RD, and R¯, the significant relationships between I components, and the complex role plant surfaces play on the generation of I fill an important scientific gap in this area of forest hydrology.