NE Mexico Research Articles

Upper Cretaceous (Cenomanian-Turonian and Turonian-Coniacian) open marine plattenkalk deposits in NE Mexico

In NE Mexico, the Cenomanian-Turonian plattenkalk of Vallecillo (state of Nuevo Leon) and the Turonian-Coniacian plattenkalk of Muzquiz (state of Coahuila) yield abundant fossil vertebrates and invertebrates with an exceptional preservation of soft parts. Inoceramid bivalves are the only benthic organisms in both deposits. They allow for detailed biostratigraphic subdivisions, precise dating and correlation with biozonations based on ammonites and foraminifers in both sections. In contrast to many other plattenkalks, the Mexican sediments were deposited in an open marine shelf environment, in a distance of >200 km from the nearest coast. Both Konservat-Lagerstatten formed near the southern opening of the Western Interior Seaway and contain mixtures of Western Interior Seaway and Tethyan faunal elements.

Chicxulub impact predates K–T boundary: New evidence from Brazos, Texas

Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of the new core Mullinax-1 and outcrops along the Brazos River and Cottonmouth Creek, Falls County, Texas, reveal the complex history of the Chicxulub impact, the event deposit and the K–T boundary event. The K–T boundary, as identified by the negative δ 13C shift, first occurrence of Danian planktic foraminifera and palynomorphs occurs 80 cm above the event deposit in core Mullinax-1. The underlying 80 cm interval was deposited in a shallow low oxygen environment during the latest Maastrichtian, as indicated by high stress microfossil assemblages, small shells and burrows infilled with framboidal pyrite. The underlying event deposit, commonly interpreted as K–T impact tsunami, consists of a basal conglomerate with clasts containing Chicxulub impact spherules, repeated upward fining units of spherule-rich sands, followed by hummocky cross-bedded and laminated sands, which are burrowed by Thalassinoides, Planolites and Ophiomorpha and truncated by erosion. This suggests a series of temporally separated storm events with re-colonization of the ocean floor by invertebrates between storms, rather than a series of waning tsunami-generated waves. The lithified clasts with impact spherules at the base of the event deposit provide strong evidence that the Chicxulub impact ejecta layer predates the event deposit, but was eroded and re-deposited during the latest Maastrichtian sea level lowstand. The original Chicxulub ejecta layer was discovered in a 3 cm thick yellow clay layer interbedded in undisturbed late Maastrichtian clay- and mudstones 40 cm below the base of the event deposit and near the base of planktic foraminiferal zone CF1, which spans the last 300 kyr of the Maastrichtian. The yellow clay consists of cheto smectite derived from alteration of impact glass, as indicated by rare altered glass spherules with similar chemical compositions as reworked spherules from the event deposit and Chicxulub impact spherules from NE Mexico and Haiti. The Brazos sections thus provide strong evidence that the Chicxulub impact predates the K–T boundary by about 300 kyr, consistent with earlier observations in NE Mexico and the Chicxulub crater core Yaxcopoil-1.

Eocene strata from the Sabinas Basin and their bearing in sedimentary basin correlation in NE Mexico

The El Arco section, located on the southeast margin of the Sabinas Basin (Adjuntas Sub-basin), includes a succession consisting of Upper Cretaceous formations typical for this unit, as well as Paleogene strata similar to those previously reported from the La Popa Basin, adjacent to the Sabinas Basin. The El Arco carbonate lentil includes microfossils and nautiloids that indicate a middle Eocene age, which is consistent with previous stratigraphic inferences for the La Popa Basin. The presence of the nautiloid Hercoglossa sp. cf. H. peruviana in the El Arco Lentil and in the upper portion of the Rancho Nuevo Formation of Parras Basin, suggests a new correlation scheme for the Tertiary stratigraphic units of the three basins (Parras, La Popa and Sabinas basins). All three units had sediment input as late as middle Eocene time.

Diagenesis in porosity evolution of opening-mode fractures, Middle Triassic to Lower Jurassic La Boca Formation, NE Mexico

Opening-mode fractures (joints) in Middle Triassic to Lower Jurassic La Boca Formation sandstones, northeastern Mexico, have patterns of fracture porosity, mineral-fill structures, and size distributions not previously described from outcrop. Patterns match those found in cores from many basins. We used aperture measurements along lines of observation (scanlines), fracture-trace maps, petrography, high-resolution scanning-electron-microscope-(SEM)-based cathodoluminescence, and fluid inclusions to characterize fracture populations. Open fractures are lined by quartz that precipitated while fractures were opening, whereas sealed fractures additionally contain calcite deposited after fractures ceased opening. Large fractures and arrays of contemporaneous microfractures have consistent power-law aperture-size scaling over approximately three orders of magnitude. Our results imply that open fractures and fracture sizes depend on diagenetic state. The interplay of fracture mechanics and diagenetic history is a determinant on effective porosity within fractures and, thus, open fracture persistence, connectivity, and fluid flow.

Rapid digital quantification of microfracture populations

Populations of microfractures are a structural fabric in many rocks deformed at upper crustal conditions. In some cases these fractures are visible in transmitted-light microscopy as fluid-inclusion planes or cement filled microfractures, but because SEM-based cathodoluminescence (CL) reveals more fractures and delineates their shapes, sizes, and crosscutting relations, it is a more effective structural tool. Yet at magnifications of 150–300×, at which many microfractures are visible, SEM-CL detectors image only small sample areas (0.5–0.1 mm 2) relative to fracture population patterns. The substantial effort required to image and measure centimeter-size areas at high-magnification has impeded quantitative study of microfractures. We present a method for efficient collection of mosaics of high-resolution CL imagery, a preparation method that allows samples to be any size while retaining continuous imagery of rock (no gaps), and software that facilitates fracture mapping and data reduction. Although the method introduced here was developed for CL imagery, it can be used with any other kind of images, including mosaics from petrographic microscopes. Compared with manual measurements, the new method increases several fold the number of microfractures imaged without a proportional increase in level of effort, increases the accuracy and repeatability of fracture measurements, and speeds quantification and display of fracture population attributes. We illustrate the method on microfracture arrays in dolostone from NE Mexico and sandstone from NW Scotland. We show that key aspects of microfracture population attributes are only fully manifest at scales larger than a single thin section.

Elemental dispersion and stable isotope fractionation during reactive fluid-flow and fluid immiscibility in the Bufa del Diente aureole, NE-Mexico: evidence from radiographies and Li, B, Sr, Nd, and Pb isotope systematics

The 31.6±0.3 Ma old Bufa del Diente alkali-syenite (NE Mexico) intruded a sequence of Cretaceous limestones with intercalated sub-horizontal chert layers. The cherts acted as aquifers that facilitated transport of brines and pegmatitic melts within the shallow-level (<1 kbar) contact-metamorphic aureole. Fluid-driven reactions between chert and marble wallrock, and the influx of late melts and various fluids gave rise to distinct chemical and isotopic signatures within the aquifer and across the zones of infiltration and fluid-driven reaction. Aqueous brines of magmatic origin produced thick wollastonite mantles around the chert layers. Wollastonite formation occurred at the expense of limestone and chert and generated CO2. This CO2-induced fluid unmixing into an aqueous brine and a low-density CO2-rich fluid, which was lost to the overlying marble where it oxidized organic matter and caused δ13C and δ18O shifts in a zone some 5–10 cm wide. After wollastonite formation, the chert aquifers were locally intruded by pegmatite veins carrying alkali feldspar, quartz, aegirine-augite, eudialyte, zircon, and apatite. Aqueous fluids that exsolved during crystallization of the pegmatite veins escaped along late cross-fractures and migrated along the inner and outer borders of the wollastonite margins. Chemical dispersion patterns of U, Al, Na + K, P, S, Fe, and REE across the chert-to-marble boundary and its metasomatic rims are shown by autoradiography and neutron-induced radiography. Scavenging of cations at mineralogical contacts and cation transport into the marbles occurred only on the mm to cm scale. Isotopic data for Pb and Sr across a simple metachert-marble boundary and for Pb, Sr, Nd, B, and Li across a metachert-pegmatite-marble sequence demonstrate the following: (1) The Pb and Sr isotopic signature of early fluids was buffered by the carbonate wallrock. Only late fluids, shielded from wallrock interaction by a wollastonite mantle, variably preserved a memory of their initial magmatic signature. (2) Since the Nd isotope signature of marble and chert is bound to calcite and clay minerals, systematic shifts to unradiogenic Nd in marble reflect loss of carbonate-bound Nd as the wollastonite margin is approached. Nd in the wollastonite margin is dominated by Nd originally bound to clay minerals. The later emplacement of the pegmatite, which carried the Nd isotope signature of its alkali-syenite source, had little effect on the Nd isotopic composition of the wollastonite rim. (3) Although the Li and B isotopic compositions reflect the alkali-syenite source, they are also affected by isotopic fractionation and partitioning between melt, fluid, and solids.

Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, NE Mexico: Comment and Reply: REPLY

Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, NE Mexico: Comment and Reply: REPLY

Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, NE Mexico: Comment and Reply: REPLY

Keller and Adatte raise four objections to the tsunami backflow hypothesis proposed by [Lawton et al. (2005)][1] for strata at the Cretaceous-Pa-leogene boundary in the La Popa basin. We summarize and address those objections in sequence below. 1. East-southeast flow directions recorded in sediment

Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, NE Mexico: Comment and Reply: COMMENT

[Lawton et al. (2005)][1] describe valley-like deposits in the continental to shallow marine La Popa basin northwest of Monterrey, Mexico, and interpret these as the result of Chicxulub impact induced-tsunami backflow. They further speculate that the thick siliciclastic units, known from the deep

Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, NE Mexico: Comment and Reply: COMMENT

Valley-fill deposits in the continental to shallow marine La Popa basin to the northwest of Monterrey, Mexico, are interpreted by [Lawton et al. (2005)][1] as the result of Chicxulub impact-induced tsunami backflow. There is little if any support for this notion in their paper and it contradicts

Geometry and kinematics of compressional growth structures and diapirs in the La Popa basin of northeast Mexico: Insights from sequential restoration of a regional cross section and three‐dimensional analysis

Diapirism in the La Popa basin NE Mexico was triggered and sustained by compressional décollement tectonics. Coeval development of contractional structures and diapirs was recorded by growth strata of Late Cretaceous‐Tertiary age. A palinspastic reconstruction of a regional cross section, based on the restoration of growth strata related to both diapirs and detachment folds, was carried out. On the basis of this reconstruction and field data, a three‐dimensional geometrical study was done to quantify the movement of evaporites within the detachment horizon and two diapirs. The latter allowed determining the tectonodiapiric potential of a structure or set of structures (i.e., the amount of ductile rocks forced to flow in association with the growth of a tectonic structure, which is not accommodated by thickening of the ductile horizon nor by the tectonic structure itself, and is capable of producing diapiric phenomena). This study demonstrates that there is a direct coupling between tectonodiapiric potential and diapiric activity. Geometrical results show that the main factors that controlled the amount of ductile material moved as a consequence of compressional tectonics were shortening, the depth to detachment, the folding style, and the style of deformation process (i.e., pure shear/simple shear). In response to folding, the overburden experienced a downward movement that was the major cause of diapiric phenomena. In addition to field and geometrical data, mechanical data indicate that forceful intrusion was the prevailing emplacement mechanism. Temperatures (&gt;150°–197°C) and strain rates (in the order of 10−16–10−17 s−1) calculated for top of the evaporite layer were adequate for the flow of these rocks from the initiation of compression onward. However, an inferred overpressure in the ductile layer should be considered the key factor for the emplacement mechanism.

Spherule deposits in Cretaceous–Tertiary boundary sediments in Belize and Guatemala

Large spheroid deposits at Albion Island and Armenia in northern and central Belize and the spherule deposits of southern Belize and eastern Guatemala have the same glass origin based on the presence of almost pure Cheto smectite derived from alteration of impact glass from the Chicxulub impact on Yucatan, Mexico. The same origin has also been determined for altered glass spherules in Mexico, Haiti and the Caribbean. However, the spherule layers have variable ages as a result of erosion and redeposition, with an early Danian ( Parvularugoglobigerina eugubina ) zone Pla(1) age in southern Belize, Guatemala, Haiti, southern Mexico and the Caribbean, and a pre-K–T ( Plummerita hantkeninoides ) zone CF1 age of 65.27 ± 0.03 Ma in NE Mexico. A pre-K–T age for the Chicxulub impact has now also been determined from the new Yaxcopoil 1 core drilled in the impact crater. These data show that Chicxulub was not the K–T impact that caused the end-Cretaceous mass extinction, but an earlier impact event. A multiple impact hypothesis, volcanism and climate change appears the likely scenario for the end-Cretaceous mass extinction.

New Teleostei from the Agua Nueva Formation (Turonian), Vallecillo (NE Mexico)

A new genus and new species of an ichthyodectiform fish, a new species of the pachyrizodontid Goulmimichthys, as well as specimens of Araripichthys sp. are described from the Agua Nueva Formation (Turonian) of Vallecillo, State of Nuevo León, NE Mexico. The ichthyodectiform fish shows a combination of characters from different families, warranting the creation of a new genus and questioning the monophyly of these families. We report herein the first record of Goulmimichthys and Araripichthys in North America. To cite this article: A. Blanco, L. Cavin, C.R. Palevol 2 (2003).

Fe-rich and K-rich mafic spherules from slumped and channelized Chicxulub ejecta deposits in the northern La Sierrita area, NE Mexico

Spherule deposits, commonly interpreted as ejecta from the Chicxulub impact at Yucatan, Mexico, are present in many K-T (Cretaceous-Tertiary) sections. Geological mapping of the northern La Sierrita area, NE Mexico, revealed the presence of (1) multiple spherule deposits embedded in late Maastrichtian marls, which are folded or disaggregated (breccia-like). They are up to 6 m thick, locally present in two outcrop areas, and show limited lateral continuity. These deposits consist of mm–cm sized spherical to drop-shaped vesiculated spherules, angular to filamentous (ejecta-) fragments and abundant carbonate. They are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps-slides, liquefaction, and debris flows; welded components suggest an initial ground surge-like ejecta-dispersion mode. (2) A spherule deposit, 10–60 cm thick that constitutes the base of a channelized sand-siltstone deposit at, or close to, the K-T boundary and is characterized by wide lateral continuity. It is of similar petrologic composition to deposit (1), though slightly enriched in terrigeneous detritus, thus reflecting influx from proximal shelf areas. It is interpreted to result from debris flows and turbidite currents, though no size sorting and abrasion of ejecta has been observed. Petrological, mineralogical, and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the Chicxulub impact, with multiple deposits produced by subsequent remolding, reworking, and redeposition. Spherules and fragments have an Fe- (25–30 wt%), Al-, Mg-rich and Si-poor (<25 wt% SiO2) composition, and are altered to chlorite and iron-oxides, though rare K-rich mafic glass (~50 wt% SiO2; 5–8 wt% K) is also present. They contain Ti-, Fe-, K-rich schlieren, Fe-, Mg-rich globules, and rare µm-sized metallic and sulfidic Ni-, Co-rich inclusions. Carbonate as clasts and within spherules and fragments shows textures indicative of quenching and/or liquid immiscibility. Although potential ejecta fractionation and alteration make accurate evaluation difficult, this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments, in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination.

The Cretaceous/Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE Mexico

ABSTRACT In the El Mulato section (NE Mexico), the Upper Cretaceous marly Méndez and the Lower Palaeogene marly Velasco Formations are separated by a clastic unit. Benthic foraminifera from both marly formations indicate lower bathyal depths. The clastic unit, in contrast, contains platform sands, muddy pebbles and neritic (shallow) faunas mixed with microspherules, indicating that it was allochthonously deposited into the deep basin. The diversity and the variability in origin of the components in the clastic unit, and its sedimentological features, support a model of deposition by turbidity currents related to mass‐wasting processes triggered by the Cretaceous/Tertiary (K/T) boundary impact. Planktic foraminifera were affected by a catastrophic extinction at the K/T boundary, whereas benthic foraminifera show reorganization of the community structure rather than significant extinction. The benthic faunal turnover may have resulted from the drop in primary productivity after the asteroid impact at the end of the Cretaceous.

ABSTRACT: Isolated to Coalesced Carbonate Buildups Developed on Passive Salt Diapir Bathymetry, La Popa Basin, NE Mexico

ABSTRACT: Isolated to Coalesced Carbonate Buildups Developed on Passive Salt Diapir Bathymetry, La Popa Basin, NE Mexico

ABSTRACT: Detailed Sequence Stratigraphic Interpretation of Mixed Carbonate-Evaporite Reservoir Systems: The Permian (Zechstein) of Germany and the Lower Cretaceous of NE Mexico

ABSTRACT: Detailed Sequence Stratigraphic Interpretation of Mixed Carbonate-Evaporite Reservoir Systems: The Permian (Zechstein) of Germany and the Lower Cretaceous of NE Mexico

Abstract: Paleogeographic and Sequence Stratigraphic Framework for Mesozoic Carbonate Exploration on the Northwest Gulf of Mexico (NW GOM) Rim&amp;nbsp;

ABSTRACT Mesozoic stratigraphy of the NW GOM rim from east-central Mexico to TX-LA (USA) records: (1) U. Triassic-late M. Jurassic rifting marked by creation of basement highs (e.g., Sabine uplift) and lows (e.g., Sabinas Basin, Mexico; east Texas and northern Louisiana salt basins (ETSB and NLSB)), and deposition of red beds and Callovian age salt (Louann). (2) U. Jurassic-early U. Cretaceous passive margin accumulation (15,000-20,000 ft); (3) late U. Cretaceous Laramide foreland basin development (east-central, NE Mexico) and basement reactivation. NW GOM passive margin stratigraphy consists of four 2nd-order supersequences (SS 1--U. Bathonian to L. Kimmeridgian ("158.5" - "144" myr), SS 2--L. Kimmeridgian to Berriasian ("144" - "128.5" myr), SS 3--Valanginian to L. Aptian ("128.5" - "112" myr), SS 4--L. Aptian to U. Albian ("112" - "98" myr) marked by regional patterns of facies retrogradation (2nd-order TST) overlain by facies progradation (2nd-order HST). Productive carbonate reservoirs are assigned to specific 2nd-order systems tracts of each supersequence, thus providing a predictive framework for exploitation (reservoir characterization), as well as providing a template for exploration. Rift-generated basement structures and patterns of early salt movement influenced U. Jurassic and early Cretaceous facies architecture and paleogeography, controlling the location of principally stratigraphic traps (e.g., grainstone reservoirs and pinnacle reefs of the Cotton Valley Lime/Troy Lime and James Lime in the ETSB and NLSB). Structural traps affecting Barremian Sligo and Albian Edwards reservoirs in south Texas result from a combination of post-U. Cretaceous salt-influenced tectonics and Laramide basement reactivation (e.g., Totanaca, Sabinas Basin). End_of_Record - Last_Page 361-------

Abstract: Sequence Stratigraphic Analysis of the Lower Cupido Formation (Lower Cretaceous), NE Mexico: Preliminary Interpretations

Abstract: Sequence Stratigraphic Analysis of the Lower Cupido Formation (Lower Cretaceous), NE Mexico: Preliminary Interpretations

Research into the Quaternary sediments and climatic variations in NE Mexico

The valleys of the Sierra Madre Oriental and its foreland contain abundant fluvial and lacustrine sediments ranging from the Pliocene up to the present. The fluvial sediments consist of a sequence of at least five terraces above recent river level, caused by climatically induced rhythmic change between accumulation and erosion during more or less constant tectonic uplift. These cycles correspond to the global variations of Quaternary climate, but there is a lack of detailed knowledge about the climatic characteristics of the accumulation and erosion phases (phases of activity and stability, Rohdenburg, 1970 ) in semihumid to semiarid NE Mexico. The Faculties of Forestry and of Geosciences of the UANL started a project to investigate the connection between Quaternary sedimentation and climatic variations in NE Mexico. Research on this subject started with geological and pedological field work, identifying, classifying and mapping fluvial terraces. Lacustrine sediments of different ages, from palaeolakes in the Sierra, may contain indications of chronology and climate in the form of volcanic ashes, palaeomagnetic orientation of fine sediments, micro- and macrofossils and calcicrusts. These will be studied intensively, in cooperation with various Mexican and international institutions. This research might also help to understand the tectonic and geomorphological development of the Sierra Madre Oriental and its foreland from the Pliocene up to the present.