BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS, A.C.
VOLUMEN LXII NÚMERO 1 ENERO-JUNIO 2020
N 1300 El Madrono
00
16 0
0 1400
2 1
1100
1300 La Anacahuita 1200
1100 10 00
9 00
El Huizachal ‘ 1 4 0 0 1 300 1200
0 1100 0 0 1 La Joya Verde 1000 Cementerio
1 000 Aguas de Minas
0021
1200 13 1100 00 1400 12 00
1300
Explanation
Undifferentiated Cretaceous strata (Ku) La Casita Formation (Jc) Olvido Formation (Jo) Novillo Formation (Jn)
BOLETÍN DE LA ASOCIACIÓN MEXICANA GEÓLOGOS PETROLEROS, A.C. VOLUMEN LXII, NÚMERO 1, ENERO-JUNIO 2020. La Joya Formation (Jlj) Rhyollite (Ji) La Boca Formation La Boca Formation upper member (Jlbs) lower member (Jlbi)
Geologic contact Locality Symbols Inferred geological Coordinate system: UTM contact School Topografic base map from INEGI: CiudadVioctoria F-14-A-20 INSTRUCCIONES A LOS AUTORES
El Boletín de la Asociación Mexicana de Geólogos Petroleros es una publicación semestral dedicada a la divulgación de artículos sobre geología, especialmente aquellos relacionados con la aplicación de las geociencias a la industria petrolera.
Los trabajos factibles a publicarse se pueden dividir en tres tipos principales:
Reportes de investigación originales, no publicados con anterioridad, que no excedan de 25 cuartillas. Notas técnicas originales que no excedan de 10 cuartillas. Notas técnicas de divulgación que no exceden de 10 cuartillas.
Los trabajos deberán enviarse a:
COMISIÓN DE ESTUDIOS TÉCNICOS
Ernesto Cabalero García [email protected]
Leonardo Enrique Aguilera Gómez [email protected]
Dionisio Figueroa Rodríguez [email protected]
En caso de que el trabajo sea aceptado, la Comisión de Estudios Técnicos turnará el mismo a la Comisión Editorial, quien se encargará de su preparación y adecuación para su publicación.
COMISIÓN EDITORIAL Chamaly Revelez Ramírez Jorge Antonio Velasco Segura
Editor Técnico Sharon Carolina Carrillo Zoto
Ilustración de portada:
Figure 5: Generalized modified geologic map of Valle de Huizachal (Rubio-Cisneros and Lawton, 2011). Stars and polygons indicate the units studied in this work, and correlate to those formations explained in Figure 4. Map symbols: Jlbi—lower member of La Boca Formation; Jlbs—upper member of La Boca Formation; Ji—rhyolite domes; Jlj—La Joya Formation; Jn—Novillo Formation; Jo—Olvido Formation; Jc—La Casita Formation; Ku—undifferentiated Cretaceous strata. BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS, A.C.
Directiva Nacional (Bienio 2018-2020)
Dr. Faustino Monroy Santiago Presidente
Ing. María de Lourdes Clara Valdés Ing. Josías Samuel Estrada Macías Vicepresidenta Tesorero M. en G. Daniela Romero Rico Dra. Sandra Ortega Lucach Secretaria Protesorera Ing. Sergio Arturo Ruíz Chico Ing. Juan Medina de la Paz Coordinador de Ayuda Mutua Subcoordinador de Ayuda Mutua Ing. Chamaly Revelez Ramírez Biol. Judith Rosales Lomelí Ing. Jorge Antonio Velasco Segura Comisión de Membresía Comisión Editorial Ing. Román Sánchez Martínez Ing. Leonardo Enrique Aguilera Gómez Ing. Mitzi Berenice Benítez Canchola Ing. Ernesto Caballero García Comisión de Excursiones
Ing. Dionisio Figueroa Rodríguez Ing. Jaime Patiño Ruíz Comisión de Estudios Técnicos Comisión Legislativa Dr. Efraín Méndez Hernández Ing. Luis Francisco Fuentes Pacheco Comisión de Asuntos Internacionales Comisión evento del 70th aniversario Boletín de la Asociación Mexicana de Geólogos Petroleros
volumen lxii número 1 enero - junio 2020
CONTENIDO
Editorial
A collection of sandstones to discriminate types of sedimentary basins analyzing detrital modes: a case study in northeastern Mexico Igor Ishi Rubio-Cisneros and Yam Zul Ernesto Ocampo-Díaz
Analysis of mineralogy and porosity on a carbonaceous mudstone of the Pimienta Formation, western margin of the Tampico Misantla Basin, Mexico Análisis de mineralogía y porosidad en mudstone carbonáceo de la formación Pimienta, en el margen centro-oeste de la Cuenca Tampico Misantla, México Carlos Vega-Ortiz , Bryony Richards, John D. McLennan, Raymond Levey, Néstor Martínez-Romero Editorial
Como sabemos el análisis petrográfico y mineralógico de rocas, bajo el microscopio petrográfico y electrónico de barrido, ha sido una disciplina que proporciona al geólogo petrolero evidencias directas de la calidad de rocas generadoras, almacenadoras y sellos, además de proporcionarnos datos de las características intrínsecas de estas rocas para interpretar sus orígenes. El geólogo que realiza un estudio petrográfico requiere del conocimiento profundo de varias ciencias, entre ellas, cristalografía, diagénesis, sedimentología, paleontología, geoquímica, etc., para poder interpretar lo que está observando. Varios de nuestros asociados tienen una amplia experiencia en esta disciplina, pero cada día es menos común entre los jóvenes profesionistas. Aquellos que dominan esta disciplina podrán atestiguar lo apasionante que es el estudio de las rocas a esta escala, que últimamente también se ha usado para detallar cuestiones tan especializadas como la determinación de características o atributos de fracturas naturales de los yacimientos más importantes de nuestro país.
En este Boletín de la AMGP, se incluyen dos trabajos técnicos: el primero es una investigación e integración de una base de datos petrográficos y de clasificación y madurez textural de areniscas de varias áreas, con el objetivo de buscar una firma que identifique y caracterice a un tipo de cuenca en específico. Además, propone un método, que junto con la estadística podría determinar, según los autores, la proveniencia y tipo de cuenca de los componentes que conforman estas rocas. Como ejemplo, los autores analizaron las areniscas de cuatro formaciones del noreste de México, concluyendo que los componentes provienen de cuencas de tipo rift, cuenca tras arco extensional y strike-slip. Este es un trabajo que principalmente tiene una aplicación directa en el estudio de plays terciarios productores del país.
El segundo trabajo de este Boletín, es un ejemplo de un análisis mineralógico y de porosidad en carbonatos de la Fm. Pimienta, de la Cuenca Tampico Misantla, enfocada a evaluar el potencial no convencional de esta formación. El objetivo principal, de acuerdo a los autores, es elaborar una descripción detallada a nivel micro y nano escala para comprender las implicaciones, de las propiedades petrofísicas y de la distribución de porosidad, en la capacidad de almacenamiento de hidrocarburos, el flujo de fluidos y la permeabilidad de esta formación. Con base a 12 muestras de siete pozos, usando microscopia de barrido y pruebas de difracción de rayos x, muestran un análisis detallado de la composición química, morfológica, tipo de materia orgánica y distribución de porosidad. Basado en los resultados de este estudio, los autores determinan que la Fm. Pimienta es análoga a las formaciones Eagle Ford y Bakken de Norte América, sin embargo, concluyen que, si bien el área analizada no tiene propiedades óptimas, es posible encontrar zonas estructurales en donde las propiedades geoquímicas y petrofísicas puedan conformar un yacimiento no convencional con potencial comercial. A pesar de esto, este trabajo es sin duda un aporte de datos importantes en el estudio de plays no convencionales en nuestro país y enriquece el conocimiento que tenemos de este tipo de yacimientos.
Atentamente Dr. Faustino Monroy S.
A collection of sandstones to discriminate types of sedimentary basins analyzing detrital modes: a case study in northeastern Mexico
Igor Ishi Rubio-Cisneros (1) and Yam Zul Ernesto Ocampo-Díaz (1, 2)
(1) Grupo De Geología Exógeno y Del Sedimentario, freelance. [email protected] (2) Área de Ciencias de la Tierra, Facultad de Ingeniería, Universidad Autónoma de San Luis Potosí, Av. Manuel Nava No. 8, San Luis Potosí, San Luis Potosí. CP. 78290
Submitted to Boletín de la Asociación Mexicana de Geólogos Petroleros, February 2018.
ABSTRACT This work develops a statistical bivariate analysis and a discriminant analysis on 1411 sandstones from nine types of sedimentary basins. The study rates the variations of framework components and differentiates the modal composition for each basin by partitioning the data into discriminant fields in a ternary plot. The discriminant analysis of the full sedimentary framework petrography indices improves the use of ternary sub- compositions (Qm, Qp, P, K, Lv, Ls, Lm), and provides additional support for sandstone provenance analysis.
Petrographic indices in basins related to subduction represent the processes of major newly formed source- areas like intra-oceanic arcs and continental-margin arcs. Indices in rift, foreland, and accretionary basins indicate sedimentary processes like particle sorting, textural maturity, and the exhumation/unroofing of the sedimentary carapace. In contrast, the indices strike-slip basins hold a mixture of the processes previously described, but with significant input from crystalline and metamorphic rocks.
The analyses with statistical and discriminant methods are for interpreting which basins occur where some sandstones deposited in the Sierra Madre Oriental northeastern Mexico. This exploratory method is for Upper Triassic–Lower Cretaceous sandstones selected from four different formations: El Alamar, La Boca, La Joya, and La Casita. The framework composition in sandstones discriminates among the types of basins in a ternary plot. The analysis indicates a rift, forearc, and strike-slip basins, respectively, to the age of the formations from Late Triassic, Early–Middle Jurassic, Middle Jurassic, and Late Jurassic to Early Cretaceous.
Keywords: sandstone petrography, discriminant analysis, provenance, tectonic setting, sedimentary basins, source-rock
RESUMEN Este trabajo desarrolla un análisis estadístico bivariante y un análisis discriminante en 1411 areniscas de nueve tipos de cuencas sedimentarias. EL estudio evalúa las variaciones de los componentes principales y diferencia la composición modal para cada cuenca, mediante la partición de los datos en campos discriminantes en un diagrama ternario. El análisis discriminante del total de los índices en la petrografía de los componentes
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 5 principales sedimentarios mejora el uso de las subcomposiciones ternarias para la procedencia (Qm, Qp, P, K, Lv, Ls, Lm) y provee apoyo adicional en el análisis de procedencia de areniscas.
Los índices petrográficos en cuencas relacionadas con la subducción representan los procesos de áreas fuente recién formadas, como arcos intra-oceánicos y arcos de margen continental. Los índices en las cuencas de rift, foreland y acreción indican procesos sedimentarios como la clasificación de partículas, madurez textural y exhumación de la cubierta sedimentaria. Contrastantemente, los índices en las cuencas strike-slip tienen una mezcla de los procesos descritos anteriormente, pero con un aporte significativo de rocas cristalinas y metamórficas.
Los análisis con métodos estadísticos y discriminantes son para interpretar cuáles cuencas existen para un depósito de areniscas en la Sierra Madre Oriental, noreste de México. Este método exploratorio es para las areniscas del Triásico Superior-Cretácico Inferior, seleccionadas de cuatro formaciones diferentes: El Alamar, La Boca, La Joya, and La Casita. La composición de las areniscas se discrimina entre los tipos de cuencas en el diagrama ternario. El análisis discrimina cuencas de tipo rift, cuenca tras arco extensional y strike-slip, respectivamente, a la edad de las formaciones del Triásico Tardío, Jurásico Temprano-Medio, Jurásico Medio y Jurásico Tardío al Cretácico Temprano.
Palabras clave: petrografía sedimentaria, análisis discriminante, procedencia, ambiente tectónico, cuencas sedimentarias, áreas fuente.
1. INTRODUCTION–PROVENANCE
This work uses petrographic data sets from previous works for solving multivariate and discriminant analyses. The goal is to correlate the compositional characteristics in sandstones among the types of basins where sediment deposits, for either recent or ancient settings. Also, this work restricts to link between types of basins and framework composition in clastic sediments. • VOL. LXII No. 1 ENERO-JUNIO 2020 The modal composition of siliciclastic sediments reflects factors such as weathering, climate, relief, source- rock composition, and tectonic setting (Johnsson, 1993). Quantitative studies of lithic fragments are the best way to distinguish source rocks (Garzanti, 2010, personal communication). A compositional variability in sandstones can be shared in different types of depocenters by plate-tectonic interaction (e.g., Busby and Ingersoll, 1995). Sandstone composition may prove exhumation and unroofing of rocks, or the formation of new source areas by magmatic processes (Ocampo-Díaz and Rubio-Cisneros, 2013).
Tectonics studies the erosion of orogenic source areas using petrographic and mineralogical data (Crook, 1974; Dickinson et al., 1983; Critelli et al., 1995; Garzanti et al., 2004; 2010). Modal composition and petrofacies in sandstones are sensitive to changes in source-areas for explaining depositional sequences (Ingersoll, 1983; Arribas et al., 2003).
Some publications have contributed to studies using sandstone composition for classifying tectonic settings in ternary diagrams. (e.g., Dickinson and Suczek, 1979; Ingersoll and Suczek, 1979). Meanwhile, other works study some constituents in sandstones and their type of basin in tectonic settings (e.g., Ingersoll and Suczek, 1979; Marsaglia and Ingersoll, 1992; Garzanti et al., 2003). Other authors calculate an empirical and statistical Sedimentary Recycling Index (SeReIn) for detecting compositional variability in detrital modes, an indicator of facies (e.g., storm deposits versus sand flat), grain size (e.g., tidal channels versus mixed flat),
6 or intra-formational recycling called “cannibalism” versus formation of unconformities (Ocampo-Díaz and Rubio-Cisneros, 2013). However, provenance analyses have not reached a consensus to correlate the types of known sedimentary basins with the composition of detrital constituents in sandstones.
Although this work does is not intended for petroleum purposes or geological-economic implications, it explains petrographic characteristics of formations comparable to reservoirs of siliciclastic rocks, with applications to sedimentary basins in the oil and gas industry.
The tectonic setting classification in this work is according to the QmFL diagram from Dickinson et al. (1983). The characteristics of basins and their classification belong to Ingersoll and Busby (1995) and Miall (1996). To avoid confusion about the terminology of basins and tectonics, we adopted those described in Busby and Ingersoll (1995) and Busby and Azor (2011).
1.1 INTRODUCCIÓN - PROCEDENCIA
Este trabajo utiliza conjuntos de datos petrográficos en trabajos previos para calcular análisis multivariados y discriminantes. El objetivo es correlacionar las características de composición en las areniscas entre los tipos de cuencas donde se depositan sedimentos, ya sea para ambientes recientes o antiguos. También, este trabajo se restringe a vincular los tipos de cuencas y la composición de sedimentos clásticos.
La composición modal de los sedimentos siliciclásticos refleja los factores como el intemperismo, clima, relieve, la composición de la roca fuente y el ambiente tectónico (Johnsson, 1993). Los estudios cuantitativos de fragmentos líticos son la mejor manera para distinguir las rocas fuente (Garzanti, 2010, comunicación personal). La variabilidad composicional en las areniscas puede compartirse en diferentes tipos de cuencas mediante la interacción de las placas tectónicas (p.ej., Busby e Ingersoll, 1995). La composición de areniscas puede comprobar la exhumación y erosión de rocas, o la formación de áreas fuente por procesos magmáticos (Ocampo-Díaz y Rubio-Cisneros, 2013).
La tectónica estudia la erosión de las áreas fuente orogénicas utilizando datos petrográficos y mineralógicos (p.ej., Crook, 1974; Dickinson et al., 1983; Critelli et al., 1995; Garzanti et al., 2004; 2010). La composición modal y las petrofacies en areniscas son sensibles a los cambios en las áreas fuente para explicar las secuencias del depósito (Ingersoll, 1983; Arribas et al., 2003).
Algunas publicaciones han contribuido al estudio usando la composición de las areniscas para clasificar los ambientes tectónicos en diagramas ternarios (p.ej., Dickinson y Suczek, 1979; Ingersoll y Suczek, 1979). Mientras tanto, otros trabajos estudian algunos componentes en las areniscas y su tipo de cuenca en ambientes tectónicos (p.ej., Ingersoll y Suczek, 1979; Marsaglia e Ingersoll, 1992; Garzanti et al., 2003). Otros autores calcularon un índice de reciclaje sedimentario (SeReIn) empírico y estadístico para detectar variabilidad en las composiciones de las modas detríticas, un indicador de facies (p.ej., depósitos de tormenta contra planicie de lodos), tamaño de grano (p.ej., canales de marea contra planicies mareales), o reciclaje intraformacional llamado “canibalismo” contra la formación de discordancias (Ocampo-Díaz y Rubio-Cisneros, Category Definition 2013). Sin embargo, los análisis de procedencia no Qt total quartz han alcanzado un consenso para correlacionar el Qm monocrystalline quartz tipo de cuencas sedimentarias conocidas con la Qp polycrystalline quartz composición de los constituyentes detríticos en F potassium feldespar areniscas. P plagioclase feldespar Lv volcanic lithic Aunque este trabajo no está destinado a fines Lm metamorphic lithic fragment petroleros o implicaciones geológico-económicas, Ls sedimentary lithic fragment explica las características petrográficas de formaciones comparables con yacimientos de rocas Table 1. Principal detrital group components following the SeReIn siliciclásticas, de aplicación a cuencas sedimentarias method proposed by Rubio-Cisneros and Ocampo-Díaz (2014) and en la industria del gas y petróleo. Ocampo-Díaz and Rubio-Cisneros (2013).
La clasificación del ambiente tectónico en este trabajo All data is set to center log-ratio transformation (clr- está de acuerdo con el diagrama QmFL de Dickinson log) and isometric log-ratio transformation (ilr-log). All et al. (1983). Las características de cuencas y su indices adopt the ln- prefix to scale the compositional clasificación pertenecen a Ingersoll y Busby (1995) y information in a simplex of Euclidean characteristics. Miall (1996). Para evitar la confusión en la terminología The methods to convert compositional data applying de cuencas y tectónica, hemos adoptado los descritos log-ratio transformations “clr-log” and isometric log- en Busby e Ingersoll (1995) y Busby y Azor (2011). ratio transformations “ilr-log” are in Aitchison (1986, 1992), Barceló et al. (1996), and Ohta and Arai (2007).
2. MATERIALS AND METHODS We used the methods from Swan and Sandilands, (1995), Agrawal (1999) and Agrawal et al. (2004) for The parameters used in here are some of the classic testing predictor variables in a canonical discriminant sandstone constituents such as i) Qt (total quartz), analysis. Wilk’s lambda method helped us to select Qm (monocrystalline quartz), and Qp (polycrystalline the variables to reduce the dataset. quartz) that indicate transport and textural maturity; ii) Lm (metamorphic lithic fragments), Lv (volcanic We run the “Statistica-Statsoft/PC+” statistical lithic grains), K-feldspar, and P (plagioclase) – for the software to analyze the discrimination of samples. nature and composition of source rocks; and iii) Ls Every canonical discriminant score arranges in (sedimentary lithic grains) –relates to recycling. The cases with a normal distribution. The analyses for petrographic parameters and their corresponding discrimination examine each group of samples at a tectonic settings in this work were gathered from time, calculating all possible combinations of groups. various publications, as described in Table 1. All the values represent the main tectonic settings, including The discriminant analysis determines which those proposed as provenance-types from Dickinson variables classify among the dataset to group and Suczek (1979) and Dickinson et al. (1983). All together in basins. Then, all orthogonal components basins fall into two main categories of tectonics are recalculated on a composition to solve the settings, extensional basins and non-subductable; discriminant scores and fit the data in a ternary for example, foreland basins, surrounding arc diagram using a closure operation (Ohta and Arai, massive basins (e.g., forearc basins), and strike-slip 2007). Each tectonic group of samples comes after basins (s.s., Busby and Ingersoll, 1995). The selected solving its discriminant score D, to then classify a compositional parameters have restrictions based on sample into a given compositional tectonic setting. the Sedimentary Recycling Index (SeReIn; Ocampo-Díaz and Rubio-Cisneros, 2013). Samples not corresponding to any compositional field are discarded from the analysis and do not qualify for any specific type of basin. We consider that at each discrete point in the stratigraphy, the composition of the basin is not limited by time, undertaking instead lateral variability in the stratigraphy driven by autogenic processes. Therefore, samples not corresponding to any compositional field at every time in the evolution of the crust fit neither basin nor the “hybrid” category.
3. PREVIOUS WORKS AND RESULTS: COMPOSITIONAL ANALYSIS (QFL) FOR BASIN DISCRIMINATION
We compiled 1411 samples of source rock composition from sandstones reported on nine basins: (I) Accretionary n=85 (Critelli et al., 2007 n=83; Garzanti et al., 1996 n=2), (II) Back- arc n=164 (Critelli et al., 2002 n=34; Li et al., 2004 n=130), (III) Collisional n=52 (Critelli and Reed, 1999), (IV) Continental-margin arc n=189 (Critelli et al., 1997 n=4; Ingersoll and Eastmoond, 2007 n=135; Lee and Lee, 2000 n=23; Michaelsen and Henderson, 2000 n=27), (V) Forearc n=443 (Critelli and Nielsen, 2000 n=38; Garzanti et al., 1996 n=3; Krueger, 1990 n=28; Kutterolf et al., 2008 n=337; Marsaglia et al., 1992 n=17; Rubin, 2002 n=20), (VI) Foreland n=74 (Critelli and Le Pera, 1995 n=10; Garzanti et al., 1996 n=5; Hossain et al., 2010 n=33; Lawton et al., 2009 n=26), (VII) Intra-arc n=49 (Colquhoun et al., 1999 n=23; Schwarzer et al., 2003 n=26), (VIII) Rift n=104 (Arribas et al., 2003 n=11; Garzanti et al., 1996 n=1; Gonzalez-Acebrón et al., 2007 n=26; Mader and Neubauer, 2004 n=24; Marsaglia et al., 2007 n=42), (IX) Strike-slip n=248 (Critelli and Ingersoll, 1995 n=59; Critelli et al., 1995 n=73; Critelli et al., 1997 n=9; Rumelhart and Ingersoll, 1997 n=71; Spencer et al., 2011 n=36).
All samples from the nine sedimentary basins relate to four main tectonic settings, according to their detrital modes (Table 2). For more details about the types of basins and tectonic settings, see Table 3 for Basin Classification from Ingersoll and Busby (1995).
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 9 Continental block Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 45 2.81636 2.41411 3.21861 2.45786 3.14302 1.0045 1.00226 1.37852 ln-Qp 45 0.52293 0.27232 0.77353 0.16614 0.24102 0.3899 0.62442 1.59682 ln-Qm 45 2.63298 2.30443 2.96152 2.44926 2.63640 0.6701 0.81862 -0.02674 ln-Ls 45 0.92472 0.44473 1.40471 0.51958 0.34756 1.4303 1.19597 2.70331 ln-Lm 45 1.16902 0.55589 1.78216 0.62474 0.34756 2.3339 1.52772 2.30221 ln-Lv 45 1.84918 0.40364 3.29472 0.62609 0.34756 12.9728 3.60178 6.01710 ln-F 45 5.06340 2.71172 7.41509 1.73755 1.99849 34.3344 5.85956 -0.33356 ln-P 45 14.46375 4.55028 24.37722 2.83190 2.49433 610.1323 24.70086 2.63502
Magmatic arc Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 566 2.38897 2.21573 2.56222 1.72380 2.60565 2.54308 1.594704 42.23142 ln-Qp 566 0.80531 0.68143 0.92918 0.26233 0.26871 1.30022 1.140273 3.46785 ln-Qm 566 2.86831 2.72748 3.00914 2.21164 3.13227 1.68046 1.296326 -0.20926 ln-Ls 566 0.81423 0.65477 0.97369 0.21561 0.17658 2.15454 1.467836 11.59491 ln-Lm 566 2.49100 2.21097 2.77103 0.80796 1.66154 6.64435 2.577664 -0.48740 ln-Lv 566 4.77919 4.41452 5.14385 2.41062 4.76758 11.26759 3.356723 -1.09979 ln-F 566 1.20605 1.10602 1.30608 0.69099 1.25599 0.84785 0.920786 2.96314 ln-P 566 4.04062 3.80201 4.27924 3.44611 3.53986 4.82443 2.196459 0.24979
Recycle orogen Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 710 1.93490 1.87498 1.99482 1.77235 2.03506 0.38212 0.618157 0.33816 ln-Qp 710 0.71505 0.66533 0.76476 0.39413 0.72896 0.26309 0.512922 -0.31226 • VOL. LXII No. 1 ENERO-JUNIO 2020 ln-Qm 710 1.58375 1.52865 1.63885 1.43177 1.66120 0.32313 0.568447 0.19469 ln-Ls 710 4.28426 3.85217 4.71636 2.22935 2.70695 19.87192 4.457793 5.53477 ln-Lm 710 3.79742 3.43913 4.15572 1.38865 2.95457 13.66372 3.696447 0.37896 ln-Lv 710 2.84090 2.49696 3.18484 1.04006 1.51478 12.59084 3.548357 5.67102 ln-F 710 0.72131 0.66198 0.78064 0.47514 0.56702 0.37466 0.612094 2.42696 ln-P 710 1.08285 0.99217 1.17353 0.65366 0.80588 0.87522 0.935533 0.42336
Mixed provenance Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 97 1.94771 1.785587 2.10984 1.795891 2.209222 0.369172 0.607595 -0.12812 ln-Qp 97 0.50969 0.410779 0.60859 0.329874 0.475052 0.137392 0.370664 0.85394 ln-Qm 97 1.70483 1.642170 1.76748 1.688252 1.675885 0.055136 0.234811 0.31816 ln-Ls 97 2.74315 2.143078 3.34322 1.798389 2.070361 5.057304 2.248845 1.88456 ln-Lm 97 1.68370 1.126865 2.24053 0.825333 0.955756 4.354765 2.086807 3.15732 ln-Lv 97 1.04560 0.693536 1.39767 0.439245 0.779449 1.740863 1.319418 11.11062 ln-F 97 1.22288 1.046644 1.39911 1.024485 1.061379 0.436210 0.660462 -0.30456 ln-P 97 1.69233 1.511729 1.87293 1.497183 1.832098 0.458089 0.676822 0.10824
Table 2. Basic statistics for different provenance settings, according to Dickinson and Suckzek (1979).
10 Compositional types of basin Tectonic setting equivalent Basin classification (Rubio-Cisneros and to Busby and Ingersoll (c.f., Busby and Ingersoll, 1995) Ocampo-Díaz, this work) (1995) Accretionary –type basins Convergent setting Acretionary prims, Trenches, Trenches –Slope basins Back-arc basins Convergent settings Back-arc Collisional basins Convergent settings Piggyback Basins, Trenches, Trench-Slope Basins Forearc basins Convergent settings Forearc Foreland basins Convergent settings Retroarc Foreland Basins, Peripheral Foreland Basins, Foreland Intermontane Basins (Broken Forelands) Intra-arc basins Convergent settings Intrerarc Basins: Continental-margin arc Convergent settings Interarc Basins Rift basins Divergent settings Terrestrial Rift Valley, Proto-Oceanic Rift Troughs Intraplate settings Continental Rises and Terraces, Continental Embankments, Intracratonic Basins, Active Ocean Basins, Passive margins (Oceanic Islands, Aseismic Ridges and Plateaus, Dormant Ocean Basins, Intraplate Basin) Strike-Slip Transform settings (and Transtensional Basins, Transpressional Basins, transcurrent fault-related basins) Transrotational Basins:
Table 3. Basins and their equivalent tectonic setting. (modified after Dickinson, 1974b, 1976a, and Ingersoll, 1988, in Ingersoll and Busby, 1995).
We describe the characteristics of each type of basin and its relationship to any known tectonic setting. The bivariate and multivariate statistical analysis helped by organizing the data in basins regarding their composition. Then, we calculated the mean compositional parameters by sorting the composition of sand and sandstones in each type of basin, discriminating against any other sand or sandstone among the basins.
3.1 FRAMEWORK MODES: COMPOSITIONAL DIAGRAMS AND PROVENANCE TYPES Our database consists of 1411 individual samples from sandstone point counts reported in 26 different references on peer-reviewed journals. The data was used to calculate compositional framework modes.
3.2 A COMPILATION OF TYPES OF BASINS AND THEIR COMPOSITION To identify the basin from which provenance originates, we considered their tectonic occurrence, compositional features, and associations to the plots from Dickinson et al. (1983; see Table 3).
• 3.2.1 ACCRETIONARY–TYPE BASINS Basins developed by accretionary orogen tectonics hold ocean plate stratigraphy, a fundamental structure for recognizing recent or ancient accretionary wedges (Condie, 2007; Kusky et al., 2010; Santosh et al., 2010). Accretionary basins contain sediments eroded from sequences related to subduction or duplexing. Sandstones contain a suite of polycrystalline quartz, with high content of lithic fragments from high-middle grade metamorphic rocks (e.g., gneisses and schists), or middle-low grade metamorphic rocks (psammites- phyllites), rock fragments from mélange, high quartz content from the olistostrome accretionary complex, chert, basic volcanic lithics, calcareous arenites, including bioclasts, and fine-grained detritus in a matrix of mafic mudstones from continental regions. These quartzo-feldspathic sands contain detritus indicative of
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 11 quartzose to mixed recycled orogenic sources, formed on a passive continental margin (Figure 1c). Accretionary basins are defined by three main discriminant compositional parameters: (i) ln-Qm: 2.356, (ii) ln-Ls: 5.038, and (iii) ln-P: 1.732 (Figure 2; Table 4).
(A) Qm (B) Qm Explanation Forearc Back-arc Accretionary Continental- Collisional margin arc Recycled orogen Foreland Rift Intra-arc mixed Strike-slip
Magmatic Continental Block arc F Lt F Lt
Accretionary basins Backarc basins Collisional basins )C( Qm )D( Qm )E( Qm
l
n
o
F Lt F Lt F Lt Forearc basins Foreland basins Intra-arc basins )F( Qm )G( Qm )H( Qm • VOL. LXII No. 1 ENERO-JUNIO 2020
Mixed T
T T
F Lt F Lt F Lt Continental-margin arc basins Rift basins Strike-slip basins )I( Qm )J( Qm )K( Qm
T T
F Lt F Lt F Lt
Figure 1: QmFLt diagram from Dickinson et al. (1983), with 1411 samples taken from 26 different references. The data distributes in nine diagrams for better visualization of each type of sedimentary basin.
12 3.5 1.6
3.0 1.4 1.2 2.5
t 1.0 2.0 0.8
ln-Qp ln-Q 1.5 0.6 1.0 0.4 0.5 Mean 0.2 Mean±0.95 Conf. Interval 0.0 Mean standard errors calculated 0.0 using pooled variance -0.5 -0.2 4.0 10
3.5 8
3.0 6 2.5 4 2.0
ln-Qm ln-Ls 2 1.5 0 1.0
0.5 -2
0.0 -4 10 16 14 8 12 6 10
4 8
ln-Lv ln-Lm 2 6 4 0 2 -2 0 -4 -2 3.0 9 2.8 2.6 8 2.4 7 2.2 2.0 6 1.8
ln-F 1.6 5
1.4 ln-P 4 1.2 1.0 3 0.8 0.6 2 0.4 1 0.2 0.0 0 Explanationn Forearc Back-arc Accretionary Continental- Collisional margin arc Foreland Rift Intra-arc Strike-slip
Figure 2: Box-plot diagram with values from the log-ratio transformations of the main compositional indices of sandstones, employing compositional data from nine basins.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 13 • 3.2.2 BACK-ARC BASINS from axial nappes incorporate fragments from the Back-arc basins belong to convergent settings shallow, intermediate, and deep structural levels that (Ingersoll and Busby, 1995), but with either a provide sedimentoclastic lithics, metamorphiclastic contractional or extensional behavior (Stern, 2010). quartzolithic, and quartzofeldspathic compositions, Back-arc basins locate next to volcanic arcs. They respectively — these three lithic fragments vary in are oceanic basins behind intra-oceanic magmatic their grade of metamorphism. arcs (including intra-arc basins between active and remnant arcs), or continental basins behind In contrast, detritus from the shallower structural continental-margin magmatic arcs without foreland level consist of calcareous, pellitic, and psammitic rock fold-thrust belts. The stratigraphy records variability fragments. Quartz and feldspar contents are generally in the composition of sandstones, according to the low, but recycling of arenaceous turbidites produces nature of the arc and pre-established rocks (e.g., quartzofeldspathic compositions. Metamorphic Kusky et al. 2010). Some back-arc basins related detritus consists of low rank metasedimentary to oceanic arc systems with sedimentation at lithic grains. Sandstone compositions from the high latitudes or in equatorial regions. The basins intermediate structural level at the accretion may contain high biological productivity that may complex include fragments from retrograde high- contribute considerably to large proportions of pressure metamorphic nappes, intermediate quartz, biogenic components in sandstones (Marsaglia, subordinate feldspars, and abundant metamorphic 1995). The framework composition of back-arc lithic grains. Metasedimentary rocks commonly basins suggests input from components from newly supply recrystallized to foliated metacarbonate formed source-areas (e.g., volcanic lithic grains; fragments. Detritus from deep structural levels and Figure 1d). Statistically, the main discriminant the external thrust belts are quartzofeldspathic composition for back-arc basins comes from three in composition, with very high-rank metamorphic primary parameters: (i) ln-Lv: 4.841, (ii) ln-Ls: 3.891, rock fragments from old basement sources. All (iii) ln-Qt: 1.794 (Figure 2; Table 4). constituents are mixed in various proportions with medium-rank to non-metamorphic lithic detritus, • 3.2.3 COLLISIONAL BASINS such as metamorphiclastic to sedimentaclastic Basins related to crustal collisions occupy convergent compositions, mixing with fragments from axial
• VOL. LXII No. 1 ENERO-JUNIO 2020 settings (Ingersoll and Busby, 1995). The geometry nappes. Detritus from sedimentary thrust-sheets of the basin comes while suturing a tectonic collision are lithic sands dominated by carbonate grains unless and following frontal subduction at the final stage carbonate strata are absent from the sedimentary of accretion (Dewey, 1977). Collisional basins form section in the thrust belt (Maruyama et al., 2010). before developing foreland basins; in both of its fronts are collision orogens with double vergence Collision-orogenic sediments are complex to (e.g., Santosh et al., 2010). Detritus from axial nappes determine. However, some significant considerations recycle with basement rocks and uplifted cover units for improving the provenance analysis are determining from external thrust belts. The basin develops by (a) the metamorphic history of the axial nappe stack, merging the recycling of accreted molasses and (b) occurrence of old crystalline relics within both axial alluvial plain deposits. nappes and external belts, (c) recycling of accreted molasses, glacial, and alluvial deposits, (d) mixing of Each structural level determines the sediment detritus from unrelated sources during long-distance composition in collisional basins, primarily while transport, and (e) selective destruction of unstable unroofing the metamorphic complex (Figure 1e). components during transport and diagenesis (Garzanti Detritus from each structural level correspond to either et al., 2007). Discriminant values detect the framework oceanic or continental crusts, alternating in sources complexity of collisional basins according to three from the protolith at the basement and shallow units prime compositional parameters: (i) ln-Lm: 6.635, (ii) of the nappe pile (Garzanti et al., 2004). Detritus ln-Qm: 2.00, and (iii) ln-P: 1.023 (Figure 2; Table 4).
14 • 3.2.4 FOREARC BASINS foredeep induced by predecessor rift and back-arc The basin subdivision for convergent settings basins. The provenance of foreland sediments is from includes forearc basins. The forearc is the lithosphere source areas forming the fold-thrust belt (Dickinson, that lies between the trench and the volcanic- 1974a, 1976). The uplift of the depocenter along magmatic arc. They also occur in arc-trench gaps. thrust faults and climate are the two major geologic The stratigraphy of forearc basins represents the processes affecting the basin (Lawton, 1986). Clastic split of an arc, lying immediately above arc volcanism. sediments in the foreland basin are mixtures of detritus Forearc basins preserve a juvenile arc lithosphere from both axial nappes and external belts, which have and its arc sequences. Sometimes forearc basins plutoniclastic, metamorphiclastic and sedimentaclastic may be associated with an accretionary prism. Each compositions, grouping into several of the provenance structural zone in a forearc contrasts according to its types. The provenance of many ancient retroarc erosion rates, newly formed source areas, and detrital foreland basins is predominantly from recycling the transport (Figure 1f). The zoning consists of a stable sedimentary cover (Jordan, 1995; DeCelles and Giles, inner forearc with thin rock sequences, in contrast 1996). The massive sedimentary fill in foreland basins to a deformed outer zone. Forearc basins with contains quartz-rich, feldspar-poor detritus eroded sedimentation under high biological productivity may from cratons and basement blocks; however, the bulk present considerably larger proportions of biogenic of the fragments is less quartz-rich. Upsection lithic components in sandstones (Marsaglia, 1995). Detrital fragments become more abundant than the underlying compositions in forearc basins constrain six main profile. Source-areas of sediments are orogenic, either discriminant parameters: (i) ln-Lm: 1.654, (ii) ln-Qt: from, old continental margin deposits exposed in 1.537, (iii) ln-Qm: 1.146, (iv) ln-Lv: 1.419, (v) ln-P: sedimentary and metasedimentary nappes, or from 1.07, and (vi) ln-Ls: 0.965 (Figure 2; Table 4). early sediments deformed in the fold-thrust belt (Figure 1g). Sources that supply the least in foreland basins • 3.2.5 FORELAND BASINS are subduction complexes or magmatic arcs, mainly Foreland basins develop mainly in convergent because the upland zone topographically shields such settings. These sedimentary basins lie between the sources, or because longitudinal sediment dispersion front of a mountain and the adjacent craton in the covers the sources along the strike of the suturing extents of the shield zone (Allen et al., 1986; Ingersoll orogenic belt (Schwab, 1986). Then, the conditions of and Busby, 1995). Foreland basis includes Retroarc sedimentary environments in proximity to source-rocks Foreland Basins and Peripheral Foreland Basins. basins impact heterogeneity of sandstone composition Retroarc foreland basins are elongate trough located (e.g., Damanti, 1993). Foreland basins relate to five on the continental side of continental-margin arc- principal compositional values: (i) ln-Ls: 3.903, (ii) ln- trench systems. These systems form between narrow Qm: 2.785, (iii) ln-Qt: 2.482; (iv) ln-Lm: 1.426, and (v) contractional orogenic belts related to an active arc ln-P: 1.095 (Figure 2; Table 4). and a stable craton, with progressive compression and collision during subduction (DeCelles and Giles, • 3.2.6 INTRA-ARC BASINS 1996). Peripheral Foreland Basins lie above rifted Intra-arc basins form along the margins of island continental margins pulled into subduction zones chains overlying the basement of young continental during a crustal collision. Mini foreland basins may set crust (de Ronde et al., 2003). They form at the next to uplifted blocks at strike-slip basins caused by juncture of thin back-arc basins, forearc basin crust, the flexural loading of the marginal crust. and thick crust beneath the volcanic–magmatic arc. The basin is deep with deposits of volcaniclastic The modal composition of foreland fold-thrust belts, sediments originated from an arc. In general, the especially during initiation, is significantly influenced sedimentary fill comes from a destructive plate by the former tectonic regime. Also, the evolution margin with an active magmatic center, where hinge of foreland basins depends on preexisting basin faults or fracture zones intervene. Sandstones vary in configuration and the patterns in subsidence at the composition, depending on the magmatism through
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 15 subduction. Also, intra-oceanic arcs are genetically crust of contamination and assimilation of magmas related to other structures occurring in the Island arc contribute to lately formed minerals to the basin model and herein treated as systems like a trench, (Figure 1i). forearc, arc, and back-arc regions. Ocampo-Díaz and Rubio-Cisneros (2013) Sediment input is dominantly volcanogenic and documented a modal composition of sands from derives mainly from the active volcanic arc. Sands continental-margin arcs related to a change in are volcaniclastic and plutoniclastic in composition. source-area and sedimentary recycling. The results Source-areas correspond to magmatic arcs that lie from the discriminant statistical analysis solve five along continental margins where the crust is thicker compositional values corresponding to: (i) ln-P: 3.02, than in intra-oceanic arcs, or where the arc massif (ii) ln-Qm: 2.798, (iii) ln-Lv: 2.285, (iv) ln-Qt: 2.00, remains partly submerged (Figure 1h). Other sources and (v) ln-Lm: 1.231 (Figure 2; Table 4). The suite of emerge from breaking an arc massif by parallel composition correlates to nascent arc activity, with transforms or faults, exposing plutons and their similar values in newly active continental margins. wall rocks that supply arkosic detritus to the forearc region (Marsaglia and Ingersoll, 1992). • 3.2.8 RIFT BASINS Rift basins are depocenters over continental crust. Detrital modes in sandstones indicate the composition They are commonly associated with bimodal of petrogenetic igneous processes, such as magma volcanism and incipient oceanic basins floored by generation in intra-arc basins. Partial melting in the new oceanic crust. Young rifted continental margins Earth’s upper mantle can modify the composition flank the basin. Tectonic activity is principal factor of primary magmas. Thus, magma composition, controlling sedimentation in rift basins (Prosser, crystal fractionation, and air-fall deposits account 1993). Faults in these systems reactivate during for the variation of detrital modes in intra-arc basins. stages of lithosphere extension. The erosion and Magmatism at intra-oceanic arc systems increases dispersion of sediments in the basin determine in alkalinity away from the trench; consequently, the the composition of sandstones (Arribas et al., composition of in clastic successions varies as the 2003; González-Acebrón et al., 2007; Marsaglia magmatic center migrates away from the sedimentary et al., 2007). Although a variety of characteristics
• VOL. LXII No. 1 ENERO-JUNIO 2020 basin (Wilson, 1989, 2007; Gill, 2010). The petrography distinguish rift basins (Garzanti et al., 2003), the of sandstones from intra-oceanic arcs correlates provenance for its sedimentary sequence defines to the magma series from calc-alkaline to potassic the periods of extension, sedimentary renovation, alkaline suites with high-MgO. Sandstone in intra-arc climatic conditions, and the composition of the basins is highly porphyritic, generally containing major basement blocks, which eventually are buried by the ferromagnesian minerals. Plagioclase is usually the sedimentary cover and subsidence (Johnsson, 1993). most abundant phenocryst. Groundmasses can vary Besides allogenic factors, autogenic processes affect from glassy to microcrystalline, but generally, contains sediment composition too, but to a lesser extent. the same minerals as in phenocryst phases. Rock fragments also include xenocrysts. Intra-arc basins The first stage of deposition in a rift and pull-apart include five main discriminant compositional values: basins starts with the erosion of the pre-existing (i) ln-Lv: 7.203, (ii) ln-P: 5.43, (iii) ln-Qt: 1.22, (iv) ln-Qp: sedimentary cover and in fewer proportions 0.95, and (v) ln-Qm: 0.857 (Figure 2; Table 4). basement rocks (volcanic rifted-margin provenance to rift-shoulder provenance; cf., Garzanti et al., 2001). • 3.2.7 CONTINENTAL-MAGMATIC ARC BASINS The subsequent stages involve deep erosion of the Basins at continental-margin arcs present magmatism basement and its recycling with previous sequences related to the subduction of an oceanic plate beneath a (cf., Ocampo-Díaz and Rubio-Cisneros, 2013). continent (Wilson, 1989). Partial melting and fractional crystallization in the mantle and processes in the
16 Volcaniclastic sands at rifted-margins are fault zone and plate boundaries. These sectors have feldspatholithic, but with bimodal lithics either from irregular collision fronts, where constriction expels basalt or rhyolite. Sands contain abundant granophyre pieces of crust or splinters denominated “scholles” grains and low rates of plagioclase/total feldspar (P/F) (McKenzie, 1972; Burke and Sengor, 1986). The eroded from syn-rift hypersolvus alkali granites in a fragmentation of crust supplies a suite of detrital younger crust (Garzanti et al., 2001). The classification assemblages to sandstones. of rift-shoulder provenance has compositions of quartzolithic sedimentaclastic, arkosic, and Framework petrography of strike-slip basins basementaclastic. The provenance of detrital suites in points out polycyclic sedimentary episodes, under rift-shoulder is continental blocks. Sandstones decrease multiple phases of subsidence, uplift of source- in quartz content when deeper the erosion, as in the rift lands, and basin migration (Figure 1k). Sandstone stages of undissected to dissected. However, sand from compositions tend to be extraordinarily variable arc terranes containing paleovolcanic to metabasite and complex, depending on whether the basins are lithics comes from recycled orogens. Sedimentary submarine, sublacustrine, subaerial, or some random detritus from undissected rift shoulders comprise combination of these (Nilsen and McLaughlin, 1985). recycled quartz and carbonate lithic fragments. Arkosic Strike-slip basins discriminate in composition upon sands from exposed basement rocks on dissected rift five framework parameters: (i) ln-Qm: 2.244, (ii) ln-P: shoulders contain an excess of quartz contrary to the 2.217, (iii) ln-Lv: 2.156, (iv) ln-Lm: 1.788, (v) ln-Qt: fact of an “ideal arkose”. For instance, clastic suites 1.974 (Figure 2; Table 4). of rifted-margin commonly include quartzfeldspathic sands, but also quartzolithic and feldspatholithic 3.3 DISCRIMINANT FUNCTIONS volcano-plutonic sands. Rift clastics can share sources The analysis identifies three general fields for from continental blocks, recycled orogens, and compositional discrimination; each of them solved by magmatic arcs in a standard quartz-feldsparlithics a discriminant function. Overlapping the three general triangular plot (QmFL; Figure 1j). The framework functions are nine fields representing the geometric composition to discriminate rift basins associates with means for each basin (Figure 3a-k). four parameters: (i) ln-Qm: 3.078, (ii) ln-Qt: 2.565, (iii) ln-Ls: 1.818, and (iv) ln-F: 1.244 (Figure 2; Table 4). The top part of the ternary plot is the discriminant function 1-one (DF1) that is populated by forearc • 3.2.9 STRIKE-SLIP BASINS basins, foreland basins, rift systems, accretionary This work considers strike-slip basins as depocenters basins, or suture complexes (Figure 3f, g, and j). DF1 existing in various tectonic settings (Mann et al., has an increase in positive values of Qt, Ls, and Qp. 1983), mostly in transform settings and basins with The petrographic indices in discriminant function 1 transcurrent faults (Ingersoll and Busby, 1995). support the processes of sediment transport, the Some structural styles divide strike-slip basins into exhumation of the sedimentary carapace, and a different classes: (1) Transtensional basins –basins moderate supply of metamorphic rocks (ln-Qt, ln-Ls, formed by extension along strike-slip fault systems, (2) and ln-Qp; Tables 2 and 6). Transpressional basins –basins formed by compression along strike-slip fault systems, and (3) Transrotational At the low left angle of the plot lies discriminant basins –basins formed by rotation of crustal blocks function 2-two (DF2). It stands for the formation of with vertical axes in strike-slip fault systems. new source-rocks in collisional zones, continental- margin arcs, and strike-slip basins (Figure 3e, f, i, The composition of sandstone relies on the geometry and k). DF2 estimates increasing values in Qp, Lm, of the structures like releasing or restraining bends and Qm. The detrital components near DF2 relate and pull-apart basins (Nilsen and Sylvester, 1995; to moderate–high sediment transport, and the Noda, 2013). Equally, fractures and faults depend exhumation of plutonic or metamorphic source-lands on the bending or (over-) stepping geometry in the (ln-Qp, ln-Qm, ln-F, and ln-Lm; Tables 2 and 6).
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 17 Accretionary-type basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 85 1.53000 1.31146 1.74855 1.15026 1.96472 0.58441 0.764468 -0.94610 ln -Qp 85 0.85546 0.60614 1.10478 0.36899 0.45548 0.76061 0.872132 -1.32907 ln -Qm 85 2.64433 2.38374 2.90493 2.35641 2.65006 0.83098 0.911583 1.65828 ln -Ls 85 6.18316 5.04391 7.32241 5.03846 4.82542 15.88131 3.985136 3.43002 ln -Lm 85 2.43169 1.90745 2.95593 1.28596 2.98839 3.36290 1.833822 -1.00782 ln -Lv 85 0.41387 0.02837 0.79938 0.13356 0.09492 1.81851 1.348520 39.32859 ln -F 85 0.91470 0.75553 1.07388 0.66716 0.95175 0.31002 0.556792 0.28879 In-P 85 2.12268 1.75090 2.49446 1.73204 1.95011 1.69132 1.300509 15.27716 SeReIn 85 9.08475 8.69354 9.47596 8.87765 9.35994 1.87270 1.368465 18.20286 X=a SeReIn 85 14.33574 13.75368 14.91780 14.20997 14.12568 4.14555 2.036063 5.23164 Y=a
Back-arc basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 164 2.60001 2.30146 2.89855 1.79455 2.83344 2.1518 1.46691 -1.18031 ln-Qp 164 1.07687 0.88170 1.27203 0.54429 0.83198 0.9196 0.95895 -0.09579 ln-Qm 164 1.52644 1.30787 1.74501 1.02393 1.23567 1.1534 1.07396 -0.73830 ln-Ls 164 9.67173 7.78380 11.55966 3.89157 6.82876 86.0511 9.27637 0.30670 ln-Lm 164 0.17490 0.16772 0.18207 0.17132 0.17327 0.0012 0.03525 -1.03841 ln-Lv 164 11.52398 9.59361 13.45434 4.84166 9.71538 89.9628 9.48487 -1.37302 ln-F 164 0.82428 0.61721 1.03134 0.43721 0.32794 1.0351 1.01741 3.94849 ln-P 164 5.01983 3.14921 6.89044 0.70855 0.27584 84.4804 9.19132 0.56048 SeReIn 164 11.16871 10.57549 11.76192 10.48242 12.37813 8.4958 2.91476 2.78514 X=a • VOL. LXII No. 1 ENERO-JUNIO 2020 SeReIn 164 29.52323 26.68072 32.36574 25.80397 27.50941 195.0701 13.96675 -1.17381 Y=a
Collisional basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 52 1.76388 1.66340 1.86437 1.74610 1.69436 0.073333 0.270801 3.680199 ln-Qp 52 0.38149 0.25777 0.50521 0.28500 0.23472 0.111170 0.333422 3.387706 ln-Qm 52 2.02233 1.93504 2.10961 2.00975 2.02049 0.055334 0.235232 2.124866 ln-Ls 52 1.61508 0.98037 2.24979 0.74086 0.92799 2.925957 1.710543 0.722741 ln-Lm 52 7.83858 6.96430 8.71287 6.83540 8.51167 5.551678 2.356200 2.780206 ln-Lv 52 0.55350 0.33432 0.77269 0.28638 0.31569 0.348938 0.590710 0.739361 ln-F 52 0.97127 0.70799 1.23455 0.67378 0.88217 0.503450 0.709542 -0.563966 ln-P 52 1.34867 1.06127 1.63607 1.02338 1.39648 0.599920 0.774545 -0.700760 SeReIn 52 8.19929 8.14934 8.24924 8.19820 8.21248 0.018120 0.134611 -0.491134 X=a SeReIn 52 14.22727 13.25721 15.19733 13.89488 14.89735 6.834701 2.614326 3.978060 Y=a
18 Forearc basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 443 1.77826 1.69591 1.86062 1.53796 1.99751 0.44893 0.670021 0.19197 ln-Qp 443 0.71209 0.66841 0.75577 0.56726 0.72541 0.12627 0.355344 -0.12144 ln-Qm 443 1.23448 1.18552 1.28344 1.14640 1.23452 0.15868 0.398345 0.27315 ln-Ls 443 1.47989 1.34800 1.61177 0.96593 1.27677 1.15126 1.072969 1.94549 ln-Lm 443 2.75639 2.48527 3.02750 1.65439 2.42289 4.86538 2.205762 -0.25309 ln-Lv 443 2.41945 2.10541 2.73350 1.41966 1.67303 6.52838 2.555070 5.31715 ln-F 443 0.65968 0.58193 0.73743 0.41019 0.49583 0.40014 0.632567 5.56783 ln-P 443 1.90163 1.59162 2.21164 1.07462 0.97084 6.36146 2.522194 8.52663 SeReIn 443 6.68459 6.60419 6.76499 6.64028 6.95409 0.42788 0.654129 15.24983 X=a SeReIn 443 10.86558 10.42563 11.30552 10.32229 10.00846 12.81189 3.579370 0.61007 Y=a
Foreland basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 74.000 2.568 2.378 2.758 2.483 2.482 0.383 0.619099 -0.69645 ln-Qp 74.000 0.569 0.367 0.771 0.145 0.125 0.431 0.656589 -1.53047 ln-Qm 74.000 2.804 2.709 2.898 2.786 2.841 0.095 0.307416 1.66909 ln-Ls 74.000 5.212 4.448 5.976 3.903 5.862 6.182 2.486291 -0.48581 ln-Lm 74.000 3.396 2.523 4.269 1.427 3.974 8.068 2.840421 -1.08249 ln-Lv 74.000 1.787 0.966 2.609 0.457 0.541 7.137 2.671588 5.71969 ln-F 74.000 0.563 0.418 0.708 0.359 0.506 0.222 0.471203 9.48428 ln-P 74.000 1.589 1.142 2.035 1.095 0.757 2.110 1.452503 5.01166 SeReIn 74.000 10.434 10.318 10.551 10.427 10.488 X=a SeReIn 74.000 15.217 14.723 15.711 15.139 15.180 Y=a
Intra-arc basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 49 3.06331 1.75594 4.37068 1.22275 1.60269 11.64156 3.411973 0.668065 ln-Qp 49 2.48617 1.43332 3.53902 0.95353 1.43219 7.54998 2.747723 0.668065 ln-Qm 49 2.40301 1.22587 3.58015 0.85777 0.64569 9.43774 3.072090 0.668065 ln-Ls 49 0.71244 0.14886 1.27603 0.24678 0.11699 2.16335 1.470833 0.668065 ln-Lm 49 2.43610 0.58791 4.28430 0.27579 0.10541 23.26525 4.823407 0.668065 ln-Lv 49 16.94799 13.20948 20.68650 7.20390 20.30065 95.19409 9.756746 0.668065 ln-F 49 2.34080 0.81818 3.86342 0.37522 0.10992 15.79047 3.973722 0.668065 ln-P 49 10.88974 8.10763 13.67185 5.43568 10.73585 52.71823 7.260732 0.668065 SeReIn 49 14.67324 11.00998 18.33650 11.40568 12.52310 91.40043 9.560357 0.668065 X=a SeReIn 49 36.58722 33.40676 39.76768 35.47031 40.66000 68.89574 8.300346 0.668065 Y=a
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 19 Continental-margin arc basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 189 2.79578 2.48343 3.10813 2.00362 2.82697 2.72295 1.650138 -0.61459 ln-Qp 189 0.80219 0.52672 1.07767 0.17837 0.05534 2.11804 1.455349 3.62556 ln-Qm 189 3.67080 3.26985 4.07176 2.79836 3.44082 4.48703 2.118262 0.10409 ln-Ls 189 0.52768 0.32344 0.73192 0.17252 0.10868 1.16425 1.079005 15.67077 ln-Lm 189 4.30051 3.47505 5.12596 1.23158 2.40112 19.01765 4.360923 -1.48083 ln-Lv 189 6.30710 5.36890 7.24531 2.28523 7.32873 24.56790 4.956602 -1.62622 ln-F 189 1.23475 1.02428 1.44522 0.64305 1.01936 1.23635 1.111914 1.89923 ln-P 189 4.90834 4.27192 5.54477 3.20266 4.68158 11.30478 3.362258 -0.27635 SeReIn 189 12.70724 11.97225 13.44224 11.82360 12.97593 15.07770 3.883002 0.40037 X=a SeReIn 189 20.45149 19.91151 20.99147 20.24397 20.90572 8.13810 2.852735 -0.62309 Y=a Rift basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 104 3.00653 2.65897 3.35409 2.56567 2.93524 1.82403 1.350566 -0.82718 ln-Qp 104 0.42924 0.29223 0.56625 0.12673 0.09818 0.28345 0.532397 1.06835 ln-Qm 104 3.17774 2.97890 3.37659 3.07604 3.05483 0.59703 0.772679 0.86085 ln-Ls 104 6.50478 4.72934 8.28022 1.81821 3.73095 47.59723 6.899075 -0.67533 ln-Lm 104 4.00631 2.80619 5.20644 1.45858 2.43284 21.74836 4.663514 2.43931 ln-Lv 104 1.90148 0.82004 2.98291 0.34069 0.13150 17.65918 4.202282 4.76897 ln-F 104 2.51631 1.82991 3.20271 1.24411 1.63433 7.11419 2.667244 5.80250 ln-P 104 2.16937 1.40499 2.93374 0.88963 1.61276 8.82232 2.970239 24.97969 SeReIn 104 11.78801 11.55292 12.02310 11.74981 12.25460 0.83451 0.913514 1.82323 X=a • VOL. LXII No. 1 ENERO-JUNIO 2020 SeReIn 104 19.73127 17.18163 22.28091 15.87214 20.81888 98.15881 9.907513 -0.55475 Y=a Strike-Slip basins Confidence Confidence Geometric Standard Valid N Mean Median Variance Kurtosis -99.000% +99.000% Mean Deviation ln-Qt 248 2.25139 2.06384 2.43894 1.97497 2.02671 1.294543 1.137780 5.14998 ln-Qp 248 0.46954 0.38932 0.54977 0.22561 0.34200 0.236888 0.486711 5.70571 ln-Qm 248 2.45959 2.29811 2.62107 2.24461 2.25201 0.959710 0.979648 4.02192 ln-Ls 248 0.32960 0.22083 0.43837 0.11845 0.06812 0.435412 0.659857 33.71980 ln-Lm 248 2.57310 2.26144 2.88475 1.78824 2.20044 3.574667 1.890679 1.56958 ln-Lv 248 3.62629 3.22942 4.02316 2.15667 3.58891 5.796779 2.407650 -0.70913 ln-F 248 1.20569 1.11724 1.29415 0.98720 1.24762 0.287967 0.536626 0.25276 ln-P 248 2.70574 2.48472 2.92677 2.21735 2.89696 1.797902 1.340859 2.87606 SeReIn 248 8.77579 8.49825 9.05334 8.57305 8.72662 2.834969 1.683736 3.69280 X=a SeReIn 248 12.63470 12.27309 12.99631 12.33179 13.04824 4.812447 2.193729 7.24978 Y=a Table 4. Basic statistics for nine basins with each detrital mode parameter. Data in sandstone petrography is recalculated using the values from the publications.
20 Meanwhile, discriminant function 3-three (DF3) is the right-side angle grouping back-arc basins forearc basins, intra-arc basins, continental-margin arcs, and strike-slip basins (Figure 3f, h, i, and k). DF3 plots increments of Lv, F, Qp. Function DF3 marks the development of new source-areas and recycling of ancient clastic sequences (ln-F, ln-Lv, ln-Ls, and ln-Qp; Tables 2 and 6).
(A) (B) D.F1 Explanation D.F1 Forearc Back-arc Accretionary Continental- Collisional margin arc 0.25 0.75 Foreland Rift 0.25 0.75 Intra-arc Strike-slip
0.50 0.50 0.50 0.50
Increasing Qt, Ls, Qp m Increasin 0.75 Lm, Q 0.25 0.75 0.25 g L ing Qp, v, F, Qp Increas
D.F2 D.F3 0.25 0.50 0.75 D.F2 D.F3 (C)(D) (E) Accretionary basins Back-arc basins Collisional basins D.F1 D.F1 D.F1
0.25 0.75 0.25 0.75 0.25 0.75
0.50 0.50 0.50 0.50 0.50 0.50
0.75 0.25 0.75 0.25 0.75 0.25
D.F2 D.F3 D.F2 D.F3 D.F2 D.F3 (F)(Forearc basins G) Foreland basins (H) Intra-arc basins D.F1 D.F1 D.F1
0.25 0.75 0.25 0.75 0.25 0.75
0.50 0.50 0.50 0.50 0.50 0.50
0.75 0.25 0.75 0.25 0.75 0.25
D.F2 D.F3 D.F2 D.F3 D.F2 D.F3 Continental-margin arc basin Rift basins Strike-slip basins (I) D.F1 (J) D.F1 (K) D.F1
0.25 0.75 0.25 0.75 0.25 0.75
0.50 0.50 0.50 0.50 0.50 0.50
0.75 0.25 0.75 0.25 0.75 0.25
D.F2 D.F3 D.F3 D.F3 D.F2 D.F3
Figure 3: Distribution of the discriminant analysis for the composition of sandstones from nine types of basins according to their petrographic indices.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 21 4. CASE STUDY: A DISCRIMINANT FUNCTION FOR CLASTIC SEQUENCES IN NORTHEASTERN MEXICO
A case study proves the functionality of the method and its statistical approach, using compositional and modal values from samples collected in northeastern Mexico (Figure 4, Figure 5, and Figure 6). Samples are middle to coarse-grained sandstones from Upper Triassic to Lower Cretaceous formations: El Alamar, La Boca, La Joya, La Casita, and Taraises. The description of these units and their locations, as well as the number of samples included in this work, are available in the next references: Ocampo-Díaz (2007; n=56), Rubio-Cisneros (2008; n=20), Ocampo-Díaz (2011; n=108), Rubio-Cisneros et al. (2011; n=7), Ocampo-Díaz et al. (2012; n=56), Rubio-Cisneros (2012; n=129), and Ocampo-Díaz and Rubio-Cisneros (2013; n=300), Ocampo-Díaz et al. (2014; n=16). Based on previous works, the samples and their corresponding sequences deposited in the following basins: rift, back-arc, forearc, continental-margin arc, and strike-slip.
Explanation Triassic-Lower Jurassic sequences N 25° Upper Jurassic Sequences N Lower Cretaceous Sequence 0 50 km Upper Cretaceous Sequences
Village Thrust fault Monterrey
Saltillo Santiago
Allende Montemorelos
100°30'0''W 100°10'0''W
Rayones 100°50'0''W N San Rafael 25° MONTERREY N Potrero Prieto Galeana Linares 101°10'0''W
N''0'03°52 Triassic and Juriassic Sequences Villa de Santiago • VOL. LXII No. 1 ENERO-JUNIO 2020 SALTILLO COAHUI L A San Roberto Iturbide S Allende i e Montemorelos r 101°W r 100°W a Locations of the M NUEVO LEÓN sampled formations a Linares d Galeana El Alamar Formation r e Iturbide San Roberto La Boca Formation O r La Joya Formation i e La Asención La Casita Formation n
t a USA La Escondida l El Barretal Aramberri MEXICO Tinajas Study area
C I UDAD V I C T OR I A Detail in Miquihuana TAMAUL I PAS Figure 5
99°50'0''W 99°30'0''W 99°10'0''W 0 30 06 mk
Figure 4: Geologic sketch and map of northeastern Mexico. The map with the coordinate system has two highlighted zones showing the area of study. The map in the upper right-hand locates each formation for this work with a star or polygon in a circle; it also details the units studied herein (modified form Ocampo-Díaz et al., 2012). The second highlighted zone is near the locality of Ciudad Victoria, described in Figure 5. See text for citations and Figure 6 to extend the description of the units analyzed.
22 473000 474000 475000476000477000478000 Explanation 1100062 0 130 fidnU ferentiated Cretaceous strata )uK( N La Casita Formation (Jc) El Madrono Olvido Formation (Jo) Novillo Formation (Jn) La Joya Formation (Jlj)00 16
Jn Rhyollite (Ji) 0 La Boca Formation
0 1400 2
00 upper member (Jlbs) 1 Ku La Boca Formation 00162 lower member (Jlbi)
1100 Symbols Geologic contact Locality Ji 1300 Jc Inferred geological School La Anacahuita contact Jlbi 1200 Coordinate system: UTM Topografic base map from INEGI: Ji CiudadVioctoria F-14-A-20 1100 10 Ji 00
0009062 9 00 Ji Ji El Huizachal ‘ 1 4 0 0 1 300 1200
0 1100 0 0 1 Ji La Joya Verde 1000 Cementerio
0008062
1 000 Aguas de Minas
0021 Jlbs Jn Jo Jlj
1200 13 1100 00
0007062 1400 12 00
0 12 km 1300 Graphic scale
Figure 5: Generalized modified geologic map of Valle de Huizachal (Rubio-Cisneros and Lawton, 2011). Stars and polygons indicate the units studied in this work, and correlate to those formations explained in Figure 4. Map symbols: Jlbi—lower member of La Boca Formation; Jlbs—upper member of La Boca Formation; Ji—rhyolite domes; Jlj—La Joya Formation; Jn—Novillo Formation; Jo—Olvido Formation; Jc—La Casita Formation; Ku—undifferentiated Cretaceous strata.
4.1 REGIONAL GEOLOGIC FRAMEWORK The central region of the state of Nuevo Leon is a world-class outcrop for visiting the clastic sequences for the stratigraphic column of the Sierra Madre Oriental, specifically within Monterrey Trough. The rock sequences appear mainly in the vicinity of the towns of San Pablo Tranquitas near Galeana, and Rayones. The clastic sequence extends south to Ciudad Victoria in the state of Tamaulipas (Figure 4).
The clastic sequences in the Monterrey Trough include fluvial-alluvial deposits of Upper Triassic age, alluvial-lacustrine-fluvial deposits of the Early-Middle Jurassic, deposits from a deltaic coastline of the Upper Jurassic, delta deposits influenced by tides, and also marine marginal sedimentary environments of the Lower Cretaceous (Michalzik, 1991, Michalzik and Schumann, 1994, Ocampo-Díaz, 2007, Ocampo-Díaz et al., 2008, Barboza-Gudiño et al., 2010; Ocampo-Díaz, 2011, 2012, Rubio-Cisneros, 2012).
4.2 GENERAL COMPOSITION OF SANDSTONES A modal analysis demonstrates significant changes in the composition of sandstones in northeastern Mexico, indicated by the contents of lithics and feldspars (Figure 7). The lithics vary in composition correspondingly to the concentration of metamorphic rock detritus of low- mid-grade and volcanic fragments. All samples from the clastic sequences plot in the
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 23 NW SE 4000 m Lithostratigraphic units Age Epoch
puourGatnufiD Foreland related to .mroF +sarraP Maestricht. Méndez Laramide orogenic Formation Campan- reppU event ian
San Felipe Form. Santoniano Coniacian Agua Nueva Form. Turonian Cuesta del Cura Form. Cenomanian 3000 m
Tamaulipas superior Albian suoecaterC Formation La Peña Formation Cupido Aptian Formation
rewoL
Barremian Tamaulipas inferior Hauteriv- 2000 m ian
Taraises Valanginian Formation Berriasian La Casita Tithonian Formation Kimme- ridgian ZuloagaForm. reppU
cissaruJ 1000 m Oxfordian MinasViejas Formation
elddiM • VOL. LXII No. 1 ENERO-JUNIO 2020 Callovian La Joya Form.
cissairT La BocaFormation Alamar reppU Lower-Middle Jurassic Formation 0 m External shelf Explanation carbonates Exposed areas, Open shelf carbonates nondeposition Platform border Coarse grained continental carbonates sediments Restricted marine evaporites (Sabkha) gypsum and anhydrite Outer ramp mudstone and shale Moderatly deep marine calcareous External shelf shale, silstone (phospatic lime mudstone) carbonates Basinal deep-water Lagoonar carbonates, carbonates and shales peritidal carbonates High energy carbonate Nonmarine to marginal grainstone (shoal) marine coarse clastics
Restricted marine Transgressive evaporite (sabkha), salt Regressive sequence sequence
Figure 6: Lithostratigraphic column of northeastern Mexico based on Michalzik (1991) and others cited herein. Stars and polygons represent the same sampled formations as in Figure 4.
24 QFLt diagram contrasting compositional polygons, allowing interpreting how sedimentary petrology evolved in the basin and the periods of supply from source-rocks (Figure 7). Upper Triassic sandstones from the Alamar Formation (Michalzik, 1991; Rubio-Cisneros, 2008a; Rubio-Cisneros, 2008b) have a high textural maturity and plot in the upper part of the recycled orogen field (Figure 7). La Boca Formation contains the most immature sandstones with high lithic content (Rubio-Cisneros and Lawton, 2011; Figure 7). The provenance of both the La Boca and La Joya formations evolve from a dissected arc to continental transition (Rubio-Cisneros et al., 2011; Figure 7).
Late Jurassic to Early Cretaceous sandstones from La Casita Formation plot between the fields of transitional continental and recycled orogeny (Figure 7). The feldspar content indicates recycling during the deposition of the La Joya and further enrichment of the overlying formations of Upper Jurassic to Lower Cretaceous (Figure 7). The stratigraphy of Upper Triassic to Lower Cretaceous sandstones northeastern Mexico comprises four main periods of supply from source-areas. Also, the sequence of sandstone composition discriminates three types of basins, starting with the rift, then forearc, and finally strike- slip (Figure 8).
(1) During the Late Triassic, there is a supply of sediment and recycling from crystalline basement rocks and Paleozoic sedimentary carapace. Samples of Upper Triassic discriminate into a rift basin against all other data, increasing positive values of Qp, Qt, and Ls. Sandstone composition associates with high indices from metamorphic lithics, polycrystalline and monocrystalline quartz. Rock fragments derive from low–middle-grade metamorphic, volcanics, and in minor proportion sedimentary rocks.
(2) The Early–Middle Jurassic sandstones have an abrupt change in the composition of source-rocks from newly formed source-areas. The Lower Jurassic sandstones discriminate into a forearc basin, with significant increments of Lv, F, and Qp concerning volcanic fragments, feldspars from volcanic and metamorphic sources (Figure 7 and 8).
(3) During the Middle Jurassic, most unstable framework components progressively disappear with subsequent low-rate recycling of Upper Triassic and Lower Jurassic formations, explained by the rise of Qm and the abundance of monocrystalline quartz with syntaxial overgrowths.
(4) Throughout the Late Jurassic to Early Cretaceous, tectonic activity recycled the preexisting sedimentary sequence in northeastern Mexico, predominating strike-slip basins. The Upper Jurassic sandstones increase in feldspars, volcanic, and metamorphic rock fragments produced by a small lapse of exhumation/unroofing of plutonic and basement rocks. Further on, the sedimentary lithics and monocrystalline quartz content prove moderate recycling of sedimentary rocks (Figure 7). The modal composition of Lower Cretaceous sandstones indicates an increase in feldspar content, volcanic detritus, and metamorphic sources. The composition correlates to the formation of new source-rocks (Figure 7).
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 25 Q Qm
r 3 Explanation Interio n interior El AlamarFormation (Al) o
rat Craton 18 La Boca Formation (LB) C La Joya Formation (LJ)
LJ La Casita Formation (LC) Quartzose recycled LJ ALAl LC Al Transitional Continental Transitional continentalLC 45 Mixed LB RecycledRecycled OrogenOrogen Dissected 50% 37 arc Transitional lift recycled Dissected p Arc t u LB 25 en Transitional Basement Uplift Basem 13 Transitional Arc Arc Undissected Lithic Arc Undissected recycled arc F 50 L F 50% Lt
Figure 7: Ternary diagrams QFLt and QmFLt with confidence regions for tectonic environments (Dickinson et al., 1983). The scattered compositional data is for Late Triassic–Early Cretaceous clastic sequences in northeastern Mexico (Rubio-Cisneros and Ocampo-Díaz, 2010).
DF 1 0.00 1.00
0.25 0.75 • VOL. LXII No. 1 ENERO-JUNIO 2020 0.50 0.50
0.75 0.25
1.00 0.00 DF 2 DF 3 Explanation Forearc Back-arc Accretionary Continental- Collisional margin arc Intra-arc Rift Strike-slip NE Mexico Formations El Alamar Fm. La Boca Fm. La Joya Fm. La Casita Fm.
Figure 8: A ternary diagram with the discriminant functions in its vertices and confidence regions for the composition of nine basins analyzed. The figure overlaps the petro-tectonic evolution of clastic sequences of Late Triassic to Early Cretaceous in northeastern Mexico.
26 5. DISCUSSION
The framework composition of sandstones from Late Triassic to Early Cretaceous in northeastern Mexico served for testing a discriminant diagram. The analysis indicates the development of rift, forearc, and strike-slip basins (Figure 8; Table 4). Previous works reported rift sequences for Late Triassic in the region (cf., Michalzik, 1991; Rubio-Cisneros, 2008a; Rubio-Cisneros, 2008b; Barboza-Gudiño et al., 2010, Dickinson and Gehrels, 2010; Ocampo-Díaz, 2011). The discriminant function in this work suggests a partial relationship to Late Triassic samples in a rift system. The framework petrography remarks positive indices of metamorphic lithics and quartz (Qt, Qp, and Qm). Sources are rocks of low–mid- grade metamorphism, volcanic, and in minor proportion sedimentary rocks.
Considering that our data from the rift samples represent the west of the southernmost expression for the circum-Atlantic rifting, the composition of sandstones correlates to no magmatic history of lithosphere that thinned at preexisting weak zones. Else, the samples tend to belong to strike-slip basins (Ocampo-Díaz, 2011; Ocampo-Díaz et al., 2014). The Late Triassic Alamar Formation lacks in composition associated with bimodal volcanism, which is evidence for an amagmatic extension over a dense crust of crystalline basement. We suggest a strict rift laying more to the east in the Gulf of Mexico, were rifting started under a tectonic force by magmatic accommodation and further subsidence (Buck, 2004). Back in northeastern Mexico, the thermally dense lithosphere thinned followed by uplifting source-rocks and a type of rift sequence formed from isostatic subsidence.
During the Early to Middle Jurassic, there was a magmatic arc with extensional activity developing a forearc basin. New source-rocks supplied the basin, showing the most significant increments of Lv, F, and Qp related to volcanic components. Besides rock fragments from volcanic genesis are feldspars from metamorphic sources. In the course of this event, some angular unconformities developed after thinning the low-density crust. The framework composition and the values of the Sedimentary Recycling Index (SeReIn) of La Boca and La Joya formations correlate with an unconformable stratigraphy (Ocampo- Díaz and Rubio-Cisneros, 2013; Table 4). Perhaps this long-term effect of stretching continental lithosphere turned into regional subsidence proven by angular unconformities in most outcrops across northeastern Mexico. Some unstable framework components in La Joya Formation disappear upsection while recycling from underlying units ceased all supply; however, monocrystalline quartz (Qm) occurs with syntaxial overgrowths.
Subsidence accommodated a thick sedimentary sequence of La Casita Formation, forming a strike-slip basin on Late Jurassic–Early Cretaceous (Ocampo-Díaz et al., 2014). Rock fragments in sandstones like feldspars, volcanic, and metamorphic lithics eroded from plutonic rocks, basement units, and sedimentary sources.
The data presents some degree of scattering, and it seems plausible that previous works classified the types of framework components using limited compositional parameters. Also, unconsolidated sands rather than sandstones may be a factor that introduced some bias into the analysis (e.g., Dickinson et al., 1983). Albeit these challenges, the library of framework petrography (QmFL) solved compositional indexes in a discriminant analysis for correlating sand and sandstones to a basin.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 27 Basins associated with suture zones were excluded from this work for its lack of statistical representation since only three samples were available in the literature (e.g., Garzanti et al., 1996). Any additional statistics require the use of more sandstones for better confidence in explaining the compositional discrimination with the type of suture.
6. CONCLUSION
Herein we test how framework composition and statistical parameters discriminate the provenance of sandstones among detrital populations from nine types of basins. The method in this work uses a ternary diagram in conformity to some conventional representations for sandstone provenance. The diagram is suitable for either ancient or recent clastic successions to plot sands and sandstones in a sedimentary basin. In general, the mean modal compositions of sandstones can distinguish among rock components in basins with newly formed source-rocks and the process of unroofing. Meanwhile, other compositional indices discern basins where deeper structural levels are brought to the surface and eroded.
Each vertex from the ternary plot is a discriminant function, representing an increase in specific compositional parameters 1) Qt, Ls, and Qp support the processes for sediment transport, the exhumation of the sedimentary carapace, and a moderate input of metamorphic rocks at rift systems, suture complex basins, foreland, and forearc basins; 2) Qp, Lm, F, and Qm relate to moderate–high sediment transport, and the exhumation of plutonic or metamorphic source-lands at forearcs, collisional zones, continental-margin arcs, and strike-slip basins; and 3) Lv, F, Qp, and Ls mark new source-areas and recycling of ancient clastic sequences in basins such as back-arc, intra-arc, strike-slip, continental- margin arcs, and forearc.
• VOL. LXII No. 1 ENERO-JUNIO 2020 The dataset is a compilation of different works, considering the limits on the interpretation of sands or sandstones by the authors. Some restrictions in the data are sampling method or how the author classified samples from its framework petrography (e.g., Dickinson, 1970).
Any sample not corresponding to a compositional field is discarded from the analysis and does not qualify for any specific type of basin. We consider that at each discrete point in the stratigraphy, the composition of the basin is not limited by time, undertaking instead lateral variability in the stratigraphy driven by autogenic processes. Therefore, samples not corresponding to any compositional field at every time in the evolution of the crust fit neither basin nor the “hybrid” category.
The tool of this method supports some interpretations of the composition of sandstone, source-rocks, tectonic setting, and processes within basins. The analysis correlates framework compositions to some genetic factors in basins; endogenic or exogenic events may match for specific stratigraphic records of sandstones. Besides, its application reduces ambiguities in sandstone provenance analysis with the parent basin and improves the history of well-established tectonic settings.
28 Nowadays it exists controversy about the tectonic architecture and evolution of suture basins, either by the amalgamation of multiple terranes or accretion regarding a single forearc (Ingersoll and Schweickert 1986; Mossakovsky et al., 1993; Sengör et al., 1993; Busby and Ingersoll, 1995). This work leaves an open possibility to examine the connection between the composition of the orogenic source and its basin. For a better understanding of Suture zone basins, consult Dewey (1977), Miall (1999), and Todd (2000).
Any interpretation of sandstone provenance may be misled if not considering the type of basin or tectonic settings that produced them, even if extensive knowledge is available about source-rock lithologies, sediment texture, and modal composition. The analysis in this work shares the same fundaments of multivariate statistics and discriminant functions in the SeReIn, but for basin discrimination. Successive geologic events at any tectonic setting can significantly affect detrital modes in sands and sandstones differently among basins. Compositional variation in basins reflects an increase in the heterogeneity of principal components in sandstones. The sedimentary indexes provide sufficient data to guide a better interpretation of source areas, basins, unconformities, and loading histories.
ACKNOWLEDGMENTS
This research was partly funded by stewardships of CONACyT, DAAD-GOAL, IAS, and SEPM. The authors appreciate the help from Martín Guerrero-Suastegui, Margarita Martínez-Paco, Huna, Ixba, Abhijit Basu, Nadia Rubio-Cisneros, John Holbrook, Timothy Lawton, Eduardo Garzanti, and Juan Alonso Ramírez Fernández. We are also thankful for the mathematical support given by Aarón Ulises Ocampo-Díaz, Roberto Soto-Villalobos, and Ernesto Sotuyo. Finally, we acknowledge Pilar López Rodríguez and Juan Rogelio Román Ramos for reviewing and improving the writing.
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BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 33 Analysis of mineralogy and porosity on a carbonaceous mudstone of the Pimienta Formation, western margin of the Tampico Misantla Basin, Mexico Análisis de mineralogía y porosidad en mudstone carbonáceo de la formación Pimienta, en el margen centro-oeste de la Cuenca Tampico Misantla, México
Carlos Vega-Ortiz(a)1 , Bryony Richards(b), John D. McLennan(a,b), Raymond Levey(b), Néstor Martínez-Romero(c)
(a) Department of Chemical Engineering, The University of Utah, Salt Lake City, UT 84112 (b) Energy & Geoscience Institute, The University of Utah, Salt Lake City, UT 84108 (c) Universidad Nacional Autónoma de México, Mexico 1 Correspondencia autor principal: [email protected], Carlos Vega Ortiz
ABSTRACT The Pimienta Formation of the Tampico Misantla Basin offers a high potential for unconventional reservoir development. Among other attributes, this is due to its organic properties and sedimentary depositional environment. It is well known that the porosity and permeability of shales differ significantly from those of conventional reservoirs; therefore, a proper accurate characterization at micro- and nanoscales is valuable for understanding the implications of the petrophysical microstructure, and porosity distribution on the storage of
• VOL. LXII No. 1 ENERO-JUNIO 2020 hydrocarbons, fluid flow, and permeability. A key observation is the identification of the mineral composition depending on the location and depth of sampling with respect to the geologic structure and sedimentary environment. A total of 12 samples of the carbonaceous mudstone of Pimienta Formation, obtained from Mexico’s Geological Core Repository (Litoteca Nacional CNH), provide representative coverage of the analyzed block at the foothill of the Sierra Madre Oriental. A series of Scanning Electron Microscopy (SEM) images provide detailed analyses of the chemical composition, morphology, organic matter, and porosity distribution.
RESUMEN La formación Pimienta de la Cuenca Tampico Misantla ofrece un alto potencial para el desarrollo de yacimientos no convencionales. Entre otras propiedades, se debe al alto contenido orgánico y el ambiente de depositación sedimentario. Es ampliamente conocido que las características de permeabilidad y porosidad son diferentes a las de yacimientos convencionales, por lo que es necesario elaborar una precisa descripción a escalas micro y nano dimensionales para el entendimiento de las implicaciones en las propiedades petrofísicas, así como también de la distribución de porosidad, para efectos de almacenamiento de hidrocarburos, transporte de fluidos y permeabilidad. Es de particular interés identificar la composición mineralógica de acuerdo con la localización y profundidad de la formación dentro de la estructura geológica de la cuenca y el ambiente de depositación. Se analizan un total de 12 muestras del mudstone carbonáceo de la formación Pimienta, obtenidas de la Litoteca Nacional de la Comisión Nacional de Hidrocarburos, las cuales proveen una cobertura representativa de la zona prospectivas analizada al pie de la Sierra Madre Oriental. Una serie de pruebas de
34 caracterización como son imágenes de microscopia de barrido con capacidad de análisis mineralógico, así como pruebas de difracción de rayos x, proveen un análisis detallado de la composición química, morfológica, materia orgánica y distribución de porosidad.
1. INTRODUCTION / INTRODUCCIÓN
The development of unconventional reservoirs in Mexico is a topic of great interest provided by the successful unconventional shale oil and gas developments in North America (Bowker, 2007; Pollastro, 2007; Stevens and Moodhe, 2015). There is anticipation of high economic potential for the Jurassic Pimienta Formation in the Tampico Misantla Basin (TMB), as it has good quality source rock with potential for production (Granados- Hernández et al., 2018; Jarvie and Maende, 2016; Morelos-García, 1996; Vega-Ortiz et al., 2020a) comparable to successful unconventional plays elsewhere in the world (US-EIA, 2013). As of 2019, the estimated reserves in the TMB are 1P 804 MMBOE, 2P of 3098 MMBOE, and 3P of 5570 MMBOE (CNIH Reservas, 2019). In 2015, Mexico’s Secretary of Energy (SENER), collaborating with Mexico’s National Hydrocarbon Commission (CNH), issued a 5-year development plan establishing areas of prospective fields including conventional and unconventional reservoirs in order to expand the country’s hydrocarbon production (SENER, 2019).
El desarrollo de yacimientos no convencionales en México es un tema de gran interés, dado el éxito logrado en yacimientos de shale oil y shale gas en EUA (Bowker, 2007; Pollastro, 2007; Stevens and Moodhe, 2015). Se anticipa que la formación Pimienta del Jurásico Titoniano Superior tiene un alto potencial económico dadas las buenas condiciones de calidad de roca generadora (Granados-Hernández et al., 2018; Jarvie and Maende, 2016; Morelos-García, 1996; Vega-Ortiz et al., 2020a), y su potencial de producción que es comparable con plays de yacimientos no convencionales en diferentes zonas del mundo (US-EIA, 2013). A la fecha de la redacción de este documento, 2019, las reservas estimadas en la Cuenca Tampico Misantla (CTM) son 1P = 804 MMBOE, 2P = 3098 MMBOE, y 3P = 5570 MMBOE (CNIH Reservas, 2019). En 2015, la Secretaria de Energía (SENER), en colaboración con la Comisión Nacional de Hidrocarburos (CNH) de México, emitieron el Programa Quinquenal de Licitaciones para la Exploración y Extracción de Hidrocarburos 2015-2019, en el cual se establecen las zonas prospectivas de yacimientos no convencionales, con lo que se busca expandir las capacidades de producción del país. (SENER, 2019).
The area of study (AOS) designated for this study is a block that covers an area of 69.6 km2, located in the central-western sector of the TMB. The AOS is at 150 km to the NW of the prolific Chicontepec Basin and Golden Lane field (CNH-SENER, 2010; Viniegra and Castillo-Tejero, 1970), including the territory of San Luis Potosi and Veracruz states (Fig 1). It is geographically delimited in the north by the Tamaulipas Arch, to the east by the Gulf of Mexico, to the south by the Teziutlan Masif and the Veracruz Basin and to the west the by the Sierra Madre Oriental (Fitz-Díaz et al., 2018). The AOS was explored for commercial development of conventional zones with 42 wells drilled from 1912 to 2000, although no successful targets were encountered (CNH México, 2020; López-Ramos, 1952). Geological samples of the Pimienta formation are available in only seven wells, with location shown in Figure 1. Provided the crescent interest in the international oil and gas market towards unconventional reservoirs development, it is of critical importance to perform thorough technical analysis in these legacy areas to elaborate on the previous assessments of reserves quantification and production feasibility in Mexico.
Geográficamente la CTM es delimitada al norte por el Arco de Tamaulipas, al oriente por el Golfo de México,, al sur por el Macizo de Teziutlán y la Cuenca de Veracruz, y al occidente por la Sierra Madre Oriental (SMO) (Fitz- Díaz et al., 2018). El área de estudio (AE) designada para este análisis es un bloque que cubre un área de 69.6
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 35 km2, ubicado en el sector centro-occidental de la CTM, al piedemonte de la SMO. El AE se encuentra a 150 km al NO de la prolífica Cuenca de Chicontepec y de la Faja de Oro (CNH-SENER, 2010; Viniegra and Castillo- Tejero, 1970), dentro de los límites territoriales de los estados de San Luis Potosí y Veracruz (Fig 1). El AE fue explorada para desarrollo comercial de yacimientos con 42 pozos perforados desde los años 1912 hasta el 2000, sin haber encontrado algún yacimiento con condiciones aptas para producción convencional (CNH México, 2020; López-Ramos, 1952). A la fecha de elaboración de este estudio, en la Litoteca Nacional únicamente hay existencia de muestras geológicas de la formación Pimienta de siete pozos, cuya localización se muestra en la figura 1. Dado el creciente interés de los mercados petroleros internacionales hacia el desarrollo de yacimientos no convencionales, es de suma importancia realizar un análisis desde la perspectiva actual para evaluar zonas potencialmente productoras omitidas al momento de perforación, y contribuir con información técnica para la evaluación del yacimiento, cuantificación de reservas y factibilidad de producción en México.
Figure 1. Location of the area of study, located in the western-central edge of the Tampico Misantla Basin. Location of the seven wells with Pimienta fm samples available and granted for this study. (Base Map from CNIH Mapas (2020) and (SGM, 2020)). • VOL. LXII No. 1 ENERO-JUNIO 2020 Figura 1. Localización del area de estudio, ubicada en el margen centro-occidental de la cuenca Tampico Misantla. Ubicación de los siete pozos con muestras disponibles de la formacion Pimienta, facilitadas para la realización de este estudio (Mapas de referencia CNIH Mapas (2020) y (SGM, 2020)).
In present-day terminology, unconventional reservoirs refer to a scenario where the source rock also acts as reservoir rock (Mccarthy et al., 2011). The organic content of a rock is one indicator of its potential as the source rock for hydrocarbon extraction (Jarvie, 2015; Jones, 1984; King et al., 2015). The key of the success of unconventional oil and gas resources relied on the systematic implementation of hydraulic fracturing techniques, aiming to increase the area of flow from the reservoir into the well (Algadi et al., 2014; Fernandez-Badessich et al., 2016; Jabbari, 2013). The proper planning and execution of the drilling, fracking, and completions requires the thorough understanding of the geological formation characteristics (Rybacki et al., 2016; Zhang et al., 2016), as no all shale reservoirs can be approached in the same manner (Rickman et al., 2008). Additional to recognizing the inherent low permeability and porosity is necessary to characterize porosity size, distribution, and interconnectivity, as well as the chemical composition and distribution of the minerals that comprise the Pimienta formation in the AOS, which is the objective of this study.
En terminología actual, los yacimientos no convencionales, comúnmente conocido como plays tipo shale-, se refieren al escenario en donde la roca generadora actúa también como roca almacén (Mccarthy et al., 2011). El contenido orgánico de la roca es uno de los principales indicadores del potencial productor de hidrocarburos (Jarvie,
36 2015; Jones, 1984; King et al., 2015). La clave del éxito en yacimientos no convencionales radica en la implementación sistemática de técnicas de fracturamiento hidráulico, enfocado a incrementar el área de flujo de los fluidos del yacimiento hacia el pozo productor (Algadi et al., 2014; Fernandez-Badessich et al., 2016; Jabbari, 2013). La planeación y ejecución adecuados de los programas de perforación, fracturamiento hidráulico y completaciones requiere de un entendimiento detallado de las propiedades geológicas y petrofísicas de los yacimientos (Rybacki et al., 2016; Zhang et al., 2016), ya que no todos los plays tipo shale pueden ser abordados bajo el mismo criterio (Rickman et al., 2008). Además de identificar la problemática inherente de las reducidas permeabilidad y porosidad, es necesario caracterizar el tamaño de los poros, su interconectividad y distribución, así como también la composición química y distribución de los minerales que conforman la estructura de un play como los es la formación Pimienta, lo cual es el objetivo de investigación en este estudio.
2. GEOLOGICAL BACKGROUND / MARCO GEOLÓGICO
The stratigraphic sequence and the structural frame in the AOS discussed in this section is shown in figure 3, which is a North-South fence diagram with the strata identified the wells DD, HH, GG and AA, based on the formation tops from drilling reports and available GR logs. The depth in this diagram is referred to sea level. The basement of the TMB is a sequence of continental sediments identified as red rocks and metamorphic complex, deposited in the western margin of the Pangea, shoreline with the paleo-pacific ocean.
In the early Jurassic, the breakup of Pangea and it is associated continental rifting produced a sequence of marine transgressional and receding shoreline events (Cantú-Chapa, 2001). The Huayacocotla formation is related to the post-rift shallow marine and basinal environment, identified with black shales and siltstones (Rueda-Gaxiola et al., 1993). Later in the mid-Jurassic, the Yucatan platform southbound drift (Marton and Buffler, 2016) and the opening of the Gulf of Mexico produced a marine regression and a continental basin deposition (Pindell and Kennan, 2009), where the Cahuasas formation was deposited.
La secuencia lito estratigráfica y el marco estructural del AE descrito en esta sección se ilustra en la figura 3, que es un diagrama seccional de los estratos identificados en los pozos DD, HH, HH y AA, basado en las cimas de formación reportadas durante la perforación y los registros geofísicos de rayos gamma (GR) disponibles. La profundidad indicada el diagrama es referenciado al nivel medio del mar. El basamento de la CTM es una secuencia de depósitos sedimentarios continentales que se identifican como lechos rojos y complejo metamórfico, depositado en el extremo occidental de Pangea, en el litoral del paleo-océano pacífico.
En el Jurásico Inferior, la división continental de Pangea y el rift continental asociado originaron una secuencia de eventos transgresivos y retrocesos de la lineal litoral (Cantú- Chapa, 2001). La formación Huayacocotla está relacionado con ambientes post-rift de aguas someras y de cuenca, identificado por las intercalaciones de lutitas y areniscas (Rueda-Gaxiola et al., 1993). Posteriormente en el Jurásico Medio el desplazamiento de la Plataforma de Yucatán hacia el sur y la apertura del Golfo de Mexico, ocasionaron un ambiente de deposición de cuenca continental por el retroceso marino (Pindell and Kennan, 2009), en donde fue depositada la formación Cahuasas.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 37 The late Jurassic period is dominated by a marine transgression, which created a low-energy, shallow water sea with a reducing environment (Peterson, 1983). According to Goldhammer and Johnson (2001), sediments of fine grain and organic-rich marine lithofacies deposited over preexisting carbonate ramps, that would become the source rock for the petroleum systems in the TMB. The Oxfordian Santiago and Zuloaga formations, identified elsewhere in the TMB are sparsely present in the AOS. The Kimmeridgian produced three different formations; The Taman formation is associated with a shallow marine, oxic to anoxic environment, with a organic content up to 1.6 wt. %, as reported by Vega-Ortiz et al, (2020a) analyzing samples from the well GG. The Chipoco Formation is formed from deposits near the shoreline, deducted from its mixed composition of oolitic limestone, developed in dynamic intertidal waters, and the high content of clastic minerals from fluvial deposition, as observed in the well DD in this study. The calcarenite San Andres formation is interlayered with the Taman formation, and often considered as lateral continuation of the Tithonian Pimienta formation, depending on the area of deposition (Cantú-Chapa, 1992).
El periodo Jurásico Superior fue dominado por una transgresión marina, que genero condiciones marinas someras de baja energía de ambiente reductor (Peterson, 1983). De acuerdo con Goldhammer y Johnson (2001), sedimentos de grano fino y facies marinas de alto contenido orgánico se depositaron sobre rampas de carbonatos preexistentes, que eventualmente producirían las rocas generadoras de hidrocarburos en los sistemas petroleros de la CTM. Las formaciones de Santiago y Zuloaga del Oxfordiano son identificadas en otras zonas de la CTM, sin embargo, con escasa presencia en el AE. El Kimeridgiano produjo tres diferentes facies: La formación Taman depositada en aguas someras de ambiente anóxico, con contenido orgánico de 1.6 wt.% como se reporta en Vega-Ortiz et al, (2020a) analizando muestras del pozo GG. La formación Chipoco es asociada en la zona de rampa del litoral en la Plataforma San Luis-Valles, deducido de la composición mezclada de calizas oolíticas producidas en aguas dinámicas intermareales, y el alto contenido de minerales clásticos de deposición fluvial, observada en el pozo DD
• VOL. LXII No. 1 ENERO-JUNIO 2020 de este estudio. La formación calcarenita de San Andrés se encuentra intercalada con la formación Taman, y en ocasiones considerada como continuación lateral de la formación Pimienta del Titoniano, dependiendo del área de depositación (Cantú-Chapa, 1992).
The Pimienta formation was deposited during the Upper Jurassic Tithonian period. A marine transgression from the Gulf of Mexico flooded the area that today corresponds to the TMB (Fig. 2), extending to the Yucatan Peninsula. The flooding event created a shallow marine, low-energy depositional environment (Peterson, 1983), where the organic-rich, carbonaceous mudstone of the Pimienta formation created a homogeneous and conformable stratum on top of the Kimmeridgian (Salvador, 1987). The organic sediments of the Pimienta formation became the source rock for the giant offshore Sonda de Campeche fields in the southern Gulf of Mexico (Magoon et al., 2001; Santamaria Orozco, 2000). In the AOS, the exposed land of the Valles-San Luis Platform (Carrillo-Bravo, 1971) created a shoreline with a marine slope and basin dipping towards the SE into the TMB, allowing the accumulation of kerogen mixed Type II/Type III (Vega-Ortiz et al., 2020a). The typical petrology description of the Pimienta formation in the AOS from drilling reports (CNH México, 2020) is black to dark brown carbonaceous mudstone, with recrystallized fragments, with thin intercalations of black carbonaceous mudstone, light gray carbonates, and gray cryptocrystalline limestone.
38 La formación Pimienta fue depositada durante el periodo Jurásico Superior, en la era Titoniano. La transgresión marítima del Golfo de México cubrió el área que hoy en día corresponde a la CTM (Fig. 2), extendiéndose desde el centro de México hasta la Península de Yucatán. La transgresión dio lugar a un ambiente marino somero de baja energía (Peterson, 1983), donde el mudstone carbonáceo rico en materia orgánica de la formación Pimienta, genero un estrato homogéneo y conformable sobre los sedimentos del Kimerigdiano (Salvador, 1987). Dichos sedimentos orgánicos en la formación Pimienta dieron lugar a la roca generadora en los principales yacimientos de México , incluidos los de la Faja de Oro, Cuenca de Chicontepec y la Sonda de Campeche (Magoon et al., 2001; Santamaria Orozco, 2000). En el AE, el bloque expuesto de la Plataforma Valles-San Luis Potosí (Carrillo-Bravo, 1971) originó un litoral y pendiente con buzamiento en dirección SE, hacia el centro de la CTM, permitiendo la formación de kerógeno mezclado tipo II/tipo III (Vega-Ortiz et al., 2020a). La descripción petrográfica de la formación Pimienta en el AE en general se describe como mudstone carbonáceo gris oscuro a negro, con fragmentos recristalizados y laminaciones delgadas de lutitas negras, fracturas selladas con calcita y caliza criptocristalina gris.
Figure 2. Jurassic paleographic map displaying the shallow marine depositional environment of the Pimienta Formation in the Tampico Misantla basin, (Adapted from (Salvador, 1987)) Figura 2. Mapa paleografico del Jurasico, indicando el ambiente de depositacion marino somero de la formación Pimienta. (Adaptada de Salvador, 1987)
During the Cretaceous, the compressional tectonic events resulting from the Farallon plate subduction underneath the North American plate (Martini, 2018) originated the Laramie orogeny that uplifted the Sierra Madre Oriental (SMO). According to Mitrovica et al. (1989), the subsequent tilting of the North American plate formed a foreland basin in the current area of the TMB. In addition to this, the higher eustatic sea levels of the mid to late Cretaceous resulted in a major oceanic transgression originating the North American Interior Seaway (Slattery et al., 2015), and a deep-water environment in the TMB area. In the area of the AOS, a paleographic, morphostructural and stratigraphic study by (Eguiluz de Antuñano et al., 2000), concluded that the Huayacocotla sector of the SMO dominated the structural and sedimentary environment, developing evaporitic carbonate platforms. The Tamaulipas group of the Lower Cretaceous, and the Mendez, San Felipe and Agua Nueva limestones were formed during this period (Aranda-Gomez et al., 2000).
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 39 Durante el Cretácico los esfuerzos compresionales resultantes de la subducción de la placa Farallón por debajo de la placa Norteamericana (Martini, 2018) causaron la orogenia Laramide que produjo el levantamiento de la SMO. De acuerdo con estudios realizados por Mitrivica et al. (1989), la subsecuente inclinación de la placa de Norteamérica originaron una cuenca tipo ante-país en el área de la CTM. Adicionalmente, el elevado nivel eustático del mar en la época Cretácico superior provocó una transgresión marina dando lugar al llamado Mar Interior de Norteamérica (Slattery et al., 2015), y un ambiente de aguas profundas en la región centro-oriental de la CTM. Eguiluz de Antuñano et al. (2000), a través de un estudio paleográfico, morfoestructural y estratigráfico, concluyó que el sector Huayacocotla de la SMO dominó el ambiente estructural y de depositación en el AE, desarrollando plataformas de carbonatos evaporíticos. El grupo estratigráfico de la formación Tamaulipas y los depósitos de carbonatos de las formaciones Méndez, San Felipe, y Agua Nueva, fueron originados en el Cretácico Inferior (Aranda-Gomez et al., 2000).
Finally, in the Cenozoic when the Gulf Of Mexico receded (Cossey et al., 2016), the foreland basin was filled with clastic material that was eroded from the SMO, creating today’s coastal plain and allowing the deposition of conglomerate strata like the Chicontepec formation, where vast quantities of hydrocarbons migrated to produce oil and gas reserves, allowing the development of production fields in the prolific Golden Lane field and Chicontepec Basin (Estrada et al., 2010).
Por último, en la Cenozoico después del retroceso del Golfo de México (Cossey et al., 2016), los depósitos clásticos y fluviales que fueron erosionados de la SMO rellenaron la cuenca antepaís, originando la actual planicie costera y permitiendo la acumulación de conglomerados como la formación Chicontepec, donde vastas cantidades de hidrocarburos emigraron desde las rocas generadoras del Jurásico para formar yacimientos productores de aceite y gas natural en la cuenca de Chicontepec y la zona de la Faja de Oro (Estrada et al., 2010). • VOL. LXII No. 1 ENERO-JUNIO 2020 3. SAMPLE DESCRIPTION / DESCRIPCIÓN DE LAS MUESTRAS
The rock samples of the Pimienta Formation for the mineral analysis were obtained from Mexico’s Geological Core Repository under the authorization of the Ministry of Energy (SENER) and CNH, from the wells in the AOS (Fig. 3). The geological layout of the Pimienta Formation in the AOS includes elevated areas to the NW, dipping slightly towards the SE. X-ray diffraction (XRD) Mineral composition was done in samples from wells AA, BB, DD, EE, GG, HH, and II. Scanning electron microscopy (SEM) microphotographs were taken from wells DD and GG. No preservation technique used on the samples during storage.
Las muestras geológicas para este estudio fueron obtenidas de la Litoteca Nacional de la Comisión Nacional de Hidrocarburos, con autorización de la Secretaria de Energía (SENER) como convenio académico para tesis doctoral. La localización de la muestras y la clave de los nombres de los pozos se indica en la Figura 3. La estructura geológica en el AE muestra una elevación en el sector NO, con buzamiento hacia el SE. Análisis de difracción de rayox X se realizó en las muestras de los pozos AA, BB, DD, EE, GG, HH e II. Toma de imágenes con microscopio de barrido electrónico SEM, fueron tomados en los pozos DD y GG.
40 Figure 3. Geological structure of the Pimienta Formation in the Area of Study (AOS). The northeastern has higher elevation due to its proximity to the Valles-San Luis Platform shoreline. The thickness of the Pimienta formation varies from 40 to 120 m Figura 3. Estructura del área de estudio delineado con líneas isocronicas. El área noroccidental tiene una mayor elevación debido a la cercanía con el litoral de la Plataforma Valles-San Luis. El espesor de la formacion Pimienta varia entre 40 y 120 m.
4. METHODS / MÉTODOS
4.1 X-RAY DIFFRACTION (XRD) / DIFRACCIÓN DE RAYOS X (XRD) X-ray diffraction (XRD) analysis was completed at the Energy and Geoscience Institute at the University of Utah using a Bruker D8 Advance and subsequently interpreted using Topaz software. The bulk sample preparation for XRD consisted of grinding and milling to a particle size of < 44 μm by using a 325-mesh screen. Clay sized particles were further separated to 5 μm size fraction by mixing the powder with deionized water, stirring, and allowing to settle for 37 min. Subsequently, a 100 ml aliquot is centrifuged at 1500 rpm for 15min. The resulting slurry is mixed with ethylene glycol and dried in an oven at 65°C for 12 hrs. The operating parameters for Bruker DS8 diffractometer are 0.02o2θ step size, 40 kV and 40 mA for CU-K-α radiation, and 0.6 and 0.4 seconds per step, for bulk and clay samples, respectively.
El análisis de difracción de rayos X (XRD) fue realizado en el Instituto de Energía y Geociencias (EGI) de la Universidad de Utah, empleando un instrumento Bruker D8 Advance y utilizando el software Topaz para la interpretación de resultados. La preparación de muestras crudas consistió en molienda y trituración a un tamaño de partículas < 44 μm usando una pantalla de malla 325, seguida de una segunda separación para partículas arcillosas de 5 μm, mezclando el polvo con agua desionizada, agitando y permitiendo decantación de sólidos por 37 min. Posteriormente una alícuota de 100 ml es centrifugada a 1500 rpm por 15 min. La mezcla resultante es combinada con etilenglicol y secada en un horno a 65 °C por 12 hrs. Los parámetros de operación del instrumento de difracción Bruker 8 son 0.02o2θ de incremento de fase, 40 kV y 40 mA para la radiacion CU-K-α, así como 0.6 y 0.4 segundos por paso, para las muestras crudas y de arcillas, respectivamente.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 41 4.2 ENERGY-DISPERSIVE SPECTROSCOPY (EDS) / ESPECTROSCOPIA DE ENERGÍA DISPERSIVA (EDS). Energy-Dispersive X-Ray Spectroscopy (EDS) measures the x-ray wavelength of the photons emitted after an incident electron interacts with the electrons on the surface of a mineral. Each element will produce a single x-ray, which is used as a signature for the identification of that particular chemical element present in the sample. The EDS analysis was completed with an X-ACT PentaFet Precision detector at the University of Utah’s Energy & Geoscience Institute (EGI). The samples were polished in a Struers Tegrapol-21, using a 220 grit polishing disc with water as a lubricant.
La técnica de Espectroscopía de Energía Dispersiva, (EDS por sus siglas en inglés Energy- Dispersive Spectroscopy) mide la longitud de onda de los rayos-X que son emitidos después de la interacción de un electrón incidente sobre la superficie de un mineral, enfocado en detectar presencia de elementos químicos y elaborando un mapa de la distribución del elemento en la zona analizada.. El análisis EDS se realizó en los laboratorios el EGI con un instrumento X-ACT PentaFet Precision Detector. Las muestras fueron preparadas con desbaste en la máquina Struers Tegrapol-21, con un disco pulidor de 220 grit, usando agua como lubricante.
4.3 SCANNING ELECTRONIC MICROSCOPY (SEM) / MICROSCOPIA DE BARRIDO ELECTRÓNICO The SEM images were obtained using a FEI Quanta 600F scanning electronic microscope, located at the Utah Nanofab, University of Utah. This Quanta SEM uses a high-resolution field emission source (FEG) to analyze samples, allowing higher-magnifications and resolution than a standard tungsten SEM. The samples analyzed were uncoated and unpolished, in order to observe the topography of the surfaces in their natural state after splitting the rock sample into small pieces suitable as SEM specimens. The settings for the microscope were adjusted to mitigate charging effects as much as possible: electron beam
• VOL. LXII No. 1 ENERO-JUNIO 2020 2 KeV, Spot 5, high vacuum pressure, working distance WD 10.
Las imágenes de microscopía electrónica fueron obtenidas en un instrumento SEM FEI Quanta 600F, en el laboratorio NanoFab de la Universidad de Utah, de alto vacío y fuente emisora de alta resolución. Las muestras no tuvieron preparación, sin pulido ni recubrimiento, para observar la topografía y textura de las rocas en su estado natural después de ser fracturadas en pequeños fragmentos de ~ 2 mm. Los parámetros de operación del SEM fueron ajustados para mitigar los efectos de saturación electroestática: haz de electrones de 2 KeV, spot 5, alto vacío, distancia operativa WD 10.
5. RESULTS / RESULTADOS
5.1 XRD MINERALOGY / MINERALOGÍA XRD The XRD mineralogy analysis of the samples indicates that the predominant mineral content in the Pimienta formation is carbonates; the full results included in Table 1 and XRD
diffractograms shown in Appendix A. Calcite (CaCO3) is the most abundant mineral overall, with
an average of 70.4 wt. %, dolomite (CaMg(CO3)2) is also present in a lower quantity with 1.3 wt. %
42 average content and Mg-rich calcite ((Ca,Mg)CO3) found mientras que el Plagioclase está contenido en in the well EE at 1.0 wt. %. The sandstone is composed los pozos HH, GG, II y AA. Los minerales arcillosos of quartz (SiO2) with an average of 16.9 wt. %. The identificados son Ilita (K0.65Al2.0[Al0.65Si3.35O10](OH)2), metamorphic tectosilicates of plagioclase (NaAlSi3O8 siendo el más abundante con 6.4 wt. % promedio, y
– CaAl2Si2O8) and K-Felspar (KAlSi3O8) are considered Caolinita (Al2(Si2O5)(OH)4) con 2 wt.%, identificado en as part of the sandstone mineral composition, with an el pozo AA. Trazas de Ilita-Esmectita interlaminada average of 0.74 and 2.28 wt. %, respectively. ((Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2 · nH2O) fue detectada de las muestras de los pozos HH, GG y AA, siendo A relevant observation is that the K-feldspar occurred la proporción Ilita a Esmectita de más de 90%. Otros only in the shallower wells DD, BB and EE, and the minerales identificados en menor cantidad son Pirita plagioclase is observed in the deeper wells HH, (FeS2), el cual está presente en todas las muestras,
GG, II, and AA. Clay minerals are identified as illite Barita (BaSO4) con contenido de 1 wt.% en el pozo BB,
(K0.65Al2.0[Al0.65Si3.35O10](OH)2), the most abundant y Anhidrita (CaSO4), con una concentración relativa alta constituent with an average of 6.4 wt. %, and de 3 wt.% en el pozo somero DD, y en menor cantidad kaolinite (Al2(Si2O5)(OH)4) only present at the deepest en los pozos GG y AA. sample obtained from well AA, with 2 wt. % mineral abundance. Traces of interlayered illite-smectite Different authors have reported the implications of
((Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2 · nH2O) was measured different minerals in the reservoir and source rocks. from wells HH, GG and AA, being the illite to smectite Diagenetic filamentous illite reduces permeability by proportion greater than 90 %. Other lower quantities coating the pore walls (Pallatt et al., 1984). Swelling of minerals were identified as traces of pyrite (FeS2), clays like smectite may increase the pore pressure present in most of the samples, barite (BaSO4) with by altering the geological stress distribution in the a content of 1 wt. % in the well BB, and anhydrite formation. Anhydrite reacts with organic matter
(CaSO4), with a relatively high average concentration through the reaction CaSO4 + 2CH2O = CaCO3 + H2O of 3 wt. % in the shallower well DD, and smaller + CO2 + H2S, producing calcite that can be leached quantities in wells GG and AA. into the porosity of the rock, and sulfidic acid that becomes soluble and generating sour oil and gas El análisis de mineralogía XRD indica que el mineral (Selley, 1997). Kaolinite is also a cementing clay that predominante en las muestras de la formación will occupy the pore spaces after precipitating from Pimienta son carbonatos. La tabla 1 muestra la lista the solution. In terms of wellbore stability and design del contenido mineral, los respetivos difractogramas of drilling fluid systems, appropriate fluids like oil- están en el Apéndice 1. La calcita (CaCO3) es el based mud and silica-based mud (Soric et al., 2004) mineral más abundante, con un promedio de 70.4 might be considered in those regions where mineral wt.%. Dolomita (CaMg(CO3)2) también está presente clay and anhydrite content makes the borehole en menor proporción con 1.3 wt.%, destacando la susceptible to swelling. A detailed analysis of the muestra del pozo EE en donde se encontró calcita rica effect of mineral composition on the geomechanical en Magnesio ((Ca,Mg)CO3) con 1 wt.%. Las areniscas properties of the Pimienta formation trough multi- se identifican con el mineral de cuarzo (SiO2) con un stage triaxial tests is presented by Vega-Ortiz et al. contenido promedio de 16.9 wt.%. Los tectosilicatos (2020b). metamórficos de plagioclase (NaAlSi3O8 – CaAl2Si2O8) y K-Felspato (KAlSi3O8) se consideran como parte de Diferentes autores han reportado las implicaciones la composición de areniscas, con una mínima cantidad de los minerales contenidos en las rocas generadoras de 0.74 y 2.28 wt.%, respectivamente. y almacenadoras. La ilita diagenética filamentosa reduce la permeabilidad cuando recubre las paredes Una observación relevante es que el K-Feldespato de los poros (Pallatt et al., 1984). Algunas arcillas ocurre en los pozos DD, BB y EE, que son los que como la esmectita se dilatan en contacto con agua, se encuentran en el sector elevado NO del AE, lo cual altera la distribución de esfuerzos geológicos
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 43 en la roca y por consecuencia modificando la presión mineralógica (Fig 4), consolidando los minerales de poro. La anhidrita reacciona con materia orgánica observados en tres grupos minerales de acuerdo a
a través de la reacción CaSO4 + 2CH2O = CaCO3 + la clasificación de Dana: Carbonatos (14: Carbonatos
H2O + CO2 + H2S, produciendo calcita que se filtra normales anhídridos), Areniscas (75: Tectosilicatos en la porosidad de la roca sellando fracturas y – Estructuras de Silicio) y Arcillas (71: filosilicatos – poros interconectados, y ácido sulfhídrico que se laminas o aros hexagonales). El diagrama ternario es mezcla con los fluidos orgánicos de la formación superpuesto sobre la clasificación “sCore: clasificación produciendo crudo de alto contenido de azufre (Selley, de mudstones orgánicos” de Gamero Diaz, 2013, que 1997). La caolinita también es un agente cementante identifica a la formación Pimienta como mudstone cuando se precipita de la solución acuosa, que carbonáceo, lo cual es una descripción más adecuada reduce la permeabilidad de la roca. En términos de comparada con la comúnmente conocida de caliza estabilidad geomecánica del pozo y diseño de fluidos arcillosa (shaly limestone) como se observa en los de perforación en las zonas donde existen arcillas reportes de perforación. Los carbonatos dominan la susceptibles a dilatación. Un análisis detallado de los composición mineral. Las arcillas se cuantifican en efectos de la composición mineral en las propiedades un rango de 3 a 23 wt.%. En contraste, las areniscas geomecánicas de la formación Pimienta a través de se encuentran en un rango de 2 a 41 wt.%. Una análisis triaxial multi-etapa es presentado por Vega- tendencia relevante es el contenido de cuarzo basado Ortiz et al. (2020b). en la profundidad de la formación Pimienta; los pozos más someros BB y DD tienen mayor contenido de X-ray Diffraction (XRD) results are also presented in a cuarzo, comparado con el resto de los pozos en áreas mineral composition ternary diagram (Fig. 4), grouping profundas. the different constituents according to the Mineral classification from (Dana et al., 1997): Carbonates (14: 5.2 ENERGY-DISPERSIVE ANHYDROUS NORMAL CARBONATES), Sandstones X-RAY SPECTROSCOPY (EDS) / (75: TECTOSILICATES Si Tetrahedral Frameworks and ESPECTROSCOPÍA DE ENERGÍA 76: TECTOSILICATES Al-Si Framework) and Clays DISPERSIVA (71: PHYLLOSILICATES Sheets of Six-Membered The sample selected for EDS analysis is a segment Rings). The ternary diagram is superimposed over of the core ID 261344, recovered from the well
• VOL. LXII No. 1 ENERO-JUNIO 2020 the “sCore: A Classification for Organic Mudstones” DD. According to the mineral content the bulk of by Gamero-Diaz et al. (2013). The distribution of the sample is “mixed mudstone”. XRD mineral the mineral composition confirms the classification composition for this sample (Table 1) is Calcite 50 wt. of the Pimienta formation as ‘silica-rich carbonate % , Quartz 36 wt. %, K-Feldspar 6 wt. %, Illite 5 wt. %, mudstone, rather than the more generic term ‘shaly Anhydrite 2 wt. %, and traces of Pyrite. Fig A6 shows limestone”, as reported in drilling reports (CNH México, the XRD Difractogram of this sample. Form the core 2020). Carbonates dominate the composition for all slab fragment (Figure 5) the texture indicates an samples. The clay -illite- content remains relatively extremely fine-grained compact black mudstone, constant for all the samples averaging 6.6 wt. %, with showing a cemented fracture that is inclined to a minimum of 3 wt. % and a maximum of 23 wt. %. bedding, indicating that the infilling material was In contrast, the sandstone content ranges from 2 to transported and precipitated after deposition. A ~1 41 wt. %, averaging 19.9 wt. %. A noticeable trend in mm thick vein of calcite and a thinner occurrence of the quartz content is based on the burial depth of the pyrite were deposited in the fracture. Considering Pimienta formation; shallower samples at wells BB that the density of pyrite (5.01 g/c3) is higher than and DD contain higher quartz content, compared to calcite (2.71 g/c3), it may be assumed that the pyrite the rest of the wells in deeper areas. occupies the lower side of the fracture. Figure 5 also display the wireline logs at the interval where the Los resultados del análisis XRD también son core was retrieved, cutting through a ~4m thick layer presentados en el diagrama ternario de composición of limestone, identified from the shift in the GR curve
44 to 100 GAPI with respect to the shale line (200 GAPI), a near-zero porosity, overlap of density and porosity curves provided with the appropriate compatible scale in the log header. Also displayed the results from pyrolysis analysis with an average TOC = 1.2 wt.%. Note that top of the Pimienta formation is taken from drilling reports, although the GR curve shows a transition from sand line at a shallower depth.
Las muestras seleccionadas para el análisis EDS es de un fragmento del núcleo ID 261344, recuperado del pozo DD. Se identifica como mudstone mixto, de acuerdo con la composición mineralógica que consiste en Calcita 50 wt. % , Cuarzo 36 wt. %, K-Feldspato 6 wt. %, Ilita 5 wt. %, Anhidrita 2 wt. %, y trazas de Pirita, El difractograma del EDS se muestra en la Fig. A6. En el fragmento del núcleo usada en el análisis EDS (Fig 5) se aprecia la textura de los granos es muy fina y compacta. Se distingue una fractura la cual se desarrolla en un alta pendiente, cuasi-paralela al eje longitudinal del núcleo (y del pozo, el cual es vertical). Los minerales en solución de agua que infiltraron la fractura fueron precipitados, cementando con calcita y pirita como se observa en la vena de ~ 1mm de espesor. Considerando que la densidad de la pirita (5.01 g/c3) es mucho mayor que la calcita (2.71 g/c3), se puede asumir que la pirita ocupa el espacio inferior de la fractura. En la Figura 5 se presentan los registros geofísicos del intervalo donde fue obtenido el núcleo, penetrando una capa de ~4m de espesor de caliza (limestone), identificada por una reducción el de GR a ~100 GAPI (comparado con la línea de lutitas a ~200 GAPI), nula porosidad NHPI, el empalme de curvas densidad y porosidad en el segundo canal con las escalas adecuadas compatibles, así como un incremento en la curva DT de sónico de porosidad. Se observa una ligera diferencia en las curvas de resistividad siendo la curva profunda RT ~20 ohm-m más resistiva que la curva superficial RS. Así como también se muestra el contenido orgánico total, obtenido por pruebas de pirolisis hídrica en esta muestra con promedio de TOC = 1.2 wt.%.
MINERAL Carbonates Sandstones Clays Sulfite/ates GROUP
Sample ID Illite Pyrite Barite Calcite (Well) Quartz Kaolinite Dolomite Anhydrite Mg Calcite Mg K-Feldspar % Illite in I/S Plagioclase Interlayered Illite/Smectite
261344 (DD) 50 tr 36 6 5 tr 2 261342 (DD) 34 1 23 15 23 1 4 261331 (BB) 51 4 41 1 3 tr 260551 (EE) 84 1 1 6 8 tr 261338 (BB) 95 3 2 261049 (HH) 65 tr 21 1 13 tr >90 260973 (GG) 89 1 5 Tr 4 tr 261318 (GG) 70 19 2 6 tr 1 1 261341 (GG) 51 2 34 5 7 tr >90 tr 1 261011 (II) 94 2 3 261006 (II) 96 2 2 261347 (AA) 66 17 1 10 2 tr >90 2 2
Table 1 XRD Mineral Abundance Pimienta Formation. Samples are sorted in-depth, increasing order. Tabla 1 Composición mineral XRD de las muestras analizadas de la formación Pimienta. Las muestras se muestran en orden creciente de profundidad.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 45 Figure 4. Mineral Composition of the Pimienta Formation displayed in a clay/sandstone/limestone ternary diagram, superimposed over the “sCore: A Classification for Organic Mudstones” by (Gamero-Diaz et al., 2013). The classification of the Pimienta formation is carbonate mudstone. Major shale plays of the world are mapped, identifying the Eagle Ford and Bakken from North America, and Hanifa from Saudi Arabia, as analogous to the Pimienta Formation. Figura 4. Composición mineralogica de las muestras analizadas de la formación Pimienta, mostradas en diagrama ternario arcillas- arenas-carbonatos, de acuerdo a la clasificación “sCore: A Classification for Organic Mudstones” por Gamero-Diza et al. (2013). La formacion Pimienta puede ser clasificada como mudstone carbonáceo. Se muestran también plays productores tipo no convencional, identificanfo a las formaciones Eagle Ford y Bakken de Norteamérica, y Hanifa de Arabia Saudita, como análogos a la formacion Pimienta. • VOL. LXII No. 1 ENERO-JUNIO 2020
Figure 5. Top view of a core fragment of Pimienta formation, sample ID 261344, from well DD. Extremely fine-grained black mudstone conforms to the bulk of the sample. A vein of calcite-pyrite crosses the core at a high angle with respect to the vertical. The areas in the blue squares are the selected spots for EDS analysis. Zone A is selected over the calcite-pyrite vein. Zone B covers an area over the bulk carbonaceous mudstone. Right side is are a set of wireline logs over the interval of Pimienta formation. Figura 5. Vista lateral de un fragmento de slab de la formación pimienta, muestra ID 261344, obtenida del pozo DD. La matriz de la muestra esta compuesta de mudstone negro de grano muy fino. Una fractura sellada con calcita y pirita corta el núcleo, paralela al eje longitudinal. Las zonas A, B y C son seleccionadas para análisis EDS. La zona A cubre la vena de calcita y pirita. La zona B analiza una zona de la matriz de mudstone. En la derecha se muestran los registros geofísicos en el intervalo correspondiente a la formación Pimienta.
46 • MINERAL SPECTRUM ANALYSIS Energy-Dispersive X-Ray Spectroscopy (EDS) analysis consists of mineral mapping over the zones areas highlighted in Figure 5. Higher accuracy on the mineral characterization is achieved by selecting individual spots for spectrum analysis. A total analysis of 12 spectrum spots were completed in the sample, distributed in 3 spots (S1-S3) for Zone A, four spots (S4-S7) in Zone B and five spots (S8-S12) Zone C. The EDS results have units of weight percent (wt. %), which are used to predict the mineral composition, estimated from the proportion of each of the elements to that of the chemical composition. Figures 6A, 6B, and 6C show SEM images of the different zones and the selected spots for spectrum analysis. The results of elemental quantification from EDS analysis are displayed in table 2.
El análisis EDS se realizó en la zonas señaladas en la figura 5, así como también se seleccionaron 12 puntos para análisis espectral (Sx) el cual provee análisis detallado en áreas reducidas, distribuidas en tres puntos (S1-S3) en la zona A, cuatro puntos (S4-S7) en la zona B, y cinco puntos (S8-S12) en la zona C. El análisis mapeo espectral se realizó para los elementos Calcio, Oxigeno, Carbono, Silicio, Hierro y Azufre. Los resultados de análisis espectral tienen unidades de peso porcentual wt.% por elemento químico analizado, desplegados en la Tabla 2.
Spectrum C O Na Mg Al Si S Ca Fe Zn Total Predicted Mineral Label + Traces Clay amd Map Zone A 22.7 40.5 0.2 0.1 3.2 8.5 17.6 7.1 0.2 100 Dolomite
Spectrum 1 18.4 55.2 1.4 25.1 100 Calcite (CaCO3)
Spectrum 2 65.5 31.3 3.2 100 Quartz (SiO2) Spectrum 3 67.3 22.7 1.2 3.0 1.0 4.7 100 Kerogen (C,H,O,N) Map Zone B 20.7 52.7 0.1 0.4 0.2 2.3 0.9 22.1 0.7 100
Spectrum 4 11.3 48.8 3.1 36.8 100 Pyrite (FeS2) Kerogen (C,H,O,N) + Spectrum 5 66.9 24.4 1.0 3.4 4.3 100 Quartz (SiO2)
Spectrum 6 11.4 43.9 44.7 100 Calcite (CaCO3) Calcite (CaCO ) + Spectrum 7 12.3 53.3 4.8 29.6 100 3 Quartz (SiO2) Map Zone C 20.0 40.2 10.6 11.2 9.3 8.7 100
Spectrum 8 4.6 58.6 35.3 0.8 0.8 100 Quartz (SiO2)
Spectrum 9 14.8 8.7 0.8 45.3 30.5 100 Pyrite (FeS2) Calcite (CaCO ) + Spectrum 10 16.9 51.7 0.8 0.9 0.5 29.3 100 3 Quartz (SiO2) Spectrum 11 22.2 49.9 0.6 1.0 25.0 1.2 100 Kerogen (C,H,O,N) Pyrite (FeS ) / Spectrum 12 29.8 29.3 6.8 34.1 100 2 Anhydrite (CaSO4)
Table 2 EDS Spectrum analysis results for each of the locations as selected from Figure 5, sample ID 261344. Tabla 2. Resultados de Espectroscopía de Energía Dispersiva EDS en las zonas indicadas en la Figura 5. Muestra de formación Pimienta del pozo DD.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 47 The Zone A in Figure 6A has a scale of 500 μm. The mapeo general de la zona A se encontraron trazas de upper region is the homogeneous mudstone. The Mg, Al y Zn, que son elementos de las estructuras de brighter (therefore higher density) diagonal vein is the arcillas, instrinsicamente contenidas en la muestra. pyrite. Underneath, the calcite vein is parallel with the distinguishable microfractures in the perpendicular The minerals of Zone B in Figure 6B are direction. Spot S1 has a high content of Ca, C, and O, homogeneously, and well-sorted grains conform to indicating positively that the white infilling material the bulk sample of the carbonate mudstone. Grain of the natural fracture is calcite. size is in the order of 10 μm. Features in this zone are pyrite framboids and distinctive oval and concave Spot S2 is predominantly Si and O, which are the patterns, presumably resulting from organic matter constituting elements of quartz. No other elements or microfossils. Spot S4 performed on a distractive typical of clays or feldspars, such as Al, K, Na, pyrite framboid, confirmed with high Fe and S are identified in this particular spot analysis. The content. Spot S5 measured one of the dark spots sharp edges of this object could indicate that it is arranged in a distinctive concave pattern, presumably part of a network of microfractures in the calcite a section of a microfossil. The high content of C and vein. The microfractures are ~20 μm wide and run O in mineral analysis confirms this spot as organic perpendicular to the calcite and pyrite vein. Spot S3 is matter. Spot S6 is selected from a gray spot or grain, a representative area of the darkest, low density, an which is delimited by a perimeter of darker, less irregular spot in the mudstone area. The predominant dense material. The identified minerals are Ca, C, and mineral occurrence of C and O confirms that this O, which are the constituents of Calcite. Spot S7 is particular location is organic material or kerogen. chosen from a brighter, higher density spot, although Note for Zone A mineralogy: Besides the mineral due to imminent charging affects the brightness and quantification in the spots S1, S2 and S3, there contrast may not truly represent the morphology. are traces of Mg, Al, and Zn, measured by mineral The EDS spectrum analysis indicates that the mapping in the entire zone. These are components composition in this spot is dominantly calcite, with a of clays that are intrinsically present in the sample. minor proportion of Si. Additional elements identified in Zone B are traces of Na, Mg, and Al, which are La zona A en la Figura 6A tiene una referencia de components of clay.
• VOL. LXII No. 1 ENERO-JUNIO 2020 escala de 500 μm. La región superior-izquierda de la imagen es mudstone homogéneo. La franja brillante Los minerales de la zona B (Fig. 6B) están (densidad alta) es la depositación de pirita, que es constituidos en un agregado homogéneo y coherente paralela a la vena de calcita que se distingue por las que forman la matriz mudstone de la roca. El tamaño múltiples microfracturas. La esquina inferior derecha de los granos es del orden de 10 μm. En la zona se es nuevamente la matriz de mudstone. El punto S1 identifican framboides de pirita y característicos tiene alta concentración de Ca, C y O, confirmando núcleos ovalados y cóncavos resultados de materia que el material cementante de la fractura es calcita. orgánica y microfósiles. El análisis espectral en el El punto S2 es predominantemente Si y O, que son punto S4 se realiza en un framboide de pirita, los elementos que constituyen el cuarzo. Los ángulos confirmado con la detección de elementos S y Fe. bien marcados en ese cuerpo sugieren que es un El punto S5 caracteriza la región obscura con forma grano dentro de la red de microfracturas dentro de la cóncava, posiblemente de un fósil, confirmado vena de calcita. Las microfracturas tienen un espesor como materia orgánica por el alto contenido de C y de ~20 μm, con una orientación perpendicular a la O. El punto S6 se realiza en un área con matiz gris vena principal, es decir a la fractura cementada. El claro, delimitado por un contorno obscuro de baja punto S3 es un área obscura (baja densidad) en una densidad, obteniendo concentraciones de Ca, C y O, zona irregular de la matriz mudstone. Los elementos lo cual son constituyentes de la calcita. El punto S7 predominantes son C y O, confirmando que es es elegido en un punto brillante de alta densidad, sin material orgánico o kerógeno. Adicionalmente en el embargo por el efecto de saturación electrostática
48 no se puede observar la textura de la zona en detalle. la fractura, aunque depositados en diferente evento El análisis espectral arroja composición de calcita, geológico. El elemento carbono presenta una alta con una menor proporción de Si. Otros elementos concentración en el punto S3, que fue determinado identificados en la zona B son trazas de Na, Mg, y Al, como kerógeno en el análisis espectral. que son componentes de arcillas. Sulfur (Fig. 7D) is mostly present in the pyrite vein, The EDS analysis in the Zone C in Figure 6C is follows the same distribution as the iron mapping (Fig. completed over a similar region as Zone A, centered 7E). The isolated spots where S concentrates (other around the pyrite vein, identifying the spots: S8 than pyrite), but not correlating to Fe concentration Quartz, S9 Pyrite, S10 Kerogen, S11 Kerogen, and over the same area, could be an indication of other S12 Framboid. isolated minerals containing S, such as the anhydrite
(CaSO4), as reported in XRD results. A significant El análisis EDS en la zona C (Fig. 6C) se realiza sobre consequence of sulfur in the kerogen is the potential zonas similares a la Zona A, centrado alrededor de la for H2S generation as a maturation byproduct. vena de pirita. Los elementos identificados del análisis espectral concluyen la distribución de minerales: S8 La distribución de S y Fe, en las Figuras 7D y 7E tiene Cuarzo, S9 Pirita, S10 Kerógeno, S11 Kerógeno, y S12 una marcada presencia en la vena de pirita, así como Framboide de Pirita. en las estructuras framboides. También se identifican puntos de alta concentración de S, que no se replican • MINERAL MAPPING / MAPEO DE en la distribución de Fe con lo que se descarta que ELEMENTOS QUÍMICOS sean núcleos de Pirita, sin embargo podrían ser A 2D distribution map for each element is constructed identificados como anhidrita, basado en el análisis from the spectral analysis over a surface. Figure 7 de XRD. Una consecuencia importante de contenido shows the compositional distribution maps of the Zone de azufre es la generación de H2S como producto de A in Figure 5 for the elements Ca, C, O, Fe, S, and Si. la maduración del yacimiento.
El mapeo superficial de la distribución de elementos Finally, the mapping for Silicon (Fig. 7F) concentrates químicos de se muestra en la Figura 7, realizado en la mostly in the lower region. The EDS mapping zona A para los elementos Ca, O, C, S Fe y Si. demonstrates that Si occurs in minor veins, 20 μm thick. The focused presence of Si indicates that Mapping of calcium (Fig. 7A) and oxygen (Fig. 7B) the silica-dominated infiltration into the carbonate indicate a strong presence of the elements throughout mudstone matrix in aqueous solution occurred. This the bulk sample of carbonate mudstone, determining infiltration followed channels and microfractures in the lithology of the rock matrix deposited during the the calcite vein but was unable to permeate beyond formation of the Pimienta formation. Calcite crystals the pyrite vein. are also present as infilling material in the naturally occurring fractures. Carbon (Fig. 7C) is also present Finalmente, el mapeo de Si (Fig 7F) indica que in most of the analyzed surface, but there is a higher la distribución se concentra en el sector inferior- concentration in spot S3, that was identified as organic derecha, así como en las microfracturas de la vena matter, suggesting the presence of kerogen. de calcita, que tienen un espesor de 20 μm. La distribución de los minerales sugiere que la secuencia El mapeo de los elementos Ca (Fig. 7A), O (Fig. 7B) y C de depositación del cuarzo ocurrió en un evento (Fig. 7C) indican una distribución dominante en toda la no detrítico, post-fracturamiento y cementación extensión de la superficie de la zona A, determinando de calcita, como filtración en una solución acuosa, la matriz litológica como mudstone carbonáceo de permeando en las microfracturas de la calcita y el la formación Pimienta. Cristales de calcita también mudstone, y en menor proporción a través de la vena están presentes en el material de cementación de de pirita.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 49 Figure 6A. SEM image of the area of analysis Zone A. Scale 500 Figure 6C. Scanning electron microscopy (SEM) image of the area of μm. Spot S1 is selected in order to analyze the calcite vein. S2 is analysis Zone C. Scale 250 μm. Spot S8 performed on a region of selected from a low-density area that is at the boundary of the slightly darker gray hue, next to the pyrite vein. S9 is over the pyrite white calcitic vein. S3 is an analysis of a cluster of organic material. vein. S10 and S11 analysis completed on organic dark spots. S12 Figura 6A. Imagen de microscopia electronica de barrido, SEM de la is completed on an isolated high density, bright spot. zona A. Referencia 500 μm. El punto S1analiza la vena de calcita. Figura 6C. Imagen de microscopia electronica de barrido, SEM de El punto S2 es un punto de baja densidad (coloración obscura) la zona C. Referencia 250 μm. El punto S8 se realiza en una región en el margen de la vena de calcita. El punto S3 es un nódulo de identificada por la tonalidad gris obscuro -en la escala de color material orgánico. de SEM indica poca conductividad- cercano a la vena de pirita, donde se ubica el punto 9. Los puntos 10 y 11 se realizan sobre regiones de material orgánico. El punto 12 caracteriza un punto de alto brillo.
5.3 POROSITY ANALYSIS / ANÁLISIS DE POROSIDAD The sample selected for porosity analysis is the sample ID 261318 from well GG. Porosity obtained
• VOL. LXII No. 1 ENERO-JUNIO 2020 with N2 porosimeter indicates 0.7 p.u. Lithologic classification is that of a clay-rich carbonate mudstone with the XRD analysis of carbonates as calcite 70 wt. %, silicates from quartz 19 wt. % and plagioclase feldspar 2 wt. %, clay as illite, 6 wt. %, Sulfates in the form of barite 1 wt. % and anhydrite 1 wt. %, and traces of pyrite. Pyrolysis analysis indicates Figure 6B. Scanning electron microscopy (SEM) image of the medium-high total organic content (TOC) of 2.51 wt. area of analysis Zone B, Scale 100 μm, located in the Mudstone area. The quality of the image is affected by the charging effect % (Vega-Ortiz et al., 2020a). The high TOC ensured due to the high siliceous (Si) content. Spot S4 is taken over a that there would be organic matter (kerogen) present Pyrite framboid. S5 is selected from non-conductive dark spots in the rock matrix. Similar to the sample from well DD, characteristic of organic matter. S6 targets a gray grain/cluster delimited by a distinctive darker perimeter. S7 is an analysis of a the sample ID 261318 contains microfractures filled highly conductive area. with calcite. The features observed in this sample Figura 6B. Imagen de microscopia electronica de barrido, SEM de are believed to be representative of the Pimienta la zona B. Referencia 100 μm.LA calidad de la imagen es afectada por el efecto de carga electrostática por el alto contenido de Silicio formation at this particular depth and location. (Si). El punto S4 es tomado en un framboide de pirita. El punto S5 es seleccionado en una región no conductiva característico La muestra seleccionada para análisis de porosidad de materia orgánica. El punto S6 se enfoca en una región no conductiva delimitado por un contorno obscuro. El punto S7 es la muestra ID 261318 del pozo GG. La porosidad analiza un área altamente conductiva. medida con porosímetro de N2 es de 0.7 p.u. La
50 clasificación de litología es mudstone carbonáceo rico en arcilla, con contenido mineralógico 70 wt.% calcita, areniscas de 19 y 2 wt.% de cuarzo y feldespato plagioclase, respectivamente, contenido de arcillas como Ilita en 6 wt.%, así como sulfatos en forma de barita 1 wt%, anhidrita 1 wt.%, y trazas de pirita. Análisis de pirolisis indica un valor medio de contenido orgánico total TOC de 2.5 wt.%, como se reporta en Vega-Ortiz et al, (2020), asegurando que en esta muestra asegura que hay presencia de kerógeno en la matriz. Al igual que la muestra analizada del pozo DD, esta muestra tiene fracturas selladas con calcita.
Ramsay (1980) studied the formation of veins trough the crack-seal mechanism. Geological stress deforms and induces microfractures in the rock matrix, creating new surfaces. The deposition of crystallized minerals transported by aqueous solution leads to the growth of the infilling crystals, sealing the cracks, and forming the vein (Fyfe et al., 1978).
Ramsay (1980) estudió el mecanismo fractura-cementación en la formación de venas. Los esfuerzos geológicos deforman e inducen microfracturas en la matriz de la roca, creando nuevas superficies. La depositación de minerales cristalizados a través de soluciones acuosas permite el crecimiento de cristales que sellan y cementan la fractura, formando las venas de minerales (Fyfe et al., 1978).
Figure 7. EDS Compositional map of the Zone A from sample ID 261344. Calcium, oxygen, and carbon are present in the carbonate mudstone and calcite vein, analyzed by spot S1. A high concentration of C occurs at spot S3, where kerogen is identified. Sulfur and iron occur in the pyrite vein. Isolated sulfur spots may correspond to anhydrite. Quartz is seen in the O and Si maps, verified by the spectrum analysis in spot S2. Figura 7. Imagen de Barrido Electronico de Dispersion., EDS, de la zona A, realizada en la muestra ID 261344, identificando los elementos Calcio (Ca), Oxigeno (O) y Carbono (C) en la región de la matriz de mudstone y en la fractura sellada con calcita (punto S1). Una alta concentración de C ocurre en el punto 3 donde se puede identificar un nódulo de kerogeno. Los elementos Hierro (Fe) y Azufre (S) están presented en la vena de pirita. Los puntos aislados de S son indicación de cristales de Anhidrita -se descarta presencia de pirita por la ausencia de Fe en los mismos puntos-. Depositos de arenas, o cuarzo, es observada por el mapeo del elemento Silicio (Si), verificado por el análisis espectral del punto S2
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 51 Figure 8. Large scale image of Pimienta formation sample. The location of the sample for SEM is indicated in the wireline logs over the Pimienta formation interval. Figura 8. Imagen de una muestra de la formación pimienta. En la derecha se indica la ubicación de la muestra analizada usando los registros geofísicos como referencia.
The overall layout of the sample is shown in Figure of the Pimienta formation. The porosity curve derived 8, an SEM image with magnification 30x of an from Sonic log shows a slight increase (no neutron unpolished sample. Clay-rich carbonate mudstone porosity curve is available). The last track displays is noted as the dominant lithofacies. The vein is the organic content with a peak at TOC 1.8 wt.% in formed by two parallel crystal layers of calcite the Pimienta formation. The Kimmeridgian Taman and pyrite, deposited along the fracture surface. formation below shows a higher TOC up to 2.2 wt.%. At this magnification of 30x, the texture and grain sorting of the mudstone looks evenly distributed La configuración de los minerales en la muestra se
• VOL. LXII No. 1 ENERO-JUNIO 2020 with random and isolated clusters of minerals in explica en la Figura 8, es tomada con SEM a una the form of irregular shapes or bright, denser spots. magnificación de 30x en una muestra sin pulir, Also recognizable at this relatively large scale is a siendo la facie litológica dominante el mudstone fracture (dashed red) that runs across the mudstone carbonáceo rico en arcillas. La vena está formada section parallel to the vein, likely as a consequence por dos capas paralelas cristalinas de calcita y pirita from in-situ geological stress. The vein is ~0.5 mm depositadas a lo largo de la superficie de la fractura. wide. The calcite crystals in the vein are identified En la magnificación de 30x la textura y distribución by characteristic cleavage planes, which are perfect de los granos parece homogénea, con distribución rhombohedral {10ī4} (Rachlin et al., 1992), produced aleatoria y aislada de grupos de cristales de formas from the hexagonal, space group R3c calcite structure irregulares. También se identifica una fractura (línea given by Chessin (1965). A thinner pyrite layer, width punteada roja) que se desarrolla a lo largo de la matriz ~ 0.1 mm, is observed in the vein. de mudstone y paralelo a la vena. El espesor medido de la vena de calcita es de ~0.5 mm, así como también The wireline logs of the Pimienta formation are una capa de pirita delgada de ~ 0.1 mm de espesor. displayed in Figure 8, indicating the location where Los cristales de calcita en la vena se identifican por the sample for SEM analysis is taken. The GR in the los planos de clivaje característicos que consisten en suprajacent formation of K Tamaulipas Inferior (K-TI) romboedros {10ī4} (Rachlin et al., 1992), producidos is a low 20 GAPI curve. The J-K boundary sets an por la estructura hexagonal de calcita, grupo R3c. increase in the GR curve, which is the typical signature (Chessin et al., 1965).
52 Los registros geofísicos en la formación Pimienta se clear example of intercrystalline porosity. The muestran en la figura 8. Indicando la profundidad a crystals in Figure 10B are interpreted as anhydrite la cual se obtuvo la muestra para análisis SEM. La (CaSO4), which is orthorhombic and classified in curva de GR en la formación K Tamaulipas Inferior the space group Amma. (Shindo and Nozoye, 1992). (K-TI) indica valor bajo 20 GAPI. El contacto J-K se The characteristic anhydrite cleavage is the result identifica con un incremento en las curvas de GR, of the crystal nucleation and growth precipitated característico de la formación Pimienta. La curva de from aqueous solution (Pina, 2009). The presence of porosidad derivada de registro sonico muestra in leve anhydrite confirms the hypothesis of shallow marine incremento a ~3 p.u. (no existe curva de neutrón- conditions since calcium sulfate minerals are known porosidad). El ultimo registro es el contenido orgánico to form in tidal environments (Young and Chan, 2017). total, con un máximo de TOC=1.8 wt.% para la The gaps between the crystals produce voids with formación Pimienta y 2.2 wt.% en la formación Taman. dimensions in the range of 2 to 20 µm. By analyzing the morphology of the crystals, it can be concluded • INTERGRANULAR POROSITY / POROSIDAD that these pores are interconnected and contribute INTERGRANULAR to the effective porosity. This connectivity, therefore, An example of the intergranular porosity is observed represents favorable conditions for fluid transport in Figure 9, which has a magnification of 1924X. The within the rock. texture of the carbonate mudstone bulk section of the sample shown is composed of flake-like grains, A una magnificación de 181x se observa una approximately 5.0 x 5.0 µm. All of the grains align agrupación de cristales incrustada en la matriz de with the same orientation with respect to the vertical, mudstone (Fig. 10A). A la magnificación de 1025x producing an aggregated accumulation of well-sorted (Fig. 10B) se observan los cristales y la porosidad grains. Intergranular pore space is highlighted in the intercristalina con mayor detalle. La estructura red frame. The dimensions of this pore are 3.3 x 2.6 ortorrómbica de los cristales los define como µm. The intergranular porosity is limited, and the anhidrita, clasificados por Shindo y Nozoye (1992) connectivity between pores is limited. This likely dentro de grupo espacial Amma. El clivaje característico considerably restricts the overall permeability of the de la anhidrita es resultado de la nucleación cristalina rock matrix. y crecimiento de la precipitación de solución acuosa (Pina, 2009). La presencia de anhidrita confirma la Un ejemplo de porosidad intergranular se observa en hipótesis de condiciones marinas someras dado la Figura 9, que tiene una magnificación de 1924x. que los minerales de sulfato de calcio se desarrollan La textura del mudstone carbonáceo tiene una en ambientes sedimentarios de marea (Young and composición de granos tipo hojuela de dimensiones 5.0 Chan, 2017). Los espacios intercristalinos producen x 5.0 µm. Todos los granos tienen la misma alineación, una porosidad de dimensiones en el rango de 2 a produciendo un compuesto agregado de granos bien 20 µm. Analizando la morfología de los cristales organizados. El espacio poroso intergranular, así como se observa que los poros están interconectados la conexión entre los poros, es limitado lo cual restringe contribuyendo positivamente a la porosidad efectiva el transporte de fluidos y ocasiona una permeabilidad y la permeabilidad. muy baja en la matriz de la roca. • MICRO-FRACTURE POROSITY / POROSIDAD • INTERCRYSTALLINE POROSITY /POROSIDAD DE MICROFRACTURAS INTERCRISTALINA At the boundary between the calcite vein and the At 181x magnification, a crystalline cluster was carbonate mudstone, there is a microfracture that runs detected in the clay-rich carbonaceous mudstone parallel to the area of contact between the two rock (Fig. 10A). The crystal cluster is embedded within components, observed in Figure 11 with magnification the mudstone matrix. A 1025x magnification 131X. The width of this microfracture is 5 µm. A of the inset square (Fig. 10B). That view shows a mechanism for the microfracture occurrence is the
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 53 poor bonding between the matrix and the precipitate material in the veins, combined with the geomechanical deformation and fracture caused by in-situ stresses. This type of porosity may represent major channels for fluid transport. When the reservoir is subject to pressure differential, the fluid stored in the intergranular and intercrystalline porous networks and will flow through microfractures. Unfortunately, these fractures may likely be closed at in-situ stress conditions.
En la unión entre la vena de calcita y la matriz de mudstone existe un espacio entre los dos grupos minerales, como se observa en la Figura 11 que tiene magnificación 131x. El espesor de esa microfractura es de 5 µm. El mecanismo de formación de la Figure 9 Clay-rich carbonate mudstone composed of well- fractura es la débil unión entre la matriz y el material sorted fillosilicate flake shaped grains deposited uniformly. The de cementación, en combinación con los esfuerzos intergranular porosity is in the order of 3 μm geológicos de deformación. Este tipo de porosidad Figura 9. Imagen de alta resilucion (escala 30 um) de una muestra de mudstone carbonáceo rica en arcilla. La textura es de representan canales amplios para el transporte filosilicatos -hojuelas- apiladas, depositados uniformemente. La de fluidos del yacimiento hacia el pozo, en caso de porosidad intergranular es del orden de 3 μm. permanecer abiertos. • VOL. LXII No. 1 ENERO-JUNIO 2020
Figure 10. Crystalline structure imbedded in the limestone matrix. The porous network between the anhydrite crystals is interconnected, creating favorable conditions for storage and permeability. Pore dimensions are on the order of 2 to 20 μm Figura 10. Estructura cristalina de anhidrita incrustada en la matriz de mudstone carbonáceo. La red de porosidad entre los crsitales de anhidrita están interconectados, crando condiciones favorables para almacenamiento y permeabilidad. El tamaño de los poros es en el orden de 2 a 20 μm.
54 • ORGANIC MATTER – KEROGEN / MATERIA ORGANICA - KERÓGENO Kerogen is a geopolymer that derives from accumulated organic material that was deposited and buried with the rock. Depending on the depositional environment, the accumulated organic material can be terrestrial, lacustrine or marine, origin, composed of micro or macroscopic forms of life. The composition of the kerogen is a complex arrangement of organic fabric and tissues. The organic material may be preserved in an anaerobic environment where decomposition is minimized. Further burial exposes the organic matter to elevated temperature and pressure, leading to diagenetic processes, which are the chemical reactions that convert the kerogen into lineal chains of over geological time. The type of hydrocarbon generated from the kerogen will depend on the initial elemental constituents, particularly C, H, O, and N. The products vary from a range combination of light compounds C1-C4 natural gas and volatiles to heavier chains that produce heavy wax and bitumen. The byproducts CO2 and H2S are also commonly found in oil and gas reservoirs.
El kerógeno es un geo polímero que se deriva de la materia orgánica que fue acumulada y enterrada junto con los depósitos sedimentarios. Dependiendo del ambiente de depositación, el material orgánico puede ser de origen terrestre, marino o lacustre, compuesto de tejidos orgánicos complejos o residuos de paleo organismos microscópicos. Los residuos orgánicos pueden ser conservados en ambientes anaeróbicos, en donde la descomposición es inhibida, sin destruir o transformar los compuestos orgánicos en elementos minerales. Siguiendo el mecanismo tectónico de subducción, la materia orgánica llega a ser sometida a condiciones elevadas de presión y temperatura dando lugar al proceso de diagénesis, que consiste en las reacciones químicas que convierten la materia orgánica en kerógeno, y eventualmente en la transformación en cadenas lineales de hidrocarburos a través de los tiempos geológicos. El tipo de hidrocarburos generados dependen de los elementos constitutivos, particularmente C, H, O y N. Los productos generados varían en un rango de compuestos ligeros como gas natural y crudo ligero (C1-C4) hasta cadenas más pesadas que producen crudo pesado y bitumen. Los productos colaterales como CO2 y H2S también son comúnmente encontrados en yacimientos de aceite y gas.
With field emission (FEG) SEM, the backscattered secondary electron images can infer the presence of kerogen as dark, lower density spots. The kerogen in Figure 12 is identified as isolated clusters of organic matter in a fined grained mudstone matrix. This dispersed occurrence is consistent with deposition having occurred in low energy, shallow marine reducing environment.
En las imágenes obtenidas con SEM, el kerógeno se identifica como áreas de tonalidad obscura debido a material de baja densidad. En la Figura 12 están señalados los nódulos de kerógeno incrustados en la matriz de mudstone, que son los que proporcionan el contenido orgánico total TOC en el análisis de pirólisis.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 55 Figure 11. Shear-induced micro-fracture in the interface between calcite and shaly limestone, caused by the difference in the geomechanical properties of each of the materials and poor bonding between the surfaces. These fractures may have been the result of distressing during sample recovery from the in-situ environment. Figura 11. Microfractura inducida por esfuerzos de cizalla en la interface de la vena de calcita y la matriz de mudstone, causada por las diferentes propiedades geomecánicas de los minerales y la reducida cementación entre las superficies. Estas fracturas pudieron haber sido resultado de la reducción de los esfuerzos in-situ, en la recuepracion del núcleo a superficie.
Figure 12 SE- SEM Image carbonaceous mudstone from Pimienta
• VOL. LXII No. 1 ENERO-JUNIO 2020 Formation at 10 KeV. Kerogen appears as darker spots. Limestone topographic features are observed on a grayscale. The areas covered with pyrite material exceptionally bright, caused by the excess of scattered electrons in the surface. Figura 12. Imagene de SEM de la formación Pimienta, mudstone carbonáceo con 10 KeV. La textura del mudstone se observan en escalas de grises. El kerogeno se observa como manchas obscuras. Las zonas cubiertas con pirita se manifiestan como alto brillo, causado por el exceso de electrones dispersados en la interfase metálica.
56 6. MONTE CARLO SIMULATOR CASINO / SIMULADOR NUMÉRICO CASINO
The Monte Carlo CASINO (Université de Sherbrooke, Québec, 2000) is used to simulate the electron trajectories upon penetration on a surface of defined material (Fig. 13). Simulations below show the electron trajectories for the three components (organic matter, mudstone, and pyrite) for beam voltages of 2 and 10 KeV. All of the images have the same scale z=1500, x=2000.
Scanning electron microscopy (SEM) imaging relies on the interaction between an electron beam and the surface layers of a sample. The electrons will either penetrate the sample or will be scattered back into the SEM chamber, where the secondary electrons detector can measure, quantify and process the signal produced from the scattered electrons and translate this into a meaningful 2D image. The image contrast will vary according to the sample composition. For this particular sample of the Pimienta formation, there are three components: rich clay carbonate mudstone (SiO2-CaCO3) is the primary matrix constituent, residual kerogen is present as organic material. Pyrite, along with calcite, infilled the naturally occurring fractures in the rock.
El simulador CASINO utiliza método MonteCarlo (Université de Sherbrooke, Québec, 2000) para predecir la trayectoria de los electrones incidentes después de interactuar con capas de distintos minerales, simulando el cañón de electrones operado a 2 y 10 keV. En el caso de la muestra analizada de la formación Pimienta, existen tres componentes: la matriz mudstone, la vena cementada con calcita y pirita, y los nódulos de kerógeno (Fig. 13). Las imágenes de SEM se producen de la interacción entre el haz incidente de electrones y los átomos en la superficie la muestra, pudiendo ser reflejados en caso de materiales de alta densidad, o bien penetran hacia el interior de la muestra si no existen las interacciones necesarias para ser reflejado. El cañón de electrones y el detector se ubican encima de la muestra. El haz de electrones recorre el área expuesta de la muestra, enfocado secuencialmente en pequeñas áreas a manera de pixeles; el detector mide, cuantifica y procesa la energía de los electrones reflejados en cada uno de estos pixeles. La compilación de la respuesta de cada uno de los pixeles genera una imagen representativa de la textura de la muestra analizada. El contraste y matiz de cada píxel depende de la composición de elementos químicos en cada punto en particular; metales densos reflejan una alta cantidad de electrones, produciendo imágenes brillantes, mientras que elementos de baja densidad reflejan una menor cantidad de electrones, produciendo imágenes obscuras.
For the simulations of the images taken with 2 keV, the electron interacts only with the surface layers of the material, leading to shallow penetration. The contrast and brightness of the images are exceptionally homogeneous, and the topography features and textures of the sample are identifiable, although the grey hue scale is not sufficient to distinguish between mineral components of the sample.
La simulación de la interacción con 2 keV, la interacción de los electrones con la muestra es mínima, limitada a la capa superficial. El contraste y brillo de las imágenes producidas son excepcionalmente homogéneas, siendo difícil distinguir entre los distintivos en la textura de los componentes.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 57 Figure 13. Numerical Monte Carlo simulation of the possible trajectories of the electron inside different materials, using the CASINO® software. At 2 KeV, the interaction volume is small, and the electrons from the SEM beam remain on the surface. At 10 KeV, the electrons will penetrate deeper into the material: Organic matter offers the least resistance, and the image will appear darker. In the Pyrite metallic elements, the electrons will remain closer to the surface and will be scattered back to the detector, creating charged surfaces and brighter images. Figura 13. Simulacion numerica utilizando el método Montecarlo del programa CASINO, indicando las trayectorias de penetracion del haz de electrones del SEM a energías de 2, 5 y 10 KeV, dispersas hacia dentro de la muestra después de interactuar con la superficie de los materiales. A 2 KeV, el volumen de interacción es reducido y los electrones incidentes del SEM permanecen el la superficie. A 10 KeV, los electones penetran a una mayor profundidad en la estructura de la muestra: El material orgánico ofrece la menor resistencia permitiendo una penetración mayor, -sin reflejar electrones hacia el exterior-, produciendo una imagen obscura. En las superficies metalicas de pirita, los electrones tendrán poca penetración, ya que en su mayoría son reflejados hacia el exterior de la muestra, produciendo una imagen muy brillante y saturada.
The mineral response will be identifiable using higher energy in the electron beam, as displayed in simulations corresponding to 10 KeV. For organic-rich samples, it is particularly useful for kerogen identification. Since organic matter is a complex organic structure of
• VOL. LXII No. 1 ENERO-JUNIO 2020 C, H, O, N and S, the electron beam penetrates deep into the subsequent layers from the surface in a narrow distribution of trajectories, and fewer electrons are scattered back to the detector, producing darker areas. On the other hand, pyrite is composed of crystalline grains containing the heavier metallic elements FeS2, which offers a higher resistance path for the incident electrons. The electron trajectories are distributed in a shallower and wider region in the layers closer to the surface, which produces an excess of electrons scattered back to the chamber; hence the high amplitude of the signals in the detector produces a saturated bright image in Figure 12.
La respuesta de los minerales es distinguible usando energía más elevada en el cañón de electrones, como se muestra en las simulaciones a 10 keV. Es particularmente útil para muestras que contienen alto contenido orgánico para identificación de la distribución del kerógeno. Dado que la composición química con elementos C, H, O, y N, el haz de electrones penetra en capas más profundas, con pocos electrones reflejados hacia el detector. En contraparte, la pirita está compuesto de elementos metálicos Fe y S , ofreciendo una mayor resistencia en la trayectoria de los electrones, provocando trayectorias más dispersas y cercanas a la superficie, ocasionando que gran parte de los electrones incidentes sean reflejados hacia el detector y produciendo imágenes brillantes y saturadas.
58 7. MICROFOSSILS / MICROFÓSILES
Microfossils are remains of life that were buried in sediments and are used as geological markers and diagnostics of depositional environments. Marine organisms often lived in shallow water, where the proper conditions of temperature, solar radiation were favorable to support life. Figure 14A is an example of fossils observed in the Pimienta formation sample ID 261344 from well DD. The oval shape is a sectioned microfossil with a well- defined layer in the perimeter of the body of the organism. In the lower section of the body, there is a characteristic spiral structure rotating along the longitudinal axis, resembling the shell of present-day organisms. The length of these microfossils is about 50-100 µm. This particular microfossil matches the description of a tapered morphogroup (Bernhard, 1986), in Figure 14B. In a study by (Omaña and González Arreola, 2008), benthic foraminifera microfossils are described from a Kimmerigdian formation outcrop in a nearby location, Figure 14C.
Los microfósiles son restos de organismos que fueron enterrados y preservados en forma mineral estudiados en el área de micropaleontología, y que son usados como marcadores geológicos y métodos de diagnóstico para ambientes de deposición. En las zonas neríticas existe abundancia de organismos marinos por las condiciones de temperatura y radiación solar, óptimas para el sustento de formas de vida. La Figura 14A es un ejemplo de los fósiles observados en la muestra ID 261344 del pozo DD. El contorno cónico-ovalado es una sección de un microfósil de 50 a 100 µm de longitud. En la sección inferior se distingue una característica geometría espiral de las conchas o exoesqueletos de los moluscos encontrados en la actualidad. El microfósil tiene características similares a los morfogrupos descritos por Berhnhard (1986) en la Figura 14B. En un estudio por Omaña y González Arreola (2008) describe un ejemplo de foraminífero bentónico encontrado en un afloramiento del Kimeridgiano en una locación cercana, Figura 14C.
Figure 14. A) Microfossils found in the Tithonian Pimienta formation core. B) Classification of foraminifera morphogroups by (Bernhard). C) Kimmeridgian Foraminifera (Kurnubia palastiniensis) as described by (Omana and Gonzalez Arreola, 2008) Figura 14. A) Microfosiles observados en la muestra de formación pimienta del pozo DD. B) Clasificación de morfo-grupos foraminiferos, descritos por Berhnard (1986). C) Ejemplar de foraminífero del kimmerigdiano (Kurnubia palastiniensis), descrito por Omaña y González Arreola, (2008).
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 59 8. PIMIENTA FORMATION PROSPECTIVE REVIEW / COMPARATIVO DEL POTENCIAL DE LA FORMACIÓN PIMIENTA
A source rock analysis in the Pimienta formation studied in the central-western margin by Vega-Ortiz et al, (2020a) reports a range of TOC of 0.25 to 2.3 wt.%, being the structurally deeper areas with the higher organic content. The maximum Hydrogen Index is 179 mg
HC / g TOC, whereas the Oxygen Index is in a range 20-151 mg CO2 / g TOC. Since most of the samples are thermally mature it is not possible to determine the thermal maturity, presenting Tmax values from 425 to 451 º C. Other studies of Pimienta samples in the south of the TMB (Granados-Hernández et al., 2018; Morelos-García, 1996) reports a TOC range of 0.8 to 8 wt.%, and kerogen type II and III deducted from HI less than 600 mg HC / g TOC.
Based on the mineral composition, it is determined that the Pimienta formation is analogous to the Eagle Ford and Bakken formations from North America (Anderson, 2014; Bromhead et al., 2017). As of 2018, the reserves estimates in these tight oil plays are 4,734 and 5,862 MMBBL, respectively (EIA, 2020). Although, the geochemical properties of the Eagle Ford report TOC of 2 to 12 wt.%, with kerogen type II-III prone to produce oil and gas, with porosity 8-12%. According to Whitson and Sunjerga (2012), the fluids produced in the Eagle Ford and other plays in North America vary from condensate oil to gas condensates API 28-62º. The production in the Eagleford as of March 2020 is 1,230 BODP and 4,194 Mscf/d. The Bakken formation properties are average TOC of 11 wt.%, kerogen types I and II, with some Type III in the shallower flanks (Sonnenberg, 2011), producing 1,250 BOPD and 2000 Mscf/d in March 2020.
La evaluación de roca generadora en la formación Pimienta realizada en el AE por Vega- Ortiz et al, (2020a), reporta un valor de TOC en el rango de 0.25 a 2.3 wt.%, siendo las zonas estructuralmente más profundad las de mayor contenido orgánico, como se describió
• VOL. LXII No. 1 ENERO-JUNIO 2020 anteriormente. El Índice de Hidrogeno (HI) máximo es de 179 mg HC / g TOC, mientras que
el Índice de Oxigeno (OI) está en un rango de 20-151 mg CO2 / g TOC. Dado que la mayoría de las muestras son térmicamente maduras, no es posible definir un tipo de kerógeno, presentando valores Tmax de 425 a 451 º C. Otros estudios realizados en la formación Pimienta en el sur de la CTM (Granados-Hernández et al., 2018; Morelos-García, 1996) reportan TOC en un rango de 0.8 a 8 wt.%, y kerógeno tipo II y III, deducido de HI menor a 600 mg HC / g TOC.
Basado en la composición mineral, se determina que la formación Pimienta es análoga a las formaciones Eagle Ford y Bakken de Norte América (Anderson, 2014; Bromhead et al., 2017). Al ano de 2018, las reservas estimadas en estos plays de baja permeabilidad es de 4,734 y 5,862 MMBBL, respectivamente (EIA, 2020). Sin embargo, las propiedades geoquímicas de la formación Eagle Ford consideran TOC de 2 a 12 wt.%, con kerógeno tipo II-III potencial productor de aceite y gas, y porosidad en el rango de 8 a 12%. De acuerdo con Whitson y Sunjerga (2012), los fluidos producidos en la formación Eagle Ford son condensados de aceite y gas condensado de grado API 28-62º. Las propiedades de la formación Bakken son promedio TOC de 11 wt.%, con kerógeno tipo I y II, con presencia de tipo III en los flancos someros (Sonnenberg, 2011).
60 9. CONCLUSIONS / CONCLUSIONES
The analysis of SEM images demonstrates that the clay-rich carbonate mudstone of the Pimienta formation is comprised of a complex arrangement of sediments, crystalline structures, and textures. The distribution and geological structure layout of the Pimienta formation influences strongly on the mineral composition of the samples, identifying presence of 46 wt.% silicates and 49 wt.% carbonates in the shallow shoreline ramp in the north of the AOS, and a deeper marine basin in the south where carbonaceous mudstones dominate, with up to 96 wt.% carbonates.
The images provide enough resolution to determine that the grains are sorted uniformly over the area of interest, with isolated nucleation of organic matter (kerogen) that produces TOC of up to 2.3 wt. % in the deeper sector of the area of study. The most relevant observation is the very low porosity in the form of intergranular and intercrystalline porosity. In addition to low permeability (poor porous space interconnectivity), which reduced the intercrystalline pores are present to the order of 2-3 µm. The presence of embedded anhydrite crystalline structures is postulated to improve the permeability of the rock since the gap in between the crystals is larger than 20 µm, improving the porosity and permeability conditions of the rock.
En análisis de las imágenes de microscopia electrónica SEM demuestran que la formación Pimienta en el área analizada se clasifica como mudstone carbonáceo, compuesta de una compleja de sedimentos, estructuras cristalinas y texturas. La distribución y estructura geológica de la formación Pimienta influye en la composición mineral, encontrando 46 wt.% silicatos y 49 wt.% carbonatos en la zona superficial de rampa del litoral, y hasta 96 wt.% de carbonatos en la zona más profunda de cuenca marina.
Las imágenes proveen suficiente resolución para analizar la distribución uniforme y compacta de granos fino, con nucleaciones de material orgánico (kerógeno), que producen TOC de hasta 2.5 wt.% en el sector SE del área estudiada. Una de las observaciones más relevante son las dimensiones de la porosidad intergranular e intercristalina en el orden de 2 a 20 µm, resultando en una porosidad extremadamente reducida. Se estipula que la presencia de estructuras cristalinas en la matriz del mudstone, como la anhidrita que incrementan la permeabilidad y porosidad efectiva en la roca debido a la porosidad intercristalina medida en 20 µm.
The crack-seal veins, although closed -infilled with precipitated calcite, provide the conditions for microfractures to occur in between the boundaries of the different materials due to the weak bonding and effect of tectonic events and geo-stresses.
Las fracturas cementadas con calcita y pirita, a pesar de sellar los conductos originados por la fractura, proveen posibles canales de flujo a través de las microfracturas observadas en la interfase entre los diferentes minerales debido al enlace deficiente y los esfuerzos compresivos que deforman las rocas.
The information from the Pimienta and analogous formations concludes that despite the Pimienta formation is not as optimum as their counterparts in North America, it might
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 61 be possible to find structural spots where the geochemical and petrophysical properties feature potential commercial unconventional reservoirs, upon assessment on producible reserves.
La información recopilada de las formaciones Pimienta concluye que si bien la formación Pimienta en el bloque analizado no tiene propiedades optimas como sus análogos en Norteamérica, es posible encontrar zonas estructurales en donde las propiedades geoquímicas y petrofísicas puedan conformar un yacimiento no convencional con potencial comercial, una vez que se realice la evaluación de posibles reservas.
10. ACKNOWLEDGMENTS / AGRADECIMIENTOS
The geological samples for this study were obtained from México’s National Core Repository (Litoteca Nacional), under the authorization from the National Hydrocarbon Commission (CNH) and Secretary of Energy (SENER). Carlos Vega-Ortiz is a holder of the National Hydrocarbon Scholarship, by CONACYT and SENER. Authors are thankful to the University of Utah and the Energy and Geoscience Institute for the facilities provided for this study.
Las muestras geológicas utilizadas en este estudio fueron aprobadas por la Litoteca Nacional de la Comisión Nacional de Hidrocarburos de Mexico. El autor Carlos Vega-Ortiz realiza tesis doctoral con fondos de la Beca Nacional de Hidrocarburos de la Secretaria de Energía y de CONACYT. Los autores agradecen al Energy and Geoscience Institute de la Universidad de Utah por las facilidades otorgadas para este estudio. • VOL. LXII No. 1 ENERO-JUNIO 2020
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64 APPENDIX A. XRD DIFFRACTOGRAMS
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 65 Fig A1. Pimienta sample from well GG, depth 2453 m. Composition: Carbonates: Calcite 70%. Clastics: Quartz 19%, Plagioclase 2%, Pyrite Trace. Shales: Illite 6%, Barite 1% and Anhydrite 1%. • VOL. LXII No. 1 ENERO-JUNIO 2020
Fig A2. Pimienta sample from well BB, depth 1838 m. Composition: Carbonates: Calcite 51%, Dolomite 4%. Clastics: Quartz 41%, K-Feldspar 1%, Pyrite Trace. Shales: Illite 3%
66 Fig A3. Pimienta sample from well BB, depth 1877 m. Composition: Carbonates: Calcite 95%, Dolomite 3%. Clastics: Quartz 2%. Shales: None
Fig A4. Pimienta sample from well GG, depth 2453 m. Composition: Carbonates: Calcite 51%, Dolomite 2%. Clastics: Quartz 34%, Plagioclase 5%, Pyrite Trace. Shales: Illite 7%, Barite 1%
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 67 Fig A5. Pimienta sample from well DD, depth 1570 m. Composition: Carbonates: Calcite 34%, Dolomite 1%. Clastics: Quartz 23%, K-Feldspar 15%, Pyrite 1%. Shales: Illite 23%, Anhydrite 4%, • VOL. LXII No. 1 ENERO-JUNIO 2020
Fig A6. Pimienta sample from well DD, depth 1568 m. Composition: Carbonates: Calcite 50%, Dolomite Traces. Clastics: Quartz 36%, K-Feldspar 6%, Pyrite Traces. Shales: Illite 5%, Anhydrite 2%,
68 Fig A7. Pimienta sample from well AA, depth 3038 m. Composition: Carbonates: Calcite 66%, Clastics: Quartz 17%, Plagioclase 1%, Pyrite 2%. Shales: Illite 10%, Kaolinite 2%, Anhydrite 2%.
Fig A8. Pimienta sample from well EE, depth 1859.6 m. Composition: Carbonates: Calcite 84%, Mg Calcite 1%, Dolomite 1%. Clastics: K-Feldspar 6%, Pyrite Traces. Shales: Illite 8%.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 69 Fig A9. Pimienta sample from well II, depth 2605.7 m. Composition: Carbonates: Calcite 96%, Dolomite 2%. Clastics: Quartz 2%, Shales: None • VOL. LXII No. 1 ENERO-JUNIO 2020
Fig A10. Pimienta sample from well II, depth 2603.9 m. Composition: Carbonates: Calcite 95%, Dolomite 2%. Clastics: Quartz 3%, Shales: None
70 Fig A11. Pimienta sample from well GG, depth 2396 m. Composition: Carbonates: Calcite 89%, Dolomite 1%, Clastics: Quartz 5%, Plagioclase Traces, Pyrite traces. Shales: Illite 4%.
Fig A12. Pimienta sample from well HH, depth 2155 m. Composition: Carbonates: Calcite 65%, Dolomite Traces, Clastics: Quartz 21%, Plagioclase 1%. Shales: Illite 13%.
BOLETÍN DE LA ASOCIACIÓN MEXICANA DE GEÓLOGOS PETROLEROS 71 Responsabilidad: Los escritos publicados, declaraciones y opiniones expresadas en este Boletín son completa y en su totalidad responsabilidad de los autores y no debe interpretarse como una opinión oficial de la AMGP. Fecha de Publicación: Agosto 2020. Tiraje 1,000 ejemplares. INSTRUCCIONES A LOS AUTORES (continuación)
Todos los trabajos deberán enviarse a la Comisión de Estudios Técnicos en formato digital compatible con Word para Windows. El orden que se recomienda es el siguiente: Título, nombre de (los) autor(es), lugar de trabajo indicado con un asterisco (*) al final de nombre y por un pie de figura al final de la página, resumen en español, resumen en inglés, texto, referencias, tablas y figuras. Todas las páginas deberán estar numeradas en la esquina superior derecha. NO OLVIDAR; Email, celular o teléfono del autor principal.
Idioma: Los idiomas aceptados para publicarse en el Boletín son: español e inglés. Título: El título debe ser claro, no muy extenso y deberá reflejar concisamente el contenido del trabajo en cuestión. Nombre del autor o autores: El nombre del autor o autores debe ser completo, sin abreviaciones.
Resumen: Tanto el resumen en español como en inglés no deben exceder de 300 palabras cada uno. Deberán contener el propósito y conclusiones significativas de la investigación. No deben incluirse en él citas bibliográficas.
Texto: El texto debe estar escrito claramente. De ser posible, deben evitarse al máximo los anglicismos, en caso necesario, éstos deben escribirse con letra cursiva o entre comillas. Las citas bibliográficas dentro del texto deberán citarse de acuerdo al caso en cuestión: p.ej.: 1) Al inicio de una oración: Gómez (1984) propone un modelo…; 2) Dentro de la oración: …por lo que Gómez (1982) propone un modelo…; 3) Al final de la oración: …lo que concuerda con el modelo propuesto por otros autores (Gómez, 1984; Sánchez, 1989). Las figuras y tablas señaladas en el texto deben mencionarse en estricto orden cronológico para que puedan ser intercaladas adecuadamente.
Figuras y Tablas: Deberán ser perfectamente visibles y de buena calidad al imprimirse en hoja tamaño carta, dejando un margen de 2.5 cm, tanto en la parte inferior como superior de la hoja, y de 2 cm en los extremos derecho e izquierdo de la misma. Todo gráfico o fotografía será considerado como figura.
Referencias: Deben incluirse únicamente todas y cada una de las citas mencionadas en el texto. Las referencias deberán mencionarse en estricto orden alfabético.
Pies de figura y encabezados de tablas: Deberán ser claros, concisos, explicar el significado de todo lo representado en ella y contener, en su caso, una escala gráfica. Utilizar color únicamente cuando el caso lo amerite. Las figuras y tablas previamente publicadas deberán contener la cita de la fuente original.
Ilustración de contraportada:
Logotipo AMGP. BOLETÍN DE LA ASOCIACIÓN MEXICANA GEÓLOGOS PETROLEROS, A.C. VOLUMEN LXII, NÚMERO 1, ENERO-JUNIO 2020.
Directiva Nacional Bieno 2018 - 2020