Scielo RSS <![CDATA[Latin American journal of sedimentology and basin analysis]]> http://www.scielo.org.ar/rss.php?pid=1851-497920130001&lang=es vol. 20 num. 1 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <link>http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792013000100001&lng=es&nrm=iso&tlng=es</link> <description/> </item> <item> <title><![CDATA[Paleosuelos y niveles límnicos desarrollados en sucesiones aluviales del Pleistoceno tardío y Holoceno del Piedemonte Andino de Mendoza (33°-34° ls), Argentina]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792013000100002&lng=es&nrm=iso&tlng=es Los depósitos aluviales del Pleistoceno tardío y Holoceno de la cuenca del Arroyo La Estacada, en el piedemonte andino mendocino, entre los 33° y 34° LS, componen tres unidades geomorfológicas conspicuas: una planicie de agradación regional (PAR, Pleistoceno tardío - Holoceno temprano), una terraza de relleno aluvial (TRA, Holoceno medio y tardío) y la planicie de inundación actual (posterior a los 400 a AP). La PAR y la TRA registran procesos alternantes de agradación y pedogénesis, siendo estos últimos más frecuentes en los depósitos holocenos, caracterizados también por una mayor abundancia de niveles con contenido orgánico elevado (niveles límnicos). Este trabajo evalúa el registro de paleosuelos y niveles límnicos de la cuenca, con el objetivo de inferir sus implicancias en la dinámica paleoambiental y paleoclimática de la región centrooeste de Argentina durante el Pleistoceno tardío y Holoceno, y aportar información al marco paleoclimático del extremo sur de Sudamérica. Se muestrearon depósitos aluviales que exhiben paleosuelos y niveles límnicos en cuatro perfiles litoestratigráficos en las márgenes del Arroyo La Estacada y su tributario el Arroyo Anchayuyo; se utilizó el color como indicador de campo. Se describieron atributos en forma cualitativa (granulometría, color; consistencia, tipo y grado de estructuración de los sedimentos; forma y tipo de límites, sustancias cementantes y/o aglutinantes, rasgos redoximórficos, etc) y cuantitativa (contenido de materia orgánica y carbonato de calcio); se realizaron análisis micromorfológicos en muestras de sedimentos no disturbadas. Los resultados se presentan con un criterio cronológico decreciente basado en la calibración cronológica de los depósitos aluviales. Los paleosuelos de la PAR revelan un pobre desarrollo pedológico, con presencia de carbonato de calcio en la masa, y en forma de nódulos y concreciones. Por su parte, los paleosuelos de la TRA presentan mayor desarrollo relativo, y ausencia de carbonatos en general. Los niveles límnicos reflejan un incremento en la productividad vegetal en ambientes de la planicie de inundación saturados en agua; y quizás también un mayor transporte de MO por parte de las corrientes de agua en el valle fluvial. La mayor concentración de rasgos de carbonatación de la PAR reflejaría condiciones de mayor evaporación en los ambientes depositacionales del Pleistoceno tardío - Holoceno temprano; mientras que la abundancia de rasgos redoximórficos en los niveles de la TRA, registraría la saturación en agua de los depósitos del Holoceno medio y tardío, quizás en respuesta a frecuentes fluctuaciones del nivel freático. Las sucesiones aluviales analizadas registran los cambios paleoambientales / paleoclimáticos acaecidos en el piedemonte andino oriental entre los 33° y 34° LS, en vinculación con la transición climática del Pleistoceno tardío - Holoceno. Los paleosuelos y niveles límnicos observados resultaron herramientas útiles para la calibración geocronológica de las sucesiones aluviales estudiadas.<hr/>The late Pleistocene and Holocene alluvial deposits of the Arroyo La Estacada basin, located in the Andean piedmont of Mendoza province between 33° and 34° SL (Fig. 1a-b), are arranged in three conspicuous geomorphological units, a regional aggradational plain (RAP, late Pleistocene - early Holocene), a fill terrace (FT, middle and late Holocene) and a present floodplain (developed ca. 400 yr BP) (A-A', B-B', Fig. 1c). The RAP (Figs. 2a, 3a) and the FT (Figs. 2b, 3b) record aggradational and pedological proccesses; the latter are more frequents in the Holocene deposits together with abundant sedimentary levels showing high organic matter content (limnic levels). High organic matter content deposits have been studied by the international scientific community, particularly in North America, where some authors discussed the paleoenvironmental and paleoclimatic implicances of the 'black mats' (Haynes, 1968; 2008; Firestone et al., 2007, among others). Toledo (2008) reinforced the idea of a global climatic change by correlating the 'black mat' deposits developed in the widely described fluvial sequences of the Central Pampean region of Argentina with those studied in North America. In such a context, this work evaluates the paleosoil-limnic level record of the Arroyo La Estacada basin, in the eastern Andean piedmont, with the aim of infering their implicantions in the paleoenvironmental and paleoclimatic dynamics of the central-west Argentinean region during the late Pleistocene and the Holocene. Besides, it provides information to the paleoclimatic framework of southern South America. Alluvial deposits exhibiting paleosoils and limnic levels were sampled using color as a field indicator (Wills et al., 2007, and references therein), in four lithostratigraphic sections located in the banks of Arroyo La Estacada and its tributary the Arroyo Anchayuyo. Qualitative (grain size, color, consistency, type and grade of pedal structure, limit forms and types, cements, redoximorphic features, etc.) and quantitative (organic matter and calcium carbonate contents, table1) attributes were described; also micromorphological analyses were conducted on undisturbed samples (Fig. 4). Results are presented according to a chronological criterion, from the oldest to the youngest paleosoils and limnic levels, based on a chronological calibration of pedosedimentary sequences already reported (Zárate, 2002; Zárate and Páez, 2002; Toms etal., 2004; Zárate and Mehl, 2008) and two new radiocarbon ages (Table 1). The analyzed late Pleistocene and Holocene alluvial deposits record the development of four main pedological processes, affecting not only paleosoils but also limnic levels. They are, organic matter decomposition, calcium carbonate accumulation, redoximorphic features formation and bioturbation. Paleosoils are conspicuous and widely extended along the arroyos basin. They can be recognized in the alluvial deposits as dark bands showing lighter colors downward. Paleosoil top limits are dominantly clear and smooth, the bases are mostly diffuse to smooth and wavy to irregular (Fig. 3a,b). RAP paleosoils are poorly developed showing dearth of pedological features and exiguous horizonation. Calcium carbonate appears in the soil mass and also forming nodules and concretions. FT paleosoils exhibit a greater relative development when comparing with the RAP paleosoils and calcium carbonate is in general absent. Limnic levels are also dark levels, but they present a homogeneous appearance without gradual color variation downwards (Figs. 4a, 5a, h). Its lateral extension is restricted when compared with the one exhibited by paleosoils. Nonetheless some of them can be recognized by several metres throughout the outcrops. The morphology of limnic levels is characterized by the occurrence of lenses formed by organic matter immersed in a fine-grained clastic matrix (Fig. 5h). Its configuration is similar to that described for gyttias o sedimentary peats (Uggla etal., 1969 in Fox, 1985). Limnic levels form due to the precipitation of organic matter suspended in water or by direct action of aquatic organisms (Fox, 1985). The Holocene limnic levels are fair indicators of a vegetation productivity increment in the floodplain, especially in waterlogged environments (Fig. 6a,b). Also, they likely record an increase in the amount of organic matter carried by water along the fluvial valley. The major concentration of carbonates in the RAP paleosoils would likely indicate more evaporation in the alluvial basin at the RAP formation time. In turn, the abundance of redoximorphic features in the FT would record waterlogged episodes occurring during the middle and late Holocene, probably in response to frequent water table fluctuations. Analyzed alluvial sequences of the late Pleistocene and Holocene record paleoenvironmental and paleoclimatic changes in the eastern Andean piedmont between 33° and 34° SL, in relation to late Pleistocene - Holocene climatic transition. Paleosoils and limnic levels have resulted in useful tools to calibrate the alluvial sequences and to analyse them geochronologically. <![CDATA[Ciclos mixtos carbonáticos/silicoclásticos en el miembro superior de la formación mulichinco (Yacimiento Cañadón Amarillo, Cuenca Neuquina Central, Argentina): Implicancias secuenciales y para caracterización de reservorios]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792013000100003&lng=es&nrm=iso&tlng=es Con el objetivo de dilucidar relaciones temporo-espaciales y controles entre intervalos carbonáticos y silicoclásticos dentro de sucesiones cíclicas marinas, en este trabajo se presenta un estudio facial, paleoambiental y secuencial de alta resolución del Miembro Superior de la Formación Mulichinco en el subsuelo del extremo austral de la Provincia de Mendoza (yacimiento Cañadón Amarillo). La unidad posee entre 65 y 80 m de potencia en la región y se caracteriza por una recurrente alternancia de escala métrica de intervalos silicoclásticos y otros con dominancia de componentes carbonáticos. El estudio se basa en el análisis sedimentológico de detalle de cuatro testigos de corona que abarcan la totalidad del intervalo estudiado y en total representan 240 m de espesor. En el Miembro Superior de la Formación Mulichinco se identificaron e interpretaron cinco asociaciones de facies, tres dominadas por depósitos silicoclásticos y dos con dominio de componentes carbonáticos. Las asociaciones silicoclásticas se depositaron en un sistema marino dominado por procesos de olas de buen tiempo y tormenta y representan un espectro continuo de condiciones de sedimentación desde ambientes someros de shoreface inferior, pasando por un ambiente intermedio o zona de transición, hasta regiones ubicadas por debajo de la base de olas de tormenta u offshore. Por su parte las asociaciones de facies mixtas y calizas puras representan el desarrollo de un sistema de rampa con alta producción de materiales carbonáticos, en donde se reconocen condiciones de alta energía o rampa somera (grainstones y packstones oolíticoesqueletales), y condiciones más distales de rampa media, con generación de depósitos con alta participación de fango micrítico (wackestones, packstones y floatstones esqueletales). El análisis de diseños estratales, superficies clave y distribución espacial de las asociaciones de facies indica que estos dos sistemas de acumulación no co-existieron, sino que se reemplazaron cíclicamente debido a variaciones de alta frecuencia del nivel relativo del mar. De esta manera los ciclos de pequeña escala (3 a 18 m de espesor) reconocidos en el Miembro Superior de la Formación Mulichinco se interpretan como secuencias de alta frecuencia limitadas por superficies transgresivas de erosión y están típicamente compuestas por hemiciclos transgresivos relativamente delgados y dominados por componentes carbonáticos, seguidos por hemiciclos silicoclásticos más potentes, los cuales representan fenómenos de progradación de una línea de costa. La superficie no erosiva que los limita representa una superficie de máxima inundación. Los resultados de este trabajo contribuyen a avanzar en la caracterización de los niveles productivos alojados en esta sucesión cíclica. Se definieron tipos de facies con buenas perspectivas de constituir reservorio y sus características principales (geometría, espesor, conectividad, heterogeneidades internas), y fue posible elaborar un modelo con carácter predictivo dentro del yacimiento, que explica desde un punto de vista genético, cuál sería la posición más probable de dichas facies dentro de una secuencia de alta frecuencia. La incorporación de estos elementos a un modelado geológico estático puede finalmente contribuir a un mejor y más eficiente desarrollo del campo y sus niveles reservorio.<hr/>The presence of carbonate strata within siliciclastic- dominated marine successions (i.e. mixed carbonate-siliciclastic successions) poses serious challenges for palaeoenvironmental reconstructions and reservoir characterization, and unambiguous interpretations can emerge only when the spatial vs. temporal relationship between carbonate production and siliciclastic input is well understood. This study integrates sedimentology and high-resolution sequence stratigraphy in order to better understand the temporal/spatial relationships and controls in the origin of a Lower Cretaceous, mixed carbonatesiliciclastic succession in the subsurface of the Neuquén Basin, west-central Argentina (Figs. 1, 2). This mixed succession, so-called Upper Member of the Mulichinco Formation, accumulated in a shallow, epeiric sea during third-order highstand conditions (Fig. 3), and is presently widely distributed in the central part of the basin, both in outcrops and subsurface (Schwarz et al., 2009; Schwarz et al., 2011). The study area, covering an area of about 80 km², is located in the Cañadón Amarillo hydrocarbon field (Fig. 4), where this unit has been in production since the 1970's. This study is based on a detailed description and interpretation of four cored wells (three of them covering the entire unit), complemented with calibrated well-log suites from additional 22 wells (Fig. 5). The Upper Member of the Mulichinco Formation (65-80 m thick) has a cyclic alternation of relatively thick (up to 16 m) siliciclastic packages and thinner carbonate-dominated intervals (Fig. 6). Three facies associations were identified within the siliciclastic packages, and they are inferred to represent shoreface, offshore-transition, and offshore settings in an open marine system influenced by storm- and fair-weather waves. The lower-shoreface facies association (Fig. 7) is composed of amalgamated, siliciclastic sandstone beds (with minor contribution of carbonate particles) mostly having hummocky cross-stratification, horizontal lamination or ripple cross-lamination. Bioturbation varies from low to high and the trace fossil suite (Arenicolites, Gyrochortes, Palaeophycus, Ophiomorpha, Skolithos y ?Macaronichnus) is interpreted to represent an Skolithos ichnofacies (MacEachern et al., 2007). The offshore-transition facies association groups intensely bioturbated muddy sandstones and less bioturbated (i.e. better preserved) sandstone-rich heterolithics (Fig. 8), with occasional medium-bedded sandstone beds (< 15 cm thick) having HCS and rippled tops. Siliciclastics largely dominate within these sediments, but bioclasts (mostly from oysters) can be common locally. The assemblage of trace fossils (Planolites, Palaeophycus, Thalassinoides, Teichichnus, Phycosiphon, Ophiomorpha, Schaubcylindrichnus y Asterosoma) is attributed to represent a Proximal Cruziana ichnofacies (MacEachern and Bann, 2008), and, together with the sediments, reflect a stormdominated offshore-shoreface transition, between the storm and fair-weather wave bases (Reading & Collinson, 1996). In turn, the offshore facies association comprises mostly massive or laminated mudstones, as well as mudstone-dominated heterolithics. In the latter, very thin-bedded siltstone beds with wavy tops are abundant, likely reflecting the distal ends of storm-related flows. Carbonate-dominated intervals are composed of two facies associations that collectively are inferred to represent subenvironments within a carbonate ramp, namely shallow (inner) and middle sectors of it. The shallow-ramp facies association is characterized by cross-bedded ooid-skeletal grainstones/packstones, with subordinated skeletal rudstones and packstones (Fig. 10). Bioclasts derived mostly from mollusks and echinoids, whereas terrigenous material is less than 25%. These sediments deposited in open-marine high-energy settings, likely shoals and intershoals areas (Rankey y Reeder, 2011; Christ et al., 2012). In contrast, the middle-ramp facies association is composed of muddominated textures, mostly skeletal wackestones and floatstones (Fig. 11). They are massive, but argillaceous seams might create a nodular aspect. Bioclasts from epibenthic (oysters) and endobenthic bivalves, as well as from serpulids and echinoids are dominant, but glauconite and intraclasts are locally abundant. Compared to the previous association, these sediments were deposited in lower energy and deeper parts of the ramp. The nature of key stratigraphic surfaces, facies associations distribution and analysis of stacking patterns within this cyclic carbonate/siliciclastic succession suggest that the siliciclastic- and carbonate-dominated depositional systems were not coeval, but replaced over time. Correlation panels show that individual carbonate and siliciclastic hemicycles extend across the entire area and lateral transition between them were not recorded (Figs. 12, 13). Carbonate packages are invariably bounded by sharp, erosive surfaces (Fig. 14a,b), which are interpreted to represent transgressive ravinement surfaces (Swift, 1968; Nummedal and Swift, 1987). Facies associations in these hemicycles suggest a deepening-upward trend, whereas in the overlying siliciclastic packages the stratal patterns indicate normal (i.e. not forced) regressive conditions (Fig. 15). Therefore, the seven small-scale cycles (plus two incomplete cycles) recorded in the Upper Member of the Mulichinco Formation (3-18 m thick) are interpreted to represent high-frequency sequences (nomenclature following Zecchin and Catuneanu, 2013), comprising relatively thin, transgressive, carbonate-rich hemicycles and thicker, siliciclastic regressive hemicycles (Fig 16). The non-erosive boundary between both hemicycles (Fig. 14c) could correlate with the maximum flooding surface (Van Wagoner et al., 1990), or being slightly younger, as it reflects enough terrigenous supply to dilute carbonate productivity (Abbot, 1997). In this context, it is considered equivalent of a downlap surface (Fig 16). These high-frequency sequences were most likely controlled by short-term, low-amplitude, relative sea-level changes, and the thickness of transgressive hemicycles could have been influenced by carbonate productivity and/or rate of transgression. The results of this study provide with a more accurate reservoir characterization of this mixed (and complex) succession. Two reservoir-type facies associations were identified, namely the lowershoreface and shallow-ramp facies associations. The understanding of key reservoir attributes, such as geometry, thickness, connectivity and internal heterogeneity were improved with this study. Additionally, the findings of this work provided with a high-resolution sequence-stratigraphic model that help predicting the occurrence of the reservoirtype facies within a high-frequency sequence. The integration of all these elements within a geological model could contribute to define for example the most efficient development strategy for the reservoir horizons (e.g. vertical versus horizontal wells) which would, eventually, impact in the recovery factor of the field. <![CDATA[Relaciones Estratigráficas de las Formaciones Quebrada de los Colorados y Cngastaco (Paleógeno-Neógeno), Valles Calchaquíes, Salta (Argentina): significado en el análisis de la cuenca del Grupo Payogastilla]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792013000100004&lng=es&nrm=iso&tlng=es El Grupo Payogastilla representa el registro sedimentario de la cuenca de antepaís andina en los Valles Calchaquíes. La Formación Quebrada de los Colorados, unidad basal, es de singular importancia debido a que preserva evidencias de los primeros episodios de contracción con deformación intracuencal, cambios en las áreas de aporte y asociaciones de fósiles que la datan paleógena pre-oligocena, hecho que llevó a replantear el modelo de cuenca de antepaís propuesto para el Noroeste argentino. Asimismo, la suprayacente Formación Angastaco, además de contener similar registro tectono-sedimentario, documenta el inicio del magmatismo en el borde oriental de la Puna. Los recientes trabajos de investigación llevados a cabo en estas unidades han permitido identificar y mapear superficies de discontinuidad sedimentaria, incluso de discordancias que obligan a modificar el cuadro estratigráfico existente. En la presente contribución se describen las relaciones estratigráficas de la Formación Quebrada de los Colorados con el objetivo de actualizar el conocimiento sobre la misma y discutir el esquema estratigráfico actualmente vigente. Esta formación se asienta en relación de discordancia y de disconformidad sobre las Formaciones Lumbrera, Maíz Gordo y Mealla (Subgrupo Santa Bárbara) y sobre el Subgrupo Pirgua, del Grupo Salta. Asimismo, se describe y discute el alcance de la identificación de una discontinuidad sedimentaria intra-Quebrada de los Colorados, señalada por el cambio abrupto de facies sedimentarias y la presencia de una superficie de meteorización con desarrollo de una calcreta. Esta superficie separa una sucesión netamente fluvial de otra fluvio-eólica con características sedimentarias distintivas. Por último, se describen las relaciones de transición y de concordancia entre la sucesión fluvio-eólica con la suprayacente Formación Angastaco. En base a estas relaciones se propone redefinir la Formación Angastaco con la incorporación de la sucesión fluvio-eólica con el rango de Miembro Tin Tin y retomar la definición original del Miembro Las Flechas. Finalmente y en base la nueva información disponible se propone a la quebrada Grande (área de cerro Tin Tin) como hipoestratotipo para la Formación Quebrada de los Colorados, localidad que servirá como complemento de las descripciones originales.<hr/>The sedimentary record of the Andean orogenic basins in the Calchaquies Valleys (Fig. 1), consists of nearly 6000 m of an overall coarsening and thickening upward clastic succession (Díaz and Malizzia, 1983) known as the Payogastilla Group. The Payogatilla Group is composed of the Quebrada de los Colorados, Angastaco, Palo Pintado and San Felipe Formations (Díaz and Malizzia, 1983; Díaz et al., 1987 - see Fig. 2). Our investigation and previous research in the Quebrada de los Colorados Formation (e.g. Galli and Hernández, 1999; Coutand et al., 2006; Carrapa et al., 2011a,b; Galli et al., 2011) allowed the identification of several unconformity surfaces, including an angular relationship between the Quebrada de los Colorados Formation and the underlying Salta Group. Moreover, the identification of an intra-formational unconformity led us to the reconsideration of the stratigraphic scheme of the Payogastilla Group. Here, we address the regional stratigraphic relations of the Quebrada de los Colorados Formation, the lower unit of the Payogastilla Group, in order to update the knowledge and to discuss the validity of the present stratigraphic framework. Along the Calchaquies Valleys, the Quebrada de los Colorados Formation rests on different units of the Salta Group. The more frequent relation is with the uppermost unit, the Lumbrera Formation (Fig. 3), but in some areas, for example at Saladillo, the Quebrada de los Colorados Formation rests in angular relationship on the Maíz Gordo Formation (del Papa et al., 2004), as in the Esquina Azul locality (Fig. 4). In the cerro Bayo site, the Quebrada de los Colorados Formation lies also upon the Maíz Gordo Formation but few meters laterally directly overlays the Mealla Formation (Figs. 2 and 4). In other places, like in the Pucará valley (Fig. 1), the Quebrada de los Colorados overlays the Pirgua Subgroup (Villanueva García, 1992; Sabino, 2004). These variable stratigraphic relationships are key features that document the tectonic inversion of the Salta Group contemporaneous with the Quebrada de los Colorados sedimentation. The Quebrada de los Colorados Formation consists of red fine-grained floodplain facies and sandy to gravelly clastic fluvial channels facies (Fig. 6). The original description of this unit includes an eolian succession in the upper section (Díaz and Malizzia, 1983). In some localities, like at Tin Tin and Tonco (Fig. 1), the eolian and fluvio-eolian successions have thicknesses ranging from 450 to 600 m (Starck and Vergani, 1996; del Papa et al., 2013) representing a very distinctive erg record. The contact with the underlying fluvial deposits is sharp and a calcrete paleosol (Fig. 5) is locally recognized suggesting the presence of an unconformity within the Quebrada de los Colorados Formation. Moreover, this fluvio-eolian succession has a transitional contact with the overlying fluvial conglomeratic facies of the Angastaco Formation. This stratigraphic relation suggests that the former could be formally included within the Angastaco Formation. Thus we propose a redefinition of the Angastaco Formation (Díaz and Malizzia, 1983; nom. transl. Díaz et al., 1987); including the fluvio-eolian succession as the basal Tin Tin Member and to return to the previously defined Las Flechas Member. We propose the Tin Tin area (25º13'51.6'' Lat. S and 66º00'58.5'' Log. W - 25°16'12'' Lat. S and 66°2'39.45'' Log. W) as stratotype area (Fig. 7). In this locality, pale red silty sandstones to siltstones overlie coarse conglomeratic strata (Figs. 5 and 6) and are overlain by white eolian sandstones that grade to gray conglomeratic strata of the Angastaco Formation sensu Díaz and Malizzia (1983). The age of the Tin Tin Member is considered late Oligocene to early Miocene according to the 21 Ma U/Pb zircon datings (Carrapa et al., 2011a; del Papa et al., 2013). Finally we propose the Quebrada Grande locality (25º12'59.1'' Lat. S and 66º01'33.1'' Log. W), along state route Nº 42, Tin Tin area, Calchaquí Valley (Fig. 7) as hypostratotype of the Quebrada de los Colorados Formation. In this locality, this unit rests unconformably, and locally through an angular unconformity, on the Lumbrera Formation (Salta Group, Figs. 2, 3 and 4). In this area the formation is 792 m thick and is characterized by two coarsening upward successions of red siltstone, lenticular to shallow lenticular coarse sandstones and horizontally stratified conglomerates (Fig. 5). Based on mammalian biostratigraphy recorded at sites in Cerro Bayo, Tin Tin and Luracatao (Fig. 1) the age of the Quebrada de los Colorados Formation is Casamayoran (sub-age Barrancan), SALMA, suggesting a Middle Eocene age for the basal levels (Powell et al., 2011). In summary, we propose that the fluvio-eolian section of the Quebrada de los Colorados Formation should be incorporated into the Angastaco Formation, as the Tin Tin Member. This modification will simplify recognition in the field, mapping, and genetic interpretation of these foreland basin deposits.