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Abstract

Taphonomic analysis was performed on palynological samples of marine successions from the Cuyo Group of the Neuquén Basin. The group comprises the Los Molles and Lajas Formations (Middle Jurassic) and represents the first major marine depositional episode after the configuration of the basin. A total of 21 outcrop samples from five sections, located in the central-western part of the basin, were analyzed. The palynological counts of each sample were carried out taking into account the preservation state of the palynomorphs, which was mainly influenced by two parameters: their intrinsic properties and the environmental depositional conditions. Four main deterioration types (corrosion, degradation, mechanical damage, and concealment by authigenic minerals) and their six combinations were identified. The growth of pyrite crystals within the palynomorphs was strongly influenced by the exine structure, being dominant in bisaccate pollen grains. Mechanical damage appears to be the most important deterioration type, reflecting the highly dynamic conditions of shelfal marine environments. The term Palynotaphofacies (Pt) was proposed to characterize a sedimentary rock yielding palynological associations with distinctive preservational features. Three palynotaphofacies have been recognized: Pt-1 (tidal-influenced environments) is characterized by the highest percentage of deteriorated forms, reflecting either intermittent exposure to weathering or intense reworking. Pt-2 shows the highest percentage of well-preserved palynomorphs associated with rapid burial due to a high sedimentation rate and it comes from the delta-front facies of fluvial-dominated deltas. Finally, Pt-3 was identified in samples of prodelta hyperpycnites with a wide predominance of terrigenous components and it is characterized by the coexistence of well-preserved and deteriorated palynomorphs.

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... En un trabajo posterior, Martínez et al. (2016) analizan nuevamente las muestras antes mencionadas junto con muestras obtenidas de la Formación Lajas, en esta ocasión desde un punto de vista tafonómico. Reconocen un total de 3 palinotafofacies de acuerdo a las propiedades de los palinomorfos y al tipo de ambiente depositacional involucrado. ...
... En general, el daño mecánico es el tipo de deterioro principal en todos los grupos, reconociéndose como roturas (Fig. 17a-c) y/o plegamientos (Fig. 17d y e). Este daño mecánico se genera en respuesta a un intenso transporte (sin-depositasional) o rotura por compactación de la columna durante las primeras etapas de diagénesis (post-depositasional) (Martínez et al., 2016). Sin embargo, Campbell (1991) y Campbell y Campbell (1994) sugieren que el daño mecánico generado por ciclos húmedo-seco repetitivos sería más importante que el que ocurre por colisión con partículas sedimentarias durante el transporte. ...
... La degradación es el segundo tipo de deterioro más importante, se identifica tanto en granos de polen como en esporas por un adelgazamiento y/o pérdida de rasgos estructurales de las capas de la exina (Fig. 17f), producto de la oxidación química durante la exposición subaérea de los palinomorfos (Martínez et al., 2016). Ejemplos de corrosión han sido observado en esporas, dada por cavidades en la exina generadas por ataque de hongos y/o bacterias (Fig. 17g). ...
Thesis
Se realizó un estudio multidisciplinario de detalle sobre el tramo basal de la Sección “Don Silverio” perteneciente a la Formación Los Molles, en la Subcuenca de Picún Leufú, Neuquén. El objetivo del presente trabajo es contribuir al conocimiento integral de la Formación Los Molles (Jurásico Temprano-Medio) al sur de la Dorsal de Huincul y evaluar el potencial oleogenético de la sección estudiada. A partir del estudio sedimentológico/estratigráfico, se reconocieron hiperpicnitas fangosas y arenosas depositadas en un Delta Hiperpícnico Subacuático. Este delta se habría desarrollado en porciones distales de la plataforma, por debajo de la acción de oleaje, durante períodos de mayor eficiencia del sistema deltaico. En cuanto al análisis de la materia orgánica palinológica, se reconoció una predominancia absoluta de materia orgánica de origen continental. Un total de 4 palinofacies tipo fueron definidas, las cuales reflejan las diferentes condiciones de depositación y energía presentes en los diferentes flujos hiperpícnicos. En base a la variedad de taxones continentales reconocidos (Cheirolepidiaceae, Araucariaceae, Botryococcaceae, entre otros) y las diferencias de requerimientos paleoecológicos que tienen cada uno de ellos, se evidencia el largo camino y los distintos ambientes que atravesaron los flujos hiperpícnicos hasta alcanzar la cuenca receptora. A partir del análisis geoquímico de las muestras, se reconoce que los valores de carbono orgánico total son mayores al 1% en casi todos los casos, lo que permitiría asociar a estas rocas con buena a muy buena capacidad de generación de hidrocarburos. Sin embargo, los bajos valores obtenidos de S2 no confirman dicha asignación, por lo que finalmente se las clasifica como rocas con pobre potencial. El querógeno presente es de tipo III/IV y IV, constituido por materia orgánica esencialmente rica en carbohidratos de plantas vasculares. La interpretación del potencial oleogenético que se obtiene a partir del análisis palinológico presenta una correlación con los resultados obtenidos a partir del estudio geoquímico, por lo que la sección de estudio no cumple con las condiciones para ser considerada un buen reservorio no convencional de tipo shale gas.
... The Middle and Upper Jurassic of the Neuqu en Basin was studied by Volkheimer et al. (2015) andMart ınez et al. (2016). Volkheimer et al. (2015) is a review of the Middle and Late Juras- sic phytogeography of the Ca~ nad on Asfalto and Neuqu en basins. ...
... 8). The palynofacies of the Middle Juras- sic Los Molles and Lajas formations (Cuyo Group) of the central western part of the Neuqu en Basin was studied by Mart ınez et al. (2016). This short paper focussed on palynofacies and pollen-spores, and introduced the term 'palynotaphofacies'. ...
... This short paper focussed on palynofacies and pollen-spores, and introduced the term 'palynotaphofacies'. However, the dinoflagellate cyst species Jansonia psilata was illustrated from the Lajas Formation of the Lohan Mahuida sec- tion (Mart ınez et al. 2016, fig. 6o, p). ...
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Since the production of three literature compilations in 2012, 2013 and 2014, 266 further published contributions on Triassic, Jurassic and earliest Cretaceous (Berriasian) dinoflagellate cysts were issued between April 2014 and January 2018, or have been discovered. These 266 items are listed alphabetically herein with full details, including digital object identifier (doi) numbers where applicable. A full description of each publication as a string of keywords is given. These studies are placed in one or more of 14 global regions, and the most significant contributions are reviewed for all these areas except Central America. The region with the most studies is West Europe (37.2%), but sub-Arctic Russia (10.5%), the Arctic region (10.2%), East Europe (7.1%) and sub-Arctic North America (4.1%) are also well represented. The proportions of these publications over the Triassic, Early Jurassic, Middle Jurassic, Late Jurassic and Jurassic–Cretaceous transition intervals are relatively similar. However, the Middle Jurassic is best represented, and the Triassic has the smallest number of contributions.
... Those "extrabasinal turbidites" (see Zavala and Arcuri, 2016) show characteristic sedimentary arrangements (not discussed here) where plant remains occur in most of their facies (Ponce and Carmona, 2011a,b;Zavala et al., 2012). In this regard, global studies focused on the palynological content of hyperpycnites are relatively scarce (Carrillo-Berumen et al., 2013;Martínez et al., 2016;Mignard et al., 2017;Slater et al., 2017;Quattrocchio et al., 2018). ...
Article
The basal succession of the Lajas Formation at Trasandino section, Arroyo Covunco area, constitutes an excellent example of proximal prodelta facies cut by sediment-waves formed during a complete acceleration-deceleration hyperpycnal discharge cycle. The main outcome of this contribution was to present a new studied locality in which the Lajas Formation outcrops. Nine mudstones and fine-grained heterolites levels deposited during the waning stage, were sampled to palynological analysis. The recovered assemblages are dominated by sporomorphs, which are characterized by a great diversity of the trilete spores. Among them, is interesting to highlight the first mention of Manumia variverrucata and the extension of the last occurrence of Striatella seebergensis until to Callovian in Argentina. Based on selected key taxa a Late Bathonian–Callovian age is proposed for the Lajas Formation at the Trasandino section in this area. The Trasandino section spore assemblages show the greatest similarity with the Arroyo Covunco section spore associations when they are compared with the Lajas Formation of other studied localities. The endemic development of certain types of bryophyte (sensu lato) spores, e.g. Taurocusporites quattrocchiensis, was favored by locally humid conditions inferred at the Arroyo Covunco area. Large abundance of phytoclasts, sporomorphs and fresh-water algae characterize the recovered organic matter suggesting a high input of continental organic particles to the basin, as the result of fluvial-derived density discharges. Three palynofacies type (PT) had been identified which allow to evaluate the hydrodynamic characteristics of the flow, taking into account the differential buoyancy of the opaque particles. The large amount of equidimensional opaque particles recognized at the PT-B, characterizes the beginning of the deceleration phase of the flow and the abundance of blade-shape opaque particles, identified in the PT-A, point out a deposition from the final buoyant plume of hyperpycnal flow. The PT-C shows transitional features between these two conditions.
... Curiously, the work of Canale et al. (2015a,b) is later recurrently discussed. In addition, the authors ignored a large number of contributions related to detailed palynological analyses, which provided significant paleoenvironmental information of the Lajas Formation in these localities (Volkheimer, 1970(Volkheimer, , 1978Quattrocchio and Sarjeant, 1992;Martínez et al., 2001Martínez et al., , 2016Quattrocchio et al., 2001;Martínez and Quattrocchio, 2005). 4- Pazos et al. (2019) stated that their paper "… confirms the original idea of Zavala (2002) and invertebrate palaeontologists (see below) that the Covunco section is Bathonian-Callovian in age." ...
... We will discuss the result organic association (palynofacies type) recovered from these hyperpycnites (hyperpycnal flow deposits). At present, studies focused on the palynological content of hyperpycnites are scarce (e.g., Biscara et al. 2011;Carrillo-Berumen et al. 2013;Martínez et al. 2016;Mignard et al. 2017;Slater et al. 2017). ...
Article
The Miocene deposits in the Punta Basílica locality, southernmost Argentina, are included within the Cabo Viamonte Beds, Cabo Domingo Group, in the Austral foreland basin of Tierra del Fuego province. The prograding clinoform systems were accumulated during a weak compressional tectonic regime that allowed the development of a narrow shelf. Paleoenvironmental reconstructions suggest that these clinoforms comprise two dominant architectural elements, channel-levee and lobe complexes, formed mainly by density hyperpycnal currents in outer shelf to depositional slope environments. The transitional and recurrent (vertical and lateral) alternation between sedimentary structures without rheologic boundaries associated with the co-occurrence of plant remains (Nothofagus) are diagnostic criteria for the recognition of hyperpycnites. This type of density flow typically transports large volumes of sediment and organic matter from proximal to deep-marine settings. Four palynofacies types were recognized in a cluster analysis. In general, the palynofacies show predominance of spores and pollen grains, tissues, cuticles, and spongy to fibrous amorphous organic matter (plant and/or freshwater to brackish algae derived), which reflect different positions within the depositional system (e.g., levee-channel and lobe deposits). The co-occurrence of inshore (Batiacasphaera spp., Lingulodinium sp.) with relatively more oceanic (Operculodinium centrocarpum, Spiniferites spp.) dinoflagellates is a strong indication that shallow-water assemblages have been displaced into deep-water settings. Due to the presence of Lingulodinium hemicystum (first appearance data: 23.0 Ma.) and Pentadinium laticinctum (last appearance data: 11.6 Ma.) an age not older than Miocene and not younger than the Serravallian/Tortorian boundary for the Punta Basílica section is proposed.
... These pollen grains are mainly transported by rivers and/or run-off (e.g. Caccavari, 2003;Olivera et al., 2015;Martínez et al., 2016), therefore the high percentage of these families suggests an environment close to the terrestrial source area. Furthermore, the UNSP-MQN4634 level shows higher frequencies of bissacate pollen grains such as Podocarpaceae, Pinaceae and Caytoniaceae (repre- senting the long-distance influx to the depositional setting), and the dinoflagellate cysts as the main component of the OWMM. ...
Article
This study documents for the first time the occurrence of Shanbeipollenites proxireticulatus Schrank in levels of the Vaca Muerta Formation, Neuquén Basin, Argentina. It represents the first record of this species in high latitudes of the Southern Hemisphere. The Argentinian specimens are associated with useful palynostratigraphical indicators which suggest an early Valanginian age for the palynoflora yielding S. proxireticulatus. Therefore, this finding constitutes the first record from the Cretaceous. This taxon is related to the orders Cycadales/Bennettitales/Ginkgoales. During the Cretaceous in Patagonia cycads and bennettitaleans groups show marked adaptations to warm and strongly seasonal dry climate periodically influenced by volcanic activity. The paleogeographic distribution of the records of S. proxireticulatus, symmetrically located on both sides of the equator, together with its relationship with the climate zones or Biomes, suggest that the parental plants of this pollen grain thrived under warm climate and probably stressed paleoenvironmental conditions. Since the studied sample is located near 1000 m below the Intravalanginian unconformity, and older age (i.e. late Berriasian) cannot be discarded.
... This group is composed of deposits consisting of a prograding clastic section with offshore fine-grained deposits of the los Molles formation (Weaver, 1931) (fig. 2), isolated turbidite intervals and hyperpycnal flows (Zavala et al., 2011(Zavala et al., , 2014Martínez et al., 2016). This formation is progressively overlain by sandstones and conglomerates reflecting shallow marine to continental environments belonging to the lajas formation (Weaver, 1931). ...
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The Mesozoic Era is crucial for analyzing the replacement of microplanktonic lineages resulting from the beginning of the break-up of Pangea. The paleogeography of South America, and hence of Argentina, underwent successive changes since this time. The opening of different seaways, mainly during the Jurassic, affected the global circulation pattern of the oceans which determined the composition of the organic-walled marine microplankton associations of the Neuquén Basin. These Jurassic marine palynofloras are summarized here, based on the information from outcrop samples of 12 units, which were analyzed from a paleobiogeographic point of view. The configuration of the basin during the Early Jurassic was characterized mainly by partially interconnected depocenters, with restricted marine circulation that favored the development of associations dominated by components of the green lineage (acritarchs and prasinophytes). The Cuyo and Lotena groups (Middle Jurassic) were accumulated during two important flooding episodes which generated the paleoecological conditions for an increase in the diversity of the red lineage (dinocysts). Since the late Callovian the Hispanic Corridor connected the Neuquén Basin with the Tethyan realm allowing the free interchange of species. The Late Jurassic marine palynofloras are best characterized in the Vaca Muerta and Picún Leufú formations. The anoxic condition that prevailed during the accumulation of the Vaca Muerta Formation marked the return to the dominance of the green lineage. Conversely, the Picún Leufú Formation represents neritic more oxygenated bottom waters that favored a relative increase in the abundance and diversity of dinoflagellate cysts. KEY WORDS. Jurassic. Marine palynofloras. Paleobiogeography. Neuquén Basin. Argentina. Resumen. MICROPLANCTON MARINO DE PARED ORGÁNICA, JURÁSICO DE LA CUENCA NEUQUINA. DISTRIBUCIÓN, BIOESTRATIGRAFÍA Y PALEOBIOGEOGRAFÍA. UNA REVISIÓN. El Mesozoico constituye un momento crucial para analizar el recambio de los distintos linajes microplanctónicos producto del inicio de la ruptura de Pangea. La paleogeografía de Sudamérica y por lo tanto la de Argentina, experimentó sucesivos cambios durante este lapso de tiempo. La apertura de diferentes corredores oceánicos, principalmente durante el Jurásico, afectó los patrones de circulación global de los océanos, evidenciado en la Cuenca Neuquina en la variabilidad de composición de las asociaciones microplanctónicas de pared orgánica. Se reúne la información proveniente de muestras de afloramiento de 12 unidades jurásicas, cuyas palinofloras marinas fueron analizadas desde un punto de vista paleobiogeográfico. La configuración de la cuenca durante el Jurásico Temprano se caracterizó principalmente por la presencia de una serie de depocentros parcialmente interconectados con circulación marina restringida. Este contexto favoreció el desarrollo del linaje verde (acritarcos y prasinofíceas). Dos grandes episodios de inundación marina provocaron la acumulación de los grupos Cuyo y Lotena (Jurásico Medio) generando las condiciones paleoecológicas para un incremento en la diversidad del linaje rojo (dinoquistes). A partir del Caloviano tardío la apertura del Corredor Hispánico permitió la conexión de la Cuenca Neuquina con el Dominio Tethiano y con ello, el libre intercambio de especies. El Jurásico Tardío es aquí caracterizado por las palinofloras marinas de las formaciones Vaca Muerta y Picún Leufú. Las condiciones anóxicas que prevalecieron durante la acumulación de la Formación Vaca Muerta constituyen un retorno al predominio del linaje verde. Por el contrario, la Formación Picún Leufú caracterizada por ambientes de plataforma con aguas relativamente más oxigenadas, favorecieron el incremento en la abundancia y diversidad de dinoflagelados. PALABRAS CLAVE. Jurásico. Palinofloras marinas. Paleobiogeografía. Cuenca Neuquina. Argentina.
Article
Being the main oil-bearing basin of Argentina, the Neuquén Basin contains a well-documented stratigraphic record of continental and marine sedimentation during the Jurassic and Cretaceous in the western margin of Gondwana. Marine sedimentation started in the Early Jurassic with the deposition of the offshore to prodelta shales of the Los Molles Formation, the basal unit of the Cuyo Group. A palynological study of outcrop samples of the Los Molles Formation at two localities, Puente Picún Leufú, southern Neuquén Basin, and Cordillera del Viento, central basin area, is presented. The palynological evidence allows inferring two different palaeoceanographic contexts during the deposition of the Los Molles Fm. At Puente Picún Leufú and the lower part of the Cordillera del Viento localities, the record of acritarchs and prasinophytes suggests a stratified water column, suboxic-to-anoxic bottom conditions, and a reduced salinity within the photic zone, associated with a marginal marine environment under restricted oceanic circulation. These conditions would have last at least until the Early Bajocian. Conversely, at the middle and mainly the upper part of Cordillera del Viento locality, the predominance of dinocysts in the assemblages indicates a hydrographically unstable shelf (non-stratified water mass column) with well-oxygenated bottom waters developed under open-marine settings with non-restricted oceanic circulation. The abundance and diversity of dinocyst assemblages are comparable with those observed in the Late Callovian Lotena Formation. These evidences suggest an open oceanic circulation due to the establishment of different seaways in the Neuquén Basin, during the final accumulation of the Los Molles Formation (Early Callovian).
Thesis
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En el presente trabajo se analizan la estratigrafía y los paleoambientes deposicionales de la Formación Lajas (Jurásico medio) a partir del estudio de los afloramientos de esta unidad localizados en el suroeste neuquino, y relacionados a la Dorsal de Charahuilla-Plottier, en un área de 2800 Km2. La Formación Lajas, unidad eminentemente arenosa de ambiente de plataforma, litoral a continental, se dispone mediante un contacto diacrónico sobre pelitas de plataforma de la Formación Los Molles. A su vez es cubierta, mediante un contacto neto, por pelitas rojas de la Formación Challacó. A partir del levantamiento de 12 secciones estratigráficas de detalle se realizó primeramente un análisis de facies sedimentarias y posteriormente un análisis estratigráfico y estratigráfico secuencial de estos depósitos. Esto permitió diferenciar 19 facies sedimentarias, las que mediante su agrupamiento natural definen 13 asociaciones de facies, correspondientes a los siguientes ambientes y subambientes deposicionales: Plataforma costa afuera - prodelta; Barra de desembocadura dominada por ola/Playa; Barra mareal de plataforma a estuarina; Barra de desembocadura fluvio-dominada; Barra de desembocadura de "braid-deltas"; Llanura mareal; Llanura deltaica inferior, pantano interdistributario a bahía interdistributaria; Canal estuarino; Sistema fluvial meandriforme; Sistema fluvial entrelazado arenoso; Sistema fluvial anastomosado; Sistema fluvial entrelazado gravoso; Barreal. Mediante el análisis estratigráfico secuencial de las secciones relevadas se discriminaron 4 secuencias deposicionales de tercer orden (en el sentido de Vail et al., 1977), las que se denominan JC4, JC5, JC6 y JC7. La secuencia JC4 (Toarciano superior alto - Bajociano inferior alto) se reconoce como integrada por 5 secuencias deposicionales de un orden menor, denominadas JC4.1, JC4.2, JC4.3, JC4.4 y JC4.5. La secuencia JC4.1 es la más extendida, y corresponde principalmente a la Fm. Los Molles, en tanto que las secuencias restantes pertenecen a la Fm. Lajas. Las secuencias superiores (JC4.3, JC4.4 y JC4.5) se reconocen únicamente en el sector occidental del área de trabajo debido a problemas tectosedimentarios que se detallan más abajo. La secuencia JC5 (Bajociano inferior alto - Bajociano superior alto) muestra una amplia distribución en la zona de trabajo, correspondiendo al sector medio y superior de la Fm. Lajas. El hallazgo de Stephanoceras (Stemmatoceras) sp. (Zona de Humphriesianum a Rotundum) y de Teloceras aff. crickmayi chacayi (West. & Ricc., Zona de Rotundum) permitió datar bioestatigráficamente por primera vez a la Fm. Lajas en esta región. Las secuencias JC6 (Bajociano superior alto - Bathoniano inferior) y JC7 (Bathoniano inferior alto - Bathoniano superior alto) se integran con facies propias de la Fm. Challacó. La secuencia JC6 es la que presenta la mayor distribución regional. En base a evidencias estratigráficas se reconoce una importante actividad tectónica en la dorsal de Charahuilla-Plottier, la que habría enfatizado la discordancia estratigráfica que separa a las secuencias JC4 y JC5. En el sector occidental del área de estudio (Perfiles Lohan Mahuida y Puesto Pichonleo) esta discordancia está poco desarrollada, en tanto que en el sector centro-oriental se reconoce a partir de esta discordancia la pre¬sencia casi continua de un cuerpo sedimentario de hasta 35 metros de potencia, de la base de la secuencia JC5, el que forma la conspicua cornisa notada por varios autores en el flanco este de la Sierra de Chacaico. Se estima que dicha discordancia habría producido una truncación de unos 200 metros estratigráficos de la Fm. Lajas en este sector, ya que se encuentran ausentes las secuencias JC4.4 y JC4.5. Existen asimismo evidencias de actividad tectónica entre las secuencias JC6 y JC7, reconocida localmente en el Perfil Bosque Petrificado, y expresada mediante el desarrollo de una discordancia angular de unos 40-50º entre ambas secuencias. Cabe destacar que la secuencia JC7 se encuentra a su vez en discordancia angular por debajo de niveles conglomerádicos de la Fm. Quebrada del Sapo (= Fm. Tordillo) o cuando esta está ausente, de pelitas marinas de la Fm. Vaca Muerta.
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El grupo Cuyo (Jurásico inferior a medio) constituye el primer evento de sedimentación marina generalizada en la Cuenca Neuquina. Integra una sección clástica progradante, en la que depósitos peliticos de offshore (Fm Los Molles) con ocasionales niveles de turbiditas, son sucedidos por acumulaciones de areniscas a conglomerados marinos de plataforma a continentales (Fm Lajas). En este trabajo se presenta un esquema estratigráfico secuencial para el Grupo Cuyo basado en estudios de afloramientos localizados en los alrededores de la Sierra de la Vaca Muerta. El relevamiento de ocho secciones estratigráficas de detalle complementado con un estudio fotoestratlgráfico ha permitido identificar cinco secuenoas deposicionales, las que muestran evidencias de actividad tectónica sindeposioonal. La secuencia 1 se reconoce con base cubierta en el sector sur de la zona de estudio, y se integra por areniscas de plataforma a litorales de naturaleza cuarzo-feldespática, con zonas de aporte localizadas principalmente en el sureste Las secuencias 2 a 5 se integran por areniscas y conglomerados de plataforma a litorales de naturaleza lítica, con aportes elásticos desde el suroeste. Dichas secuencias evidencian una progresiva migración hacia el norte del depocentro, el que es acompañado por un aumento general de la textura. El análisis estratigráfico permite aseverar que las secuencias 2 a 5 se habrían acumulado en depocentros elongados, con geometrías y facies controladas por actividad tectonica jurásica. Dicha actividad podría corresponder a un reflejo superficial de la inversión parcial de estructuras distensivas basamentales, como consecuencia de pulsos tectónicos compresivos desde el sureste (Macizo Nordpatagónico) durante el Bathoniano / Caloviano temprano. Los cambios en la zona de aporte permiten especular sobre el creo miento de una barrera física en la zona de la Dorsal de Huíncul, la que habría limitado progresivamente los aportes elásticos desde el sureste. En base a este estudio y anteriores en la subcuenca de Picún Leufú se discute la posición estratigráfica y significado de la Fm Challacó, y la posible pertenencia de la Formación Tábanos (evaporitas) al Grupo Lotena.
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A sequence-stratigraphic analysis, based on outcrop data, is presented for the Middle Jurassic Cuyo Group in the southern Neuquen Basin. The studied area is located 40 Km south of the city of Zapala, and comprises Middle Jurassic outcrops placed in the Lohan Mahuida - Picun Leufu - Cerro Lotena area. In these outcrops, the Cuyo Group comprises shallow marine to continental beds up to 1200 m of thickness. Twelve sedimentary sections were measured through the succession, in which facies and sequence stratigraphic analysis have been carried out. The study allowed to recognize eight depositional sequences, related to both third and fourth-order base level cycles. Thirdorder sequences, named JC4, JCS, JC6 and JC7, show an internal predictive succession of systems tracts, indicative of a mainly eustatically driven mechanics. Except for the last two sequences, which are continental deposits all over this area, ammonoid fossils remains indicate an Upper AalenianUpper Bajocian age. The JC4 depositional sequence is internally composed by a progradational fourth order sequence set. These minor sequences are named JC4.l, JC4.2, JC4.3, JC4.4, and JC4.S. Local to regional studies allow to recognize an extensive truncation - non deposition episode (up to 200 meters) between the JC4.1-JC4.2 and JCS sequences, because three fourth order depositional sequences (JC4.3, JC4.4, and JC4.S) are missing in the central-east area. Tectonic evidences have also been found between the JCS-JC6 and JC6-JC7 sequences in the Puesto Bascuii.an and Bosque Petrificado area. In this last position, the JC7 sequence rests over the JC6 sequence with a SO" angular uncorformity. The tectonic vs. eustatic controls of each sequence boundary is discussed. A detailed outcrop map of each recognized depositional sequences in the studied area is also included.
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The Middle Jurassic Cuyo Group in the~uthern Neuquen Basin comprises shallow marine to continental beds up to 1200 m of thickness. Twelve sedimentary sections were measured through the succession, in which facies and sequence stratigraphic analysis have been carried out. The study allowed us to recognize eight depositional sequences, related to both third and fourth-order scales (sensu Exxon). Because these outcrops extend from mainly fluvial deposits on the east to coeval shallow marine deposits on the west, they allow to analyze sequence stratigraphic relationships, facies, and paleoenvironmental changes during the evolution of a depositional sequence. (1) In shallow marine environments, third-order sequences start with a major erosive and non-depositional event followed by up to 20 meters of sandy-braided fluvial to high sinuosity estuarine channel deposits linked with a late lowstand systems tract - early transgressive systems tract stage. The transgressive systems tract deposits are characterized by 2-6 meters thick shallowing upward tidal bars with a retrogradational parasequence set. Highstand systems tract deposits starts with open-shelf mudstones followed by 4-6 meters of shallowing upward cycles of input to wave dominated stream-mouth bars, with a progradational parasequence set. (2) In mainly continental areas, third order sequences begin with up to 10 meters of coarse grained braided-river deposits resting over a regional discontinuity. These deposits are interpreted as developed in early transgressive systems tract stage. The Transgressive systems tract deposits are expressed by 12-14 meters of marsh levels, with tidal influence. The highstand systems tract deposits start with off-shore marine mudstones, followed by a strongly prograding input-dominated deltaic systems, and ending with thick high-sinuosity sandy fluvial deposits.
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Recent studies of marine continental shelves show that hyperpycnal flows are responsible for offshore transport of large volumes of sediment. Detailed facies analysis and petrography of the lower Genesee Group in the Northern Appalachian Basin (NAB) shows a wealth of sedimentary textures and fabrics that indicate mud deposition by lateral transport across and along the shelf under energetic conditions. Intervals of silt-rich mudstones and muddy siltstones with internal scours, diffuse stratification, soft-sediment deformation, normal and inverse lamina-set grading, and a reduced intensity and diversity of bioturbation occur in multiple facies types and "interrupt" what appears to be the overall background sedimentation. These intervals and their sedimentary features are interpreted as products of high-density fluvial discharge events, which generated turbulent flows that carried fine-grained clastics several tens of kilometers offshore from the paleoshoreline. Recognizing these sediments as products of river-flood- and storm-wave-generated offshore-directed underflows challenges previous depositional models for organic-rich mudstones in the lower Genesee succession, which call for clastic starvation and suspension settling of clay and silt in a deep stratified basin. Rapid deposition of fine-grained intervals from hyperpycnal plumes in a setting favoring preservation of organic-rich mudstones calls for a reappraisal of the depositional setting of not only the Genesee Group, but also of comparable mudstone successions in the Appalachian Basin and elsewhere.
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Intrabasinal and extrabasinal turbidite deposits: origin and distinctive characteristics According to its original conception, turbidites were related to re-sedimentation processes in deep waters. Basically, sediments initially stored in littoral/shallow marine environments were periodically transferred (or re-sedimented) into the inner basin by slope instability. Since these turbidites originate within the marine basin, the resulting sediment gravity flows could be considered intrabasinal turbidites. More recently, an increasing number of evidences show that turbidites commonly originates from the direct discharge from rivers in flood. These turbidites result from relatively dense turbulent suspensions entering the sea as hyperpycnal flows. Since these turbidites originate in the continent, they are extrabasinal turbidites. The deposits of intrabasinal and extrabasinal turbidites have several diagnostic features allowing a clear differentiation. Intrabasinal turbidites are surge-like flows, and commonly initiate with a cohesive debris flow that progressively dilutes and transform into a granular and finally a turbulent flow. On the contrary, extrabasinal turbidites are fully turbulent flows driven by a relatively dense and sustained river discharge. Depending on the grain-size of suspended materials, the resulting hyperpycnal flow can be muddy or sandy. Sandy hyperpycnal flows also can carry bedload, resulting in sandy to gravel composite beds with sharp to gradual internal changes, laterally associated with lofting rhythmites and abundant plant remnants. Muddy hyperpycnal flows are loaded by a suspension of silt and clay, and accumulate silty-clay graded beds with plant remnants and displaced marine microfossils. It is interpreted that most of the shales of the Los Molles and Vaca Muerta formations in the Neuquen Basin were accumulated in this way.
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Palynomacerals damaged by shear, displaying characteristic tension gashes (subparallel tearing pattern), are reported from Middle to early Late Devonian shales of the Los Monos Formation, in the subsurface of Southern Subandean Bolivia. Shear has affected not only marine and terrestrial palynomorphs (trilete spores, organic-walled microphytoplankton, chitinozoans) but also land-derived phytoclasts. Shear-torn palynomorphs have been previously recorded in oil-producing sedimentary basins of Brazil. Here, their origin was attributed to faulting because of the following facts: (1) the shear-torn palynomorphs were recovered from wells drilled in areas infested by growth faults; (2) they occur mainly in Albian to Paleogene strata that immediately overlie the Aptian salt, and thus are severely affected by salt tectonics; (3) the subparallel tearing pattern of palynomorphs is suggestive of deforming processes that took place when the host sediment was still in a rather plastic (partly unconsolidated) state. In the investigated Los Monos sections, several samples present a considerable proportion of the palynomacerals sheared to varied degrees. The frequency of shear-torn palynomacerals is especially high in middle to upper parts of the formation. This suggests that thrusting, faulting and other deformation processes could have affected more plastic (pelitic) strata in those intervals. Tectonic disturbances of the normal stratal succession are not always distinguished on the basis of strictly biostratigraphic evidence. However, other apparent palynological anomalies (involving abrupt changes in composition, nature and/or preservation of the organic residues) occur in different intervals of the investigated wells. Some of these match intervals where palynomorph shear becomes more frequent and intense, thus pointing out to possible tectonic controls. Other palynological anomalies, dissociated from shear-torn palynomorphs, are more probably related to faciological causes.
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ABSTRACT. Paleogene continental Palynomorphs of the formations Chorrillo Chico and Agua Fresca, Punta Prat, Magallanes, Chile. The Paleogene section of Punta Prat, Chile is located at 53°10’S-71°20’W in southern Magallanes-Austral Basin, includes Chorrillo Chico and Agua Fresca Formations. Both units contain a palynological assemblage composed of marine and continental palynomorphs indicative of a marine depositional environment with terrigenous input. The continental taxa found in the studied formations reflect a forest developed under a humid warm to temperate climate, dominated by Podocarpaceae, Proteaceae and Nothofagaceae accompanied by abundant ferns belonging to the Schizaeaceae, Polypodiaceae and Dicksoniaceae families. The relationship of marine/continental palynomorphs indicates a marine transgression from the Paleocene to the Middle Eocene. This transgression caused the decline of wetlands towards the top of the column, as shown by the low rate of swamp inhabiting palynomorphs in the upper levels of the Agua Fresca Formation.
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A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.
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Different sedimentary settings can influence preservation of pollens, which would lead to misinterpretation of fossil pollen spectrum. This study investigates the influence on the preservation of Pinus tabulaeformis pollen by simulating alkaline and oxidative environment in the laboratory. There was no obvious change in the content of Pinus tabulaeformis pollen while comparing the original with the ones that were immersed with 10% NaOH liquor for ten days, or boiled for five hours, and or boiled with 20%–30% NaOH for one hour, respectively. However, the pollen fossils were obviously corroded and eroded after being boiled with 40% NaOH for one hour and were seriously corroded after five hours. The result indicates that Pinus tabulaeformis pollen is quite durable in alkaline environment and heating condition within a shorter period of time, although alkaline environment has a disadvantage for its preservation. We also tested the influence of oxidation on Pinus tabulaeformis pollen preservation with KMnO4 as oxidant. The result presents that the number of remaining Pinus tabulaeformis pollen grains decreased quickly after being dipped in KMnO4 along with extending the reaction time and reinforcing oxidant. The rate of remnant pollen grains was less than 1% after being dipped with 2% KMnO4 for one hour. It is suggested that oxidative environment has stronger influence on Pinus tabulaeformis pollen preservation than alkaline environment.
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The history of fossils during fossilization is a subject of taphonomy. According to the most common classification system over the last forty years, taphonomy may be subdivided in several (sub)disciplines. Biostratinomy and fossildiagenesis are two taphonomic disciplines, having their own concepts, subjects, goals and methods. However, they have not application fields clearly delimited. In order to solve the current ambiguity, biostratinomy should deal with pre-burial modifications, and fossildiagenesis should comprise modifications after the initial burial. Although taphonomy is subdivided into biostratinomy and fossildiagenesis, fossilization processes do not imply the occurrence of biostratinomic and fossildiagenetic modifications, phases, stages or time-intervals. Biostratinomic and fossildiagenetic modifications should be considered as contingent processes during fossilization.
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Two simple experiments show that mechanical pollen damage is not caused by pollen‐clast collisions during transport, but that wet‐dry cycles may be very effective at degrading pollen. These experiments suggest that horizons of damaged pollen in subaqueous sediment more likely result from redeposition of pollen previously exposed to subaerial weathering, rather than from damage incurred during transport.
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Experimental degradation of pollen by repeated wet‐dry cycles in saline and desalinated sediments show differences in preservation between taxa and between salinity environments. In desalinated sediment, from which the salts were removed artificially, pollen is rapidly degraded, with a significant net loss of pollen after ten wet‐dry cycles. Picea pollen, which remains identifiable even when heavily damaged, suffers greater breakage in desalinated sediments. Artemisia pollen is rapidly rendered unidentifiable by degradation of the sculptural elements in both saline and desalinated sediments. In comparison to desalinated sediments, saline sediments appear to contain less damaged pollen. Growing salt crystals may envelop the pollen grains and stabilize them against mechanical breakage otherwise incurred by flexing of the pollen wall during desiccation. Caution should be exercised when analyzing sediments subject to wet‐dry cycles, and laboratory procedures modified if necessary to avoid desiccation of pollen during processing.
Book
Paleopalynology, second edition, provides profusely illustrated treatment of fossil palynomorphs, including spores, pollen, dinoflagellate cysts, acritarchs, chitinozoans, scolecodonts, and various microscopic fungal and algal dispersal bodies. The book serves both as a student text and general reference work. Palynomorphs yield information about age, geological and biological environment, climate during deposition, and other significant factors about the enclosing rocks. Extant spores and pollen are treated first, preparing the student for more difficult work with fossil sporomorphs and other kinds of palynomorphs. Recognizing that palynomorphs occur together in rocks because of chemical robustness and stratigraphic distribution, not biological relationship, the central sections are organized stratigraphically. Among many other topics presented are the sedimentation and geothermal alteration of palynomorphs, and palynofacies analysis. An appendix describes laboratory methods. The glossary, bibliographies and index are useful tools for study of the literature.
Article
Sporomorphs and paleomicroplankton identified from the Middle Jurassic, Los Molles Formation, Cuyo Group, are described and illustrated in this contribution. The palynomorphs were recovered from three of the five sampled surface sections (Lohan Mahuida, Puente Picúin Leufú, Puesto Policía, Los Molles and Cerro Lotena) located near Zapala city, Neuquén Basin, Argentina. The studied microfloras include 50 species of sporomorphs (20 spores and 30 pollen grains) and 31 species of paleomicroplankton (9 green algae, two dinoflagellate cysts and 20 acritarchs). Specimens belonging to the genera Divisisporites, Callialasporites, Monosulcites and one spore gen. et sp. indet. are described. Systematics include prasinophyte of the genera Cymatiosphaera, Pleurozonaria and Tasmanites. Also included are acritarchs of the genera Baltisphaeridium, Filisphaeridium, Micrhystridium, Leiosphaeridia, Polygonium and Veryhachium. The new combination Cymatiosphaera volkheimerii (Quattrocchio) is proposed. The occurrence of the acritarchs Filisphaeridium balmei (Sarjeant) Sarjeant and Stancliffe, F. castaninum (Valensi) Sarjeant and Stancliffe, F. densispinum (Valensi) Sarjeant and Stancliffe and Veryhachium valensii (Valensi) Downie and Sarjeant is mentioned for the first time in the Neuquén Basin. The studied palynofloras are correlated with the Biozone of Callialasporites "complex" (Sub-biozone of Callialasporites trilobatus (Balme) Dev, Antulsporites saevus (Balme) Archangelsky and Gamerro and Klukisporites labiatus (Volkheimer) Baldoni and Archangelsky) previously proposed for this area of the Neuquén Basin. A Late Aalenian - Early Bajocian age is suggested for the studied sections.
Chapter
The study of the organic matter in sediments and sedimentary rocks focuses on the interaction between the biosphere and geosphere. A proper appreciation of the subject requires an understanding of the environmental controls which govern the production of organic matter in the biosphere, the ecological and sedimentological processes which control its deposition and distribution, the biogeochemical, and geomicrobiological factors which influence its preservation, and the geochemical and physical processes which determine its modification during its incorporation in the geosphere. This makes the study of sedimentary organic matter one of the most multidisciplinary pursuits within the whole field of earth sciences.
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There are few recognized examples of fluvial-dominated deltaic systems affected by hyperpycnal discharges. The development of predictive models in those systems are essential to understand the distribution of sedimentary facies and for determining the location of the main sandy bodies, which constitute the potential hidrocarbon reservoirs. In Portada Covunco and Sierra de la Vaca Muerta areas (Neuquén, Argentina), the Lajas Formation constitutes an excellent example of a deltaic fluvio-dominated succession consisting of prodelta and deltaic front deposits, affected by hyperpycnal discharges and reworked by wave action (storm and normal wave action). Prodelta deposits show a strongly tabular geometry alternating between mudstones and fine sandstones with abundant organic matter and development of an impoverished Cruziana ichnofacies. Deltaic-front deposits are integrated by mudstones, fine to coarse sandstones and fine conglomerates showing tabular geometries and development of the Skolithos and Glossifungites ichnofacies, the later related to deltaic lobe avulsión. Normal progradation of this deltaic system shows stratigraphic intervals consisting of tabular and lenticular bodies of variable thicknesses assigned to hyperpycnal-channel and lobe systems. Internally, these deposits show transitional and recurrent passages between different sedimentary structures with marked textural variations, multiple internal reactivation surfaces and abundant organic matter content. Hyperpycnal channels systems have different dimensions and fill patterns. At the foot of the areas with the greatest gradients, hyperpycnal discharges produced mayor channels with aggradational fill, whereas in areas with lower gradients, high sinuosity channels developed. Hyperpycnal lobes were accumulated in areas where hyperpycnal flows lost confinement. The presence of conglomeratic levels affected by wave action on top of the lobe deposits indicates pauses in sedimentation during which colonization windows could develope, allowing the establishment of the benthic fauna.
Article
The occurrence of pyrite crystals embedded in the exines of spores and microplankton is described from some Upper Palaeozoic sediments of Britain. Solution of the pyrite produces a variety of cavities which reflect the state of aggregation of the mineral. The morphology of these cavities or pyrite relic structures is described in detail and a classification into simple, cribrate and faviform structures is proposed. The form and distribution of the pyrite crystals favour an organic origin, possibly bacterial.
Article
Degradation patterns in the walls of fossil pollen grains and spores are described. The smoothness and multiplicity of the wall perforations are indicative of biologic activity, assumed to be fungal in nature. Spore or pollen exines may be selectively attacked and removed from the microflora.
Article
ABsTRAGr.-Within the past quarter century palynology has become an increasingly important component of archaeological research. Applications have included elucidation of site and room functions, ceremonial and medicinal practices, prehistoric diet and food preparation, correlative construction and chronologies, human modification of the local environment and the nature, magnitude and duration of climatic perturbations, particularly as related to human demography and subsistence strategies. Apprehension concerning the nature and magnitude of palynological bias related to human activities, particularly as reflected by the sources of pollen commonly employed in such studies, is justified but remained largely unexplored. Examination of pollen production, dispersal and preservation leads to the conclusion that once the probability and magnitude of limitations are assessed, they can often be obviated or even be exploited as new potential application of palynology in archaeology.
Article
A model of the predicted palynologic response to sea-level changes was formulated and tested in three different depositional areas. Both the subsurface Mancos Shale-Tocito Sandstone interval of New Mexico and the St. Stephens quarry section in Alabama show a correspondence between systems tracts and the composition of the palynoflora. These intervals are not directly associated with deltaic sedimentation. The third area is a subsurface Wilcox section studied in southwestern Louisiana that lay on the distal edge of a major deltaic system. Both the electric log stacking patterns and palynofloral compositions show a correspondence to the systems tracts. The results of this investigation are in general agreement with the results of earlier organic petrologic studies on some of the same sample material. -from Authors
Article
Reconstructions of Quaternary environmental history based upon modern pollen/vegetation/climate calibrations are more tenable if the factors responsible for variation in pollen assemblages are evaluated. Examination of the state of preservation of Quaternary palynomorphs provides quantitative data concerning the degree of information loss due to alteration of pollen assemblages by syndepositional and post‐depositional deterioration. The percentage, concentration, and influx values for total indeterminable pollen are useful criteria in providing an objective and quantitative basis for evaluating the comparability of pollen spectra within and between sites. Supporting data concerning sediment particle‐size distribution, organic matter content, and concentration, influx, and taxonomic composition of both determinable pollen and plant macrofossils aid in reconstructing past depositional environments. The potential is high for deterioration of pollen in sediments from the southeastern United States, although considerable variation is found in both kind and degree of deterioration between lacustrine and alluvial sites of different ages and in different latitudes. Modern analogs are a basis for late Quaternary environmental reconstructions when pollen deterioration has not significantly biased the information content of fossil pollen assemblages.
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Article
The micromorphological features of decay in service timbers in a tropical inter-tidal zone were studied to ascertain the pattern of biodeterioration. Bacterial tunneling, soft-rot cavities and basidiomycete attack were evident in parts of the timbers between low and high tide water levels. Bacterial erosion was frequently encountered below the waterline at low tides while tunneling was rare and soft-rot or basidiomycete attack was not observed. However, only rare soft-rot and frequent basidiomycete degradation were observed above the waterline at high tide. A microchemical test indicated that lignin was attacked only in wood areas above the waterline at high tide while cellulose degradation occurred in all areas. The observation on the pattern of decay may be useful in predicting the service life of timbers in the tidal zone.
Article
Conifers of the Cheirolepidiaceae, on the basis of palynological evidence, extended from the Triassic to the Late Cretaceous or perhaps to the Early Tertiary. They were geographically widespread and especially important in the Jurassic and Early Cretaceous at low palaeolatitudes. Recent research on both pollen (Classopollis) and macroremains has demonstrated considerable diversity within the group. Aspects of pollen-exine structure, seed-cone organization as well as vegetative morphology and anatomy suggest high degrees of biological specialization. A number are believed to have been tropical halophytes but others probably occupied a wide range of warm habitats prior to the rise to dominance of angiosperms.
Article
Transmission electron microscope studies of three types of pollen grains, i.e. Balmeiopsis, Callialasporites and Araucariacites, found in Early Cretaceous strata of Patagonia have shown that they possess several similar ultrastructural patterns. The nexine is uniformly lamellate and the sexine is composed of granular to vermiculate sporopollenin units. Sometimes granular elements may form ill defined collumella-like structures oriented radially near the surface of the grains. Balmeiopsis has a thickened equator that may contain a small empty space, while Callialasporites has rudimentary sacci formed by the separation of both exine layers. However, the inner surface of the sexine does not form an endoreticulum and there are no thin sporopollenin threads that fill the cavities between nexine and sexine. This type of primitive saccus is different from the eusaccate or protosaccate types found in gymnosperms. Araucariacites has the thinnest exine of the three and no equatorial thickening or rudimentary sacci. All three types belong to conifers and comparisons are made with fossil and extant members of the Podocarpaceae and Araucariaceae, two families that are now represented in the Andean region.
Article
Colonies of the green alga Botryococcus occur in the Precambrian and throughout the Phanerozoic succession and have been interpreted as indicators of freshwater environments or influence. It has long been known that Botryococcus is a source of hydrocarbons in geological deposits and this has stimulated much research on the research on the living alga. B. braunii Kützing. This research has shown, for example, that the nature of the hydrocarbon produced may be related to the physiological state of the alga. In a study of Mesozoic samples it has been observed that the Botryococcus colonies exhibit different stages of development, similar to the physiological states of the living alga; the different stages appear to be specific to certain samples and are seldom, if ever fo und together. Material from Swedish Palaeozoic and Mesozoic sediments has been studied to investigate possible relationships between environment and the state of development of the alga. Torbanite from Scotland, kerosene shale from New South Wales, Australia, and colonies of modern Botryococcus have also been studied for comparative purposes. Detailed examination and the recognition of the stages of development at which Botryococcus colonies are preserved may yield more information about the palaeoenvironment than was previously recognised, leading, in some cases, to firmer interpretations of depositional conditions.
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Cluster analysis is a collective term covering a wide variety of techniques for delineating natural groups or clusters in data sets. This book integrates the necessary elements of data analysis, cluster analysis, and computer implementation to cover the complete sequence of steps from raw data to the finished analysis. The author develops a conceptual and philosophical basis for using cluster analysis as a tool of discovery and applies it systematically throughout the book. He provides a comprehensive discussion of variables, scales, and measures of association that establishes a sound basis for constructing an operational definition of similarity tailored to the needs of any particular operational definition of similarity tailored to the needs of any particular problem, and devotes special attention to the problems of analyzing data sets containing mixtures of nominal, ordinal, and interval variables. (Author)
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The Neuquén Basin in western Argentina offers a variety of attractive hydrocarbon plays in both the Jurassic and Cretaceous sequences. Exploration to date has proved hydrocarbon reserves of 800 million cu.m oil-equivalent 60% of which are gas. These reserves have been found mainly in relatively small structures along the stable platform area, where good reservoir-quality sandstones and carbonates are present. In the western thrust-belt, large structures remain untested; however, reservoir quality in this area is a problem. The exploration dilemma is therefore. whether to search for “elephants”, with a high risk of finding adequate reservoirs, or be satisfied with the less risky but smaller rewards associated with foreland traps.