Palaeogene deposits in North-East Greenland

Scattered occurrences of Palaeogene sediments are found in North-East Greenland, where they overlie unconformably Cretaceous sediments and are capped by Palaeogene basalts. These sediments have received little attention (Watt 1994), except for relatively recent studies (Nøhr-Hansen & Piasecki 2002; Jolley & Whitham 2004; Larsen et al. 2005; Heilmann- Clausen et al. 2008). As part of an ongoing petroleum geological study that focuses on the Jurassic–Cretaceous succession, the Palaeogene sediments were included to better constrain their age, depositional environment and relation to the basalts. Several localities were investigated on Wollaston Forland, Sabine Ø and Hold with Hope, a few of which are described here (Fig. 1)

Miocene semidiurnal tidal rhythmites in Madre de Dios, Peru: Reply

Hoorn et al. commented on the following aspects of our 2005 Geology article: 1) the age of the sediments, 2) the interpreted brackish water affi nity of the studied deposits, and 3) the possible connection between Paraná and western Amazonia depositional systems during the late Miocene

Icnofacies en la base de la formación Marcavilca: asociaciones icnolitológicas y análisis paleoambiental

El primer estudio de trazas fósiles en el Morro Solar, afloramiento ubicado al sur del distrito de Chorrillos, Provincia de Lima, se realizó a comienzos del siglo pasado por Lisson (1904, 1908), siendo posteriormente abordadas por otros investigadores (Fernández Concha, 1958; Rivera, et. al., 1975) con énfasis en el género Diplocraterion, reconocido en la Formación Salto del Fraile. En las secuencias superiores de esta misma localidad (Fig.1), las trazas fósiles de crustáceos fueron inicialmente descritas por Geyer & Alleman (1984) y mal atribuidas a la Formación La Herradura debido a un error en la definición de un contacto estratigráfico. El presente estudio incorpora al estudio de la icnofacies, la influencia de la naturaleza del sustrato en base a la asociación icnolitologica (Sagasti & Poiré, 1998) y al evento de bioturbación (Bromley, 1996). Asimismo, precisa la posición estratigráfica y refiere las trazas fósiles a una plataforma detrítica correspondiente a la base de la Formación Marcavilca

Nueva nomenclatura estratigráfica del paleógeno – neógeno en la Amazonía peruana

En este resumen proponemos una nomenclatura basada en un trabajo detallado de recopilación bibliográfica y elaboración de un léxico estratigráfico del Paleógeno-Neógeno para la amazonía peruana, lo que permitirá uniformizar criterios para el uso de los diferentes nombres formacionales. En el marco del convenio entre el proyecto BIODAMAZ y el INGEMMET, se elaboró una base de datos sobre los trabajos realizados en la Amazonía con la finalidad de producir un nuevo mapa geológico. La nomenclatura utilizada está basada en los trabajos de Williams (1949) para las cuencas Santiago, Huallaga y Marañón; los trabajos de Kummel (1948) para la cuenca Ucayali; y los de Sullins (1960), Hatfiled (1962) y la reciente revisión de Hermoza (2004) para la cuenca Madre de Dios. Inicialmente en los años 60 las compañías petroleras exploraron la región, trabajos remarcables como los informes de la Gulf Petroleum, Shell, etc. han sido la base para la revisión

The nature of Miocene Amazonian epicontinental embayment: High-frequency shifts of the low-gradient coastline

A sedimentological and ichnological data set that covers the Lower-Upper Miocene sedimentary series of western Amazonian foreland basin indicates that widespread, restricted marine ingressions shaped western Amazonia throughout the Miocene. The late Lower–early Upper Miocene sedimentary series (Pebas Formation) consists of stacked, 3- to 10-m-thick, tidally influenced, brackish to freshwater, bay-margin sequences. The overlying Upper Miocene (“post-Pebas”) strata bear tidally influenced, low-salinity, channel deposits that are interbedded with continental deposits. The data suggest that several tens of high-frequency ingressions reached the basin during the Miocene. The ingressions were shallow and restricted, and were interspersed with rapid progradation. Along with the prograding shorelines, the continental environments—swamps, lagoons, floodplains and forests—constrained the extent of the marginal marine embayment. Consequently, the Miocene marginal marine and continental strata are closely interbedded throughout the basin. These results refine the recent depositional models for Miocene Amazonia, and challenge the theory that marine ingressions shaped the area only during one brief time interval (late Middle-early Late Miocene) during the epoch. Much of recent literature has documented fossils of mangrove pollen, brackish-euryhaline fish and brackish-water ostracods, brackish-water trace fossil assemblages, and tidal deposits from various Miocene stratigraphic levels. Commonly, these data sets are collected from the same outcrops as those for which data sets imply freshwater conditions. We propose that these seemingly contrasting data sets can be unified, if the repetitive nature of the ingressions is considered, and all the paleoenvironmental data are presented in a detailed lithological and stratigraphical context

The Rødryggen-1 and Brorson Halvø-1 fully cored boreholes (Upper Jurassic – Lower Cretaceous), Wollaston Forland, North-East Greenland – an introduction

Two fully cored boreholes, the Rødryggen-1 and the Brorson Halvø-1, were drilled in Wollaston Forland, North-East Greenland, in 2009 and 2010, respectively. The objective was to test the stratigraphic development of the Upper Jurassic – Lower Cretaceous mud-dominated succession in two different settings within the same fault block of a developing half-graben: centrally (Rødryggen-1 borehole) and near the uplifted crest of the rotating fault block (Brorson Halvø-1 borehole). The drilled deposits are equivalent to the principal petroleum source-rock sequence of the petroliferous basins of North-West Europe, Siberia, and basins off eastern Canada and provide a new record of an important phase of marine deoxygenation in the proto-North Atlantic region

Organic geochemistry of an Upper Jurassic – Lower Cretaceous mudstone succession in a narrow graben setting, Wollaston Forland Basin, North-East Greenland

The Oxfordian–Ryazanian was a period of widespread deposition of marine organic-rich mudstones in basins formed during the early phases of the rifting that heralded the formation of the present-day North Atlantic. Occasionally, uninterrupted deposition prevailed for 20 million years or more. Today, mudstones of this time interval are found on the shelves bordering the North Atlantic and adjacent areas from Siberia to the Netherlands. Here, we report data on two fully cored boreholes from Wollaston Forland (North-East Greenland, approx. 74° N), which represent an uninterrupted succession from the upper Kimmeridgian to the Hauterivian. The boreholes record basin development at two different positions within an evolving halfgraben, located at the margin of the main rift, and thus partially detached from it. Although the overall depositional environment remained an oxygen-restricted deep-shelf setting, rifting-related changes can be followed through the succession. The Kimmeridgian was a period of eustatic highstand and records the incipient rifting with a transgressive trend straddling the transition to the lower Volgian by a gradual change from deposits with high levels of total organic carbon (TOC) and kerogen rich in allochthonous organic matter to deposits with lower TOC and a higher proportion of autochthonous organic matter. This is followed by a slight regressive trend with lower TOC and increased proportions of allochthonous organic matter until rifting culminated in the middle Volgian–Ryazanian, indicated by increasing autochthonous organic matter and higher TOC, which prevailed until basin ventilation occurred towards the end of the Ryazanian. The properties of the reactive kerogen fraction remained rather stable irrespective of TOC, underlining the effect of terrigenous matter input for TOC. These variations are also captured by biological markers and stable carbon isotopes. The deposits are very similar to equivalent successions elsewhere in the proto-North Atlantic region, albeit the proportion of terrigenous kerogen is greater

Middle Jurassic sandstone deposition in the Wandel Sea Basin: evidence from cardioceratid and kosmoceratid ammonites in the Mågensfjeld Formation in Kilen, North Greenland

Age assessments from both palynostratigraphy and macrofossil biostratigraphy of the sandstone-dominated Mågensfjeld Formation, Wandel Sea Basin, North Greenland were hitherto hampered by post-burial thermal degradation of dinoflagellate cysts and a lack of well-preserved macrofossils. The formation was previously assigned to the Upper Cretaceous based on erroneous fossil identifications. Finds of cardioceratid and kosmoceratid ammonites during recent field work now provide the first age control of the unit, demonstrating it to be of late Bajocian – late Bathonian and perhaps Callovian (Middle Jurassic) age. This makes it among the oldest Jurassic units, perhaps even Mesozoic units, recorded in Kilen, North Greenland and eastern North Greenland. Previously, the complex structural and tectonic evolution of the area was poorly understood, and the structural relation of the Mågensfjeld Formation to the surrounding Mesozoic units was a puzzle. The new age assessment simplifies the structural situation in the area significantly. Further, the inference of a large reverse fault previously required to explain the proximity of the Mågensfjeld Formation to neighbouring Jurassic units is now unnecessary. The data show that the Wandel Sea Basin was influenced by the Middle Jurassic transgression and had sufficient accommodation space for marine deposition earlier than previously thought. The unit serves as a key datapoint and analogue for possible Middle Jurassic units in adjacent offshore basins