The relative roles of CO2 and palaeogeography in determining Late Miocene climate: results from a terrestrial model-data comparison

The Late Miocene (∼11.6–5.3 Ma) palaeorecord provides evidence for a warmer and wetter climate than that of today and there is uncertainty in the palaeo-CO2 record of at least 150 ppmv. We present results from fully coupled atmosphere-ocean-vegetation simulations for the Late Miocene that examine the relative roles of palaeogeography (topography and ice sheet geometry) and CO2 concentration in the determination of Late Miocene climate through comprehensive terrestrial model-data comparisons. Assuming that the data accurately reflects the Late Miocene climate, and that the Late Miocene palaeogeographic reconstruction used in the model is robust, then results indicate that the proxy-derived precipitation differences between the Late Miocene and modern can be largely accounted for by the palaeogeographic changes alone. However, the proxy-derived temperatures differences between the Late Miocene and modern can only begin to be accounted for if we assume a palaeo-CO2 concentration towards the higher end of the range of estimates

La macroflora oligocena de la cuenca de Cervera, Lérida, España (Colección del Museu Comarcal de Cervera)

This paper is the follow-up of another study of the Oligocene macroflora from Cervera (Ebro Basin, Spain), started with the 'Madern Collection' from the Museu de Geologia de Barcelona (Sanz de Siria, 1992). The present paper analyses 226 specimen from the Museu Comarcal de Cervera. 29 species, not mentioned before, are included and 3 new species of the tertiary flora are established. A likely model of the vegetation existing in the area in the low Oligocene is established by comparision with the models existing today of similar content and structure. Similar models are presently located in tropical regions between 15o and 25o latitude north. The main vegetal community that has been found correspond to the tropical deciduous forest. In upper, wetter levels, evergreen forest with laurisilva communities appear. The climate in the low Oligocene in the region was probably of the tropicalk kind, with a long dry period followed by a rain period. The average temperature would be around 22o-26o. Key words: Paleobotany, Macroflora, Oligocene, Paleoecology, Ebro Basin, Cervera, Spain, Museu Comarcal de Cervera.En el presente trabajo se prosigue el estudio de la flora oligocena de Cervera (Lérida, España) iniciado con la 'Colección Madern' del Museu de Geologia de Barcelona (Sanz de Siria, 1992). Se estudian ahora 226 ejemplares depositados en el Museu Comarcal de Cervera. Se menciona la presencia de 29 especies no citadas anteriormente y se crean 3 especies nuevas para la flora terciaria. Asimismo, se determina el posible modelo de vegetación existente en la zona durante el Oligoceno, por comparación con los modelos actuales de parecida composición y estructura. Modelos similares se localizan actualmente en regiones tropicales, entre los 15o y los 25o de latitud Norte. La principal comunidad vegetal encontrada corresponde a bosques tropicales deciduos. En niveles superiores más húmedos aparecen bosques perennifolios de tipo laurisilva. El clima de la región, durante el Oligoceno inferior, parece que fue de tipo tropical, con una estación seca prolongada seguida de un período de lluvias. Las temperaturas medias anuales podrían situarse entre los 22o-26o. Palabras clave: Paleobotánica, Macroflora, Oligoceno, Paleoecología, Cuenca del Ebro, España, Museu Comarcal de Cervera

Estudio paleoambiental de nuevos yacimientos de plantas y vertebrados de la “Unidad Intermedia” del Mioceno Medio de la cuenca de Madrid.

Se dan a conocer los vegetales fósiles (macrorrestos foliares, frutos y palinomorfos) y una asociación de microvertebrados encontrados en yacimientos descubiertos en la “Unidad Intermedia” del Mioceno de Madrid. Los restos paleobotánicos y palinológicos se encuentran en cinco yacimientos, mientras que los de microvertebrados aparecen en otro distinto, cercano a los anteriores y estratigráficamente por encima de éstos. En general la palinoflora identificada es bastante uniforme en todos los yacimientos; no así la macroflora que presenta peculiaridades en alguno de ellos. Los datos paleobotánicos ponen de manifiesto una vegetación muy diversa con géneros y especies característicos de medios montanos, abanicos aluviales, márgenes lacustre-palustres y lagunares. Los resultados del estudio de la macroflora y de los palinomorfos se representan y ubican en un perfil sintético y en un bloque diagrama esquemático. [ABSTRACT] Some palaeobotanical assemblages (spores, pollen, leaves, seeds and fruits) and microvertebrates found in the “Unidad intermedia” from middle Miocene deposits of the Madrid basin are studied. The fossil plants appear in five sites, and the vertebrate fossils in other site, near the formers, but stratigraphically above these. The palynological assemblages are quite similar in all the sites, but the macroremains associations present taphonomic peculiarities in some of them.The fossil plants identified show some elements of acuatic, flooded, riparian and of river banks environments with some deciduous and evergreen forest taxa. The palaeobotanical data are symbolized and ecologically located in a syntetic section and in a diagram. The different environments which had been delimited are represented. The vertebrate fossil assemblage is made of two taxa of Reptilia (one Lacertidae and one Anguidae), and, among the mammals, the Sciuridae Heteroxerus cf. rubricati, the Gliridae cf. Armantomys sp., the Cricetidae Megacricetodon collongensis - crusafonti, one Insectivora and some remains of Lagomorpha. From a biostratigraphical point of view, this faunal assemblage may corresponds to the Middle Miocene, to the Upper Aragonian, but not to latest among the Zones F, G1 and G2 (sensu Daams and Freudenthal, 1988a) that can be correlated with the NM 6 Unit (sensu Mein, 1975). This fauna suggests a mainly open environment and a relatively dry climate

A preliminary review of the biostratigraphy of the uppermost Permian, Triassic and lowermost Jurassic of Gondwanaland

Main articleThis review pager was born out of a desire to visualize in some detail the picture of the evolving Gondwana Triassic landscape and the story of life and ecology upon it; a desire to provide a general setting in which to view the details of the work in which we are actively involved at the present-the macro flora (H.M.A.) and microflora (J. M.A.) of the Molteno 'Formation' of the Karroo Basin of South Africa.Non

Evidence for coal forest refugia in the seasonally dry Pennsylvanian tropical lowlands of the Illinois Basin, USA

The Moscovian plant macroflora at Cottage Grove southeastern Illinois, USA, is a key example of Pennsylvanian (323–299 Million years ago) dryland vegetation. There is currently no palynological data from the same stratigraphic horizons as the plant macrofossils, leaves and other vegetative and reproductive structures, at this locality. Consequently, reconstructions of the standing vegetation at Cottage Grove from these sediments lack the complementary information and a more regional perspective that can be provided by sporomorphs (prepollen, pollen, megaspores and spores). In order to provide this, we have analysed the composition of fossil sporomorph assemblages in two rock samples taken from macrofossil-bearing inter-coal shale at Cottage Grove. Our palynological data differ considerably in composition and in the dominance-diversity profile from the macrofossil vegetation at this locality. Walchian conifers and pteridosperms are common elements in the macroflora, but are absent in the sporomorph assemblages. Reversely, the sporomorph assemblages at Cottage Grove comprise 17 spore taxa (∼16% and ∼63% of the total assemblages) that are known from the lycopsid orders Isoetales, Lepidodendrales and Selaginallales, while Cottage Grove’s macrofloral record fails to capture evidence of a considerable population of coal forest lycopsids. We interpret our results as evidence that the Pennsylvanian dryland glacial landscape at Cottage Grove included fragmented populations of wetland plants living in refugia

The late Miocene macroflora of the La Cerdaña Basin, Eastern Pirenees, Spain. Towards a Synthesis

The fossil plant-bearing beds of the Tortonian (late Miocene) intramontane basin of La Cerdanya (Eastern Pyrenees, Catalonia, Spain) have been investigated for more than a century, and 165 species from 12 outcrops have been described in previous publications. The sediments with rich plant fossil assemblages, which correspond to lacustrine diatomitic deposits, contain large numbers of plant remains, mainly leaf compressions and impressions. These assemblages are well preserved, a consequence of the rapid accumulation of plant remains in the sediments of the basin's ancient lake, and the often close proximity of its shores to wetland and upland vegetation. This paper provides a comprehensive taxonomic and nomenclatural review of the historic and new collections of late Miocene macroflora for the La Cerdanya Basin. Examination of the newer materials allowed emendments to be made to the diagnoses ofAbies saportana, Acer pyrenakum,Alnus occidentalis, Quercus hispanka and Tilia vidali provided by REROLLE for the basin at the end of the 19th century. In addition, 24 species of vascular plants are identified for the basin for the first time, including one horsetail, three conifers, 19 arboreal or bushy dicotyledonous angiosperms, and one monocotyledonous angiosperm. Indeed, this is the first time that Cedrela helkonia (UNGER) KNOBLOCH, Decodon sp„ Hedera cf multinervis KOLAKOVSKII, Mahonia cf pseudosimplex KVACEK & WALTHER, Smilax cf. aspera L. vm.fossilis and Ulmus cf. plurinervia UNGER have been recorded anywhere in the Iberian Peninsula. The La Cerdanya Basin plant assemblages of the late Miocene mainly consisted of conifers and deciduous broadleaved taxa of Arctotertiary origin; evergreen Palaeotropical elements were less well represented. This flora is similar to those recorded at coeval sites in northern Greece, northern Italy and central and eastern France. Within the Iberian Peninsula, the late Miocene macroflora reported for the nearby Seu d'Urgell Basin is the most similar

Experiments using an artificial stream to investigate the seasonal growth of chalk-stream algae

Research into the production ecology of chalk streams using a large artificial recirculating stream is described. Physical chemical processes including calcium and inorganic phosphate levels, and exchange of gaseous carbon dioxide in both a simple closed system and a circulating system with gravel substrate have been monitored in both light and dark conditions. Further experiments were concerned with the seasonal changes in algal growth over the gravel substrate with constant water velocities and replenishment. The algal population, composed mainly of the diatoms Achnanthes minutissima, Meridion circulare, Nitzschia fonticola and Synedra ulna reached a peak in mid May and declined rapidly during June. Concentrations of phosphate phosphorus fell as the diatoms grew but was not thought to limit growth. Silicate concentrations followed the diatom cycle closely but never fell below 0.8 mg/l Si. It is possible that one of the nutrients may have been limiting the rate of growth due to steep diffusion gradients through the algal mat. In the last summer and autumn a hard calcareous crust composed of the green alga Gongrosira incrustans and the blue green alga Homeothrix varians , developed. The channel stream is compared with the natural conditions found in chalk streams

Estudio paleoecológico y paleoclimático de la macroflora oligocena de Cervera (Lleida, España)

After the taxonomic revision of the macroflora from Cervera (Lleida, Spain) of the 'Martí Madern' (Museu de Geologia de Barcelona and Museu Comarcal de Cervera collections). We present here their palaeoecological and palaeoclimatic study. A likely model of the vegetation existing in the area in the low Oligocene is established by comparison with the models existing today of similar content and structure. Similar models are presently located in tropical regions about 20o latitude North. The main vegetal community that has been found corresponds to the tropical deciduous forest. In superior wetter levels, evergreen forest with laurisilva communities appears. The climate in the early Oligocene in the region was probably of the tropical kind, with a long dry period followed by a rain period. The average temperature would be around 22o - 26o. Key words: Palaeobotany, Macroflora, Oligocene, Palaeoecology, Palaeoclimatology, Ebro Basin, Cervera, Spain.Este trabajo es continuación de las revisiones taxonómicas realizadas de las colecciones de macroflora fósil 'Martí Madern', del Museu se Geologia de Barcelona y del Museu Comarcal de Cervera. Partiendo del estudio del conjunto de taxones fósiles hallado, se obtienen datos paleoecológicos y paleoclimáticos acerca de la cuenca y se intenta establecer el modelo de vegetación que debió existir durante el Oligoceno en esa zona. La principal comunidad vegetal presente correspondió a bosques deciduos de tipo tropical. En niveles superiores se ubicaron bosques perennifolios semejantes a las actuales laurisilvas. El clima en la región en el Oligoceno inferior fue de tipo tropical, con una estación seca prolongada a la que seguía un período de lluvias. Las temperaturas medias podían situarse en torno a los 22o-26o. Palabras clave: Paleobótanica, Macroflora, Oligoceno, Paleoecología, Paleoclimatología, Cuenca del Ebro, Cervera, España