Sedimentology,palaeoenvironments and biostratigraphy of the Pliocene–Pleistocene carbonate platform of Grande‐Terre (Guadeloupe,Lesser Antilles forearc)

Pliocene and Pleistocene deposits from Grande‐Terre (Guadeloupe archipelago, French Lesser Antilles) provide a remarkable example of an isolated carbonate system built in an active margin setting, with sedimentation controlled by both rapid sea‐level changes and tectonic movements. Based on new field, sedimentological and palaeontological analyses, these deposits have been organized into four sedimentary sequences (S1 to S4) separated by three subaerial erosion surfaces (SB0, SB1 and SB2). Sequences S1 and S2 (‘Calcaires inférieurs à rhodolithes’) deposited during the Late Zanclean to Early Gelasian (planktonic foraminiferal Zones PL2 to PL5) in low subsidence conditions, on a distally steepened ramp dipping eastward. Red algal‐rich deposits, which dominate the western part of Grande‐Terre, change to planktonic foraminifer‐rich deposits eastward. Vertical movements of tens of metres were responsible for the formation of SB0 and SB1. Sequence S3 (‘Formation volcano‐sédimentaire’, ‘Calcaires supérieurs à rhodolithes’ and ‘Calcaires à Agaricia’) was deposited during the Late Piacenzian to Early Calabrian (Zones PL5 to PT1a) on a distally steepened, red algal‐dominated ramp that changes upward into a homoclinal, coral‐dominated ramp. Deposition of Sequence S3 occurred during a eustatic cycle in quiet tectonic conditions. Its uppermost boundary, the major erosion surface SB2, is related to the Cala1 eustatic sea‐level fall. Finally, Sequence S4 (‘Calcaires à Acropora’) probably formed during the Calabrian, developing as a coral‐dominated platform during a eustatic cycle in quiet tectonic conditions. The final emergence of the island could then have occurred in Late Calabrian times.     

Holocene palaeoenvironments at the timberline in the French Alps—a multidisciplinary approach

An attempt is made to reconstruct the palaeoenvironmental Holocene history at the timberline on the basis of the analysis of various palaeoecological proxy indicators available on a marshy area and its surroundings in the Taillefer Massif (Isère. France). The multidisciplinary approach involves analyses of pollen assemblages. plant macrofossils, coleoptera remains. subfossil trunks extracted from lakes or peat-bogs. and charcoals derived from the surrounding soils. This enables definition of the respective roles of five forest taxa ( Pinus uncinata Mill., Pinus cembra L., Larix decidua Mill., Abies alba Mill, and Picea abies L. Karsten) in the evolution of high altitude forests during the Holocene. Pinus uncinata was present on the plateau throughout the Holocene. Larix and Pinus cembra were present only during two periods: 7500-5000 BP and 3500-2000 BP. All trees disappeared from the plateau at about 2000 BP, while, at lower altitude. Abies was replaced by Picea. The action of both climate and early human impact can explain these changes.     

Columnar calcites as testimony of diagenetic overprinting at the boundary between Upper Tournaisian dolomites and limestones (Belgium): multiple origins for apparently similar features

In topographic flat areas, sedimentary settings may vary from one outcrop to another. In these settings, calcite precipitates may yield macroscopically similar columnar features, although they are products of different sedimentary or diagenetic processes. Three columnar calcite crystal fabrics, i.e. rosettes, palisade crusts and macro-columnar crystal fans, have been differentiated near and at the contact between Upper Tournaisian dolomites and limestones along the southern margin of the Brabant-Wales Palaeohigh. Their petrographic characteristics, and geochemical and fluid inclusion data provide information on the (dia)genetic processes involved. Rosettes composed of non-luminescent columnar calcite crystal fans (1–5 cm in diameter) developed on top of one another, forming discrete horizons in repetitive sedimentary cycles. The cycles consist of three horizons: (I) a basal horizon with fragments from the underlying horizon, (II) a micrite/microspar horizon with incipient glaebules, (III) an upper horizon consisting of calcite rosettes, with desiccation features. The petrographical features and δ¹⁸O signatures of −10·0 to −5·5‰ and δ¹³C values of −5·5 to −3·2‰ support either evaporative growth, an evaporative pedogenic origin, or overprinting of marine precipitates. Palisade crusts, composed of a few to 10 mm long non-luminescent calcite crystals, coat palaeokarst cavities. Successive palisade growth-stages occur which are separated by thin laminae of micrite or detrital quartz, displaying a geopetal arrangement. Palisade crusts are interpreted as intra-Mississippian speleothems. This interpretation is supported by their petrographic characteristics and isotopic signature (δ¹⁸O = −8·7 to −6·5‰ and δ¹³C = −4·8 to −2·5‰). Macro-columnar crystals, 1–50 cm long, developed mainly perpendicular to cavity walls and dolomite clasts. Crystal growth stages in the macro-columnar crystals are missing. δ¹⁸O values vary between −16·4 and −6·8‰ and δ¹³C values between −5·2 and −0·9‰. These features possibly support a late diagenetic high temperature precipitation in relation to hydrothermal karstification.     

Nonparametric Estimates of the Sea State Bias for the Jason-1 Radar Altimeter

The Jason-1 sea state bias (SSB) is analyzed in depth from the first year of GDR products. Compared to previous missions, this work benefits from two aspects of the empirical determination of the SSB from the altimetric data themselves. First, from a methodological point of view, a nonparametric technique (NP) has been developed and largely tested on TOPEX/Poseidon 1, GFO and Envisat data. The NP estimator has proven to be a useful tool in the SSB estimation, and it is now mature enough to be used for a refined analysis. On the other hand, the SSB can be extracted from three different data sets (crossovers, collinear data, and residuals) with different characteristics. It is then possible to cross calibrate various estimations of the SSB models and to determine the most accurate one. A systematic comparison is made between these different estimates for the Jason-1 altimeter. The collinear and crossover data sets yield very similar estimates despite their difference of spatial and temporal distributions. These SSB models assure consistency with the TOPEX mission when comparing Jason-1 and TOPEX residuals during the tandem phase. Thanks to the present work, the impact of the short wavelengths filtering on the SSB estimation is evidenced. More generally, our understanding of potential errors affecting the sea surface height and their impact onto the SSB estimation is also improved.