Loading...
7 results
Search Results
Now showing 1 - 7 of 7
- Detection of speleothem growth bands with an open source geophysical softwarePublication . Veiga-Pires, C.; Moura, Delminda; Luis, JoaquimSpeleothem growth bands are commonly referred as one of the parameters that are used for paleoclimate reconstructions. Accordingly, this work presents a new tool for detecting these bands based on the gray-scale image of the speleothem using the Mirone open source geophysical software.
- A first last glacial maximum to younger dryas stalagmite record from southern PortugalPublication . Veiga-Pires, C.; Ghaleb, Bassam; Hélie, Jean-François; Moura, Delminda; Luis, Joaquim; Hillaire-Marcel, C.A newly launched research program permitted the sampling of speleothem deposit in the Algarve area (Southern Portugal) with the primary objective of constraining the ages of past humid intervals in the area from U-series measurements.
- First isotopic records from stalagmites in Algarve (South Portugal)Publication . Veiga-Pires, C.; Moura, Delminda; Luis, Joaquim; Varela, J.; Ghaleb, Bassam; Hélie, Jean-François; Hillaire-Marcel, C.Os espeleotemas representam registos paleoclimáticos continentais de alta resolução e estão a ser cada vez mais estudos para fins de reconstrução climática de períodos não afectados por acções antropogénicas. Na região do Algarve (Sul de Portugal), a existência de formações carbonatadas do Jurássico e Cretácico permitiu um desenvolvimento de sistemas cársicos onde se encontram actualmente estruturas estalagmíticas. Neste estudo preliminar realizado sobre estas estalagmites da região do Algarve, foram realizadas datações U/Th e análises de isótopos estáveis que demonstram pela primeira vez a possibilidade de obter registos isotópicos continentais representativos do paleoclima do extremo Sudoeste da Península Ibérica.
- An open source geophysical software for studying speleothem growth bands and comparing with a reference curve: MironePublication . Veiga-Pires, C.; Coelho, Catarina; Moura, Delminda; Luis, JoaquimSpeleothem growth bands are commonly referred as one of the parameters that are used for paleoclimate reconstructions. Accordingly, this work presents a new tool for detecting these bands based on the gray-scale image of the speleothem using the Mirone open source geophysical software. This program has initially been developed for working on georeferenciated images for geophysical studies, as for instance for recognizing paleomagnetic inversions from deep-sea sediments. This recognition based on gridded images is very similar to what is needed for the recognition and detection of speleothem growth bands.
- A first last glacial maximum stalagmite record from southern PortugalPublication . Veiga-Pires, C.; Ghaleb, Bassam; Hélie, Jean-François; Moura, Delminda; Luis, Joaquim; Hillaire-Marcel, C.A newly launched research program permitted the sampling of speleothem deposits in the Algarve area (Southern Portugal). Unfortunately, this stalagmite yielded very small amounts of U (~ 20 ppb), making the setting of a U-series chronology difficult due to both the relative importance of a detrital contaminating fraction and the lack of precision on overall 230Th measurements. Nevertheless, based on the top and most recent sample, we extracted a first order estimate for the 230Th/232Th ratio of the contaminating fraction and for its 234U/232Th and 238U/232Th ratios as well, assuming a secular equilibrium between 234U and 238U in this fraction.
- Algarve: a study case for global vs regional climatic changes in mid latitude estuaries during the HolocenePublication . Veiga-Pires, C.; Mestre, Nélia; Moura, Delminda; Luis, Joaquim; Boski, T.Located at the extreme southwestern end of the Iberian Peninsula, in the South of Portugal, the Algarve province is bordered to the north by the Alentejo province, to the east by the Guadiana River, and to the west and south by the Atlantic Ocean. Its coastal region can be divided into two different sectors: the eastern sector, which is mainly made of barrier island and lagoon system named the Ria Formosa, and the western sector mainly represented by clastic and carbonated cliffs. In each sector, we sampled long and short sedimentary cores (ca. 30m and 3m, respectively) in two different estuaries. Therefore, the different sedimentary records obtained from the four estuaries should permit to identify global vs. west-eastern regional climatic changes through the observation of several proxies. Two of these proxies are sediment color and magnetic susceptibility, which have been acquired every five centimeters along core depth, using the Colortron II spectrophotometer and SM-20 magneto-susceptometer, respectively. Sediment surfaces of short cores were also digitized using the Mustek 1200 A3 PRO Scanner. Furthermore, short cores have been sampled every five centimeters along depth in order to analyze the sediment for its major and minor elements content, its organic carbon content, and its granulometry and mineralogy. Some shell fragments have also been sampled and sent for radiocarbon radiometry or AMS dating, allowing therefore constructing some absolute chronologies for the several cores. Some relative chronologies based on digital color profiles are also being used in order to correlate sedimentary sequences between cores. All the cores are mainly composed of clay, with the existence of soil horizons at the top of the cores and frequent sand layers towards their base. Several element profiles along depths are compared, namely those regarding Sr, Ca, F, Ba, Al and Ti, as well as their ratios. First results indicate that geochemical and color data allow to identify similar sequences from west to east probably related to major climate episodes. Although, pronounced differences in mineralogy and accumulation rates from on site to another are probably due to differences, respectively, in the geochemistry of the drainage basin substratum and in the flow rate of the rivers, and therefore to local precipitation. We acknowledge FEDER and OE that financed this study through the Portuguese Foundation for Science and Technology (FCT) (POCTI/CTA/39733/2001).
- An attempt to develop spectrophotometry as a proxy for sedimentary studies in estuarine environmentsPublication . Veiga-Pires, C.; Mestre, Nélia; Moura, Delminda; Luis, Joaquim; Boski, T.In deep-sea sediment studies, reflectance has been used as a proxy for high vs. low productivity intervals for several years. This value of the white-black scale is obtained through the use of spectrophotometers when using the CIE Lab color system, which also gives values on green-red and blue-yellow scales. In estuarine/continental sediment studies, color data are still often based on Munsell Table which does not allow to obtain numeric and continuous data and which is biased by the observer’s choice.