Diagenesis of Holocene Beachrock in Northeastern Brazil: Petrology, Isotopic Evidence and Age

Q3 Earth and Planetary Sciences Quaternary and Environmental Geosciences Pub Date : 2018-10-09 DOI:10.5380/ABEQUA.V9I2.53011
Antônio Vicente Ferreira Júnior, Bárbara Carla Ehrhardt Paes, M. M. Vieira, A. Sial, V. Neumann
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引用次数: 5

Abstract

This work aims to understand beachrock formation during Holocene through petrology, geochemistry and dating of a core located 5,43m deep in relation to present-day sea-level in the Piedade Beach in Jaboatao dos Guararapes- PE. The core is located 143 meters distant from the coast line towards mainland. Four lithofacies have been identified, taking into account differences in texture and sedimentary structures. The framework grain size ranges from medium to very coarse sand, indicating variations in depositional energy. Petrographic data indicate that the beachrocks have values of 64.23% to 70.69% of framework composed of quartz grains. Carbonate cement (represents 13.5%) consisting of high magnesium calcite surrounding grains as isopachous fringe (4.15% to 11.95%), micritic cement (0.60% to 6.42%) and equant cement (0.26% to 7.01%), indicates marine environment precipitation. The results of the isotopic composition of carbon and oxygen present valuesof 3.09‰ to 3.89‰, with an average of 3.63‰ to δ 13 C PDB and of -0.91‰ to 0.96‰, with an average of 0.54‰ to δ 18 O PDB, suggesting that the cement is formed in a shallow marine environment with freshwater influence. The values obtained in paleotemperature vary from 21oC to 30oC, with an average of 23oC, with little variation indicating precipitation in a shallow water environment. In the study area, the beachrocks are indicators of sea level and the results suggest that between 7.509 years B.P. and 5982 years B.P. there was a marine transgression process, with sea level 9.18 m lower than the current sea level.
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巴西东北部全新世Beachrock的成岩作用:岩石学、同位素证据和时代
这项工作旨在通过岩石学、地球化学和测年来了解全新世海滩岩石的形成,该岩芯位于距离海岸线143米的地方,距离海岸线向大陆。考虑到质地和沉积结构的差异,已确定了四种岩相。骨架粒度范围从中粗砂到极粗砂,表明沉积能量的变化。岩石学数据表明,海滩岩石由石英颗粒组成的骨架的价值为64.23%至70.69%。碳酸盐胶结物(占13.5%)由高镁方解石组成,周围颗粒为等厚条纹(4.15%至11.95%)、微晶胶结物(0.60%至6.42%)和均匀胶结物(0.26%至7.01%),表明存在海洋环境降水。碳和氧同位素组成的值为3.09‰至3.89‰,与δ13C PDB的平均值为3.63‰;与δ18O PDB的比值为-0.91‰至0.96‰,平均值为0.54‰。获得的古温度值从21摄氏度到30摄氏度不等,平均为23摄氏度,变化不大,表明浅水环境中有降水。在研究区域,海滩岩石是海平面的指标,结果表明,在7.509年B.P.至5982年B.P.之间,存在海侵过程,海平面比当前海平面低9.18m。
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来源期刊
Quaternary and Environmental Geosciences
Quaternary and Environmental Geosciences Earth and Planetary Sciences-Earth-Surface Processes
CiteScore
0.40
自引率
0.00%
发文量
0
审稿时长
24 weeks
期刊介绍: Quaternary and Environmental Geosciences (QEG) is for the publication of unpublished works in the areas of quaternary and environmental geosciences. QEG aims to publish high quality works on all Quaternary areas and environmental geosciences, from laboratory techniques to synthesis works. It aims to publish works from areas as diverse as climate variability and change, paleovegetation, paleoclimate and paleoenvironments, coastal geology and geomorphology, sea level variations, neotectonics, continental morphogenetic processes and products, sediment and soil geochemistry, geological hazards and paleoenvironment. , relationships between natural and anthropic geological processes, among others. We emphasize interest in interdisciplinary work. We discourage the publication of works that are not clearly linked with the Quaternary or the Environmental Geosciences. The main criterion for acceptance of the papers is their quality, originality, significance and interest to a broad regional to international community.
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