Siliceous fossils in sediments of the Ibero-Moroccan shelf and adjacent deep sea plains

• Main Author: Schrader, Hans-Jürgen
• Format: Other/Unknown Material
• Language: English
• Published: PANGAEA 1972
• Subjects: Atlantische Kuppenfahrten 1967/1-3; Cape Blanc/Meteor Bank/Portugal; GIK/IfG; Gravity corer (Kiel type); Institute for Geosciences; Christian Albrechts University; Kiel; KAL; Kasten corer; M1048B; M8; M8_004-2; M8_008-3; M8_016-2; M8_017-2; M8_018-4; M8_020-2; M8_031-2; M8_057-2; M8_058-2; M8/16-2 M8016B; M8004B; M8008C; M8017B; M8018B; M8031A; M8057B; M8058B; Meteor (1964); North Atlantic Ocean; SL; North Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.548410; https://doi.org/10.1594/PANGAEA.548410

Siliceous skeletons were investigated in two core profiles (9 cores), one off Cap de Sines, Portugal and the other off Cap de Mazagan, Morocco. Total number of skeletons was determined per gram of dried sediment at different core depths of the fraction >21 µ. Results are compared with a core profile from the Arabian Sea. Diatoms are of four groups: (A) marine-planktonic, B) marine-benthic, (C) freshwater and (D) Tertiary species (Trinacria e.g.). Species from groups (B), (C) and (D) are redeposited in all cores taken at a water depth of greater than 100 m. Small numbers of Silicoflagellates and Radiolarians were found throughout the cores from the Ibero-Moroccan shelf. In the Arabian Sea core, Radiolarians were concentrated in distinct horizons in which Tertiary material was redeposited (40-50, 140-150, 250-260 cm). The number of siliceous skeletons per gram of dried sediment decreases more or less rapidly with increasing depth in all cores. Whereas about 2500 skeletons were found in sediments close to the surface, approximately 100 skeletons only were found in deeper (>40 cm) layers. Deeper horizons with more than 100 specimens were interpreted as redeposited material. This sediment contained robust skeletons, resistant against dissolution, as well as benthic and Tertiary material. The decrease of siliceous skeletons relative to core depth depends upon the sedimentation rate. Where the sedimentation rate is high, the opal dissolution zone extends down to 30-60 cm, where the sedimentation rate is low, it is located at 10-30 cm. Below these depths opals disappears. These zones also have approximately the same age (4000 years) everywhere. Siliceous skeletons dissolve differentially, first the Silicoflagellates disappear, second the Diatoms, third the Radiolarians, and fourth the Sponge Spicules. Surface structure of skeletons from near the opal dissolution zones are similar to those of skeletons treated with NaOH. Tertiary diatoms (Trinacria e. g.) and benthic diatoms (Campylodiscus e.g.) dissolve less ...