Benthonic and planktonic foraminifera in relation to the Early Holocene stagnation in the Ionian Basin, Central Mediterranean

• Published in: Boreas
• Main Author: RASMUSSEN, TINE LANDER
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1991
• Subjects: Planktonic foraminifera
• Online Access: http://dx.doi.org/10.1111/j.1502-3885.1991.tb00285.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1502-3885.1991.tb00285.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1502-3885.1991.tb00285.x

The distribution patterns of benthonic and planktonic foraminifera in cores from the Ionian Basin, central Mediterranean, were investigated in relation to the deposition of sapropel S‐1. The sapropel is a dark organic‐rich sediment deposited under anoxic conditions during the last marine stagnation in the Early Holocene. The major divisions between both benthonic and planktonic faunas correspond to changes in the core lithology and coincide with the transitions between pre‐sapropel, sapropel/‘oxidized layer’ and post‐sapropel sediments. The faunal evidence shows that the oxidized layer belongs to the sapropel sequence. The planktonic faunas have the same species composition as in the sapropel sediment and the high density of planktonic species continues into the oxidized layer. The oxidized layer is devoid of a benthonic fauna or contains a ‘sapropel‐associated’ fauna composed of infaunal species with an affinity to high supply of organic material material and low oxygen. High depletion in the heavy oxygen isotope in the oxidized layer substantiates the faunal evidence. A peak in abundance of the planktonic species Globorotalia inflata at the top of the oxidized layer marks the time when turnover of the water masses ended the stagnation phase and sapropel sedimentation in the Ionian Basin at about 6000 BP. The distribution of the benthonic and planktonic foraminifera shows that the sapropel in the central part of the Ionian Basin was originally almost twice as thick as it is today. When oxygen returned to the deep sediments the top of the sapropel was oxidized to 4–7 cm below its original surface. Only the lower part of the sapropel is preserved. The remainder is now a red laminated layer, the ‘oxidized layer’.