This study evaluates changes in the environmental and climatic conditions in the Nile Delta during the late Pleistocene-Holocene based on diatom analyses extracted from the sediment of four cores obtained from the central portion of the Nile Delta. Diatom taxa were abundant to rare and poorly to well-preserved throughout the core's sediments. A total of 216 species and varieties representing 49 genera were identified from the investigated 196 samples. The most dominant planktonic genera were Aulacoseira, followed by infrequent distribution of Cyclostephanos, Cyclotella, Lindavia, Pantocsekiella, Stephanocyclus, and Stephanodiscus species. The distribution pattern of benthic diatoms represented by a frequent abundance of Staurosira, Staurosirella, and Ulnaria taxa associated with low frequencies of Craticula, Diploneis, Fragilaria, Navicula, Anomoeoneis, Caloneis, Diploneis, Gyrosigma, Pinnularia, Pseudostaurosira, Stauroneis, Nitzschia, Tryblionella, Cymatopleura, Surirella, and Campylodiscus. The epiphytic diatoms were recorded by the frequent occurrence of Encyonema and Gomphonema species besides a low ratio of Eunotia, Cocconeis, Amphora, Cymbella, Epithemia, and Rhopalodia taxa. The planktonic forms were dominant in the Mit Ghamr formation and decreased gradually in their abundance, simultaneous with the abundance of the periphytic taxa in the Bilqas formation. Most recorded diatoms preferring slightly alkaline to alkaline water occurred in the sediments, which is documented by the most abundance of the alkaliphilous diatom group. Concerning the salinity, the recognized diatom assemblage from the sediments of Mit Ghamr formation is composed mainly of a freshwater oligohalobous group associated with a low occurrence of the mesohalobous forms. In contrast, the relative abundance of oligohalobous diatoms decreased relatively, accompanied by a marked increase in the abundance of both mesohalobous and polyhalobous diatom taxa in the Bilqas formation. Based on the relative abundance of dominant and subdominant taxa and the cluster-constrained analysis, the investigated core sections are divided into several diatom zones, which revealed an interesting history of changes in paleosalinity, pH, and water level of the Nile Delta basin as the water body filled in. The variation in the relative abundance of the recognized diatom taxa revealed five phases of Nile Delta development during the Quaternary time. The first two phases are characteristic of the Mit Ghamr formation, which are distinguished by the dominance of planktonic, oligohalobous, and alkaliphilous diatoms that reflect eutrophic, slightly alkaline, moderate stands of the freshwater level during humid, warm climate. Three phases represent the Bilqas formation and are marked by an increased abundance of the periphytic taxa over the planktonic forms, with the conspicuous occurrence of brackish and coastal marine taxa. The recognized diatom assemblages revealed marked lowering of water levels with increases in salinity and alkalinity during warm-arid conditions of Holocene time.

Quaternary Diatom Records of Environmental and Climate Changes in the Nile Delta, Egypt

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发表日期：

2025年

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Abdelfattah A. Zalat

摘要

This study evaluates changes in the environmental and climatic conditions in the Nile Delta during the late Pleistocene-Holocene based on diatom analyses extracted from the sediment of four cores obtained from the central portion of the Nile Delta. Diatom taxa were abundant to rare and poorly to well-preserved throughout the core's sediments. A total of 216 species and varieties representing 49 genera were identified from the investigated 196 samples. The most dominant planktonic genera were Aulacoseira, followed by infrequent distribution of Cyclostephanos, Cyclotella, Lindavia, Pantocsekiella, Stephanocyclus, and Stephanodiscus species. The distribution pattern of benthic diatoms represented by a frequent abundance of Staurosira, Staurosirella, and Ulnaria taxa associated with low frequencies of Craticula, Diploneis, Fragilaria, Navicula, Anomoeoneis, Caloneis, Diploneis, Gyrosigma, Pinnularia, Pseudostaurosira, Stauroneis, Nitzschia, Tryblionella, Cymatopleura, Surirella, and Campylodiscus. The epiphytic diatoms were recorded by the frequent occurrence of Encyonema and Gomphonema species besides a low ratio of Eunotia, Cocconeis, Amphora, Cymbella, Epithemia, and Rhopalodia taxa. The planktonic forms were dominant in the Mit Ghamr formation and decreased gradually in their abundance, simultaneous with the abundance of the periphytic taxa in the Bilqas formation. Most recorded diatoms preferring slightly alkaline to alkaline water occurred in the sediments, which is documented by the most abundance of the alkaliphilous diatom group. Concerning the salinity, the recognized diatom assemblage from the sediments of Mit Ghamr formation is composed mainly of a freshwater oligohalobous group associated with a low occurrence of the mesohalobous forms. In contrast, the relative abundance of oligohalobous diatoms decreased relatively, accompanied by a marked increase in the abundance of both mesohalobous and polyhalobous diatom taxa in the Bilqas formation. Based on the relative abundance of dominant and subdominant taxa and the cluster-constrained analysis, the investigated core sections are divided into several diatom zones, which revealed an interesting history of changes in paleosalinity, pH, and water level of the Nile Delta basin as the water body filled in. The variation in the relative abundance of the recognized diatom taxa revealed five phases of Nile Delta development during the Quaternary time. The first two phases are characteristic of the Mit Ghamr formation, which are distinguished by the dominance of planktonic, oligohalobous, and alkaliphilous diatoms that reflect eutrophic, slightly alkaline, moderate stands of the freshwater level during humid, warm climate. Three phases represent the Bilqas formation and are marked by an increased abundance of the periphytic taxa over the planktonic forms, with the conspicuous occurrence of brackish and coastal marine taxa. The recognized diatom assemblages revealed marked lowering of water levels with increases in salinity and alkalinity during warm-arid conditions of Holocene time.