Environmental significance of foraminiferal morphogroups in Jurassic North sea deltas
Abstract The distribution of morphological groups of foraminifera has been analysed in Toarcian and Bajocian deposits of the northern North Sea and the Yorkshire coast. The deposits are referred to prodeltaic, lower delta front and interdistributary bay environments, and contain mainly or entirely agglutinating assemblages of low to intermediate diversity. A total of 33 agglutinating species are recognized in the studied material, and these are arranged into eleven morphotypes composing seven subgroups and four morphogroups. The categories are distinguished on the basis of main morphological features of the taxa, combined with their life positions and micro habitats as inferred from modern analogues. The prodelta deposits were formed in a normal saline and slightly stagnant depositional setting with foraminiferal faunas composed mainly of surficial and infaunal morphogroups. The lower delta front and interdistributary bay sediments were deposited in shallow hyposaline waters strongly dominated by an epifaunal morphogroup with a partly phytal association. A model of agglutinated morphotype distribution reveals increasing morphotype diversity (and by inference, ecological niche span) from interdistributary bay, through lower delta front, to prodeltaic environments.