Facies Controlled Distribution of Foraminifera in the Jurassic North Sea Basin
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Foraminiferal faunas have been analyzed from three localities of the Jurassic North Sea basin: the Statf jord area — Pliensbachian to Bajocian; the Yorkshire coast — Bajocian; north Scotland — Sinemurian, Pliensbachian and Callovian. The various assemblages are defined by distribution of suborders, genera, species and diversities. Based on these parameters and sedimentary f acies data the assemblages are attributed to various marine shelf and deltaic conditions.
Organic-lean shelf deposits contain high diversity assemblages dominated by species of Marginulina, Lenticulina, and Dentalina. Locally high frequency of Ammodiscus as per suggests increased terrestrial influence. Organic-rich shelf sediments show strong dominance of suborder Textulariina and high abundance of Haplophragmoides pygmaeus.
Distal deltaic strata contain almost exclusively Textulariina, which forms assemblages having low to intermediate diversity and dominance of Trochammina, Verneuilinoides and Reophax. Proximal deltaic assemblages in the Statf jord area consist of Textulariina, while on the Yorkshire coast they locally include significant amounts of Lagenina and Spirillinina in addition to the agglutinated component. At both places the diversity is extremely low and Ammodiscus yonsnabensis is most common.
Comparison of the studied assemblages reveals that environments divergent from those of a normal marine shelf potentially produce low diversity faunas consisting mainly or entirely of Textulariina, as demonstrated in organic-rich shelf, proximal deltaic, and distal deltaic facies. Assemblages from these facies types show, however, marked differences in their generic composition.
KeywordsTotal Organic Carbon Middle Jurassic Total Organic Carbon Content Foraminiferal Assemblage Delta Front
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