Abstract

Seafloor processes are often destructive of biogenic remains, while at the same time promoting growth of authigenic minerals such as hematite, fluorapatite, glauconite, and chalcedony. Middle to Late Permian sedimentary rocks in the Sverdrup Basin are cool-water marine sandstones, shales, limestones, and cherts, rich in carbonate and siliceous biotic components. The authigenic minerals hematite, fluorapatite, glauconite, and chalcedony are abundant, from the interactions of nutrient elements (silica, phosphorus, and iron), with carbonate and siliceous biotas in ramp environments of variable energy and sediment accumulation rate. These authigenic phases represent, in part, faunas that are no longer preserved, and should not be viewed simply as diagenetic products.

Early middle Permian siliciclastic rocks (the Assistance Formation) contain carbonate heterozoan biotas with widespread siderite and hematite, and local void-filling phosphate, deposited under moderate sediment accumulation rates. Sponge spicules were dissolved unless encased in hematite or siderite, and incorporated in silica cement. In contrast, more slowly deposited younger middle Permian inboard cherty limestones (the lower Trold Fiord Formation) underwent frequent physical and biological reworking, resulting in dissolution of biogenic silica and precipitation of glauconite, and carbonate fluorapatite. Sediment reworking also excavated and produced rounded glauconite and phosphate clasts; much of the glauconite was then oxidized to hematite on the seafloor. Again, unless encased in phosphate, sponge spicules were dissolved and the silica precipitated as glauconite or chalcedony. Coeval deeper-water phosphatic cherty limestones (the Degerböls Formation) do, however, contain sponge spiculites. Reduced sediment reworking led to retention of silica in pore fluids and slowed dissolution of sponge spicules, resulting in local preservation of sponge spiculite facies.

Late Permian organic-rich cherts (the Lindström Formation), with prolific siliceous sponges and a less plentiful carbonate biota, accumulated relatively slowly. Sponge spicules were preserved and carbonate biota partially dissolved in these organic-rich deposits, implying that the biota had to be overwhelmingly dominated by siliceous components to overcome ambient silica undersaturation in pore fluids.

Each succession has a distinct composition depending upon the rate of sediment accumulation, the original benthic biota, and the nature and abundance of silica, phosphate, and iron in seawater at any given time. These characteristics controlled the formation of authigenic minerals and the preservation or dissolution of carbonate and silica biotas.

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