Relative sea-level changes recorded by paralic liptinite-enriched coal facies cycles, Middle Jurassic Muslingebjerg Formation, Hochstetter Forland, Northeast Greenland

The Middle Jurassic Muslingebjerg Formation of Hochstetter Forland, Northeast Greenland, consists of a succession of shallow marine sandstones encasing four coal seams formed in low-lying coastal mires. The seams are up to 3.45 m thick and contain coal facies cycles with high liptinite contents (up to 70 vol%). The cycles generally start with huminite-rich bright or banded coal and end with dull coal or clayey coal/coaly claystone. The dull coals are characterized by a high proportion of liptinite, commonly resinite, and often mineral matter. Liptodetrinite, resinite and cutinite dominate the liptinite maceral group. Similarity in the relative proportions of the liptinite macerals in the bright and dull coals and the general association of bright coal and dull coal with a high resinite concentration suggest, that the dull coals represent a residue after selective removal of ligno-cellulosic tissues in the precursor peat of primarily the bright lithotype. The clayey coal/coaly claystone lithotypes have high contents of mineral matter and commonly contain alginite and pyrite. Occurrence of pyrite in levels with high diasterane C₂₇C₂₉ ratios and sometimes also alginite in the clayey coal/coaly claystone lithotypes, indicates a marine influence during flooding of the mires. This suggests a causal link between base-level rise in the coastal mires and relative sea-level rise. Accommodation space available for thick peat accumulations was governed by overall relative sea-level rise and the dulling-upward cycles record outpacing of peat accumulation due to accelerated rise in base level/relative sea level. The Muslingebjerg Formation consists of four depositional sequences, beginning with a thick coal seam resting on a sequence boundary. Peat accumulation reflects onset of base-level rise in the coastal area and the coals represent the lower part of the transgressive systems tract. The overlying shoreface sandstones form the upper part of the transgressive systems tract and a progradational highstand systems tract. Alternatively the two lower seams in the succession may form a transgressive-regressive couplet separated by a lagoonal sandstone split. In this case a sequence boundary occurs at the top of the upper regressive seam. The dulling-upward cycles within the coal seams represent parasequences or possibly higher order sequences. Minimum age-estimates suggest that they accumulated over 4000–11000 yr.