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Palynology as a palaeoenvironmental indicator in the Brent Group, northern North Sea

Abstract The Brent Group of the northern North Sea can be subdivided into a series of 12 assemblage units on the basis of palynomorph and kerogen abundances. These assemblages, which can be identified on a regional basis, have been recognized extensively throughout wells of the Brent Group depositional area. They represent changes in the environment, kerogen source and depositional setting and can be linked to lithostratigraphical units. Changes in assemblages through the Brent Group reflect an initial restricted marine environment followed by progradation in a regressive regime. Progradation ceased and the maximum point of regression occurred within the ‘Mid’ Ness Formation, after which deposition occurred within an abandonment and transgressive regime. These features are defined by palynological data, thus providing input into the regional understanding of Brent Group deposition. The palynological assemblages of the Brent Group are illustrated with reference to two wells: 211/18a-A31 from the Thistle Field and 3/3-5A from the Ninian Field. Palynomorph assemblages within the Brent Group are largely facies controlled and have an intimate relationship with lithofacies. The identification of these assemblages, therefore, allows for the positive identification of individual lithostratigraphical and reservoir units, particularly in problematic sections where stratigraphical interpretations based on other disciplines are hampered by faulting and truncation or lack of conventional core material and wireline log data, particularly where sidewall core samples are available.