Basin analysis and sequence stratigraphy of the synrift Tilje Formation (Lower Jurassic), Halten terrace giant oil and gas fields, offshore mid-Norway

Abstract

ABSTRACT The stratigraphic organization of early synrift clastic successions is controlled by the rates of tectonic subsidence and the growth of the master faults, which, coupled with eustatic base level change, control the generation of accommodation. The 100- to 300-m (328- to 984.2-ft)-thick, highly heterolithic Lower Jurassic upper Åre and Tilje succession (Halten terrace, offshore Norway) represents an example of ancient synrift deposits that accumulated within a north–northeast-south–southwest-oriented structurally controlled embayment where sedimentation was strongly influenced by tidal currents but with significant river influence and minor wave action, except in exposed distal locations. The shallowing-upward, deltaic Tilje succession was deposited near the lowstand shoreline. The Tilje Formation consists of two tabular second-order sequences, each of which overlies structurally influenced sequence boundaries (SB2 and SB3 in local terminology) associated with rift-related tectonic pulses. The first pulse led to formation of SB2 (shallow incision into the Åre Formation) and caused a regional geomorphological change of the basin from an open, wave-dominated setting (upper Åre Formation) to a funnel-shaped, tide-dominated setting (Tilje Formation), in which the lower sequence 2 accumulated. Sequence 3 rests erosively on sequence 2 and is characterized by proximal tidal deposits showing at least two main oblique to axial fluvial input points (north–northwest and northeast), with an increase in wave influence and deepening toward the south. Local rapid subsidence of elongated, narrow hanging wall basins exerted a subtle control on the succession thickness and distribution of tidal–fluvial distributary channels. The overall tabular geometry and internal architecture of the Tilje Formation is less complex than that of other tidal successions worldwide, showing lateral and vertical compartmentalization of the best tidal–fluvial sandstone reservoirs.