Bayfill Successions in the Lower Jurassic Åre Formation, Offshore Norway: Sedimentology and Heterogeneity Based on Subsurface Data from the Heidrun Field and Analog Data from the Upper Cretaceous Neslen Formation, Eastern Book Cliffs, Utah

Abstract

Interdistributary bays form a major sedimentary subenvironment within many delta systems. These interdistributary bays occur as open bodies of water that are typically open to the sea. They may cover large areas of the lower delta plain and are normally surrounded by marsh and distributary-channel features. The interdistributary bay deposits in the Åre Formation of Heidrun field, offshore Norway, and in the Neslen Formation, Utah, occur as shallow, 2- to 7-km-wide features that were deposited in brackish to marine waters. Within these bays, low-energy wave action reworked a large proportion of the sedimentary features, such as crevasse splays, bayhead deltas, and distributary-mouth bars. The resulting wave-influenced bayfill lithofacies association (WLA) shows a relatively similar vertical development of lithofacies in both the Åre and the Neslen Formations. Normally the WLA is 2 to 8 m thick and contains a basal mudstone overlain by a wave-influenced lenticular and/or wavy-bed-ded heterolithic unit. The upper few meters consists of wave-rippled and small-scale hummocky cross-laminated sandstone with good reservoir qualities. Roots or coal or both are present at the top. Within the sandstone, mud drapes or heterolithic layers are common. In the Neslen Formation these drapes seem to be concentrated along gently dipping clinoform surfaces. Laterally, along the depositional strike and landward, the reservoir quality changes abruptly as the WLA passes into the bayhead delta, marsh, sub-bay/lake, and distributary-channel-fill lithofacies associations. Although individual bayfill successions are relatively thin, continuing subsidence and repetition of similar processes resulted in a stacking of one bayfill succession on top of another, building an 80-m-thick package of lower delta plain deposits.

Structural geology and basin development of the Norwegian Sea

“…This is because fluvial sandstones of the formation are considered to be the lowermost potential reservoir units in the investigated area. The coal-bearing Åre Formation was deposited in extensive flood plains (Gjelberg et al, 1987;Dalland et al, 1988;Kjaerefjord, 1999;Svela, 2001), and the coal development is consistent with the well-established interpretation of a humid climate throughout the Early Jurassic. The thickest coal beds, situated in the lower part of the Åre Formation, have a good source potential for gas (Helgesen et al, 2000;Martinius et al, 2005;Messina et al, 2014).…”

Evolution of provenance in the NE Atlantic rift: The Early–Middle Jurassic succession in the Heidrun Field, Halten Terrace, offshore Mid-Norway

“…lower unit is entirely non-marine in nature, and consists of fluvial to lower delta plain sediments with thick coal-bearing floodplain deposits. The upper unit was deposited initially in coastal plain and delta plain environments, and subsequently in a marginal marine setting (Kjaerefjord, 1999). The overlying Tilje Formation (Sinemurian-Pliensbachian) is composed of interbedded sandstones, mudstones and siltstones, often heterolithic, deposited in a deltaic to shallow marine setting (Dalland et al, 1988).…”

Preservation of Last Interglacial and Holocene transgressive systems tracts in the Netherlands and its applicability as a North Sea Basin reservoir analogue

“…3), where the formation is about 670 m thick and represents c. 13 Ma, is regarded characteristic for the Åre depositional system (Thrana et al, 2014). The Åre Formation has an overall transgressive nature (Kjaerefjord, 1999;Thrana et al, 2014), reflecting the gradual tectonic development (i.e. 2 nd to 3 rd -order greenhouse-type cycle cf.…”

“…Leren et al, 2010;Martinius and Gowland, 2011;Martinius and Van den Berg, 2011;Ahokas et al, 2014;Howell et al, 2014;Aschof et al, 2018), and cores and seismic logs of buried hydrocarbon reservoirs (e.g. Kjaerefjord, 1999;Martinius et al, 2001;Kombrink et al, 2007;Thrana et al, 2014). Another way is to use Quaternary analogues, most-often Holocene systems, for which well-accessible and well-dated information exists, and architecture and heterogeneity can be quantified and understood in higher detail.…”