Palaeoecology of syn-rift topography: A Late Jurassic footwall island on the Josephine Ridge, Central Graben, North Sea

Abstract

Understanding rift topography is essential for determining source areas, sediment pathways, and the type of sediment delivered to a rift basin; factors essential for interpreting petroleum systems in ancient rifts. Here we investigate Upper Jurassic sediments from the Josephine Ridge region of the Central Graben, North Sea, by integrating geophysical, palynological, petrophysical and sedimentological datasets to analyse the palaeoenvironments of the Jade and Judy horsts, the tops of which are not preserved.Interpretation of geophysical and petrophysical data together with core descriptions show study wells to step progressively away from the Josephine Ridge into adjacent grabens. One hundred and five palynological samples from six wells range from the Oxfordian to the Lower Tithonian, spanning the syn-rift period of the Central Graben. Samples from the adjacent grabens and the Jade Horst are rich in dinoflagellate cysts and possess <20% terrestrial palynomorphs. Samples from the Judy Horst contain a wide range of terrestrial palynomorphs, dominated by lycopsid, fern and moss spores, representing c.50% of the recovered palynomorphs. Correspondence analysis of the assemblages imply Jade did not possess a terrestrial ecosystem; Judy samples define seven groupings of related miospores, A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 all interpreted to represent very low lying, relatively early successional type environments.This implies subaerial exposure of the Judy Horst during the Late Jurassic, which is interpreted to have formed an isolated, low relief, footwall crest island. This study provides a new methodology for investigating rift topography, particularly in cases where the tops of horsts were subsequently removed by erosion. The Judy Island would have separated the Central Graben into its eastern and western arms earlier than previously predicted, in the Late Oxfordian, with consequences for distribution of shallow and deep-marine reservoir quality sediments.

Quantitative analysis of a footwall‐scarp degradation complex and syn‐rift stratigraphic architecture, Exmouth Plateau, NW Shelf, offshore Australia

“…Our interpretation is consistent with large‐scale, palaeogeographic maps from the J30 sequence (Longley et al, 2002) that show deposition in narrow rift valleys and palaeo‐coastlines fringing exposed fault blocks. Similar scenarios of uplifted and exposed footwall highs and islands supplying hangingwall basins are interpreted in the Late Jurassic North Sea (Berger & Roberts, 1999; McArthur, Jolley, Hartley, Archer, & Lawrence, 2016; Nøttvedt et al, 2000; Roberts, Kusznir, Yielding, & Beeley, 2019; Yielding, Badley, & Roberts, 1992) and the Quaternary‐modern Aegean Sea (Papadopoulos & Pavlides, 1992; Stiros et al., 1994).…”

Episodic river flooding events revealed by palynological assemblages in Jurassic deposits of the Brent Group, North Sea

“…Stukins et al, 2013), and Cheirolepidiaceae, a globally common extinct Jurassic gymnosperm, has been interpreted from a range of environments, including dry coastal (e.g. Hughes and Moody-Stuart, 1967;McArthur et al, 2016b) and upland settings (e.g. Filatoff, 1975).…”

“…Whitaker et al, 1992) and from the Jurassic of the central (e.g. McArthur et al, 2016b) and southern North Sea (e.g. Abbink, 1998;Abbink et al, 2001Abbink et al, , 2004.…”

Palynology and weathering proxies reveal climatic fluctuations during the Carnian Pluvial Episode (CPE) (Late Triassic) from marine successions in the Transdanubian Range (western Hungary)

“…Bonis & Kürschner 2012) representing hinterland vegetation elements, while the spores are confined usually to lowland or riverine habitats (Abbink 1998;Abbik et al 2004). The Cheirolepidiaceae, represented by the Circumpolles originate from a range of environments including hinterland and dry coastal settings (Batten 1974;Abbink 1998;McArthur et al 2016;Slater et al 2017). Due to the strong differentiation between hinterland and lowland (also riverine, coastal) elements, the second principal component on axis 2 might be a function of proximity which distinguishes lowland or coastal vegetation elements and the regional pollen rain.…”

“…Spores reach a greater abundance in the Dolomites, Julian Alps, the "Raibler Schichten" or the Lunz Formation (Planderová 1980;Blendinger 1988;Roghi 2004;Roghi et al 2010;Mueller et al 2016b) than in the TR. The parent plants of the conifer pollen grains are considered to be overproducers and their pollen have the ability to be transported by wind over great distances (hundreds of kilometres), while spores are more common in nearshore proximal settings (e.g., Chaloner & Muir 1968;Vakhrameev 1991;McArthur et al 2016). The TR was located in a relatively more distal depositional setting at the start of the CPE compared to the Northern Calcareous Alps, Julian Alps or the Dolomites (Haas & Budai 1995).…”