GEOSCAN, résultats de la recherche


TitreKey stratigraphic elements within Orphan Basin, offshore Newfoundland, Canada
AuteurDafoe, L T; Keen, C E; Williams, G L; Dehler, S A
SourceThird conjugate margins conference, abstracts; 2012 p. 1-2
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120136
RéunionThird Central and North Atlantic Conjugate Margins Conference; Dublin; IE; août 22-24, 2012
ProvinceRégion extracotière de l'est
Lat/Long OENS-52.0000 -48.0000 52.0000 48.0000
Sujetscapacité de production d'hydrocarbures; hydrocarbures; stratigraphie; géologie marine; combustibles fossiles; Mésozoïque; Crétacé; Jurassique
Illustrationslocation maps; profiles; plots
ProgrammeGéoscience en mer, Analyse de bassin et ressources géoscientifiques
Résumé(disponible en anglais seulement)
Early exploration in the Orphan Basin (Fig. 1A) focused primarily along its western margin and typically penetrated basement, revealing little about the economic potential of the area. Recently, however, renewed interest in this frontier basin has arisen from its proximity to the petroleum-rich Jeanne d'Arc Basin and potential for correlation with source rocks in neighboring basins. Our aim is to establish a stratigraphic framework to explain the succession of depositional events linked to rifting and development of the North Atlantic Ocean. Our approach incorporates analyses of well logs, cores, cuttings, biostratigraphy, seismic data, and subsidence histories to understand key stratigraphic elements within Orphan Basin and the adjacent Flemish Pass and northern Jeanne d'Arc basins.
The effects of progressive northward rifting are recorded in two major transgressive-regressive packages driven by tectonic forces (Fig. 1B). The first package begins with the onset of relatively rapid subsidence in the Middle to Late Jurassic in the Jeanne d'Arc and Flemish Pass basins. During this time, 100s of metres of nearshore restricted marine deposits accumulated during a lowstand or stillstand when sedimentation rates outpaced the rate of relative sea-level rise during initial rifting. The ragged gamma-ray profiles that characterize this depositional phase may correlate to those seen at depth in Great Barasway F-66 (this hypothesis is currently being tested with biostratigraphic analyses). The brackish, restricted nature of the Jurassic deposits may represent limited marine circulation within a stagnant arm of the nascent North Atlantic.
Following accumulation of thick, nearshore, restricted marine strata, the stratal patterns in the Upper Jurassic become fining upward, signifying a transgression (T1) demarcated by a transgressive flooding surface (TSE1) and capped by a maximum flooding surface (MFS1). The thin transgressive package can include green, pyrite-bearing shales and the influx of marine fossils such as ammonites in Baccalieu I-78. This transgression also marks a transition from restricted- to open-marine conditions and is attributed to renewed rifting that resulted in enhanced oceanic circulation.
Above MFS1, the Upper Jurassic through Cretaceous succession is characterized by a regressive phase (R1). Upper Jurassic and Lower Cretaceous strata are predominantly aggradational with weakly progradational shelf to distal shoreface packages. In the northern Jeanne d'Arc and Flemish Pass basins, the Lower Cretaceous Avalon unconformity appears to reflect uplift and erosion (Sinclair, 1995) of the uppermost Lower Cretaceous and much of the Upper Cretaceous succession. Major unconformities in Orphan Basin, however, tend to reflect missing time in the mid to later Cretaceous succession that may record uplift of basement blocks or non-deposition in more distal marine settings. Thick Upper Cretaceous strata preserved along the western margin of Orphan Basin record continued regression with short-lived, rapid progradation of shelf to shoreface successions suggestive of a decrease in the rate of relative sea-level rise. The overall regressive package (R1) can be explained by a decrease in the rate of subsidence (as seen on basement subsidence curves; Fig. 1B) during which sedimentation rates outpaced the ongoing rate of subsidence. At the end of the Late Cretaceous (Maastrichtian) and into the Paleocene, the end of regression is marked by a fining-upward sequence signifying renewed transgression (T2). Wells along the western margin of Orphan Basin show transgressive ravinement (TSE2) and abrupt truncation of progradational shoreface strata. The fining-upward transgressive package is typically thin and capped by a Paleocene maximum flooding surface (MFS2) marked by: a prominent gamma ray spike; associated abundance of glauconite; presence of chalks; and/or development of green shales. This MFS2 reflects a condensed marine interval in which sediment bypass took place (like that described by Deptuck et al., 2003, for the Jeanne d'Arc Basin) in which associated unique sedimentological properties are likely linked with strong reflections seen in seismic data and the prominent gamma-ray spike seen in some wells. A combination of the TSE2 (where present), MFS2, and (in some wells) Cretaceous unconformities have likely been previously used to identify the "Base Tertiary Unconformity." It appears, however, that much of the missing succession can be attributed to Cretaceous unconformities, while the MFS2 is correlative with the onset of major subsidence across the study area that began around 60 Ma (middle Paleocene). The overlying Tertiary succession is characterized by a gradual decrease in the rise of relative sea level as the continental shelf built seaward during a second regressive phase (R2). Our preliminary results above and our planned integrated studies should provide a more comprehensive understanding of the evolution and petroleum potential of Orphan Basin and associated basins of the conjugate margin.