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Peripheral-Bulge Controlled Depositional Architecture of a Clastic Foredeep Succession: Paleocene, Spitsbergen*
By
Rikke Bruhn1 and Ron Steel2
Search and Discovery article #40104, 2003.
*Adapted from “extended abstract” for presentation at the AAPG Annual Meeting, Salt Lake City, Utah, May 11-14, 2003.
1Geological Institute, University of Copenhagen, Denmark
2Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming ([email protected])
The Paleogene Central Basin on Spitsbergen, together with the West Spitsbergen Orogenic Belt, occupy a 100 km broad, NNW-SSE striking zone in the western and central parts of the island. The deformation zone is situated along the De Geer Zone immediately west of Spitsbergen, and its development is presumably closely connected to the evolution of this major intra-plate transform fault zone (Figure 1). Compression along west Spitsbergen probably began in the Late Cretaceous to early Paleocene and culminated in the Eocene, based on fission track modelling, crosscutting relations, and comparison to the offshore record of sea-floor spreading (Braathen and Bergh, 1995; Teyssier et al., 1995; Blythe and Kleinspehn, 1998; Braathen et al., 1999). The Central Basin probably evolved as a foreland basin in front of the West Spitsbergen Orogenic Belt during the earliest phases of compression.
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Click to view sequence of depositional architecture (a-e, Figure 3).
The sedimentary fill in the Central Basin unconformably overlies Lower Cretaceous marine shales. The unconformity corresponds to a hiatus that spans the entire Upper Cretaceous and increases in a northward direction. It is probably a combined result of thermal doming or rift shoulder uplift of the northeast Barents Shelf, and erosion connected to passage of the initial peripheral bulge. The basin-fill, originally minimum 3600 m thick (cf., Manum and Throndsen, 1978), is overall eastwards migrating and reflects the eastward translation of the entire basin in response to lithospheric shortening in the West Spitsbergen Fold-Thrust Belt. The oldest, Paleocene, parts of the present basin fill consist of landward-stepping (eastwards) deltaic and shoreface-to-shelf deposits, 700 m thick, derived from the peripheral bulge area east of the basin and deposited along the eastern margin of the foredeep (Kellogg, 1975; Steel et al., 1981; Bruhn and Steel, in press). In the Early Eocene the basin-fill, 1400 m thick, was derived from the rising orogen east of the basin. Clastic wedges with impressive clinoform geometries of up to 350 m amplitude record the main progradational (eastwards) infilling of the basin from the West Spitsbergen Orogenic Belt (Steel et al., 1985; Plink-Björklund et al., 2001). A zone of deep-water shales separates the Paleocene and Eocene successions and marks the eastward passage of the foredeep.
The overall transgressive, Paleocene succession consists of two intermediate-scale, transgressive-regressive cycles, (a) the Firkanten Formation and (b) the Grumantbyen and Basilika Formations (Figure 2). The intermediate-scale cycles in turn consist of numerous small-scale, 10-60 m thick, coastal plain-shoreface-shelf sequences, separated by subaerially formed unconformities (Bruhn and Steel, in press). The sequences represent short-term coastal progradations and have average durations of 0.5-1 million years. Sequences forming the transgressive parts of the intermediate-scale cycles are relatively thin, sheet-like, and onlap the eastern basin-margin, while sequences of the regressive parts are wedge-shaped, basinward-stepping, and associated with regional unconformities along the basin-margin.
The transgressive-regressive cycles were probably largely controlled by peripheral-bulge dynamics with episodic uplift and erosion of the peripheral-bulge, in turn controlled by episodic thrust wedge build-up and collapse in the West Spitsbergen Orogenic Belt (Figure 3) (cf., Braathen et al., 1999). During tectonic quiescence the basin was downwarped due to sediment loading and gradually widened. The peripheral bulge migrated eastwards, away from the thrust belt and was gradually eroded, supplying decreasing amounts of sediment to the low-gradient basin margin. The peripheral bulge margin of the foreland basin was thus gradually transgressed (cf., Flemings and Jordan, 1989, 1990). During emplacement of thrust sheets, loading of the elastic lithosphere resulted in uplift and basinward translation of the peripheral bulge toward the thrust front, and narrowing and deepening of the foreland basin. This resulted in regression of the depositional systems close to the peripheral bulge, where the increased relief resulted in increased sediment supply to fill-in accommodation in the basin. (cf., Flemings and Jordan, 1989, 1990). The general behaviour of the peripheral bulge is mainly predicted from published models, as the sedimentary record on the distal margin of the foreland basin is commonly dominated by hiati. Well-exposed fieldwork-based examples of a relatively complete clastic, peripheral bulge-derived foredeep succession thus provides a unique opportunity to confirm predicted responses of depositional systems on the distal foreland basin margin to adjustments in the basins flexural profile.
Blythe, A.E., and K.L. Kleinspehn, 1998, Tectonically versus climatically driven Cenozoic exhumation of the Eurasian plate margin, Svalbard: Fission track analyses: Tectonics, v. 17, p. 621-639. Braathen, A., and S.G. Bergh, 1995, Kinematics of Tertiary deformation in the basement-involved fold-thrust complex, western Nordenskiöld Land, Svalbard: tectonic implications based on fault-slip data analysis: Tectonophysics, v. 249, p. 1-29. Braathen, A., S.G. Bergh, and H.D. Maher, 1999, Application of a critical taper wedge model to the Tertiary transpressional fold-thrust belt on Spitsbergen, Svalbard: GSA Bulletin, v. 111, p. 1468-1485. Bruhn, R., and R. Steel, 2003, High-resolution sequence stratigraphy of a clastic foredeep succession (Paleocene, Spitsbergen): An example of peripheral-bulge controlled depositional architecture: Journal of Sedimentary Research., v.73, p. 745-755. Flemings, P.B., and T.E. Jordan, 1989, A Synthetic stratigraphic model of foreland basin development: Journal of Geophysical Research, v. 94, p. 3851-3866. Flemings, P.B., and T.E. Jordan, 1990, Stratigraphic modeling of foreland basins: Interpreting thrust deformation and lithosphere rheology: Geology, v. 18, p. 430-434. Kellogg, H.E., 1975, Tertiary stratigraphy and tectonism in Svalbard and continental drift: AAPG Bulletin, v. 59, p. 465-585. Manum, S.B., and T. Throndsen, 1978, Rank of coal and dispersed matter and its geological bearing in the Spitsbergen Tertiary: Norsk Polarinstitutt årbok 1977, p. 169-177. Plink-Björklund, P., D. Mellere, and R.J. Steel, 2001, Turbidite variability and architecture of sand-prone, deep-water slopes: Eocene clinothems in the Central Basin, Spitsbergen: Journal of Sedimentary Research, v. 71, p. 895-912. Steel, R.J., A. Dalland, K. Kalgraff, and V. Larsen, 1981, The central Tertiary Basin of Spitsbergen: Sedimentary development of a sheared margin basin, in Kerr, J.W. and A.J. Fergusson, (eds.): Canadian Society of Petroleum Geologists Memoir 7, p. 647-664. Steel, R.J., J. Gjelberg, W. Helland-Hansen, K. Kleinspehn, A. Nφttvedt, and M. Rye-Larsen, 1985, The Tertiary strike-slip basins and orogenic belt of Spitsbergen: Society of Economic Paleontologists and Mineralogists, Special Publication 37, p. 339-359. Teyssier, C.K., K. Kleinspehn, and J. Pershing, 1995, Analysis of fault populations in Western Spitsbergen - Implications for deformation partitioning along transform margins: GSA Bulletin, v. 107, p. 68-82. |
Figure
1. Paleogeographic reconstruction of the Arctic in Late Cretaceous -
earliest Paleocene time showing the main spreading zones in the Arctic.
Figure
2. Dip sections across the northeast margin of the Central Basin of each
of the two transgressive-regressive cycles,
Figure
3. Development of depositional architecture and stacking patterns of
small-scale sequences in the Firkanten, Basilika and Grumantbyen
Formations. 