1999 Expedition to Billefjorden Trough, Svalbard
(in construction 4/14/99)
Time frame: August 2nd-17th, 1999
General objective: An increased understanding of the structural geology and history of the Carboniferous-age Billefjorden trough in light of recent developments in thought on fault and basin segmentation and in light of reactivation tectonics. At a first order level the first objective will involve looking for changes in Carboniferous structures and sedimentary facies patterns along strike.
A major objective is to identify major and minor fault segments and associated transfer zone. Existing maps ( Harland & others, 1974; Lauritzen & others, 1989; Dallmann & others, 1994; Lamar & Douglas, 1995; McCann & Dallmann, 1996) will be used to identify this geometry prior to field work. One segment and associated transfer zones can be readily identified as existing immediately north of Pyramiden. The Odellfjellet fault dies out to the south, and appears to transfer slip to the Balliobreen fault in a right stepping pattern. Carboniferous slip of the northern part of the Balliolbreen fault is constrained as minor by overlapping Billefjorden Group strata, while to the south of Pyramiden it is the major border fault. The transfer zone is an area of greater structural complexity, and may be one of three localities we will focus on. Results here can be compared to those from the Odellfjellet fault further north.
Another major objective is to document the kinematics of the Carboniferous tectonism. Fault slip orientation data will be acquired from these faults within the segmentation framework (e.g. from the middle and end portions of individual segments). When possible attention will be focused on faults that had a lack of Tertiary reactivation or other complications (for example the suite of small normal faults in Ebbadalen and Ragnardalen; Dallmann & others, 1994). This may also include mapping at a more detailed scale of some areas. When the occasion arises we will also aquire fault-slip data of likely Tertiary age to extend the island-wide coverage we already have.
Another third major objective is to understand the 3-D geometry of basinal sediments as related to the fault segmentation pattern. There is evidence that the Billefjorden trough deepens to the north along strike (Johannessen & Steel, 1992). We will look for along strike sedimentologic changes and see if we can relate those to Carboniferous fault segmentation. Placement of alluvial fans and paleocurrent patterns may prove useful. Attention will also be paid to likely source terranes. Some evidence indicates that most of the fill can not be from the local footwall fault block, but must be farther traveled. Perhaps infilling was primarily in an axial pattern. We will also look for evidence of syn-sedimentary deformation or seismites, and their stratigraphic position. The Minkinfjellet Fm. shows some thickness changes that indicate that some of the axial syncline development (McCann & Dallmann, 1996) is not soley Tertiary. Such a fold may be related to development of the transfer zone.
Understanding the role of reactivation in the development of segmentation and along strike changes is another objective. The role Devonian structures played in localizing the Carboniferous fault margin will be paid close attention to. Relatively less is known about the detailed geometry of the Devonian structures.
Elsewhere there is evidence of a significant discrepancy between Billefjorden and Gipsdalen Group thermal maturation. An objective is to collect samples to see if we can detect a similar discrepancy here. Also, differences in thermal history may be expected proximally and distally to the main border fault which may have channeled fluids and hence heat when it was active.
Possible areas field work will concentrate on:
Dallmann, W. K., Ohta, Y., Birjukov, A. S., Karnousenko, E. P. & Sirotkin, A.N., 1994, Geological map of Svalbard 1:100,000 sheet C7G Dicksonfjorden. Digital version, Norsk Polarinstitutt.
Harland, W. B., Cutbill, J. L., Friend, P. F., Gobbet, D. J., Holliday, D. W., Maton, P. I., Parker, J. R. & Wallis, R. H., 1974, The Billefjorden Fault Zone - Spitsbergen - the long history of a major tectonic lineament; Norsk Polarinstitutt Skrifter, # 161, 1-77.
Johannessen, E. P. & Steel, R. S., 1990, Mid-Carboniferous extension and rift-infill sequences in the Billefjorden Trough, Svalbard; Norsk Geologisk Tidsskrift, vol. 72. p. 35-48.
Lauritzen, Ø., Salvigsen, O., & Winsnes, 1989, Billefjorden C8G - Geological Map Svalbard 1:100,000; Norsk Polarinstitutt Temakart Nr. 5., 1 sheet.
Lamar, D. L. & Douglas, D. N., 1995, Geology of an area astride the Billefjorden fault zone, Northern Dicksonland, Spitsbergen, Svalbard; Norsk Polarinstitutt Skrifter 197, 43.
Lyberis, N. & Manby, G., 1999, Continental collision and lateral escape deformation in the lower and upper crust: An example from Caledonide Svalbard; Tectonics, v. 18, p. 40-63.
McCann, A. J. & Dallmann, W. K., 1996, Reactivation history of the long-lived Billefjorden Fault Zone in north central Spitsbergen, Svalbard; Geol. Mag., v. 133, 63-84.
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