Late Precambrian sedimentary rocks, E. , and the Trollf!'ord-Komagelv Fault 533

1972b. The stratigraphy and sedimentology of the Smog, A. 1972. Kongsfjord Formation---a late Pre- Lakesfjord Group, Finnmark. Norg. geol. Unders. 278, cambrian flysch sequence from the Varanger Peninsula, 13-40. Finnmark. Norg. geol. Unders. 2"/8, 41-80. Imvm.t., B. K. & ROBERTS, D. 1977. A re-investigation of 1973. The late Precambrian IDst-Finnmark the geology of north-west Varanger Peninsula, East Supergroup--a new lithostratigraphic unit of high rank. Finnmark, north . Norg. geol. Unders. 334, 83- Norg. geol. Unders. 2,119, 55-60. 90. 1975. Late Precambrian stratigraphy and structure of PRICE, N. J. 1968. A dynamic mechanism for the develop- the north-eastern margin of the Fennoscandian Shield ment of second order faults and related structures. Proc. (East Finnmark-Timan Region). Norg. geol. Unders. of Conf. on Research in Tectonics (Kink bands and brittle 316, 313-48. deformation) Ottawa 1968. Geol. Surv. Can. 68-52, & SIEDLECra, S. 1967. Some new aspects of the geology 49-72. of Varanger Peninsula (). Norg. geol. PR~GLE, R. 1972. Rb-Sr age determinations on shales as- Unders. 2,47, 288-306. sociated with the Varanger Ice Age. Geol. Mag. 109, & 1971. Late Precambrian sedimentary rocks of 465-72. the - region of Varanger Penin- RAMSAY, D. M. 1973. Possible existence of a stillborn margi- sula, northern Norway. Norg. geol. Unders. 269, 246-94. nal ocean in the Caledonian orogenic belt of northwest & 1972. Lithostratigraphic correlation and Norway. Nature, Phys. Sci. 245, 107-9. sedimentology of the late Precambrian of Varanger & STtmT, B. A. 1970. Polyphase deformation of a Peninsula and neighbouring areas of East Finnmark, polymict Silurian conglomerate from MagerOy, Norway. northern Norway. 24th Int. geol. Congr. Sect. 6, 349-58. J. Geol. 78, 264-80. & in press. Late Precambrian of the northeastern READING, H. G. 1965. The Eocambrian and Lower margin of the Fennoscandian Shield: A review of stratig- Palaeozoic geology of the Digermul Peninsula, Tanaf- raphy and sedimentation. Norg. geol. Unders. jord, Finnmark. Norg. geol. Unders. 234, 167-91. SPRY, A. 1969. Metamorphic Textures. Pergamon Press, Ox- & WALTER, R. G. 1966. Sedimentation of Eocambrian ford, 350 pp. tillites and associated sediments in Finnmark, northern WALLACE, R. E. 1973. Surface fracture patterns along the Norway. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2, San Andreas fault. In: KovAot, R. L. & Ntm, A. (eds) 177-212. Proc Con[. on Tectonic Problems o[ the San Andreas ROBERTS, D. 1972. Tectonic deformation in the Fault System. Stanford Univ. Pub., Geol. Sei., 13, 248- region of Varanger Peninsula, Finnmark. Norg. geol. 50. Unders. 282, 1-39. Wm¢ox, R. E., ~~G, T. P. & S~v, D. R. 1973. Basic ROOEgS, T. H. 1973. Fault trace geometry within the San wrench tectonics. Bull. Am. Ass. Petrol. Geol. 57, 74--96. Andreas and Calaveras Fault Zones--A clue to the YEATS, R. S. 1973. Newport Inglewood fault zone, Los evolution of some transcurrent fault zones. In: KovAc8, Angeles basin California. Bull. Am. Ass. Petrol. Geol. R. L. & NUR, A. (eds) Proc. of Con]. on Tectonic 57, 117-35. Problems of the San Andreas Fault System. Stanford Univ. Pub., Geol. Sci., 13, 251-8.

Received 22 March 1977; read 2 November 1977; revised typescript received 17 January 1978. HOWARD DAVID JOhnSON, Koninklijke/Shell Exploratie en Produktie Laboratorium, Rijswijk (ZH), The Netherlands. BRUCE KEVIN LEVELL, Dept. of Geology & Mineralogy, Parks Road, Oxford OX1 3PR. STANISLAW SIEDLECKI, Norges Geologiske Undersekelse, P.O. Box 3006, 7001 Trondheim, Norway.

Disemsion MR W. B. HARLAr,~ commented on the clear descrip- of breccia and mylonite in so important a transcurrent tion of the Trollfjord-Komagelv fault as an example of fault and he suggested that the fault surface transpression in which strike-slip coupled with com- irregularities might not only be accommodated by sup- pression seemed to have acted together judging by the plementary strike-slip and splay faulting but possibly appearance in cross-sections of steeply dipping strata by squeezing out of material, in reverse dip-slip mo- and minor high angle faults near the major fault. The tion, that would then be lost to view. authors confirmed that the intensity of deformation decreased away from the main fault. Transpressive tectonics should, in theory, be very common, occurring THE Atymoas REPLY" The fault zone was, in fact, at any plate margin oblique to plate motion and yet initially interpreted as a reverse fault system (Sied- the structures were often not so easily interpreted. Mr lecka & Seidlecki 1967) on the basis of the associated Harland was surprised at the relatively small amount steep dips and small-scale reverse faults. Although

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there is no evidence of the amount, or even the axes parallel to the fault zone perhaps suggests that direction of any dip-slip movement on the fault, it is the regional transpressive component was minor. entirely probable, to judge from recent strike-slip fault The small amount of fault brec~a and mylonite had systems, that dip-slip did occur. This could have been also surprised the authors, who were grateful for any related to a regional transpression or a local compres- suggestions (such as that of Mr Harland) which might sion across the fault. However the lack of regional fold help clarify the problem.

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