The Evolution of Sedimentary Basins

802 Nature Vol. 292 27 August 1981 intracellular metabolic processes and the potentials'' or radial propagation along In the session on basin formation, A.B. binding of charged dye molecules might muscle fibre T -tubules12 • These, together Watts (Lamont-Doherty Geological interfere with important membrane with the elegant studies of Kamino, Hirota Observatory) discussed the role of crustal processes mediating biological responses. and Fujii', suggest that such techniques flexure, showing that this becomes a major In addition, dyes may react with the have an important future in many factor in basins more than 200 km wide and exogenous reagents, whose effects are investigations involving molecular that the best overall fit to the observations being examined, to form non-fluorescent mechanisms at the cellular level. [] is an elastic plate model with crustal complexes. This would make dose strength increasing with age. This predicts response curves difficult to interpret and l. Kamino, K., Hirota, A. & Fujii, S. Nature 290, 595 a sedimentary geometry with coastal on lap would complicate kinetic calculations. (1981). and it seems that Vail's eustatic sea-level 2. Cohen. L.B. eta/. J. Membrane Bioi. 19,1 (1974). Furthermore, even with modest 3. Ross, W.N. eta/. J. Membrane Bioi. 33, 141 (1977). changes based on evidence of onlap may in illuminations, some dyes can cause cellular 4. Hoffman, J.F. & Laris, P.C. J. Physiol., Lond. 239, reality be a record of basin subsidence. The 519 (1974). photodynamic damage. These con 5. Sims, P.J. et al. Biochemistry 13, 3315 (1974). thermal effects of subsidence were siderations have prompted intensive work 6. Hladky, S.B. & Rink, T.J. J. Physiol., Lond. 263, discussed by D.L. Turcotte (Cornell to produce dyes with better responses and 287 (1976). 7. Waggoner, A.S. eta/. J. Membrane Bioi. 33, 21 (1977). University) (all basins appear to be initiated biological inertness. 8. Baylor, S.M. & Chandler, W.K. Biophys. J. 25(2), by a thermal event), while C. Beaumont It is possible to end on an optimistic 119a. (Dalhousie University) compared foreland 9. Morad, M. & Selema, G. J. Physiol., Lond. 292, note, for recent reports (to quote but two 267 (1972). and Atlantic-type basins and concluded examples) have described how potential 10. Waggoner, A.S. A. Rev. Biophys. Bioengng 8, 47 (1979). that the major contrast is the thermal age of II. Johnson, L. V. et al. J. Cell Bwl. 88, 526 (1981 ). sensitive dyes can be used to advantage to 12. Nakajima, S. & Gilai, A. J. gen. Physiol. 76, 751 the lithosphere. The old, cooler and thicker monitor either mitochondrial membrane (1980). lithosphere of the foreland compressive area will respond to loading with greater rigidity and depression wavelength than the younger, hotter, thinner and less rigid rifted continental margin basin. Some of the outstanding problems in understanding sedimentary basin sub The evolution of sidence, in particular the origin of tensile stresses in the crust which initiate the sedimentary basins normal faulting, were discussed by M. H .P. Bott (Durham University). Their origin from C.A. Williams may be found in stresses at convergent plate boundaries, hence, for example, the THE selection of 'The evolution of studies, whilst producing the most detailed origin of the Northern European Carbon sedimentary basins' as the topic for a Royal information we yet have on this margin, iferous basins may be related to stress fields Society discussion meeting* reflects the also indicate the limitations of fragmentary in operation during the subduction of the impetus given to the field by new models of evidence in reassembling faulted strata. Hercynian Ocean. basin formation, in particular the crustal Robert's interpretation requires infinite In summarizing the meeting, A. W. Bally stretching model of McKenzie, and by the stretching of the lower crust but less (Shell) cautioned that the folded belts, for availability of quantitative data on crustal stretching in the upper crust than that example Zagros, Franklinian Basin and the loading and flexure which are allowing required by Foucher's interpretation, yet Precambrian basins, are too complicated models to be tested. The McKenzie model both studies are based on essentially the for modelling with currently available (Earth planet. Sci. Lett. 40; 25, 1978) same data set. The range of disagreement is data. The complexity of listric faulting proposes that sedimentary basins are such as to encourage the acquisition of causes inherent problems in estimating formed by rapid stretching of the more and better data to allow more fault displacement. While in some spec continental lithosphere by normal faulting, accurate estimation of fault displacements. tacular cases the sole of the listric fault has instigated by a passive upwelling of hot The continental margin basin section been observed, more high-quality seismic asthenospheric material beneath the crust. was completed by an exposition of the data across basins are required for better Once the thermal stage has passed, the North-west Australian margin by D.E. evidence of the actual existence and shape lithosphere thickens as the heat is Powell (Hudbay), a margin remarkable in of listric faults. The question of whether conducted to the surface and undergoes a that the basins seem to be related to the late symmetric graben are purely a function of slow subsidence which is not associated Palaeozoic phase of abortive rifting with geological imagination was also raised, with faulting and which may be amplified little or no modification during the since observed graben are either asym by sediment loading. eventually successful rifting in the early metric or exist as half graben. The meeting made no attempt to cover Cretaceous. The general conclusion was that the all types of basin, but concentrated on An intriguing puzzle came from stretching model gives a reasonable explan those where good-quality data are discussion of intracontinental basins. ation of the formation of many basins. It available. Discussion of continental There appear to be two types of basement was a little disappointing that among the margin basins was dominated by con beneath basins, one in which normal excellent and often complicated strati tributions on the Biscay margin (presented faulting occurs as expected; but in cratonic graphical histories described in oil-company by D.O. Roberts, lOS, and J.-P. Foucher, shelf basins, for example, Witwatersrand, presentations, studies on subsidence, CNEXO, Brest), largely based on the Transvaal and Michigan Basins, the base flexure, fault displacements and so on were results of IPOD drilling on the North-west ment does not appear to be normally not emphasized, leaving one to wonder Biscay margin and on associated seismic faulted and some other mechanism of whether the oil companies are way ahead reflection and refraction data. Both basement subsidence, other than extension in considering these effects in a quantit Roberts and Foucher showed seismic by faulting, must be evoked. The Michigan ative way, though refrained from divulging reflection evidence of listric faults dipping Basin, nonetheless, shows the same same, or whether in fact it is the academics consistently oceanwards. These two exponential subsidence as other basins and who are leading in this area. L the existence of COCORP seismic *The meeting was organized by Sir Peter Kent, M.H.P. Bott, reflection data across it suggests a clear line D.P. McKenzie and C.A. Williams and the proceedings will be C.A. Williams is in the Bullard Laboratories, published in the Philosophical Transactions of the Royal of future study into the apparent lack of Department of Earth Sciences, University of Society, January 1982. basement faulting. Cambridge. 0028.0836/81/350802-01$01.00 101981 Macmillan Journals Lid .

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