3D facies architecture of flood basalt provinces and their internal heterogeneity: examples from the Palaeogene Skye Lava Field, The

(1) The SMLS of the north of the Minginish district may be essentially divided into three main architectural sequences, each representing different eruptive styles. These are (a) lower compound-braided lavas, (b) transitional mixed lavas, and (c) upper massive tabular-type lavas.

(2) Correlation of individual lava flows becomes increasingly more possible as we move higher up the stratigraphy.

(3) Individual lava flow thicknesses increase up stratigraphy to flows of >8 m thickness in the higher parts of the succession with a maximum thickness of c. 20 m. Flow thickness increase is coupled with increases in flow aspect ratio, geochemical evolution (also viscosity) and lateral extent. Increases in thickness up through the succession are coupled to decreases in architectural complexity, lateral heterogeneity and eruption frequency.

(4) The lower architectural sequence basalts are considered to have formed on the low-angle flanks of a shield volcanic centre.

(5) A magma source for the lower and intermediate sequences is indicated by flow indicators to be generally from the NE. Flow indicators supporting this notion include pipe vesicles, pahoehoe surfaces and lava conduits.

(6) Lava feeder tubes and pipes are present in the inflated pahoehoe section of the lower sequence of lavas in Talisker Bay. These feeder systems are particularly associated with this style of pahoehoe volcanism, as in present-day Hawaii.

(7) The intrafacies component scheme for classification of geological facies may be utilized to make estimates of geophysical parameters for a volcanic succession.

(8) Accurate geophysical models of flood basalt provinces (their lava sequences and associated intrusions) need to incorporate both the lava field scale geometric architecture and smaller intra-flow (intrafacies) rock property heterogeneity. This information can be incorporated into detailed 3D geological Earth models, as in the present study, to aid further characterization of the volcanological and geophysical nature of flood basalts.

This work was supported by funding provided by Elf GRC and the EU 5th Framework Project SlMBA (contract no. ENK.6-CT-2000-00075). The authors would like to thank all members of the SIMBA Consortium for their discussion and support, and A. J. Mallon for help with geophysical rock properties. Special thanks go to Jane, Steve and Coaster (the dog) of Bay View B&B in Talisker for their hospitality and company during the fieldwork aspects of the research. The manuscript has greatly benefited from detailed comments and suggestions by C. H. Emeleus and D. G. Pearson and the in depth reviews made by B. Bell and K. Goodcnough.

References

ALLEN, J.R.L. 1983. Studies of fluviatile sedimentation: bars, bar-complexes and sandstone sheets (low sinuosity braided streams) in the Brownstones (L. Devonian), Welsh Borders. Sedimentary Geology, 33, 237-293.

ANDERSON, F.W. & DUNHAM, K.C. 1966. Geology of Northern Skye. Memoirs of the Geological Survey, Scotland, Sheet 80 and parts of 81, 90 and 91.