Hostname: page-component-cd9895bd7-fscjk Total loading time: 0 Render date: 2024-12-24T02:17:31.619Z Has data issue: false hasContentIssue false
  • English
  • Français

Depositional Features of Dittonian Rocks: Pembrokeshire compared with the Welsh Borderland

Published online by Cambridge University Press:  01 May 2009

J. R. L. Allen
J. R. L. Allen
Affiliation:
Sedimentology Research Laboratory, The University, Reading.
Get access Rights & Permissions [Opens in a new window]

Abstract

The Dittonian Stage in Pembrokeshire comprises the Lower Marl Group (higher beds), the Sandstone-and-Marl Group, and the Upper Marl Group (at least lower half). These formations cannot be distinguished lithologically from Dittonian strata of the Welsh Borderland 100 miles away along the depositional strike.

Cyclothems of intraformational conglomerate (scoured surface below) → sandstone → siltstone with concretions recur vertically in each area. The conglomerates in both districts consist of intraformational siltstone and concretionary debris. Flat-bedding, primary current lineation, planar cross-bedding, trough cross-bedding, and ripple-drift bedding are common to the sandstones. Suncracked siltstones abound in both Pembrokeshire and the Welsh Borderland. Slumped bedding, sandstone pipes, and animal burrows are the structures penecontemporaneous with deposition in each area.

The Dittonian strata of the Welsh Borderland are shown to be probably floodplain deposits, by reason of their close similarity to the modern sediments of the Colorado Delta floodplain and Colorado River. The occurrence of an identical facies in Pembrokeshire suggests the even wider extent of this floodplain in early Lower Old Red Sandstone times, when the sea lay far to the south of both areas.

Type
Articles
Information
Geological Magazine , Volume 100 , Issue 5 , October 1963 , pp. 385 - 400
Copyright
Copyright © Cambridge University Press 1963

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Allen, J. R. L., 1960. Cornstone. Geol. Mag., 97, 43–8.Google Scholar
Allen, J. R. L., 1961a. The highest Lower Old Red Sandstone of Brown Clee Hill, Shropshire. Proc. Geol. Ass., Lond., 72, 205–219.Google Scholar
Allen, J. R. L., 1961b. Sandstone-plugged pipes in the Lower Old Red Sandstone of Shropshire, England. J. sediment. Petrol., 31, 325–335.Google Scholar
Allen, J. R. L., and Tarlo, L. B., 1963. The Downtonian and Dittonian facies of the Welsh Borderland. Geol. Mag., 100, 129–155.CrossRefGoogle Scholar
Allen, P., Allen, J. R. L., Goldring, R., and Maycock, I. D., 1960. Festoon bedding and “mud-with-lenticles” lithology. Geol. Mag., 97, 261–3.CrossRefGoogle Scholar
Ball, H. W., and Dineley, D. L., 1961. The Old Red Sandstone of Brown Clee Hill and the adjacent area. I. Stratigraphy. Bull. Brit. Mus. (Nat. Hist.), Geology 5, 178–242.Google Scholar
Clarke, B. B., 1955. The Old Red Sandstone of the Merbach Ridge, with an account of the Middlewood Sandstone, a new fossiliferous horizon 500 feet below the Psammosteus Limestone. Trans. Woolhope Nat. Fid. Cl., 34, 195–218.Google Scholar
Denison, R., 1956. A review of the habitat of the earliest vertebrates. Fieldiana, 11, 359–457.Google Scholar
Dineley, D. L., 1951. The northern part of the Lower Old Red Sandstone outcrop of the Welsh Borderland. Trans. Woolhope Nat. Fld. Cl., 34, 127–147.Google Scholar
Dineley, D. L., 1961. A sandy facies in the Dartmouth Slates. Abs. Proc. 3rd Conf South-west of England Geologists and Geomorphologists, Bristol, 1960, 12–13.Google Scholar
Dixon, E. E. L., 1921. The geology of the South Wales Coalfield. Part XIII. The country around Pembroke and Tenby. Mem. geol. Surv., London.Google Scholar
Folk, R. L., and Ward, W. C., 1957. Brazos River Bar: a study in the significance of grain size parameters. J. sediment. Petrol., 27, 3–26.Google Scholar
Gill, W. D., and Kuenen, P. H., 1958. Sand volcanoes on slumps in the Carboniferous of County Clare, Ireland. Quart. J. geol. Soc, Lond. 113, 441–457.Google Scholar
Greenly, E., 1919. The geology of Anglesey. Mem. geol. Surv., London.Google Scholar
Hamblin, W. K., 1961. Micro-cross-lamination in Upper Keeweenawan sediments of Northern Michigan. J. sediment. Petrol., 31, 390–401.Google Scholar
King, W. W., 1934. The Downtonian and Dittonian strata of Great Britain and North-Western Europe. Quart. J. geol. Soc, Lond. 90, 526–566.Google Scholar
Kuenen, P. H., 1949. Slumping in the Carboniferous rocks of Pembrokeshire. Quart. J. geol. Soc, Lond. 104, 365–380.Google Scholar
Kuenen, P. H., 1953. Graded bedding, with observations on Lower Palaeozoic rocks of Britain. Verhand. Kon. Ned. Akad. Wet., 20, 3, 1–47.Google Scholar
McDowell, J. P., 1960. Cross-bedding formed by sand waves in Mississippi point bar deposits (Abs.). Bull. geol. Soc. Amer., 71, 1925.Google Scholar
McKee, E. D., 1938. Original structures in Colorado River flood deposits of Grand Canyon. J. sediment. Petrol., 8, 77–83.Google Scholar
McKee, E. D., 1939. Some types of bedding in the Colorado River delta. J. Geol., 47, 64–81.CrossRefGoogle Scholar
McKee, E. D., and Weir, J., 1953. Terminology for stratification and cross stratification in sedimentary rocks. Bull. geol. Soc. Amer., 64, 381–390.Google Scholar
Shrock, R. R., 1948. Sequence in layered rocks. New York.Google Scholar
Sorby, H. C., 1908. On the application of quantitative methods to the study of the structure and history of rocks. Quart. J. geol. Soc., Lond., 64, 171–233.CrossRefGoogle Scholar
Stokes, W., 1947. Primary current lineation in fluvial sandstones, a criterion of current direction. J. Geol., 60, 52–3.Google Scholar
Sundborg, Å., 1956. The River Klarälven. A study of fluvial processes. Geogr. Ann., 38, 127–316.Google Scholar
Sutton, J., and Watson, J., 1960. Sedimentary structures in the Epidotic Grits of Skye. Geol. Mag., 97, 106–122.CrossRefGoogle Scholar
Sykes, G., 1937a. The Colorado Delta. Carnegie Institute of Washington PublicationNo. 460, Washington.Google Scholar
Sykes, G., 1937b. Delta, estuary, and lower portion of the channel of the Colorado River, 1933 to 1935. Carnegie Institute of Washington Publication, No. 480, Washington.Google Scholar
Ten Haaf, E., 1956. Significance of convolute lamination. Geol. en Mijnb., 18, 188–194.Google Scholar
Welch, F. B. A., and Trotter, F. M., 1961. The geology of the country around Monmouth and Chepstow. Mem. geol. Surv., London.Google Scholar
Wentworth, C. K., 1922. A scale of grade and class terms for clastic sediments. J. Geol, 30, 377–392.Google Scholar
Whitaker, W., 1889. The geology of London. Vol. II. Appendices. Mem. geol. Surv., London.Google Scholar
White, E. I., 1938. New pteraspids from South Wales. Quart. J. geol. Soc, Lond., 84, 85–115.CrossRefGoogle Scholar
White, E. I., 1946. The genus Phialaspis and the “Psammosteus” Limestones. Quart. J. geol. Soc, Lond., 101, 207–242.CrossRefGoogle Scholar
Wills, L. J., 1950. The palaeogeography of the Midlands. 2nd Ed., Liverpool.Google Scholar