Changing Alluvial Style in Response to Changing Accommodation Rate in a Proximal Foreland Basin Setting: Upper Cretaceous Dunvegan Formation, North-East British Columbia, Canada

  1. Michael D. Blum3,
  2. Susan B. Marriott4 and
  3. Suzanne F. Leclair5
  1. Matthew P. Lumsdon-West and
  2. A. Guy Plint

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304350.ch26

Fluvial Sedimentology VII

Fluvial Sedimentology VII

How to Cite

Lumsdon-West, M. P. and Plint, A. G. (2005) Changing Alluvial Style in Response to Changing Accommodation Rate in a Proximal Foreland Basin Setting: Upper Cretaceous Dunvegan Formation, North-East British Columbia, Canada, in Fluvial Sedimentology VII (eds M. D. Blum, S. B. Marriott and S. F. Leclair), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304350.ch26

Editor Information

  1. 3

    Baton Rouge, Louisiana, USA

  2. 4

    School of Geography and Environmental Management, University of the West of England, Bristol BS16 1QY, UK

  3. 5

    Department of Earth and Environmental Sciences, Tulane University, Dimwiddie Hall, New Orleans, LA 70118, USA

Author Information

  1. Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada

  1. 54 Belorun Court, London, Ontario N6K 3K8, Canada

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 15 FEB 2005

Book Series:

  1. Special Publication Number 35 of the International Association of Sedimentologists

Book Series Editors:

  1. Ian Jarvis

Series Editor Information

  1. School of Earth Sciences and Geography, Centre for Earth and Environmental Science Research, Kingston University, Penrhyn Road, Kingston-upon-Thames KT1 2EE, UK

ISBN Information

Print ISBN: 9781405126519

Online ISBN: 9781444304350

SEARCH

Keywords:

  • changing alluvial style in response to changing accommodation rate;
  • palaeogeography and subsidence;
  • lower to middle Cenomanian Dunvegan formation;
  • stratigraphical and palaeogeographical framework;
  • sedimentary facies;
  • alluvial plain and fluvio-lacustrine facies;
  • platy mudstone (lacustrine silt and mud);
  • sandier upward successions (crevasse delta or mouth-bar);
  • alluvial responses to accommodation change

Summary

The early–mid-Cenomanian Dunvegan Formation represents a major deltaic complex that prograded > 400 km from the north-west to the south-east, parallel to the rising Rocky Mountain Cordillera, over about 2 Myr. The formation comprises at least ten regressive–transgressive allomembers, separated by regional marine transgressive surfaces and, further up-dip, by lacustrine flooding surfaces. The lower five allomembers (J–F) have a sigmoidal geometry, thinning up-dip towards the north-west. Allomember E differs in showing in the north-west a pronounced isopach ‘moat’, into which strata thicken from 35 to 80 m over 120 km, suggestive of renewed subsidence along the basin margin. Collectively, allomembers D–A show an even more pronounced thickening towards the active basin margin, from 30 to 100 m over 250 km, and this geometry persists in the lower units of the overlying Kaskapau Formation. Outcrop sections of the Dunvegan Formation in the Chetwynd–Pine River area are located within the thickened isopach ‘moats’ of allomembers E–A, and are dominated by alluvial deposits about 160 m thick. Non-channelized alluvial facies represent lake, mouth-bar, levee and crevasse splay environments, and organic histosol (coal), poorly drained, intermediate redox and better drained palaeosols. Siderite, organic debris and dinosaur tracks are ubiquitous elements of these facies. Channelized facies are dominated by non-migrating (probably anastomosed) sandstone channel-fills. Non-channelized facies form two associations: A, which is dominated by crevasse splays, levees, intermediate redox and better drained palaeosols; B, which is dominated by lakes, mouth-bars, organic and poorly drained palaeosols. Facies association A, indicating relatively well-drained conditions, dominates allomembers G to the lower part of E. From near the middle to near the top, allomember E is progressively dominated by facies association B, but the uppermost 5 m shows an abrupt return to better drained palaeosols. Allomembers D to A show alternations between associations A and B, although overall, association B predominates upward. The basal units of the overlying Kaskapau Formation comprise a transitional succession 40–50 m thick dominated by facies of association B, but including brackish-water lagoonal deposits, overlain by marine deposits.

The thinning of allomembers H–F towards the north-west suggests minimal accommodation in that direction, and this is reflected in their constituent alluvial facies (association A), dominated by relatively well-drained environments. The upward change within allomember E, from association A to relatively poorly drained association B, is interpreted to record an upward increase in accommodation rate. This change is independently suggested by the isopach ‘moat’ in allomember E, attributed to renewed flexural subsidence. A pedocomplex 5 m thick at the top of allomember E suggests a final phase of very low accommodation rate. Allomembers D–A are again dominated by poorly drained freshwater environments, which pass upward into rocks of the basal Kaskapau Formation which show progressively increasing marine influence. This facies succession reflects an increasing accommodation rate, also suggested by regional isopach patterns.