Truncated Prograding Strandplain or Offshore Sand Body?—Sedimentology and Geometry of the Cardium (Turonian) Sandstone and Conglomerate at Willesden Green Field, Alberta
- D. J. P. Swift2,
- G. F. Oertel2,
- R. W. Tillman3 and
- J. A. Thorne4
Published Online: 14 APR 2009
Copyright © 1991 The International Association of Sedimentologists
Shelf Sand and Sandstone Bodies: Geometry, Facies and Sequence Stratigraphy
How to Cite
Keith, D. A. W. (1992) Truncated Prograding Strandplain or Offshore Sand Body?—Sedimentology and Geometry of the Cardium (Turonian) Sandstone and Conglomerate at Willesden Green Field, Alberta, in Shelf Sand and Sandstone Bodies: Geometry, Facies and Sequence Stratigraphy (eds D. J. P. Swift, G. F. Oertel, R. W. Tillman and J. A. Thorne), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303933.ch14
Norfolk, Virginia, USA
Tulsa, Oklahoma, USA
Plano, Texas, USA
- Published Online: 14 APR 2009
- Published Print: 30 JAN 1992
Print ISBN: 9780632032372
Online ISBN: 9781444303933
- truncated prograding strandplain or offshore sand body—geometry of Cardium (Turonian) sandstone and conglomerate at Willesden Green field, Alberta;
- Cardium Formation - overlain by mudstones and sandstones of Wapiabi Formation;
- Cardium Formation stratigraphy at Willesden Green and adjacent fields;
- Facies 5 - interbedded sandstones and silty mudstones;
- clast supported conglomerates;
- vertical facies successions and depositional units;
- external geometry of Willesden Green;
- Willesden Green and Ferrier fields - offlapping depositional units;
- regressive Cardium A sandstone sequence - comprising five individual upward coarsening deposition units
Study of over 1200 well-logs and over 175 cores in and around the Willesden Green field area has allowed recognition in the Cardium Formation of eight facies, mapping of their distribution and large-scale lateral relationships. The Cardium Formation at Willesden Green is an upward-coarsening succession of offshore to lower shoreface mudstones, siltstones and very fine to fine-grained sandstones. The sandstones are informally referred to as the Cardium A sandstone and are unconformably overlain by chert-pebble conglomerates, which are in turn overlain by marine mudstones.
The upper surface of the Cardium A sandstone is undulatory in nature and at Willesden Green forms a convex ‘high’ with relief of about 30 m. A ‘low’ separates Willesden Green from the adjacent Ferrier field. Sandstones are restricted to highs whereas siltstones and mudstones typify interfield lows.
The Cardium A sandstones at Willesden Green are subdivided into five upward-coarsening successions termed depositional units, up to three of which are present in any one well. Based on relationships with overlying and underlying geophysical well-log markers, the depositional units demonstrate an eastward offlapping geometry. This offlapping geometry can be demonstrated in Ferrier and other adjacent Cardium fields.
Previous studies have interpreted some Cardium fields as offshore sand bodies. However, in light of the offlapping sandstone geometry within Willesden Green, the relationship with adjacent Cardium fields, and recent studies by others, an alternative interpretation seems appropriate.
The offlapping depositional units may represent lower shoreface to offshore expressions of prograding strandplains developed during falling sea-level. The relatively thin nature of the Cardium A sandstones suggests that the rate of sea-level fall was greater than subsidence and during basinward progradation of the strandplain, subaerial erosion of previously deposited Cardium sandstones would have occurred. During sea-level lowstand and subsequent sea-level rise all remaining upper shoreface, foreshore and subaerial deposits were eroded. Erosion was not uniform, as is evident in the region between the Willesden Green and Ferrier fields, where even lower shoreface sediments were eroded.
Conglomerates that unconformably overly the sandstones may have been introduced to the foreshore during sea-level lowstand. Erosion and reworking of foreshore deposits during stillstand and rising relative sea-level would concentrate the conglomerate. With rising sea-level, southeast-flowing currents accumulated the conglomerate as NW–SE oriented pods in the topographic lows within the upper surface of the Cardium A sandstone.