Quantified Fluvial Architecture in Ephemeral Stream Deposits of the Esplugafreda Formation (Palaeocene), Tremp-Graus Basin, Northern Spain

  1. M. Marzo and
  2. C. Puigdefábregas
  1. T. Dreyer

Published Online: 14 APR 2009

DOI: 10.1002/9781444303995.ch23

Alluvial Sedimentation

Alluvial Sedimentation

How to Cite

Dreyer, T. (1993) Quantified Fluvial Architecture in Ephemeral Stream Deposits of the Esplugafreda Formation (Palaeocene), Tremp-Graus Basin, Northern Spain, in Alluvial Sedimentation (eds M. Marzo and C. Puigdefábregas), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303995.ch23

Editor Information

  1. Barcelona, Spain

Author Information

  1. Norsk Hydro Research Centre, Sandsliveien 90, N-5020, Bergen, Norway

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 16 SEP 1993

ISBN Information

Print ISBN: 9780632035458

Online ISBN: 9781444303995

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Keywords:

  • coarse-grained ephemeral stream deposits;
  • Esplugafreda Formation and overlying Claret Formation;
  • sandy sheetflood-deposits interbedded with oxidized floodplain fines;
  • In-traformational conglomerates occur locally at base of some sandstones;
  • Scales and morphological elements;
  • mainly horizontal to low-angle inclined planar-stratified sands

Summary

The Esplugafreda Formation belongs to the Tremp Group of the Tremp-Graus Basin, and consists of coarse-grained ephemeral stream deposits interbedded with dominantly red-coloured floodplain fines. Six coarse member and two fine member facies associations have been recognized. For each facies association, analysis of depositional environment were combined with geometrical studies. The most common coarse member deposits are strongly to moderately incised sand- and gravel-bodies with low width (W)/thickness (T) ratios (‘ephemeral ribbons’), and multistorey lobe-like sandbodies with intermediate W/T ratios (stacked sheetflood deposits). Ephemeral stream sandbodies with high W/T ratios (sheet-like braided stream deposits) are only present at the top of the formation. Factors which encouraged the formation of mainly ribbon-like coarse member deposits include proximality to source area, channel incision due to upwarping of the basin margin, and a mean rate of sediment supply equal to or only slightly higher than the accommodation rate. In the multistorey ephemeral ribbon-bodies, it can be demonstrated that the W/T ratio decreases as the number of storeys increases. Three megacycles, formed by variations in sediment supply, subsidence rate and palaeoslope gradients, have been recognized in the Esplugafreda Formation and the overlying Claret Formation. These show a marked fining upwards tendency, with the most mature palaeosols present in the upper part. From the basal to the middle parts of the lower two megacycles, there is an upwards increase in the number and lateral extent of sandbodies. The upper megacycle is dominated by fine member deposits, the only notable channel unit being a laterally extensive multistorey sand- and gravel-body at the base.

The fine member deposits are characterized by the influence of pedogenic processes. Between sedimentation episodes, these processes created ‘pause-planes’ at exposed sandy surfaces within the inactive channels. In the interchannel areas, variegated palaeosols formed. Mature palaeosols mainly occur at the top of megacycle 1 in proximal parts, but become widespread in areas where clastic supply was less frequent. The mature palaeosols are traceable over distances of several kilometres, and represent promising correlation-horizons.