Lava-Fed Gilbert-Type Delta in the Polonez Cove Formation (Lower Oligocene), King George Island, West Antarctica

  1. Albina Colella2 and
  2. David B. Prior3
  1. S. J. Porȩbski and
  2. R. Gradziński

Published Online: 2 APR 2009

DOI: 10.1002/9781444303858.ch19

Coarse-Grained Deltas

Coarse-Grained Deltas

How to Cite

Porȩbski, S. J. and Gradziński, R. (2009) Lava-Fed Gilbert-Type Delta in the Polonez Cove Formation (Lower Oligocene), King George Island, West Antarctica, in Coarse-Grained Deltas (eds A. Colella and D. B. Prior), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303858.ch19

Editor Information

  1. 2

    Universita della Calabria, Italy

  2. 3

    Atlantic Geoscience Center, Nova Scotia, Canada

Author Information

  1. Instytut Nauk Geologicznych, Polska Akademia Nauk, Senacka 3, 31-002 Kràkow, Poland

Publication History

  1. Published Online: 2 APR 2009
  2. Published Print: 19 OCT 1990

ISBN Information

Print ISBN: 9780632028948

Online ISBN: 9781444303858



  • Oberek hydroclastic delta;
  • Polonez cove formation;
  • Coccolith assemblages;
  • plane-bedded sandstones, occurring in fine- to medium-grained beds;
  • northern deltaic body;
  • southern deltaic body


The Oberek hydroclastic delta of the Polonez Cove Formation (Lower Oligocene, King George Island, South Shetland Islands) originated through coalescence of two, Gilbert-type bodies, more than 600 m in radius each, that prograded on to a c. 20 m deep marine storm-dominated shoreface. A deltaic body begins with a basal unit (3.5 m thick) of flat-bedded, petromict volcaniclastic breccia overlain by a foreset-bedded unit (16–23 m) of basaltic breccia and hyaloclastite (angle of dip up to 35°), in turn, overlain by a topset (min. 5 m) of sheet-like lava-breccia. This stratigraphy is interpreted to reflect initiation of delta growth by laharic debris flows, followed immediately by incursions of basaltic lava, that on passing through the shoreline, produced a subaqueous hydroclastic prism and a subaerial lava platform on top of the prism.

The foreset unit consists of six lithofacies: (A) ill-bedded cobble breccia; (B) bedded pebble breccia; (C) lag breccia; (D) interbedded breccia and sandy hyaloclastite; (E) ill-stratified, bimodal hyaloclastite; and (F) graded-laminated hyaloclastite. The lithofacies are arranged to form three major segments of the foreset unit: inner, indistinct planar (facies A); medial, planar (facies B, C); and outer, tangential having upper planar ends (facies E) and wide, low-angle toes (B, C) passing downwards into well-developed bottomset beds (B, D, F). This architecture records accretion of the delta slope through mass-gravity processes, changing in importance with continued delta growth from grain free-falling and avalanching (inner, indistinct planar segment) to slump-generated fluidal sediment gravity flows (outer tangential segment). Such change is considered to reflect primarily the increasing grain-size range of hydroclastic detritus made available for remobilization, in response to changing feeding-lava behaviour towards lower viscosities and smaller, possibly surging discharges.