Definition card for:
Status of unit: Formal
Replaces: Marburg Formation
Reserved by: Wells A.T. on: 01-MAR-88
Approved by: NSW SNSC on: 27-FEB-91
Parent: Bundamba Group
Name source: The name is derived from the town of Marburg in the Ipswich 1:250 000 Sheet area, Queensland.
Unit history: The unit is redefined from Marburg Formation and upgraded to the Marburg Subgroup. The name was originally used by Reid (1921) as Marburg Stage of the Wolloon Coal Measures and finally evolved to the Marburg Formatioon of McTaggart (1963).
Constituents: The basic two fold sub-division of the Marburg Subgroup comprises the Koukandowie Formation and the underlying Gatton Sandstone and their respective members. The names Koukandowie and Gatton were formerly applied to members, but as it has been demonstrated that they extend basinwide as mappable units, they are redefined as formations. The Marburg 'Formation', of which they were a part, is therefore upgraded to Marburg Subgroup.
Geomorphic expression: See description of constituent formations and members. The cleaner quartzose conglomeratic sandstone intervals form prominent benches and cliffs. The lithic and silty sandstones form rounded hills and slopes and the siltstone and mudrocks weather recessively.
Type section locality: Reference section: Outcrops of most units are incomplete and deeply weathered and thus a reference section was nominated by Grey (1975) in GSQ Ipswich 18 stratigraphic drill hole over the interval 203'5" (620 m) to 2874.0' (876 m). Type Section: The type section of the Marburg Subgroup is described under the two constituent formations - the Koukandowie Formation (GSQ Ipswich 24), and the Gatton Sandstone (GSQ Ipswich 18). GSQ Ipswich 24 and Ipswich 18 were originally logged and described by officers of the Geological Survey of Queenlsand (Gray, 1975; Cranfield, 1981) and subsequently relogged by A.T. Wells and P.LLE. O'Brien of the Bureau of Mineral Resources.
Description at type locality: The Marburg Subgroup comprises the Koukandowie Formation and the underlying Gatton Sandstone and their respective component members, and as such are described under each of the members. The Marburg Subgroup is conformably overlain by the Walloon Coal Measures in GSQ Ipswich 18 and 24 and conformably overlies the Woogaroo Subgroup in GSQ Ipswich 18. The base of the Subgroup was not reached in GSQ Ipswich 24. The Ma Ma Creek Member of the Koukandowie Formation is differentiated in GSQ Ipswich 18 and 24 but no members of the Gatton Sandstone are apparent in either well section.
Extent: Throughout the Clarence Moreton Basin.
Lithology: The Marburg Subgroup contains labile quartzose-lithic and feldspathic sandstones whereas the underlying Ripley Road Sandstone is predominantly clean quartzose sandstone that is very resistant to weathering. The sandstones in the overlying Walloon Coal Measures are volcanolithic and very friable.
Relationships and boundaries: In all outcrops where the upper contact is visible (there are very few) it is conformably overlain by the Walloon Coal Measures. The lower contact is an unconformity over wide areas particularly on the western margin of the basin where the Subgroup overlaps Late Triassic sediments, and Palaeozoic basement rocks. In the southern part of the Clarence-Moreton Basin notably in the Coast Range, Glenreagh and Nymboida areas, an angular unconformity occurs at the contact with the underlying Woogaroo Subgroup. Elsewhere the Marburg and Woogaroo Subgroups are apparently conformable. McElroy (1962) used the base of the lowest fossil wood horizon as the base of his Marburg 'Formation'. The top was taken as the first pebble band below the Walloon Coal Measures or alternatively at the base of the coal bearing sequence of dark shales, claystones and friable sandstone of the Walloon Coal Measures. These boundary criteria have proved to be unsatisfactory and it is proposed that sandstone composition is the most reliable method of distinguishing the Marburg Subgroup from bounding sequences. The Marburg Subgroup contains labile quartzose-lithic and feldspathic sandstones whereas the underlying Ripley Road Sandstone is predominantly clean quartzose sandstone that is very resistant to weathering. The sandstones in the overlying Walloon Coal Measures are volcanolithic and very friable.
Identifying features: See NSW for def.
Age reasons: Palynofloral assemblages in the Marburg Subgroup indicate an Early Jurassic age (Rhaetian to possibly basal Bajocian) (Cranfield et al., 1976; McKellar, 1981). Details of the ages of each formation and member of the Subgroup are described later in this report.
Proposed publication: Wells A.T., et al. BMR Journal of Geology and Geophysics
State(s): NSW and QLD