Definition card for: Narrabundah Ashstone Member

State(s): ACT, NSW,
Status of unit: Formal
Usage: Redefined
Stratno: 24420
Replaces: Narrabundah Ashstone

Reserved by: Abell, R.S. (after Opik 1958) on: 26-OCT-90
Approved: Y
Approved by: Brakel, A. on: 26-OCT-90

Parent: Canberra Formation

Name source: Named after the Canberra suburb of Narrabundah (Opik 1958).

Unit history: None.

Type section locality: A disused quarry in the suburb of Narrabundah ( Lat 35o 20'S Long 149o 9'E). BMR Strat. drillhole (C284) penetrated 30m of hard pale grey fine to medium-grained tuff below the floor of the quarry (Henderson 1983); this core is stored at the BMR Core and Cuttings Laboratory, Fyshwick, ACT. Supplementary reference section: Exposed in roadcutting in Fairbairn Avenue (Lat 35o 18' Long 149o 10') - a westerly dipping sequence of tuffaceous sandstone and fine to medium grained tuff 56m thick. Top and bottom of unit not exposed.

Extent: Apart from a few scattered outcrops its distribution is known mainly from drillholes and trench excavations in the Fyshwick-Narrabundah area.

Thickness range: Estimated at up to 70m (Hendersen 1981).

Lithology: Fine-medium grained tuff with cherty laminations and pale brown tuffaceous sandstone.

Depositional environment: Volcaniclastic submarine mass-flow deposit laid down by turbidity currents in locally deeper parts of the Canberra-Yass Shelf (Owen and Cas, 1980).

Relationships and boundaries: A conformable member unit near the top of the Canberra Formation.

Age reasons: Unfossiliferous. Late Wenlock based on fossil and stratigraphic evidence for the Canberra Formation.

Correlations: Probably in part co-eval with volcanic units in the Canberra Formation north of the ACT-NSW border.