Bremer Sub-basin 3D model

(B.B. Hardy, C. Mitchell, D. J. Ryan, & C. J. Nicholson)

• About the Bremer Sub-basin 3D model
• Metadata

• View the 3D model online
• Download the model as a zip file (~ 41 MB)
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About the Bremer Sub-basin 3D model

Geographic extent

The Bremer Sub-basin is located off the south coast of Western Australia, adjacent to the coastal towns of Albany, Bremer Bay and Esperance.

Contents

This VRML model contains fault and horizon interpretations, images of seismic data, geological dredge data and high-resolution swath bathymetry of the Bremer Sub-basin study area.

Size

Approximately 44.3MB. Startup download only 452KB - remaining data downloads when layers are selected.

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Metadata

• Introduction
• Data
• Interpretations
• Basin Outline
• Surfaces
• Coordinates

1.1. Introduction

In May 2003, the Australian Government provided $A25 million to fund a four year New Oil program aimed at developing new exploration opportunities in offshore Australia, through an integrated program of seismic acquisition, geological sampling, and seep detection in key frontier basins. This VRML of the Bremer Sub-basin was created as an output of the Bremer Sub-basin Study within the New Oil program (Geoscience Australia Record 2005/21). It provides a 3D visual compilation of key interpretations within the sub-basin, and also some of the key data sets used.

Key interpretations and data include:

• Basement surface
• Gridded Bathymetry
• Locations of seismic data and large scale JPEG images
• Locations of dredge sites and dredge information

This tool is ideal for those interested in quickly understanding the geometry and structural architecture of the Bremer Sub-basin, as well as a quick look at the seismic interpretations and dredge analyses carried out during the study.

The results of the Bremer Sub-basin study have been published in Geoscience Australia Record 2005/21 (Geology and Petroleum Potential of the Bremer Sub-basin, Offshore Southwestern Australia) which is available from the Geoscience Australia Sales Centre.

More information on the Bremer Sub-basin is available on the Southern Australian Frontiers.

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1.2. Data

1.2.1. Dredge and Bathymetry data

During GA Survey 265 in February and March 2004, the geomorphology of sub-marine canyons that incise into the Bremer Sub-basin was mapped by collecting over 6200 km of high-resolution swath bathymetry. Using this improved bathymetry data, sample sites were selected and rock samples were recovered by dredging the canyon walls. About 283 rock samples were recovered from 45 dredge sites providing the only sub-surface geological data from the Bremer Sub-basin. The results of geochemical, biostratigraphic and sedimentological analyses of the dredge samples were then used to produce a stratigraphic framework for the Bremer Sub-basin, and to underpin a petroleum prospectivity assessment.

Note: Some dredge sites that were tied to seismic can be selected using the mouse to bring up additional information including:

• Dredge location.
• Start depth
• Finish depth
• Dredge line tie and accuracy
• Dredge sample summary

1.2.2. Seismic data

Interpretations from two seismic data sets were used to produce the model of the Bremer Sub-basin. These are Esso Australia's R74a seismic data set (reprocessed by Fugro in 2001), and the Geoscience Australia Survey 280 seismic data set. In October and November 2004, Geoscience Australia's Geophysical Survey 280 acquired 2700 km of seismic data across the southwestern continental margin of Australia. 1300 km of industry-standard seismic reflection data, comprising nine dip lines and three strike lines, were acquired over the Bremer Sub-basin during the survey.

Note: Selecting a Survey 280 seismic line in the model with your mouse will open a large scale JPEG of the seismic line with interpretation.

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1.3. Interpretations

Before 3D modelling could commence, interpreted seismic horizons and faults were imported from Geoquest into GOCAD in two way time. The raw fault and horizon traces provide some insight into the geometry and structural architecture of the sub-basin. GOCAD was then used to create surfaces connecting the fault traces and basement interpretation picks. The process of creating fault and basement surfaces in GOCAD was useful in aiding quality checking of interpretations. In some cases, the 3D model helped identify structures that had been misinterpreted in GeoQuest, with unrealistic geometries evident in the 3D model. This enabled the interpretation to be refined and corrected.

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1.4. Basin Outline

While the northern boundary of the Bremer Sub-basin directly borders shallow basement, the southern boundary is more transitional, characterised by a down-stepping series of fault blocks onlapped by sediment fill of the Recherche Sub-basin.

The western and eastern boundaries of the sub-basin are defined by NNE striking, near-vertical faults that are hard-linked to basement. These structures are sub-perpendicular to the main sub-basin axis, and may have been controlled by underlying basement structures. Alternatively they may have formed as release faults accommodating variable strain across the hanging wall of basin-bounding structures.

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1.5. Surfaces

Bathymetry grid

During GA Survey 265, sub-marine canyons were mapped by collecting over 6200 km of high-resolution swath bathymetry data across the basin. This data set was combined with existing bathymetry data and is visible as a grey scale layer in this VRML. The bathymetry data set was used to help determine the location of sub-marine canyons and then accurately position dredge sites.

Basement surface

The basement surface was created in GOCAD using horizon traces of interpreted seismic data imported from GeoQuest. All basement interpretation data is in two way time. The depth to basement in TWT reaches about 8 seconds, which correlates to a depth of about 11 km using the depth-time function used for depth conversion in the Bremer Sub-basin.

Fault surfaces

GOCAD was used to create surfaces connecting fault traces imported from Geoquest and based on seismic interpretation of the data. When viewed in 3D (with the basement surface also turned on), the fault surfaces clearly show the en-echelon nature of the rift border faults in the north along with the relay ramps that connect these structures. Other structural styles such as the ENE trending Lenita-Harlequin trend in the central part of the sub-basin can also be clearly visualised when displayed in 3D.

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1.6. Coordinates

Projection

Universal Tranverse Mercator (UTM) Zone 50 South

Datum

World Geodetic System (WGS84).

Bounding box

Map Grid of Australia 1994 (MGA94) coordinates

• Lower left:   520000 E   6020000 N
• Upper right: 980000 E   6260000 N

Translation

• X shift:          -754464
• Y shift:         -6125113
• X Y Z scale:  1 / 10000

This translation has been applied to enhance graphics performance within this model.

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