Mathematics – Logic
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.214d&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 214
Mathematics
Logic
Scientific paper
In late 1990, Ampol Exploration drew the attention of the senior author to an enigmatic structure located in Mesozoic rocks in the Dandaragan Trough of the Perth Basin about 200 km north of Perth, Western Australia. The basin-like Yallalie structure, centred on coordinates ca. 30 degrees 28'S, 115 degrees 47'E, is subcircular in plan view and about 15 km in diameter. Recognizing structures beneath the basin likely to contain oil, Ampol carried out an intensive geophysical survey of the area, and subsequently drilled a well (Yallalie 1). The well proved to be dry and exploration ceased. Generously, Ampol and their partners have made available the results of their exploration for a research project into the nature of the structure. Geology and regional setting: The exposed geology of the Yallalie basin area comprises discontinuous sequences of sedimentary rocks (sandstones, siltstones and shales) of Middle Jurassic to Late Cretaceous age that are capped by laterite and locally covered by thin (<50 m) Cenozoic eolian, colluvial and alluvial deposits (Cockbain, 1990). Modern, high-resolution, seismic reflection profiles across the Yallalie structure show a basin-shaped area of chaotic reflections that extend down to a depth of approximately 2 km below the surface. The structure has sharp boundaries with surrounding faulted, but otherwise relatively undisturbed rocks. At the base of the structure there is a central uplifted area approximately 3-4 km across similar to those described from complex impact structures (Dence et al., 1977). A preliminary survey of the area has shown that exposed rocks of the Yarragadee Formation (Middle Jurassic to Lower Cretaceous) and the succeeding Warnbro (Lower Cretaceous) and Coolyena (Late Cretaceous) Groups dip gently and their deposition appears to have postdated the underlying structure of intensely disturbed rocks. Although the structure is "draped" by a thin (a few hundred metres) veneer of late Jurassic to Cretaceous rocks it has some surface expression. A broad depression approximately 120 m deep is centered on Yallalie Well and is bounded to the west and north by a marked "rim." The area is characterized by a radial pattern of drainage that flows into the depression and which is gradually exhuming the buried structure. A southerly flowing stream drains the depression and has breached the "rim" to the south. Evidence for impact at Yallalie: Quartz grains taken from the core at a depth of 430-460 m in the Yallalie 1 well show widesprad development of prismatic cleavage fractures and irregular, slightly curved planes formed by brittle fracture. Quartz grains from a depth of 150-180 m in the well are essentially undeformed (McInerney, 1991). However, multiple sets of closely spaced planar features in quartz, characteristic of highly shocked rocks, have yet to be observed in core material from the Yallalie structure. Nevertheless, the morphology of the Yallalie structure determined from geophysical data suggests strongly that it is of impact origin. Work is continuing on the core material to search for diagnostic shock-metamorhic effects, and to constrain the age of the structure. References Cockbain A. E. (1990) In Geology and Mineral Resources of Western Australia, Western Australia Geological Survey, Memoir 3, pp. 514-516. Dence M. R., Grieve R. A. F., and Robertson P. B. (1977) In Impact and Explosion Cratering (eds. D. J. Roddy, R. O. Pepin, and R. B. Merrill), Pergamon Press, pp. 247-275. McInerney K. B. (1991) Honors Thesis (unpublished), University of Western Australia.
Bevan Alex W. R.
Dentith M. C.
McInerney K. B.
No associations
LandOfFree
A Preliminary Investigation of the Yallalie Basin: A Buried 15 KM Diameter Structure of Possible Impact Origin in the Perth Basin, Western Australia does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A Preliminary Investigation of the Yallalie Basin: A Buried 15 KM Diameter Structure of Possible Impact Origin in the Perth Basin, Western Australia, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Preliminary Investigation of the Yallalie Basin: A Buried 15 KM Diameter Structure of Possible Impact Origin in the Perth Basin, Western Australia will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1209679