298 



GUILCHER 



[chap. 13 



predominantly marine and range from Cambrian to Pleistocene. Post- 

 Carboniferous rocks seem to outcrop only in the Carnarvon and Perth basins. 

 It seems that corres])ondin<i; features, namely submarine rises and depressions, 

 exist on the shelf off the coast, so that it is believed that the geotectonic 

 elements on the shelf and in the adjacent mainland are the same, except in the 

 north-west where the North Kimberley block, between Bonaparte and Rowley 

 depressions, divides seaward into two relatively narrow ridges between which 

 the Browse depression opens. Unfortunately, no accurate information seems to 



10' 



I20°E 



125° 



130° 





x^ 



''il^ 



'\'i>'^/:-' 



INDIAN 



Ashmore Reef,-,'-)'--""-'t-0; 



BONAI^ARTE 



r&c 



GULF DEPRESSION 

 / BROWSE~-.^^>^ ^^ .., 



OCEAN /^DEPRESSION/ 



/ , ^ /l'^/"^-^ Ri nrK BONAPARTE 



v<- ROWLEY t.^\\^ -\X / / /GULRiiBASIN 



"^"J"' Rowley' /:::::::\ ff::::oVv ^\^ / I i I'- '■'■■'— \ 



4, ©Atolls \ h;:;:;:;:;i!^:;:;:;:;;i^§^^^ y tW^:"^ 



^ "' DEPRESSION li:;:i:::;i;:!:i:;:;:::;:;:;iI?inTf5^, Y V^y-^M 



<b /^■'■■::-:'.\-'r'A\\i^\\id-':-':':':'':'\'':>/:>.^'^ -• 



PILBARA V 

 i^V VV BLOCK 



IO°S 



120° E 



125° 



Fig. 9. Relationshiias between geotectonic units on continent and on shelf in North-west 

 Australia. (Simplified from Fairbridge, 1953.) Maximum thicknesses in feet of sedi- 

 mentary rocks in Canning Basin and in Bonaparte Gulf Basin, from Teichert (1958). 



be available about the thickness of the sedimentary column on the shelves, and 

 the gravimetric observations by Vening Meinesz are not very conclusive here, 

 except for the Rottnest shelf off Perth basin where an anomaly of -140 mgals 

 has been observed. A subsidence is supposed in depressions from bathymetric 

 data, esiiecially in the Bona])arte and Ro\\'ley depressions A\here the shelf is as 

 deep as .'JOO fm — a fairly unusual figure. In this north-western region, it may be 

 that sedimentation has not been able, everywhere at least, to keep pace with 

 subsidence (Tertiary rocks are not reported from the Canning and Bonaparte 

 basins) ; the downwaqiing, however, has been slow enough to allow coral reefs 

 to grow as far as the edge of the shelf (Teichert and Fairbridge, 1948). Further 

 to the south, off the Carnarvon and Perth basins, where the shelf is narrower. 



