H e a d a nd B a s i l e v s k y ( 1996) also r e c og n i s e s e q u e n c e s o f st ructural d ef o r m at i o n that c a n be p l a c e d in c o n t e x t wi t h i n the g l obal s t r a t i g r a p h y m o d e l . T h is ser ies o f t e c t o n i c e p i s o d e s is i n t e r p r e t e d by t h e m to i n d i c a t e d i s t i n c t , i f n o t o c c a s i o n a l l y ove r la pp i ng , p er iods o f global to regional def or mat ion. F i gu r e 2.2 s h o w s these e pi sodes in relation to the stratigraphie units, as a function o f time.
Fhese d e f o r m a t i o n a l s e q u e n c e s can be d iv i de d into t w o ma i n gr oups: structures as s oc i a t e d wi th t es ser a and s truct ure s that d e f o r m pl ai ns mat er ia l s. T e s s e r a mat er i a ls ha ve u n d e r g o n e i nt ensi ve mul ti pl e e p i s o de s o f d e f o r m a t i o n , w h i c h m a y h a ve c h a n g e d o v e r t i me f r om c o m p r e s s i o n to ext ens ion ( B i n d s c h a d l e r a nd He ad, 1991; B i n d s ch ad le r et al., 1992a; I v a n o v a nd He ad, 1993, 1995, 1996; B a s i l e v s k y et al., 1997). Plains
G L O B A L S T R A T I G R A P H Y A N D L A R G E V O L C A N O D E V E L O P M E N T 52
d e f o r m a t i o n i ncludes first ridge belt for ma ti on (lar ge scale c o m p r e s s i o n ) , t hen wr i nkl e r i dge for ma ti on (large scale regional co mp r e ss io n wi t h s o m e local c o m pr e s s l o n a l events i.e. at c o r o n a e [ B as i l e vs ky et ah, 1997]), and finally f aul t ing that m a y o r m a y not be assoc ia te d with rifts (B a s il ev s ky et ah, 1997; B a s il ev s ky and He ad, 2000).
A s e q u e n c e o f d e f o r ma t i o n associat ed with c o r o n a e is also s u gg e s t ed (B a s il ev sk y and He ad, 1995b, 1996, Bas il evs ky et ah, 1997), g i v i ng rise to the units C od f, C o a r and Go a f. T h i s ‘ideal s e q u e n c e ’ for c o r o n a e f o r m a t i o n i m p l i e s s p e c i f i c e p i s o d e s o f d e f o rm a t i o n restricted within the Periods desc ri bed above.
VENUS REGIONAL AND GLOBAL STRATIGRAPHY
S t r a t i g r a p h i e U n its C o l u m n P». PI. COaf P». PI COdf E v e n t s • Wind S treak s • D ebris S h e e ts • Paraboloid C raters • Local In ten se Fracturing • Sm o o th Plains P r o c e s s e s • Rlftmg • A ss o c ia te d V olcanism • Minor F ractu res
• Sm o o th Plains E m placem ent
• Minor E x ten sio n a l T ec to n ic s • B asaltic V olcanism • WrInRle Ridge Form ation • C o ronae/A rachn. R idges •_ P laln s_ E m g lace^ • C o m p re sslo n a l T ecto n ics • Volcanism • Ridge Belt Form ation • Plains Em placem ent
• C o m p re sslo n a l T e c to n ic s • V olcanism
• Plains Fracturing • Plains Em placem ent
• Vast E x ten sio n a l T eclo m sm • Corona Formation • V olcanism • T e ss e ra -F o rr D eform atlot •T e ss e ra P rec u rso r F o r m a t i o n
• Vast E x ten sio n a l a n d
C o m p re sslo n a l D efo rm atio n
a o
_ lU
Figur e 2.2. A s u m m a r y o f the regional and global st ra t i gr a ph y a nd g e o l og i c history o f V e n u s p r o p o s e d by B a s i l e v s k y and H e a d (1994) . In t he left c o l u m n m a p unit s are s h o w n in o r d e r o f st rat igraphie position (oldest at the b o t t o m ) and as so ci at ed structures (in bra cket s) . I nt er pret ed geol ogi ca l history is s ke t c he d in the next c o l u mn . T h e right h a n d c o l u m n s d e s c r i b e the g e o l o g i c a l p r o c e s s e s r e s p o n s i b l e for t he units. After B a s i l e v s k y a nd H e a d (1994).
GLOBAL STRATIGRAPHY AND LARGE VOLCANO DEVELOPMENT 53