Stratigraphy and Carbonate Microfacies of the Hirna Mesozoic Sequence
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Date
1981-12
Authors
Journal Title
Journal ISSN
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Publisher
Addis Ababa Universty
Abstract
The study are apresent sex posuresr a n g i n g i n a ge
from the Precam bria n ( b a s e m e n t ) t h r o u g h M e s o z o i c
(s e d i m e n t s) t o t h e T e r t i a r y ( v o l c a n i cs) w it h a l l u v i a l
s e d i m e n t s o f r e c e n t a g e a l s o p r e s e n t. T h e d i f f e r e n t
l i t h o l o g i c a l u n i t s h a v e b e e n m a p p e d a s w e l l a s
des c r i b e d base d o n fi e l d o b s e r v a t i o n s.
T h e M e s o z o ic s t ra t i gr a p hy o f H i r n a ar e a h a s b e e n
s t u d i e d w i t h p a r t i c u l a r r e f e r e n c e t o t h e c a r b o n a t e
l ith o l o g y. T h ree m ai n c ar b o na t e m i c r of a c i e s ha v e b e e n
i d e n t i f ied a s b e i n g r e p r es e n t a t iv e major c o n s t i t u e n t s
o f t h e s e c a r b on a t e s. T h e s e m i c r o fa c i e s a re d i st r i b u t e d
i n a c y c l i c m a n n e r w i t h t i me. T h e c y c l ic i t y h a s b e e n
i n t e r p r e t ed a s s h ow i ng s ma l l ch a n g e s o f se a l e ve l i n a
g ene r a l l y s h a l l o win g u p s eq u en c e.
B i o s t r a t i g r a p h i c a n d pa l e o g e o gr a p h i c co n si d e r a t i o n s
s h o w t h a t t he L o w e r S a n d s t o n e U n i t ( T ri a s s i c.- M i d d l e
J u r a s si c) i s c or r e l at i v e w i t h t he regionally i d en t i f i e d
A d i g r a t. S a nd s t o n e s. T h e c a r b o n a te s o n t h e o t h e r h a n d
c a n b e r ef e rr e d i n p a r t t o t h e H a m a n l e i s e q u e n c e
(?B a t- h o n i a n- Lower Ox f o r d ia n a g e i n H ir n a a r e a ) a n d i n
p a r t ' t o t h e U a r a n d a b s e q u e n c e ( K i m m e r i d gi a n a g e i n
Hir n a ar e a). T h e U p p e r S a n d st o n e U n i t i s a p a r t o f t h e.
Y e s o m m a s e q u e n c e a n d i s o f C r e t a c e ou s a g e i n H i r n a
a r e a. Tectonically , Hirna area is only lightly deformed ,
with a SW - NE fault trend dominating the structures.
Other trends , however , do exist with not so clear a
relationship with the dominant, trend. Gentle dips of
local significance are shown by some of the Phanerozoic
lithologies.
Description
Keywords
Hirna Mesozoic Sequence