LOS PROYECTOS DE AULA

S h a le a s in d ic a te d on

pebbly in p 1 a c e s , e s p e c i a l l y near the t o p , and s l i g h t l y c a l c a r e o u s . I t has a s i l t y m a t r i x and c ont ai ns s c a t t e r e d coal c h i p s , dark

c h e r t g r a i n s g i v i n g i t a speckl ed appearance, and minor g l a u c o n i t e .

The g r a i n s are mode r at el y s o r t e d . Very t h i n and minor bands o f coal are pr e se nt near the uppermost p a r t of the u n i t . The sand­ stone is f r i a b l e in places and c o n s o l i d a t e d in o t h e r s . I t e x h i -

v e r t i cal

b i t s s e v e r a l types o f se di me nt ary s t r u c t u r e s such as/worm burrows, r i p p l e marks, deformed s t r u c t u r e s , c onv ol ut e l a m i n a t i o n s , p l a n a r and trough c r o s s - b e d d i n g , and r i p - u p c l a s t s ( P l a t e 1 ) . S i l t s t o n e beds are abundant in the lower p a r t o f t h i s sandstone l i t h o f a c i e s . The s i l t s t o n e is g r e y , a r g i l l a c e o u s , c on ta in s s c a t t e r e d sand g r a i n s and carbonaceous f r ag me nt s. I t is a ls o s i d e r i t i c and s l i g h t l y

c a l c a r e o u s . The t h i c k n e s s o f t h i s sandstone l i t h o f a c i e s is 185 f t . (56 m).

The sandstone l i t h o f a c i e s is o v e r l a i n by a t h i n dark gr<y shale 1 i t h o f a c i e s 3 w h i c h c ont ai ns very t h i n s t r i n g e r s of very f i n e ­

g r a i n e d s a n d s t o n e , s i l t s t o ne and s h a l e . The s t r i n g e r s are very s i m i l a r to those d es cr ibe d in the u n d e r l y i n g shale l i t h o f a c i e s . In the middle o f the s ha ly l i t h o f a c i e s a f i n e - g r a i n e d micaceous sandstone i n t e r v a l is p r e s e n t . The t h i ck n es s o f t h i s t h i n shaly l i t h o f a c i e s is 50 f t . (15 m).

The t h i n sha le l i t h o f a c i e s is o v e r l a i n by a sandstone l i t h o ­ f a c i e s f, medi um- to c o a r s e - g r a i n e d , m o de r a t e l y s o r t e d , a r g i l l a c e o u s and s i l t y , and s l i g h t l y s i d e r i t i c . I t cont ai ns dark c h e r t g r a i n s , g i v i n g i t a speckled appearance, coal chips and s c a t t e r e d carbon­ aceous f rag me nts . Minor bands o f very t h i n coal are also p r e s e n t . The sandstone Is f r i a b l e in some pl aces and more c o n s o l i d a t e d in o t h e r s . In i t s lower p a r t the sandstone l i t h o f a c i e s contains s e v e r a l i n t e r b e d s of brownish g r e y , s h a ly s i l t s t o n e which

31.

Plate I . Trough cross-beds on medium scale in very