Stratigraphy and palaeoceanography o f a top og ra p h y-co n tro lle d
con tou rite d rift system in the Pen Duick area, Southern G ulf o f Cadiz
V a ndorpe T h o m a s ', D avid Van R o o ij', H enk De Haas2 and Francisco Javier H e rn a n d e z -M o lin a 3
1 Renard C entre o f M arine G eology, D e p a rtm e n t o f G e o lo g y and Soil Science, G h e n t U n ive rsity,
K rijg sla a n 281 S8, B-9000 Gent, B elgium
E-mail: T h o m a s.va n d o rp e @ u q e n t.b e
2 D e p a rtm e n t o f M arine G eology, NIOZ Royal N e th e rla n d s In s titu te fo r Sea Research, D e p a rtm e n t o f
M arine G eology, PO Box 59, 1790 AB Den Burg, th e N e th e rla n d s
3 D e p a rtm e n t o f Earth Science, Royal H o llo w a y U n iv e rs ity L ondon, Egham, S urrey TW 20 OEX,
U nited K in g d o m
The n o rth e rn p a rt o f th e G u lf o f C adiz has and s till is re ce ivin g a lo t o f a tte n tio n fro m th e s c ie n tific
c o m m u n ity due to (a m o n g s t o th e rs ) th e re ce n t IODP E x p e d itio n 3 3 9 (N o ve m b e r 2 0 1 2 - January
20 1 3 ). On th e c o n tra ry , th e s o u th e rn p a rt o f th e G u lf received fa r less a tte n tio n , a lth o u g h m ud
volcanoes, d ia p iric rid g e s and c o ld -w a te r co ra ls are p re se n t in th is re g io n (Van R ensbergen e t al.,
2 0 0 5 ; W ie n b e rg e t al., 2 0 0 9 ). The El A rra ic h e m ud vo lca n o fie ld is c h a ra c te riz e d by a co m p re ssive
re gim e (op p o se d to th e e x te n sive re g im e in m o s t o f th e G ulf), c re a tin g several rid g e s and a id in g the
m ig ra tio n o f h y d ro c a rb o n s to w a rd s th e surface. T h is s tu d y p re se n ts se ism ic and m u ltib e a m
evidence fo r th e e x iste n ce o f a c o n to u rite d r ift a t w a te r d e p th s betw een 550 and 6 5 0 m e te rs along
th e so u th w e s te rn fla n k s o f th e Pen D u ick e s c a rp m e n t (PDE) and G em ini m ud vo lc a n o (GMV), w ith in
th e El A rra ic h e m ud vo lca n o fie ld . From th e o n s e t o f th e Q u a te rn a ry, w hen th e e s c a rp m e n t sta rte d
to lift and th e m ud vo lca n o o rig in a te d , c o n to u ritic d e p o s itio n was in itia te d a t th e fo o t o f both
to p o g ra p h ie s . In itia lly , fa irly low -speed b o tto m c u rre n ts gave rise to sheeted d r ift d e p o s its , a ffe c te d
by th e u p lift o f th e PDE o r e x tru s io n o f m ud fro m th e GMV. From th e M id-P leistocene on w a rd s,
separated m o u n d e d d r ift d e p o s its fo rm e d due to in te n s ifie d b o tto m c u rre n ts . The m o u n d e d nature
o f th e d e p o s its increases u p w a rd , in d ic a tin g an in cre a sin g b o tto m c u rre n t speed. A re ce n t AAIW
in flu e n ce fo r th e d r ift is p ro p o se d based on CTD d a ta and its in flu e n c e d u rin g g la c ia l p e rio d s is also
like ly. H ow ever, as th e n o rth e rn e x te n t o f g la cia l AAIW is n o t y e t c o n s tra in e d , g la c ia l n o rth A tla n tic
in te rm e d ia te w a te r m ig h t also p lay a role in th e fo rm a tio n o f th e d rift. The
in flu e n c e o f the
M ed ite rra n e a n O u tflo w W ater (MOW) is n o t obse rve d at p re s e n t and th e changes re co rd e d w ith in
th is c o n to u rite d r ift d iffe r fro m th e M O W -dom inated c o n to u rite d e p o s itio n a l syste m in th e n o rth e rn
G u lf o f C adiz and th e Le D anois area (Van Rooij e t al., 2 0 1 0 ; B ra cke n rid g e e t al., 2 0 1 3 ). D rift
d e p o s its in th e Pen D u ick area o n ly o c c u r as e a rly as th e base o f th e Q u a te rn a ry (co m p a re d to the
Early-Pliocene fo r th e n o rth ) and m o u n d e d d r ift d e p o s its o n ly o c c u r fro m th e M id d le -P le isto ce ne
o n w a rd s (co m p a re d to th e Early-Pleistocene). A ll o f th e se in d ic a tio n s rule o u t a M O W -influence on
th e d r ift system . C o ld -w a te r co ra l m o u n d s have been fo u n d w ith in and on to p o f th e s e d im e n ta ry
sequence a t th e fo o t o f th e PDE. T h is im p lie s th a t e n v iro n m e n ta l c o n d itio n s in w h ic h c o ld -w a te r
corals th riv e w ere p re s e n t in th e past at th e fo o t o f th e PDE and n o t o n ly on to p .
References
B rackenridge R.E., F.J. H e rn á n d e z-M o lin a , D.A.V. S tow and E. Llave. 2 0 1 3 . A Pliocene m ixe d
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