Late Neogene molluscan faunas from the North- east Atlantic (Portugal, Spain, Morocco). [Les faunes de mollusques du N6og6ne sup6rieur de l'Atlantique nord ...
LATE NEOGENE MOLLUSCAN FAUNAS FROM THE NORTHEAST ATLANTIC (PORTUGAL, SPAIN, MOROCCO)
Josl~ ANGEL G O N Z A L E Z D E L G A D O , I N M A C ~ A
A N D R E S & FRANCISCO
J . SIERRO
GONZALEZ DELGADO J.A., ANDRES I. & SIERRO F.J. 1995. Late Neogene molluscan faunas from the Northeast Atlantic (Portugal, Spain, Morocco). [Les faunes de mollusques du N6og6ne sup6rieur de l'Atlantique nordoriental (Portugal, Espagne, Maroc)]. GEOBIOS, 28, 4 : 459-471. Villeurbanne le 15.09.1995. Manuscrit d6pos6 le 28.12.1993 ; accept6 d6finitivement le 18.07.1994.
ABSTRACT
The age of the main Neogene molluscan deposits from Lisboa, Algarve (Portugal), Sevilla, Huelva (Guadalquivir Basin, SW of Spain) to Dar bel Amri (South Rifian Basin, NW of Morocco) has been established and correlated with the global sea level changes on the basis of micropaleontological event-stratigraphic evidence. The time period ranges from the Early Tortonian to the Late Zanclean. The deposits consist of sands with levels of concentration of molluscs that are generally shell-supported, with a variable morphology and arrangement. They deposited in infralittoral environments, and are included in Transgressive Systems tracts or in Highstand Systems tracts. The taphonomic, sedimentologic and paleogeographic characteristics of most of the deposits suggest they originated by discontinuous processes of winnowing and bypassing of sediment, probably due to the action of storms in shallow waters (mainly in bay environments). From the paleoecologic point of view, a greater richness in the molluscan diversity is seen in the Pliocene outcrops with respect to the Tortonian ones. Also, there is a difference in the abundance of specimens from several families: Turritellidae and Veneridae are more abundant in Tortonian outcrops, whereas Naticidae, Nassariidae and Lucinidae are in Pliocene ones. In the Miocene deposits the filter feeding molluscs are dominant, while in the Pliocene the carnivorous, sedimentivores and scavengers are abundant as well. These changes in the trophic structure are probably related to changes in substratum, hydrodynamics, and climatic conditions from the Tortonian to the Pliocene. KEY-WORDS : MOLLUSCS, NE ATLANTIC.
TAPHONOMY,
GLOBAL
SEA LEVEL
CHANGES,
PALEOECOLOGY,
NEOGENE,
RESUME
L'~ge des principaux gisements contenant des Mollusques a 6t6 6tabli depuis Lisbonne, l'Algarve (Portugal), Seville, Huelva (Bassin du Guadalquivir, Espagne) jusqu'~ Dar bel Amri (Bassin Sud-Rifain, Maroc) ~ partir d'6tudes stratigraphiques des 6v6nements et il a 6t6 corr616 avec les changements globaux du niveau de ta mer. La p6riode 6tudi6e est comprise entre le Tortonien inf6rieur et le Zanclien sup6rieur. Les gisements sont form6s par des concentrations de coquilles dans des s6diments sableux infra-littoraux ; elles ont en g6n6ral peu de matrice s6dimentaire et pr6sentent une morphologie et une disposition variable. En relation avec tes changements eustatiques, ils forment des complexes transgressifs ou des complexes de haut niveau de l a m e r . Les caract6ristiques taphonomiques, s6dimentologiques et pal6og6ographiques de la plupart des gisements sugg6rent que leur origine se trouve dans les processus discontinus de lessivage du s6diment dans des zones de baies affect6es par les temp~tes~ Du point de vue pal6o6cologique, il y a une plus haute diversit6 de mollusques dans les gisements du Ptioc6ne que dans ceux du Tortonien. D'apr6s l'abondance des individus d'une m6me famille, on observe aussi des changements temporels : les Turritellid6s et les V6n6rid6s sont plus abondants au Tortonien, les Naticid6s, Nassarid6s et Lucinid6s au Plioc6ne. On observe aussi des changements dans les cat6gories trophiques en relation avec des diff6rences d'habitat s6dimentaire et les conditions climatiques entre le Tortonien et le Plioc6ne. MOTS-CLI~S : MOLLUSQUES, TAPHONOMIE, ATLANT~QUE NORD-ORIENTAL.
CHANGEMENTS
EUSTATIQUES,
PALI~OECOLOGIE,
NI~OGI~NE,
460 RESUMEN Se ha establecido la edad de los principales yacimientos con Moluscos de Lisboa y el Mgarve (Portugal), Sevilla y Huelva (Cuenca del Guadalquivir), y Dar bel Amri (Cuenca Surifefia, Marruecos), correlacionandose con los cambios globales del nivel del mar, a partir de estudios micropaleontol6gicos evento-estratigr~ficos. E1 tiempo comprendido abarca desde el Tortoniense inferior al Zancliense superior. Los yacimientos estfin formados por concentraciones de conchas, generalmente con poca matriz sedimentaria, de morfologla y disposicidn variable, en sedimentos arenosos infralitorales. Se incluyen en cortejos transgresivos o en cortejos de alto nivel del mar. Las caracterlsticas tafon6micas, sedimentol6gicas y paleogeogr~ficas de la mayorla de los yacimientos sugieren que se originaron por procesos discontinuos de lavado de sedimento en zonas de baMa afectadas por tormentas. Desde el punto de vista paleoeeol6gico, se apreeia una mayor diversidad de Moluscos en los yacimientos del Plioceno con respecto a los del Tortoniense. Tambi6n se observan cambios en la abundancia de individuos de varias familias : los Turritellidae y Veneridae son mils abundantes en los yacimientos del Tortoniense, mientras que los Naticidae, Nassariidae y Lucinidae lo son en los del Plioceno. Los moluscos filtradores dominan en los yacimientos del Tortoniense, y en los plioc~nicos son abundantes tambiSn los carnivoros, sedimentivoros y carrofieros. Estos cambios en la estructura trdfica probablemente est~n relaeionados con variaciones en el substrato y en las condiciones hidrodinfimieas y climfiticas en la regidn desde el Tortoniense al Plioeeno. PALABRAS CLAVE : MOLUSCOS, TAFONOMiA, EUSTATISMO, PALEOECOLOGiA, NEOGENO, NE ATL~TICO.
INTRODUCTION A s t u d y h a s b e e n m a d e in t h e deposits w i t h moll u s c a n f a u n a f r o m t h e U p p e r Miocene a n d L o w e r Pliocene, w h i c h are s i t u a t e d in a g e o g r a p h i c r a n g e close to t h e c u r r e n t N E A t l a n t i c coastlim,. i n c l u d i n g a n a r e a e x t e n d i n g f r o m C e n t r a l Pm'l~gal (the L i s b o a region, d e p o s i t s of Foz do Re~, a n d F o n t e d a Telha), t h e A l g a r v e (Cacela), SW c,f S p a i n (Sevilla, A r r o y o Trujillo outcrop, Huelva~, to t h e N W of Morocco ( D a r - b e l - A m r i ) (Fig. 1). T h e lithology of s u c h dep~)sits is sandy. U n l i k e t h e s i t u a t i o n in m a n y bc(t.~ with m,,lluscs from t h e M e d i t e r r a n e a n Neogcm,. ~m l ~ t ~ the Tortonian and Tabianian stratotyi.l(~,hba 1968, 1990 ; Pelosio 1967), t h e silt and ,~ ,~ lacws cont a i n v e r y few m o l l u s c s in this zorn. I n o r d e r to b e t t e r c o m p a r e t h e d a t , (mtv the deposits w i t h s i m i l a r d e p o s i t i o n a l con(htmn.~ were c o n s i d e r e d (those w i t h t h e great~,st species r i c h n e s s a n d good p r e s e r v a t i o n both fi~r calcit(, a n d for a r a g o n i t e shells). T h e calcarenitic facies, w h i c h a r e v e r y c o m m o n in t h e N o r t h e a s t e r n p a r t of t h e G u a d a l q u i v i r b a s i n a n d Morocco (i.e. calcar e n i t e of N i e b l a F o r m a t i o n , of U p p e r T o r t o n i a n age, H u e l v a , S p a i n ; O u e d - A k r e c h calcarenite, of s i m i l a r age, Morocco), u n d e r w e n t i m p o r t a n t processes of f o s s i l - d i a g e n e t i c d i s s o l u t i o n t h a t f a v o r e d t h e p r e s e r v a t i o n of O s t r e i d s a n d Pectinids, a n d c o r r o d e d t h e m a i n c o m p o n e n t s of t h e m o l l u s c a n assemblage.
CHRONOSTRATIGRAPHIC
SETTING
M a n y of t h e outcrops s t u d i e d h e r e a r e well k n o w n in t h e paleontologic l i t e r a t u r e since t h e
~q
R /
~
~
~
~ ~_J J
~
MarineNeogene 1-FozdeRogo 4- Huelva 5- Arroyo Trujillo 6- Dar beI.Amri
Figure 1 - Geographical situation of the area studied. Situatzon ggographique de la zone dtudige.
e n d of t h e l a s t c e n t u r y b y t h e i r m o l l u s c a n r i c h n e s s ( P e r e i r a d a C o s t a 1866-67 ; Dollfus e t a l . 1903-04 ; W e n z 1942 ; L e c o i n t r e 1952). T h e age of the deposits w a s o b t a i n e d b y p l a n k t i c F o r a m i n i f e r a e v e n t - s t r a t i g r a p h y (Fig. 2). T h e N e o g e n e f o r a m i n i f e r a l r e c o r d h a s let~ a series of isochronous e v e n t s (Sierro 1985 ; Sierro e t al. 1993) defined b y c h a n g e s in t h e coiling direction or t h e r e p l a c e m e n t of p o p u l a t i o n s of k e e l e d Globorotaliids. T h e s e e v e n t s h a v e b e e n c o r r e l a t e d
461
N.a. Chron
P.F.events ~_FODG. puncticulata I
4~
k.
El
Rompido
(Huelva) .u
(D 5,7
FODG" margaritael
