LATE CRETACEOUS-EARLY TERTIARY ECHINOIDS 



83 



Basque region 



Salvatierra 



A15 



Pamplona< 



Fig. 1 Location maps, a, The three main areas in Spain and southern France from which the echinoid faunas are described, b. The location of the main 

 echinoid-bearing horizons in the Irurtzun region, Navarra, studied in this paper. 1 = Olazagutia Pass; 2 = Casas de Oraien; 3 = Larumbe; 4 = Sarasate; 5 : 

 Erice; 6 = Aristregui. 



should help shed light on the immediate causes that led to the end 

 Cretaceous extinctions. 



We have been studying the echinoid faunas on either side of the 

 Cretaceous - Tertiary boundary from three regions in Northern 

 Spain. These faunas come from the open shelf sandy carbonate 

 succession to the West of Santander, the continental slope deposits of 

 the Basque region (Sopelana to Bidart), and the carbonate platform 

 to intraplatform basinal facies around Irurtzun in the Province of 

 Navarra (Fig. la). New collections from the Santander region 

 (Gallemi, Jeffery & Smith), Basque region (Peter Ward) and Navarra 

 region (Ernst, Gallemi, Jeffery & Smith) have been made, and the 

 taxonomy updated and standardized. Using this new data we com- 

 pare levels of extinction in the three faunas to see if there is any 

 environmental signal. We also compare the level of extinction in 

 northern Spain with that recorded from other European regions, 

 specifically with Limburg and the Danish basin, to discover whether 

 there is a latitudinal bias to extinction at this time. It has been shown 

 that foraminifera suffered less intense extinction at higher 

 palaeolatitudes (MacLeod & Keller, 1994, MacLeod, 1995) whereas 

 no such pattern was evident for molluscs (Jablonski & Raup, 1994). 



GEOLOGICAL SETTING 



The late Cretaceous is represented by a wide range of facies and 

 palaeoenvironments in the Basco-Cantabrian basin of northern Spain. 

 By middle Campanian times this region formed a single flysch 

 trough with lateral slope deposits, bordered by narrow shelf plat- 

 forms. The southern margin of the evolving Biscay ocean developed 

 as a series of pull-apart basins (Wiedman era/., 1983) which became 

 progressively more strongly affected by strike-slip tectonics to the 

 east. Shallow-water carbonate facies developed across this narrow 



shelf, with black shale facies forming in local basins. The Biscay 

 trough extended approximately east-west along the line now formed 

 by the Pyrenees. This oceanic arm, which is estimated to have had a 

 palaeodepth of approximately 1.500 m (Delacotte, 1982), separated 

 the shallow marine deposits of the Navarra-Cantabria platform to the 

 south from the corresponding shallow shelf deposits of the South 

 Aquitaine platform to the north-east. 



There is a strong sea-level signature recognizable in the deposits 

 of this region. Maastrichtian deposition falls within a single sea-level 

 cycle (Wilmsen et al., 1996). A major facies change occurs more or 

 less coincident with the K-T boundary, brought about by rapid sea- 

 level rise (Haq et al., 1987, Keller et al., 1993). During the Danian 

 sea-level fell gradually, but began to rise once more in the late 

 Thanetian. Climate towards the end of the Cretaceous was deterio- 

 rating (Barrera, 1994). 



DETAILS OF SECTIONS 



The Santander region 



In the immediate vicinity of Santander, from Cabo Mayor west- 

 wards, Maastrichtian-Palaeocene sediments are exposed along the 

 coastal cliffs (Fig. 2). The stratigraphy of this section has been 

 studied in detail by Heredia et al. (1990) as part of the geological 

 mapping of Cantabria. Here the Upper Campanian to Maastrichtian 

 beds belong to the Cabo de Lata Formation (Garcia-Mondejar & 

 Pujaite, 1982). The Maastrichtian part of the succession falls within 

 a single sea-level cycle referred to as Megasequence 5 by Wilmsen et 

 al. (1996). The basal beds comprise cross-bedded calcarenites with 

 many hardgrounds and temporary hiatuses in sedimentation, and 

 were deposited under falling sea-level. The presence of occasional 

 tempestites suggests deposition within storm wave-base. 



