Planet Mars
Universidad Internacional Menéndez Pelayo
Palacio de Magdalena, Santander, Cantabria (Spain)
5th to 9th July, 2004
Fieldtrip Guide to the K/T Boundary at Santander
Fernando Ayllón & Jesús Martínez-Frías
Centro de Astrobiología (CSIC/INTA)
Associated to the NASA Astrobiology Institute
Instituto Nacional de Técnica Aeroespacial
Ctra de Ajalvir, km 4
28850 Torrejón de Ardoz, Madrid (SPAIN)
AIM OF THE EXCURSION AND BRIEF DESCRIPTION OF THE
STRATIGRAPHIC SECTION
Spain presents two areas where the transition from the Cretaceous to the Tertiary
system (K/T boundary) is very well preserved, with associated Ir anomalies which have
been studied in some of the most relevant publications about meteoritic impact markers
in the stratigraphic record (see references). The most representative localities of both
zones are: Zumaia, in Guipúzcoa (Basque-Cantabrian Basin), and Agost and Caravaca
in Levante (Betic cordillera).
Along the Cantabrian coast west of Zumaia there are several sections where the
Cretaceous-Tertiary transition crops out. Regarding impact studies, these sections have
not been investigated in detail due to the apparent lack of a specific clay layer of
material attributed to the end Cretaceous meteoritic impact. Stratigraphical and
paleontological studies point to a more gradual, ill defined, sedimentary transition for
this area. In this context, at the Centro de Astrobiología we have initiated the
investigation of the K/T boundary sections in Cantabria, focussing in the mineralogical,
geochemical and isotopic changes that have taken place in the rocks (sand-bearing
limestones and dolomites) deposited just below, along and above the boundary.
The aim of this excursion is to introduce the participants to the geology and
general features of the sedimentary rock section placed along the North coast of
Santander. These rocks were deposited on an open shelf, sandy carbonate succession at
the time of the transition from the Cretaceous to the Tertiary period, around  65 Ma.
As we walk westwards along the coast, the gentle dipping section evolves from
relatively shallow inner platform clastic materials, deposited within fair-weather wave
base (Cabo de Lata Fm), to a shallow restricted internal platform, probably emerged at
times (San Juan Fm). In the three planed stops, attention will be focussed on the
environments on which sedimentation took place, on the abrupt faunal decline as we
progress upwards in the section and on the diagenetic processes that modified the
sedimentary rocks after deposition.
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STOP 1: PANTEÓN DEL INGLÉS
Bioclastic accumulations on the Maastrichtian.
Here we have a fair view of the coast to the west. The small promontory, marked
by a tombstone, is formed by sandy limestones with tempest associated deposits
(tempestites). The tempestites are formed by significant accumulations of fossil
fragments.
STOP 2: CABO DE LATA
Silicification of fossil fragments and formation of geodes.
At this point the sandy limestone beds present fist-sized brownish lumps, more
resistant to erosion, formed by fossil fragments cemented by silica. A few meters above
in the section one limestone bed presents numerous small, white and cm-sized geodes
formed by amorphous silica + quartz + calcite, with relict micro-crystals of anhydrite.
Both features are considered to represent early cementation (diagenetic) processes
diagnostic of arid climatic conditions and supratidal coastal environments after
deposition. Our results, based on a fluid inclusion study of the geode minerals, support
this hypothesis.
Just ahead this bed, above a soft brown marl bed, lies the last bioclastic-rich bed
of the section.
STOP 3: BAJOS DE MALASMAÑAS.
Dolomitization at the K/T boundary.
In these rocky reefs the transition from the Cabo de Lata Fm to the San Juan Fm,
where the K/T boundary lies, is reflected in the geomorphology. The San Juan Fm,
formed by laminated dolomites with hardgrounds, shrinkage cracks and sandy lenses, is
more easily eroded. This gives a rugged profile to these rocks, which lie above well
bedded tabular limestones also affected by dolomitization. At this zone, very scattered
foraminifera are the only fossils present. Further upwards in the San Juan Fm,
gasteropods and ostracodes are also found.
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SELECTED REFERENCES
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lowermost Tertiary hemipelagic successions in the Basque Country (western Pyrenees):
evidence for a sudden extinction of more than half planktic foraminifer species at the K/T
boundary. Bulletin Societé Geologique de France, 168 (6): 783-793.
Arinobu, T., Ishiwatari, R., Kaiho, K. & Lamolda, M.A. (1999) Spike of pyrosynthetic
polycyclic aromatic hydrocarbons associated with an abrupt decrease in delta C-13 of a
terrestrial biomarker at the Cretaceous-Tertiary boundary at Caravaca, Spain. Geology, 27 (8):
723-726.
Arz, J.A., Arenillas, I., Molina, E. & Sepulveda, R. (2000) Planktonic foraminiferal stability in
the Upper Maastrichtian and the catastrophic mass extinction at the Cretaceous-Tertiary (K/T)
boundary at Caravaca (Spain). Revista Geológica de Chile 27 (1): 27-47.
Canudo, J.I., Keller, G. & Molina, E. (1991) Cretaceous Tertiary boundary extinction pattern
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Díaz-Martínez, E., Sanz, E. & Martínez-Frías, J. (2002) “Sedimentary record of impact events
in Spain” Geological Society of America Special Papers, 356: 551-563.
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during diagenesis of the K/T boundary ejecta layer in the Agost section (SE Spain): implications
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Ortega-Huertas, M., Martinez-Ruiz, F., Palomo, I. & Chamley, H. (2002) Review of the
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mineral patterns across the Cretaceous-Tertiary boundary in Mediterranean and Atlantic
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