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Impact Events in Spain: Evidence and Potential Impactoclastic Units in the Sedimentary Record

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Impact Events in Spain: Evidence and Potential Impactoclastic Units in the Sedimentary Record Catastrophic Events Conference 3073.pdf IMPACT EVENTS IN SPAIN: EVIDENCE AND POTENTIAL IMPACTOCLASTIC UNITS IN THE SEDIMENTARY RECORD. E. Díaz-Martínez, E. Sanz-Rubio & J. Martínez-Frías, Centro de Astrobiología (CSIC- INTA), Crtra. Torrejón-Ajalvir km. 4, 28850 Torrejón de Ardoz, Madrid, Spain <[email protected]> Introduction: The sedimentary record of Spain pre- nants of the ejecta blanket deposits (Pelarda Formation; sents evidence for impact events, as well as units with [25]), with an outcrop of roughly 30 km2 and a thick- potential to be interpreted as impactoclastic beds (some ness of 200 m, overlie clastic alluvial fan deposits of the of them currently under study). We herein summarize adjacent Calatayud-Montalbán basin. Part of our current and review the information available on the sedimentary research focuses on the sedimentological and paleon- record of meteorite impacts in Spain, most of it pub- tological evidence in both the Ebro and Calatayud- lished in Spanish journals. In addition, we propose Montalbán basin, to contribute to solve the controversial other stratigraphic units with potential for future re- impact vs. tectonic origin of the Azuara structure, and search. to determine the age of the Pelarda Fm. Distal record of impact events: Evidence for distal Potential impactoclastic beds: One important crite- impact ejecta is found in relation with the Dogger-Malm ria for the recognition of impact-related units in the and Cretaceous-Tertiary boundaries. The Middle-Upper sedimentary record is the presence of breccia or diamic- Jurassic (Dogger-Malm) boundary at Ricla and Pozuel tite beds or well-dated massive extinction events with del Campo (Iberian Range) presents conspicuous geo- ages roughly coinciding with those of known meteorite chemical anomalies (e.g., heavy metals, platinum-group impacts. Breccia and diamictite beds are frequent in elements), volcanic and hydrothermal activity, subma- Spain, although they are usually interpreted as synsedi- rine corrosion, high concentration of spherules, and Fe- mentary redeposition related with slope and/or tectonic Mn bacterial-fungal stromatolites [1]. The K-T bound- instability, and more rarely as glacigenic deposits. Apart ary has been thoroughly studied at several stratigraphic from those more clearly related with active tectonism or sections with deep marine deposits (Zumaya and Eibar eustacy, other units exist displaying a strong potential as in the western Pyrenees -corresponding to the eastern impact-induced. For most of them, evidence is not une- Basque-Cantabrian basin-, Agost and Caravaca in the quivocal, and many features still remain to be ex- Bethic Cordillera, etc.), where unequivocal evidence plained. was found for an impact origin in relation with a major Vendian-Cambrian boundary. Deep marine breccias faunal turnover [2-15]. At Caravaca, a marked Ir anom- and olisthostromes of the "Nivel de Fuentes" (Fuentes aly was found, in conjunction with V, Cr, Fe, Ni, Zn Bed, Membrillar Megabreccias and Olisthostrome, Na- and As anomalies, and abundant spherules [2,3]. The valpino Breccia) in the Valdelacasa and Navalpino anti- absence of volcanic products at this section strengthens clines (Central Iberian Zone of the Hercynian Massif) the case for an extraterrestrial hypothesis [10,11]. High- broadly coincide with the Vendian-Cambrian boundary resolution biostratigraphy of planktic foraminifera at [26-33], and have been traditionally related to the Ca- Osinaga and Musquiz (Navarra Pyrenees) has further domian/Pan-African orogeny. detected a small hiatus with iron oxides at the K-T Latest Ordovician. Shallow-marine Hirnantian boundary [16], to be considered in the interpretation of diamictites (the so-called "Pelitas con fragmentos" or related biotic changes. Many other sections exist in fragment-bearing shales) are present throughout the Spain with continuous exposure and detailed Central Iberian Zone with different formational names biostratigraphy of the K-T boundary, and with potential [34-36]. They have been generally assigned to coeval to identify distal impact ejecta within them. north African glaciation. Proximal record of impact events: The only Late Devonian. Shallow-marine diamictites within proximal impact ejecta bed in Spain is the Pelarda For- the "Phyllite-Quartzite Group" of the Iberian Pyrite Belt mation, related with the Azuara impact structure, near (South-Portuguese Zone of the Hercynian Massif) are Zaragoza (Spain). After its first recognition and inter- commonly interpreted as mega-debris flows related with national consideration [17-19], a strong debate arose tectonism [37,38]. regarding its tectonic or impact origin [20-24]. The Triassic-Jurassic boundary. In most of Spain this Azuara impact structure is located on the eastern branch boundary is marked by a regional erosional of the NW Iberian Range, which separates the Tertiary unconformity and/or earliest Jurassic (Hettangian) brec- Ebro and Calatayud-Montalbán basins. The diameter of cias. Some are interpreted as related with rifting and the ring-like remanent structure is 30 km, and the total eustacy [39-42], whereas others are considered the re- original diameter is estimated between 35 and 40 km. It sult of collapse after evaporite dissolution [43]. is considered as late Eocene-Oligocene in age [20], and Cenomanian-Turonian boundary. Impact ejecta have is outlined by Mesozoic and Paleozoic rocks. The rem- recently been found north of Nazaré (Mesozoic Lusi- Catastrophic Events Conference 3073.pdf SEDIMENTARY RECORD OF IMPACT EVENTS IN SPAIN: E. Díaz-Martínez et al. tanian basin of Portugal), near the Cenomanian- 161-164. [35] Robardet, M. & F. Doré (1988) Palaeo- Turonian boundary, and in probable relation with the geogr., Palaeoclim., Palaeoecol., 66, 19-31. [36] Gar- Tore seamount impact structure located off the coast of cía-Palacios, A. et al. (1996) Geogaceta, 20, 19-22. [37] Portugal [44-47]. The potential exists in Spain to find Moreno, C. & R. Sáez (1990) Geogaceta, 8, 62-64. [38] distal ejecta in the frequent excellent exposures of shal- Moreno, C. et al. (1995) Geogaceta, 17, 9-11. [39] low and deep marine sequences covering this same in- Aurell, M. et al. (1992) III Congr. Geol. España, 1, 50- terval (Cenomanian-Turonian boundary). Some of these 54. [40] San Román, J. & M. Aurell (1992) Palaeo- Spanish sections are already well dated based on cal- geogr., Palaeoclim., Palaeoecol., 99, 101-117. [41] careous nannoflora, planktic foraminifera, and ostracod Gallego, R. et al. (1994) Geogaceta, 15, 26-29. [42] biostratigraphy [48-49]. Campos, S. et al. (1996) Geogaceta, 20, 887-889. [43] The present contribution attempts (a) to bring the Gómez, J.J. & A. Goy (1998) Geogaceta, 23, 63-66. attention of the international community towards recent [44] Pena dos Reis, R.P. et al. (1997) Geogaceta, 22, and ongoing research relating the sedimentary record of 149-152. [45] Monteiro, J.F. et al. (1997) LPS XXIX, 2, impact events in Spain, and (b) to promote new research 967. [46] Monteiro, J.F. et al. (1998) Meteoritics & regarding the aforementioned units to search for evi- Planet. Sci., 33, A112-A113. [47] Monteiro, J.F. et al. dence of an impactogenic origin. (1999) Rep. Polar Res., 343, 64-66. [48] Gil, J. et al. References: [1] Meléndez, G. et al. (1987) Geoga- (1993) Geogaceta, 13, 43-45. [49] Gorostidi, A. & ceta, 2, 5-7. [2] Smit, J. & J. Hertogen (1980) Nature, M.A. Lamolda (1996) Geogaceta, 20, 887-889. 285, 198-200. [3] Smit, J. & G. Klaver (1981) Nature, 292, 47-49. [4] Smit, J. & W.G.H.Z. ten Kate (1982) Cretaceous Res., 3, 307-332. [5] Groot, J.J. et al. (1989) EPSL, 94, 385-397. [6] Lamolda, M.A. (1990) Global Bio-Events, Springer, 8, 393-399. [7] Smit, J. (1990) Geologie en Mijnbouw, 69, 187-204. [8] Canudo, J.I. et al. (1991) Marine Micropal., 17, 319-341. [9] Arz, J.A. et al. (1992) III Congr. Geol. España, 1, 487-491. [10] Martínez-Ruíz, F. et al. (1992) Chemical Geology, 95, 265-281. [11] Martínez-Ruíz, F. et al. (1992) Geoga- ceta, 12, 30-32. [12] Molina, E. et al. (1994) Eclogae Geol. Helv., 87, 47-61. [13] Molina, E. et al. (1996) Rev. Micropal., 39, 225-243. [14] Baceta, J.I. et al. (1997) Geogaceta, 22, 225-231. [15] Arz, J.A. et al. (1998) Geogaceta, 23, 15-18. [16] Arenillas, I. et al. (1997) Geogaceta, 21, 25-28. [17] Ernstson, K. et al. (1985) EPSL, 74, 361-370. [18] Ernstson, K. et al. (1987) Meteoritics, 22, 373. [19] Grieve, R.A.F. (1987) Ann. Rev. Earth Planet. Sci., 15, 245-270. [20] Ernstson, K. & J. Fiebag (1992) Geol. Runds., 81, 403- 425. [21] Aurell, M.et al. (1993) Geol. Runds., 82, 750- 755. [22] Ernstson, K. & J. Fiebag (1993) Geol. Runds., 82, 756-759. [23] Cortés, A.L. & A.M. Casas (1996) Rev. Soc. Geol. España, 9, 51-66. [24] Langen- horst, F. & A. Deutsch (1996) LPS XXVIII, 2, 725-726. [25] Ernstson, K. & F. Claudín (1990) N. Jb. Geol. Paläont. Mh., 10, 581-599. [26] Moreno, F. (1974) Bol. Geol. 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