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Perfil de iridio durante 10 millones de años a través del límite Cretácico-Terciario en Gubbio (Italia)
W Alvarez1, F Asaro, A Montanari
1Department of Geology and Geophysics, University of California, Berkeley 94720, USA.
Science (New York, N.Y.)
|December 21, 1990
Resumen
La anomalía del iridio en el límite Cretácico-Terciario (KT) muestra una intrincada estructura fina, que no se explica completamente solo por el impacto. Este análisis detallado refina nuestra comprensión del evento KT y las extinciones masivas.
Área de la Ciencia:
- La geoquímica es la geoquímica.
- Paleontología Paleontología.
- Ciencias planetarias Ciencias planetarias.
Sus antecedentes:
- La anomalía del iridio en el límite Cretácico-Terciario (KT) sugiere un evento de impacto extraterrestre que coincide con las extinciones masivas.
- Estudios previos en Gubbio, Italia, basados en muestras limitadas, llevaron a interpretaciones de esta anomalía.
- La controversia persistió con respecto a la forma precisa y el origen del perfil de iridio en el límite de KT.
Objetivo del estudio:
- Para llevar a cabo una investigación más detallada de la anomalía de iridio en el límite de Gubbio KT.
- Para aclarar la estructura fina y las posibles causas de la distribución del iridio.
- Para refinar la comprensión del evento KT y su extinción masiva asociada.
Principales métodos:
- Análisis de una secuencia geológica de 57 metros de espesor que abarca 10 millones de años.
- Utilizó técnicas mejoradas de análisis de activación de neutrones (NAA) para mediciones precisas de la concentración de iridio.
- Se examinó la distribución del iridio a través de la capa límite del KT.
Principales resultados:
- Se confirmó una única y distinta anomalía de iridio precisamente en el límite de la KT.
- La anomalía exhibe una intrincada estructura fina, particularmente en las "colas" flanqueantes.
- La concentración máxima de iridio (3000 ppt) se encuentra en una capa de arcilla de 1 cm, con colas que van desde 20-80 ppt por encima del fondo (12-13 ppt).
Conclusiones:
- El detallado perfil de iridio en el límite de Gubbio KT tiene una compleja estructura fina.
- Factores como la reelaboración, la difusión, la bioturbación y la ciclicidad de Milankovitch probablemente contribuyen a la estructura fina de la anomalía.
- El origen exacto de esta estructura fina requiere más investigación, refinando los modelos de impacto-evento.
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