イリジウムのプロファイルは,1000万年前,グッビオ (イタリア) のクレタセアス-第3期境界を越えています

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

まとめ

クレータ紀・三次紀 (KT) 境界のイリジウム異常は,衝突だけで完全に説明できない複雑な微細構造を示している. この詳細な分析は,KTイベントと大量絶滅に関する私たちの理解を洗練します.

科学分野:

地質化学地質化学
パレオントロジー・パレオントロジー
惑星科学は惑星科学である.

背景:

クレタセア - 三次紀 (KT) 境界のイリジウム異常は,大量絶滅と一致する地球外衝突の出来事を示唆しています.
以前のイタリアのグブビオでの研究は,限られたサンプルに基づいて,この異常の解釈につながりました.
KTの境界にあるイリジウムプロフィールの正確な形状と起源については,論争が続いた.

研究の目的:

Gubbio KTの境界にあるイリジウム異常のより詳細な調査を行うために.
イリジウム分布の微細構造と潜在的な原因を明らかにする.
KTイベントとその関連の大量絶滅の理解を洗練する.

主な方法:

厚さ57メートルの地質学的配列を分析し,1000万年をカバーしています.
正確なイリジウム濃度測定のために,改良された中性子活性化分析 (NAA) 技術を活用した.
KT境界層におけるイリジウムの分布を調べた.

主要な成果:

単一の,明確なイリジウム異常が,正確にKT境界で確認されました.
この異常は,特に側面の"尾"では,複雑な細かい構造を示しています.
イリジウムのピーク濃度 (3000 ppt) は,1cmの粘土層にあり,背景の上の尾は20-80 ppt (12-13 ppt) 程度である.

結論:

Gubbio KT境界の詳細なイリジウムプロフィールは,複雑な細かい構造を持っています.
再処理,拡散,バイオターバーション (掘り起こし),ミランコビッチ周期性などの要因は,異常の微細構造に寄与する可能性があります.
この微細な構造の正確な起源については,さらなる調査が必要であり,衝撃-イベントモデルを精製する必要があります.

キーワード:

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