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Book Chapter

Reconstruction of a 20th Century Varve Chronology from the Central Gulf of California

By
Tim R. Baumgartner
Tim R. Baumgartner
Centro de Investigatión Cientifica y de Educatión Superior de Ensenada Ensenada, B.C., MEXICO
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Vicente Ferreira-Bartrina
Vicente Ferreira-Bartrina
Centro de Investigatión Cientifica y de Educatión Superior de Ensenada Ensenada, B.C., MEXICO
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James Cowen
James Cowen
Institute for Marine Sciences University of California, Santa Cruz Santa Cruz, California, U.S.A. Present address: Hawaii Institute of Geophysics University of Hawaii Honolulu, Hawaii, U.S.A.
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Andy Soutar
Andy Soutar
Scripps Institution of Oceanography University of California, San Diego La Jolla, California, U.S.A.
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Published:
January 01, 1991

Abstract

The retrieval of useful environmental information from the annual layers of natural high-resolution records such as tree rings, coral banding, or marine varves first requires reconstruction and validation of the chronological sequence in which this information has been preserved. This chapter describes the detailed reconstruction of a varve chronology from the central Gulf of California which encompasses most of the 20th century. The chronology was developed from a set of five box cores taken from the anaerobic slope off Guaymas, Sonora, and consists of a unique sequence of lamina couplets identifiable throughout the study area stretching more than 20 km along the slope. The reconstruction was initially hampered by the fact that each core site has suffered a history of small-scale mass movement that has disrupted the stratigraphic continuity of its lamina sequence. Because these breaks generally do not occur at the same level in all of the cores, a continuous varve stratigraphy could be developed by piecing together short lamina sequences from four of the five box cores available. The chronostratigraphy commences with the winter/spring lamina of the year 1908. This lower boundary is imposed by a stratigraphic discontinuity that cuts across all five core sites and is inferred to be a sediment gravity flow triggered by a nearby large-magnitude earthquake in the autumn of 1907. The surface lamina is dated from the time of collection in 1978. Independent 210Pb dating of specific lamina intervals indexed to the lamina stratigraphy from all five cores strongly supports our interpretation that the reconstructed varved interval represents 70.5 years of continuous sedimentation.

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Contents

AAPG Memoir

The Gulf and Peninsular Province of the Californias

J. Paul Dauphin
J. Paul Dauphin
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Bernd R. T. Simoneit
Bernd R. T. Simoneit
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American Association of Petroleum Geologists
Volume
47
ISBN electronic:
9781629811130
Publication date:
January 01, 1991

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