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A Rare Exposure of an Ancient Submarine Canyon, Black’s Beach, California, USA

By
Jeffrey A. May
Jeffrey A. May
1
EOG Resources, Denver, Colorado, USA
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John E. Warme
John E. Warme
2
Colorado School of Mines, Department of Geology and Geologic Engineering, Golden, Colorado, USA
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Published:
January 01, 2008

Abstract

Beach cliffs north of San Diego, California, provide superb three-dimensional exposures of an exhumed Eocene submarine-canyon complex. This interpretation is based on large-scale erosional and depositional geometries, channel architecture, lithofacies relationships, sedimentology, and micropaleontology. The canyon fill is composed of multiple, cross-cutting channels on a multitude of scales and with widely diverse lithologies. Individual channels range from subtly scoured and only a few meters (feet) deep to more than 1 km (0.6 mi) wide and up to 100 m (328 ft) deep. Photomosaics aid in analyzing bounding surfaces and lithologic patterns. An irregular sequence boundary defines the canyon base. Two stratigraphic sequences are truncated by the canyon floor; two sequences compose the canyon fill. Lagoonal and tidal deposits of the underlying Delmar andTorrey sequences are unconformably separated from bathyal units of the Ardath Sequence, which comprises the lowermost canyon interval. A second submarine-sequence boundary occurs within the canyon succession, eroding into the top of the Ardath Sequence and dividing it from the overlying Scripps Sequence. A fifth (shallow-marine) sequence, which is not described here, truncates the Scripps Sequence to the north and inland. Pleistocene wave-cut terraces plane off the Eocene interval at the top of the cliffs. The lowermost canyon section (Ardath Sequence) comprises amalgamated, pebbly, and diffusely laminated sandstones. These fine upward to convolute-bedded, fine-grained sandstones, which then grade into laminated to bioturbated silty mudstones. The mudstones fill channels that exhibit a sinuous morphology. Multiple erosional episodes scoured each channel; channel fill predominantly occurred during abandonment. Subsequent flows evacuated a multitude of cross-cutting conduits.

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AAPG Studies in Geology

Atlas of Deep-Water Outcrops

Tor H. Nilsen
Tor H. Nilsen
Desceased
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Roger D. Shew
Roger D. Shew
University of North Carolina
Wilmington, North Carolina
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Gary S. Steffens
Gary S. Steffens
Shell International E&P
Houston, Texas
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Joseph R. J. Studlick
Joseph R. J. Studlick
Maersk Oil America Inc.
Houston, Texas
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American Association of Petroleum Geologists
Volume
56
ISBN electronic:
9781629810331
Publication date:
January 01, 2008

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