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A High-resolution Record of Deep-water Processes in a Confined Paleofjord, Quebrada de las Lajas, Argentina

By
Mason Dykstra
Mason Dykstra
1Institute for Crustal Studies, University of California, Santa Barbara, California, USA
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Ben Kneller
Ben Kneller
2Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom
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Juan Pablo Milana
Juan Pablo Milana
3CEAZA - Universidad de La Serena, La Serena, chile
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Published:
January 01, 2008

Abstract

Fjords can become so overdeepened below sea level during protracted glaciations that they fill with hundreds of meters (>1000 ft) of seawater when glacioeustatic rise occurs during and following deglaciation. Fjords, therefore, can host true deep-water environments, which are commonly laterally confined but longitudinally extensive. Outcrops of ancient paleofjord sediments offer three-dimensional views of the evolution of these deep-water, confined sedimentary environments, where the factors controlling sediment supply are both climatic (deglaciation and eustasy) and tectonic (isostatic rebound). Quebrada de las Lajas, near San Juan, western Argentina, preserves a Pennsylvanian glacial to postglacial succession that was deposited in an over-deepened paleofjord.

The sedimentary succession exposed in the paleofjord is divided into four evolutionary stages: Stage I was an ice-contact delta and proglacial lake, Stage II was a relatively quiet, deep-water marine environment punctuated by turbidity currents, Stage III was an aggradational confined sheet system, and Stage IV was the subaqueous portion of a progradational, coarsening- and shoaling-upward fan delta. The entire sedimentary succession comprises approximately 350 m (1150 ft) of remaining exposed thickness.

Each of the four evolutionary stages has distinct architectural characteristics associated with its depositional environment. Stage I is chatacterized by predominandy lobe-shaped, sheetlike conglomerate and sandstone bodies associated with the ice-contact delta and a subaqueous fan. Stage I also preserves several small, turbidite channel bodies and a small-scale, highly aggradational channel-levee system with a conglomeratic channel axis and thin-bedded sandstone and siltstone levees. Stage II is characterized by thin beds of shale and siltstone punctuated by medium

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Contents

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

GeoRef

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