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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 783

Last Page: 783

Title: Experimental Compaction of Lime Sediment: ABSTRACT

Author(s): Eugene A. Shinn, Daniel M. Robbin, Randolph P. Steinen

Article Type: Meeting abstract

Abstract:

More than 30 in-situ cores of modern lime sediments, including environments from tidal flat to shallow marine, have been compressed under loads simulating depths ranging from 280 to 14,000 m of burial. Cores 10 cm in diameter and 30 to 40 cm in length were reduced to between one-quarter to one-third of their original length, resulting in porosity reduction from an initial 70 to 80% to 30 to 45%.

Experimental compaction produced sedimentary structures common to many ancient limestones, including (1) wavy organic seams similar to horsetail or microstylolite swarms; (2) reorientation of randomly oriented fossils toward a more horizontal posture; (3) flattening of filled burrows; (4) complete obliteration of birdseye voids; and (5) color mottling in tidal flat sediments produced by collapse and flowage of oxidized sediment surrounding burrows.

These studies have shown that, during geologically instantaneous periods of compaction (up to 30 days), the bulk of porosity reduction occurred under conditions simulating less than 300 m of overburden. Although fossils generally are not crushed during compaction, the obliteration of birdseye voids indicates that early cementation or infill by evaporitic minerals was necessary for preservation of ancient birdseye or fenestral structures. Pellets in soft lime mud were obliterated, but slightly hardened pellets in Bahamian muds were preserved during experimental compaction. This observation suggests that well-preserved pellets in ancient limestone indicate predepositional hardening or synsedimentary cementation.

Heating of cores to 100°C during compaction has produced hydrocarbon effluents, suggesting that some ancient limestones may have been source rocks.

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