Selective preservation of burrows in deep-sea carbonates

Abstract

Burrow preservation is a function of the rates of burrow production and burrow destruction and the rate of burial. These rates are related to water depth and therefore burrow preservation can be a depth indicator in deep-sea sediments. Box cores from fourteen localities in the eastern equatorial Pacific, taken from water depths of 3500–4850 m, showed a three-layer stratigraphy: a mixed layer with intense bioturbation (upper 5–7 cm), a transition layer (extending down to 20–35 cm), and a historical layer below. To be preserved, a burrow must reach below the mixed layer and into the transition layer. Abundance of vertical burrows is inversely proportional to water depth down to 4500 m, where vertical burrows disappear completely due to sediment shear and/or lack of burrow production. Within box cores the various burrow assemblages display an array of colors. Cross-cutting relationships of differently colored burrows help to establish a bioturbation chronology: burrow color fades with age. Two possible models for the observed burrow stratigraphy are presented: a steady-state model and a historical model. The steady-state model focuses on the activity of record-making burrowers versus the destruction of burrows by homogenizing burrowers, redox diagenesis and sediment flow. The historical model focuses on the effects of the early Holocene dissolution pulse on the observed burrow stratigraphy.