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proposed. Bio-retexturing is defined as the processes
by which burrowing biota may modify or transform
original textures by relocating significant volumes of
unlithified sediment into or out of the sedimentary lay-
ers (Pedley 1992).
quiet-water sheltered embayments, e.g. lagoons, muddy
tidal flats) and deeper water environments below fair-
weather and storm-wave base. Recent shallow-marine
carbonate environments in Florida and the Bahamas
are dominated by burrows of the shrimp Callianassa,
which affect up to 75% of the sediment. Repetition of
burrow excavation and storm infilling results in the for-
mation of a storm-derived sediment textures dominated
by mottled packstone with coarse skeletal patches
(Shinn 1968; Tudhope and Scoffin 1984; Curran and
White 1991; Wanless and Tedesco 1993).
Burrowing is common in many slope sediments
(Henderson et al. 1999; Pl. 137/1, 6). The occurrence
of pelagic bathyal and abyssal deep-sea bioturbation
(Pl. 19/ 2, 3; Pl. 139/1) in the upper few tens of centi-
meters of the sea bottom depends on the nature of the
seafloor sediment, the oxygen content of the bottom
and of the pore waters, and the nutrient resources
(Ekdale et al. 1984; Wetzel 1984; Meadows and Mead-
ows 1994). Because the rates of deep-sea bioturbation
are high, in contrast to the low sedimentation rates,
deep-sea bioturbation structures often represent mul-
tiple episodes of burrowing (Magwood and Ekdale
1994).
Occurrence and origin of bioturbation
Bioturbation occurs in shallow- and deep-marine
environments as well as in lacustrine settings and even
in eolian environments (e.g. carbonate dunes: Ahlbrandt
et al. 1978). Burrows are the most common features
observed in shelf limestones (e.g. Pl. 135/1). Burrow-
ing occurs in carbonates both in intertidal and espe-
cially subtidal settings, and in deep-marine bathyal en-
vironments where a high density of endobionts in con-
junction with low sedimentation rates may cause mul-
tiple episodes of burrowing and churning-up of the sedi-
ment. Bioturbation is ubiquitous in outer-ramp settings
where crustacean-dominated bioturbation results in in-
tensive bio-retexturing of the primary depositional fab-
rics and masks inorganic process-related structures.
Infaunal burrowing organisms are particularly fre-
quent in calcareous muds deposited in shallow-marine
Plate 19 Burrowing and Bioturbation: SeaBottom Conditions and PostSedimentary Diagenetic Changes
Burrows are formed within soft unconsolidated sediments (muds, sands, firmgrounds) by the activity of animals.
The term 'bioturbation' designates the churning and stirring of sediments by organisms resulting in the destruc-
tion of sedimentary structures (e.g. bedding). Bioturbation fabrics are typified in terms of spatial arrangement
and geometry of burrows, burrow density (using semi-quantitative 'bioturbation indices'), burrow abundance,
and texture and filling of burrows. These criteria can be studied in the field but can also be applied to large thin-
sections. Burrows and bioturbation are the most common features observed in shelf limestones and deep-marine
carbonates. The common criteria of burrowed limestones is a mottled appearance differing in color and texture
(-> 6), or by dolomitization from the host rock.
1
Indications of bioturbation are the circular swirls (arrows) of skeletal debris (trilobite and echinoderm fragments), the
patchy distribution of these structures, and variations in packing densities of grains. Well-oxygenated subtidal mid-shelf
environment. Red bedded limestones. SMF 9. Ordovician: Öland Island, Sweden.
2
Burrowed radiolarian wackestone. Note the difference in the packing of radiolarian tests in the infilling of the burrow and
outside the burrow. Bathyal environment. Late Jurassic: Northern Alps.
3
Burrowed calcisphere packstone . Note different packing of the spheres (corresponding to calciodinoflagellate cysts). The
calcisphere content exceeds 35%. The irregular texture is partly caused by synsedimentary sliding of the sediment (Voigt
and Häntzschel 1964). Open-marine deep-shelf environment. Red bedded limestones alternating with flint layers. Late
Cretaceous (Pläner marl, Late Turonian): Northern Germany.
4
Burrow filling consisting of benthic foraminifera and shell bioclasts. Note absence of compaction indicating firmground
substrate consistency. Late Jurassic (Sequanian): Beze, France.
5
Burrow within microbial crusts, infilled with oncoids and coated grains. Upper slope environment. Late Triassic (Raibl
Beds): Schlern, Dolomites, Italy.
6
Distinct mottling due to bioturbation in a deep-shelf lime mudstone with pelagic ostracods (see Pl. 93/3,4). Note differ-
ences in color shades and compaction of burrows indicating softground substrate consistency. Early Carboniferous (Late
Viséan): Betic Cordillera, southern Spain.
7
Burrowing indicated by skeletal grains (predominantly trilobite debris) forming twisted structures. Bedded intermound
mid-shelf limestones. Early Devonian (Emsian): Anti-Atlas, southern Morocco.
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