Tool for Microscopic Identification Home

 

Drilling Artifacts

HSPDP-NAW14-1A-81Q-1

Extreme ‘biscuiting’ in a core penetrating indurated Plio-Pleistocene lacustrine sediment. A matrix of injected drilling mud (light grey) supports disconnected wafers of internally coherent sediment. Individual wafers are rotated up to ~30º in the z dimension, and have unknown orientation in the x-y plane. Similar features may be present but far less obvious, depending on the character of the cored material.

Show Annotations



ODP-OLO12-1A-80Q-2

Pervasive homogenization of the upper 90 cm of a core penetrating weakly lithified Pleistocene lacustrine sediment collected using rotary drilling tools and drilling mud. Voids are also interpreted as artifacts. Matrix-supported blocks of intact sediment are apparent from 60-80 cm.

Show Annotations



ODP-OLO12-1A-62Q-1

Brecciation, local homogenization, and drilling mud injection in a core penetrating weakly lithified Pleistocene volcaniclastic sediment collected using rotary drilling tools and drilling mud. Illustrating the problematic interpretation of some drilling artifacts, this drill core section is interpreted to show matrix-supported textures both as a result of drilling disturbance (0-16 cm) and as a primary depositional feature (20-50 cm). Sub-parallel, near-horizontal gray fine-grained features (49-58 cm; 76-90 cm) are continuous with annular accumulation of drilling mud, and are interpreted as injection artifacts highlighting incipient ‘biscuiting’ (differential rotation and shearing) of core material. This phenomenon may be amplified by drilling practices.

Show Annotations



ODP-OLO12-1A-55Q-1

Differential rotation of an internally coherent, intact 29-cm section of lithified volcaniclastic sediment (65.5 - 94.5 cm) offsets the disturbed material an unknown amount in the x-y plane. Rotation occurred along distinct horizontal fractures. Drilling practices (discontinuous advance of the drill bit) may play a role in this style of artifact.

Show Annotations



ODP-OLO12-1A-67Q-2

Pervasive brecciation in a core penetrating weakly lithified volcaniclastic sediment, collected using rotary drilling tools and drilling mud. Both matrix-supported (drilling mud) and clast-supported textures are present. Brecciation in this material appears to have produced a relatively uniform, 2-5 mm clast dimension, frequently angular.

Show Annotations



ODP-OLO12-1A-77Q-1

Discontinuous brecciation (with matrix support by drilling mud?) and homogenization isolating intact blocks of weakly lithified lacustrine sediment. Brecciated feature in upper 10 cm is tentatively interpreted as a natural mud crack infill with brecciated material. Core recovery used rotary tools and drilling mud.

Show Annotations



HSPDP-WTK13-1A-68Q-2

Differential rotation revealed by offset bedding orientations in lithified lacustrine sediment of early Pleistocene age. Injection of annular material and drilling mud occurs along joints formed or amplified by rotary drilling. Compressional deformation also attributable to drilling forces produced the conjugate faults at 138 cm.

Show Annotations



Piston Coring Artifacts

AK-BAK06-3A-1N-2

Moderate to severe apical doming with unusual bicuspid structure in a percussion core penetrating heterogeneous clastic sediment (Holocene?).

Show Annotations



CAB-MCF12-1A-7L-1

Localized drive-top suction deformation in a Livingstone core penetrating a sequence of glacial varves (late Pleistocene?).

Show Annotations



ICE4-HVT08-1A-1N-2

Severe, pervasive apical stretching and flow deformation in a percussion core penetrating heterogeneous clastic sediment (Holocene).

Show Annotations



ICE4-HVT08-1A-1N-4

Minor to severe apical doming and flow deformation in a percussion core penetrating heterogeneous Holocene volcaniclastic sediment. The recumbent fold (axial plane near 110 cm) is interpreted as a slump within the sediment sequence, unrelated to coring.

Show Annotations



ICE4-HVT08-4A-1N-1

Extreme plastic deformation in a laminated volcaniclastic sediment (Holocene).

Show Annotations



ICE4-HVT08-4A-1N-2

Severe to extreme apical doming and flow deformation in a laminated volcaniclastic sediment of Holocene age. Severity of deformation generally increases upward. More severe deformation amounts to near-homogenization of sediment.

Show Annotations



AK-BAK06-2A-1N-1

Complex deformation in a percussion core penetrating ornately laminated and heterogeneous clastic sediment (Holocene?). Rheological contrasts and the down-section distribution of coring stresses combine to produce the complicated interplay of ductile and brittle deformation seen here. The upward increase in the severity of ductile deformation is a relatively common feature of deformed percussion cores. Effective sampling resolution may vary widely in a core such as this, especially in less structured sediment where deformation is more difficult to discern.

Show Annotations



SHAP-JONES97-1A-6L-1 (upper) and SHAP-JONES97-1B-6L-1 (lower)

Missing sediment sequence shown by overlapping drives of closely juxtaposed (sites within ~2 m) Livingstone piston cores. Artifacts of this nature are thought to occur most commonly in sediment sequences with strongly contrasting compressional strength and/or coefficients of friction. In JONES97 1B-6L-1, the Mazama tephra appears to have impeded underlying sediment from moving into the core barrel during some 30 cm of advance. JONES97 1A-6L-1 reveals the missing sequence (distorted), the existence of which would otherwise be impossible to discern.

Show Annotations



ICE4-HVT08-5A-1N-1

Extreme doming, ‘apical irruption’, and effective 90º axial rotation of sediment structure from depositional orientation in laminated volcaniclastic sediment of Holocene age, collected with a Nesje percussion coring device. Note that whole-core geophysical features (density and magnetic anomalies) may be entirely masked by this degree of coring disturbance.

Show Annotations



ICE4-HVT08-5A-1N-2

Severe apical doming and near-homogenization of volcaniclastic sediment of Holocene age collected using a Nesje percussion-coring device. In the zone of apical doming, the highlighted coarse clastic intervals (basaltic tephras?) are deformed into overlapping stratigraphic positions that will reduce magnetic anomalies to a nearly homogenized signature in whole-core scanning, despite retaining their stratigraphic identity.

Show Annotations



ICEBERG-ICE01-1A-5L-1 (upper) and ICEB2-ICE10-1B-1V-6

Late Holocene glaciolacustrine varves recovered in a Livingstone core (upper) and in a vibracore, a high-frequency percussion core (lower). The sediment sections shown are lithologically related and from nearby sites but are not directly correlative. Sediment liquefaction under percussive vibration produced a thick but variable unstructured rind along core margins of the vibracore, as well as moderate to severe sediment doming. The up-core increase in the severity of coring artifacts is commonly observed in percussion cores. The Livingstone core demonstrates the sharpness of contacts in minimally-disturbed equivalent material.

Show Annotations



Sediment Disturbance, Not Artifacts

TDP-TOW15-2B-5H-2

Normal microfaulting interpreted as seismically-triggered sediment deformation. Fault offsets diminish and end up-section and are not bounded by core margins, suggesting post-disturbance burial of the microstructures.

Show Annotations



SHAP-EVANS97-1A-7L-1

Syndepositional and post-depositional deformation of laminated aragonite mud (Holocene), recovered by Livingstone piston coring. None of the features displayed in this core are interpreted as coring artifacts. Rather, slumping and ductile deformation of a weak and unstable sediment package are reflected in the complex sequence of non-planar lithologic contacts seen here.

Show Annotations



FISH-RDF07-2A-1K-5

A matrix-supported soft-sediment breccia resulting from a seismically-triggered subaqueous slump, recovered by Kullenberg piston coring. Brecciated and locally homogenized features in this sequence are not attributed to coring artifacts, but rather to subaqueous slope failure and gravity transport of discrete sediment blocks, some including lithologies exotic to the coring site.

Show Annotations



ICE4-HVT08-4B-1N-4

This complex and enigmatic assemblage of deformational structures is interpreted as dominantly reflecting slumping, overturned folding, and shearing of the sediment package. Basaltic tephras (highlighted) show clean core-wall boundaries and are distorted mainly along apparent slump folds (but may be locally pinched by coring at 11 cm and 70 cm). High-angle microfaults near 50 cm are truncated by low-angle zones of sediment shearing, and do not appear to be coring artifacts.

Show Annotations



FISH-RDF07-1A-1K-2

The lower lithologic unit in this core (material below 125 cm) is a locally massive, matrix-supported material that in isolation could be misinterpreted as exhibiting pervasive coring disturbance. However, the unit is actually the upper gravity-transported facies of a large-scale subaqueous slump, as shown by the thick white overlying unit, which is a fining-upward ‘cap clay’ (mostly in fine the medium and fine silt range) representing the slump-generated material entrained in the water column. The irregularity of the contact between the two units is likely a coring artifact caused by the thixotropic character of the capping silt. The core is composed of Holocene-aged diatomaceous silt and was collected by a Kullenberg piston-coring device.

Show Annotations



FISH-WOW07-1A-1K-5

Holocene sandy silt and silty sand recovered in a Kullenberg piston core. The lithostratigraphic unit from 45 to 120 cm appears locally massive and might be mistaken for a pervasive homogenization artifact if seen in isolation from its stratigraphic context. In fact it is an unusually thick (for lacustrine sediment) turbidite sequence produced by failure of a rapidly accumulating delta front. Look for diagnostic basal and capping textures, which would not be expected in a homogenized artifact. Note that the thickness of this event deposit would often place basal coarse material and the capping silt in different core sections.

Show Annotations



HSPDP-CHB14-2B-4H-2

Cross-cutting secondary infill feature interpreted as a deep desiccation crack, recovered in a hydraulic piston core. Massive or weakly structured infill is capped by brecciated sediment and the up-section resumption of laterally continuous sediment structure. Between 110 cm and 85 cm, conformable sediment could be selectively sampled from this core, but not from the central core face.

Show Annotations