Visual Core Descriptions

The sediment core graphic descriptions, or barrel sheets, summarize data obtained during shipboard visual inspection of each core. The standard ODP conventions were used for the compilation of the core description forms; the exceptions to these procedures adopted by the Leg 184 Shipboard Scientific Party are described below.

Graphic Lithology Column

All sediment core descriptions were made with the software package AppleCore, using a lithology custom file containing patterns for the standard ODP sediment classification scheme, a modified version of the lithologic classification of Mazzullo et al. (1988). The classification adopted here is outlined in "Rock Classification and Principal Names". Sediment type is represented graphically on the core description forms (Fig. F2A) using the patterns illustrated in Figure F2B.

In the graphic lithology column, a maximum of two different lithologies (for interbedded sediments) or three different components (for mixed sediments) can be represented within the same core interval. Percentages of the main lithologic components are rounded to the nearest 5%. Lightness values collected from the Minolta spectrophotometer (see also "Physical Properties") are shown in the column to the left of graphic lithology. All core images and graphic lithology columns are included (see the "Core Descriptions" contents list).


Five degrees of bioturbation were differentiated (Fig. F2B), following Droser and Bottjer (1986). "Barren" indicates that sediments are undisturbed, whereas primary bedding and structures are fully obliterated by burrowing for "abundant" bioturbation.

Sedimentary Structures

Sedimentary structures include features related to deposition, erosion, and deformation. The location and type of sedimentary structures are shown in the graphic lithology column of the core description form. The symbols used to designate structures found in Leg 184 cores are shown in Figure F2B.

Ichnofossils and Fossils

Ichnofossil and fossil columns indicate the occurrence of ichnofossil genera and major groups of macro- and microfossils. Symbols shown in this column are described in Figure F2B.


The accessories column indicates the position of a variety of features such as pyrite, "iron sulfides," lamina, and shell fragments. Symbols shown in this column are described in Figure F2B.

Core Disturbance

Observations of drilling-related disturbance were recorded in the core disturbance column using the symbols shown in Figure F2B. The degree of drilling disturbance in soft and firm sediments is as follows:

  1. Slight: bedding contacts are slightly deformed.
  2. Moderate: bedding contacts have undergone extreme bowing.
  3. Extreme: bedding is completely destroyed; original structure cannot be recognized.

This degree of drilling disturbance is illustrated by the thickness of the symbol (thickest = extreme). In addition to the degree of disturbance, the character of the disturbance is also described as follows (Fig. F2B):

  1. Disturbed: bedding is generally intact, but sediment near the core liner is missing or homogenized.
  2. Deformed: bedding contacts have been bent.
  3. Soupy: sediment is water saturated, and original structure is lost.
  4. Flow-in: sediment displays vertical structure caused by coring.
  5. Slurry: sediment homogenized during drilling.
  6. Biscuit: pieces of partially indurated sediment in the core barrel. The pieces may represent contiguous stratigraphy with millimeter cracks (slight) to small (<3 cm) pieces floating in slurry.
  7. Gas expansion: sediment voids or bubbles in sediment caused by gas expansion.


The positions of samples taken from each core for analysis are indicated by letters in the sample column of the core description form as follows: SS (smear slide), WHC (whole-core sample), PAL (micropaleontology), and IW (interstitial water).


Color was measured with a Minolta CM-2002 spectrophotometer. These measurements were determined on the damp core surface, and GladWrap brand clear plastic film was used to cover the core. The Minolta CM-2002 measures reflected visible light in thirty-one 10-nm-wide bands ranging from 400 to 710 nm. Routine measurements were made at 2-cm spacing for Holes 1143A and 1143B and at 4-cm spacing for all other holes, excluding voids within the sediment section.

Before obtaining measurements from each core, the spectrophotometer was calibrated for white color reflectance; it was "zero calibrated" twice a day, at the beginning of each work shift. The white color calibration was made to avoid variation in color readings stemming from the laboratory environment (temperature, humidity, and background light) and instrument variations.

Lithologic Description

The text description for each core consists of a list of major lithologies followed by a more detailed description of the composition (as determined from smear slides), sedimentary structures, and other notable features. Descriptions and locations of thin, interbedded, or minor lithologies are also included in the text.

Smear Slides

Tables summarizing data from smear-slide analyses are presented (see the "Core Descriptions" contents list). These tables include information about the sample location, whether the sample represents a dominant (D) or a minor (M) lithology in the core, and the estimates of sand, silt, and clay (particle size), together with all identified components (both terrigenous and biogenic material is described and estimated).

Sediment and Rock Classification

Grain Types and Classifications

Grain types in granular sediments and rocks were classified according to composition: biogenic (calcareous and siliceous) and siliciclastic particles. Their definitions are as follows:

  1. Biogenic grains are skeletal debris produced in open-marine environments by calcareous microfauna and microflora (foraminifers, pteropods, nannofossils, and associated organisms), and siliceous microfauna and microflora (radiolarians, diatoms, and associated organisms).
  2. Siliciclastic grains comprise minerals and rock fragments eroded from plutonic, sedimentary, and metamorphic rocks, as well as glass shards, rock fragments, and mineral crystals produced by volcanic processes.

Rock Classification and Principal Names

Sediments and rocks were named on the basis of composition and texture using a principal name together with major and minor modifiers. Principal names define the degree of consolidation (induration) and granular sediment class. Table T1 summarizes the granular sediment classification scheme for pelagic and siliciclastic rocks. Composition and texture of cored sediments and rocks were determined aboard ship by visual observation of the core and by visual estimates in smear slides and coarse fractions. Carbonate content was estimated qualitatively in smear slides and quantitatively by coulometric analysis (see "Organic Geochemistry").


Induration of recovered materials was defined as in Gealy et al. (1971). Three classes of induration were used to describe calcareous sediments and rocks:

  1. Unlithified: soft sediments that have little strength and are readily deformed under the pressure of a fingernail or the broad blade of a spatula. This corresponds to the term ooze for pelagic biogenic sediments.
  2. Partially lithified: firm but friable sediments that can be scratched with a fingernail or the edge of a spatula blade. The term chalk is used for firm or friable pelagic calcareous material.
  3. Lithified: hard, nonfriable cemented rock, difficult or impossible to scratch with a fingernail or the edge of a spatula. The term limestone (lithified ooze) is used for pelagic calcareous material.

Two classes of firmness were used to describe siliciclastic sediments and rocks:

  1. Soft: sediment core can be split with a wire cutter. Soft terrigenous sediment, pelagic clay, and transitional calcareous sediments are termed sand, silt, or clay.
  2. Hard: the core is hard (i.e., consolidated or well indurated) if it must be cut with a hand or diamond saw. For these materials, the suffix -stone is added to the soft-sediment name (e.g., sandstone, siltstone, and claystone).

Sediments and Rocks

Principal names used to describe sediments and rocks during Leg 184 are as follows:

  1. Clay: unconsolidated authigenic material (>15%) and siliciclastic sediment (lithified examples are termed claystone);
  2. Ooze: unconsolidated calcareous and/or siliceous sediment; and
  3. Chalk: firm sediment composed predominantly of calcareous grains.

Siliciclastic Sediments and Rocks

For siliciclastic sediments and rocks, texture, structure, and composition are the main criteria for the selection of a principal name. The Udden-Wentworth grain-size scale (Fig. F3) (Wentworth, 1922) defines the grain-size ranges and the names of the textural groups (gravel, sand, silt, and clay) and subgroups (fine sand, coarse silt, etc.). When two or more textural groups or subgroups are present, the principal names appear in order of increasing abundance. Eight major textural categories can be defined on the basis of the relative proportions of sand, silt, and clay (Fig. F4). Distinguishing between some size categories is difficult (e.g., silty clay and clayey silt) without accurate measurements of weight percentages. The terms conglomerate and breccia are the principal names of gravels with well-rounded and angular clasts, respectively.

Major and Minor Modifiers

To describe the lithology of the granular sediments and rocks in greater detail, the principal name of a granular sediment class is preceded by major modifiers and followed by minor modifiers (Table T1). Minor modifiers are preceded by the term with. The most common uses of major and minor modifiers are to describe the composition and textures of grain types that are present in major (25%-40%) and minor (10%-25%) proportions.

The composition of pelagic grains can be described in greater detail with the major and minor modifiers such as nannofossil, foraminifer, calcareous, and siliceous. The terms calcareous and siliceous are used to describe sediments that are composed of calcareous or siliceous pelagic grains of uncertain origin.

The textural designations for siliciclastic grains utilize standard major and minor modifiers such as gravel(-ly), sand(-y), silt(-y), and clay(-ey). The character of siliciclastic grains can be described further by mineralogy using modifiers such as quartz, feldspar, glauconite, mica, lithic, or calcareous. In addition, the provenance of rock fragments (particularly in gravels, conglomerates, and breccias) can be described using modifiers such as sed-lithic and meta-lithic. The fabric of a sediment can be described using major modifiers such as grain supported, matrix supported, and imbricated. Generally, fabric terms are useful only when describing gravels, conglomerates, and breccias.