LITHOSTRATIGRAPHY AND SEDIMENTOLOGY

Analysis of rocks and sediments starts with the recognition, identification, and physical description of individual sedimentary grains. Based on the suite of grain types and texture that results, sediments and rocks can be classified. Hence, this section consists of two parts: (1) grain type and (2) sediment and rock classification.

Grain Types

Grain types in granular sediments and rocks were classified in five categories according to mineralogy and origin:

1. Pelagic calcareous and siliceous. Pelagic sediments are characterized by fine-grained skeletal debris primarily produced within the upper part of the water column in an open-marine environment by calcareous microfauna and microflora (e.g., foraminifers, pteropods, and nannofossils) and siliceous microfauna and microflora (e.g., diatoms and radiolarians). During Leg 194, only very minor amounts of siliceous microfossils were recognized.
2. Hemipelagic calcareous and siliceous. Hemipelagic sediments contain the same components as pelagic sediments with the addition of >10% neritic carbonate and/or siliciclastic material. Because of the continental margin setting of the Marion Plateau and the influence of carbonate platform sedimentation, virtually all nonneritic sediments were deemed to be hemipelagic.
3. Neritic calcareous and siliceous. Neritic sediments consist of coarse- to fine-grained particles originating from shallow-water areas (e.g., platform upper slope or periplatform) and consist mostly of carbonate skeletal (i.e., bioclastic) components, nonskeletal fragments, and micrite. The term micrite is used to define very fine calcareous particles (<20 µm) of various origin. Neritic carbonate grains (Tucker and Wright, 1990) observed during Leg 194 include the following:

   a. Skeletal components. These include the remains of large and small benthic foraminifers, bivalves, gastropods, coralline algae, corals, bryozoans, echinoderms, and minor green algae. Additionally, rhodoliths were commonly observed. These consisted of gravel-sized (60 mm in diameter), subspherical nodules of concentrically encrusted coralline algae.

   b. Nonskeletal components. Minor intraclasts and lithoclasts were occasionally encountered. Ooids, peloids, pellets, and oncolites were problematic; they may be present in some lithologies, but extensive dolomitization prevented positive identification.

4. Siliciclastic. Siliciclastic grains, composed of quartz, feldspar, mica, and rock fragments that were eroded from igneous, metamorphic, and noncarbonate sedimentary rocks were observed in some intervals.
5. Marine noncarbonate authigenic minerals. Phosphate and glauconite were the most common authigenic minerals observed. Glauconite is a black to greenish, iron-rich sheet silicate, which can infill test chambers and pores or appear as rounded sand-sized grains. Phosphates constitute a complex family of phosphorous-rich minerals. They are commonly black and occur as sand-sized grains. Unoxidized framboidal pyrite was also commonly found.

Principal Rock Names

Principal names of the sediments and rocks observed are formulated on the basis of composition and texture in conjunction with major and minor modifiers. Four main categories of principal rock names were used: (1) carbonates (including dolomitized limestones and dolostones); (2) siliciclastics; (3) mixed carbonate and siliciclastics, which are further subdivided as carbonate-dominant and siliciclastic-dominant; and (4) basement (Fig. F1).

Major and Minor Modifiers

To describe the lithology of the granular sediments and rocks in greater detail, the principal name (i.e., grainstone) is often preceded by a major modifier (i.e., skeletal) and followed by minor modifiers. Minor modifiers are preceded by the term "with" (for example, "skeletal grainstone with clay"). Minor modifiers associated with principal names were used sparingly for simplicity. Minor modifiers were used to supply greater detail in the "Lithologic Description" section of the barrel sheets (see the "Core Descriptions" contents list). In general, the most common use of major and minor modifiers was to describe grain types that were present in major (>25%) and minor (<25%) proportions. In addition, major modifiers were used to provide additional information on grain size, constituent mineralogy, and rock composition.

Carbonate Nomenclature

For pure carbonate lithologies (0%-25% noncarbonate grains), the original Dunham (1962) textural classification was applied in conjunction with the depositional textures described by Embry and Klovan (1971) (Fig. F2). Following Dunham (1962), carbonate crystals or fragments that are smaller than 20 µm (hence not visible with a hand lens) are referred to as micrite. Constituents >20 µm are called grains. For clarity, we used the definitions cited below:

1. Mudstone = mud-supported fabric with <10% grains.
2. Wackestone = mud-supported fabric with >10% grains.
3. Packstone = grain-supported fabric with intergranular mud.
4. Grainstone = grain-supported fabric with no mud.
5. Floatstone = matrix-supported fabric (at least 10% of grains >2 mm in size).
6. Rudstone = grain-supported fabric (at least 10% of grains >2 mm in size).
7. Boundstone = components organically bound during deposition.

Matrix in floatstones and rudstones may be anything from mudstone to grainstone. For example, a sediment with 10-mm-diameter rhodoliths in grain contact with each other and having a skeletal grainstone matrix is a rudstone.

Subdivisions within this group include

a. Bafflestone: formed by organisms that act as baffles;

b. Bindstone: formed by organisms that encrust or bind; and

c. Framestone: formed by organisms that build a rigid framework.

In lithologies where the dominant grain size was 20-63 µm and the sediments were well-sorted with grains in contact with each other, we placed the major modifier "silt-sized" before Dunham's (1962) principal name (e.g. silt-sized grainstone). The major modifier "skeletal" was not used in this case if the bioclastic components could not be identified because of the fine grain size. Modifiers such as "fine sand-sized" are also used to refine the description of sand-sized grainstones in the "Lithologic Description" section on the barrel sheets.

The major modifiers "skeletal" and "nonskeletal" are used to indicate the occurrence of bioclastic fragments and nonbioclastic allochems (e.g., ooids), respectively, within the carbonate sediments. The lack of such a modifier implies that components have not been identified or that the sediments include an even proportion of skeletal and nonskeletal allochems. If the nonskeletal components exceed 25%, then the lithology is determined to be nonskeletal.

Whenever dolomite or dolomitic texture was recognized (>25%) in carbonate sediments, the term "dolomitic" was used as a major modifier (e.g., dolomitic mudstone with clay). When a lithology appeared to contain >~75% dolomite, it was called "dolostone" or, if skeletal components can be recognized, "skeletal dolostone."

Siliciclastic Sediments and Rocks

The nomenclature of siliciclastic sediments and rocks (>50% clay = claystone; >50% silt = siltstone; and >50% sand = sandstone) is based on the Udden-Wentworth grain size scale (Fig. F3) (Wentworth, 1922). Grain mineralogy is expressed by both major and minor modifiers (i.e., quartz sandstone with glauconite). Modifiers for mixed grain sizes (i.e., silty claystone) are used in accordance with Figure F4 (Shepard, 1954). When two or more textural groups or subgroups are present, the principal names appear in order of increasing abundance.

Mixed Carbonate and Siliciclastic Rocks and Sediments

Carbonate-dominated sediments and rocks (50%-75% carbonate) were described as pure carbonates with the grain size of the siliciclastic fraction added as a major modifier after the principal name (e.g., skeletal wackestone with quartz) (Fig. F1). Siliciclastic-dominated lithologies (>50%-75% siliciclastic) were described as pure siliciclastic rocks and sediments with the addition of the main carbonate constituent after the principal name (e.g., quartz siltstone with bryozoans) (Fig. F1).

Basement Rocks

Basement rocks that were recovered are lithologically complex and difficult to characterize in hand specimens, and thin section petrography was used to better characterize these horizons. All basement rocks encountered were either olivine basalt or breccia deriving from those basalts (Fig. F1).

General Procedure

Leg 194 sedimentologists adopted the following strategy before writing comments on the visual core description (VCD) form used for each core section (Fig. F5):

1. The core was examined to pick boundaries, determine lithologies, identify key features, and determine the samples to be collected (i.e., smear slide, thin section, and/or close-up photograph sites).
2. Cores were then described in detail on VCDs following the procedure outlined in the next section. The archive halves of soft-sediment cores (not segmented rock fragments) were analyzed with the MST to obtain color reflectance data (see "Core Physical Properties"). Other than for the upper part of Site 1192, magnetic susceptibility data were not collected with the MST. Additionally, digital photographs were taken on a separate track installed for the first time during Leg 194 (see below).
3. Information recorded on the VCDs were then entered on a computer using the AppleCORE program (version 8.1) to produce the barrel sheets (see the "Core Descriptions" contents list).
4. Ultimately, data from the barrel sheets coming from different holes at a site were compiled into one figure and one table used to distinguish lithologic units. These figures can be found in the "Lithostratigraphy and Sedimentology" section of each site chapter in this volume.

Visual Core Descriptions

The VCD form used on previous ODP legs was modified to meet the specifics of sediments and rocks encountered during Leg 194 and to facilitate data entry into the AppleCORE program (Fig. F5). Description guidelines were established to homogenize the observations made by different shifts and by scientists within a shift (Table T2).

Barrel Sheets

The sediment core description forms, or barrel sheets, summarize shipboard observations and descriptions of the sediments retrieved in each core (Fig. F6). A barrel sheet uses the separate VCDs established for each section (including the core catcher). Effectively presenting information on the barrel sheets often required a nonquantitative, subjective reduction and synthesis of data from the VCDs. Leg 194 scientists supplemented the available symbols in the AppleCORE program in order to graphically display the sediments encountered (Fig. F7).

The ODP conventions used for the compilation of barrel sheets and the modifications to these procedures adopted by the Leg 194 Shipboard Scientific Party are described below. The order of the following headers reflects the order from left to right of the columns in the barrel sheets (see Fig. F6):

1. Meters: This column lists the nominal depth below seafloor (mbsf) of the core.
2. Core and section: Each core was cut into 1.5-m sections and numbered according to ODP convention. The core and section number are listed in this column.
3. Texture: Textural classifications are represented here by a vertical line displayed in the appropriate column (Fig. F6). For siliciclastics or dolostone where texture was lost, this column was left blank.
4. Graphic lithology: Lithologies were represented by patterns (Fig. F1) displayed in the graphic lithology column. Mixed lithologies were indicated on the barrel sheets by splitting the graphic symbol vertically, with the width of each pattern showing the relative proportions of constituents.
5. Bioturbation: Five degrees of bioturbation were differentiated (Fig. F7), similar to the scheme of Droser and Bottjer (1986), and are shown in the "Bioturbation" column on the barrel sheet (Fig. F6). Bioturbation ranges in degree from "barren" to "abundant," with "rare," "moderate," and "common" in between.
6. Structures, accessories, ichnofossils, fossils: These four categories are represented in the same column. The location and nature of primary sedimentary structures (e.g., planar laminations) and deformational structures (e.g., microfaults) are shown in the "Structure" column of the barrel sheet (Fig. F6). Lithologic accessories include a variety of structures, nonskeletal grains, and diagenetic features such as pyrite concretions. Finally, occurrences of ichnofossils and major groups of macro- and microfossils were also graphically indicated in this column.
7. Core disturbance: Observations of drilling-related disturbance over an interval of 20 cm or more were recorded in the "Disturbance" column using the symbols shown in Figure F7. The degree of drilling disturbance in soft and firm sediments is as follows:

   a. Slightly disturbed: Bedding contacts are slightly deformed.

   b. Moderately disturbed: Bedding contacts have undergone extreme bowing.

   c. Very disturbed: Bedding is completely deformed by flowing coring/drilling slough and other soft sediment, or by stretching and/or compressional shearing structures attributed to the boring/drilling.

   d. Soupy: Intervals are water saturated and have lost all aspects of original bedding.

   The degree of disturbance in indurated sediments and rocks is described using the following categories:

   a. Fractured (in various degrees of severity): Core pieces are in place and broken or partly displaced from their original orientation.

   b. Biscuits (in various degrees of severity): Uniquely shaped, rounded, oblong rock fragments preserved or recognizable (drilling slurry may surround these fragments).

   c. Fragmented (in various stages of severity): Core pieces are probably in correct stratigraphic sequence although they may not represent the entire sequence. The original orientation is lost. The fragments were each separately stored and archived within small plastic partitions within each half-core tube.

   d. Drilling breccia: The rocks are crushed and broken into many small and angular or rounded pieces with the original orientation and stratigraphic position lost. Often drilling breccia is completely mixed with drilling slurry.

8. Samples: Samples taken from each core for analysis are indicated in the "Sample" column of the barrel sheets. SS = smear slide, THS = thin section, PAL = micropaleontology, DCP = close-up photo, and IW = interstitial water.
9. Consolidation (firmness): For a better visualization of the different intensities of sediment lithification, degrees of firmness are shown in the "Consolidation" column of the barrel sheets (Fig. F7). Firmness of recovered materials was defined according to Gealy et al. (1971). Five degrees of lithification were used:

   a. Extreme: Rock cannot be scratched or broken without the help of a saw.

   b. Strong: Rock breaks with difficulty. This includes hard, nonfriable, cemented, and/or compacted rock that is difficult or impossible to scratch with a fingernail or the edge of a spatula.

   c. Moderate: Hard but friable sediments can be broken easily or scratched with a spatula or a fingernail.

   d. Poor: Firm, cohesive, plastic sediment shows some resistance to finger pressure. This is common in clay-rich lithologies.

   e. Unlithified: Soft sediments have little strength and are readily deformed under the pressure of a fingernail or the broad blade of a spatula.

10. Facies: Nearly all of the facies described for sediments and rocks obtained during Leg 194 were formally presented as neritic (N), hemipelagic (H), or basement (B) on the barrel sheets. However, in the "Lithologic Description" section many informal terms were used to describe facies and environments (e.g., deep shelf, reef, reef talus, proximal and distal slope, proximal and distal periplatform, sediment drift, open plateau, etc.).
11. Lithologic description: This section of the barrel sheet contains a written summary of the lithologies graphically presented. Leg 194 sedimentologists adopted the following format (Fig. F6):

    a. A principal name (written in capital letters) with modifiers, as discussed above, is placed just below the upper limit of each primary lithologic unit as defined by a contact graphic symbol.

    b. If an entire core consists of the same lithology, the principal name is then placed at the top of the "Description" column on the barrel sheet. When a core consists of thin (<10 cm) interbeds of distinctive lithology, or if the texture is intermediate between two types, two or more principal names separated by a slash can be used (e.g., skeletal grainstone/packstone).

    c. The color is listed directly beneath the principal name without using the Munsell Color Company (1994) color codes, as these are more accurately determined with the spectrophotometer (see "Core Physical Properties").

    d. Directly beneath the color is the "General Description," where the lithologic unit is described. Dominant and supporting skeletal components are listed in order of importance as well as other distinctive observations that are not indicated graphically. Key features such as exposure surfaces, changes in mineralogy, sudden porosity changes, etc., are noted for emphasis where they are critical to identifying lithologic unit boundaries. The terminology for the thickness of sedimentary beds and laminae follows McKee and Weir (1953): very thick bedded (>100 cm), thick bedded (30-100 cm), medium bedded (10-30 cm), thin bedded (3-10 cm), thickly laminated (>0.3 cm), and thinly laminated (<0.3 cm).

Other Lithostratigraphy and Sedimentology Analyses

Smear Slides and Thin Sections

Tables summarizing data, such as grain size and relative abundance of sedimentary components from smear slides, were generated using a spreadsheet program (Sliders). Thin sections were analyzed using a Zeiss Axioplan microscope equipped with a digital camera. Digital photomicrographs were obtained, labeled, processed (sharpness, contrast, focus, etc.), and stored as TIF files. Observations were recorded on a customized spreadsheet.

Digital Camera Imagery

A track-mounted Kodak DCS 460 digital camera was set up in the core laboratory so that complete cores or specific sections of interest could be imaged, cataloged, and stored. Color hard copies were made available to ensure that both shifts could see images of the sediments and rocks that had been packed away and not available for their direct inspection. Additionally, these images were extremely useful for the site-report authors to review lithologies and to illustrate key features.