Core Layout

The tables of the CER can hold between 500–600 feet of core, which amounts to about 60 boxes of core or one and a half pallets. Before laying out the core boxes, the logger should ensure that the work area and tables are clean and clear from clutter. A clean area limits contamination, maintains a safe working environment, and removes potential tripping hazards that can lead to personal injury and dropped boxes.

Maintaining proper core orientation and the correct order of boxes facilitates easier and more accurate data collection. However, knowing which way the core is oriented in the box can be challenging, especially because USGS-drilled and contractor-drilled core often have different orientations (fig. 3). There are a few indications in any core box that the logger can use to determine top from bottom and deep from shallow. Many cores, especially those drilled by the USGS, are marked with two parallel lines colored red and blue (fig. 3a). When the core is properly oriented, or where shallow is at the top and deep is at the bottom, the red line is always on the right side of the core.

The orientation of the core is also directly indicated by depth markings, where more shallow depths are expected at the top of the box and deeper depths are expected at the base of the box (fig. 3). Depth is frequently marked on the core itself in permanent marker and often indicated by writing on wooden or foam blocks, core boxes or lids, and other pieces. Knowing the depth of the core is vitally important for logging and sampling. Therefore, a logger must also confirm that the depths on the core are marked properly and that all missing intervals are accounted for. The logger should pay special attention to rubbly intervals, sedimentary interbeds, and lithologic contacts when confirming depths and missing intervals because these areas often have low recovery, which can be challenging to measure and indicate properly.

The logger should use as many of the orientation and depth indicators as possible to determine proper core orientation and placement because the core could have been misplaced or mislabeled. If drill core has been marked incorrectly, multiple depth indicators do not match, there are missing intervals that have not been indicated or recorded within the core box, or if there are any other questions, the logger should alert the CSL Custodian. Working with the CSL Custodian, the logger may properly orient and mark the drill core by using any of the orientation indicators and additional resources such as drilling and sampling notes. Marking the core includes adding red and blue orientation lines or adding or altering depth indicators where appropriate.

Core Photographs

Every box of core needs to be photographed before being logged. A photograph of a box of core serves many purposes, including:

At the INLPO, core is photographed using a specially designed photographic jig (fig. 4). Using the jig for photographing ensures consistent lighting, reduces artifacts caused by lighting such as glare, and includes metadata information like corehole name, box orientation, and interval depth.

The photographic jig remains in the CER, though it is not permanently affixed to any location. If necessary, the logger should move the jig with permission and help from CSL personnel to a safe, secure, and accessible location. Before photographing, the logger should ensure that the jig is set up properly (fig. 4) by checking for the following:

The CSL keeps and maintains multiple handheld, digital cameras for photographing core. CSL personnel will show the logger where the cameras, spare batteries, and battery chargers are stored, as well as provide verbal instruction on camera maintenance and use. Before securing the camera to the jig, the logger should ensure that the camera is set-up properly by checking for the following:

Once the camera is set up properly, the logger can attach the camera to the jig. The camera screws into the back arm of the jig through a pilot hole on the bottom of the camera. Before tightening the camera completely, ensure that the camera is level by using the bubble level in the jig toolbox (fig. 4). Place the bubble level on the flattest part of the camera and use the mirror to make adjustments as needed. Once leveled, tighten the screw just until the camera is snug. Use the mirror to check that the core box and data plate will be within the frame of the picture. Adjust the height of the camera on the arm as needed by using the levers.

With the camera and the jig set up properly, the logger can begin to take photographs by placing each core box on the jig. The long axis of the core box is always placed against the long axis of the jig, but the exact orientation of the box is controlled by depth direction. The core box must be placed in the jig where the core orientation follows the directions of the “up” and “depth” arrows on the jig (fig. 4). If needed, the depth arrow can be replaced with an arrow going the opposite way. If the arrow placements still do not align with the core orientation, alert the CSL Custodian before taking any pictures. Once the core box aligns with the arrows, the logger should push the box until it is flush against the back rest and the data plate and is positioned squarely. The logger needs to write the name of the corehole and the depth interval represented in core box using legible handwriting in the designated areas, which are labeled “corehole name” and “depth interval” in figure 4. The name of the corehole remains the same throughout all pictures and does not need to be erased and rewritten before each picture, unless the logger is photographing drill core from multiple coreholes. The depth interval changes for each core box and does need to be rewritten before each photograph. The depth interval is often found written on the box or its corresponding lid and needs to be recorded on the jig in the same precision as it was found. Before taking the picture, the logger should ensure that the red and blue parallel lines (fig. 3) as well as other depth indicators will be clearly visible in the photograph.

To take the picture, the logger holds the trigger, steps away from the box, and depresses the button on the trigger. The camera should be set to auto focus, so there is no need to manually focus here. To produce consistent and quality core photographs, the logger should:

Core Photographs Post-Processing

Once all core boxes have been photographed or the logger is finished photographing for the day, the logger should:

As soon as practical, the logger should transfer the core photographs from the SD card to an internal INLPO file server to prevent potential loss and support data archiving (fig. 5). Every photograph will include a .jpeg and a raw file. Original photographs should be retained to serve as backup in case other copies are lost, misplaced, or corrupted. If the logger is unable to transfer pictures, alert CSL personnel. CSL personnel will work with the logger to transfer the pictures.

Standard Practices

There are a few practices that any logger should follow when logging core. These practices include:

Lithologic Description

The main aspect of the core log, and the one that contains the most information, is the lithologic description. The lithologic description is a written description of certain characteristics of the drill core such as color, texture, mineralogy, and alteration, though its exact contents vary by the interval of description and its lithology. A lithologic description provides details of the core not visible in pictures and context for sampling. A lithologic description also provides important data and context researchers can use to better understand the geologic history of the area, assess the chemical and physical properties of the different lithologies, and support scientific studies. To create a lithologic description, the logger must be as specific as possible while minimizing interpretation. Ultimately, logging drill core is an individualized experience and always contains some level of interpretation. However, consistency is the key to good lithologic descriptions.

Interval Selection

The first step a logger takes when beginning a lithologic description is choosing the interval of the description. The interval is the depth in feet BLS to the top and to the base of the portion of core being described. The thickness of the interval is dependent on the lithology of the core, the occurrence of missing intervals, and the personal preference of the logger.

On a broad scale, a lithologic core log describes change. Substantial changes in the core, such as a compositional or lithologic change, warrant a new lithologic description to prevent generalizations and loss of detail (fig. 6). Other changes in the core, such as a textural or color change, warrant noting in the lithologic description but not necessarily a new lithologic description. For INLPO core logs, a new lithologic description is required each time the lithology changes regardless of the stratigraphic thickness of that lithology (fig. 6). A change in lithology occurs when the lithology changes from basalt to sediment, or from basalt to rhyolite, for example. A new lithologic description is also required after each missing interval (fig. 6). Even if the lithology immediately above and below the missing interval appears continuous, it is possible the missing interval could have contained a lithologic contact.

On a fine scale, the same continuous lithologic type should be broken into multiple lithologic descriptions, which is especially true for basalt. Each drill core consists of tens to hundreds of feet of layered basalt flows (fig. 6). A flow refers to all eruptive products from the same eruptive event. Basalt flows can be broken into two or more subdivisions called basalt flow units. A basalt flow unit represents a single eruptive product from an event and therefore defines the minimum subdivision of a basalt flow. It is required at the INLPO for a logger to include at least one lithologic description for every basalt flow (fig. 6). If the basalt flow has multiple flow units, it is recommended the logger create a lithologic description for each flow unit (fig. 6).

Differentiating between basalt flows and layers in drill core can be challenging because of their visual similarities. However, the contact between different flows and layers often produces predictable features that are occasionally preserved in the drill core. These features include oxidation, alteration, flow molds, spatter features, and rubble zones. If the logger notices and recognizes one or more of these features in the drill core along with other features such as missing intervals and distinct mineralogical or textural changes, the logger should initiate a new lithologic description for the basalt package following the observations (fig. 6). Because these features are not unique, the logger does not need to determine or name if the package of basalt is a flow or layer. In general, differentiating between and correlating basalt flows and layers requires additional datasets such as paleomagnetism and geochemistry. However, identifying and defining basalt flows and their flow layers in a core log provides important context for collecting samples for these and other datasets. Ultimately it is up to the discretion of the logger to determine and distinguish between basalt flows and flow layers. While this requires some interpretation, which logging attempts to minimize, a recommended practice is to include more lithologic descriptions rather than less.

Assigning a Generalized Lithologic Name to Intervals

Once the logger has chosen an interval for the lithologic description, the logger must assign a generalized lithologic name to that interval (table 2). An interval can only have a single generalized lithologic name. Assigning a generalized lithologic name is important for maintaining consistent and predictable data collection across multiple loggers and different drill cores. The generalized lithologic name controls the specific components or categories of the lithologic description and therefore the features of the core that the logger describes. The lithologic description itself includes a detailed lithologic name that a logger can use to expand on and refine the generalized lithologic name if possible.

The generalized lithology for most lithologic units in CSL drill cores will fall into one of the following five categories: basalt, rhyolite, volcanic ash, consolidated sediment, and unconsolidated sediment (table 2). Choosing the generalized lithologic name for the interval is up to the discretion of the logger, and figure 7 presents a flow diagram to help the logger make this choice (fig. 7). If the logger encounters a general lithology that does not fall within one of these five categories, the logger should alert the CSL Custodian and work with the Custodian to determine the new category for the lithologic description.

Many of the basalt flows in drill core are separated by intervals of sediment. The generalized lithologic name of any sediment-bearing interval is controlled by the degree of sediment compaction. For CSL core logs, the two possible generalized lithologic names of the sediment intervals are “unconsolidated sediment” and “consolidated sediment.” Unconsolidated sediment is a sediment interval that consists primarily of loose material. This material ranges from loose, disaggregated grains to large, individual chunks of aggregated grains.

There are two different types of consolidated sediment: cemented and compacted. Cemented sediment consists of grains that are bound together by materials such as quartz, calcite, and iron oxides, which fill the space between grains as the rock forms. Compacted sediment is sediment that has undergone compression, which reduces volume and increases the density of the sediment, because of the weight of the overlying materials. Both cemented and compacted sediment have the same categories for the lithologic description.

Ultimately, it is up to the logger to distinguish between consolidated and unconsolidated sediment. There is a continuous spectrum between consolidated and unconsolidated sediment, and figure 7 presents a flow diagram to help the logger with assigning a generalized lithologic name to a sedimentary interval (fig. 7).

Consistency in naming consolidated and unconsolidated sediment intervals matters more than the name itself. The format of the lithologic description for consolidated and unconsolidated sediment is very similar, which means that similar data are collected for both intervals regardless of their generalized lithologic names. The primary purpose of distinguishing between consolidated and unconsolidated sediment is to facilitate consistent and predictable core logs.

Assigning a Detailed Lithologic Name to Intervals

A detailed lithologic name usually provides more context and information than the generalized lithologic name. A detailed lithologic name is dependent on specific properties of the interval, including texture, grain size, composition, and compaction. If these properties are descriptive only, then the detailed lithologic name and the generalized lithologic name will remain the same. For example, a basalt containing macroscopic minerals is often referred to as “porphyritic basalt.” While “porphyritic” is an important textural term, it describes the lithology of the interval without changing its name. However, if these properties change the overall generalized lithologic name of the interval, then the generalized lithologic name and the detailed lithologic name will diverge. For example, a volcano erupts fragments of rocks, glass, and other materials that can solidify (weld) into a rock called a “tuff” under the right conditions. If the tuff is primarily rhyolitic in composition, then the generalized lithologic name of the interval is “rhyolite” and the detailed lithologic name of the interval is “welded rhyolite tuff.” In this example, rhyolite becomes a descriptive term while “tuff” is the overall name of the rock. Ultimately, it is up to the logger to determine a detailed lithologic name. To assist with this process, figure 8 represents a flow chart that recommends detailed lithologic names based on overall rock type and specific observations expected in CSL drill core (fig. 8). If the logger is unable to assign a detailed lithologic name, the generalized lithologic name may be used as the detailed lithologic name.

Igneous rocks, including basalt and intermediate rocks, will always have the same generalized and detailed lithologic name (fig. 8a). While the basalt and intermediate rocks might have unique textures and mineral sizes, these observations qualify rather than alter the generalized lithologic name of the interval. Textures, mineral sizes, and other descriptive features are mentioned in the texture and composition categories of the log and do not need to be included in the detailed lithologic name.

The detailed lithologic name for rhyolite is dependent on how the interval formed and its overall grain size. If the rhyolite was formed as a lava flow cooled, similar to how basalt is formed, the generalized and detailed lithologic name are both “rhyolite.” If a volcano erupted rhyolitic ash that was later welded (consolidated), the generalized lithologic name is rhyolite and a partial detailed lithologic name would be “welded rhyolite.” The detailed lithologic name is further quantified by the dominant grain size in the interval. If the grain size is less than 2 millimeters (mm), the detailed lithologic name is a “welded rhyolite tuff.” If the grain size is greater than 2 mm, the detailed lithologic name is “welded rhyolite tephra.” The groundmass of welded rhyolite tuff and tephra is generally finer grained than rhyolite and includes other eruptive products such as lithics and pumice.

The detailed lithologic name for volcanic ash is dependent on the composition of the ash. The composition of the ash can be basaltic, andesitic, dacitic, or rhyolitic, which depend on the minerals present and their relative abundances. Basaltic ash contains mafic minerals such as biotite and olivine in high quantities, while rhyolitic ashes will contain high quantities of felsic minerals such as quartz and feldspar with few to no mafic minerals. Volcanic ash is assigned to intervals that are not welded, which means the intervals consist of loose ash particles.

Sedimentary Unit Naming

Assigning Color

Describing color follows the same process for every lithology. Color is estimated using a Munsell color chart provided by the CSL. Color must be taken on a weathered (not recently fractured) and non-altered surface of the core that is clear from sediment and drilling artifacts like staining or striation. Every description of color needs to include the alphanumeric code from the Munsell color chart (for example, N7) and its associated description (for example, light gray). If the color of the core does not match an option in the Munsell color chart, the logger should determine the closest match in the Munsell color chart and then briefly describe how the color deviates (for example, N7 light gray with a pale purple tint).

In some cases, the interval chosen for the lithologic description will have multiple different colors. If this is the case, the logger must note the interval of each color. For example, a logger might say N6 medium light gray from (715.0–716.6 ft) and N7 light gray from (716.26–720.1 ft).

In other cases, the interval oscillates between colors on a fine scale of millimeters-centimeters (cm). If this occurs, the logger should note the individual colors using the Munsell color chart, the nature of the contact(s) between the different colors, and estimate a single, average color for the interval. The logger does not need to note the interval of each color because that causes extraneous and tedious data collection beyond the scale the INLPO is looking for.

Assigning Texture

The most important feature of any lithologic description is the texture. The texture describes the overall appearance of a rock, which is controlled by the rock’s evolution and the arrangement of its components like grains or minerals. The texture and its description for any rock are highly dependent on lithology. It is beyond the scope of this document to account for every possible texture in CSL core.

In many cases, the interval chosen for the lithologic description will have multiple different textures. If this is the case, the logger must note the interval of each texture and the degree of the texture if applicable (app. 3, table 3.1). For example, a logger might say vesicular from (131.2–136.4 ft) and vesicular and strongly diktytaxitic from (131.2–136.4 ft).

Sedimentary Textures

For consolidated and unconsolidated sediments, texture refers to select characteristics of the overall sediment grains, including how the grains appear and how they are aggregated together (Compton, 1985; Retallack, 1988). These descriptions are limited by visibility factors such as grain size, lighting, and individual eyesight. A visual description of the sediment grains should include:

• • Size: A description of the overall range of grain sizes of all grains given in common grain size terms (table 4).

• • Rounding: A description of the overall range of rounding of all grains given in qualitative terms, where rounding refers to the degree of how round a grain is (fig. 9).

• • Sorting: A description of the overall range of sorting of all grains given in qualitative terms, where sorting refers to the degree of uniformity in size and degree of roundness of grains in an interval (fig. 10). More uniform intervals indicate better sorting.

For unconsolidated sediments, the overall texture of the interval is also dependent on how the individual grains are packed together and the shape the aggregated grains make, which is called packing. The aggregated grains are called peds. If the grains are completely loose and not connected, there are no peds and the packing of the interval is referred to as single-grained. If there are peds, the peds can form blocky, columnar, or platy shapes, which is reflected in the type of packing (table 5). The texture for every unconsolidated sedimentary interval must include a description of packing using the terms outlined in table 5.

Table 4.    

Description of grain size and name.

[“Lower diameter and upper diameter” columns give the upper and lower dimensions for each grain size name. “Grain size name” column provides the name given to the grain being described if it falls between the upper and lower dimensions. “Group name” column lists the common, less-detailed name given to the grain sizes. Modified from Wentworth (1922). Abbreviations: mm, millimeter; >, greater than; <, less than]

Table 4.    Description of grain size and name.

Lower diameter (mm)	Upper diameter (mm)	Grain size name	Group name
256	>256	Boulder	Gravel
128	256	Coarse cobble	Gravel
64	128	Fine cobble	Gravel
32	64	Very coarse pebble	Gravel
16	32	Coarse pebble	Gravel
8	16	Medium pebble	Gravel
4	8	Fine pebble	Gravel
2	4	Very fine pebble	Gravel
1	2	Very coarse sand	Sand
0.5	1	Coarse sand	Sand
0.25	0.5	Medium sand	Sand
0.125	0.25	Fine sand	Sand
0.06	0.125	Very fine sand	Sand
0.008	0.06	Silt	Mud
<0.004	0.008	Clay	Mud

Table 5.    

Description of packing types and how to recognize each type in core stored at the Lithologic Core Storage Library.

[“Packing” column provides the name of the type of packing being described. “Definition” column displays the definition of the packing adapted from the Glossary of Geology by the American Geosciences Institute (2025) and Retallack (1988). “Description” column provides a list of potential defining features or characteristics of the packing to help the logger identify that packing in the core. “Additional comments” column provides additional descriptions, recommendations for logging, and other characteristics of the packing not included in the previous columns. Abbreviations: cm, centimeter; mm, millimeter]

Table 5.    Description of packing types and how to recognize each type in core stored at the Lithologic Core Storage Library.

Packing	Definition	Description	Additional comments
Single-grained	No peds; disaggregated, loose sediment with no cohesion.	Interval consists of disaggregated grains with no cohesion.	Interval often consists entirely of loose sand or silt; always accompanied by a loose consistence.
Massive	Peds occur as large clods.	The interval consists of large clods of sediment that are hard to break apart. It can be challenging to choose an individual ped.	Closest texture to consolidated sedimentary rock.
Granular	Peds occur as individual, pebble-sized pieces of sediment.	Individual peds are subrounded to rounded and generally do not exceed the size of coarse pebbles. Peds are often disconnected from each other and move freely.	Peds of this texture resemble crumbs.
Blocky	Peds occur as irregular blocks of sediment.	Individual peds are angular to subangular and range in size from coarse pebble to very coarse pebble. Peds are often disconnected from each other and move freely.	Peds are generally larger and more angular in this texture than in intervals with granular texture.
Platy	Peds occur as thin, flat plates of sediment.	Individual peds are flat layers that are often stacked on each other. Layer thickness generally ranges from 1 mm to over 10 cm.	Similar to lamination in a consolidated sedimentary rock.
Prismatic	Peds occur as vertical columns of sediment that stretch up to a few cm long.	Individual peds are columns that generally range from 1 to over 10 cm tall with a width that is generally less than a few cm.	Peds can have flat or domed top as used here.

Assigning Structures

Also included in the texture category of a lithologic description is a place to note any igneous and sedimentary structures (table 6). It is beyond the scope of this document to account for every possible structure in CSL core.

For any igneous and sedimentary structure, the logger should note the depth (single occurrence, given in feet BLS) or interval (multiple occurrences, given in top and base in feet BLS) of the structure, its recurrence interval (that is, how many times it occurs in the interval), and if the structure seems to be controlled or influenced by any other features of the core (for example, fractures, banding, and grain size change). Using these observations and table 6, the logger also needs to name the structure. If there is a structure present in the core but not mentioned in table 6, the logger should alert the CSL Custodian and describe the structure as much as possible. These descriptions should include the same information mentioned in the “Assigning Composition” section, as well as the shape, overall appearance, and size of the structure.

Common igneous structures include vesicle alignments such as vesicle sheets and vesicle cylinders, emplacement features such as flow molds and spatter, and select textural characteristics such as rheomorphic folding and lithophysae (table 6). Common sedimentary structures include bedding features such as trough-crossbeds, bedding types such as massive, thin, or graded bedding, and additional features such as mud cracks and root casts (table 6). If a logger recognizes any of these structures, the logger should note the depth or interval of the structure and describe any additional information such as size, shape, and extent in the texture category of the lithologic description.

Assigning Composition

To fully describe the composition of an interval, the logger must describe the visual and physical characteristics of every mineral and other major components like lithics and pumice to the best extent possible. Composition descriptions are limited by visibility factors such as grain size, lighting, and individual eyesight. However, all composition and mineral descriptions should include:

Assigning Alteration

Alteration is a change in the physical, chemical, or mineralogical composition of a rock that occurred after its formation. Physical and chemical alteration is noted here, while mineral alteration is noted in the composition category of the lithologic description. Noticeable aspects in the core related to physical or chemical alteration include, but are not limited to, staining, spotting, or color changes in the core that cannot be attributed to changes in lithology or texture alone. When describing alteration, the logger should include its interval, prevalence and extent, color, and texture. Color should be described using the Munsell color chart as much as possible. The logger should also note if the alteration follows any other structures, patterns, or other features in the core. Sediment and (or) calcium carbonate in fractures and vesicles are also a form of alteration and should be recorded here. If the alteration is sediment in fractures and vesicles, the logger should include a general grain size, composition, and reaction to hydrochloric acid (HCl) of the sediment if possible.

Assigning Xenoliths

A xenolith is a fragment of rock that is incorporated into a magma before the magma cools and solidifies around it. Xenoliths are most often found in basalt and intermediate igneous rocks. Xenoliths are rare in the basalts and intermediate rocks stored at the CSL, but possible. If the interval does not have a xenolith, which is most likely, the recommended way to fill out this section of the lithologic description is to write “None noted.” If the interval does have a xenolith, the logger must describe the xenolith as if the xenolith is its own lithologic interval. The description for the xenolith needs to follow the lithologic description for the rock type it shares.

Assigning Consistence

The consistence of an interval is assessed for unconsolidated sedimentary intervals. Consistence is the degree of how resistant a ped is to being crushed or deformed, where a ped is a collection of grains aggregated together. To assess consistence, the logger chooses a ped (already broken, loose in the box, and <1 cm) or breaks a subunit off a larger (>1 cm) ped. The ped is then pinched between the logger’s fingers, and its deformation behavior indicates the consistence of the interval (table 8). Testing one or two peds per interval is sufficient to estimate the interval’s consistence. It is possible for an interval to have a range in its consistence if more than one kind of ped exists. Table 8 lists expected types of ped deformation and how to recognize each. If the interval consists of very loose, mostly to completely unconsolidated grains, the interval has a loose consistence. The shape of the individual peds and how the peds interact with each other is called packing and is described as part of the interval’s texture (table 5).

Assigning Strength of Reaction to Acid

The strength of an interval’s reaction to hydrochloric acid (HCl) is described for both unconsolidated and consolidated sediment. HCl is the chosen acid because it reacts with calcium carbonate, which often cements sediment grains together or is incorporated into sedimentary intervals by the wind. Assessing the relative amount of calcium carbonate in sediment by judging the strength of its reaction to HCl provides important context for the rest of the lithologic description and core log. Judging the strength of the reaction is ultimately subjective, so consistency is key. Appendix 3 lists qualitative terms with their definitions that a logger should use when describing HCl reaction strength.

To assess the strength of the reaction to HCl, a logger takes an acid bottle filled with dilute HCl, which is provided by the Core Storage Library, and drops 2–3 drops of acid onto the sediment. The logger observes the reaction and assigns a strength to the reaction using the terms in appendix 3, table 3.1. It is a good practice to test reaction strength at multiple locations, especially if there are color, grain size, or textural changes within the interval. If reaction strength changes substantially and for an extended interval (>1 ft), the logger should note the interval and strength of each response. Otherwise, recording an average reaction strength is sufficient.

Assigning Roots and Fossils

Consolidated and unconsolidated sediment intervals occasionally contain evidence of biological activity such as root casts or fossils. For any evidence of biological activity, including fossils, the logger should note its depth or interval of occurrence, size, shape, color, and name of the feature, if possible. Evidence of biological activity is also noted in the “Texture” category because biological activity is included in sedimentary structures. The descriptions do not have to be reproduced in both categories, so describing the biological activity once is sufficient. It is recommended that evidence of biological activity is described here to emphasize its presence and because it helps to limit the length of the “Texture” category.

Other Aspects of a Lithologic Description

Finally, the lithologic description of the core log gives a logger a chance to describe, note, or recognize any other aspect of the core that has not been noted elsewhere. Examples include noting if the core is mislabeled, if the box containing the core was dropped, if there were problems encountered during the logging progress, or if there are other features of the core that were not described elsewhere, such as evidence of faulting or magnetic properties. When describing any feature, the logger should include as much detail as possible, such as depth or interval, color, size, and shape. If the logger chooses to describe any additional aspects, the description should be added at the end of the lithologic description under an optional “Additional notes” category.

Igneous Vesicle Characterization

Basalt is often vesicular, so recording the size and concentration of vesicles provides important context. However, data on vesicle size and concentration are not recorded in the “Texture” category of the lithologic description. Instead, vesicle size and concentration data are collected separately from the lithologic description and constitute a separate portion of the core log. Separate data collection minimizes excessive text and confusion in the lithologic log, organizes data better, and hastens the logging process. In addition, most of the data in a lithologic description are qualitative, while vesicle size and concentration data are quantitative.

Fracture Frequency

An INLPO core log includes a numerical estimate of the fracture frequency of an interval given on a scale of 0 to 5, where 0 is unfractured and 5 is extremely fractured (table 9; app. 6). Fracture frequency data are collected only for intervals of igneous rocks and consolidated sediment. Fracture frequency data are not collected for intervals of unconsolidated sediment because fractures are not preserved in loose, disaggregated material. When assessing the fracture frequency of an interval, the logger needs to consider both natural and drilling fractures, which are fractures caused by the drilling and storage of core. While fracture frequency includes drilling fractures, the logger must note the depth or interval where drilling fractures occur within the lithologic description under the optional “Additional notes” category; if there are no drilling fractures within the lithologic interval, the logger does not need add any notes related to drilling fractures under “Additional notes.” Drilling fractures are generally horizontal, clean, do not look weathered, and are usually without oxidation, sedimentation, and precipitated minerals.

Assessing fracture frequency is similar to collecting vesicle characterization data. The logger must record an average fracture frequency for igneous and consolidated sedimentary lithologic intervals. The fracture frequency will change throughout the lithologic interval, so the logger should establish multiple subintervals to characterize and record the variation. A good practice is to choose an interval where the fracture frequency is constant and record the fracture frequency for that interval. When the fracture frequency changes, the logger should initiate a new interval and repeat the process. An additional good practice is to include small intervals (<0.3 ft) where fracture frequency changes sharply, especially for very broken or rubbly core and rubble zones, to collect data as accurately as possible. The logger must record the fracture frequency and its interval of occurrence given in feet BLS to its top and base.

Missing Core Intervals

Almost any drill core will be incomplete and have portions missing. Portions of missing core exist for a variety of reasons, including that the interval was not recovered during drilling, was misplaced or lost, or was sampled by a previous researcher. While it is not required, it is good practice to note the interval of missing portions of core. Having this data will be helpful for creating a continuous lithologic log, recording where missing data are expected rather than accidental.

Finalizing a Lithologic Core Log

At the end of the logging process, the logger should have numerous notes of lithologic descriptions and data for vesicle size, vesicle concentration, and fracture frequency in either digital or written format. Regardless of the medium, the logger needs to scan and upload all notes and drafted logs to the folder structure if the purpose of the core logging is to contribute to CSL records (fig. 5). If the core is logged for research or sampling purposes, sharing the log with CSL personnel is encouraged but not required. The logger also needs to alert the CSL custodian that the logging is complete.

To clean up, the logger needs to replace the lids on all the core boxes and return all equipment to their original locations. The CSL custodian or other CSL personnel will help the logger return the core to the pallets and return the pallets back to the shelves.

If the purpose of the logging was to characterize an entire drill core rather than describe portions of it for a sampling or research campaign, the data that were collected needs to be visualized for effective and easy access by others. The USGS uses proprietary software to compile, organize, and display the data from a lithologic core log. The logger would need to contact the Core Library Custodian to obtain the most recent version of the software and instructions on how to use it.