GAMMA RAY ATTENUATION POROSITY EVALUATION (GRAPE) DATA
The Gamma Ray Attenuation Porosity Evaluation (GRAPE) data
files contains information generated onboard JOIDES
Resolution by the shipboard physical properties scientists
and technicians. Each whole round core section is moved
along a horizontal Multi-Sensor Track (MST) where successive
intervals are continuously bombarded by a beam of radiation.
Gamma rays which transmit through the entire core are
detected and counted. The amount of gamma radiation
transmitted through the core is inversely proportional to the
bulk density of the rock or sediment.
The GRAPE data files represent measurements obtained from all
cores from a given hole. Each record in the data file
represents a density/porosity evaluation measurement at a
given point in the whole round core. During Leg 146 there was
no Boyce correction formula used for the attenuation of
hydrogen in water in high-porosity sediments.
Boyce, R.E., 1976. Definitions and laboratory techniques of
compressional sound velocity parameters and water-wet
content, wet-bulk density, and porosity parameters by
gravimetric and gamma ray attenuation techniques.
In: Schlanger, S.O., et al., 1976, Initial Reports of the
Deep Sea Drilling Project, vol. 33: Washington (U.S.
Government Printing Office) pp. 931-958.
Explanatory Notes chapters, 1986 - present. In proceedings of
the Ocean Drilling Program, Initial Reports.
DATA ITEM FORMATS
The GRAPE data is presented in the following format:
EXPLANATION OF THE GRAPE PROCESSED DATA ITEMS
LEG - Number identifying the cruise.
SITE - Number identifying the site. A site is the position of
a beacon around which holes are drilled.
HOLE - Letter identifying the hole.
CORE - Number identifying the core. Cores are numbered
serially from the top of the hole downward.
CORETYPE - A letter code identifying the drill bit/coring
method used to retrieve the core. The coretype codes are:
B - Drill Bit
C - Center Bit
D - Positive Displacement
H - Hydraulic Piston Core
M - Miscellaneous
N - Downhole Mud Motor (Navidrill)
P - Pressure Core Barrel
R - Rotary
S - Side Wall Core
W - Wash Core
X - Extended Core Barrel
SECTION - A core is cut into 1.5 meter long sections that are
numbered serially from the top of the core. A core with full
recovery will have 7 sections and a core catcher and be app-
roximately 9.8 meters long.
TOP_INTERVAL - Distance in centimeters from the top of the
section to the top of the sample interval.
SUB_BOTTOM_DEPTH - Distance in meters from the seafloor to
the top of the sample interval.
BULK_DENSITY - This is the calculated bulk density in g/cm3
for a specific sample interval in the core section.
GAMMA_COUNTS - The cumulative transmitted gamma ray count
detected by the GRAPE apparatus over a specific sample
RUN_NUMBER - Each run of the MST is given a number which
increments by one with every test.