A note on the geochemistry procedures and the geochemical data base of the Ocean Drilling Program

Marine Geology, 87 (1989) 329-337

329

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Letter Section

A Note on the Geochemistry Procedures and the Geochemical Data Base of the Ocean Drilling Program KAY-CHRISTIAN EMEIS and PATRICIA BROWN Ocean Drilling Program, Texas A&M University Research Park, 1000 Discovery Drive, College Station, TX 77840 (U.S.A.) (Received September 6, 1988; revised and accepted January 4, 1989)

Abstract Emeis, K.-C. and Brown, P., 1989. A note on the geochemistry procedures and the geochemical data base of the Ocean Drilling Program. Mar. Geol., 87: 329-337. We present a brief description of routine and special geochemical analyses, including methodology and instrumentation, performed onboard R.V. JOIDES Resolution SEDCO/BP 471 during drilling campaigns of the Ocean Drilling Program. The organic geochemical program is centered on hydrocarbon monitoring and produces data on organic matter abundance, composition, and maturity. Specialized equipment is available for examining interstitial gas composition and concentration, and lipid composition of solvent extracts. Interstitial water analyses measure major dissolved ions and nutrients. The structure and content of the ODP data base that incorporates these new data and those from 96 DSDP legs contains at present results of more than 95,000 analyses, mainly of carbonate and organic carbon content. Data base structure enables specific searches and relational sorting, which makes regional or temporal searches possible.

Introduction The main prerequisites for scientific advancement, second only to inspiration and true genius, have always been acquisition of highquality data, access to modern instrumentation, and the use of data-handling facilities and data bases that are comprehensive, powerful, and able to cope with results gained through laboratory work. The Ocean Drilling Program (ODP), the latest international effort of scientific ocean drilling, recognized the potential and the need for state-of-the-art chemistry laboratories at the locus of interest, the drill site, in order to capture many of the chemical characteristics that 0025-3227/89/$03.50

are usually lost during extended periods of sample storage. The prime objectives of shipboard geochemical programs of past scientific ocean drilling ventures were mainly safety-oriented hydrocarbon monitoring programs. Cruise participants working in JOIDES Resolution's 5000m 2 laboratory facility are now able to analyze almost every property of sediments and rocks, ephemeral or resident, according to modern analytical and data-handling techniques. These data are recorded, in part automatically, and are incorporated into a geochemical data base that contains invaluable details on the chemistry of sediments, rocks, and interstitial waters recovered during 96 Deep Sea Drilling Project (DSDP) and 21 ODP legs (to date).

© 1989 Elsevier Science Publishers B.V.

330

With this communication we hope to familiarize marine geologists and geochemists who are not aware of procedures and standards of the chemistry program of ODP with the extent and quality of data, describe routine analyses and techniques, and lay out the structure and content of the geochemical data base. These data are available to qualified scientists upon request to the ODP Data Librarian.

The routine chemistry program, equipment, and types of data produced

Organic geochemistry The original intention of establishing an organic-geochemistry program on board the drilling vessel Glomar Challenger, the predecessor of JOIDES Resolution, was to prevent accidental tapping of hydrocarbon accumulations. In the early legs of the DSDP, this was accomplished by routinely sampling gas pockets and bubbles and injecting the gas mixture into a gas chromatograph for determinations of ratios of methane to higher hydrocarbons. From this ratio and the downhole-temperature gradient, the proximity to hydrocarbon reservoirs can be estimated. Later legs saw the installation of gas chromatographs equipped with capillary columns for analyses of lipid extracts and of pyrolysis instruments to check for anomalous hydrocarbon abundance. As was the case during the DSDP, the prime responsibility of the shipboard organic geochemists a n d / o r petroleum geologists on ODP legs still is the monitoring of hydrocarbons, because the ship operates without risers or blowout preventers. Apart from serving the safety aspects, however, the data obtained during the routine hydrocarbon-monitoring program (Fig. 1) are scientifically meaningful and of high quality, thus adding to the scientific data pool collected during drilling (Emeis and Kvenvolden, 1986; Kvenvolden and McDonald, 1986). Two methods are used for the purpose of gas monitoring:

(1) Traditional analyses of interstitial-gas composition in gas pockets, using a simple gas chromatograph equipped with a packed column and a flame ionization detector, yield ratios of methane to higher volatile hydrocarbon gases C2 and C3. These analyses are not quantitative, because the volume of sediment from which the gases evolved is undetermined. (2) These data are supplemented by analyses of free and sorbed gas in a sediment sample of known volume after temperature desorbtion in a commercial Hewlett-Packard (HP) Headspace Analyzer. After desorbtion (70°C for 30 min) a volume of the known headspace is injected into the sample loop of an HP model 5890 gas chromatograph, modified to simultaneously separate and analyze hydrocarbon (C1 through Clo) and stationary gas phases (02, N2, H2S and CO2). Samples for this procedure are obtained according to the routine sampling scheme outlined in Fig. 2. The gas content of the sample is determined on a volume/volume basis; truly quantitative analysis, however, will be achieved only after routine sampling with a pressure core barrel and sampling system currently being built. At present, degassing during core-barrel retrieval results in loss of gas, and probably in fractionation and preferential loss of light hydrocarbons. A second HP 5890 gas chromatograph is equipped with a 50-m fused silica chromatographic column. This instrument is used for analyses of hydrocarbons and other lipids in sediment extracts, which are usually prepared by ultrasonication in reagent-grade solvents. Facilities for thin-layer chromatography, rotary evaporation, or blowdown under inert gas are provided, as are compound standards for coinjection or comparison of retention times. Data from both gas chromatographs and instruments in the interstitial-water section are collected in a HP Laboratory Automation System, which serves as a data station, integrator, and reporting facility. Data manipulation, storage and transfer to the shipboard VAX mini-

331

I

INDURATED ROCK

SlIGNS

I

I

CHECK FOR OF GAS (VISUAL, GAS SNIFFER)

I

SOFT SEDIMENT CHECK FOR GAS POCKETS

NEGATIVE POSITIVE

POSITIVE

I

NEGATIVE

I_ I GRINDROCK ~ IN BALL MILL /

I COLLECT AND ANALYZE VACUTAINER SAMPLE

-~1 COLLECT AND ANALYZE HEADSPACESAMPLE

NORMAL I BACKGROUND I ANDTREND

I

'1 ANOMALOUS COMPOSITION FORSEDIMENT

ANDENVIRONMENT

SECURITY PRIORITY FOR ROCK EVAL AND TOC

NORMAL I TREND AND I BACKGROUND I

SPLIT CORE SECTION FOR STAIN AND FLUORESCENCE ANALYZESEDIMENT

1

I WAIT FOR ROCK EVAL I AND TOC RESULTS

t

I NORMAL ANOMALOUS I

IPLuGANOABANOON I

CUT NEXT CORE

TIME ESTIMATES VACUTAINER SAMPLING & ANALYSIS C1,C2,C3+ HEADSPACE SAMPLING & ANALYSIS C1,C2 HEADSPACE SAMPLING & ANALYSIS C3 - C6+ ROCK-EVAL SAMPLING & ANALYSIS TOTAL ORGANIC CARBON SAMPLING & ANALYSIS

= 5 MINUTES = 5 MINUTES = 30 MINUTES = 90 MINUTES = 90 MINUTES

Fig. 1. Schematic representationof proceduresand decision-makingduringroutine hydrocarbonmonitoringwhile drilling.

computer is accomplished by an HP 1000 microcomputer. A further technique used primarily during hydrocarbon monitoring employs a commercial programmed pyrolysis instrument (Delsi Nermag RockEval II) equipped with module to determine total organic carbon (TOC). The technique of programmed pyrolysis is widely used in hydrocarbon exploration as a guide to sourcerock quality and maturity, and as an indicator of migrated hydrocarbons (Tissot and Welte,

1984). Aside from determining TOC in a sample by combustion at 600°C, the instrument measures hydrocarbons desorbed at a temperature of 300°C ($1, mg hydrocarbons/g sample), and hydrocarbons cracked from kerogen during the temperature program (300-600°C; $2, mg hydrocarbons/g sample). The temperature of maximum hydrocarbon release, Tmax, is considered to be an indicator of thermal maturity of the organic matter. CO2 liberated at temperatures below 390°C from decomposition of

332 Core IW G IW* G IW OG IW* iW ~ IW OG G

G OG IW

G IW OG

IW OG G

IW OG G

IW OG G

IW OG G

Fig. 2. Routine sampling schemefor chemicalanalysesof sedimentsand interstitialwaters. Samplingdensitycan be extendedupon requestand approval of the curatorand cochief scientists. G -- gas sample; I W - - interstitial water sample;I W * - - IW samplefromshipboardhalfofthe working half; O G - - frozenorganicgeochemistrysample. oxygen-bearing organic molecules is monitored as $3 (mg CO2/g sample). Normalizing $2 and $3 to TOC content yields the hydrogen and oxygen indices, which correlate favorably with elemental analyses of H/C and O/C used to classify organic-matter types (Van Krevelen, 1961; Espitali~ et al., 1985 ). In spite of limitations of this technique for analyses of thermally immature sediments and sediments of low TOC

content, the hydrogen and oxygen indices of organic matter and downhole plots of maturity aid considerably in determinations of organic facies. Routine analysis of the character of organic matter by pyrolysis is performed on squeezed cakes from interstitial-water analysis (see following section) and on headspace residues in order to maximize parameters determined on the same samples. Indispensable for sedimentologists and physical properties programs is the determination of carbonate content of sediments and, to a lesser extent, TOC concentrations; the instruments used for these analyses are the work horses of the chemistry laboratory on board JOIDES Resolution. Carbonate analyses are routinely performed at a minimum rate of three per core (about 9.6 m long). The samples are simultaneously subjected to index-properties and X-ray-diffraction studies in the physicalproperties and sedimentology programs (see Fig. 3). The instrumentation used currently consist of two CO2 coulometers (Coulometrics model 5030 Carbonate Carbon Apparatus and model 5020 Total Carbon Apparatus), which analyze CO2 from acid digestion (2N HC1) or combustion ( 1000 ° C ), respectively. Organic carbon is calculated by difference of total and carbonate carbon. While the coulometric carbonate technique was used on all ODP legs as the standard, some legs employed the carbonate-bomb method in addition in order to process very large numbers of samples. The instrumentation for total-carbon analysis, while always using combustion, will be changed after Leg 112 from an elemental analyzer (Perkin Elmer model 240D ), which measured total nitrogen and hydrogen in addition to carbon. In the near future, the instrument will be replaced by another elemental analyzer (Carlo Erba NA1500) that simultaneously determines C, N and S concentrations in samples. An evaluation of all three methods shows that the accuracy and precision of the three instruments are comparable; the decision to replace the current coulometric

333

I CORERECEIVEDONCOREPREPARATIONDECKII I

!

I

I INSPECTIONFORGASBUBBLESIN CORELINER NO / YES I

I SAMPLINGOFGAS IN VACUTAINER

GAS CHROMATOGRAPHY

I

CO.ECU. I

INTOSECTIONS

vI

:1

LABORATORY

8

>-

< © b-

WHOLEROUNDSAMPLESTAKENFOR: I ORGANIC GEOCHEMISTRY WATERS

I INTERSTITIALI

.I,

v I

10cm3

=7

WETSEDIMENT

n-

O <

I PACK,LABEL, I ~ FREEZE,STORE,

SQUEEZE~-~

I

HEADSPACE ANALYSES

]

IANALYZEI .ONCHROMA,OGRAP.Y

ORY, GR.ND

pH ALKALINITY SALINITY(NUTRIENTS) AMPOULES+ CAKE

I CaC°'C°rI Rock-Eval (Extr.of Hydrocarbons)

Fig. 3. Flow diagram of samples through the chemistry, physical-properties, and X-ray laboratories on board JOIDES Resolution.

technique is governed mainly by the desire to accommodate the need for multi-element analysis with a working automatic sampler to free technicians and scientists for other tasks. All quantitative analyses obviously require accurate and precise weight measurements to ascertain correct results, which is not an easy task on board a ship in motion. Adequate weighing accuracy and precision are achieved in the chemistry laboratory of J O I D E S Resolution with electronic balances (Cahn model 29

for weights to 1250 mg and Scientech twin balances for weights to 40 g) connected to a computer and mounted on gimbaled weighing tables. All balances are routinely calibrated during port calls. During the weighing process, computer programs either average a number of measurements (usually on the order of 50 counts) specified by the user, or use a convergence routine so that the computer continues measuring as long as the standard deviation exceeds a specified limit. These routines are used

334 for taring and for weighing of unknowns, and the weighing error is estimated to be < 1% from measurements of known weights. Interstitial-water program

The interstitial-water program performed in the chemistry laboratory is a continuation of the program performed routinely during DSDP legs. Because the unique sampling method is performed under less than ideal conditions, radically different approaches are required to obtain pristine and unadulterated interstitialwater samples, thereby offsetting the deleterious effects of drilling mud, exposure to different temperature and pressure during core retrieval, and (in part ) exposure to air. While such a novel approach in the form of an in-situ waterfiltration probe that will sample water ahead of the drill bit in the borehole is in the testing phase, the time-proven squeezing technique is still the standard for obtaining interstitial waters for analyses and curation. During this process, whole-round samples, 5-10 cm long, are .exposed to pressures of up to 25 tons in stainless steel piston squeezers. The expelled water (from a few tens to less than 1 ml per 300 cm 3 sediment) is captured, filtered, and stored or analyzed according to the methods and procedures detailed by Gieskes and Peretsman (1986). Routine analyses include measurement of pH with a combination electrode (Metrohm model 605 pH meter with B r i n k m a n n electrode) prior to titration of alkalinity. Alkalinity is titrated with a 0.1M HC1 solution from a Metrohm model 655 automatic burette, which is monitored and driven by an H P 86B microprocessor. A computer program uses the Gran function to calculate alkalinity. Standardization of pH measurements is accomplished with Tris and Bis buffers, while alkalinity is standardized with NaHCO3 solutions of various molarity ranges. All standards are prepared with ultrapure laboratory water (18 M~J/cm resistivity) which is provided by a Barnstead reverse-osmosis water-

purification system. Dissolved Ca 2+, Mg 2+ and C1- concentrations are titrated with automatic burettes (Metrohm Dosimat 655 ), and all analyses are standardized against IAPSO artificial seawater. Sulfate concentrations are determined with a Dionex Ion Chromatograph, which is linked to the LAS system for data retrieval, storage and reports. Colorimetric determinations of Si02, P043- and N H 4 are performed on a Bausch and Lomb model 1001 spectrophotometer, if sample size and workload permit. A recent addition to the chemistry laboratory ia a Varian model 10/20 atomic adsorbtion spectrophotometer with lamps for the elements Li, Na, Mg, K, Ca, Mn, Fe and Sr, which will be used to automate the chemical analysis of interstitial waters further. The interstitial water remaining after aliquots for on board analysis have been taken is sealed in plastic and glass ampoules, stored at 4°C, and curated in the ODP Gulf Coast Repository. Acidified interstitial-water samples from alkalinity determinations are also saved, with the amount of acid noted. Data collection on board JOIDES

Resolution The collection of geochemical data on board J O I D E S Resolution has undergone several changes over the 4½ years of its operation. Datacollection methods greatly affect the quality of the data. To ensure data of the highest quality, ODP is in the process of computerizing shipboard data collection. Originally, chemical analyses were recorded by hand on triplicate paper forms, which were returned to the ODP Data Base Group after the leg and entered into the data file onshore. This method of data collection resulted in some errors being introduced into the data file. Typical problems were wrong sample identifiers, negligent processing of forms, incomplete records, and lack of standardization for hand calculations that produced inconsistent or incorrect results. Errors introduced by shore personnel during data entry,

335

such as mistyped numbers and incorrect spelling, were often due to an inability to read the handwriting on the forms. By providing computerized shipboard data collection, these errors can be caught immediately, while the scientist or technician is still holding the sample and observing the analyses. Data are computerized in the chemistry laboratory either by the use of computerized dataentry screens for the entry of data directly into the appropriate data file or by automatic data transmission from the measuring instrument. The first method, using a screen form, performs routine editing checks on the data before adding the records to the data file. The editing checks include scanning the sample identifier to make sure it is from a valid core and section. All data required by the data file must be entered before the record is accepted into the data file; data that are outside a predefined range and field for a particular data parameter are not accepted by the form. Finally, calculations are performed by the computer, thus keeping t h e m standardized. Computerizing the data immediately on the ship eliminates all sources of error from shore personnel. Currently, this method

is used for the carbon-carbonate and interstitial-water data collection and will be implemented for gas-chromatography data collection in the near future. The second method captures data directly by the computer from a machine conducting an analysis using a screen form to enter the sample identifier, while all the editing checks listed previously are performed. This method is used for the collection of pyrolysis data. D a t a base and data requests

Sediment-chemical-analyses data are stored, along with all data archived by ODP, in a relational, general-purpose data base management system called S1032 (a product of CompuServe) that operates on the VAX computer. The data are organized into data files that reflect the type of analyses performed on the samples. For example, all data generated by the pyrolysis instrument are stored together in one file, while all carbon analyses are stored in another. The data files containing the chemical data are briefly described in Table 1 and include total carbon, organic carbon, carbonate, hydro-

TABLE 1 Overview of the chemistry data base at the ODP, with brief descriptions of the data type Data file

Data source

Description

Legs available

Total carbon/ carbonate

Shipboard and shore-based data

Legs l topresent (except Legs 46,83,88,91,92,102,106,109 and 118)

Total hydrogen/ total nitrogen

Shipboard data

Weight percentages of total carbon, organic carbon, and carbonate-carbon of samples by acid digestion and combustion Elemental weight percentages by combustion

Interstitial water chemistry

Shipboard and shore-based data

Legs 1 to present (except 46, 66, 83,88,90,94,102,106,109 and 118)

Gas chromatography

Shipboard Data

Rock evaluation

Shipboard Data

Alkalinity, pH, salinity, major ions (calcium, magnesium, sulfate, ammonia, phosphate and silicate ) Hydrocarbon composition from gas chromatography of volatile hydrocarbons Pyrolytic yield of hydrocarbons and carbon dioxide, thermal maturity of organic matter

Legs 101,103, 104 and 106-108

Legs 101 and to present (except Legs102,106,107,109, 111 and 118) Legs 101 to present (except Legs 102,106,107,109,114 and 115)

336 TABLE 2

chemical analyses of sediments and interstitial waters are available at ODP. Table 2 shows the number of samples by type of analyses and by ocean. Figure 4 shows the increase in carbonate and organic-carbon analyses since the beginning of scientific ocean drilling in 1968. Each record in the data file represents a sample and includes a standardized sample identifier, along with the analytical results. The sample identifier consists of leg, site, hole, core, section, and interval which can be correlated to sub-bottom depth. This standardized identifier and the use of S1032 make it possible to cross reference chemical data to any other data items archived at ODP. For example, a data search could be performed to find all records with CaC03 greater than 50% located in the North Atlantic Ocean. Documentation is available for every data file. Each document describes the structure of the data file and gives an explanation of the data items and general information about the methods used. ODP Technical Note 9, Deep Sea Drilling Project Data File Documents (ODP, 1988), contains information on the chemical data collected by DSDP. Individ-

Number of carbonate and organic-carbon analyses in the ODP data base, grouped by ocean basins (status August, 1988)

CaCO~ TOC IW RE

Pacific

Atlantic

Southern

Indian

Total

15,596 9506 6782 343

26,062 12,522 7046 952

1562 919 556 128

8023 3654 2075 621

51,243 26,601 16,459 2044

TOC - - total organic carbon; IW - - interstitial water; RE - Rock-Eval pyrolysis

gen, and nitrogen weight percentages, interstitial-water chemistry, borehole water chemistry, gas chromatography, and pyrolysis results. These data were generated from cores collected on DSDP Legs 1-96 and ODP Legs 101 to the present. Data from Legs 1-96 include shipboard measurements from the chemistry lab of Glomar Challenger and measurements made at onshore laboratories. Data from Legs 101-121 consist only of shipboard measurements although participants are required to provide measurements made in onshore laboratories in 'appropriate formats. Currently, over 95,000 50000 -- 0 •

/

TOG Carbonate

/

40000

= ~,, 3 0 0 0 0

E Z

sOD.. - - 0 -

20000

--0-

.0-

-4"

.-4D"

10000

I

I

I

i

L

I

I

i

I

I

I

J

I

I

I

I

I

I'

I

Year

Fig. 4. Diagram of cumulative data on carbonate and total organic carbon content entered into the D S D P and ODP data bases since the beginning of the D S D P in 1968.

337

ual data file documents are available for the data collected by ODP. Upon request, data can be provided as hardcopy printout, on tape in ASCII format, or sent through the B I T N E T network. All data, datafile documents, and information on the data can be obtained from: Data Librarian, Data Base Group, Ocean Drilling Program, 1000 Discovery Drive, College Station, T X 77840 U.S.A. Telephone number: (409) 845-8495, or (409) 845-2673 Telex number: 62760290 Easylink number: 62760290 Bitnet address: %DATABASE @ TAMODP. Following each leg, data concerning results of the leg are restricted in distribution to the members of the particular scientific party for a period of 12 months after completion of the

cruise. Thereafter, all data are available to the public.

References Emeis, K.-C. and Kvenvolden, K.A., 1986. Shipboard organic geochemistry on J O I D E S R e s o l u t i o n . Ocean Drill. Program Tech. Note, 7:1-123. Espitalid, J., Deroo, G. and Marquis, F., 1985. La pyrolyse Rock-Eval et ses applications, Part I. Rev. Inst. Fr. Pet., 40 (5) :563-579. Gieskes, J. and Peretsman, G., 1986. Water chemistry procedures aboard J O I D E S R e s o l u t i o n - some comments. Ocean Drill. Program Tech. Note, 5:1-46. Kvenvolden, K.A. and McDonald, T.J., 1986. Organic geochemistry aboard J O I D E S R e s o l u t i o n - a n assay. Ocean Drill. Program Tech. Note, 6:1-147. O.D.P. (Ocean Drilling Program), 1988. Deep Sea Drilling Project data file documents. Ocean Drill. Program Tech. Note, 9:1-185. Tissot, B. and Welte, D.H., 1984. Petroleum Formation and Occurrence. Springer, Berlin, 2nd ed., 699 pp. Van Krevelen, D.W., 1961. Coal. Elsevier, Amsterdam, 352 pp.