10. CARBON-CARBONATE CONTENT OF SEDIMENTS FROM THE WESTERN EQUATORIAL PACIFIC: LEG 7, GLOMAR CHALLENGER

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1 0. CARBON-CARBONATE CONTENT OF SEDIMENTS FROM THE WESTERN EQUATORIAL PACIFIC: LEG, GLOMAR CHALLENGER E. L. Geary, Scripps Institution of Oceanography, University of California, La Jolla, California A to cubic centimeter sample of sediment was taken aboard ship from each section recovered on Leg for determination of carbon and carbonate content, and analyses were made on shore. This report reviews the techniques and presents the results of those analyses. All of the analyses were made on a LECO 0 Second Analyzer, and details of the procedures used are set forth in Appendix III of Volume IV of the Initial Reports of the Deep Sea Drilling Project (0). In general, each sample is pulverized, dried, split and weighed. One part (about 0. gram) of the sample is processed, untreated, in the LECO 0 Analyzer, and the percentage of total carbon is obtained by dividing a calibrated digital readout by the sample weight. The second part (about 0. gram) of the sample is treated with hydrochloric acid to remove the carbonate, washed, dried and processed in the LECO 0 Analyzer. The percentage of organic carbon is calculated by dividing the calibrated digital readout by the sample weight. ate percentage is determined, assuming that all carbonate is calcium carbonate: Per cent carbonate = (% total carbon ~% organic carbon). Where the sample is known to contain dolomite, the carbonate percentage must be adjusted: organic carbon are impossible, and were handled as follows: All values < -0. per cent were considered to be erroneous and were omitted. Values -0. to per cent were called. Values > 0 per cent were considered to be erroneous and were omitted. Values 00 to 0 per cent were called 00 per cent. After samples taken on Leg were analyzed for carbon-carbonate, selected duplicate samples from Leg and other legs were analyzed by R. E. Boyce of the Deep Sea Drilling Project, using the LECO 0 acid-base method under carefully controlled conditions. The acid-base method will be presented in detail, together with comparison of results by the LECO 0 and acid-base techniques for Leg and earlier legs, probably in Volume IX of the Initial Reports of the Deep Sea Drilling Project. Mr. Boyce states that analyses by the acid-base method yield data with the following precision: carbon (. to.0 per cent by weight) = ± 0.% absolute (0 to. per cent by weight) = ± % absolute carbon carbonate (0 to 00 per cent by weight) (0 to 0 per cent by weight) = ±% absolute = ±.% absolute = ± 0.% absolute Per cent CaMg (CO.) = [% Ca(COo)]. For rhodochrosite, the percentage of carbonate must be adjusted: Per cent MnCO^ = [% CA(COo)] H T o. The carbonate percentage is shown as a function of depth on the core description charts and Site Summaries in Chapters through ; total carbon, percentage of organic carbon and of carbonate are listed in Table of this chapter, and selected values are listed in the tables of physical and chemical properties in Chapters through. Because of errors inherent in the analytical process, a few of the values derived for both carbonate and In the acid-base technique, each sample is pulverized, dried, split and weighed, as in the LECO 0 technique. One-half is analyzed intact; one-half is acidified to remove the carbonate. Samples are burned at 00 C in a LECO carbon furnace. The volume of the liberated gas (commonly carbon dioxide and oxygen) is measured in a solution of dilute sulfuric acid and methyl orange. The gas is passed through a potassiumhydroxide solution which preferentially absorbs carbon dioxide, and the volume of the effluent gas is measured. The difference between the two gas volumes is the volume of carbon dioxide. Comparison of measurements by the two methods indicates that the LECO 0 second technique renders values of carbon contents that are too low (Table, Figure ), and the percentage error appears to increase with increased carbon content.

2 TABLE Comparison of Values of, and ate Obtained by LECO 0 and Acid Base Methods; Samples from Leg. from <Y (LECO 0) C T (Acid Base) LECO 0 0 Acid Base 0. Δ T = <r <y 0. c o' (LECO 0) c 0 Base) o = c o - c o' CaCO Per Cent wt. (CO (CO,)' )' (LECO0) Δ=(CO ) - (CO ) (Sample #).0 (Sample #)

3 TABLE Estimated Correction Factors, Measurements of and ate by LECO 0 Method, Leg 0 C T< = TOTAL CARBON, PER CENT WEIGHT: (LECO 0 METHOD) Figure. Comparison:, LECO 0 and Acid-Base Methods. The scatter in the data is wide and no absolute correction factor can be applied. However, the values of total carbon and carbonate reported for this leg are probably low by amounts listed in Table. CARBONATE RESULTS Values by LECO 0 (This Volume) % 0% % % % % 0% 00% 0% 0% 0% 0% 0% 0% 0% 0% 0% Estimated Correction Factor +0 to.% +0to.% +0to.% +0 to.% +0 to 0.% +0 to 0.% +0 to 0.% +0 to.0% +0to.0% +0to.0% +0 to.0% +0 to.0% +0 to.0% +0 to.0% +0 to.0% +0 to.0% +0to.0% Site Analyses of two samples from Site (.-- and.--) showed no measurable carbon content. Site The nannofossil ooze-chalk-limestone sequence penetrated at Site is carbonate-rich. Few samples contain less than 0 per cent calcium carbonate; most contain more than 0 per cent calcium carbonate. Near surface samples are most poor in carbonate. The Quaternary changes from a nannofossil marl ( to per cent carbonate) near the surface to a nannofossil ooze ( to 0 per cent carbonate) at 0 meters. There is a steady increase in carbonate content with depth throughout the Pliocene and Late Miocene materials to a depth of 0 meters, where the carbonate content exceeds 0 per cent in most samples. This zone of maximum carbonate coincides with the zone rich in foraminifera. From 0 per cent at 0 meters, the carbonate content decreases steadily to about 0 per cent at 0 meters (Middle-Late Miocene), then increases to 0 per cent at 00 meters, and decreases again to about 0 per cent at 00 meters (Early and Middle Miocene). The carbon content of the dolomite recovered from.0- was not determined. Most of the section penetrated is devoid of organic carbon in amounts detectable by techniques used. However, at the surface and at several intervals in the hole, organic carbon was detected in amounts ranging up to. per cent (Table ). The deepest sample in which organic carbon was detected was from s.0-, and, in an Early Miocene nannofossil chalk. The presence of pyrite throughout the ooze-chalk sequence at this site infers a reducing condition which would permit the preservation of organic debris. Site The upper to 0 meters of the section penetrated at Site is a Pliocene sequence of alternating clays, marls and calcareous oozes. The carbonate content increases irregularly from only per cent at the surface to about 0 per cent in the Late Miocene ooze at 0 meters. The carbonate content is lower in the Middle Miocene at 00 to 0 meters (about 0 per cent), below which it appears to increase steadily with depth

4 TABLE -ate Results: Leg, Glomar Challenger ate. Porcelanite, mudstone, shale and siltstone..0 Porcelanite, mudstone, shale and siltstone & chalk & chalk & chalk & chalk & chalk..0 & chalk...0 & chalk & chalk & chalk.. Foraminiferal nannofossil. 0. Foraminiferal nannofossil

5 TABLE - Continued ate

6 TABLE - Continued ate & chalk & chalk & chalk

7 TABLE - Continued ate & chalk & chalk & chalk & chalk & chalk & chalk & chalk & chalk & chalk & chalk & chalk & chalk & chalk & chalk & chalk & & & & & & & & & & & & & & & & & & & & & & & & A

8 TABLE - Continued ate & & & & & & & & & & & & & & Nannofossil marl & marl ooze. 0. & 0.. & 0.. & 0.. & 0..0 & 0.. &

9 TABLE - Continued ate ,0...0,

10 TABLE - Continued ate Nannofossil-foraminiferal marl ooze Chalk ooze..0. Marl ooze... Marl ooze Nannofossil marl

11 TABLE - Continued ate Nannofossil marl Nannofossil marl ^ CO ' oo

12 TABLE - Continued ate.0..' ' oo' XI * r oo os. J.0.0.0

13 TABLE - Continued ate and limestone and limestone and and and and 0... and 0... and.0.. and 0..

14 TABLE - Continued ate..0 and 0... and and and... and and 0... and and 0... and and and... and

15 TABLE - Continued ate Calcareous radiolarian ooze Calcareous radiolarian ooze Calcareous radiolarian ooze..

16 TABLE - Continued ate Nannofossil radiolarian ooze Nannofossil radiolarian ooze Nannofossil radiolarian ooze Nannofossil radiolarian ooze Nannofossil radiolarian ooze Nannofossil radiolarian ooze Nannofossil radiolarian ooze Radiolarian marl ooze with chert with chert with chert with chert with chert ]fn.}^' p

17 TABLE - Continued ate Volcanic mud Volcanic mud

18 TABLE - Continued ate to a maximum of over 0 per cent at 0 meters (Early Oligocene). carbon was detected in about half of the samples processed in amounts up to 0. per cent. A sample of Early Oligocene marl at meters contained 0. per cent. Site The nannofossil ooze-chalk-limestone sequence penetrated at Site contains more carbonate in the upper part than does either Site or Site. However, as at the other two sites, carbonate content is lowest in near surface Quaternary materials (0 per cent). ate content increases to 0 per cent in.0- and remains reasonably constant through the Middle Eocene chalk at the bottom of the hole (0 meters). Detectable organic carbon is more sparse at Site than at Sites and. Amounts are small (< 0.) and confined largely to depths greater than 0 meters (Early Miocene or older). Site The Late Eocene-Early Oligocene nannofossil radiolarian ooze and silicified limestone at 0 to 0 meters in Site is relatively rich in carbonate, containing as much as. per cent. However, the radiolarian ooze section, both that above and below this sequence, contains negligible carbonate throughout (<.0 per cent). Small amounts (< 0. per cent) of detectable organic carbon are present throuthout the section penetrated. Site Except for a layer in.0-- where the carbonate content is. per cent, the carbonate content of both the radiolarian ooze and the pelagic clay penetrated at Site is nil. Small amounts of organic carbon (< 0. per cent) are present throughout the section. Site One sample from.0-- was analyzed. It contained no carbonate and 0. per cent organic carbon.

17. CARBONATE SEDIMENTARY ROCKS FROM THE WESTERN PACIFIC: LEG 7, DEEP SEA DRILLING PROJECT

17. CARBONATE SEDIMENTARY ROCKS FROM THE WESTERN PACIFIC: LEG 7, DEEP SEA DRILLING PROJECT Ralph Moberly, Jr., Hawaii Institute of Geophysics, University of Hawaii, Honolulu, Hawaii and G. Ross Heath,