Answers to Problems Chapter 1 lowest values are reached in the oceanic basins far offshore where red clay accumulates extremely slowly. Sedimentation rate for biogenic sediments Answer 1 – calcareous as well siliceous – depends on high biogenic production, on carbonate compensation Deep-sea or red clay covers the deep ocean depth CCD) and dilution by terrigenous sediments basins below CCD. Calcareous sediments cover is low. topographic highs like ocean ridges above CCD. Siliceous sediments occur in the Southern Ocean Answer 5 around Antarctica, along the equator in the Indian and Pacific oceans. Terrigenous sediments Deep sea sediments are generally best described drape the continental margins. by composition according to particle origin, e.g. non-biogenic (terrigenic, volcanic) versus bioge- Answer 2 nic and can further be differentiated according to mineralogy (carbonate or opal) and/or texture Because of chemical tropical weathering, Kaolinite (mud, ooze, clay). is considered the “clay mineral of low latitudes”. With respect to relative distance from shore or As a product of continental weathering Illite continents sediments are called “pelagic sedi- shows high concentration at mid-latitudes of the ments” consisting of biogenic oozes (carbonate northern oceans surrounded by great land mas- and/or siliceous) and only very little admixtures of ses. Chlorite as a product of physical weathering extremely fine-grained land derived material. They is essentially inversely related to kaolinite and are distinguished from “hemipelagic sediments” referred to as the “high latitude mineral”. Smectite typically deposited along continental margins and showing a very variable distribution in the oceans containing a substantial portion of land or shallow is generally considered as an indicator of a “vol- water derived components. canic regime”. Answer 3 Chapter 2 Large quantities of sediment are provided by rivers and directly from land and deposited on the Answer 1 shelf and/or directly beyond the shelf edge on the continental slope. The youngest crust occurs Bulk parameters are based on a volume-oriented along the mid-Atlantic ridge and increases with model which only depends on the total amount of distance from the ridge to the margin where more pore fluid and sediment grains. Acoustic/elastic time is available to accumulate greater sediment parameters like P- and S-wave velocity and atte- thicknesses. nuation are based on a micro-structure oriented model which considers both the amount and Answer 4 distribution of pore fluid and sediment grains. Basically, sedimentation rate decreases with Answer 2 increasing distance from the sediment source. Since for terrigenous sediments fluvial input is the A direct method is the analysis by weight and major source sedimentation rate decreases with volume, indirect methods are gamma ray atte- distance from river mouth and/or coast. The nuation and electrical resistivity measurements. 549 Answers to Problems 2- Analysis by weight and volume primarily deter- coefficient for SO4 in pore water under these 2 -1 mines the wet bulk density, gamma ray attenuation conditions is Dsed = 3.3E-10 m s . The gradient in the wet bulk density (by assumption of a proces- the depth interval between 0 and 6 m is 28 mol m-3 sing porosity), and electrical resitivity the porosity. per 6 m = 4.7 mol m-3 m-1. The downward flux of 2- -2 -1 Porosity values can be converted to density values SO4 is Jsed = 0.7 · 3.3E-10 · 4.7 mol m s = 1.1E-9 (and vice versa) by using equation 2.3. mol m-2 s-1 or 34 mmol m-2 a-1. Answer 3 Answer 3 SW Calcareous and siliceous sediment differ Diffusion coefficient in seawater D for O2 at 5°C significantly by their sediment grain density. It is 1.23E-9 m2 s-1. Tortuosity for a sediment with a amounts to about 2.7 g cm-3 for calcareous ooze porosity of φ = 0.7 is θ2 = 1.71. Diffusion coefficient -3 and to about 2.1 g cm for siliceous ooze, so that a for O2 in pore water under these conditions is Dsed = downcore grain density model has to be developed 7.2E-10 m2 s-1. The steepest gradient close to the from the carbonate (and opal) content, in order to sediment surface (depth interval between 0 and ca.1 -3 -1 calculate wet bulk densities from porosities. mm) is 28 mol m m . The downward flux of O2 is Jsed = 0.7 · 7.2E-10 · 28 mol m-2 s-1 = 1.4E-8 mol m-2 s-1 or -2 -1 Answer 4 0.45 mol m a . With an O2/DIC-ratio of 138/106 (cf. Eq. 3.10 and Fig. 3.11) this rate is equivalent to The (mean) grain size mainly influences the 0.34 mol DIC m-2 a-1 or 4.1 g C m-2 a-1. ultrasonic wave propagation. P-wave velocity and attenuation increases with increasing (mean) grain Answer 4 sizes. A glove box with an inert gas atmosphere is Answer 5 necessary for all steps from sampling to analyzing anoxic pore water and/or sediment for consti- The strength of a reflection horizon is determined tuents which would be oxidized in contact with by the reflection coefficient R = (I2 - I1 ) / (I2 + I1 ), the normal atmosphere. Such constituents are e.g. 2+ 2+ + 2- which depends on the acoustic impedance Fe , Mn , NH4 , S . Only especially pure and contrast of the two adjacent layers. The acoustic expensive nitrogen does not contain interfering impedance (I) depends on the P-wave velocity (vP) oxygen concentration. Normal argon usually and wet bulk density (ρ) and is defined as the contains sufficiently low oxygen concentration ρ product of both parameters, I = vP . and is much cheaper. Answer 5 Chapter 3 Elements of mainly terrestrial origin are: Ti, Al, Fe, K, Rb, Mg. A mainly marine input is characteristic Answer 1 for Ca, Sr, (Ba). The elements Mn, S, (Fe) reach the sediment solid phase mainly by diagenetic Measurement in fresh sediment: oxygen, pH-value, processes. sulfide. As soon as possible in squeezed or centrifuged pore water: alkalinity, ammonia, total iron. After preservation within some weeks: Chapter 4 manganese, nitrate, potassium. Without preser- vation even after long time: chloride, sodium, sulfate. Answer 1 Answer 2 Enrichment of organic matter in marine sediments is mainly favored by the combined effects of low SW 2- Diffusion coefficient in seawater D for SO4 at oxygen concentrations, either already in the water 5°C is 5.72E-10 m2 s-1. Tortuosity for a sediment column or at shallow depth in the pore water with a porosity of φ = 0.7 is θ2 = 1.71. Diffusion system of the sediments, and high sedimentation 550 Answers to Problems rates, particularly in areas of high primary biopro- cyclic triterpenoids have proven particularly ductivity. The stagnant basin and the productivity useful as biological markers or molecular fossils. model are used to illustrate favorable conditions for organic matter preservation. In addition, high Answer 5 sinking velocities, adsorption or organic matter to mineral matter (clay) and small grain sizes of the A key question to be answered by organic geo- deposits, restricting exchange with the oxygen- chemists is that of the marine or terrigenous origin containing ocean water after sedimentation, of organic matter in sediments and the extent of contribute to organic matter preservation. mixing of the two components, respectively. A number of bulk and molecular organic geochemical Answer 2 parameters are available to address this question, including elemental analysis, carbon stable iso- Molecular oxygen and seawater sulfate are the main tope analysis, organic petrography and specific electron acceptors which mediate organic matter biological markers for marine and terrestrial metabolization during early diagenesis by aerobic organic matter. Sea surface temperatures can be and anaerobic bacteria, respectively. Nitrate, reconstructed by the analysis of the degree of iron(III), and manganese(IV), often in that order of unsaturation of long-chain alkenones from hapto- K' significance, are additional electron acceptors in phytes preserved in sediments (U 37 index) or by organic matter respiration. Ultimately, methano- the determination of the number of cyclo-pentane genesis uses carbon as electron acceptor at greater rings in fossilized Crenarchaeotal membrane lipids sediment depth, when sulfate is depleted. (TEX86 index). Information on the sedimentary methane cycle can be obtained by the combined Answer 3 analysis of specific membrane lipids of the orga- nisms involved in this process and by the deter- Not all parts of the biomass of decayed organisms mination of the carbon stable isotope signal of have the same chance of being preserved in the lipids from methanotrophic microorganisms. fossil record. Water-soluble organic compounds Subtle changes in molecular structure and their or organic biopolymers easily hydrolyzed into sterical orientation reveals information of the small water-soluble monomers are rapidly recycled progress of diagenesis and catagenesis. already in the water column or early during diagenesis. Examples are proteins and carbohy- drates and their monomeric forms, sugars and Chapter 5 amino acids, respectively. Hydrophobic lipids have a significantly higher preservation potential, which increases with increasing molecular weight. Answer 1 Reaction of organic matter with reduced sulfur inorganic sulfur species (e.g. hydrogen sulfide) A simplified calculation of diffusion distance, L = formed during bacterial sulfate reduction, further (2Dt)0.5 (Eq. 5.7), is made here for chloride: The enhances the preservation potential by the diffusion coefficient for Cl- at deep-sea tempe- formation of high-molecular-weight organic mate- rature (4ºC) is D = 11 · 10-10 m2 s-1 (see Chapter 3, rial. Table 3.1); the time is 10,000 years = 3.2 · 1011 s; thus, L = (2 · 11 · 10-10 · 3.2 · 1011)0.5 = 26 m.