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1 Pleistocene-Holocene Fluxes Are Not the Earth's Norm WILLIAM W. HAY University of Colorado ABSTRACT It has long been recognized that global Pleistocene-Holocene material fluxes are qualitatively distinct from those of the earlier Cenozoic and Mesozoic, but the full extent of the differences has only recently begun to emerge. Quantitative estimates of the masses of material eroded, transported, and deposited during the Pleistocene-Holocene have been difficult to obtain because of the lack of consistent information on the thicknesses and areal extent of the deposits on land and in shallow seas. Geologic maps commonly show extensive areas of Quaternary cover on older sediments, but information on the thickness of the tills, alluvium, and colluvium that make up these deposits is scattered throughout the literature and is often incomplete. Several major changes in the erosion-sedimentation regime have affected material fluxes. These have occurred in response to alternations in the climatic regime, to related changes in the sediment transport agents, to increasing amplitude of sea-level fluctuations, and to extensive regional tectonic uplift. The Pleistocene climatic regime results in alternations of glacial and temperate conditions at mid- and high latitudes, and arid and humid conditions at lower latitudes. Both types of change affect the rates of chemical weathering. At mid- and high latitudes the major transport agent alternates between glaciers and rivers. Glaciers are effective at removing, pulverizing, and transporting clastic sedimentary and low-grade metamorphic rocks, but less effective in attacking crystalline rocks. The glacial sediment is commonly transported uphill and deposited in such large quantities that it results in reorganization of the fluvial drainage systems. The Mississippi system of North America is an excellent example, the preglacial drainage having been truncated by two ice edge rivers, the Ohio and the Missouri. During times of deglaciation, supplies of fluvioglacial sediment often exceed the competence of the rivers, resulting in extensive alluviation. Both of these processes expose extensive areas of unweathered debris to soil-forming processes. At
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lower latitudes the alternation of arid and humid climates results in alternating cycles of alluviation and incision in river valleys as well as an alternation of soil-forming processes. The late Cenozoic-Pleistocene glaciations resulted in a series of sea-level falls of increasing amplitude. Erosion of exposed unconsolidated clastic shelf sediments and consequent isostatic compensation has resulted in large masses of sediment being off-loaded from the continental shelves onto deep-sea fans and abyssal plains by turbidity currents. Modern continental shelves with clastic sediments are adjusted to the Pleistocene low stands of sea level. The present widespread development of estuaries is a result of this condition. Interglacials are too short and the sediment supply is too small to allow shelves to build back to equilibrium grade with high sea-level stands. Although during the interglacials a few large rivers can build deltas to the shelf break and spill sediment into the deep sea, most estuaries do not fill with sediment before the next sea-level fall. In contrast, carbonate sediments become cemented by fresh water infiltration when sea level falls and, as a result, carbonate-dominated shelves and banks reflect equilibrium with high sea-level stands. Carbonate extraction from the ocean is at a maximum as shallow shelf seas flood during the late stages of deglaciation. The largest supplies of clastic sediment come from the largest regional uplifts, the Tibetan Plateau-Himalayas and western North America. Evidence suggests that both of these regions were uplifted in the late Pliocene and Pleistocene. Their uplift may be the ultimate cause of the onset of continental glaciation and the global climatic alternations that have characterized the Earth's recent past. Pleistocene-Holocene fluxes do not reflect the long-term state of the planet but are the result of a set of unusual conditions. It is, however, against this rapidly changing background that future global change will take place. RECOGNITION, DEFINITION, AND LENGTH OF THE QUATERNARY AND HOLOCENE Information on the distribution and thickness of Pleistocene and Holocene deposits is often highly inconsistent. Ordinarily, geologic maps do not show glacial deposits but do show other Quaternary sediments and volcanics, and often large areas are simply designated Quaternary alluvium. Maps of the thickness of glacial sediments have been published for a few regions, but for most areas there are not even cross sections from which thicknesses can be estimated. The areas shown as Quaternary on geologic maps, even excluding the areas covered by glacial drift, are much larger than the areas of older deposits. Gilluly (1969) reported the measured area of Quaternary sediment shown on the Geologic Map of North America (Geological Society of America, 1965) to be 2.185 x 106 km2 and the sum of older Cenozoic sediments to be 2.075 x 106 km2. He noted that the Geologic Map of South America (Geological Society of America, 1950) shows almost twice as large an area covered by Quaternary sediments, 4.276 x 106 km2, and only 2.889 x 106 km2 of Tertiary sediment. The base of the Quaternary is taken to be the base of the Pleistocene, originally defined by Lyell (1839) as sediments characterized by fossil content containing more than 70 percent living species of mollusc. The Pleistocene later became associated with Northern Hemisphere glaciation, but because it was recognized that the beginnings of glaciation were only vaguely known, the base of the Pleistocene came to be defined by the first significant cooling of the Mediterranean, marked by the Calabrian Stage in Italy. Dispute over indications of the first cooling of the Mediterranean has led to disagreement over the criteria used to define the base of the Pleistocene in the boundary stratotype region in southern Italy. There are also difficulties in extending correlation of the base of the Pleistocene to other parts of the world. Even more serious discrepancies in the use of the term Quaternary come from those who would consider the base of the Pleistocene to be marked by the climatic change to glacial conditions in the Northern Hemisphere even though this is now thought to be between 3 and 4 million years ago (Ma). Hays and Berggren (1971), Jenkins et al. (1985), and Berggren et al. (1985) have presented useful reviews of the problems associated with the Pliocene-Pleistocene boundary. Many of the estimates of Pleistocene sediment masses involve calculation or extrapolation of accumulation rates, so that knowledge of its duration is critically important. The age of the base of the Pleistocene was thought for many years to be about 2 Ma; this was revised to 1.8 Ma by Hays and Berggren (1971), and has more recently determined to be 1.6 Ma (Haq et al., 1977). The boundary is currently thought to be just above the top of the Olduvai Normal Magnetic Polarity Event.
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The criteria used to define the base of the Quaternary and the age of the base of the Quaternary are almost never given on geologic maps or in their accompanying text. The base of the Holocene has been intended to mark the change from glacial to interglacial conditions, but this change is, of course, a more or less gradual transition. The age has usually been given as 11,000 to 10,000 yr before present (BP). Recently it has been proposed that the base of the Holocene be defined by a boundary stratotype in Sweden (Morner, 1976). The age of the base of the Holocene is now taken to be about 10,000 radiocarbon yr BP, at the end of the Younger Dryas (Harland et al., 1982). Holocene sediments are very incompletely recorded on land, generally being lumped into the general term Quaternary alluvium. The Holocene is in rare instances shown as a separate unit on specialized geological and environmental maps. MASSES OF QUATERNARY AND HOLOCENE SEDIMENT The masses of Quaternary material in the major depositional site categories are given in Table 1.1. The best data on Quaternary sediment masses are from the deep sea. This is in spite of the fact that the base of the Pleistocene usually lies below the depth of penetration of piston cores and is too shallow to be recovered completely intact and undisturbed even by the hydraulic piston corer developed in the later phase of the Deep Sea Drilling Project (DSDP) and used during the successor Ocean Drilling Program (ODP). The determinations of the base of the Pleistocene, usually based on the lowest occurrence of Globorotalia truncatulinoides or the highest occurrence of Discoaster brouweri, have resulted in a consistent determination of the thickness of strata that closely approximates the Quaternary as currently defined. The Gamma Ray Attenuation Porosity Evaluation (GRAPE) records permit a reasonable estimation of the porosity of Pleistocene sediments; hence the mass can be calculated with a high degree of certainty. The next best documentation of the existing sediment mass is from the areas with glacial sediment even though there are major inconsistencies in estimates of the areas covered by glaciers, the thicknesses of the glacial deposits, and the age of the older glacial deposits. The most incomplete data are for the distribution and thickness of nonglacial Quaternary deposits on the continental shelves and on land. The deposits on the shelves are often irregularly distributed and have highly variable thicknesses. I estimated the masses by making general estimates of global average thicknesses. Geologic maps of land areas often show large areas covered by Quaternary alluvium or colluvium, but the thicknesses of the deposits are almost never given. To estimate the masses of these nonglacial TABLE 1.1 Total Mass of Quaternary Sediment Sediment Type Mass (1021 g) Marine Ocean basins Carbonate 4.62 Noncarbonate 20.60 Total 25.22 Marginal seas Carbonate 0.51 Noncarbonate 3.96 Total 4.47 Continental Shelves Carbonate 0.44 Noncarbonate 0.15 Total 0.59 Total marine Carbonate 5.57 Noncarbonate 24.71 Total 30.28 Continental Glacial 0.94 Clastics 9.92 to 12.20 Other 0.43 Total 11.29 to 13.57 Total Quaternary sediment 41.57 to 43.85 nonmarine sediments I resorted to projection of older rates. The Holocene has been extensively sampled by gravity and piston cores in the deep sea, in shallow seas, and on the continental shelves. Holocene sediments in the sea are mostly water, and there is always a question of the completeness of the record recovered. Often the surficial sediment is blown away by the pressure wave in front of the falling coring device, and the very soft sediments are easily disturbed. Compilations of the distribution of consistently collected and analyzed Holocene sediments in many parts of the deep sea and in some marginal seas have been presented by Lisitzin (1972, 1974). However, the information on marine sediments is still far from complete. Much less information is available about Holocene deposits on land. There are relatively few places on land where the base of the Holocene (i.e., the 10,000-yr BP datum) has been determined. Hence there is no global estimate of the mass of Holocene sediment. PROCESS RATES The traditional measure of the sedimentation process is the sedimentation rate, defined as the thickness of sedi-
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ment representing a given geologic interval divided by the length of the interval, expressed as a length (thickness) per unit time. The most commonly used standard is centimeters per 1000 yr (cm/kyr), but meters per million years (m/m.y.) is also often used. Sedimentation rate does not take the porosity of the sediment into account, and for young sediments, which can be up to 70 percent or more water, it can be very deceptive. A more objective measure that can be used to compare compacted and uncompacted sediments is the accumulation rate, expressed in term of a mass per unit area per unit time (commonly g/cm2/kyr). Calculation of the accumulation rate requires that the sediment thickness be multiplied by the solidity of the sediment and by the grain density. The solidity of the sediment is one minus the porosity. The accumulation rate may be an accurate expression for the process of accumulation of modern sediments, but a problem arises in using the term in connection with older sediments. An ancient sediment accumulation rarely contains all the sediment that accumulated at a given site during the time represented by the sediment; some of the material that accumulated has been subsequently removed by erosion, dissolution, metamorphism, or subduction. The bulk of the sediment mass is simply eroded and redeposited, or recycled. Gregor (1970) suggested the term ''survival rate" for the measure of mass per unit area per unit time for an ancient deposit. The term survival rate is somewhat deceptive because it is not an expression of the rate of survival of the sediment, which would more properly be a measure of the amount of sediment remaining relative to the amount originally deposited divided by the time elapsed since deposition. Hay (1985) coined the term "apparent accumulation rate" as an alternative objective expression for the existing mass of sediment per unit area divided by the length of time it represents (= survival rate of Gregor, 1970). Rates calculated from present-day masses are always apparent accumulation rates, that is they recognize that part of the original mass of sediment deposited has been destroyed by erosion, dissolution, subduction, or metamorphism. The term accumulation rate is often interpreted as a direct reflection of a flux rate, for example, the rain rate of pelagic sediment. Interpretation of an ancient flux rate from an apparent accumulation rate is obviously troublesome, because correction for subsequent loss from erosion and other cause must be made. Analysis of the global mass/age distribution of Phanerozoic sediment indicates that it can be generally described by a decay curve of the form M1 = Aebt (1.1) where Mt is the mass in existence today representing sediment of age t, A is the zero-age intercept, b is the decay constant. If t is expressed in million years, then the decay constant for all Phanerozoic sediment is about -0.002. This means, for example, that only 82 percent of the sedimentary material that accumulated 100 m.y. ago is still in existence; the half-life of Phanerozoic sediment is about 350 m.y. The sediment flux at times in the past can be estimated by multiplying the zero-age intercept by the proportional difference between the observed mass of ancient sediment and the value of the decay curve for that time (Wold and Hay, 1988, 1990; Hay and Wold, 1990). Although conversion to flux rates requires caution, it is useful to express accumulation rates in terms of flux rates so that they can be compared with modern process rates. For the Quaternary, with a mean age of 0.8 Ma, the long-term (Phanerozoic) decay constant indicates that the amount of sediment remaining should be about 99.8 percent of the amount deposited, so no correction for long-term sediment cycling is made in the figures given below. It is likely that there is more rapid recycling on a shorter time scale that may be reflected in estimates of flux rates. Hence, in the discussion below, I distinguish three kinds of flux rates: (1) instantaneous flux rates, (2) short-term flux rates, and (3) long-term flux rates. In geology, instantaneous flux rates are measured over geologically insignificant lengths of time. Short-term flux rates are a measure over a geologically longer but internally homogeneous period of time, such as a 1000-yr episode during the deglaciation. Long-term flux rates are integrated fluxes over a longer, inhomogeneous period of geologic time, such as the Holocene, the Wisconsinan, or the Pleistocene. LONG- AND SHORT-TERM APPARENT ACCUMULATION RATES OF QUATERNARY AND HOLOCENE SEDIMENT Most of the information on apparent accumulation rates is from the marine realm, and most of it is for long-term rates. In a few places estimates of local short-term rates, such as those during deglaciation and during parts of the Holocene have become available. Deep-Sea Sediments The deep sea contains more than half of the total Quaternary sediment mass. The flux rates of sediment to the deep sea, based largely on the study of DSDP cores by Sloan (1985), are summarized in Table 1.2; the apparent accumulation rate in the ocean averages about 5 g/cm2/kyr. The area of continental rise deposits is that given by Sloan (1985) and includes the major deep sea fans. The area of high productivity is after Berner (1982) and includes 23.5 ∞ 106 km2 of the Pacific, 19 ∞ 106 km2 of the Southern Ocean, and 1.5 ∞ 106 km2 of margin high productivity
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TABLE 1.2 Quaternary Apparent Accumulation Rates and Sediment Masses in the Ocean Continental Rises High Productivity Ocean Basins Total Area (106 km2) 19 44 260 323 Approximate accumulation rate (g/cm2/kyr) 5.85 9.45 4.05 4.88 Total mass (1021) 1.78 6.65 16.79 25.22 TABLE 1.3 Cenozoic Deep-Sea Apparent Accumulation Rates and Carbonate/Noncarbonate Proportions (in part modified after Sloan, 1985) Apparent Accumulation Rates (g/cm2/yr) Age Unit Total Noncarbonate Carbonate Percentage Carbonate Quaternary 4.89 3.99 0.90 18.4 Pliocene 3.03 2.19 0.88 28.6 Late Miocene 1.73 0.99 0.73 42.2 Mid Miocene 1.71 1.01 0.70 40.9 Early Miocene 1.56 0.88 0.67 42.9 Late Oligocene 1.38 0.56 0.82 59.4 Early Oligocene 1.03 0.51 0.52 50.5 Late Eocene 1.50 1.07 0.43 28.7 Middle Eocene 1.73 1.08 0.65 37.6 Early Eocene 1.49 0.98 0.51 34.2 Late Paleocene 1.38 0.58 0.66 47.8 Early Paleocene 0.64 0.32 0.32 50.0 areas in the Atlantic and Indian oceans. The total of 323 x 106 km 2 includes the Pacific, Atlantic (and Caribbean), Indian, and Arctic Ocean basins. It does not include areas less than 200 m deep (mostly shelves) or the marginal seas discussed below. Table 1.3 shows apparent accumulation rates and the proportions of carbonate for sediments in the ocean basins through the Cenozoic, taken from Sloan (1985). The apparent accumulation rate of Quaternary sediments is 54 percent higher than the rate for the Pliocene, and almost three times Miocene rates. Further, carbonate is only 18.4 percent of the total Quaternary in the ocean basins, whereas it is typically 40 to 50 percent of the Miocene and earlier sediments. There has been no compilation of Holocene apparent accumulation rates for sediments in the ocean as a whole, but Lisitzin (1972, 1974) has presented maps that allow rates for large areas of the major ocean basins to be estimated, and a global deep sea average to be calculated, as shown in Table 1.4. Holocene sediment accumulation rates in the Atlantic Ocean are about three times the rate in the Pacific and Indian oceans. The global Holocene accumulation rate in the ocean is about one-fifth the Quaternary average for the ocean. Sediment supply to the deep sea is clearly in response to the glacial-interglacial changes in sea level. During sea-level low stands, material is delivered directly to the deep sea, whereas during sea-level high stands it is retained on the continental shelves and the supply to the deep sea is much reduced. Damuth (1977) presented maps of sedimentation rates for Holocene and late Pleistocene sediments in the equatorial Atlantic. Average Holocene apparent accumulation rates for different regions can be calculated from the data presented on the maps, as shown in Table 1.5. The solidity of the Holocene sediment is assumed to be 30 percent. The accumulation rates calculated from Damuth's data show that the continental rises receive almost twice as much sediment as the deep seafloor above 5-km depth,
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TABLE 1.4 Holocene Sediment Apparent Accumulation Rates and Masses in the Oceans(after Lisitzin, 1972, 1974) Atlantic Pacific Indian Total Area (106 km2) 82.8 176.0 74.2 333.0 Approximate accumulation rate (g/cm2/kyr) 1.71 0.50 0.66 0.84 Total mass (1021 g) 0.0156 0.0089 0.0054 0.0098 TABLE 1.5 Holocene Apparent Accumulation Rates for Sediment in the Equatorial Atlantic Ocean (after Damuth, 1977) Continental Rises Basins <5 km Basins >5 km Average sedimentation rate (cm/kyr) 5.5 3.0 1.5 Approximate accumulation rate (g/cm2/kyr) 4.37 2.39 1.19 which in turn receives about twice as much sediment as the deep seafloor below 5 km. From the proportional areas of rise, basin <5 km and basin >5 km, the average Holocene accumulation rate in the equatorial Atlantic can be calculated to be 2.07 g/cm2/kyr, not very different from the average Holocene accumulation rate for the entire Atlantic determined from analysis of Lisitzin's (1972, 1974) maps. The higher value for the equatorial Atlantic is expected because this area receives sediment from the Amazon. Damuth also presented maps showing sedimentation rates during the last glacial (Wisconsinan) and the last interglacial (Sangamon) for the equatorial Atlantic. From these maps it can be estimated that during the glacial, average sediment accumulation rates were 2.75 times higher than the Holocene, and during the last interglacial the average rate was 0.77 that of the Holocene. On the Amazon Cone, Wisconsinan rates were 4.18 times the Holocene rate. Marginal Sea Sediments The shallow marginal seas occupying the sites of the Northern Hemisphere ice caps—the Baltic Sea, Barents Sea, and Hudson Bay—have almost no Pleistocene sediment but do contain a thin veneer of Holocene sediment. According to Dietrich and Koester (1974), Holocene sediments in the Baltic average about 0.22 m in thickness; if a solidity of 30 percent is assumed, this indicates an accumulation rate of only 1.75 g/cm2/kyr. Some other marginal seas outside the glaciated areas but with extensive areas shallower than 200 m, such as the Persian Gulf, were exposed to erosion during the Pleistocene sea-level low stands. During much of the Pleistocene they were sites of erosion rather than sedimentation, and they have negligible amounts of Quaternary sediment. Kassler (1973) reported that the major Pleistocene unit in the Persian Gulf region is a limestone (Kargh Limestone) with thicknesses varying from 5 to 30 m. If an average thickness of 15 m and a solidity of 50 percent are assumed, the Quaternary average apparent accumulation rate is only 1.24 g/cm2/kyr. The average of late Holocene sedimentation rates given by Melguen (1973) indicates an accumulation rate of 48.9 g/cm2/kyr; projected over 10,000 yr this would give an average Holocene thickness of 6.15 m. This is of the same order of magnitude as the Pleistocene sediment, which should represent a much longer time. Clearly, little of the sediment deposited in the Persian Gulf during sea-level high stands has survived the erosional forces operating during sea-level low stands. Although the Persian Gulf produces a large quantity of carbonate sediment, some of the Holocene accumulation within the Gulf is detritus from the small rivers entering the Gulf from Iran; the high late Holocene accumulation rate may reflect the high carbonate production plus an unusually large detrital input in response to increasing aridity of the region. In terms of the Mesozoic and Cenozoic, the Gulf of Mexico is the best known of the deeper marginal seas because of the detailed atlas prepared for the Ocean Margin Drilling Program (Buffler et al., 1984). The maps and drill hole data have been analyzed, and by estimating solidity from the compaction curve of Baldwin and Butler (1985), the mass of Quaternary sediment has been compiled by Shaw (1988, 1989). The total mass of "glacial age" (<3 Ma) sediment in the northern and western Gulf of Mexico is 2.07 x 1021 g, of which 1.87 x 1021 g is Quaternary. This accounts for about 80 percent of the total Quaternary sediment in the Gulf of Mexico so that the total Quaternary sediment mass of the entire Gulf of Mexico must be about 2.34 x 10 21 g or equal to 10 percent of all the Quaternary sediment in the ocean basins proper. The average accumulation rate for the Quaternary is 88.3 g/cm2/kyr, two orders of magnitude higher than oceanic rates. Although there is no figure for the mass of Holocene sediment in the Gulf of Mexico, participants in DSDP Leg 96 evaluated the difference between Holocene and glacial Pleistocene accumulation rates on the Mississippi Cone. There, glacial accumulation rates have been determined by Wetzel and Kohl (1986) to range from 842 to 1572 g/cm2/kyr (1000 to 2000 times oceanic rates), but
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Holocene rates are only 1.5 to 12.8 g/cm2/kyr. Very high sediment accumulation rates have also been cited by Perlmutter (1985) for an episode of rapid deglaciation just prior to the Holocene. He estimated that during a 3000-yr interval the suspended load of the Mississippi may have been an order of magnitude larger than it is today. If the Mississippi's load under natural conditions (Late Holocene, prior to arrival of European settlers) was 400 x 1014 g/yr (R.H. Meade, U.S. Geological Survey, personal communication), it alone would supply sediment at the rate of 26.0 g/cm2/kyr to the entire area of the Gulf of Mexico. The average thickness of Quaternary sediment in 28 DSDP and ODP holes drilled in the Mediterranean is 182 m (Cita et al., 1978; Kastens et al., 1987), and the estimated solidity is 52 percent; the long-term apparent accumulation rate is 15.67 g/cm2/kyr. Holocene rates are more difficult to estimate because the base of the Holocene is reported in a less consistent manner. Judging from the descriptions of cores with well-preserved stratigraphy discussed by Thunell et al. (1977), the average thickness of Holocene sediment in the basins is about 0.5 m; if a solidity of 30 percent is assumed, this implies an apparent accumulation rate of 3.98 g/cm2/kyr. In the Mediterranean, as in the major ocean basins, the Holocene accumulation rate is about one-quarter the Quaternary average. Investigations by the DSDP permit comparison of Pleistocene, glacial, Holocene, and late Holocene apparent accumulation rates in the Black Sea basin. The Quaternary has been penetrated at three sites (Hsü, 1978a,b; Ross, 1978; Stoffers et al., 1978). Two of the DSDP sites were at widely separated locations in the deep basin floor; they have thicknesses of 620 and 640 m, respectively. Although the exact ages of different layers are somewhat uncertain (Degens et al., 1978; Hsü, 1978a,b; Stoffers et al., 1978). Degens and Ross (1974) and Degens et al. (1978) have calculated detailed sedimentation rates at several intervals during the Quaternary based on the varved sediments. A summary of the Leg 42 and earlier results, recalculated as accumulation rates obtained by assuming 30 percent solidity for the Holocene and late Pleistocene sediments and a solidity of 50 percent for the Quaternary as a whole, is presented in Table 1.6. Again, as in the deep sea, Holocene rates are about one-fifth of the Quaternary average. Four DSDP sites in the Red Sea, one of which did not completely penetrate the Pleistocene, can be used to compute an average thickness of 112 m for the Quaternary (Stoffers and Ross, 1974) and an estimated solidity of 49 percent. The Holocene sediment averages about 1.81-m thickness, and should have a solidity of about 30 percent. In this case the long-term average accumulation rates for the Pleistocene and the Holocene are 9.09 g/cm2/kyr and 14.39 g/cm2/kyr, respectively. The Red Sea is one of the rare places where the Holocene accumulation rate is higher than the Quaternary average. The average thickness of Quaternary sediments in the Bering Sea is 207 m, the estimated solidity is 53 percent, and the average apparent accumulation rate is 18.17 g/cm2/kyr. Lisitzin (1972, 1974) presented maps of the Holocene accumulation rates in the Bering Sea. The average rate for the Holocene determined from measurement of his maps is 10.1 g/cm2/kyr, about half the Quaternary average. This may be the result of continuing supply from rivers that were unable to transport the loads during deglaciation. There are no data that would permit an estimate of the average thickness of Quaternary sediments in the Sea of Okhotsk, but Lisitzin has presented a map of the mean thickness of Holocene sediments. The average thickness of the Holocene sediments is 2.22 m; if a solidity of 30 percent is assumed, this implies an average accumulation rate of 17.66 g/cm 2/kyr, similar to the Quaternary rate for the Bering Sea. The data and estimates for marginal seas are summarized in Table 1.7. Clearly, the dominant control on sedimentation in marginal seas, as in the deep sea, is sea-level rise and fall. Typically this results in Holocene rates that are 20 to 25 percent the Quaternary average, but in marginal seas in the polar regions the difference is much less. The Red Sea apparently has received more sediment during the Holocene than the Quaternary average. During glacials, the lowered sea level exposes the shelves, and most sediments are delivered directly to the deep sea. During the high sea-level stands of the interglacials, most sediments are retained on the shelves and in shallow areas. However, each successive sea-level fall seems to have resulted in the sediments of the previous interglacial being eroded and deposited in the deep sea. TABLE 1.6 Sediment Accumulation Rates in the Black Sea Basin (after Degens and Ross, 1974; Degens et al., 1978). 0 to 1 kyr BP 1 to 5 kyr BP Holocene Deglaciation Quaternary Average sedimentation rate (cm/kyr) 30 10 12 1000 40 Approximate accumulation rate (g/cm2/kyr) 23.85 7.95 9.54 795 53
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TABLE 1.7 Quaternary and Holocene Sediment Fluxes in Marginal Seas Average Accumulation Rate (g/cm2/kyr) Marginal Sea Quaternary Holocene Gulf of Mexico 88.3 30 ? Mediterranean 15.67 3.98 North Sea 14.78 ? Red Sea 9.09 14.39 Black Sea 65.74 9.54 Bering Sea 18.17 10.10 Sea of Okhotsk ? 17.66 Continental Shelves The late Cenozoic-Pleistocene glaciations resulted in a series of sea-level falls with amplitudes up to 130 m or more. The unconsolidated clastic shelf sediments become exposed to erosion, and they are off-loaded from the continental shelves onto deep-sea fans and abyssal plains by turbidity currents, largely through submarine canyons. As the sediment load is removed, isostatic compensation raises the shelf and causes further erosion. Hay and Southam (1977) suggested that the shelf break of the present detrital sediment-dominated shelves represents a glacial equilibrium. At the low stands of sea level it would have been at a depth of about 50 m rather than 200 m. One can assume that before the Pleistocene sea-level fluctuations, the detrital sediment dominated shelves were at an average depth of 50 m. If a sea-level fall of 130 m and a sediment solidity of 65 percent are assumed, a wedge of sediment having a thickness of almost 600 m at the shelf break must be eroded to bring the position of the shelf break back to a depth of 50 m. Hay and Southam (1977) estimated that 5.10 x 1021 g of detrital sediment might have been off-loaded from the shelves into the deep sea by this process in response to the Pleistocene sea-level falls. The pattern of the falls would be important to the delivery of sediment to the deep sea. If one of the early falls was very large, most of the sediment transfer from shelf to deep sea would have taken place at that time. The data presently available do not permit the relative effect of the different sea-level falls to be assessed. Modern continental shelves with clastic sediments are adjusted to the Pleistocene low stands of sea level. The interglacials are too short and the sediment supply is too small to allow shelves to build back to equilibrium grade with high sea-level stands. The present widespread development of estuaries (drowned rivermouths) is a result of this condition. Although during the interglacials a few large rivers can build deltas to the shelf break and spill sediment into the deep sea, most estuaries do not fill with sediment before the next sea-level fall. In contrast to detrital sediment, carbonate sediments become cemented by fresh water infiltration when sea level falls; as a result, carbonate-dominated shelves and banks reflect equilibrium with high sea-level stands. During glacial low stands of sea level, carbonate removal from the ocean is carried out mostly by the carbonate-secreting plankton, chiefly planktonic foraminifers and coccolithophores. As sea level rises, reef growth and extraction by shallow water organisms return to play a major role. Carbonate extraction from the ocean is at a maximum as shallow shelf seas flood during the late stages of deglaciation. Milliman (1974) estimated the average Holocene sedimentation rate on carbonate-dominated shelves and banks to be 40 cm/kyr; this corresponds to an accumulation rate of 31.80 g/cm2/kyr. However, high rates of carbonate accumulation cannot be sustained unless sea level continues to rise. After sea level stabilizes a balance among carbonate production, sedimentation, and loss to the deep sea must be reached. Much of the aragonite secreted by algae and other organisms on carbonate banks today is exported to the surrounding deep-sea areas during storms. Hay and Southam (1977) suggested that the present carbonate flux onto shelves and banks is at least equal to the supply from rivers and might exceed the river supply by a factor of three. In the estimates presented in Table 1.8, I have assumed an average Holocene sedimentation rate of 100 cm/kyr for detrital sediment, a solidity of 33 percent, and a carbonate TABLE 1.8 Quaternary and Holocene Sediment Fluxes on Continental Shelves Accumulation Rates (g/cm2//kyr) Quaternary Holocene Area (106 km2) Total Carbonate Total Carbonate Detrial shelves 15.7 0.55 0.14 8.74 2.19 Carbonate shelves 10.3 4.53 4.08 31.80 28.62
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content of 25 percent. For carbonate shelves the sedimentation rate has been assumed to be 40 cm/kyr, the solidity 30 percent, and the carbonate content 90 percent. Glacial Sediments on Land To estimate the masses of glacial sediments on land (moraines, ground moraine, and associated glaciofluvial and glaciolacustrine deposits), I measured the areas of the peripheral parts of the glaciated regions, where the glacial sediments accumulated, shown on the Quaternary geologic maps of the continents in Gerasimov (1964). These areas were multiplied by the estimated average thickness of 20 m, an assumed solidity of 80 percent, and a solid grain density of 2.65 g/cm3. Because the same thickness and solidity were assumed everywhere, the Quaternary average apparent accumulation rate works out to be 2.65 g/cm2/kyr everywhere. Apportionment of the glacial sediment masses to the different glaciations is at best a guess, but probably about 80 percent of the deposits preserved today are referred to as the last glaciation although some of the material must be reworked from older glacial deposits. Assuming that 80 percent of the mass was deposited in 80,000 yr gives an accumulation rate for the last glacial of 33.92 g/cm2/kyr. Nonglacial Continental Sediments Nonglacial continental sediment is the least certain of all the sediment masses because geologic maps poorly represent the actual distribution of Quaternary sediments (Choubert and Faure-Muret, 1976). The extent to which Quaternary sediments are shown varies greatly from map to map. Although the largest volumes are likely to be in active orogenic areas, where large thicknesses of Quaternary sediments may accumulate in intermontane basins and in smaller structures, the largest areas of Quaternary sediments shown on the maps are in regions with flat-lying strata. Even where the extent of Quaternary deposits is accurately depicted on maps there is generally little information on the thickness of the deposits. This is especially true in Asia, Africa, Australia, and South America, where nonglacial Quaternary sediments are widespread. Because the data cannot be read directly from maps, I made two projections from Pliocene and Neogene data: first, it was assumed that the accumulation of nonglacial sediments on the continents is simply a continuation of Pliocene rates; second, it was assumed that on a global scale, all rates of sediment flux have increased in the Quaternary and that the fluxes of continental clastic sediment have increased proportionally to other flux increases. The second assumption appears to be plausible because Ronov et al. (1986) have noted that throughout the Phanerozoic an increase in one sediment reservoir almost always corresponds to increases in other sediment reservoirs. They referred to this phenomenon as a major law of sediment cycling. However, not all of the increases in Pleistocene flux rates are well known. The best known increase is the rate of accumulation of material in the deep sea. The data indicate that during the Pliocene and Pleistocene sediment accumulation in the ocean basins reflected a supply greater than that persisting through the earlier Cenozoic. According to Sloan (1985; see also Table 1.3), Quaternary apparent accumulation rates in the deep sea were 54 percent higher than they were in the Pliocene. However, Hay and Southam (1977) had noted that about 5.10 x 1021 g of the sediment in the deep sea should be material off-loaded from the shelves in response to the approximately 130-m sea-level changes of the late Pleistocene. This off-loaded material forms about 20 percent of the total of Quaternary sediment in the ocean basins, and taking this into account lowers the projected accumulation rate increase from 1.54 to 1.23 times the Pliocene rate. According to Khain et al. (1979), the average thickness of Pliocene sediments on the continents on a global scale is 256 m. Because only 5 percent of their Pliocene sediment inventory for the continents is marine, we can assume that the average thickness of nonmarine Pliocene sediments is probably close to 256 m. If a solidity of 70 percent and the duration of the Pliocene of 3.5 m.y. are assumed, the apparent accumulation rate would be 13.57 g/cm2/kyr. If a Pleistocene acceleration of 1.23 is assumed, the apparent accumulation rate might be 16.69 g/cm2/kyr, but this would be the case only if the area over which the Quaternary sediments were deposited had not increased. DISCUSSION The mass of Quaternary sediment is significantly larger than would be expected from knowledge of the masses of sediment representing older stratigraphic entities. The apparent increased mass could be the result of (1) erosion and recycling of young sediment; (2) the effect of ice-age climate and erosion; (3) general increases in erosion rates as a result of tectonic activity; or (4) a combination of all of these factors. However, it is apparent from the determinations of Holocene accumulation rates that the global Holocene rate is only a fraction of the Quaternary average. Within the Quaternary there seems to be as much variability between rates as there has been at different times during the Phanerozoic (Hay and Wold, 1986; Hay et al., 1987). Sediment Cycling Gilluly (1969) first clearly stated the idea that the sediments observed today are largely derived by cannibaliza-
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tion of older sedimentary rocks. The idea was developed by Garrels and Mackenzie (1971a,b), who suggested that post-Devonian sediment might have been recycled more rapidly than Devonian and older sediments. The notion of the possibility of differential cycling rates for younger and older sediments was further explored by Mackenzie and Pigott (1981). Wold et al. (1987) suggested that the observed mass/age distribution of sediments is a reflection of a slow rate of recycling for older (pre-Cretaceous) sediments and a rapid rate of recycling for Cretaceous and younger sediments. They emphasized that young, unconsolidated sediments are in greater jeopardy with respect to erosion than are older, more indurated and more deeply buried sedimentary rocks. Clearly, the increased mass of sediment being deposited in the Quaternary suggests that cycling rates have increased. However, the differences between Holocene and average Quaternary rates suggest that global rates of erosion and sedimentation may vary considerably on time scales of tens to hundreds of thousands of years. The Effect of Glacial-Interglacial Alternations The Pleistocene climatic regime results in alternations of glacial and temperate conditions at mid- and high latitudes, and arid and humid conditions at lower latitudes. Both types of change affect the rates of chemical weathering directly through temperature and soil moisture content, and indirectly through the changes in density and type of plant cover. At mid- and high latitudes the major transport agent alternates between glaciers and rivers. Glaciers are effective at removing, pulverizing, and transporting clastic sedimentary and low-grade metamorphic rocks, but less effective in attacking crystalline rocks. The glacial sediment may be transported uphill and deposited in such large quantities that it results in reorganization of the fluvial drainage systems. The Mississippi River system of North America is an excellent example of glacial reorganization. The preglacial drainage of the interior of North America was probably largely through the St. Lawrence into the North Atlantic (Hay et al., 1989), with the Mackenzie River, Mississippi River, and a river through Hudson Strait draining smaller areas. The Cenozoic drainage system was buried by the glaciers that deposited an average of 20 m of drift over the old topography. The drainage outside the glaciated area was truncated by ice edge rivers. In many places, the courses of the Ohio and the Missouri Rivers mark the outline of glacial advances. During times of deglaciation, supplies of fluvioglacial sediment often exceeded the competence of the rivers, resulting in extensive alluviation. Both of these processes exposed extensive areas of unweathered debris to soil-forming processes. At lower latitudes the alternation of arid and humid climates results in alternating cycles of alluviation and incision in river valleys as well as an alternation of soil-forming processes. Despite the obvious changes in the glaciated area and its periphery, it is not yet clear whether continental glaciation increases or decreases the long-term erosion rate on a global scale. The motion in an ice cap is mostly above the base, so that its ability to erode the rock on which it rests is questionable. Flint (1971) argued that the evidence suggests that the Laurentian ice cap, and probably its counterparts in Europe and Asia, was ineffective in eroding the Canadian Shield. White (1972), noting that the sites of the centers of the Laurentian and Scandinavian ice caps are now marked by shallow seas, suggested that they had removed large masses of sedimentary rock from the Canadian and Fennoscandian shields. Gravenor (1975) and Sugden (1976) countered that there was no evidence for the removal of large amounts of sediment from the sites of these ice caps, but Bell and Laine (1985) have estimated that 1.81 x 106 km3 of terrigenous sediment derived from the Laurentian ice cap was deposited in the ocean, 1.01 x 106 km3 in the North Atlantic Basin, and 0.82 x 106 km3 in the Gulf of Mexico. Shaw (1988, 1989) contended that most of the sediment in the Gulf of Mexico considered by Bell and Laine to be derived from the Laurentide region is derived from erosion of the Cretaceous deposits of the Great Plains. If continental glaciers are effective erosional agents, most of the sedimentary material on the Laurentian and Fennoscandian shields would have been eroded by the first significant ice cap, in the early Pleistocene. Increased Tectonic Activity The idea that the large mass of young sediment is the result of increased tectonic activity dominated geological thinking throughout the first half of this century (Stille, 1936). More recently it has been thought that the large masses of Pliocene (and presumably Quaternary) sediment might merely be the expression of the greater degree of preservation of younger sediments. However, it is now clear that the excess mass of Quaternary sediment over that projected from Miocene rates is very large. A number of studies have suggested that uplift of the Himalayas and Tibet (Hsü, 1978c; Zeitler et al., 1982) and western North America (Gable and Hatton, 1983; Shaw, 1988, 1989) has occurred mostly during the Pliocene and Quaternary. On a global scale the supply of sediment to the oceans increased markedly in the Pliocene, before the development of the large Northern Hemisphere ice caps. There may be a direct link between increased tectonic activity and initiation of the Northern Hemisphere glaciations. Ruddiman et al. (1986) have suggested that the uplift of the Tibet-Himalayan region and western North
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America may have caused reorganization of the atmospheric circulation, resulting in conditions favoring the growth of the Northern Hemisphere continental ice caps. CONCLUSION It seems likely that the global increase in sediment mass deposited during the Pliocene and Pleistocene does reflect a real increase of tectonic activity, and that this has climatic consequences that further enhance erosion. In any case, it is now evident that Pleistocene-Holocene fluxes do not reflect the long-term state of the planet but are the result of a set of unusual conditions. It is within this rapidly changing natural system that future anthropogenic global change will take place. ACKNOWLEDGMENTS The author has benefited from conversations with a number of colleagues, particularly Robert M. Garrels, Fred T. Mackenzie, Robert A. Berner, John R. Southam, Bruce Wilkinson, and Christopher N. Wold. This work has been supported by grants OCE-8409369 and OCE-8716408 from the National Science Foundation, grant 19274-AC2 from the American Chemical Society's Petroleum Research Fund, and gifts from Texaco, Inc. The author is grateful for the generous use of the facilities of the Institut für Palaontologie und Historische Geologie of Ludwig-Maximillians Universitat, Munich, kindly made available through Professor Dieter Herm. REFERENCES Baldwin, B., and C.D. Butler (1985). Compaction curves, American Association of Petroleum Geologists Bulletin 69, 622-626. Bell, M., and E.P. Laine (1985). Erosion of the Laurentide region of North America by glacial and glaciofluvial processes, Quaternary Research 23, 154-174. Berggren, W.A., D.V. Kent, and J.A. van Couvering (1985). The Neogene: Part 2, Neogene geochronology and chronostratigraphy, in The Chronology of the Geological Record, N.J. Snelling, ed., Geological Society (London) Memoir 10, Blackwell Scientific Publications, Oxford, pp. 211-250. Berner, R.A. (1982). Burial organic carbon and pyrite sulfur in the modern ocean: Its geochemical and environmental significance, American Journal of Science 282, 451-473. Buffler, R.T., S.D. Locker, W.R. Bryant, S.A. Hall, and R.H. Pilger, Jr. (1984). Ocean Margin Drilling Program: Gulf of Mexico Atlas, OMDP Regional Atlas Series 6, Marine Science International, Woods Hole, Mass., 36 pp. Choubert, G., and A. Faure-Muret, eds. (1976). Geological World Atlas, UNESCO, Paris, 17 sheets. Cita, M.B., W.B.F. Ryan, and R.B. Kidd (1978). Sedimentation rates in Neogene deep-sea sediments from the Mediterranean and geodynamic implications of their changes, in Initial Reports of the Deep-Sea Drilling Project 42, part 1, K.J. Hsü, L. Montadert, et al., eds., U.S. Government Printing Office, Washington, D.C., pp. 991-1002. Damuth, J.E. (1977). Late Quaternary sedimentation in the western equatorial Atlantic, Geological Society of America Bulletin 88, 695-710. Degens, E.T., and D.A. Ross (1974). The Black Sea: Geology, Chemistry and Biology, Memoir 20, American Association of Petroleum Geologists, Tulsa, Okla., 633 pp. Degens, E.T., P. Stoffers, S. Golubic, and M.D. Dickman (1978). Varve chronology: Estimated rates of sedimentation in the Black Sea deep basin, in Initial Reports of the Deep Sea Drilling Project 42, part 2, D.A. Ross, Y.P. Neprochnov, et al., eds., U.S. Government Printing Office, Washington, D.C., pp. 499-508. Dietrich, G., and R. Koester (1974). Geschichte der Ostsee, in Merreskunde der Ostsee, L. Magaard and G. Reinheimer, eds., Springer-Verlag, Berlin, pp. 5-10. Flint, R.F. (1971). Glacial and Quaternary Geology, John Wiley & Sons, New York, 892 pp. Gable, D.J., and T. Hatton (1983). Maps of vertical crustal movements in the conterminous United States over the last 10 million years, U.S. Geological Survey Miscellaneous Investigations Series Map 1-1315. Garrels, R.M., and F.T. Mackenzie (1971a). Gregor's denudation of the continents, Nature 231, 382-383. Garrels, R.M., and F.T. Mackenzie (1971b). Evolution of Sedimentary Rocks, Norton, New York, 397 pp. Geological Society of America (1950). Geologic Map of South America, Geological Society of America, New York, N.Y. Geological Society of America (1965). Geologic Map of North America, Geological Society of America, Boulder, Colo. Gerasimov, I.P. (1964). Fiziko-Geograficheskii Atlas Mira, Akademiya Nauk SSSR i Glavnoe Upravlenie Geodezii i Kartografii GGK SSSR, Moscow, 298 pp. Gilluly, J. (1969). Geological perspectives and the completeness of the geologic record, Geological Society of America Bulletin 80, 2303-2312. Gravenor, C.P. (1975). Erosion by continental ice sheets, American Journal of Science 275, 594-604. Gregor, C.B. (1970). Denudation of the continents, Nature 228, 273-275. Haq, B.U., W.A. Berggren, and J.A. Van Couvering (1977). Corrected age of the Pliocene/Pleistocene boundary, Nature 269, 483-488. Harland, W.B., A.V. Cox, P.G. Llewellyn, C.A.G. Pickton, A. G. Smith, and R. Walters (1982). A Geologic Time Scale, Cambridge University Press, Cambridge, 128 pp. Hay, W.W. (1985). Potential errors in estimates of carbonate rock accumulating through geologic time, in The Carbon Cycle and Atmospheric CO2: Natural Variations, Archaean to Present, E.T. Sundquist and W.S. Broecker, eds., Geophysical Monograph 32, American Geophysical Union, Washington, D.C., pp. 573-583. Hay, W.W., and J.R. Southam (1977). Modulation of marine sedimentation by the continental shelves: in The Fate of Fossil Fuel CO2 in the Oceans, N.R. Anderson and A. Malahoff, eds., Marine Science Series 6, Plenum Press, New York, pp. 569-604.
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Hay, W.W., and C.N. Wold (1986). A 150 m.y. cycle in erosion and sedimentation rates, Geological Society of America Abstracts with Programs18, 632. Hay, W.W., and C.N. Wold (1990). Relation of selected mineral deposits to the massage distribution of Phanerozoic sediments, Geologische Rundschau79, 495-512. Hay, W.W., M.J. Rosol, J.L. Sloan, II, and D.E. Jory (1987). Plate tectonic control of global patterns of detrital and carbonate sedimentation, in Carbonate-Clastic Transitions, L.J. Doyle and H.H. Roberts, eds., Developments in Sedimentology, v. 42, Elsevier, Amsterdam, pp. 1-34. Hay, W.W., R. DeConto, M. Leslie, and C.A. Shaw (1989). The St. Lawrence River: A major influence on the North Atlantic during the Cenozoic, Terra Abstracts1, 438. Hays, J.D., and W.A. Berggren (1971). Quaternary boundaries and correlations, in The Micropaleontology of Oceans, B.M. Funnell and W.R. Riedel, eds., Cambridge University Press, Cambridge, pp. 669-691. Hsü, K.J. (1978a). Correlation of Black Sea sequences, in Initial Reports of the Deep Sea Drilling Project 42, part 2, D.A. Ross, Y.P. Neprochnov, et al., eds., U.S. Government Printing Office, Washington, D.C., pp. 489-497. Hsü, K.J. (1978b). Stratigraphy of the lacustrine sedimentation in the Black Sea, in Initial Reports of the Deep Sea Drilling Project 42, part 2, D.A. Ross, Y.P. Neprochnov, et al., eds., U.S. Government Printing Office, Washington, D.C., pp. 509-524. Hsü, J. (1978c). On the paleobotanical evidence for continental drift and Himalayan uplift, Paleobotany25, 131-142. Jenkins, D.G., D.Q. Bowen, C.G. Adams, N.J. Schackleton, and S.C. Brassell (1985). The Neogene: Part 1, in The Chronology of the Geological Record, N.J. Snelling, ed., Geological Society (London) Memoir10, Blackwell Scientific Publications, Oxford, pp. 199-210, 251-260. Kassler, P. (1973). The structural and geomorphic evolution of the Persian Gulf, in The Persian Gulf: Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea, B.H. Purser, ed., Springer-Verlag, Berlin, pp. 11-32. Kastens, K.A., J. Mascle, C. Auroux, et al., ed., (1987). Initial Reports of the Deep Sea Drilling Project 107, Part A, Initial Report, Tyrrhenian Sea, U.S. Government Printing Office, Washington, D.C., 1013 pp. Khain, V.Y., A.B. Ronov, and A.N. Balukhovskiy (1979). Neogene lithologic associations of the world, Sovetskaya Geologiya (International Geology Rev.1981(4), 426-454). Lisitzin, A.P. (1972). Sedimentation in the World Ocean, Special Publication 17, Society of Economic Paleontologists and Mineralogists, 219 pp. Lisitzin, A.P. (1974). Osadkoobrazovanie v Okeanach, Izdatelstvo Nauka, Moscow, 438 pp. Lyell, C. (1839). Nouveaux Elements de Geologie, Pitois-Levrault et Cie., Paris, 648 pp. Mackenzie, F.T., and J.D. Pigott (1981). Tectonic controls of Phanerozoic sedimentary rock cycling, Journal of the Geological Society of London 138, 183-196. Melguen, M. (1973). Correspondence analysis for recognition of facies in homogeneous sediments off an Iranian river mouth, in The Persian Gulf: Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea, B.H. Purser, ed., Springer-Verlag, Berlin, pp. 99-114. Milliman, J.D. (1974). Marine Carbonates, Springer-Verlag, Heidelberg, 375 pp. Morner, N.-A. (1976). The Pleistocene/Holocene boundary proposed boundary stratotype in Gothenburg, Sweden, Boreas5, 193-275. Perlmutter, M.A. (1985). Deep water clastic reservoirs in the Gulf of Mexico: A depositional model, Geo-Marine Letters5, 105-112. Ronov, A., V. Khain, and A.N. Balukhovsky (1986). Quantitative distribution of sediments in oceans, Litol. Polezn. Iskop.2, 3-16. Ross, D.A. (1978). Summary of results of Black Sea drilling, in Initial Reports of the Deep Sea Drilling Project 42, part 2, D. A. Ross, Y.P. Neprochnov, et al., eds., U.S. Government Printing Office, Washington, D.C. , pp. 1149-1178. Ruddiman, B., M. Raymo, and A. McIntyre (1986). Matuyama 41,000 year cycles: North Atlantic ocean and northern hemisphere ice sheets, Earth and Planetary Science Letters80, 117-129. Shaw, C.A. (1988). Balanced paleogeographic reconstructions of the northwestern Gulf of Mexico margin and its western-central North American source area since 65 Ma, U.S. Geological Survey Open-File Report88-683, 227 pp. Shaw, C.A. (1989). Mass-Balanced Paleogeographic Modeling: Examples from Western North Atlantic Ocean and Gulf of Mexico, Ph.D. thesis, University of Colorado, Boulder, 381 pp. Sloan, J.L., II (1985). Cenozoic Organic Carbon Deposition in the Deep-Sea, Cooperative Thesis89, National Center for Atmospheric Research, Boulder, Colo., 197 pp. Stille, H. (1936). The present tectonic state of the Earth, American Association of Petroleum Geologists Bulletin20, 849-880. Stoffers, P., and D.A. Ross (1974). Sedimentary history of the Red Sea, in Initial Reports of the Deep Sea Drilling Project23, R.B. Whitmarsh, O.E. Weser, D.A. Ross, et al., eds., U.S. Government Printing Office, Washington, D.C., pp. 849-865. Stoffers, P., E.T. Degens, and E.S. Trimonis (1978). Stratigraphy and suggested ages of Black Sea sediments cored during Leg 42B, in Initial Reports of the Deep Sea Drilling Project 42, part 2, D.A. Ross, Y.P. Neprochnov, et al., eds., U.S. Government Printing Office, Washington, D.C., pp. 483-487. Sugden, D.E. (1976). A case against deep erosion of shields by ice-sheets, Geology4, 580-582. Thunell, R.C., D.F. Williams, and J.P. Kennett (1977). Late Quaternary paleoclimatology, stratigraphy and sapropel history in eastern Mediterranean deep-sea sediments, Marine Micropaleontology2, 371-388. Wetzel, A., and B. Kohl (1986). Accumulation rates of Mississippian sediments cored during Deep Sea Drilling Project Leg 96, in Initial Reports of the Deep Sea Drilling Project96, A. H. Bouma, J.M. Coleman, A.W. Meyer, et al., eds., U.S. Government Printing Office, Washington, pp. 595-600. White, W.A. (1972). Deep erosion by continental ice-sheet, Geological Society of America Bulletin83, 1037-1056.
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Wold, C.N., and W.W. Hay (1988). Estimating ancient sediment masses and flux rates, Geological Society of America Abstracts with Programs 20, A78. Wold, C.N., and W.W. Hay (1990). Estimating ancient sediment fluxes, American Journal of Science 290, 1069-1089. Wold, C.N., W.W. Hay, and K.M. Wilson (1987). Reconstructed mass-age distributions of young sediment through the Phanerozoic, Geological Society of America Abstracts with Programs 19, 895. Zeitler, P.K., R.A.K. Tahirkheli, C.W. Naeser, and N.M. Johnson (1982). Unroofing history of a suture zone in the Himalaya of Pakistan by means of fission-track annealing ages, Earth and Planetary Science Letters 57, 227-240.
Representative terms from entire chapter: