Geology topics
Frank T. Manheim
Publications and source records attributed to Frank T. Manheim.
The scientific referee
In the May 1973 issue of EOS, I criticized tendencies in earth science periodicals to discourage referee anonymity. I stressed that exposing referees to unnecessary personal and subjective influences tended to degrade standards of quality and promoted cliques, fragmentation, superspecialization, and proliferation of scientific literature. Generally speaking, division of opinion on this question, based on letters and personal contacts since 1973, has tended (with notable exceptions) to divide along two lines: the “wise old heads” favor anonymity, whereas many young idealists favor openness. Referees can help keep literature standards high (there is no evidence that they can or do thwart new ideas, determinedly pushed). but they can do little to stop literature proliferation, If individuals do scientific work, they may as well publish of not do it at all. The only real solutions to literature proliferation are fewer scientists or a drastic paper shortage, as experienced in Bulgaria.
Sources of suspended matter in waters of the Middle Atlantic Bight
Suspended matter collected in the Middle Atlantic Bight (the coastal segment of the United States between Cape Cod and Cape Hatteras) in September 1969 was predominantly organic: an average of 80% combustible organic matter in surface waters and 40)% near bottom. Total suspended concentrations decreased between the inner shelf and the shelf break by an order of magnitude in both near-surface and near-bottom waters. The noncombustible (ash) fraction of the suspended matter decreased over the same distance by one order of magnitude in the near-bottom waters and two orders of magnitude in surface waters. Recently contributed river sediment is not a significant constituent of the suspended matter in the waters of the shelf, particularly the outer shelf. Most of the inorganic material in suspension represents resuspended bottom sediments (at least some of which are relict) whose suspended concentrations are increased noticeably by storms.
Geology of Bulgaria: A review
Bulgaria is in southeastern Europe between reasonably well-described areas of predominantly Alpine crustal deformation on the north and northwest (Carpathians in Romania, Hungary, and Czechoslovakia; Alps in Austria), on the east (Pontides and Taurides in Turkey), and on the west and south (Dinaric Alps in Yugoslavia; Pindos Mountains in Greece) but has not been well described in easily available literature. There are three major east-west trending morphotectonic units. The low-relief Moesian platform of northern Bulgaria and southern Romania owes its heritage to Hercynian deformation. It is mantled by flat-lying, shelf-type Mesozoic and Tertiary sedimentary (mostly carbonate) rocks. Along its southern boundary a foredeep developed during Jurassic-Cretaceous time in which thick flysch-like sediments accumulated. There is small oil and gas production. The Lorn basin, North Bulgarian swell, and Varna trough are other major structural elements within the platform. The Rhodope massif of southern Bulgaria and northern Greece is a rugged mountainous terrain of Precambrian and early Paleozoic crystalline rocks. It is a fragment of a once much larger crustal block that began to break up in the Paleozoic and which has experienced uplift of 2,000 m in the Pliocene-Pleistocene. Between the Rhodope and Moesian crustal blocks the narrow (10-20 km) Balkan Mountains (Stara Planina zone) consist of tightly folded and metamorphosed Paleozoic sedimentary rocks that have been deformed recurrently during the Hercynian and Alpine orogenies, culminating in 3 to 4 km of vertical uplift since the Miocene. The sub-Balkan fault bounds the south side of the Balkans and is at many places a spectacular scarp. The Balkanide zone has been compressively molded between the large, relatively stable Rhodope massif and Moesian platform. Locally, north-moving gravitational glide masses lie on the platform but there has been minimal crustal shortening. A fourth morphotectonic unit, the Kraishtide zone, trends northwest through western Bulgaria and into adjacent Yugoslavia. This rugged area, 15-60 km wide, is a megashear zone within which both right-lateral strike-slip and vertical movements have been common since the Paleozoic. It parallels the better known Vardar zone of Yugoslavia. In addition to the long-lived, deep-seated faults that parallel the trend—and which are the boundary for some—of these four crustal units, a northeast-southwest fault system (Tvarditsa and Etropole), further breaks the Bulgarian crust into a giant block mosaic. Predominantly vertical movement along the major faults alternately has elevated or depressed individual blocks of the mosaic and has influenced profoundly the location and the character of sedimentation, igneous activity, occurrence of mineral deposits, and erosion.
Geological and geochemical significance of Red Sea evaporites
No abstract available.
Interstitial water studies on small core samples, Leg 22
Interstitial waters from Leg 22 in the Indian Ocean revealed two unique results: Site 214, on the Ninetyeast Ridge, penetrated through a 30-meter sequence of fine-grained basalt and reentered hard, silty clay containing carbonate skeletal debris. Such a basalt layer may well have been impervious and extensive enough to seal off underlying (fossil) seawater of Paleocene age. However, except for a marked increase in calcium and a slight increase in chloride, no appreciable changes in pore fluid chemistry could be confirmed. Site 217, at the northernmost end of the Ninetyeast Ridge, demonstrated record concentrations of interstitial calcium in clayey nannofossil oozes and a relatively small but significant increment in chloride with depth. Presumably, these increments signal the existence of evaporitic sediments or evaporite-influenced brines at considerably greater depth than penetrated.
Diffusimetry (diffusion constant estimation) on sediment cores by resistivity probe
Measurement of formation factor (ratio of rock resistivity to interstitial water resistivity) from sediment cores provides an indirect measurment of the tortuosity of the fluid channels in the sediments. From these measurements one can estimate the diffusion coefficient of the sediment with depth. The F (formation factor) values for Indian Ocean sediments varied from 1.6 for a clayey diatom ooze having 87% porosity (70% water content) to 13.6 for a cemented limestone having 25% porosity (11% water content). These formation factors would yield diffusion coefficients for chloride ions in the corresponding sediments of 6.4 x 10 -6 to 1.5 x 10 -6 cm 2 /sec. In general, surficial sediments showed diffusion coefficients about one-half to one-third of those for free solution, values decreasing with depth and porosity.
Porosity, density, grain density, and related physical properties of sediments from the Red Sea drill cores
Representative sediments from each site were chosen for examination of their dry specific gravity and grain density. The determinations were made by micropycnometer; water was used as the displacing medium, and salt corrections were based on the refractive index measurements on interstitial water. For saltier brines the "salinities" derived from index of refraction are somewhat too low but, for the most part, are adequate for these corrections. Water contents are those determined on the archived samples selected for these studies. They had been kept in cold storage (4°C) in screw-capped glass bottles with poly seal lids or in heat-sealed polyethylene bags for a period of about three months. The purpose of the measurements was to gain sufficient information on grain density to permit application of the general information or pattern to the bulk water content determinations on the small syringe samples. Bulk density, porosity, and other properties could then be calculated without using volume measurements from the syringes. Whereas the data from weight loss on drying (bulk water content) at 110-120° were considered good, the volume measurements are subject to considerable error, especially in more consolidated sediments, and are not usable at all for shales, more consolidated or cemented rocks, and anhydrite. Detailed comparisons with the GRAPE determinations were also an objective. The Red Sea cores offer a particularly good opportunity to test the validity of these measurements, which have been increasingly questioned.
Chemical analyses of Red Sea sediments
One of the prime motives for exploring the deeper subsurface sediments of the Red Sea floor was to gain information on the geochemical systems controlling the hot brine-metalliferous deposits. Accordingly, a strong effort was made to provide both shipboard and laboratory means of analysis of the recovered phases. Shipboard spectrographic analyses (semiquantitative) provided both detailed surveys of chemical properties of the cores and the ability to analyze small subsamples and separated particles such as pyrite, sphalerite, organisms, and similar minute objects. Over 5000 such analyses are provided in Tables 1 to 5. Some supplementary data provided by subsequent analyses for K, Zn, and Ag in the Denver field laboratories of the U. S. Geological Survey have been added to the tables. A second body of data is provided in Table 6, which gives quantitative data on major and minor constituents, performed by the Washington analytical laboratories of the U. S. Geological Survey. A third group of analyses are partial analyses on evaporitic rocks (anhydrite and rock salt) (Table 18, in Manheim Chapter 38, this volume). In addition to the above, a number of the collaborating laboratories are providing more specific chemical data on special phases and constituents of the Red Sea materials. Most of these data are included in chapters in the Geochemical section of this volume. The significance of the data is discussed in Manheim (Chapter 38, this volume) and in the respective reports of shipboard workers and cooperating share laboratories.
Interstitial water studies on small core samples, leg 23 (Red Sea)
No abstract available.
Red Sea geochemistry
The Red Sea drillings reveal a number of new facets of the hot-brine-metalliferous system and other geochemical aspects of the sea, its sediments, and its past history as follows: 1) Dark shales rich in organic material, and containing enhanced Mo and V concentrations, are characteristic of Plio-Pleistocene strata in the Red Sea. Values as high as 1500 ppm V and 500 ppm Mo were obtained in sediments containing up to 8 percent organic carbon. 2) Metalliferous sediments in the hot brine deep (Site 226) are similar in composition in both solids and interstitial water to previously analyzed sediments. However, one site (228) well south of the known hot-brine deeps shows zinc mineralization reaching 5 percent Zn in late Miocene shale-anhydrite breccias. 3) Pore fluid studies show that near-saturated (NaCl) brines having similar total salt concentration to the hot-brine fluids are associated with Miocene evaporites at Sites 225, 227, and 228. However, their chemical and isotopic composition precludes such fluids being part of the "hot brine plumbing system." Hydrogen and oxygen isotope studies demonstrate that fluids trapped between and among the evaporitic rocks have a strong meteoric water component, presumed to have entered the rocks during or shortly after formation in shallow evaporating pans. The composition of pore fluid at Site 227 suggests the presence of late-stage evaporite minerals of the tachyhydrite CaMg 2 Cl 6 • 12H 2 O series in the in situ rocks. 4) Diffusivity measurements show that the pre-Miocene strata permit dissolved salt or gas diffusion to the extent of from 1/2 to about 1/10 the rate in free solution. However, in anhydrites diffusivity is reduced more than 100-fold, and no diffusion could be detected through halite rock. The rates applied to interstitial salt gradients at Site 225 suggest that less than 1 meter of rock salt is removed per million years by diffusion processes. The diffusion of salt can already be detected a few meters below the sediment-water interface, and based on the interstitial water studies, one can affirm the presence of salt at depth at Sites 228, 230, and possibly 229, where rock salt was not encountered by the drill. 5) Isotopic measurements on leads show that both leads from Site 228 and the hot brine deep (Site 226) require input from igneous or volcanic sources (e.g., volcanic ash). Elsewhere, however, leads of sedimentary-pelagic origin are noted. 6) Isotopic and other evidence indicates that the long-distance transport of subterranean brines advocated by Craig (1969) is unlikely. Instead, it is proposed that the source of the hot brines is subevaporite clastic or other aquifers of early to middle Miocene age that have been disrupted by rifting. These discharge in the deeps by virtue of hydrodynamic continuity with heavy brines at higher positions on the nearby flanks of the Red Sea. In this case, the waters might be fossil (middle Miocene) Red Sea waters of relatively normal salinity that have acquired greater salt concentration by diffusion from overlying late Miocene evaporites. The model is consistent with the isolated nature of the brine deeps and suggests that flow might have been enhanced by increased hydraulic gradients during periods of lowered Red Sea levels. 7) Interstitial water evidence indicates that Pleistocene lowerings of sea level did not cause evaporative conditions leading to actual gypsum or other evaporite deposition in the deeper water zones, as has been postulated. This in turn suggests that sill depths were greater than have been assumed.
Composition and origin of interstitial waters of marine sediments, based on deep sea drill cores
No abstract available.
Red sea drillings
Recent drilling in the Red Sea has shown that much of the basin is underlain by evaporites of a similar age to that of evaporites found in the Mediterranean Sea. These evaporites and their structural positions indicate that other brine areas are present - and, indeed, several others have been discovered.
Interstitial water studies on small core samples, Deep Sea Drilling Project: Leg 10
Leg 10 interstitial water analyses provide new indications of the distribution of rock salt beneath the floor of the Gulf of Mexico, both confirming areas previously indicated to be underlain by salt bodies and extending evidence of salt distribution to seismically featureless areas in the Sigsbee Knolls trend and Isthmian Embayment. The criterion for presence of salt at depth is a consistent increase in interstitial salinity and chlorinity with depth. Site 86, on the northern margin of the Yucatan Platform, provided no evidence of salt at depth. Thus, our data tend to rule out the suggestion of Antoine and Bryant (1969) that the Sigsbee Knolls salt was squeezed out from beneath the Yucatan Scarp. Cores from Sites 90 and 91, in the central Sigsbee Deep, were not obtained from a great enough depth to yield definite evidence for the presence of buried salt. Site 86, on the northern margin of the Yucatan Platform, provided no evidence of salt at depth. Thus, our data tend to rule out the suggestion of Antoine and Bryant (1969) that the Sigsbee Knolls salt was squeezed out from beneath the Yucatan Scarp. Cores from Sites 90 and 91, in the central Sigsbee Deep, were not obtained from a great enough depth to yield definite evidence for the presence of buried salt.
Interstitial water studies on small core samples, legs 16, 17, and 18
Legs 16, 17, and 18 encountered three groups of sediment types: rapidly deposited biogenic deposits, showing marked changes in interstitial calcium, magnesium, and strontium; slowly deposited biogenic deposits, showing little variability in pore fluids other than elevated silica concentrations; and terrigenous deposits. The latter showed the usual loss of sulfate and combination of diagenetic reactions culminating in loss of Na + , K + , Mg ++ , with variable changes in Ca ++ . Very high barium concentrations (to 59 mg/kg) occurred at Site 178 (Leg 18).
Interstitial water studies on small core samples, leg 19
The sediments cored on Leg 19 consist primarily of diatomaceous oozes with variable proportions of volcanic material and terrigenous clays and silts. With a few exceptions, deposition rates are high at these sites, usually exceeding 5cm/10 3 y. The interstitial solutions sampled exhibit compositional changes which previously have been found to characterize rapidly deposited terrigenous sediments. Some of the largest changes in Na + , K + , Mg 2+ , Cl - , and HCO 3 yet found in DSDP samples occur in the pore waters studied from this leg (see Table 1).
Interstitial water studies on small core samples, Leg 15
Analyses of pore fluids from reducing environments demonstrate that reduction of SO 4 is accompanied by large increases in alkalinity and strong depletion of Ca and Mg. The data are compatible with a model of replacement of Fe 3+ in clay lattices by Mg from the interstitial solutions and the precipitation of pyrite. Depletions of Na in the interstitial solutions are related to Mg losses by a ratio of approximately 1:3. Pore fluids from oxidizing pelagic sediments exhibit little SO 4 depletion. Losses of Mg are accompanied by the addition of Ca to the pore solutions on a nearly 1:1 basis. Strong Sr enrichment is also found in these solutions. The magnitude of the Sr increase suggests that considerable carbonate recrystallization has occurred. As part of an extensive interlaboratory and analytical calibration, the effect of squeezing sediment at different temperatures has been studied in depth. Samples of a variety of lithologies have been included. Enrichment of K by as much as 24 percent and depletion of Mg and Ca by up to 7 percent occurs during warming. However, no significant effect upon Cl and SO 4 could be detected. The strongest effects are seen in the minor constituents studied. On warming, Sr, Si, and B are enriched as much as 19, 40, and 60 percent, respectively. The size of the observed concentration changes varies with the mineralogy of the sediment, but is significant in all types studied, particularly with regards to Mg and K.