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1.
The stratigraphic record in the James and Hudson Bay Lowlands indicates that the sequence of glacial events at the geographical center of the 12.6 × 106 km2 Laurentide Ice Sheet may have been more complex than hitherto imagined. Isoleucine epimerization ratios of in situ and transported shells recovered from till and associated marine and fluvial sediments cluster into at least 4 discrete groups. Two alternative explanations of the data are offered, of which we strongly favor the first. Hypothesis 1: Setting the age of the “last interglacial” marine incursion, the Bell Sea, at 130,000 yr B.P. results in a long-term average diagenetic temperature for the lowlands of +0.6°C. Using this temperature enables us to predict the age of shells intermediate in age between the “last interglaciation” and the incursion of the Tyrrell Sea 8000 yr ago. Between these two interglacial marine inundations, Hudson Bay is predicted to have been free of ice along its southern shore about 35,000, 75,000, and 105,000 yr ago based on amino acid ratios from shells occurring as erratics in several superimposed tills and fluvial sediments. These results suggest (1) that traditional concepts of ice-sheet build-up and decay must be reexamined; (2) that “high” sea levels may have occurred during the Wisconsin Glaciation; and (3) that a critical reappraisal is required of the open ocean δ18O record as a simple indicator of global ice volume. An alternative, Hypothesis 2, is also examined. It is based on the assumption that the 35,000-yr-old deposits calculated on the basis of Hypothesis 1 date from the “last interglaciation”; this, in effect, indicates that the Missinaibi Formation, commonly accepted as sediments of the “last interglaciation,” are about 500,000 yr old and that the effective diagenetic temperature in the lowlands during approximately the last 130,000 yr has been close to ?6°C. We argue for rejection of this alternative hypothesis.  相似文献   

2.
Several high-resolution “SES 2000 deep” seismic profiles and a core of bottom sediments were obtained in cruises 33, 35, and 37 of the R/V Akademik Ioffe in the area of the Columbia channel (continental rise of Brazil, South America). The analysis of seismic facies and direct correlation of acoustic and lithological data indicates that sedimentation in this area is mostly controlled by the contour current of the Antarctic Bottom Water (AABW). The gravity flows from seamounts and continental slope only episodically contributed coarser material to the deposition of the muddy contourites. The mixed gravitite-contourite systems consisting of accumulative bodies (drifts) and erosion channels are the results of interaction of these sedimentation processes.  相似文献   

3.
Surface sediments from the Outer Continental Shelf of Alaska were analyzed for hydrocarbons as part of an environmental survey sponsored by NOAA/BLM. Sediments were collected from the proposed oil lease areas of Beaufort Sea, southeastern Bering Sea, Norton Sound, Navarin Basin, Gulf of Alaska, Kodiak Shelf and lower Cook Inlet. Data on normal and branched alkanes and di- and triterpenoids from capillary gas chromatography (GC) and gas chromatography-mass spectrometry (GC/ MS) indicate that the area displays little evidence of petroleum hydrocarbons (i.e., seeps) except at a few isolated stations. Beaufort Sea sediments have the highest hydrocarbon budget, whereas Kodiak Shelf sediments have the lowest. The molecular markers of the hydrocarbons are of a mixed marine autochthonous and terrestrial allochthonous origin. Norton Sound and Cook Inlet sediments contain the highest levels of terrigenous lipids and Kodiak Shelf the lowest. The abundance of alkenes implies that relatively low oxidizing conditions exist in some of the depositional areas studied, suggesting that extraneous petroleum hydrocarbons introduced into these sediments would be expected to have a relatively long residence time. The distribution of polynuclear aromatic hydrocarbons (PAH) is complex and shows a pyrolytic origin. The data on perylene strongly favor the hypothesis that it is “performed” from terrigenous precursors and transported into the marine environment with no apparent in situ generation. Polynuclear aromatic hydrocarbons of diagenetic origin are probably dominant in Gulf of Alaska and Kodiak Shelf sediments.Two stations, north of Kalgin Island, in lower Cook Inlet and one in southeastern Bering Sea show typical weathered petroleum distribution of n-alkanes and triterpenoids. Probable pathways of transport and fate of petroleum hydrocarbons in case of an oil spill are also briefly discussed.  相似文献   

4.
Quaternary sediments from the borehole DBC-1 drilled in the Darhad Basin, northern Mongolia, have been studied by thermomagnetic analysis (248 samples) and probe microanalysis (9 samples) to determine the origin (cosmic or terrestrial) of native iron. Most of the samples showed extremely low contents of native iron. Only 26 samples have iron in contents sufficient for its reliable identification (10–5–10–3%). The negligible content of native iron in the Darhad Basin sediments distinguishes them from the earlier studied sediments of different geologic associations of Eurasia and the Atlantic, which we explain by the high sedimentation rate in this basin. However, the bimodal distribution of native-iron contents in the samples with a distinct “zero” mode, similar to that in the objects of Eurasia and the Atlantic, testifies to the predominantly cosmic origin of the native iron.  相似文献   

5.
Pollen and macrofossil analyses of two radiocarbon-dated lake sediment cores in the upper Peace River district were used to investigate the controversial late-glacial geochronology of the “ice-free corridor.” The basal mineral-rich sediments contain reworked, radiogenically “dead” palynomorphs, as well as intrusive “modern” carbon. Analyses of the basal sediments from Boone Lake show that two 14C ages greater than 12,000 yr B.P. are spuriously old due to contamination by organic matter of Cretaceous age. The data support occlusion or near occlusion of Laurentide and Cordilleran ice in the Peace River area during the late Wisconsinan period. The sediment record began around 12.000 yr B.P. in the ice-dammed and enlarged Boone Lake. An initially open, sedge-dominated cover was invaded by sage, willow, grass, and poplar by 11,700 yr B.P., suggesting that a habitable landscape has existed in the area for at least 12 millennia. The data, however, do not support the ice-free corridor arguments of B. O. K. Reeves (1973, Arctic and Alpine Research5,1–16; 1983, In “Quaternary Coastlines and Marine Archaeology: Towards the Prehistory of Land Bridges and Continental Shelves” (P. M. Masters and N. C. Fleming, Eds.), pp. 389–411. Academic Press. New York), who suggests that ice occlusion did not occur in the Peace River Valley during the last 55,000 yr.  相似文献   

6.
The results of investigations in the Sea of Okhotsk by the seismic reflection method are considered with special attention paid to the acoustic anomalies. Two types of such anomalies are definable in the basin: local (“gas channel”) and areal (“turbid sequences”). It is shown that the acoustic anomalies distinguishable in the single channel seismic profiling (SCSP) records are characteristic of sediments with partial gas filling. Many local anomalies documented on the Sakhalin slope are spatially connected with zones of faulting. The simultaneous presence of acoustic anomalies and BSR in the upper part of the section serves as a reliable diagnostic feature of gas hydrates. The dispersion of the velocities in the wave packet characterizing the acoustic anomaly associated with the lower part of the sedimentary cover in the Kurile Basin points to the significant thickness of the gas-bearing sediments in the latter.  相似文献   

7.
The amino-acid compositions of limestones whose origin is thought to be related to the activity of Cyanophyceae have been studied to determine whether the characteristic components of these organisms would be present as geochemical fossils. A significant amount of amino acids is present and the content can be divided between a “free amino-acid fraction” and a “combined amino-acid fraction” containing different amounts of acidic and basic amino acids. There is evidence to suggest that the amino acids and amino sugars isolated are indeed contemporaneous with the formation of the sediments. The absence of diaminopimelic acid and the very small amount of muramic acid present shows that these two important components of algal and bacterial cell-membranes have apparently been extensively degraded.  相似文献   

8.
Abstract

In the Oman mountains, a succession of sedimentary decollement nappes, the Hawasina nappes, is sandwiched between the Samail ophiolite nappe and its underlying melange and the “autochthonous” sequences of the Arabian platform. The sediments of the Hawasina nappes document the Mesozoic evolution of the northeastern Arabian continental margin and the adjacent Tethys Ocean. In earlier paleogeographic reconstructions, based on simple telescoping of the tectonic units, the upper Hawasina nappes represent the distal part and the lower nappes the proximal part of the margin. New stratigraphic data suggest a revision of the paleogeography and a more complex model for nappe emplacement in the central Oman mountains. The lower Hawasina nappes with their Jurassic and Cretaceous base of slope and basin sediments (Hamrat Duru, Wahrah) form the original cover of part of the upper Hawasina nappes. In the latter (Al Ayn, Haliw), Triassic pelagic sediments, locally overlain by massive sandstone successions are preserved. Complete Mesozoic sequences with pelagic Cenomanian sediments as youngest dated elements are found in the highest Hawasina units (Al Aridh and Oman Exotics). The stratigraphic data indicate polyphase thrusting in the central Oman mountains. Downward propagation of thrusting in front of the Samail is responsible for cutting the original stratigraphie sequence into a number of thrust-sheets, involving successively older and more external formations. This kind of thrust propagation eventually leads to the observed superposition of originally lower stratigraphie units onto their original cover. Regional deformation of the nappe contacts in post-nappe culminations (J. Akhdar, Saih Hatat) is related to ramp-flat-systems in the Arabian foreland.  相似文献   

9.
《Applied Geochemistry》2001,16(1):95-108
Bottom sediments and suspended matter from the shelf and slope areas off northeastern Taiwan were analyzed for sterol, n-alkanol and n-alkane compositions. The Σ(algal sterols/cholesterol) ratios (mean±1σ) were 1.00±0.31 (n=7) for the shelf sediments, 3.29±0.61 (n=7) for the slope sediments, and 1.54±0.19 (n=3) for the suspended matter. The much higher proportion of cholesterol in the shelf sediments is most likely derived from mollusks in the relict sediments. An additional sterol source for the shelf sediments probably is suspended matter in the water column although the shelf has no apparent sedimentation. Results from phytol and n-alkanols suggest recent inputs of lipids from the water column to the shelf. The stanol/stenol ratios are lower for the older shelf sediments than for the younger slope sediments.  相似文献   

10.
In this paper we describe previously unpublished trionychid turtle material, consisting of skull fragments, from the Late Cretaceous (late Turonian) Bissekty Formation of the Dzharakuduk locality in Uzbekistan. This material is assigned to two taxa: the skull-based Khunnuchelys kizylkumensis Brinkman et al. (1993, Can. J. Earth Sci. 30, 2214-2223) and Trionychini indet. Two specimens which cannot be confidently attributed to these two taxa are considered Trionychidae indet. In addition to these trionychid taxa known from skulls, the Dzharakuduk turtle assemblage includes at least two shell-based taxa, Aspideretoides cf. A. riabinini and “Trionyx” cf. “T.” kansaiensis. For this and other Late Cretaceous localities of Middle Asia and Kazakhstan, we suggest the probable skull-shell associations of Khunnuchelys spp. with “Trionyx” kansaiensis-like forms and Trionychini indet. with Aspideretoides-like forms.  相似文献   

11.
This paper presents new major and trace element data from 150 garnet xenocrysts from the V. Grib kimberlite pipe located in the central part of the Arkhangelsk diamondiferous province (ADP). Based on the concentrations of Cr2O3, CaO, TiO2 and rare earth elements (REE) the garnets were divided into seven groups: (1) lherzolitic “depleted” garnets (“Lz 1”), (2) lherzolitic garnets with normal REE patterns (“Lz 2”), (3) lherzolitic garnets with weakly sinusoidal REE patterns (“Lz 3”), (4) lherzolitic garnets with strongly sinusoidal REE patterns (“Lz 4”), (5) harzburgitic garnets with sinusoidal REE patterns (“Hz”), (6) wehrlitic garnets with weakly sinusoidal REE patterns (“W”), (7) garnets of megacryst paragenesis with normal REE patterns (“Meg”). Detailed mineralogical and geochemical garnet studies and modeling results suggest several stages of mantle metasomatism influenced by carbonatite and silicate melts. Carbonatitic metasomatism at the first stage resulted in refertilization of the lithospheric mantle, which is evidenced by a nearly vertical CaO-Cr2O3 trend from harzburgitic (“Hz”) to lherzolitic (“Lz 4”) garnet composition. Harzburgitic garnets (“Hz”) have probably been formed by interactions between carbonatite melts and exsolved garnets in high-degree melt extraction residues. At the second stage of metasomatism, garnets with weakly sinusoidal REE patterns (“Lz 3”, “W”) were affected by a silicate melt possessing a REE composition similar to that of ADP alkaline mica-poor picrites. At the last stage, the garnets interacted with basaltic melts, which resulted in the decrease CaO-Cr2O3 trend of “Lz 2” garnet composition. Cr-poor garnets of megacryst paragenesis (“Meg”) could crystallize directly from the silicate melt which has a REE composition close to that of ADP alkaline mica-poor picrites. P-T estimates of the garnet xenocrysts indicate that the interval of ～60–110 km of the lithospheric mantle beneath the V. Grib pipe was predominantly affected by the silicate melts, whereas the lithospheric mantle deeper than 150 km was influenced by the carbonatite melts.  相似文献   

12.
During the “Heidelberg-Ellesmere-Island-Expedition” to Oobloyah Valley, N-Ellesmere Island, NWT, Canada in 1978 the summerly water balance of this high arctic catchment area with continuous permafrost was investigated. The following results will be presented:
  1. Three hydrogeological areas with different physical parameters, thawing depths and drainage are distinguished and studied on slope I, II and slope III.
  2. The climatic situation of summer 1978 was mainly influenced by the change of radiating and cloudy periods. Due to air temperatures (2 m above ground), which never went below 0°C, these periods regulated the thawing of the glaciers and the respective run-off.
  3. Most of the winterly snow cover melted before July, thereafter soil thawing and its drainage began. In none of the sediments the latter reached field capacity.
  4. Considering the course of daily discharge and soil water balance the three studied streams were characterized by the “Dry-Weather-Discharge-Line”, DWL, of Peri-Creek the “Radiation-Weather-Discharge-Line”, RWL, and the “Cloudy-Weather-Discharge-Line”, CWL, of Nukapingwa River and Heidelberg River.
  5. The periglacial streams never had a measurable sediment load not even during snow melt, whereas the glacial and mixed glacial-periglacial streams as Nukapingwa River and Heidelberg River showed a sediment drift depending on their run-off. Only in Peri-Creek the ion concentrations were correlated to discharge.
  6. Precipitation (snow plus rain) add up to 51% of the summerly water balance. The glaciers contributed up to 48%, and the actual evapotranspiration is only 1%.
  相似文献   

13.
The Lower Cretaceous ammonite fauna of Japan was influenced by the Tethyan, Boreal and North Pacific realms with their oceanic current patterns and ammonite distributions. The hypothesis of oceanic circulation can be utilized to interpret the existence of the “Bering Strait” and the changing position of the “Boreal front,” that is the contact region of warm and cold-water masses. To understand such a system fully, a comprehensive understanding of the geographical distribution of ammonite faunas is required. The occurrence of twenty-five ammonite species, belonging to twenty genera, is confirmed in the Barremian to Albian of Japan. Of these, 24 species are described in this paper, including Barremites macroumbilicus sp. nov. The fauna can be divided into three associations, lower, middle, and upper, indicating late Barremian, late Aptian, and late Albian of the European standard zonation. The faunal characters suggest that the habitats of these ammonite faunas may have changed during later Early Cretaceous, with faunas characterizing three different environments, i.e., nearshore, intermediate, and distal shelf to upper slope setting. Ammonites of the lower association (late Barremian) are related to those of the Tethys, Boreal European, and circum-Pacific regions, and suggest that the Early Cretaceous Katsuuragawa Basin was deposited under the influence of currents from both high latitude and equatorial areas. The occurrence of Crioceratites (Paracrioceras) suggests that the Boreal European elements, including Simbirskites and Crioceratites (Paracrioceras), transited between Northwest Europe and Japan through the Arctic Sea, indicating that the Pacific Ocean was connected with the Arctic Sea at that time. The second association (late Aptian) is composed of ammonites of the Tethyan and circum-Pacific regions. As European Boreal ammonite taxa are absent in this association, it is concluded that the Pacific Ocean probably was not connected with the Arctic Sea at the time. Consequently, the “Boreal Front,” marking the contact between warm and cold water masses, was located at mid-latitude in the “Bering Strait” region during Barremian and subsequently moved northward during Albian. The uppermost ammonite association (late Albian) also consists of Tethyan and circum-Pacific taxa. Desmoceras (Pseudouhligella) poronaicum expanded its range with northward and eastward circulation of oceanic currents, suggesting the current must have represented a warm water-mass from the equator. The species subsequently migrated from the southern Katsuuragawa Basin to the Hokkaido area during late to latest Albian.  相似文献   

14.
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15.
The carbonate succession in the Lyalintsi section of the western Moesian Platform (western Bulgaria) displays a shallowing-upward trend. Growth of the Tithonian–Valanginian coral biostromes and low-relief bioherms was preceded by Oxfordian–Kimmeridgian sedimentation of fine-grained peloidal-bioclastic limestones and Saccocoma-bearing limestones on the homoclinal ramp and the carbonate platform slope. In the late Kimmeridgian, boundstones with very rare corals, but with easily recognisable biohermal morphology, were developed. The main components of this reef are encrusting microorganisms, microbial crusts and synsedimentary cements. Microencrusters Labes atramentosa, Crescentiella morronensis, Perturbatacrusta leini and Radiomura cautica, as well as thin crusts of calcified sponges (sclerosponges), are the main biotic components. Corals (almost exclusively microsolenids) are sparse, whereas photophilic microencrusters (e.g., “Lithocodium–Bacinella”), are absent, although they are common in the overlying shallow-water part of the Lyalintsi sequence. Microbialites and synsedimentary cements provided additional support for the reef framework. The framework, especially the biotic components, and the reefal facies position within the sedimentary succession, implies that the high-energy upper slope of the carbonate platform was the depositional setting of the microencruster-microbial-cement reef studied. Encrusting microorganisms, except for C. morronensis and sponges, are only known from the intra-Tethyan platforms. This study supports conclusion of studies of coeval Alpine reefs that the presence of the microencruster-microbial-cement framework provides insight into the palaeobathymetry, palaeogeography and tectonic configuration of the intra-Tethyan carbonate platforms.  相似文献   

16.
Until recently the age of the continental sediments overlaying marine strata of Carboniferous age at the Murzuk Basin was unknown and long distance correlation was not possible because of lack of correlation criteria. The flora now described allows, for the first time, to identify the age of parts of this strata. Together with new sedimentological criteria of subdivision worked out by R.Glaeser, H.Kallenbach and I.Zöller which will be published later, the paleobotanical investigations contribute towards a final subdivision of these continental sediments. The terms “Nubian Series”, and “Posttassilien” will be abandoned, because they are useless within the area concerned. The creation of correlatable stratigraphical data is an important prerequisite for groundwater and mineral exploration within the large areas covered by these strata. Along the eastern Murzuk Basin these sediments containFilicophytae, Pteridophyllae,Pteridospermaphytae, Cycadophytae andConiferophytae. At Jebel Ben Ghnema the upper part of the lower third of the continental sediments contains plants which are known from triassic strata in Europe, India, North America, South America, South Africa, and Asia. At Jebel Ben Ghnema the top of the strata contains Jurassic plants known from Europe, North America, and Asia. Almost 300 kilometres further South at Jebel Ati near the top of these continental sediments plants of Jurassic age were found, too. It seems that the development of this flora has taken place under a generally warm and dry climate with wet seasons. From the paleophytographical point of view the flora described is of great interest, because it contains coexisting species of the Northern and Southern hemisphere. The Jurassic flora is comparable to that known from adjacent basins in Algeria and Egypt, and to flora known from Virginia.  相似文献   

17.
The Shah Kuh Formation of the Khur area (Central Iran) consists of predominantly micritic, thick-bedded shallow-water carbonates, which are rich in orbitolinid foraminifera and rudists. It represents a late(est) Barremian – Early Aptian carbonate platform and overlies Upper Jurassic – Barremian continental and marginal marine sediments (Chah Palang and Noqreh formations); it is overlain by basinal deposits of the Upper Aptian – Upper Albian Bazyab Formation. The lithofacies changes at both, the base and top of the Shah Kuh Formation are gradational, showing that the formation is part of an overall transgressive sedimentary megacycle, and that the formational boundaries are potentially diachronous on larger distances. Analyses of facies and stratal geometries suggest that the Shah Kuh carbonate system started as a narrow, high-energy shelf that developed into a large-scale, flat-topped rudist platform without marginal rim or steep slope. The Shah Kuh Platform is part of a large depositional system of epeiric shallow-water carbonates that characterized large parts of present-day Iran during Late Barremian – Aptian times (“Orbitolina limestones” of NW and Central Iran, the Alborz and the Koppeh Dagh). Their biofacies is very similar to contemporaneous deposits from the western Tethys and eastern Arabia, and they form an important, hitherto poorly known component of the Tethyan warm-water carbonate platform belt.  相似文献   

18.
Uranium series dates on bone from the Isimila Prehistoric Site, Tanzania, indicate that this East African Acheulian site may be older than originally estimated. They raise the possibility that the Middle Pleistocene sediments containing Acheulian occurrences span a longer range of time than had been supposed. This could add to the plausibility of a contention by Hansen and Keller that differences between artifacts in the uppermost Acheulian horizon and in lower-lying beds are primarily a reflection of change through time rather than a result of different human activities.A summary of the artifact content and associations of the several archeological stratigraphic units is given, and, although a sort of “developmental sequence” can be seen, the existence of discrepant occurrences suggests that an interpretation of directional change as a “function of time” does not, in fact, well accommodate the evidence.Quantitative changes in artifact class proportions in aggregates seem just as likely to be related to local exploitation potentials for early man which were produced during the process of basin in-filling, while observed qualitative differences in the lower-lying horizons may be due to samples biased because of limited exposures which are restricted to a single sedimentary environment.  相似文献   

19.
The partial carapace of a “macrobaenid” turtle from the Geoncheonri Formation (Lower Cretaceous) in Gyeongsan City near Daegu Metropolian City, South Korea, is referred to Kirgizemys Nessov and Khozsatzky, 1973. The specimen most closely resembles K. exaratus Nessov and Khozsatzky, 1973 from the Albian of Kyrgyzstan. It is the first turtle fossil described from the Mesozoic sediments on the Korean peninsula.  相似文献   

20.
Research carried out on lacustrine Gastropods of Neogene age from sediments of continental faciès (“molasse”) on some Aegean islands (Kos, Rhodes, Naxos, Eremonisia, Makares, Paros, Anaphi, Crete, Samos, Chios, Euboea) led to the conclusion that certain strata are much older than hitherto suggested. During Serravallian and Tortonian times limnic and fluviatile sediments must have been by far more widespread in the Aegean Region than earlier supposed. It can be shown furthermore that most of these older series of sediments south of the ?Medean Christalline Belt” and on the top of the ?Attic-Cycladic Complex” are allochthonous or parautochthonous. They obviously became involved in movements of the “Central” and “Western Hellenic Nappes” as defined byJacobshagen et al., 1978. Similar events in the Northern Apennines are known by the catchword “Loiano-Effect”. During Tortonian times decoupling occured within these nappe piles. Subunits consisting in part of Neogene strata, sometimes still connected to their ophiolitic basement, started to move separately into northern (Cyclades) or southern (Kos-Island) directions. A compounded nappe, in this paper called “Aegean Nappe”, consisting of parts of the “Pelagonian Nappe”, the “Ophiolite Nappe” and slices of the “molasse”-series emerged. Locally marine sediments of Lower to Middle Miocene age suggested to be autochthonous were overthrust or cut up in front of the moving nappe (Kos, Rhodes). On some islands of the Cyclades (Naxos, Paros, Eremonisia, Makares, Mykonos) remnants of the “Aegean Nappe” rest on top of the “Lower Unit” of the “Attic-Cycladic complex” as defined byAltherr et al., 1979, and are equivalent to the “Upper Unit” of authors. The paroxysm of those decouplings happened during the upper Tortonian (8–10 Ma); it presumably influenced sedimentary processes of that time on Crete. The view is taken that the movements of nappes were caused by local crustal rising and, hence, gravity controlled.  相似文献   

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