Periods Of Low Sea Level Research Articles

Human Pleistocene adaptations in the tropical island Pacific: recent evidence from New Ireland, a Greater Australian outlier

The late Pleistocene colonization of Greater Australia by humans by c. 40,0130 b.p. is now generally accepted. This landmass, which comprised at periods of lower sea levels Tasmania, Australia and Papua New Guinea, has now produced sites with rich and diverse sequences extending towards or now mainly beyond 30,000 b.p., in the present arid country of western New South Wales (Barbetti & Allen 1972), in southwest Western Australia (Pearce & Barbetti 1981), in the Papua New Guinea Highlands (Gillieson & Mountain 1983), and recently even in Tasmania (Cosgrove 1989).Prior to 1985, with the exception of an 11,000 b.p. date for occupation in Misisjl Cave on New Britain (Specht et al. 1981), the tropical lowlands of Papua New Guinea and its attendant nearer Melanesian island chain had remained a blank on the region’s map of Pleistocene human expansion.

Archosaurian reptiles with Gondwanan affinities in the Upper Cretaceous of Europe

ABSTRACTThe Late Cretaceous (mainly Campanian and Maastrichtian) non‐marine vertebrate faunas of Europe contain archosaurian reptiles which belong to groups otherwise known mainly or only from the southern ('Gondwanan') continents. They include titanosaurid sauropods, abelisaurid theropods, and trematochampsid crocodilians. The occurrence of these forms together with others of ‘Asiamerican’ affinities gives the Late Cretaceous vertebrate faunas of Europe a peculiar composition, which makes them clearly different from the well‐known faunas from western North America and Central Asia. The Gondwanan dinosaurs and crocodilians from Europe provide evidence of faunal interchange across the Tethys Sea during the Cretaceous, possibly via the Alboran plate, or the Apulian plate, which may have functioned as ‘stepping‐stones', especially during periods of low sea level.

Pipeline route selection in an iceberg‐scoured seabed

Abstract This paper deals with the geotechnical considerations in selecting a pipeline route through a seabed subjected to iceberg scouring. Most of the continental shelf of the east coast of Canada has been subjected to ice scouring. Some of the scours are relict, having occurred during periods of lower sea levels, but modern scours can be found from the Grand Banks north to the Arctic. Scours are sporadic on the Grand Banks, where they range in depth from about 1.5 m to 2 m, whereas in places off the coast of Labrador the entire seabed has been reworked by ice scouring and the depths of the scours are greater. Localized pits created by icebergs impacting the seabed are also found over most of the continental shelf area. These are typically less than 5 m deep, but they have been documented up to 10 m in depth. Models that predict ice scour depths have been published over the past several years. These models all assume that the ice is much stronger than the seabed soils. Recent evidence and analysis, however, indicate that ice keels may fail while scouring the seabed, with the result that existing models are not adequate and may tend to overpredict scour depth. This paper deals with the various interacting forces during the scouring process in sloping seabed conditions and includes discussions of the loads that are transmitted to the seabed and the considerations required for constructing and operating pipelines safely in ice‐scoured topography.

Paleogeographical evolution of the Mahakam delta in Kalimantan, Indonesia during the quaternary and late pliocene

The Mahakam delta, which covers about 1200 km 2 on the eastern coast of Kalimantan in Indonesia, is situated at the mouth of the Mahakam river which drains a basin of about 75,000 km 2 and is presently covered with dense humid evergreen rain forest. The MISEDOR well, drilled in the delta to a depth of 638.56 m, reaches the upper Pliocene. The records of three stratigraphic markers — Phyllocladus hypophyllus, Podocarpus imbricatus, and Stenochlaena laurifolia —mmake it possible to locate the Plio-Pleistocene boundary at a depth of about 400 m. This limit is confirmed by the contrast between the uniformity of the paleogeographical features below this depth and the great variability of the environmental conditions indicated above it. The paleoenvironmental reconstruction is based on the good match between the present vegetation of the delta and its palynological record from marine and onshore surface samples. Several aspects of the paleoenvironment were noted in this study. First, a general uniformity, with a noteworthy continuance of deltaic conditions, the study site always remaining located in the subaerial or shallow parts of the delta. Second, there was a general variability in the detail of the paleoenvironments. Finally, during the upper Pliocene and Quaternary, relative sea level changes as deduced from MISEDOR data fit with those on a worldwide scale. Climatic changes appear to have left little mark on the local vegetation. A better record could have been expected from changes in the more climate-sensitive hinterland mountain vegetation, but its representatives are only minimally present as airborne grains in the spectra of the Mahakam delta. Indications of climatic changes do occur, however, in several periods of low sea level and accompanying rise of detritus, when high frequencies of grass pollen, probably due to savanna development, suggest a response to colder climatic conditions.

Submarine fans: Characteristics, models, classification, and reservoir potential

Submarine-fan sequences are important hydrocarbon reservoirs throughout the world. Submarine-fan sequences may be interpreted from bed-thickness trends, turbidite facies associations, log motifs, and seismic-reflection profiles. Turbidites occurring predominantly in channels and lobes (or sheet sands) constitute the major portion of submarine-fan sequences. Thinning- and thickening-upward trends are suggestive of channel and lobe deposition, respectively. Mounded seismic reflections are commonly indicative of lower-fan depositional lobes. Fan models are discussed in terms of modern and ancient fans, attached and detached lobes, highly efficient and poorly efficient systems, and transverse and longitudinal fans. In general, depositional lobes are considered to be attached to feeder channels. Submarine fans can be classified into four types based on their tectonic settings: (1) immature passive-margin fans (North Sea type); (2) mature passive-margin fans (Atlantic type); (3) active-margin fans (Pacific type); and (4) mixed-setting fans. Immature passive-margin fans (e.g., Balder, North Sea), and active-margin fans (e.g., Navy, Pacific Ocean) are usually small, sand-rich, and possess well developed lobes. Mature passive-margin fans (e.g., Amazon, Atlantic Ocean) are large, mud-rich, and do not develop typical lobes. However, sheet sands are common in the lower-fan regions of mature passive-margin fans. Mixed-setting fans display characteristics of either Atlantic type (e.g., Bengal, Bay of Bengal), or Pacific type (Orinoco, Caribbean), or both. Conventional channel-lobe models may not be applicable to fans associated with mature passive margins. Submarine fans develop primarily during periods of low sea level on both active- and passive-margin settings. Consequently, hydrocarbon-bearing fan sequences are associated generally with global lowstands of sea level. Channel-fill sandstones in most tectonic settings are potential reservoirs. Lobes exhibit the most favorable reservoir quality in terms of sand content, lateral continuity, and porosity development. Lower-fan sheet sands may also make good reservoirs. Quartz-rich sandstones of mature passive-margin fans are most likely to preserve depositional porosity, whereas lithic sandstones of active-margin fans may not.

Plio-Pleistocene sedimentation on the Walvis Ridge, Southeast Atlantic (DSDP Leg 75, Site 532) — Influence of surface currents, carbonate dissolution and climate

An investigation of the quantitative composition of the coarse (> 40 μm) and clay (<2 μm) fraction of HPC 532, DSDP Leg 75, in 1300 m water depth on the eastern Walvis Ridge off Southwest Africa yielded the following results: 1. (1) The sediments reflect a complete Latest Miocene to Recent depositional history. Sedimentation rates vary between 2.3 and 7.8 cm 10 −3 years. 2. (2) Preservation of calcium carbonate is subject to strong variations: short-term (<100,000 years) and long-term (about 1 m.y.) cycles in carbonate dissolution have been observed, with strongest dissolution occurring during periods of lowered sea level. 3. (3) Upwelling influence from the near-coastal upwelling centre has been detected by means of the opal content: interglacial periods show high opal contents, because the Benguela Current turned westward at about 20°S and carried opal-laden upwelled water to the west. Sediments from glacial periods, however, show opal minima. Besides these short-term cyclic variations in opal content, long-term cycles have been found, with maximum upwelling influence in the latest Pliocene/early Quaternary. 4. (4) Each CaCO 3 dissolution minimum (maximum) is correlated with an opal maximum (minimum) throughout the sediment sequence. 5. (5) The oceanographic system off southwest Africa remained essentially unchanged since the latest Miocene: sea level rose and fell periodically on a small and on a large scale, and the Benguela Current flowed southeast-northwest and turned to the west at the latitude of Site 532 during interglacial periods, when sea level was high. 6. (6) The climate in the near-coastal area of southwest Africa in the latitude of Site 532 has probably been arid throughout the investigated period.

Submerged rock platforms on the continental shelf west of Sula Sgeir

Synopsis Two major submerged erosion platforms have been identified on the north-western Scottish continental shelf to the west of Sula Sgeir. The lower, at c. −155 m, is up to 6 km broad but can only be traced for c. 15 km laterally. The upper platform, at c. −125 m, varies between 0.8 and 3 km in width and has been traced for over 50 km in a NNE–SSW direction. The platforms are attributed to marine erosion during periods of low sea level, each platform perhaps being subjected to erosion on more than one occasion. The −155 m platform is apparently the older and was formed prior to extensive glacial erosion of the shelf. It is assigned a Late Tertiary or Early Pleistocene age. The −125 m platform post-dates glaciation of the middle shelf but in major part pre-dates the Late Devensian glacial maximum. It is assigned a Middle to Late Pleistocene age. The island of Sula Sgeir and the neighbouring sea stacks were formed when sea level was c. −40 m relative to that of the present.

Depositional Environments and Diagenesis of Lower Pennsylvanian Caddo Formation, Stephens County, Texas: ABSTRACT

Since its discovery in 1916, the Lower Pennsylvanian Caddo limestone has been one of the most prolific producing intervals in the central Texas region. Favorable reservoir characteristics, with porosities from 9 to 24% and permeabilities from 0.1 to 1,000 md in the pay interval, have enabled many oil companies to initiate successful secondary recovery waterflood projects. Since its discovery, more than 200 million bbl of oil has been recovered from this formation in Stephens County alone. The Caddo reef trend developed during the Early Pennsylvanian, generally along the axis of the Bend flexure. Close examination of whole core and thin sections reveals the formation to be a series of small reef mounds characterized by wackestones. The wackestones consist of green algae, brachiopods, and some rugose corals, which are found on the leeward side (back reef). This sequence is commonly found in the top segment of the Caddo. Deeper into the formation the sequence grades into a packstone/wackestone, characteristic of an oceanward margin (fore reef), and is distinguished by red algae, foraminifera (fusulinids and miliolids), and crinoid hash. The basal sequence is a series of alternating lime mudstones and shales that are heavily silicified. Diagenesis is the key to reservoir rockmore » quality. Moldic porosity was created through dissolution of organisms composed of low magnesium calcite (brachiopods) and aragonite (corals) during periods of subaerial exposure of the back reef. During this period of low sea level, fore-reef sediments were partly cemented by CaCO{sub 3} and were not subaerially exposed. Therefore, moldic porosity was not created in the fore-reef sediments. Porosity in the fore reef was later created in places by dissolution of this cement. Secondary dolomite was later precipitated along pore walls, and in places it occluded porosity in the pore spaces.« less

Plio-Pleistocene raised channel systems of the western Sharqiya (Wahiba), Oman

Summary Extensive alluvial fans bounding the western edge of the Sharqiya (or Wahiba) Sands are characterized by complex palaeochannel systems now forming a series of superimposed gravel ridges. The oldest, most extensive fan system is crossed by numerous sinuous, superimposed palaeochannel courses comprising highly weathered, chert-rich gravels cemented by clear crystalline calcite. Many of these old fan sediments have been chemically altered to depths of over 200 m to form a pink dolomitic clayey deposit here termed barzamanite. The formation of this calcrete-like deposit was probably associated with rising water tables during long-term fan growth. The younger, more limited fan deposit, by contrast, comprises thin, coarse-grained, broad spreads and terrace veneers of weakly cemented ophiolitic gravels. The fans have been subject to entrenchment and deflation, resulting in extensive land-surface lowering and the exhumation of buried palaeochannels. Although no dates are yet available, the older channel systems are likely to date from more humid phases during the Pliocene-Early Pleistocene, whereas the younger, terraced deposits, and the period of subsequent channel exhumation, may date from semi-arid periods of lower sea level during the Pleistocene.

Character Displacement and Biogeography of the Pygmy Shrew in Northern Europe

Two ecologically similar shrew species, Sorex minutus and S. araneus, were studied in sympatry on the Swedish mainland and in allopatry on Irelend, the Outer Hebrides, and two islands in the Baltic Sea, in order to examine competitive character displacement in skull morphology. Eight skull measures were compared on a total of 228 specimens. S. minutus had significantly smaller jaws in sympatry. It was concluded that this difference is a result of interspecific competition; alternative explanations were tested and rejected. S. araneus did not exhibit morphological differences between sympatric and allopatric populations. The difference in response of the two species, it was concluded, is due to their different relative abundance in sympatry, which implies an asymmetry in their competitive effect on one another. It is suggested that late—Quaternary zoogeographic patterns during periods of low sea level can explain the present distribution of allopatric pygmy shrew populations.

Affinities and Recent History of the Avifauna of Trinidad and Tobago

Trinidad was last connected to the South American mainland about 1 1 ,000 years ago. Tobago has been separated for much longer (probably at least 2 million years), but during periods of lowered sea level, the water gap between Tobago and Trinidad may have been reduced to as little as 5 km. The avifauna of the two islands, excluding species that are widely distributed on the South American main- land, can be divided into four distributional categories, Andean, Northern Venezue- lan, Caribbean, and Amazonian-Guianan. The Andean element is very closely related to the montane avifauna of the Cordillera de Caripe and Paria peninsula of north- eastern Venezuela, more so than the latter is to the avifauna of the mountains farther west in Venezuela. The northern Venezuelan and Caribbean elements are small and undifferentiated, and their presence in the islands would be expected on the basis of their present distributions in adjacent areas. The Amazonian-Guianan element is more puzzling, as several of its members are geographically very isolated from the mainland populations; the degree of subspecific differentiation in this group is higher than that in the Andean element. The presence of the Amazonian-Guianan element in Trinidad and Tobago indicates a former extension of the Amazonian-Guianan avifauna up the east coast of Venezuela at a time when the sea level was low. In spite of the fact that Tobago has been an island for about 200 times as long as Trinidad, its avifauna is only slightly more differentiated from that of the mainland. The most likely explanation of this apparent anomaly is that Tobago was so close to the mainland during periods of lowered sea level that it was effectively in biotic contact.

Late Tertiary Evolution of Salisbury Embayment: ABSTRACT

Upper Tertiary beds of the Chesapeake Group deposited in the Salisbury embayment preserve a detailed record of periodic sedimentation that is punctuated by unconformities and diastems. Correlation of these Miocene and Pliocene units is possible by the use of various microfossil and macrofossil groups. The unconformities that separate the beds are easily recognized and regionally traceable. Detailed analysis of the beds indicates that most formations are the product of one or more marine transgressions. One transgression is represented by the Old Church Formation (upper Oligocene/lower Miocene), six by the Calvert Formation (lower and lower middle Miocene), two by the Choptank Formation (middle middle Miocene), three by the St. Marys Formation (upper middle Miocene), two by the Eastover Formation (upper Miocene), three by the Yorktown Formation (middle and upper Pliocene), and one by the Chowan River Formation (upper Pliocene). In this sequence, on the basis of mollusk data, a temperature chart can be constructed that reflects oscillation within the cool-temperate to subtropical range. The relative stability of the temperatures and the continuing submergence of the Salisbury embayment allowed a richly fossiliferous, diverse, essentially temperate molluscan assemblage to form. This nearly endemic, perched fauna was decimated during the period of low sea level after the Yorktown transgression and before the Chowan River transgression. The result was a large-scale extinction at the generic as well as specific level because of low temperatures and the loss of habitat due to the low sea level stand. Thus, the beds of the Chesapeake Group record a detailed history of regional and local tectonism, and global and local sea level fluctuations. End_of_Article - Last_Page 1451------------

Cenozoic and Upper Cretaceous Sedimentary Facies of New Jersey Continental Slope and Rise: ABSTRACT

End_Page 296------------------------------Recent Deep Sea Drilling Project (DSDP) coring along U.S. Geological Survey (USGS) multichannel seismic lines 25 and 35 provides direct sampling of the depositional sequences that constitute the lower continental slope and upper continental rise of New Jersey. The sedimentary record from four core sites, integrated with a closely spaced grid of multi-channel seismic profiles, reveals 12 depositional sequences in the upper Campanian to Quaternary section that are bounded by erosional unconformities. Equivalent unconformity-bound depositional sequences are present on the contiguous continental shelf and upper slope; most sequences have counterparts in the Vail depositional model. Of particular interest is a complicated, stacked series of buried erosional channels dramatically displayed n seismic lines paralleling the depositional strike of the upper continental rise. The channels, which cut the upper surface of nearly every depositional sequence, probably formed during periods of low sea level. Channels on the lower Eocene surface display the greatest physiographic relief. Integration of seismic and bore-hole data suggests alternative correlations for several stratigraphically significant regional reflectors, such as A*, Ac, and Au. End_of_Article - Last_Page 297------------

The Dreamtime animals: extinct megafauna in Arnhem Land rock art

Archaeology in OceaniaVolume 19, Issue 3 p. 105-116 Article The Dreamtime animals: extinct megafauna in Arnhem Land rock art Peter Murray, Peter Murray Northern Territory Museum of Arts and Sciences, DarwinSearch for more papers by this authorGeorge Chaloupka, George Chaloupka Northern Territory Museum of Arts and Sciences, DarwinSearch for more papers by this author Peter Murray, Peter Murray Northern Territory Museum of Arts and Sciences, DarwinSearch for more papers by this authorGeorge Chaloupka, George Chaloupka Northern Territory Museum of Arts and Sciences, DarwinSearch for more papers by this author First published: October 1984 https://doi.org/10.1002/j.1834-4453.1984.tb00089.xCitations: 23AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume19, Issue3October 1984Pages 105-116 RelatedInformation

Surficial sediments in the Norwegian sector of the North Sea between 60°30′ and 62°N

Based on grain-size distribution and sea floor photographs, the sea bed sediments between Bergen and Måløy have been divided into four groups: (A) sand with coarse material on the northern part of the North Sea Plateau and the Måløy Plateau; (B) very well sorted sand on the southern part of the North Sea Plateau and the upper part of the western slope of the Norwegian Trench; (C) silty, clayey sand in lower part of the slopes; (D) silty, sandy clay in the central part of the Norwegian Trench. Large local variations are found in the group A sediments, on the Måløy Plateau partly caused by relict iceberg plough marks. The net deposition after the transition to boreal conditions with Atlantic water about 10,000 yrs ago is mostly between 0 and 30 cm on the northern part of the North Sea Plateau and exceeds 200 cm in the deepest parts of the Norwegian Trench. The total thickness of sediments above assumed overconsolidated material has been mapped based on sparker records. On the northern part of the North Sea Plateau the sediment cover above a supposed wavecut platform is less than 1 m over large areas, while a Late Weichselian coastal unit fringing the plateau consists of up to 40 m of sand and gravel. On the southern part of the plateau and the upper part of the western slope of the Norwegian Trench up to 10–30 m of sediments are found, probably dominated by sand formed by wave and tidal current action during a period of low sea level. In the central part of the trench a total thickness of up to 40 m of clay deposited during varying environments is found. Most of the investigated area is believed to be underlain by a till deposited by a north-northwestward moving ice sheet.

Late Mesozoic and Tertiary sediment supply to the eastern Cape Basin (SE Atlantic) and palaeo-drainage systems in Southwestern Africa

Isopach asymmetry, and sediment component changes in DSDP cores from the SE Atlantic (Orange Basin) support the hypothesis of major drainage system changes in SW Africa during late Cretaceous—Cenozoic time. This involved alternations in the use of the 28°S (modern Orange River) and 31°S (modern Olifants River) exit points across the western escarpment by rivers carrying run-off from the Upper Orange/Vaal catchment areas, as well as radical re-organizations of internal drainage geometry. It is postulated that during late Cretaceous times the 28°S exit was used, with the Middle Orange River following a course in the interior well to the south (up to 150 km) of its modern channel. Sediment discharge rates from this river were relatively high (at least 10 × 10 6 m 3 yr −1), and resulted in rapid advancement of the continental margin sediment prism west of the mouth by large-scale slumping. The Palaeogene Orange/Vaal river exit was via the 31°S escarpment crossing, and during the later part of this period, the Cape Canyon was cut across the continental shelf and slope. A significant reduction in sediment discharge (to 2.0 × 10 6 m 3 yr −1) suggests that the Lower Tertiary climate for SW Africa was drier than that of late Cretaceous times. However, aridity did not commence until late Miocene times, when the Orange/Vaal discharge had switched back to the 28°S exit. Modern sediment discharge rates (6.5 × 10 6 m 3 yr −1) are relatively high and reflect soil erosion caused by agricultural activity. The two major alterations in exit point of the Orange/Vaal (late Cretaceous—early Tertiary, and late Oligocene—early Miocene) are related to periods of low sea level, which promoted river capture adjacent to the western escarpment. An additional factor in the first course change may have been the disruption of the Middle Orange channel by late Cretaceous igneous intrusions. Less important internal reorganizations of the drainage system are postulated in late Miocene—Pleistocene times. Economic implications for offshore diamond distribution are briefly mentioned.

Spring sapping on the lower continental slope, offshore New Jersey

Undersea discharge of ground water during periods of lower sea level may have eroded valleys on part of the lower continental slope, offshore New Jersey. Steep-headed basins, cliffed and terraced walls, and irregular courses of these valleys may have been produced by sapping of exposed near-horizontal Tertiary strata. Joints in Eocene calcareous rocks would have localized ground-water movement. Some karstlike features of the submarine topography and the outcrops suggest that solution of the calcareous rocks also took place.

The Astoria Fan: An elongate type fan

The Astoria Fan, a modern system, is located on a subducting oceanic crust and fills a north-south-trending trench along the Oregon continental margin. Well-developed channels cross the entire fan length; they display classic inner-fan leveed profiles but evolve into distributaries in the midfan area where the gradient decreases sharply. During periods of low sea level, inner- and middle-fan channels funnel sand to distal depositional sites in the outer-fan area where the sand/shale ratios are highest. This pattern of sand displacement and efficiency of transport appears to be characteristic of elongate fans fed by a major river and submarine canyon.

The magnetic susceptibility of continental-shelf sediments, west coast Vancouver Island, Canada

Measurements of magnetic susceptibility of continental-shelf sands off central Vancouver Island revealed two areas of anomalously high values: (1) at the mouths of coastal inlets, suggesting a reworking of glacial and glacio-fluvial sediments; and (2) the outer-shelf downslope from outcropping deformed Tertiary—Pleistocene strata, resulting from the winnowing of these older sediments during periods of lowered sea level. Magnetic susceptibility was highest within the silt and fine sand fractions and lowest in the clay and coarse sand fractions; though because of the grain-size distributions, the fine sand invariably contributed more to the overall sample susceptibility than the other size fractions. Although no apparent relationships were found between magnetic susceptibility and commonly measured grain-size statistics, the highest values were concentrated within a narrow range of size, sorting, skewness and kurtosis. Magnetic susceptibility is a readily determined parameter of marine sediments which can contribute to the interpretation of the depositional history of a region and which may have direct economic applications because of the association between magnetite and heavy-mineral placers.

Interannual Variation in Sea Level near Truk Island—A Bimodal Seasonal Cycle

Abstract The relationship between typical seasonal and interannual variations in Truk sea level is discussed. Periods of extreme low sea level occur episodically, at the same time that El Nino occurs in the eastern tropical Pacific. The episodes have a well-defined phase relative to the seasons and a persistence of one year. They mimic an annual cycle, but they do not repeat every year. Nevertheless, they distort the long-term mean seasonal cycle because they are very energetic. Complex demodulation shows that the amplitude of the annual oscillation is bimodal, the larger amplitude occurring during the episodes of low sea level. The phase is stable only when the amplitude is large. The amplitude and phase of the semiannual oscillation are stable; the range is approximately one-third as large as that of the interannual episodes. Thus, the seasonal cycle is bimodal in the sense that it is dominated by either the annual episode or the stable semiannual oscillation. The climate-related sea-level variation at ...