Surficial sediments of the western Gulf of Carpentaria, Australia

1987 ◽  
Vol 38 (1) ◽  
pp. 151 ◽  
Author(s):  
MR Jones
Keyword(s):  
Sea Level ◽  
Fluvial Sediments ◽  
Nearshore Zone ◽  
Sediment Sources ◽  
Surficial Sediments ◽  
Fine Grained ◽  
Marginal Areas ◽  
Waves And Tides ◽  
Water Depths ◽  
Low Rate

Modern sedimentation in the Gulf of Carpentaria is confined principally to marginal areas in water depths of less than 50 m. Within this zone, the distribution of sediments is irregular, being controlled by proximity to sediment sources and degree of exposure to waves and tidal activity. This is particularly so in the western gulf, where fluvial sediments supplied to Limmen Bight have been transported by waves and tides northwards beyond that embayment to accumulate in the sheltered environment of Blue Mud Bay. Limmen Bight is exposed to the south-easterlies, which produce sufficient wave action in the nearshore zone to prevent the widespread deposition of fine-grained terrigenous sediments. As a result, relict sand deposits occupy much of the floor of Limmen Bight in areas shallower than about 25 m. In deeper areas, terrigenous muds are deposited at a low rate over relict fluvial and marine sediments. The relict deposits accumulated in continental and nearshore marine environments during low-sea-level periods of the late Pleistocene.

Continental slope sedimentation in the Sheepbed Formation (Neoproterozoic, Windermere Supergroup), Mackenzie Mountains, N.W.T.

1996 ◽  
Vol 33 (6) ◽  
pp. 848-862 ◽  
Author(s):  
R. W. Dalrymple ◽  
G. M. Narbonne
Keyword(s):  
Sea Level ◽  
Continental Slope ◽  
Cold Water ◽  
Passive Margin ◽  
Slope Instability ◽  
Fine Grained ◽  
Windermere Supergroup ◽  
Mackenzie Mountains ◽  
Water Depths

The Sheepbed Formation (Ediacaran) is a 1 km thick, siliciclastic unit that overlies glacial deposits of the Ice Brook Formation and is overlain by carbonates of the Gametrail Formation. Observations in the Mackenzie Mountains indicate that the Sheepbed Formation accumulated in water depths of 1–1.5 km on a passive-margin, continental slope. The lower part of the formation consists predominately of dark mudstone. Fine-grained, turbiditic sandstone becomes more abundant upward, as does the scale and abundance of slope-instability indicators. Mesoscale facies successions (i.e., evidence of channels, lobes, and (or) compensation cycles) are developed in the upper half of the formation. The larger-scale changes are interpreted as reflecting a postglacial sea-level rise, followed by a relative fall and an increase in the rate of deposition. Contourites that may have been formed in response to the circulation of deep, cold water occur in the lowstand deposits. Their presence confirms previous speculation that the proto-Pacific Ocean was initiated at the beginning of Windermere deposition (ca. 780 Ma), not at the start of the Cambrian. The paleoflow direction toward the present-day northwest suggests that this part of Laurentia lay in the northern hemisphere. In situ Ediacaran megafossils are preserved on the soles of sandy turbidites; the deep-water setting indicates that these organisms were not photoautotrophs.

scholarly journals High-frequency sea-level changes recorded in deep-water carbonates of the Upper Cretaceous Dol Formation (island of Brač, Croatia)

2010 ◽  
Vol 61 (1) ◽  
pp. 29-38
Author(s):  
Damir Bucković ◽  
Maja Martinuš ◽  
Duje Kukoč ◽  
Blanka Tešović ◽  
Ivan Gušić
Keyword(s):  
Sea Level ◽  
Deep Water ◽  
High Frequency ◽  
Upper Cretaceous ◽  
Distal Part ◽  
Preferential Orientation ◽  
Sea Level Changes ◽  
Carbonate Production ◽  
Fine Grained ◽  
Platform Margin

High-frequency sea-level changes recorded in deep-water carbonates of the Upper Cretaceous Dol Formation (island of Brač, Croatia)The upper part of the Middle Coniacian/Santonian-Middle Campanian deep-water Dol Formation of the island of Brač is composed of countless fine-grained allodapic intercalations deposited in an intraplatform trough. Within the studied section 13 beds can be distinguished, each defined by its lower part built up of dark grey limestone with abundance of branched, horizontally to subhorizontally oriented burrows, and the upper part, in which the light grey to white limestone contains larger burrows, rarely branched, showing no preferential orientation. The lower, dark grey, intensively bioturbated levels are interpreted as intervals formed during high-frequency sea-level highstands, while the upper, light grey-to-white levels are interpreted as intervals formed during the high-frequency sea-level lowstands. Cyclic alternation of these two intervals within the fine-grained allodapic beds is interpreted as the interaction between the amount of carbonate production on the platform margin and the periodicity and intensity of shedding and deposition in the distal part of toe-of-slope environment, which is governed by Milankovitch-band high frequency sea-level changes.

scholarly journals Arrecifes de arenisca en el Golfo de Salamanca, plataforma continental del Caribe colombiano

2019 ◽  
Vol 48 (1) ◽  
Author(s):  
Sven Zea ◽  
Gladys Bernal ◽  
Gloria López ◽  
Marion Weber ◽  
Rocío Del Pilar García-Urueña
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Petrographic Analysis ◽  
Saline Environments ◽  
Fine Grained ◽  
Lagoon System

In tropical seas there are submerged hard bottoms that harbor corals but that are not coralline in origin. This is the case for the “Banco de las Ánimas” sector in the continental shelf of the Gulf of Salamanca, Colombian Caribbean. In its upper portion (14–16 m in depth), there are low mounds of sandstone blocks and slabs, conforming reefs, colonized by coralline biota and sparse corals. To confirm their lithology an initial petrographic analysis was carried out, which showed the rocks are made up of fine-grained sands, mature in texture, cemented by dolomite. It is proposed that these reefs were formed in a beach–dune–lagoon system during an ancient sea level, similar to the recent coastal bar of Salamanca. In these high-evaporation, supratidal saline environments, they could have been formed as beach rocks or as eolianites, by aragonite cementation, modified later into dolomite. Whether the foundation of the deeper coral formations of the bankis also sandstone or in fact coralline, remains to be determined.

Plant Taphonomy and Paleoecology of Late Pennsylvanian Intramontane Wetlands in the Graissessac-Lodève Basin (Languedoc, France)

Palaios ◽  
2005 ◽  
Vol 20 (3) ◽  
pp. 249-265 ◽  
Author(s):  
CARLES MARTÍN-CLOSAS ◽  
JEAN GALTIER
Keyword(s):  
Detailed Comparison ◽  
Alluvial Fans ◽  
Fluvial Sediments ◽  
Tree Fern ◽  
Massif Central ◽  
Fine Grained ◽  
Tree Ferns ◽  
First Time ◽  
Diverse Plant

Abstract The Late Pennsylvanian Graissessac-Lodève basin is a small, fluvio-palustrine depocenter located in the southern part of the Massif Central (France). A taphonomic and sedimentologic study carried out in this area allows a reconstruction of Late Carboniferous vegetation in an intramontane context. The paleoecology of such limnic settings is poorly known, and this study permits detailed comparison with paralic basins for the first time. The Graissessac peat mires developed in abandoned fluvial channels, in floodplains, and above distal alluvial fans. The vegetation was dominated by monospecific stands of the arborescent lycopsid Sigillaria brardii, whereas the tree fern Psaronius occurred during the later stages of mire accretion. This is in contrast to coeval North American peat mires, which generally were dominated by tree ferns and pteridosperms throughout the mire profile. Stephanian floodplains and distal alluvial fans of the Graissessac-Lodève Basin were devoid of vegetation, with the exception of isolated thickets of sphenopsids that were composed of Calamites and Sphenophyllum. These plants were found growing in situ in the floodplain mudstones as well as in fine-grained sands of secondary channels. Parautochthonous foliage assemblages of ferns and pteridosperms found in floodplain mudstones represent the most diverse plant community. The plants supplying these remains were growing in exposed areas close to floodplains. Large logs attributed to cordaitaleans and monotypic assemblages of large Cordaites leaves were found in fluvial sediments, and suggest that the plants were riparian elements in the basin.

Electrical resistivity tomography investigations in the ufita Valley (southern Italy).

2008 ◽  
Vol 51 (1) ◽  
Author(s):  
A. Giocoli ◽  
C. Magrì ◽  
P. Vannoli ◽  
S. Piscitelli ◽  
E. Rizzo ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Southern Italy ◽  
Normal Fault ◽  
Fluvial Sediments ◽  
Resistivity Tomography ◽  
Fine Grained ◽  
Sedimentary Deposits ◽  
Lacustrine Deposits ◽  
Sedimentary Deposit

Several Electrical Resistivity Tomography (ERT) surveys have been carried out to study the subsurface structural and sedimentary settings of the upper Ufita River valley, and to evaluate their efficiency to distinguish the geological boundary between shallow Quaternary sedimentary deposits and clayey bedrock characterized by moderate resistivity contrast. Five shallow ERTs were carried out across a morphological scarp running at the foot of the northeastern slope of the valley. This valley shoulder is characterized by a set of triangular facets, that some authors associated to the presence of a SW-dipping normal fault. The geological studies allow us to interpret the shallow ERTs results obtaining a resistivity range for each Quaternary sedimentary deposit. The tomographies showed the geometrical relationships of alluvial and slope deposits, having a maximum thickness of 30-40 m, and the morphology of the bedrock. The resistivity range obtained for each sedimentary body has been used for calibrating the tomographic results of one 3560m-long deep ERT carried out across the deeper part of the intramountain depression with an investigation depth of about 170 m. The deep resistivity result highlighted the complex alluvial setting, characterized by alternating fine grained lacustrine deposits and coarser gravelly fluvial sediments.

THE GEOLOGICAL EXPRESSION OF EUSTACY IN THE EARLY TERTIARY OF THE GIPPSLAND BASIN

1976 ◽  
Vol 16 (1) ◽  
pp. 73 ◽  
Author(s):  
A. D. Partridge
Keyword(s):  
Sea Level ◽  
Time Interval ◽  
Marine Environments ◽  
Fine Grained ◽  
Sedimentary Sequences ◽  
Seismic Records ◽  
Basin Morphology ◽  
The Times ◽  
Sequence Boundaries ◽  
Gippsland Basin

In the non-marine to marginal marine environments of the Latrobe Group, distinct sedimentary sequences are recognised on seismic records and these sequences are often expressed in wells by palynological zones, changes in E-log character and lithology.The succession of sequences represents variations in sea level, many of which are interpreted aseustatic. Eustatic falls are represented by unconformities and channel formation along the seaward margin and by hiatuses (frequently with dolomite cementation of underlying sands) landward in deltaic and non-marine sections. Eustatic rises are represented by dinoflagellate ingressions over truncated surfaces at sequence boundaries, followed by outbuilding of deltaic environments at the stillstand towards the end of each cycle.During the Paleocene and Eocene very little sediment was deposited beyond the limits of the marginal marine environments except within channels where the Flounder and Turrum Formations are found. In this time interval they was an overall landward encroachment of successive sequences reflecting an overall sea level rise. The interaction of rising sea level and limited deposition beyond the marginal marine edge meant that successive sequences became more restricted seaward such that within the marine environment the area of non-deposition increased. The surface thus defined, modified locally by channel erosion, constitutes the unconformity at the top of the Latrobe Group. This unconformity surface was preserved when deposition of fine-grained open marine sediments of the Lakes Entrance Formation commenced in the Oligocene.In the Tasman Sea a succession of terrigenous silts and clays present in the Deep Sea Drilling Project (DSDP) Site 283 can be correlated with periods when fine-grained sediments bypassed the Gippsland shelf. The stratigraphy of this site can be interpreted as a record of availability of sediment from the southeastern Australian continental shelf. The times of commencement and termination of stratigraphic units and disconformities at Site 283 correlate with timing of eustatic cycles. Thus the stratigraphy of Site 283 is a record, as is the Latrobe Group, of how eustacy interacts with basin morphology to modify distribution of sediments.

Late Quaternary Evolution of the Northern Aegean Shelf

1989 ◽  
Vol 32 (1) ◽  
pp. 36-50 ◽  
Author(s):  
C. Perissoratis ◽  
D. Mitropoulos
Keyword(s):  
Sea Level ◽  
Late Quaternary ◽  
Shelf Area ◽  
Seismic Profiles ◽  
Fine Grained ◽  
Nestos River ◽  
River Bed ◽  
Ephemeral Lakes ◽  
Evros River ◽  
River Mouths

AbstractA dense network of 3.5 kHz and Uniboom seismic profiles revealed the geological evolution of the Ierissos-Alexandroupolis Shelf area of the northern Aegean during the latest sea-level rise. Near the end of the Pleistocene, ca. 14,000 yr B.P., the sea was at about − 120 m, and almost 5300 km2 of shelf was exposed to subaerial erosion. Two permanet lakes existed in the Ierissos and Kavalla Gulfs, as well as a number of ephemeral lakes scattered throughout the rest of the area. Kavalla Gulf was drained by the Nestos River which joined the Strymon River at the outer Strymonikos Plateau. On the flat Samothraki Plateau were dune fields, marshes, and a number of minor seasonal rivers, while the Evros River flowed east of the plateau. By ca. 13,000 yr B.P. the sea had risen to − 70 m and covered 30% of the previously exposed shelf. The lakes at Ierissos and Strymonikos Gulfs were shallower and the sea approached to within about 5 km of them. Kavalla Gulf and the adjacent eastern Strymonikos Plateau lay 10 m above sea level, while the sea intruded along river mouths at the Samothraki Plateau. During this transgression of the sea river-bed gravels and sands were covered by silts and clays. At the Pleistocene-Holocene transition, ca. 10,500 yr B.P., the sea lay at about − 50 m and in areas of steep slope the coast was close to its present position. At Kavalla Gulf, the sea advanced along the paleochannel of the Nestos River, and the island of Samothraki was separated from the mainland. By ca. 7500 yr B.P. the sea was only 15 m below its present level and the northeastern Aegean shelf assumed nearly its present morphology. The Nestos River changed course to the east and Thassos Island was separated from the mainland. Coarse sediment formed wedges nearshore, whereas fine-grained sediments were distributed widely by current action. In many areas, relict sediments are present.

scholarly journals Early Holocene sea-level changes in Øresund, southern Scandinavia

1969 ◽  
Vol 26 ◽  
pp. 29-32
Author(s):  
Ole Bennike ◽  
Martin Skov Andreasen ◽  
Jørn Bo Jensen ◽  
Matthias Moros ◽  
Nanna Noe-Nygaard
Keyword(s):  
Sea Level ◽  
Sediment Cores ◽  
Early Holocene ◽  
Sea Level Changes ◽  
Relative Sea Level ◽  
Data Set ◽  
The North ◽  
Global Sea Level ◽  
The Baltic ◽  
Water Depths

The Baltic Sea and Kattegat are connected via three straits: Storebælt, Lillebælt and Øresund (Fig. 1). Øresund is the shallowest with a threshold around 7 m deep and increasing water depths to the north (Fig. 2). In the early Holocene, global sea-level rise led to reflooding of Øresund. It started in northern Øresund which was transformed into a fjord. However, so far the timing of the transgression has not been well determined, but sediment cores collected north of the threshold, at water depths of 12 to 20 m, and a new series of radiocarbon ages help to constrain this. As the relative sea level continued to rise, the threshold in Øresund was also flooded, and Øresund became a strait. In mid-Holocene time, the relative sea level rose until it was 4–5 m higher than at present, and low-lying areas around Øresund became small fjords. During the late Holocene, the relative sea level fell again. Part of the data set discussed here was presented by Andreasen (2005).

Benthic Habitats and the Effects of Fishing

2005 ◽  
Keyword(s):  
Large Diameter ◽  
Small Diameter ◽  
Outer Continental Shelf ◽  
Side Scan Sonar ◽  
Fine Grained ◽  
Video Observations ◽  
Red Grouper ◽  
Area North ◽  
Medium Diameter ◽  
Water Depths

<em><strong>Abstract. </strong></em>Side-scan sonar and multibeam data and video observations from six outer continental shelf sites in the northern Gulf of Mexico reveal evidence of three distinct types of seafloor pockmarks. Two sites in the northwestern Gulf (Flower Garden Banks and the Pinnacles area off Mississippi and Alabama) have large-diameter (up to 65 m) pockmarks that are probably generated by the seepage of gas through the sediments. Three sites (Madison–Swanson, Twin Ridges, and an area north of Steamboat Lumps) have small-diameter (less than 2 m) pockmarks that occur in fine-grained sediments at water depths greater than about 100 m. These may be attributed to excavation by fish and other animals. The sixth site, Steamboat Lumps, has medium-diameter (5–25 m) pockmarks in sand with loose cobblesized to boulder-sized rocks. Red grouper <em>Epinephelus morio </em>are associated with these pockmarks and appear to be maintaining and excavating them. Because this area may have experienced freshwater seeps in the past, the pockmarks may be the result of a combination of water seepage followed by fish excavation.

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