scholarly journals Seismic stratigraphy of the broad, low-gradient continental shelf of the Palaeo-Agulhas Plain, South Africa

2019 ◽  
Author(s):  
Hayley C Cawthra ◽  
Peter Frenzel ◽  
Annette Hahn ◽  
John Compton ◽  
Lukas Gander ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Tectonic Setting ◽  
Sea Level Change ◽  
Equal Proportion ◽  
Depositional Sequence ◽  
Level Change ◽  
Depositional Processes ◽  
Shelf Sediment ◽  
Stratigraphic Model

The continental shelf of the Palaeo-Agulhas Plain (PAP) is scattered with Pleistocene deposits with subdued topography. Their exaggerated lateral extension is the expression of a flat underlying substrate and availability of accommodation space, depositional processes and response to glacio-eustatic sea-level change have influenced deposition and distribution of these units. We present new results for the upper ~30 m (up to ~200 ka) of the stratigraphic record in this area and show that this shelf offers the opportunity to examine the response of a stable tectonic setting to the effects of sea-level change. This paper presents the results of extensive sub-bottom profiling surveys and chronostratigraphic investigations from marine sediment vibracores. Radiocarbon and Optically stimulated Luminescence dates are integrated into a seismic stratigraphic model composed of twenty Quaternary units, where two depositional sequences are bounded by shelf-wide unconformities. The upper sequence was cored where Pleistocene deposits were observed to be close to the seafloor and are draped in a thin veneer of marine shelf sediment and allow us to describe the environments of deposition of the PAP. The most pervasive stratigraphic pattern in these shelf deposits is made up of the depositional sequence remnant of the Falling Stage Systems Tract (FSST) forced regression from Marine Isotope Stage 5e–2. The other dominant stratigraphic group is the Transgressive Systems Tract (TST) associated with the Postglacial Marine Transgression. Surprisingly, the TST makes up an almost equal proportion of deposits in both sequences in the sedimentological record as the FSST, despite the shorter temporal span of the TST. The sub-bottom profiles were acquired on regional surveys extending from the Breede River in the west to Plettenberg Bay in the east, and to a maximum depth of 110 m below Mean Sea Level, with the exception of one ~200 m deep shelf-edge profile.

scholarly journals Seismic stratigraphy of the broad, low-gradient continental shelf of the Palaeo-Agulhas Plain, South Africa

2019 ◽  
Author(s):  
Hayley C Cawthra ◽  
Peter Frenzel ◽  
Annette Hahn ◽  
John Compton ◽  
Lukas Gander ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Tectonic Setting ◽  
Sea Level Change ◽  
Equal Proportion ◽  
Depositional Sequence ◽  
Level Change ◽  
Depositional Processes ◽  
Shelf Sediment ◽  
Stratigraphic Model

The continental shelf of the Palaeo-Agulhas Plain (PAP) is scattered with Pleistocene deposits with subdued topography. Their exaggerated lateral extension is the expression of a flat underlying substrate and availability of accommodation space, depositional processes and response to glacio-eustatic sea-level change have influenced deposition and distribution of these units. We present new results for the upper ~30 m (up to ~200 ka) of the stratigraphic record in this area and show that this shelf offers the opportunity to examine the response of a stable tectonic setting to the effects of sea-level change. This paper presents the results of extensive sub-bottom profiling surveys and chronostratigraphic investigations from marine sediment vibracores. Radiocarbon and Optically stimulated Luminescence dates are integrated into a seismic stratigraphic model composed of twenty Quaternary units, where two depositional sequences are bounded by shelf-wide unconformities. The upper sequence was cored where Pleistocene deposits were observed to be close to the seafloor and are draped in a thin veneer of marine shelf sediment and allow us to describe the environments of deposition of the PAP. The most pervasive stratigraphic pattern in these shelf deposits is made up of the depositional sequence remnant of the Falling Stage Systems Tract (FSST) forced regression from Marine Isotope Stage 5e–2. The other dominant stratigraphic group is the Transgressive Systems Tract (TST) associated with the Postglacial Marine Transgression. Surprisingly, the TST makes up an almost equal proportion of deposits in both sequences in the sedimentological record as the FSST, despite the shorter temporal span of the TST. The sub-bottom profiles were acquired on regional surveys extending from the Breede River in the west to Plettenberg Bay in the east, and to a maximum depth of 110 m below Mean Sea Level, with the exception of one ~200 m deep shelf-edge profile.

A standardized database of Last Interglacial sea-level indicators in southeast Asia: Records from coral reef terraces in a tectonically complex region

2021 ◽  
Author(s):  
Kathrine Maxwell ◽  
Hildegard Westphal ◽  
Alessio Rovere
Keyword(s):  
Coral Reef ◽  
Southeast Asia ◽  
Sea Level ◽  
Tectonic Setting ◽  
Sea Level Change ◽  
The Philippines ◽  
Sea Level Changes ◽  
Last Interglacial ◽  
Level Change ◽  
Se Asia

<p>The Last Interglacial (LIG), as well as other warmer periods in the Earth’s geologic history, provides an analogue for predicted warming conditions in the near future. Analysis of sea-level indicators during this period is important in constraining regional drivers of relative sea-level change (RSL) and in modeling future trajectories of sea-level rise. In southeast Asia, several studies have been done to examine LIG sea-level indicators such as coral reef terraces and tidal notches. A synthesis of the state-of-the-art of the LIG RSL indicators in the region, meanwhile, has yet to be done. We reviewed over 50 published works on the LIG RSL indicators in southeast Asia and used the framework of the World Atlas of Last Interglacial Shorelines (WALIS) in building a standardized database of previously published LIG RSL indicators in the region. In total, we identified 38 unique RSL indicators and inserted almost 140 ages in the database. Available data from Indonesia, the Philippines, and East Timor points to variable elevation of sea-level indicators during the LIG highlighting the complex tectonic setting of this region. Variable uplift rates (from as low as 0.02 to as high as 1.1 m/ka) were reported in the study areas echoing various collision and subduction processes influencing these sites. Although several age constraints and elevation measurements have been provided by these studies, more data is still needed to shed more light on the RSL changes in the region. With this effort under the WALIS framework, we hope to identify gaps in the LIG RSL indicators literature in SE Asia and recognize potential areas that can be visited for future work. We also hope that this initiative will help us further understand the different drivers of past sea-level changes in SE Asia and will provide inputs for projections of sea-level change in the future.</p>

Quaternary sea-level change on the continental shelf of Hong Kong

1997 ◽  
Vol 154 (6) ◽  
pp. 1031-1038 ◽  
Author(s):  
J. A. FYFE ◽  
I. C. SELBY ◽  
R. SHAW ◽  
J. W. C. JAMES ◽  
C. D. R. EVANS
Keyword(s):  
Hong Kong ◽  
Continental Shelf ◽  
Sea Level ◽  
Sea Level Change ◽  
Level Change

scholarly journals Characteristics of late Miocene Lithofacies - Paleogeography in the Southeast Region of Hanoi Depression

2021 ◽  
Vol 37 (1) ◽  
Author(s):  
Nguyen Thi Phuong Thao ◽  
Tran Nghi ◽  
Dinh Xuan Thanh
Keyword(s):  
Sea Level ◽  
Late Miocene ◽  
Large Scale ◽  
River Mouth ◽  
Sea Level Change ◽  
Alluvial Fan ◽  
Depositional Sequence ◽  
Southeast Region ◽  
Level Change ◽  
Sedimentary Evolution

The characteristics of late Miocene lithofacies in the southeast region of  Hanoi depression have been revealed on the basis of sedimentary evolution in relation to sea level change and tectonic movement. During late Miocene, global sea level change has created one depositional sequence and three sedimentary systems tract. The lowstand systems tract (LST) is characterized by 5 rhythms of  alluvial lithofacies. These rhythms are represented by rough, humoc seismic wave  fields. This environment is not favorable condition for coal formation. The transgressive systems tract (TST) is characterized by 6 transitional lithofacies rhythms. Each lithofacies rhythm consists of 4 facies: the tidal flats sand facies of the bay, the  mud facies of the river mouth lagoon, the coastal marshy mud facies creating coal and the bay greenish-gray clay facies. The pacing process involves changes in the local sea level caused by tectonic lift. Each tectonic subsidence phase takes place at a very slow velocity, so it is compensated for fine-grained sediment creating marshy mud facies to develop mangroves on a large scale. It is a prerequisite to create thick coal seams distributed near the end of each rhythm. A part of highstand systems tract (HST) are eroded due to the improved folding process, creating an angular unconformity boundary with Pliocene-Quaternary sediments. However, after reconstracting of deformated section, it was clear that this systems tract  had only one  rhythm including 2 facies: prodelta mud facies and alluvial fan sandstone facies. Keywords: Lithofacies-paleogeography, sedimentary systems tract, sedimentary rhythm

scholarly journals Indicatives of ancient conditions of sea level stability on the southern Pernambuco continental shelf

2001 ◽  
Vol 28 (2) ◽  
pp. 25 ◽  
Author(s):  
MAXIMILIANO MICHELLI ◽  
TEREZA ARAÚJO ◽  
MAURO MAIDA ◽  
HELENICE VITAL
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Sea Level Change ◽  
Main Interest ◽  
Level Change ◽  
Meandering Channels ◽  
Northeastern Shelf ◽  
Brazilian Northeast ◽  
River Mouths

The continental shelf in southern Pernambuco State (Brazilian Northeast) is characteristically narrow, and breaks around 32km from the actual coastline, in depths of 50 to 60m. The sediments on this shelf are similar in their constitution to the rest of the Brazilian Northeastern shelf, showing a prevailing fraction of coarse carbonatic sands. There is also a significant input of terrigenous material, which may be found mainly up to 20m deep. Regarding it’s geomorphology, Pernambuco’s southern shelf presents a soft slope, with long and smooth surfaces, sometimes crossed by meandering channels which show more frequently next to river mouths. Indicatives of sea level change like the presence of beach rocks and paleochannels occur along the shelf. The main interest of the present work lies on the location and characterization of the submerged beachrocks on the southern portion of Pernambuco State continental shelf. The area was investigated using sonographic techniques. Data analysis allowed to identify indicatives of ancient conditions of sea level stability on the shelf. The first evidence was found at a depth of 20m, where a beachrock of a triangular shape and rounded top with 136m wide and 6m height, was identified. The second evidence was registered at 40 to 50m depth also represented by a beachrock. Geomorphologically this second feature presents a relatively flat top, 209m of width and 4m height. Another structure indicative of sea level change identified was a paleochannel, which started at 30m depth and followed the direction northwest-southeast on the shelf.  

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