Morphology and sedimentary systems in the Central Bransfield Basin, Antarctic Peninsula: sedimentary dynamics from shelf to basin     

Marga García  Gemma Ercilla  Belén Alonso 《Basin Research》2009,21(3):295-314

A detailed regional characterization of the physiography, morphology and sedimentary systems of the Central Bransfield Basin (CBB) was carried out using swath bathymetry and high‐ and very high‐resolution seismic profiles. The basin margins show continental shelves with numerous glacial troughs, and continental slopes where relatively wide and flat slope platforms represent the middle domain in an atypical physiographic scenario in glaciated margins. Although the CBB is tectonically active, most of the morphologic features are sedimentary in origin, and can be classified into four sedimentary systems: (1) glacial‐glaciomarine, composed of erosional surfaces, glacial troughs, furrows and draping sheets; (2) slope‐basin, formed by trough mouth fans, slope aprons, the Gebra‐Magia instability complex and turbidity systems; (3) seabed fluid outflow system composed of pockmark fields; and (4) contourite, composed of drifts and moats. The sedimentary systems show a clear zonation from shelf to basin and their dynamics reflects the complex interplay among glacial, glaciomarine, marine and oceanographic processes involved in the entire shelf‐to‐basin sediment distribution. The CBB morphology is primarily controlled by glacial/interglacial cyclicity and physiography and to a lesser extent by tectonics and oceanography. These factors have affected the South Shetland Islands (SSI) and Antarctic Peninsula (AP) margins differently, creating a relatively starved SSI margin and a more constructional AP margin. They have also created two entire sediment‐dispersal domains: the shelf‐to‐slope, which records the glaciation history of the CBB; and the lower slope‐to‐basin, which records the imprint of local factors. This study provides a ‘source‐to‐sink’ sedimentary scheme for glaciated margins, which may be applied to the basin research in other margins, based on the characterization of sedimentary systems, their boundaries and the linkages among them. This approach proves to be adequate for the identification of global and local factors governing the CBB and may therefore be applied to other study areas.  相似文献   

A tephra-based correlation of marine and terrestrial records of MIS 11c from Britain and the North Atlantic     

Ian Candy  Gareth Tye  Peter Coxon  Mark Hardiman  Ian Matthews  Adrian Palmer 《第四纪科学杂志》2021,36(7):1149-1161

Resolving marine and terrestrial records of glacial and interglacial stages has long been a challenge for Quaternary studies. We present a tephra-based correlation for MIS 11c of a North Atlantic marine core and a British terrestrial record (Marks Tey). A varved chronology is presented for the annually laminated lake sequence at Marks Tey and the proxy data from this site are plotted on an annual timescale for the first time. This record shows clear evidence for an abrupt cold event and corresponding ecological and landscape response. Varve counting shows that the abrupt event lasted for ca 185 a but the impact on the landscape persisted for ca 560 a. The co-occurrence of a single tephra layer in Marks Tey and ODP 980 allows these two records to be correlated. Furthermore, this synchronisation shows that the abrupt cold event in Marks Tey was coincident with a centennial-scale cold event in ODP 980, as evidenced by an increase in Neogloboquadrina pachyderma (s) percentage. In both ODP 980 and Marks Tey the age of this abrupt event was ca 414 500 a indicating that, at this point in MIS 11c, a widespread cold event occurred in the northeastern Atlantic and the British Isles.  相似文献   

Nearshore circulation over transverse bar and rip morphology with oblique wave forcing     

Chris Houser  Ryan Arnott  Steffen Ulzhöfer  Gemma Barrett 《地球表面变化过程与地形》2013,38(11):1269-1279

There is a paucity of field data to describe the transition in nearshore circulation between alongshore, meandering and rip current systems. A combination of in‐situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at Pensacola Beach, Florida in the presence of relatively low energy oblique waves. Current speeds vary in response to the relative wave height ratio (H_s/h), which defines the degree and extent of breaking over the shoal. In the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves. As waves begin to break across the shoal (0.2<H_s/ h<0.5) the nearshore circulation is characterized by a meandering alongshore current. As conditions became more dissipative (H_s/h>0.5), the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone. The increase in wave dissipation is associated with an increase in very low frequency (VLF) variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow. The unsteady nature of the nearshore circulation is responsible for 55% of all surf zone exits under these more dissipative conditions. In contrast, only 29% of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore‐meandering current. While the currents had a low velocity (maximum of ~0.4 m s^‐1) and would not pose a significant hazard to the average swimmer, the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low‐energy rip circulation systems under oblique wave forcing. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The contribution of marine geology to the knowledge of marine coastal environment off the Campania region (southern Italy): the geological map n. 502 “Agropoli” (southern Campania)     

Gemma Aiello  Ennio Marsella 《Marine Geophysical Researches》2013,34(2):89-113

The marine geological map n. 502 “Agropoli”, located offshore the Cilento Promontory, southern Italy, is here described and the regional geology interpreted, particularly referring to water depths between the 30 and 200 m isobaths. The geologic map has been constructed in the frame of a research program financed by the National Geological Survey of Italy (CARG Project), finalized to the construction of up-to-date cartography of the Campania region. Geological and geophysical data on the continental shelf and slope offshore of the Southern Campania region have been collected in the study area, bounded northwards by the Salerno Gulf and southwards by the Policastro Gulf. A high resolution multibeam bathymetry allowed for the construction of a marine digital elevation map; sidescan sonar profiles also have been collected and interpreted. The latter, merged to the bathymetry, have represented the base for the marine geologic cartography. The integrated geologic interpretation of seismic, bathymetric and sidescan sonar data has been calibrated by sea-bottom samples. The morpho-structures and the seismic sequences overlying the outcrops of acoustic basement reported in the cartographic representation have been studied in detail using single-channel seismics. The interpretation of seismic profiles has been a support for the reconstruction of the stratigraphic and structural setting of the Quaternary continental shelf successions and the outcrops of rocky acoustic basement in correspondence to the Licosa Cape morpho-structural high. These areas result from the seaward prolongation of the stratigraphic and structural units, widely cropping out in the surrounding emerged sector of the Cilento Promontory. The cartographic approach is based on the recognition of laterally coeval depositional systems, interpreted in the frame of the system tracts of the Late Quaternary depositional sequence. We present evidence of now subaqueous terraces inferred to be palaeoshorelines representing past sea-level positions and tentatively correlated these to oxygen isotopic stratigraphy.  相似文献   

Perceptual models of uncertainty for socio-hydrological systems: a flood risk change example   总被引：2，自引：2，他引：0  

Ida K. Westerberg  Keith J. Beven  Gemma Coxon  Tobias Krueger 《水文科学杂志》2017,62(11):1705-1713

Characterizing, understanding and better estimating uncertainties are key concerns for drawing robust conclusions when analyzing changing socio-hydrological systems. Here we suggest developing a perceptual model of uncertainty that is complementary to the perceptual model of the socio-hydrological system and we provide an example application to flood risk change analysis. Such a perceptual model aims to make all relevant uncertainty sources – and different perceptions thereof – explicit in a structured way. It is a first step to assessing uncertainty in system outcomes that can help to prioritize research efforts and to structure dialogue and communication about uncertainty in interdisciplinary work.  相似文献