SEISMIC CHARACTERISTICS AND SEDIMENTARY DISTRIBUTION ON THE SOUTH SHETLAND ISLANDS CONTINENTAL MARGIN, ANTARCTICA

ABSTRACT. This work consists in characterizing the sedimentary distribution of the South Shetland Islands continental margin, Bransfield Strait, Antarctica, throughthe interpretation and correlation of high-resolution seismic profiles and geological samples. The analysis of echo-characters, seismic amplitudes and their correlationwith the collected samples, revealed five different echo types. Echo types I and II have good seismic resolution and are characterized by continuous sharp bottom echoeswith subparallel reflections. Echoes III and IV are characterized by diffuse and very prolonged bottom echoes with no subbottom reflectors. Echo V is associated withglacial deposits on the upper slope in response to deglaciation and transport of coarse grains in a muddy matrix and is characterized by diffraction hyperbolae. Theecho-characters showed good correlation with geological samples collected along the Bransfield Strait and bays of the King George Island, but the correlation with theseismic amplitude map was not as obvious. Echo I shows medium-high amplitudes and samples within its area of occurrence (AM-02 and AM-14) indicate silty sandand sandy silt, respectively. Echo II presents the lowest seismic amplitudes and the sample collected within its area (AM-17) shows approximately 90% mud content.Echoes III and IV, located on the shallowest portions of South Shetland’s continental margin, demonstrate medium-low amplitude values, and are related to samplesAM-01 and AM-04, both classified as sandy silt with approximately 35%sand. Keywords: Bransfield Strait, echo-characters, high-resolution seismic, sedimentary analysis. RESUMO. O presente trabalho consiste na interpretacao integrada da sismica de alta resolucao e da amostragem geologica, a fim de caracterizar a geologia de fundona regiao da margem continental das Ilhas Shetland do Sul, Estreito de Bransfield, Antartica. A caracterizacao geologica foi realizada atraves da analise de ecocarateres, mapas de amplitude sismica e sua correlacao com os sedimentos coletados. Cinco diferentes ecocarateres foram identificados e classificados. Ecos I e II demonstramboa resolucao e sao caracterizados por ecos continuos e nitidos com reflexoes subparalelas. Ecos III e IV sao caracterizados por ecos difusos, muito prolongados ecom ausencia de refletores subparalelos. O Eco V esta associado a depositos glaciais no talude superior, em respostas ao degelo, e ao transporte de graos grossos em uma matriz mais fina. Alem disso, e caracterizado pela presenca de hiperboles de difracao. Os ecocarateres mostraram boa correlacao com os testemunhos geologicos coletados no Estreito de Bransfield e nas baias da Ilha Rei George, mas nao apresentaram uma relacao obvia com o mapa de amplitudes. O Eco I possui amplitudes medio-altas e as amostras contidas em sua area (AM-02 e AM-14) indicam, respectivamente, um conteudo de areia siltosa e silte arenoso. O Eco II apresenta os menores valores de amplitude com conteudo de lama (argila + silte) de aproximadamente 90%, conforme a amostra AM-17. Os Ecos III e IV, localizados nas porcoes mais rasasda margem continental das Shetland do Sul, demonstram valores medio-baixos de amplitude e se relacionam as amostras AM-01 e AM-04, ambas siltes-arenosos com conteudo de areia de aproximadamente 35%. Palavras-chave: Estreito de Bransfield, ecocarateres, sismica de alta resolucao, analise sedimentar.