Basal and Frontal Accretion Processes versus BSR Characteristics along the Chilean Margin

Abstract

Multichannel seismic reflection data recorded between Itata (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mn>36</mml:mn></mml:mrow><mml:mi>°</mml:mi></mml:msup><mml:mtext>S</mml:mtext></mml:mrow></mml:math>) and Coyhaique offshores (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mn>43</mml:mn></mml:mrow><mml:mi>°</mml:mi></mml:msup><mml:mtext>S</mml:mtext></mml:mrow></mml:math>) were processed to obtain seismic images. Analysis of the seismic profiles revealed that weak and discontinuous bottom simulating reflectors were associated to basal accretion processes, while strong and continuous bottom simulating reflectors were associated to frontal accretion processes. This can be explained considering that during basal accretion processes, extensional tectonic movements due to uplifting can favour fluid escapes giving origin to weaker and most discontinuous bottom simulating reflectors. During frontal accretion processes (folding and thrusting), high fluid circulation and stable tectonic conditions however can be responsible of stronger and most continuous bottom simulating reflectors. Along the Arauco-Valdivia offshores, steep accretionary prisms, normal faults, slope basins, and thicker underplated sediment bed were associated to basal accretion, while along the Itata, Chiloe and Coyhaique offshores, small accretionary prisms, folding, and thinner underplated sediment bed were associated to frontal accretion.