Shallow gas high-resolution seismic signatures in a subtropical estuary

High-resolution seismic surveys were carried out at the Paranagua Estuarine Complex (Southern Brazil) to map the intrasedimentary shallow gas. The seismic signatures representing gas accumulation were separated according to the upper gas boundary characteristics in acoustic blanking with sharp top, acoustic blanking with diffuse top, turbidity pinnacles, and black shadows (gas accumulation at the water/sediment boundary). The main source of the gas has been recognized here as Pre-Holocene continental deposits. These deposits were capped by a seismic unit interpreted as a regressive mud deposited over the last 5000 years. This seismic unit is quite heterogeneous, the gas being trapped in its different internal layers. Each gas signature represents the efficiency of the sealing layer and has specific locations and burial depths. The results point to different phases of gas migration along with the sedimentary layers. Thus, we proposed a gas migration and accumulation model based on acoustic data and sedimentary inferences within the Paranagua Estuarine Complex.