Seismic Stratigraphy of Pleistocene Deltaic Deposits in Bahía Blanca Estuary, Argentina

Abstract

The Bahía Blanca estuary (Argentina) has a morphological configuration resulting from hydrological and sedimentary processes related to Late Quaternary sea level changes. This estuarine system occupies a large coastal plain with a dense net of tidal channels, low-altitude islands and large intertidal flats. Little is known about the sedimentary units of the marine subbottom. Therefore, a stratigraphical analysis of the northern coast of Bahía Blanca estuary was carried out using high resolution seismic (3.5 kHz) in order to: i) define Quaternary sequences, ii) describe sedimentary structures, and iii) determine the paleoenvironmental conditions of sedimentation. The seismic stratigraphic data collected and their correlation with drilling lithological data show five seismic sequences (S1, S2, S3, S4 and S5), of which S1-S2 were found to be associated with a continental paleoenvironment of Miocene-Pleistocene age. Sequences S3 and S4, whose lithology and seismic facies (paleochannel structures and prograding reflection configurations), were defined on these materials, to evidence the development of an ancient deltaic environment which was part of a large Pleistocene drainage system. The S5 sequence was formed during the Holocene transgressiveregressive process and complete the seismostratigraphic column defined in the present study.

Shallow gas features and distribution in the Patos Lagoon: a coastal trap for gas-generator sediments

“…Gas in sediments can be found in various types of coastal environments, where normally the ideal conditions for biogenic gas formation due to high biological productivity occur. Gas-charged sediments is a common phenomenon worldwide and so have been related in the most coastal environments as shallow or enclosed seas and shelves (Emeis et al, 2004;Terra et al, 2014), lakes (Lafferty et al, 2006), bays (Baptista Neto et al, 1996;Quaresma et al, 2000;Catanzaro et al, 2004;Jensen & Bennike, 2009;Marino et al, 2013;Aliotta et al, 2014;Klein et al, 2016), rias (Garcia-Gil et al, 2002;Diez et al, 2007;Duarte et al, 2007;Iglesias & Garcia-Gil, 2007), deltas (Figueiredo Jr. et al, 1996), lagoons (Baptista Neto et al, 2011;Weschenfelder et al, 2006Weschenfelder et al, , 2016 and estuaries (Frazão & Vital, 2007;Pinet et al, 2008). The gas sources and accumulation modes are closely related to the sedimentary and evolutionary processes occurring in the depositional environment (Garcia-Gil et al, 2002).…”