Resumo

PATERLINI, Marcelo  e  MOUZO, Félix. Seismic exploration of the northpatagonian San José gulf, Argentine continental shelf, Chubut province. Geoacta [online]. 2013, vol.38, n.1. ISSN 1852-7744.

Seismic records acquired by the Argentine Naval Hydrographic Service in the San José (42° 20' S y 64° 20' O) gulf with a shallow penetration, high definition Uniboom system, show a shallow seismic structure formed by a lowermost, regional layer extending continuously throughout the gulf, detectable down to some 80 ms (=70 m). Locally, that layer can be unconformably covered by another layer showing in places at least two seismic facies. The regional layer making the bedrock, generally displaying high continuity and amplitude, and moderate to low frequency, showing smooth folding and no evidence of faulting, is interpreted to be the continuation of the Middle-Late Tertiary marine beds cropping out in the coastal areas and extending over all of the adjacent continental region. The uppermost layer covering the Tertiary beds, in any of its facies, is also made up of marine sediments, as evidenced by the continuity and character of the reflections, and by the data known from cores also obtained in the gulf. This bottom-surface layer shows structures compatible with turbidity currents and/or submarine fan deposits. The seismic facies in the upper layer represent deposits formed under different conditions in a submarine current regime and point out to a short timed deposition and an Holocene age for the upper layer. It is concluded that during the Holocene transgression the Atlantic waters invaded a continental depression carved on Tertiary deposits -currently occupied by the San José gulf- after breaching the narrow land strip which separated it from the San Matías gulf. In that process a wave-cut platform -currently at a depth of 30 m- and a levee bordered submarine canyon were carved, the latter followed by a fan-complex in the deeper regions. All these features are readily identifiable in the submarine morphology, and by the external form, internal configuration, reflection geometry at boundaries, and lateral relations of the analyzed facies.

Palavras-chave : Seismic stratigraphy; Holocene; Structures; Submarine fan; Origins; Age.

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