Paleo-earthquakes in passive-margin settings, an example from the Paleocene of the Golfo San Jorge Basin, Argentina

Abstract

Paleocene sedimentary rocks in the Golfo San Jorge Basin include the marine Salamanca Formation and the continental Río Chico Formation. Both units contain soft-sediment deformation features and evidence of contemporary tectonics, which include: 1) sediment-filled fissures, hosted in muddy marine sediments of the Salamanca Formation (“Fragmentosa” Section), where the sandy infill of the fissures took place from above; 2) synsedimentary normal faults in the uppermost levels of the Salamanca Formation, with vertical throws rarely exceeding 1 m; 3) fault-graded beds in the “Banco Negro Inferior” (marine–continental transition), which show a deformed sequence with small-scale normal faults at the bottom and intraformational breccias on top; and 4) liquefaction and/or fluidization pillars, “V” or funnel-shaped, with vertical extension of up to 5 m and preserved into fluvial channels of the Río Chico Formation. Deformed strata are bounded by undisturbed horizons and some of these features can be correlated along 60 km of exposures. The suite of soft-sediment deformation structures is considered a secondary evidence of synsedimentary paleo-earthquakes (seismites) in this portion of the South American passive margin. This work shows new evidence of syndepositional tectonic activity in the lowermost Paleogene of the Golfo San Jorge Basin.