TITLE:
Rio Grande Relay Zone, Rio Grande do Sul Coastal Plain, Brazil: II—Asymmetric Delta Development and Gravity Fault Subsidence in Quinta-Cassino Strandplain
AUTHORS:
Adelir José Strieder, Iran Carlos Stalliviere Corrêa, Bruno Silva da Fontoura, Ana Carolina O. dos Santos, Paulo Rogério Mendes, Alexandre Felipe Bruch, Angélica Cirolini, José Antonio Scotti Fontoura
KEYWORDS:
Gravity Sliding Tectonics, Local Subsidence and Structural Barriers, Normal Fault and Sedimentation, Holocene Asymmetric Delta Development
JOURNAL NAME:
Open Journal of Geology,
Vol.16 No.7,
July
29,
2026
ABSTRACT: This paper describes and characterizes the Rio Grande Relay Zone as a complex structural area developed due to the interaction of the north tips of the Quinta Main Listric and south tips of the Retiro-Estreito splaying and bending faults in the Rio Grande do Sul Coastal Plain (RGSCP). The paper characterizes the structural control for the Holocene lagoon-barrier system in the central to south RGSCP, based on recently identified gravity sliding faulting. The investigated area includes mainly the Quinta-Cassino area to the south of the Rio Grande channel and the Retiro area to the north of the channel. Gravimetric data, seismic lines, GPR lines and drillholes were used to evaluate and to re-interpret some previous results to highlight the structural features developed by that fault’s interaction. Gravimetric data supported evidence that the Rio Grande Fault separates the deep Pelotas Basin, as well as the Rio Grande Structural High. The Quinta Main Listric and Retiro-Estreito Main faults are the consequence of crystalline basement tilt due to regional basin flexural subsidence. The basement tilt triggered gravity sliding tectonics from the Miocene to the Holocene. The Rio Grande High, on the other hand, set sedimentary loading anisotropies to control the listric normal faults propagation (splaying and bending). The interaction of subsided hangingwall of the Quinta Main Listric Fault and its subsidiary ones with the footwall block of the Retiro-Estreito Main Fault gave rise to a wedge-like locally subsided area and to an asymmetric delta, the Quinta-Cassino strandplain. The Rio Grande discharge channel was initially set close to Quinta Main Listric Fault scarp and was meandering according to the ramp relays in the Retiro-Estreito Fault footwall block to its actual discharge position. The Quinta-Cassino beach ridge progradation was cut by subsidiary listric faults, so that each fault block shows its own vertical sedimentation rates and a given time of displacement.