Geological aspects and evolution of the Patagonian continental margin

Abstract

The Patagonian continental margin records some of the tectonic, sedimentary, climatic, and oceanographic events that participated in the evolution of the Patagonian and south-western Atlantic regions. Those records are essential for fully understanding the geology and biodiversity of Patagonia. Regional geotectonic and morphosedimentary features are characterized by different types of continental margins (passive, transcurrent, and transpressive). In each of them the constituent features (shelf, slope, and rise) acquire particular morphological and sedimentary configurations. Characteristics of the sedimentary sequences and the limiting discontinuities document the different evolutive stages of the margin and intervening major processes. The regional tectonic, palaeoclimatic, and palaeoceanographic events that occurred after the break-up of Gondwana until the Quaternary, which conditioned the morphosedimentary characteristics, are analysed and described here. It is concluded that the region evolved in three major stages, according to the predominance of different factors: (1) a stage dominated by endogene factors, which occurred in Mesozoic times, when the major processes at work were plate tectonics and oceanic opening; (2) a transitional stage, which occurred in the lower Tertiary, when the proto-Atlantic Ocean evolved towards an open sea, and climatic and oceanographic factors became at least as important as tectonic factors; and (3) a stage dominated by exogene factors, which occurred in post-Oligocene times, when the Atlantic Ocean was definitively installed and the circulation of oceanic currents influenced the characteristics of the sedimentary environmentsthis stage ended in the Quaternary when glacioeustatic fluctuations imprinted the present morphosedimentary configuration. Continental Patagónico guarda gran parte de los registros de eventos tectónicos, sedimentarios, climáticos y oceanográficos que participaron en la evolución de la región Patagónica y del Atlántico Suroccidental. Su conocimiento es esencial para comprender cabalmente la geología y biodiversidad de Patagonia. Los rasgos geotectónicos y morfosedimentarios regionales se caracterizan por diferentes tipos de márgenes continentales (pasivo, transcurrente y transpresivo), en cada uno los cuales sus elementos constituyentes, la plataforma, el talud y la emersión, adquieren configuraciones morfológicas y sedimentarias particulares. Las características de las secuencias estratigráficas y sus discontinuidades documentan las distintas etapas de evolución del margen y los procesos mayores intervinientes. Se analizan y describen los eventos tectónicos, palaeoclimáticos y palaeoceanográficos de extensión regional que caracterizaron a la región desde la apertura de Gondwana hasta el Cuaternario y condicionaron sus aspectos morfosedimentarios. Se concluye que la región evolucionó en tres etapas mayores de acuerdo al predominio de diferentes factores: 1) etapa dominada por factores endógenos, ocurrida en tiempos Mesozoicos, cuando los procesos mayores ...

Geomorphology and shallow structure of a segment of the Atlantic Patagonian margin

“…The wide expanse of these features on the Atlantic Patagonian shelf and upper and middle continental slope indicate that endogenic processes have played a role in creating the morphology of the Patagonian shelf and slope. Contrary to Cavallotto et al (2011) supposition that endogenic processes only occurred in the Patagonian slope during the rifting and early opening of the South Atlantic, endogenic processes are still active or were active recently in the region.…”

Variations in sediment transport at the central Argentine continental margin during the Cenozoic

“…Locally, the reflector is discontinuous because canyons on the upper slope (e.g., Figure 3b, SP 2900–5300) and a channel on the lower slope are intersecting (e.g., Figure 5c, SP 3000–3200). The horizon is equivalent to formerly reported reflectors H2 [ Cavallotto et al , 2011; Ewing and Lonardi , 1971] and ARG 9 [ Schümann , 2002], which through correlation with industry well “Cruz del Sur” [ Bushnell et al , 2000] (Figure 1) is interpreted to represent the Miocene/Pliocene boundary at ∼6 Ma [ Schümann , 2002]. Unconformities of approximately this age were also drilled in well “LAPA X‐1” (Figure 1) in the western Malvinas basin [ Galeazzi , 1998] and at DSDP Site 512 on the Maurice Ewing Bank [ Ciesielski and Weaver , 1983].…”

“…Although glaciations may not play directly a major role in the increased sedimentation at the central Argentine margin, a relative sea level fall associated with the increase in ice volume [ Haq et al , 1987; Miller et al , 2005] can have led to an increase of sediment transport from the rivers and shelf toward the deeper parts of the basin. Triggering of individual mass wasting events could have been through tectonic uplift, which is postulated for the North Eastern Brazil margin [ Japsen et al , 2012] and the Central Andes [ Cavallotto et al , 2011; Gonzalez and Pfiffner , 2012].…”

Palaeogeographical evolution of the Atlantic coast of Pampa and Patagonia from the last glacial maximum to the Middle Holocene

“…However, thus far, there has been no continuous palaeogeographical model of the Patagonian and Pampean coasts following the LGM. Other available studies (Groeber, 1948; Parker et al ., 1996, 1997; Cavallotto & Violante, 2003; Perillo et al , 2005; Cavallotto, 2008; Cavallotto, Violante & Hernández‐Molina, 2011) have thoroughly discussed the morphological and sedimentological characteristics of the ACS. Finally, curves of regional sea level changes along the Argentine coastline were presented by Guilderson, Burckle & Hemming 2000; Rostami et al .…”