Depositional sequences in northern Peru: new insights on the palaeogeographic and palaeotectonic reconstruction of western Gondwana during late Permian and Triassic

Abstract

Late Permian to Early Jurassic strata in northern Peru allows us to carry out a seismo-stratigraphic, litho-tectonic and chemostratigraphic analysis connecting the Andean-Amazonian foreland basins of Huallaga, Ucayali, southern Marañón, and the Eastern Cordillera. This analysis and data integration from Ecuador to western Brazil and southern Peru and Bolivia, allow us to redefine the timing of the major documented tectonic phases and corresponding palaeogeographies of western Gondwana from the late Permian to Triassic. Three litho-tectonic sequences and four associated deformation stages are recognized: 1) A sequence, tectonic relaxation, during late Permian; 2) A-B intra-sequence, folding-and-thrusting attributed to a continuation in time of the Gondwanide Orogeny, during the Early to Middle Triassic; 3) B sequence, rifting, attributed to Gondwana breakup during the Middle and Late Triassic; and 4) C Sequence, thermal sag, during the Late Triassic. Evaporites and carbonates (A sequence) dominated a low subsidence basin with southern restricted marine inflow at the Permian-Triassic boundary. A novel palaeogeographic model for these evaporites suggests that this saline basin extended up to 50,000 km2 in a restricted environment area with a potential bullseye pattern. The last pulse of the Gondwanide Orogeny and associated fold and thrust belt (A-B intra-sequence) exhumed previous the sequence generating emerged areas with little to no sedimentation. Red beds (B sequence) characterize the rifting stage, representing the syn-depositional infill of continental grabens, likely extending to the Acre Basin in Brazil. Finally, during the thermal sag, a marine inflow likely from the northwestern part of Peru generated sedimentation of carbonates and evaporites (C Sequence) to the west and east of the Peruvian margin. This sediment differentiation was, in part, controlled by the existence of pre-existing grabens associated to the previous rifting stage. This interpretation, together with other evaporitic occurrences attributed here to a Late Triassic epoch in south and north Peru and west Brazil, suggest the existence of an evaporitic basin filling an undeformed area of probably ca. 170,000 km2. It is therefore suggestive of the existence of a Late Triassic (Norian to Rhaetian; 217 to 204 Ma) salt giant controlled by thermal sag in western Gondwana. Our results are of great relevance for any future interpretation related to mass extinctions, paleoclimatic analysis and ocean dynamics during the Permian and Triassic as well as natural resources distribution between Ecuador and Bolivia.

Sedimentology, geochronology and provenance of the late Permian and Triassic Mitu Group in Peru—The evolution of continental facies along a transform margin

“…Considering the widespread syndepositional volcanism in the southern and central Mitu basin we assume that the younger mla b of the intermittent sections in fact also indicate the age of the onset of deposition. If this can be corroborated with more data in the future this would give further substance to our interpretation of a variably diachronous onset of deposition in different segments of the Mitu basin, which is also suggested by the data of Carrillo et al (2021).…”

“…In the eastern reaches of the Cordillera Oriental and farther eastward in the present subsurface, the transition from the Copacabana Formation to the Mitu Group is partly represented by the Ene, Noi, Shinai and Lower Nia formations (Figure 2; Carrillo et al., 2021; Erlich, Fallon, et al., 2018; Grader et al., 2008; Sempere et al., 2002) here informally grouped as the Ene Group. The Ene Group is only a few tens of meters thick and consists of an association of black shales with thin limestones, evaporites and partly aeolian sandstones (Erlich, Fallon, et al., 2018; Iribarne et al., 2018).…”

“…The Ene Group is only a few tens of meters thick and consists of an association of black shales with thin limestones, evaporites and partly aeolian sandstones (Erlich, Fallon, et al, 2018;Iribarne et al, 2018). Carrillo et al (2021) determined maximum depositional ages of 258 ± 4 Ma and 247 ± 3 Ma (latest Permian/Triassic) on detrital zircon for the Ene Group in Subandean northern Peru. From the Kungurian (upper lower Permian) to the Olenekian (Lower Triassic) the Ene Group records a regressive trend towards brackish and continental conditions at the top (Carlotto et al, 2010;Dalmayrac et al, 1980;Erlich, Fallon, et al, 2018 PANCA et al et al, 2018;Sempere et al, 2002).…”

“…These faults are interpreted to have controlled the development of the southern Mitu basin F I G U R E 2 Chronostratigraphy of the Mitu Group, time-correlative units, and under-and overlying formations (mla b , Table 4). Informally named Ene Group: Ene, Noi, Shinai and Lower Nia formations (Carrillo et al, 2021;Erlich, Fallon, et al, 2018;Erlich, Hermoza, et al, 2018;Grader et al, 2008;Sempere et al, 2002). Pucarà Formation: Rosas et already in the Triassic (Carlotto et al, 2023).…”

“…Chronostratigraphy of the Mitu Group, time‐correlative units, and under‐ and overlying formations (mla b , Table 4). Informally named Ene Group: Ene, Noi, Shinai and Lower Nia formations (Carrillo et al., 2021; Erlich, Fallon, et al., 2018; Erlich, Hermoza, et al., 2018; Grader et al., 2008; Sempere et al., 2002). Pucarà Formation: Rosas et al.…”