Recovery of Scleractinian Morphologic Diversity During the Early Jurassic in Mendoza Province, Argentina

Abstract

After a diversity peak during the Late Triassic, corals were severely affected by the end-Triassic extinction. The study of their recovery is fundamental for a better understanding of the ecological rearrangement undergone by Early Jurassic marine invertebrate faunas. In this contribution we analyze the morphologic recovery shown by scleractinians in southern Mendoza Province, which is the only place in the Neuquén Basin with marine outcrops spanning the Triassic/Jurassic boundary. A two-stage recovery pattern was recognized. During the first stage (Hettangian-Sinemurian) only solitary corals, most of them discoidal, could be found. After a hiatus encompassing the latest Early Sinemurian and the Late Sinemurian, the second stage (Pliensbachian) developed. A sharp increase in morphological diversity of solitary corals is then recorded, with discoidal, cupolate, patellate, turbinate, trochoid/turbinate, trochoid/ceratoid and maybe cylindrical morphologies. Additionally, colonial forms with low degree of corallite integration (phaceloid and cerioid colonies) appeared in the basin. The diversification trend hereby described provides useful insight regarding the scleractinian recovery after the end-Triassic mass extinction event within southern basins of South America. Furthermore, this recovery pattern is comparable with the one recognized for other regions (Chile, western North America, central Asia) yet it differs from that observed in some European basins. The trend outlined herein for Early Jurassic corals from the Neuquén Basin may reflect a large-scale phenomenon and/or the action of local adverse conditions (such as fluvial influence), which is open to further testing.

Biotic recovery after the end-Triassic extinction event: Evidence from marine bivalves of the Neuquén Basin, Argentina

“…This might be referred to a recovery stage 1 (sensu Twitchett, 2006), though the presence of crinoids would indicate some tiering differentiation. At 360 m (within the D. reissi (≈late Liasicus Zone) there was a relatively rich fossiliferous shell bed with more diverse bivalves (the same 2 species recorded earlier plus at least 6 other species, including epifaunal and infaunal ecologic types); the first brachiopods (2 species) and solitary corals (Echevarría et al, 2017) recorded after the extinction appear also at this level. Tiering is fully recovered at this point (recovery stage 4 sensu Twitchett, 2006), since there are deep burrowers (pholadomyids, see Fig.…”

“…Deposits of the Arroyo Malo Formation were interpreted as ranging in palaeoenvironment from basin area far from the delta front to slopetype fan delta upper front below wave base (Lanés et al, 2008). The last 30-40 m deposits are large lenses of pebbly sandstones and clast-supported conglomerates which were either referred to the El Freno Formation (Riccardi et al, 1997a;Lanés, 2005) or to the top of the Arroyo Malo Formation (Lanés et al, 2008;Echevarría et al, 2017;here). The Triassic/Jurassic boundary occurs within the Arroyo Malo Formation, in the transicional lithofacies sequence T2-T3-T4 (Lanés, 2005), or D2-D3-D4 (Lanés et al, 2008), i.e.…”

Detrital zircon U-Pb geochronology of the Sierra de Santa Rosa Formation, Sonora, Mexico, and implications for an Early Jurassic retroarc basin

“…The Jurassic recovery of corals in the Americas, relative to the Tethys, is not well known and there may have been geographic and ecologic differences, especially in the timing and evolutionary dynamics. For example, a slower, two-stage recovery is indicated in the Early Jurassic of Argentina (Echevarría et al, 2017). Low-diversity Early Jurassic corals are reported from Chile and Peru (Prinz, 1991).…”