Systematics and taphonomy of fossil woods from a new locality in the Upper Triassic Carrizal Formation of the El Gigantillo area (Marayes-El Carrizal Basin), San Juan, Argentina

Abstract

We present a new locality with fossil woods in the southern outcrops of the Rickard Member, Carrizal Formation (Upper Triassic) of the El Gigantillo area in San Juan Province, Argentina. We analyzed the anatomical characters, systematic affinity and taphonomic conditions of permineralized trunks. A total of 58 trunks were found, although only two samples of the silicified trunks preserved anatomy details, and were characterized by a pycnoxylic homoxylic secondary wood with distinct growth rings, latewood 2–4 cells wide, tracheid pitting in radial walls of mixed type, cross-fields of cupressoid type with 1–4 oculipores, and homocellular and mainly uniseriate rays 1–19 cells high with smooth ray cell walls. The taphocenosis of the logs were preserved by carbonatic and siliceous permineralization, which are located in floodplains and channel deposits and constitute an allochthonous and parautochthonous taphocoenosis. The silicified wood presented high organic perturbation probably related to fungal activity, as well as several cylindrical and tubular galleries and pellets, which probably represented the activity of arthropods. The studied specimens were assigned to the new species Protocupressinoxylon carrizalense sp. nov. and constitute the first cite of the genus Protocupressinoxylon from the Triassic of Argentina. They thus represent the arboreal paleocommunities that grew in the top of the bars within the channels and riparian areas.