TRACKING CORRELATION BETWEEN AUTHIGENIC MINERAL CEMENTS AND LOCAL PALEOENVIRONMENTAL CONDITIONS, ISCHIGUALASTO FORMATION, NW ARGENTINA

CARINA COLOMBI; ROGERS, RAYMOND

Duluth

Congreso; 54th Annual Meeting of the North-Central Section; 2020

A significant number of studies discuss the strongness of correlation between the authigenic suite of filling minerals and the host facies at different scales. The Upper Triassic Ischigualasto Formation yields one of the most complete paleovertebrate collection. This unit is separated into four members with different fluvial architecture,types of paleosols, and taphonomy. In this contribution, we study infill patterns in Ischigualasto paleovertebrates with a focus on a broad range of authigenic minerals using a scanning electron microscope (SEM). The main authigenic mineral cements of Ischigualasto bones are calcite and hematite. However, the cements change in proportion and incorporate other complementary minerals according to member differences. La Peña Member is characterized by high sinuosity fluvial system with poorly-drained floodplain. The scarce highly weathered bones are characterized by recrystallized apatite, abundant Fe-rich minerals and barite, surrounded voids, and a second stage of calcite, filling remained voids. The fluvial system of Cancha de Bochas Member is characterized by an increase in aridity and seasonality (dominant Calcisols) and a long temporal mixing of fossils. The suite of authigenic cements is variable, although dominant recrystallized apatite, usually with calcite, thin rings of Fe-rich minerals/clay surrounded void and then the second stage of calcite. The fluvial system of succeeding Valle de la Luna Member has two particularities, an increase in humidity (dominant Argillisols) and volcaniclastic material which is also represented in the authigenic minerals. The remains show advanced bone alteration and thick Fe-rich minerals filling voids. Besides, most of the fossils are also permineralized with silica reflecting the volcaniclastic input. And the rare fossils preserved in abandoned channels are characterized by high dissolution of bones and precipitation of sulfurs and clay. Thus, the Ischigualasto fossil reveals that the diagenetic history of bones are strongly correlated with specific paleoenvironments, especially when lithologies or facies provide particular geochemical condition; this is especially true under volcaniclastic contribution or highly reduced environments.