Low density araucarian woodlands from the Jurassic of Patagonia

CÚNEO, RUBÉN; ANDREIS, RENATO; CLADERA, GERARDO; ESCAPA, IGNACIO

Utah, USA

Congreso; Botany and Mycology 2009; 2009

Botanical Society of America

The structure and paleoenvironmental conditions of araucaria stumps and logs from the Jurassic of Patagonia are analyzed. Based on density measures araucarian trees were organized in low-density woodlands that occupied extended plains affected by constant volcanic activity originated in nearby areas. At least two episodes of araucarian tree woodlands can be identified in the studied area, all of them drastically ended by explosive volcanic action. As a result, in situ fallen logs and stumps were immediately covered by massive ash falls that favored a rapid silicification process through permineralization. Tree stands analyzed indicate densities from 3 to 11 individuals, with random clustering spatial distribution; mean diameters are above 1.2 m whilst estimated mean heights overpass 40 m. In order to find modern analogues, a close comparison with Araucaria araucana stands are made, suggesting that Jurassic representatives show some ecological resemblance in terms of distributional patterns. The continuous finding in the surrounding area of Araucaria mirabilis seedcones suggests that araucarian woodlands mostly produced this type of seedcones, although other conifers such as the one that produced Pararaucaria seed cones could have been also present as secondary components. In order to better understand life conditions of one of the most incredibly preserved examples of fossil trees considerations on the paleoecological and paleoclimatological aspects of mid-latitude southern Jurassic vegetation are undertaken.