First macrofloristic study from the Chubut Group in the Canadon Asfalto basin: Albian Cupressaceae woods (Chubut, Argentina)

BREA, MARIANA; BELLOSI E. S.; UMAZANO, A. MARTIN; KRAUSE J.M.

Simposio; Simposio Argentino de Paleobotanica y Palinologia; 2015

Transported and well-preserved silicified woods occur in fluvial-channel belt deposits of the uppermost section of the Albian Bardas Coloradas Member (Los Adobes Formation, Chubut Group). Samples were collected at Estancia Aguada La Piedra, next to Gorro Frigio hill. These petrified conifers, preserved along with reptile remains, were assigned to Cupressinoxylon hallei Kräusel, 1949. The anatomical features are: slightly demarcated growth rings, tracheids are quadrangular to rectangular in shape, triangular or quadrangular intercellular spaces between tracheids and/or tracheids and ray parenchyma. Early-wood tracheids with mean tangential diameter of 41 (21?63) µm. Late-wood tracheids with mean tangential diameter of 42 (24?60) µm. Axial parenchyma scarce and diffuse. Uniserite rays, rarely biseriate. Tracheid pitting in tangential walls have pit pores with mean diameter of 14 (12?16) µm. The tracheid pitting is recognized as being of the abietinoid type. Pits are circular, areolate, spaced or contiguous, uniseriate or rarely with biseriate portions; when biseriated, pits are alternate. Pits pores with mean diameter of 17 (10?23) µm and inner apertures circular and enclosed. Pit membranes with well-developed torus. Ray cell walls thin, smooth and occasionally with small and isolated nodules. Homocellular rays. The cross-field pitting is cupressoid type with 2?6 oval to circular pits, usually ordered in rows and columns, with 5 (4?7) µm in vertical diameter. These fossil woods are the first macrofloristic remains analyzed from the Cretaceous Chubut Group in the Cañadón Asfalto basin and are the first unequivocal record of the Cupressinoxylon hallei from the Cretaceous of South America.