First macrofloristic study from the Chubut group in Cañadon Asfalto Basin: Albian cupressaceae woods (Chubut).

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

La Plata

Simposio; XVI Simposio Argentino de Paleobotánica y Palinología; 2015

Facultad de Ciencias naturales y Museo, UNLP.

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. 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. Earlywood tracheids with a mean tangential diameter of 41 (21?63) µm. Latewood tracheids with a mean tangential diameter of 42 (24?60) µm. Axial parenchyma scarce and diffuse. Uniseriate rays, rarely biseriate. Tracheid pitting in tangential wall present, pits with a mean diameter of 14 (12?16) µm. The tracheid radial pitting is recognized as being of the abietinoid type. Pits are circular, bordered, spaced or contiguous, uniseriate or rarely biseriate; when biseriate, pits are alternate. Pits with mean diameter of 17 (10?23) µm and inner apertures circular and enclosed. Pit membranes with well-developed torus. Ray cell wall thin, smooth and occasionally with small and isolated nodules. Homocellular rays. Cross-field pitting of the 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.