Abstract: Carbonate-Sand Waves, Isla Mujeres, Yucatan, Mexico

J. C. Harms, P. W. Choquette, M. J. Brady

A series of sand waves has formed since the Holocene transgression where the north-flowing Yucatan current is focused in the strait between Isla Mujeres and the mainland. Carbonate sand, composed of oolites and bioclastic debris, has been swept northward from near Isla Cancun to form a blanket 5 or 6 m thick. Sand waves form the upper surface of this blanket in a 10 sq-km area. They have angle-of-repose lee faces 1 to 4.5 m high and sinuous crests commonly hundreds of meters long.

The hydrodynamic factors causing sand waves are poorly known. For the Mujeres sand waves, flow depths range from 3.5 to nearly 10 m and average velocity ranges from about 0.5 to 1 m/sec. Small dunes 15 to 30 cm high are superimposed on the crests of the larger features. Over the deeper parts of the sand-wave profiles, current ripples are the active smaller-scale bed forms. Velocity measurements show average velocities close to the bed of about 30 cm/sec over deeper, rippled areas. But turbulent velocity fluctuations range from zero to 50 cm/sec over 0.5-sec time periods.

The Mujeres sand waves probably form in response to: (1) moderate supply of sand-sized material; (2) steady northward current of 50 to 100 cm/sec flowing in depths of several meters; (3) small tidal range, hence nearly constant current direction and velocity; (4) protection from most waves and swell by islands and shoals.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC