VORTEX WAVE RIPPLES FROM AFIKPO SANDSTONE, AFIKPO SUB- BASIN, SOUTHEASTERN NIGERIA: SIGNATURE TO PALEOWAVE HISTORY AND ANCIENT SEA CONDITION

Abstract

Vortex wave ripples from the clayey, fine grained, laminated sandstone lithofacies of Afikpo Sandstone have
been studied for the purpose of reconstruction of the paleowave characteristics and ancient sea condition. The
methodology adopted include: field measurements and calculations of parameters using analytical formulae.
Result show that the average wavelength, height and orbital diameter of the wave ripples are 16.50 cm, 2.48 cm
and 24.42 cm respectively. The ripples began to form on the sand of median grain size of 0.014 cm in diameter
at a threshold orbital velocity of 14.75 cm/s and reached its maximum at bottom orbital velocity of 51.31 cm/s.
The Campanian- Maastrichtian Afikpo Sea was characterized by a wave period of 1.47 – 5.25s suggesting low
to moderate wave conditions. Deep water wavelength on the average varied from 3.42 to 45.51 m and height
from 0.49 to 6.50 m. Average bathymetric estimate for the ancient sea is 22.76 m. This is suggestive of shallow
water depth for the epeiric sea. The average wave energy and power in deep water range from 0.37 to 61.95kJ
and 0.40 to 297.40 kW respectively. The low wind speed of 4.19m/s with duration of 8.85hrs and a fetch of 51.81
km are also characteristics of the epiericsea.