The Quaternary Period, roughly the last 2.6 million years of Earth history in which
different glaciations and the evolution of our genus happened, has much to show us its
consequences on ecosystems. The Quaternary period is categorized into the Pleistocene
(2.588 million years ago to 11.7 thousand years ago) and Holocene Epochs (11.7 thousand
years ago to today). During the Late Quaternary period, coastal regions of the Kerala coast
witnessed pompous variations in sea level.
The red coloured sediments found very close to the beach at Vettakkada, Edava
Grama panchayath, Thiruvananthapuram district has been selected for the present study.
The red sands are exposed above a laterite body/duricrust layer of post tertiary age. The
laterite possesses rounded to subrounded pebbles and sand, and also it shows few
sedimentary structures. Few fossils of corals which is lateritised is exposed within the
laterite body. No detailed study has been undertaken about this red sand deposit. The
present investigation has been undertaken with an objective to study the textural
characteristics of red sands and to deduce the palaeo-depositional environments.
The grain size parameters such as graphic mean, standard deviation, skewness,
and kurtosis have been computed from the sieve analysis data using the graphical
method. Overall, the grain size statistics such as dominance of medium to coarse grained
sediment type, moderately well sorted nature, negative skewness and leptokurtic nature
indicates a high energy depositional environment and almost uniform energy conditions.
The samples were plotted in the bivariate plots of Friedman (1967), Stewart (1958),
Moiola and Weiser (1968) and Tanner (1991). In all plots majority of the samples fall in
the fluvial environment and transportation in a high energy open channel. But in the case
of Sahu’s diagram (1983) all samples, except one sample, fall in the beach environment.
The exclusively beach environment as shown by the Sahu’s diagram indicates that the
initial deposition by the rivers and subsequent sorting by the wave action. CM diagram of
Passega (1957) reveals the dominant transportation mechanism as rolling followed by
bottom suspension and rolling, which is an indication of high energy conditions. The
sediments were mainly in traction and saltation before being deposited.

The present red sands might have deposited in periods of low sea level periods,
where much of the present shelf was exposed. There was a higher rate of sea level rise
16000 yrs BP to 7000 years BP. The sea level attained its present position at around 7000
years BP and thereafter there was some minor transgressive fluctuations towards the
present land. This period of minor transgressions tallies with the reported ‘Holocene
Climate Optimum’ or ‘Holocene Maximum’ episode. The Holocene Climate Optimum (HCO)
was a warm period. The present sediments which were deposited in a fluvial environment
got affected by such transgressive phase during 4000 – 7000 years BP. The redistribution
and reworking of fluvial sediments in the arid period of the ‘Holocene Maximum’ episode
might have given the red colouration to the sediments. Moreover, the reworking of the
fluvial sediments in a beach environment was instrumental in acquiring some beach
characteristics as shown by the Sahu’ multi discriminant analysis.
Six samples were selected for SEM analysis in the present study. Many of the sand
grains show subangular to subrounded shape in low magnification. The grains are
subangular probably due to little abrasion and rounding of grain edges, probably due to the
less distance of travel. The SEM images of the sediments predominantly exhibits those
grain surface features typical of beach environment. Only one sample which is located at
the bottom most part of the southern transect exhibits fluvial environment. The grain
surface features derived through SEM analysis supports the observations made from the
analysis of the sediment textural data, ie., the redistribution and reworking of fluvial
sediments during the transgressive phase of the ‘Holocene Maximum’ episode. The minor
transgression could make its impacts on the surface of the grains, but failed to make any
change in the sediment textural characters. The surface texture appears to be more
susceptible to change during sediment transport and deposition than do sphericity and
roundness. Removal of old surface textural features and generation of new features are
more likely to occur than marked changes in sphericity and roundness, and surface texture
is more likely to record the last cycle of sediment transport or the last depositional
environment. The sample number six shows some grain surface features of aeolian
environment apart from the beach characteristics. This particular sample falls in the
aeolian sector of the Sahu’s multi discriminant plot. The ‘Holocene Maximum’ episode is a
period of higher aridity and can bring about typical aeolian features in the grain surfaces.