31 Aug Gcians on cliff walk-Varkala, Aug.27, 12
Cliff Walk: Gcians on foot to Papanasam North Cliff, Geologycafecliffwalk, Aug, 27
(Reliving of my nostalgia)
The cliff walk invented, initiated and promoted by the GC, had participation by geoscientists of minimum three generations. The gen III, was represented by at least nearly half a dozen student gcers, gen-II by some five guys and gen-I exclusively by me.
Thus the program of GC naturally crossed the gen boundaries; aptly mirrored the vibrancy of the GC fraternity and confidence about the future too. The cliff walk started off at Panasam. Professionals (like Manu, Sajith Girinathan and Anil Das, Santosh), academics (viz., Jai kiran, Pradeep kumar and me) and a fellow geologist and GIS expert professional Riju Stephen added to scientific glitter social wellness to the trip.
The trippers who assembled at the Papnasam beach, were sincerely welcomed by Jaikiran (spirit and lead mover of GC), followed by a brief self introduction session by participants and finally toward the at the end Jaikiran sort of handed the “mike” over to me.
After brief introductory remarks, I narrated the generalities of the Warkalli series and then moved northerly along the beach to stop at the first exposure of the carbonaceous clay at the foot of the cliff.
The significance, specialties, implications of carbonaceous clay (argillaceous facies) were retold to the group. The alternation of organic matter rich and silt rich layers with occasional marcasite tubes of 4 to 6 mm are the hallmark of the carbonaceous clay (argillaceous) bed. Efflorescence of light yellowish Natrojarosite (first report appeared in the Bull GSI, by a visiting Brit. Geologist who was a member of the 1964 IGC, New Delhi) laces the surface of carbonaceous clay bed. The base of this bed is covered with a thick talus cover mostly of lateritic nature.
In addition the carb.clay samples in a dark room under a UV lamp fluoresced in orangish-yellow glow, indicating presence of uranium in the oxide state. By the way, uranium is a very mobile element and is deposited quickly in a euxenic environment and here in this case the carbonaceous cla forming environment just did that.
This bed is over lain by a bed of sandstone (arenaceous facies) coloured reddish brown at the bottom half of the exposure and yellowish brown on the upper half of the sandstone. Ripple cross lamination and dune cross bedding are characteristic of this arenaceous layer.
This arenaceous layer is overlain by an argillaceous sandstone and as one goes up section (team did not walk all the way up to look at this), what is noticed is its sort of gradual or imperceptible transition to laterite which is a very thick layer and more ferruginous at the top and less ferruginous at the bottom, i.e., toward the bottom transition layer of argillaceous bed.
This laterite capping stands at near vertical or even overhangs with a free face of roughly 10 to 13 m. Occasionally horizontal gashes, of far less lateral extent are noticed, which are interpreted as indications of original bedding or break in sedimentation in the sediment that transformed it self to laterite.
The free face, physically distinct from its base, has a cover of talus of blocks and boulders of laterite as well as the reddish sandstone. The free face is also called the waning slope, while the talus covered section is aptly denoted as waxing slope.
Further north springs are active, which emerges immediately above the carb.clay horizon. Legend has it that these springs are medicinal in nature. A piece of research exists in a MSc (chemistry) thesis submitted to Travancore University, where the attribution is to the presence of radon (?) in the spring waters.
Further these springs are ephemeral, in that they disappear at the peak of summer, while springs in the road to Sivagiri and flowing easterly are perennial in nature. Interestingly the easterly and westerly subsurface discharge in the springs indicate some sort of a subsurface divide doing this forcing.
My talk show thus ended with a thank you not to the GCians.