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K. P. Thrivikramaji ¹

Affiliations
1 Department of Geology, University of Kerala, Trivandrum 695581, IN

Abstract

The Ettikulam lagoon and the lagoonal islets lying in the coastal plain of Cannan are District, Kerala form typical lagoon-barrier complex. A series of islets dot its full length, and some of the northern islets show a boomerang shape in plan. Other important components are the modern Ettikulam barrier, the Laccadive sea to the west and the coastal plain to the east. The islets occurring in the lagoon are interpreted as remnants of a barrier-dune complex, which was dismembered into fragments (sandy shoals) by storms in the Laccadive sea at a time when the sea-level was also on the rise (in the late Pleistocene). The storms also hastened the reduction of relief of the fragments or protoislets. The destructive phase of the islets terminated with the emergence of the modern Ettikulam barrier, giving the present configuration to the shoreline.

The onset of the new flow pattern, controlled by the two inlets, one off the mouth of Karingote river in the north and the other near Ramanthali in the south, led to further modification of the plan view of the islets giving a boomerang shape.

Evidences are also cited for the migration of the northern inlet and for the closure of the inlet near Ramanthali in the south, mainly due to littoral drift, sometime between 1914 and 1965.

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S. Anirudhan ¹, K. P. Thrivikramaji ¹

Affiliations
1 University of Kerala, Kariavattom Campus-695 581, IN

Abstract

The results of analysis of textural parameters of channel sediment samples of the Bharathapuzha system using the scheme of McLaren and Bowles (1985) reveal the existence of Case B trend in the direction of transport for mainstream (Bharathapuzha) and two high gradient tributaries viz., Gayathcipuzha and Thuthapuzha. Further, Fourier amplitude spectra estimated from digitized data of grain boundaries of the sand grade sediment from selected samples and the Waddell's sphericity and roundness indices demonstrate that influx of sediment from tributaries does not alter the size or shape distribution trends of the mainstream sands to any extent.

Keywords

Sedimentology, Statistical Study, Bharathapuzha Basin, Kerala.

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Sabu Joseph ¹, K. P. Thrivikramaji ¹, S. Anirudhan ¹

Affiliations
1 Department of Geology, University of Kerala, Kariavattom - 695 581, IN

Abstract

Results of analysis of size data by frequency curves and multi-group discriminat analysis (MGDA) indicate that inland Teri Deposits (ITDs) are very much similar to colluvium, formed by mass-wasting and fluvial processes, whereas Coastal Teri Deposits (CTDs) Very likely originated in mixed environments i.e., beach and dune. further, it is proposed that the ancestral sediments of present day CTDs would have originated from the vast reservoir of shelf sand that remained subaerially exposed during the low sea leval stands which coincided with Late Pleistocene glaciation.

Keywords

Sedimentology, Teri sands, Tamil Nadu.

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Sabu Joseph ¹, K. P. Thrivikramaji ²

Affiliations
1 Department of Environmental Sciences,University of Kerala, Kariavattom - 695 581, IN
2 Department of Geology, University of Kerala, Kariavattom - 695 581, IN

Abstract

The Early-Modern red coastal/or inland sands ("Teris") in the coastal tract of southern Tamil Nadu show the infrequent occurrence of rhizolithic calcretes in the vadose zone. These are reddish brown coloured, cemented and cylindrical in form. No other types of rhizolith and/or calcrete have been recorded from here. Textural and mineralogical studies show that these rhizoliths contain notable amounts of acid insoluble detrital sands (essentially quartz and opaques) and mud, and are presumed to be derived from the host, i.e. teris. Petrographic studies reveal that these detritals are embedded in a micritic matrix and the carbonate cement shows rim, vein and blocky structures. Further, floating, alveolar and clotting textures are also noticed. Clay minerals in the rhizoliths include kaolinite as the singular component.

Rhizoliths are presumed to be formed by surface weathering and pedogenic processes in the vadose zone. The pedogenesis of host teri sands might have released ca²⁺ ions and were later deposited in the ischolar_main cavities formed by the decay and complete removal of the tissues of ischolar_mains. Another source of ca²⁺ would be the calcareous sediments which underlies part of the teris. The absence of ischolar_main anatomy is a characteristic feature of these rhizoliths.

A sample of rhizolith collected at Sattankulam at a depth of 2.5 m gave a ¹⁴c age of 3680±110 years B.P. Hence, semiarid conditions of the present day in the Teri tract of southern Tamil Nadu, should have set in at least as way back as 3680±110 yr. B.P.

Keywords

Rhizolith, Origin, Palaeoenvironment, Teris, Tamil Nadu.

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Sabu Joseph ¹, K. P. Thrivikramaji ², D. S. Suresh Babu ³

Affiliations
1 Department of Environmental Sciences, University of Kerala, Kariavattom, Thiruvananthapuram - 695 581, IN
2 Department of Geology, University of Kerala, Kariavattom, Thiruvananthapuram - 695 581, IN
3 Centre for Earth Science Studies, P.B. No.7250, Akkulam, Thiruvananthapuram - 695 03 1, IN

Abstract

The early-modern red dune sands (teris) in the erstwhile Tirunelveli District of southern Tamil Nadu are typified by the large content of heavy minerals (HM), particularly ilmenite. Size-specific studies show that HMs dominate the -80 to +100 mesh, and magnetic susceptibility (X) studies demonstrate the presence of three fractions of ilmenite, viz., a (X= 286×10^-6), b(127×10^-6) and c (72×10^-6),which the fraction b is most abundant (range = 52-85%). Optical studies show a variety of exsolution features between ilmenite and haematite dominantly in fraction a, less in b and almost absent in fraction c. Chemical and XRD data of ilmenite fractions, indicate that a and b are relatively unaltered and belong to the ferrian ilmenite state, whereas c is altered and reaches the hydrated ilmenite state with notable development of pseudorutile and rutile phases. Further, the b fraction is composed of relatively pure ilmenite compared to a and c. Based on this investigation, the boundary between altered and unaltered ilmenite has been drawn at a magnetic susceptibility of 127×10^-6 cgs units. Hence, a physical separation of bulk ilmenite in terms of grain size and magnetic susceptibility can provide commercial ilmenite concentrates of relatively homogeneous nature in respect of composition and crystallinity.

Keywords

Ilmenite, Teri Sands, Magnetic Susceptibility, Alteration, Tamil Nadu.

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