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Abstract:
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The evolution of coast through geological time scale is dependent on the
transgression-regression event subsequent to the rise or fall of sea level. This
event is accounted by investigation of the vertical sediment deposition patterns
and their interrelationship for paleo-enviornmental reconstruction. Different
methods like sedimentological (grain size and micro-morphological) and
geochemical (elemental relationship) analyses as well as radiocarbon dating are
generally used to decipher the sea level changes and paleoclimatic conditions of
the Quaternary sediment sequence. For the Indian coast with a coastline length of
about 7500 km, studies on geological and geomorphological signatures of sea
level changes during the Quaternary were reported in general by researchers
during the last two decades. However, for the southwest coast of India
particularily Kerala which is famous for its coastal landforms comprising of
estuaries, lagoons, backwaters, coastal plains, cliffs and barrier beaches, studies
pertaining to the marine transgression-regression events in the southern region
are limited. The Neendakara-Kayamkulam coastal stretch in central Kerala where
the coast is manifested with shore parallel Kayamkulam Lagoon on one side and
shore perpendicular Ashtamudi Estuary on the other side indicating existence of
an uplifted prograded coastal margin followed by barrier beaches, backwater
channels, ridge and runnel topography is an ideal site for studying such events.
Hence the present study has been taken up in this context to address the gap area.
The location for collection of core samples representing coastal plain, estuarylagoon
and offshore regions have been identified based on published literature
and available sedimentary records. The objectives of the research work are:
To study the lithological variations and depositional environments of
sediment cores along the coastal plain, estuary-lagoon and offshore
regions between Kollam and Kayamkulam in the central Kerala coast
To study the transportation and diagenetic history of sediments in the area
To investigate the geochemical characterization of sediments and to
elucidate the source-sink relationship To understand the marine transgression-regression events and to propose
a conceptual model for the region
The thesis comprises of 8 chapters. The first chapter embodies the
preamble for the selection and significance of this research work. The study area
is introduced with details on its physiographical, geological, geomorphological,
rainfall and climate information.
A review of literature, compiling the research on different aspects such as
physico-chemical, geomorphological, tectonics, transgression-regression events
are presented in the second chapter and they are broadly classified into three viz:-
International, National and Kerala.
The field data collection and laboratory analyses adopted in the research
work are discussed in the third chapter. For collection of sediment core samples
from the coastal plains, rotary drilling method was employed whereas for the
estuary-lagoon and offshore locations the gravity/piston corer method was
adopted. The collected subsurficial samples were analysed for texture, surface
micro-texture, elemental analysis, XRD and radiocarbon dating techniques for
age determination.
The fourth chapter deals with the textural analysis of the core samples
collected from various predefined locations of the study area. The result reveals
that the Ashtamudi Estuary is composed of silty clay to clayey type of sediments
whereas offshore cores are carpeted with silty clay to relict sand. Investigation of
the source of sediments deposited in the coastal plain located on either side of the
estuary indicates the dominance of terrigenous to marine origin in the southern
region whereas it is predominantly of marine origin towards the north. Further
the hydrodynamic conditions as well as the depositional enviornment of the
sediment cores are elucidated based on statistical parameters that decipher the
deposition pattern at various locations viz., coastal plain (open to closed basin),
Ashtamudi Estuary (partially open to restricted estuary to closed basin) and
offshore (open channel). The intensity of clay minerals is also discussed. From
the results of radiocarbon dating the sediment depositional environments were
deciphered.The results of the microtextural study of sediment samples (quartz grains)
using Scanning Electron Microscope (SEM) are presented in the fifth chapter.
These results throw light on the processes of transport and diagenetic history of
the detrital sediments. Based on the lithological variations, selected quartz grains
of different environments were also analysed. The study indicates that the
southern coastal plain sediments were transported and deposited mechanically
under fluvial environment followed by diagenesis under prolonged marine
incursion. But in the case of the northern coastal plain, the sediments were
transported and deposited under littoral environment indicating the dominance of
marine incursion through mechanical as well as chemical processes. The quartz
grains of the Ashtamudi Estuary indicate fluvial origin. The surface texture
features of the offshore sediments suggest that the quartz grains are of littoral
origin and represent the relict beach deposits.
The geochemical characterisation of sediment cores based on geochemical
classification, sediment maturity, palaeo-weathering and provenance in different
environments are discussed in the sixth chapter.
In the seventh chapter the integration of multiproxies data along with
radiocarbon dates are presented and finally evolution and depositional history
based on transgression–regression events is deciphered.
The eighth chapter summarizes the major findings and conclusions of the
study with recommendation for future work. |