Discrimination of tectonic dynamism, quiescence and third order relative sea level cycles of the Cauvery Basin, South India

Application of integrated stratigraphic modeling of sedimentary basins with the help of sequence and chemostratigraphic methods for improved understanding on the relative roles of depositional pattern and history of a Barremian-Danian stratigraphic record of the Cauvery Basin, India was attempted. Through enumeration of facies characteristics, tectonic structures and geochemical characteristics of the sedimentary rocks the use of geochemical signatures in distinguishing the relative roles of major factors has been evaluated. The results indicate that the geochemical signatures of the sedimentary rocks accurately record the prevalent geological processes and an ability to distinguish them through employing stratigraphic variations of compositional values and discrimination diagrams help in understanding the basinal history better. In addition, predomination of relative sea level fluctuations and active nature of tectonic movements during few time slices, which in turn was overwhelmed by sea level fluctuations are also inferred.


Introduction
The theory of sequence development defines the sedimentation system under the control of four major variables, namely, tectonic subsidence, eustatic sea level change, volume of sediment influx and climate (SARG 1988). The relative sea level cycles, first published by VAIL et al. (1977), revised by HAQ et al. (1987) espoused that the sedimentary sequences are produced principally under the influence of sea level cycles that vary between few tens of millions of years (1 st order cycle) to few million years (3 rd order cycle).
Successive studies have shown that distinct sedimentary sequences could be traced to sea level cycles up to infra seventh order (NELSON et al. 1985;WILLIAMS et al. 1988;CARTER et al. 1991). VAIL et al. (1977) stated that the sea level chart published by them is incomplete and cycles of varying order could be added, so that, more complete chart could be established. The aim behind this statement is to incorporate sea level cycles at Milankovitch scale, to which the response of the sedimentation system is proved beyond doubt (CARTER et al. 1991). RUBEN et al. (2012), HAQ (2014) and RUBAN (2015) have present-ed the updates based on the progress made in this field of research so far. HAYS et al. (1976) have convincingly demonstrated that climatic records were dominated by frequencies characteristic of variations in the Earth's tilt, precession and eccentricity relative to the Sun. In the years since, numerous studies have upheld the validity of the Milankovitch climatic cycles in terms of 100, 41, 23 Ka orbital periods that influence or control variations in global ice volume, thermohaline circulation, continental aridity and run off, sea surface temperature, deep ocean carbonate preservation and atmospheric CO 2 and methane concentrations (RAYMO et al. 1997;GALE et al. 2002GALE et al. , 2008GALEOTTI et al. 2009). While examining the compiled data on the sediment volumes (mass) or sediment fluxes of the continental and marine subsystems to determine the complete routing in terms of mass conservation for specific time periods since Cenozoic, HINDERER (2012) reported that the response times of the large sedimentary systems are within the Milankovitch band. HILGEN et al. (2014) opined that despite fragmentary sedimentation, stratigraphic continuity as revealed by cyclostratigraphy unequivocally established the dominant role of depositional processes at the Milankovitch scale.
Global chemostratigraphic signals such as those carried by organic matter (MIDDLEBERG et al. 1991;PASLEY et al. 1993;MEYERS & SIMONEIT 1989;TU et al. 1999;CALVER 2000) oxygen isotope VEIZER et al. 1999) and strontium isotope (VEIZER 1985;VEIZER et al. 1999;MUTTERLOSE et al. 2014) and their relationships with sea level changes, and in turn, the climatic fluctuations are well known. The global carbon cycle varies on a million year time scale affecting the isotopic and chemical composition of the global carbon (WALLMANN 2001). The glacial intervals coincide with shifts in δ 18 O and δ 13 C. For the carbon isotope record, rate of burial of C Org and thereby changes in atmospheric CO 2 and for the oxygen isotopic records, temperature and ice volume effects on the seawater reservoirs and thereby sea level changes may be linked (KAMPSCHULTE et al. 2001).
Spectral analysis of δ 18 O and δ 13 C shows that their significant variances are concentrated at 100, 43, 23 and 19 Ka spans (OPPO et al. 1990;OPPO & FAIR-BANKS 1989). While examining δ 18 O of Phanerozoic seawater, VEIZER et al. (1997) observed high frequency cycles within first order cycle. STRAUSS (1997) recorded fourth order cycles of sulphur isotope that stack up to form 3 rd order cycle fluctuations that in turn accommodated within 2 nd order cycles. GOLD-HAMMER et al. (1991) showed that the sequences of Paradox Basin exhibited a hierarchical stacking pattern of 5 th order (80 Ka duration) shallowing upward cycles grouping into 4 th order (400 Ka duration) cycles, which in turn stacked vertically into part of a 3 rd order cycle. Large number of studies has docu-mented the occurrences of high frequency sea level changes within major sea level cycles (for example, GIL et al. 2006;KULPECZ et al. 2009;ELRICK & SCOTT 2010;PELLENARD et al. 2014;ULIČNÝ et al. 2014). These abilities of sequence and chemostratigraphy helped successfully reinterpret the basinal history, and establish regional and global stratigraphic correlation and are being widely applied for petroleum exploration, inter-well correlation and reservoir characterization, etc. (RAMKUMAR et al. 2010(RAMKUMAR et al. , 2011. On the contrary, there are many studies that have questioned the veracity of the sequence stratigraphic concepts (MIALL 1991;2009), especially the third order cycles (for example, CLOETING 1988;MIALL 1991;HISCOTT 2001;SPALLETTI et al. 2001;STEPHENS & SUMNER 2003) and the precision of the cycle durations and the applicability of such cycles on a global scale (MIALL & MIALL 2001).
Nevertheless, there are reports that have documented the occurrences of sedimentary records typical of high-frequency cycles deposited under the primary control of tectonics (for example, BHATTACHARYA & WILLIS 2001;VAKARELOV et al. 2006) though doubts have been raised over the rate at which the tectonic movements can mimic high-frequency cycles (GOLD-HAMMER et al. 1987;MASETTI et al. 1991). Influence of regional-global plate movements over third order cycles has also been reported by BACHMANN et al. (2003) and VEIGA & SPALLETTI (2007). In an innovative study, VAN DER MEER et al. (2014) recently demonstrated the control exercised by tectonics over atmospheric CO 2 through a complex and intrinsically coupled chain of processes and thereby over climate-continental weathering and sea level fluctuations, and ensuing sedimentary records. HISCOTT (2001), SPALLETTI et al. (2001, BACHMANN et al. (2003) and BRETT et al. (2004) opined that it is a common phenomenon of sedimentary records to have sea level cycles affected by local tectonics either positively or negatively. Depending on the local, regional and global scale of processes, these cyclic changes may get preserved in the ensuing sedimentary strata, the temporal scale of which may vary from few thousand years to few or few tens of millions of years -a postulate widely utilized in seqeuence and chemostratigraphy.
Thus, the enigma of relative roles of tectonics-sea level fluctuations over depositional pattern remains to be there where it had all started when VAIL et al. (1977) proposed the sequence stratigraphic concepts. It has also raised questions on the very fundamentals of sequence and chemostratigraphic applications. At this juncture, it becomes essential to address the problem of discrimination relative influences of tectonics and relative sea level fluctuations over sedimentary records.
The Cauvery Basin (Fig. 1) is located in the southern part of Indian peninsula. It contains a near complete stratigraphic record of Barremian-Danian. It is one of the most studied basins (ACHARYYA & LAHIRI 1991). In a first ever basin-scale temporally long range chemostratigraphic study, RAMKUMAR et al. (2011) recognized six major chemozones, separated by type 1 sequence boundaries and other correlative surfaces coeval with third order cycles of sea level, which in turn contained high frequency cycles, probably in the order of 10 4 -10 6 years and found to be consistent with the timescale-sea level curve of GRAD-STEIN et al. (2004). Though there are disagreements on the connectedness of Indian subcontinent with other continental plates during Barremian to Danian, (ALI & AITCHISON 2008), the enclosed nature of Indian subcontinent by sea and its behavior as an Island akin to the present day Australia was not questioned. As the climatic conditions of Island continents are predominantly controlled by the temperature of surrounding seawater and the Cretaceous Period had experienced extended greenhouse effect (VEIZER et al. 2000;BICE & NORRIS 2002;COCCIONI & GALEOTTI 2003;HERRLE et al. 2003;NAJARRO et al. 2010), changes in seawater temperature would have affected the glaciers to retreat or advance, causing high-frequency sea level oscillations that in turn might have influenced the depositional system of the Cauvery Basin.
As the provenance area of the Cauvery basin sediments were confined to adjacently located horsts and hinterland (RAMKUMAR et al. 2004a(RAMKUMAR et al. , 2006 the sea level changes and the tectonic events might have been exacerbated (VEIGA & SPALLETTI, 2007) and reflected in the sedimentary records. The basin fill shows textural immaturity all through is sedimentary history. In addition, high-frequency sea level cycles during Barremian-Santonian and Late Cretaceous-Danian, overlap of much older lithostratigraphic units by younger units and angular unconformity surfaces characterize the basin fill and indicate the involvement of certain amount of tectonism (VEIGA et al. 2005) over deposi-Discrimination of tectonic dynamism, quiescence and third order relative sea level cycles of the Cauvery Basin tional history and creation of accommodation space. By these traits, the Cauvery Basin offers a test site to discriminate relative influences of tectonics and sea level fluctuations. As the stratigraphic record is the outcome of an exogenic system consisting of geologic setting, changes in sea level, changes in geochemical reactions between the sea and earth and climate (SRINIVASAN 1989) and as the sedimentary geochemistry is a faithful recorder of provenance, tectonic setting and palaeoclimatic conditions prevalent (BHATIA 1983;BHATIA & CROOK 1986;ROSER & KORSCH 1986;TAYLOR & MCLENNAN 1985;MONGELLI et al. 1996;CINGOLANI et al. 2003), this paper attempts understanding the dynamics of provenance, tectonic setting and sea level fluctuations of the Cauvery Basin and to discriminate them through geochemistry.
Thus, the objectives of this paper are set to examine a) hierarchical variations of geochemical signatures (sensu RAMKUMAR, 2015) in tune with prominent controls of sequence-chemostratigraphic cycles, b) ability of geochemical signatures to distinguish the relative significances of various depositional agents, provenance and tectonic setting, etc. and c) utility of application of integrated chemo-sequence stratigraphic modeling for characterizing basin fill on a long-short term cycles. Table 1. Lithostratigraphy of the exposed part of the Cauvery Basin (after RAMKUMAR et al. 2004a).

Geological setting
Among the NE-SW trending Late Jurassic-Early Cretaceous pericratonic rift basins created all along east coast of the Indian peninsular shield (SASTRI et al. 1981;POWELL et al. 1988;CHARI et al. 1995;JAFAR 1996;CHATTERJEE et al. 2013), in response to the fragmentation of Gondwana super continent and rifting of Africa-India-Antarctica (LAL et al. 2009), the Cauvery Basin (Fig. 1) is located at the southern part of the Indian peninsula. The basin continued evolving till the end of Tertiary through rift, pull-apart, shelf sag and tilt phases (PRABAKAR & ZUTSHI, 1993). It lies between the latitudes 08°30'N and the longitudes 78°30'E and covers an exposed area of about 25,000 km 2 onland and 17,500 km 2 in the offshore (SASTRI et al. 1981) of the Bay of Bengal upto 200 m isobath. It is a structurally elongated basin with NE-SW trending half-graben morphology and a regional dip of 5-10° E and SE directions.

Materials and methods
Systematic field mapping in the scale of 1:50,000 was conducted through ten traverses ( Fig. 1) in which 308 locations were logged and sampled. At each location and along the traverses, information on lithofacies, contact relationships, sedimentary and tectonic structures and occurrences of mega and ichnofossil assemblages were recorded. For characterizing the strata for sequence analysis, the conceptual standard workflow of CATUNEANU (2006) and CATUNEANU et al. (2009 were followed. It included definition of type sections, recognition of sequence stratigraphic surfaces (among the seven types of surfaces), defining them into sequence boundaries, and relating them with any of the four events of the base-level cycle, and then with any of the three systems tracts (forced regression, normal regression and transgression) based on the outcrop, facies and other relevant criteria. The sequence model so developed was presented earlier (RAMKUMAR et al. 2004a).
Based on the field data, a composite stratigraphic profile of Barremian-Danian strata was constructed that allowed selection of 157 rock samples for analyzing trace elemental composition. From these 157 samples, 70 samples were further selected and analyzed by XRF for major elemental composition following the procedures discussed in KRAMAR (1997) andSTÜBEN et al. (2002). Stable isotopic analyses were performed as per the procedures presented in KELLER et al. (2004). Analyses of 157 samples for petrography and wholerock mineralogy, 70 samples for clay mineralogy were also performed. The geochemical data were interpreted with stratigraphic variation, plotting in established discrimination diagrams (for example, ROSER & KORSCH, 1986) and computation of weathering indices (NESBITT & YOUNG, 1982), and corroboration with major geological events. Collation of all these information along with the published data allowed elucidation of the prevalent changes in provenance, tectonic setting, and fluctuations in relative sea level with which, the relative influences of various processes were interpreted and discussed.

Tectonic events
All along its western margin, basin margin faults are recognizable ( Fig. 1) which separate the Archaean shield from the sedimentary deposits. Based on the field structural criteria, contact relationships, and lithological association and displacement, basin scale tectonic movements and their relative timings were interpreted viz., initial block faulting (F1 in Fig. 1), movement of fault blocks during Albian-Cenomanian boundary interval (F2 in Fig. 1), reactivation of older fault blocks and creation of new fault during Santonian (F3 in Fig. 1) and reactivation of fault blocks during post Danian-pre Discrimination of tectonic dynamism, quiescence and third order relative sea level cycles of the Cauvery Basin Table 2. Lithofacies characteristics of the Barremian-Danian strata of the Cauvery Basin.
Discrimination of tectonic dynamism, quiescence and third order relative sea level cycles of the Cauvery Basin 25 Quaternary (F4 in Fig. 1). It is to be stated that, in addition to these major fault movements, there were minor and local scale tectonic movements, namely across Aptian-Albian boundary interval, during Cenomanian (during the deposition of Olaipadi member), and during Santonian (during the deposition of Varakuppai member) all of which were confined only to adjustment of fault blocks along the preexisted fault planes. There exists a difference in trends of post Danian fault movements (F4 in Fig.1) that have affected the Miocene to Pliocene sandstones, Danian Limestones, and Maas-trichtian deposits by folding, fracturing and faulting (RAMKUMAR 2007). Enumeration of tectonic structures and depositional history of the Cauvery Basin indicated that after initial block faulting and inception of sedimentation during Late Jurassic-Early Cretaceous, intensity of tectonic control over sedimentation was diminutive (PRABAKAR & ZUTCHI 1993;RAMKUMAR 1996;RAM-KUMAR et al. 2005a). WATKINSON et al. (2007) recognized three major tectonic stages and resultant stratigraphic groups for this basin; viz., syn-rift Gondwana Group (Early Cretaceous), syn-rift Uttatur Group (Al-bian-Coniacian) and post-rift Ariyalur Group (Santonian-Maastrichtian) and are in conformity with the present observations.

Relative sea level fluctuations
Sedimentation in this basin took place in an epicontinental sea and the bathymetry was at shallow -modest levels (<50 m -as indicated by the linear curve in Fig. 2) although variations from supratidal to basinal levels were inferred. Based on the foraminifer data, RAJU & RAVINDRAN (1990) and RAJU et al. (1993) documented six 3 rd order cycles of glacio-eustatic origin. RAMKUMAR et al. (2004a) constructed a sea level curve for this basin based on bathymetric trends of lithofacies data, which is similar to the curves presented by RAJU et al. (1993) RAVINDRAN, 1990;RAJU et al. 1993;RAMKUMAR et al. 2004a). The 3 rd order cycles are separated by type I sequence boundaries (recognized through shift of shoreline crossing shelf break as explicit in lithologic information, contact relationship between strata, evidences of subaerial exposure and erosion, advancement of fluvial channels over former offshore regions, etc.). The period from Barremian to Coniacian shows frequent occurrence of sea level lows and highs that may be interpreted as prevalent high frequency/higher order cycles. The period from Coniacian to Danian shows sea level rise and fall punctuated with lesser frequency of higher order cycles. The sea level rise during Santonian-Early Campanian shows steadily increasing pattern.

Geochemical characteristics
Geochemical elemental data having predominant affiliation with detrital (Si, Ti, Zr), biogenic (Ca), and tectonic processes (Y) and computed values of plagioclase alteration index (PIA) as climatic indicator were plotted in stratigraphic profiles (Fig. 3). These profiles depict the occurrences of inverse relationships between detrital elements and biogenic element, six major enrichment-depletion cycles coeval with 3 rd order sea level cycles within which many high-frequency enrichment-depletion cycles, significant change of the pattern across Santonian, sudden positive excursions of Y during Cenomanian and Santonian, and a major positive excursion of PIA during Turonian-Coniacian.
Plotting few selected oxides percentages against Al 2 O 3 shows sympathetic nature of SiO 2 , TiO 2 , and K 2 O, strongly anti-sympathetic nature of CaO, slightly positive yet scattered nature of MgO and Na 2 O (Fig. 4). The plot of Al 2 O 3 against CaO shows an interesting phenomenon of distinctly recognizable twin clusters. Other plots also show feebly recognizable but scattered twin clusters. Textural discrimination of the samples based on oxides percentages shows that most of the samples fall in the texturally immature fields viz., litharenite, wacke, arkose, subarkose, and only very few in the quartz arenite field (Fig. 5). Plotting the SiO 2 -Al 2 O 3 *5-CaO*2 in ternary diagrams that have average shale, smectite, illite, kaolinite fields and enrichment indicators of detrital (significant sediment influx), biogenic (warm climate, sea level high), and clay (significant weathering in the provenance) fields show that all the samples fall either near siliciclastic or biogenic fields (Fig. 6). Ternary plot of CN-A-K also shows that most of the samples fall below the feldspar join and only a few fall above the join (Fig. 7). Plot of the data in tectonic setting discriminant diagram (SiO 2 Vs K 2 O/Na 2 O) shows that the samples fall in the Arc, active continental margin and passive continental margin (Fig. 8) fields. The tectonic discrimination diagrams of SiO 2 Vs K 2 O/Na 2 O and SiO 2 /Al 2 O 3 Vs Na 2 O/K 2 O show interesting phenomenon of plot of Barremian--Santonian samples in the active continental margin field, Campanian-Danian samples except few samples of Kallamedu Formation (Late Maastrichtian) in passive continental margin field and few samples of Kallamedu and Ottakoil formations in the island arc field (Fig. 8).

Geological events and Depositional cycles of the Cauvery Basin
All along the western margin of the exposed area of the basin, the Precambrian basement rocks show the Discrimination of tectonic dynamism, quiescence and third order relative sea level cycles of the Cauvery Basin  angular basement rock boulder-cobble sized clasts and feldspar pebbles typify this formation (Plate 1.2).
As the intensity of energy conditions reduced, sediment grain size also got reduced. Significant sedimentation commenced with the establishment of fluvial   source onland and submarine fan delta in the basin (represented by the Kovandankurichchi sandstone member). Gradation of this sandstone member into deep marine claystone-siltstone member (Terani member) indicates prevalence of stabilized environmental conditions until the end of deposition of the Terani member. It was brought to an end due to renewed faulting introducing an angular unconformity associated with erosion and redeposition of older sedimentary rocks. The rejuvenated sedimentation was through deposition of shale and shale-limestone alternate beds of the Grey shale member of the Dalmiapuram Formation. The depocenter was partially and periodically closed, while grey shale was deposited. Whenever open conditions of sea circulation were prevalent, bioclastic limestone beds were deposited. These limestone interbeds show thickening upward character indicating increase in durations of openness of the sea that culminated in the development of biostromal member over the Grey shale member. The biostromal member contains principally coral clasts and algal fragments with varying proportions of bioclasts of bryozoa, bivalvia and gastropoda in addition to reef dwelling microfauna. Siliciclastic admixture is significant to minor in proportion and varies randomly. Beds of this member are parallel, even to uneven, thin to thick and have frequent erosional surfaces in between. All these signify deposition in subtidal to storm weather wave base regions under photic zone. Typical coral reef deposits developed over this member that moved gradually towards offshore regions owing to fall of sea level. At the top of this biohermal limestone member, major erosional surface associated with faulting (F2 in Fig. 1; Plate 1.3, 1.4, 1.5) and regression is observed.
This faulting had exposed the subtidal-storm weather wave base deposits to subaerial conditions that led to karstification. It also paved way for the deposition of the Olaipadi conglomerate member which contains large boulders (many of which are more than 10 m in diameter) of basement rocks, and lithoclasts of similar size, drawn from underlying bioclastic and coral limestone, Terani claystone and lithoclasts of older sedimentary conglomerates, all embedded in basinal clay sediments! Angular to sub rounded nature of the boulders, presence of basement as well as lithoclasts of older sedimentary rocks in basinal sediments clearly indicate a major faulting event, creation of steep slope and short distance of transportation. Presence of argillaceous siltstone over these boulders with lamination parallel to the boulder boundaries indicates restoration of normal depositional conditions and gradual increase of sea level. A detailed facies and sequence analysis of these deposits suggested (RAMKUMAR, 2008) the prevalence of turbiditic current controlled depositional pattern coeval with seismicity related mechanical erosion and gravity driven deposition that acted independently. Deposition of argillaceous sediments was brought to an end by rejuvenation of fluvial source resulting in influx of coarse-finer clastics and suspended sediment load. This new set of environmental conditions led to the deposition of the Kallakkudi calcareous sandstone member. This member is sandy in southern region and clayey in northern region. Occurrence of recurrent Discrimination of tectonic dynamism, quiescence and third order relative sea level cycles of the Cauvery Basin Bouma sequences that always top with a gypsiferous layer followed by an erosional surface and again by another Bouma sequence in this member indicates deposition under the influence of turbidity currents and gradual facies change from near shore to deep sea. On the whole, it could be interpreted that, deposition of this member took place in a slowly sinking basin and/or deposition with episodic sea level rise and fall coupled with active fault block adjustment (in minor scale) after major movement.
With due sinking of the coastal basin and/or sea level rise, deep marine conditions were established and thick pile of Karai Formation clays were deposited. Deposition of about 450 m thick clay alternated with ferruginous silty clays and gypsiferous layers suggests well developed fluvial system onland that supplied suspended sediment load continuously to deep marine regions. Thick population of belemnites, silty admixture, alternate thin-thick lamina of ferruginous silty clay and gypsiferous clay bands are frequent in the southern region indicative of deposition also in shallower regions of paleosea. These shallower regions were periodically exposed subaerially due to minor sea level oscillations to produce evaporites. The top surface of this formation is marked by a pronounced erosional surface that suggests major regression at the end of the deposition. This erosional surface is overlain immediately by subtidal-supratidal ferruginous sandstones along with shell banks typical of estuary and shell hash typical of shallow water shoals/distributary mouth bars that represent Kulakkanattam and Grey sandstone members of the Garudamangalam Formation. Together, their occurrences indicate shoreline retreat and associated advancement of fluvial system over former offshore areas. This inference is substantiated by sudden appearance of large tree trunks in these sandstones. Although the boundary between the Karai clays and the Kulakkanattam sandstones is an erosional unconformity, presence of conformable relationship and near parallel bedding planes of rocks between them suggests simple sea level variation and introduction of newer environmental conditions rather than fault controlled environmental change across the boundary. The deep-water conditions were restored again in this part of the basin with the introduction of deposition of the Anaipadi sandstone member that shows gradual increase of sea level. Break in sedimentation, probably influenced by major regression was witnessed at the end of deposition of the Anaipadi sandstone member.
Renewed transgression initiated during the Middle Santonian covered the regions located north and south that were not transgressed previously. This widespread transgression, associated with downwarping of fault blocks, had submerged the coastal tracts up to Pondicherry in the north resulting in generation of Archaen-Santonian and Archaen-Campanian contact (faultline located north of Kilpalur -refer F3 in Fig.   1; Plate 1.6, 1.7, 1.8, 1.9). This period was associated with widespread erosion of basement rocks and older sedimentary rocks and their redeposition in the newly created depocenters. The Sillakkudi Formation of the Ariyalur Group, which has been the product of this widespread transgression, has three members. The lowermost member is a fluvial unit and shows transition to deposition under marine influence towards top. Major channels with a width of more than a kilometer and 30 m deep that incised older sedimentary rocks (Fig.1), were recognized in the field. The strata of this member have reverse graded basement boulder and lithoclastic conglomerates (Plate 1.6, 1.7, 1.8). They also show large scale advancing cross beds (Plate 1.7), alternate with ferruginous sandstone foresets. From the detailed facies and sequence analysis and tectonic structural information recognized in the field, RAMKUMAR et al. (2005a) interpreted overwhelming influence of sea level fluctuations over the depositional pattern, and continued seismicity influenced mechanical erosion and gravity assisted fluvial transport until the deposition of the Sadurbagam member. Continued rise of sea level had submerged the fluvial/estuarine mouth sediments and deposition in subtidal to intertidal environments occurred. This sea level rise has been overwhelming and covered large tracts of western part of the basin that remained positive since inception of the basin, as indicated by the contact between Archaen-Varanavasi member of the Sillakkudi Formation (Plate 1.9). Towards top, the Varanavasi member shows frequent occurrences of pebbly sandstone layers may be as a result of prevalent periodic higher energy conditions (RADULOVIĆ et al. 2015) and/or seismic aftershocks, erosional surfaces and reworked fauna. Localized occurrences of serpulid colonies at the top of this member indicate cessation of sediment supply, reducing sea level, reduced circulation and lower energy conditions. A major erosional unconformity separates this formation from overlying Kallankurichchi Formation.
The renewed transgression during the Latest Campanian-Early Maastrichtian was marked with widespread erosion of basement rocks and older sedimentary rocks. However, the size of the basement boulders and lithoclasts of older sedimentaries in the basal conglomerate member of this formation, rarely exceed 30 cm and are more rounded than their older counter parts. These clasts seem to be recycled from older sedimentary rocks rather than sourced fresh from basement rocks. Thus, the Kallar arenaceous member has lithoclastic conglomerate deposits at its base and rests over the Sillakkudi Formation (Plate 1.10) with distinct angular erosional unconformity. Biohermal and biostromal deposits constitute the Kallankurichchi Formation and denote cessation of Santonian-Campanian fluvial sediment supply. As the initial marine flooding started to wane out, the deposits show reduction in proportion and size of siliciclastics that were increasingly replaced by gryphea colonies. As the sea level was gradually increasing, the gryphea bank shifted towards shallower regions and the locations previously occupied by coastal conglomerate became middle shelf wherein typical inoceramus limestone started developing. Break in sedimentation of this member was associated with regression of sea level that had transformed the middle -outer shelf regions into intertidal -fair weather wave base regions.
These newer depositional conditions resulted in erosion of shell banks and middle shelf deposits and redeposition of them into biostromal deposits (Tancem biostromal member). As the energy conditions were high and deposition took place in shallower regions, frequent non-depositional and erosional surfaces, punctuated with cross bedded carbonate sand beds and tidal channel grainstones and storm deposits with hummocky cross stratification were deposited. Again, the sea level rose to create marine flooding surface and as a result of which, gryphea shell banks started developing more widely than before that represent the Srinivasapuram gryphean limestone member. Towards top of this member, shell fragments and minor amounts of siliciclastics are observed that indicate onset of regression and associated introduction of higher energy conditions and detrital influx. The occurrence of non-depositional surface at the top of this formation and deposition of shallow marine siliciclastics (Ottakoil Formation) in a restricted region immediately over the predominantly carbonate depocenter and conformable offlap of much younger fluvial sand deposits (Kallamedu Formation) are all suggestive of gradual regression associated with reestablishment of fluvial system (Plate 1.11) at the end of Cretaceous Period. Towards top of the Kallamedu Formation, paleosols are recorded implying abandonment of river system and restoration of continental conditions at the end of the Cretaceous Period.
At the beginning of Danian, transgression took place that covered only the eastern part of the Kallamedu Formation. Presence of conformable contact between the Anandavadi member and the Kallamedu Formation and initiation of carbonate deposition from the beginning of Danian are indicative of absence of any major tectonic activity and fluvial sediment supply at this time. Increase in sea level and establishment of shallow, wide shelf with open circulation paved way for the deposition of the Periyakurichchi member with cyclic marl-limestone couplets (Plate 1.12). At the top, this member has distinct erosional unconformity, which in turn, when interpreted along with the presence of huge thickness of continental sandstone (>4000 m thick Miocene-Pliocene Cuddalore sandstone Formation), indicates restoration of continental conditions in this basin. Absence of any other marine strata over the Cuddalore sandstone Formation suggests that the sea regressed at the end of Danian had never returned to this part of the Cauvery Basin.
The depositional cycles in the light of lithofacies characteristics (table 2) and succession (table 1) and geological events described above are summarized in the table 3. From these tables, it follows that, under favorable climatic and other conditions, significant influx of detrital materials (either with or without chemical weathering in the provenance area) to the depositional basin and resultant reduction in carbonate accumulation during sea level lowstands and conversely, reduction of detrital influx owing to the limited availability of terrestrial areas, shortening and/or drowning of fluvial channels and significant carbonate accumulation during sea level highstands, which are considered to be the fundamental processes of sequence development were in operation in this basin for the whole of its depositional history except during the major tectonic events. From the tables 2 and 3, it could also be observed that at each change (either tectonic or sea level fluctuation), there were significant erosion (either the provenance area or former marine regions or both) and sediment recycling events, that have removed former sedimentary records partially or completely and obliterated the depositional continuum.
The sedimentation system is dominated by cyclic processes that operate on a hierarchy of temporal and spatial scales on which short-lived events are superimposed (VEIZER et al. 1997). As a consequence, only a net result of cycles and events could be recognized in rock records. Cyclic sedimentation has been documented in several sedimentary basins and there are many lines of evidences that relate those cycles to short-term (Milankovitch band) glacio-eustatic pulses (GRAMMER et al. 1996). At this juncture, report of occurrences of all the six global sea level peaks of eustatic in origin, occurrences of 100% distinct six chemozones (RAMKUMAR et al. 2010b(RAMKUMAR et al. , 2011 in tune with third order sea level cycles, pristine nature of geochemical characteristics of the rocks (RAMKUMAR et al. 2006) are all suggestive of predominance of climate-sea level cycle controlled depositional pattern in this basin. However, the major faulting during Barremian and reactivation of faults during depositional history, as observed from field and lithofacies characteristics necessitates examining the impact of these events over the depositional system.

Relative influences of tectonics and sea level fluctuations over the depositional cycles
The general knowledge about a geochemical system allows establishing a definite number of processes governing the sedimentary system namely, the redox conditions, detrital input, changes in provenance and quantum of sediment influx and climate, etc, (PINTO et al. 2004;MONTERO-SERRANO et al. 2010). The occurrences of inverse relationships between the Si, Ti, Zr and Ca, (Fig. 3), when corroborated with the lithofacies alternations between siliciclastics and carbonates (table 2) and Discrimination of tectonic dynamism, quiescence and third order relative sea level cycles of the Cauvery Basin their synchronicity with sea level lows and highs respectively (Fig. 2), allow interpretation of sea level controlled depositional pattern in this basin. Decrease in Si and many metals typical of heavy minerals are observed from these profiles (Fig. 3) and can be interpreted as the result of transgressions (HILD & BRUMSACK, 1998). Similarly, the reduction of Ca content is found to be associated with regressions. As could be observed elsewhere (RACHOLD & BRUMSACK, 2001;HOFMANN et al. 2001;BOULILA et al. 2010), whenever siliciclastic deposition ceased, carbonate deposition was initiated (WARZESKI et al. 1996) in this basin. From the Falcon Basin, northwestern Venezuela, MONTERO-SERRANO et al. (2010) reported similar geochemical elemental grouping in terms of either detrital or carbonate as a result of siliciclastic-carbonate lithofacies alternations. SARG (1988) observed that, sedimentary basins starve for detrital sediments during high stands that lead to development of carbonates. A recent review of previously published information on evolutionary stages and sequence development in the Cauvery Basin (KALE 2011) suggested the availability of larger accommodation space than the sediment influx all through its evolutionary history. It also means that there might be climatic control over the observed lithofacies-geochemical grouping alternations. RUFFEL & RAWSON (1994) and SOREGHAN (1997) opined that dry periods might cause a deficit in detrital supply and favor deposition of carbonates. It supports the interpretation of occurrences of sea level highstands during interglacial periods (warmer than glacial periods) and resultant general aridity and deprivation of clastic sediment supply. The glacial periods promote enhanced terrigenous supply to the depocenters in view of shelf erosion (KAMPSCHULTE et al. 2001) and fluvial system advancement (SARG, 1988;CARTER et al. 1991). Occurrences of paleochannel courses (Fig. 1) and their association with siliciclastic deposits, erosion during the periods of lower sea level, influenced also by the proximity to source rocks and adequate slope could be inferred from the configuration of the Cauvery Basin. Occurrences of unaltered lithoclasts and feldspar clasts in rocks that immediately follow regressive surfaces also suggest the prevalent mechanical erosion, rapid and short duration of transport and quick burial. Such rapid physical erosion and textural immaturity of ensuing sediments could have produced the co-variation of Si and other elements associated with quartz, feldspar and other silicates. Based on the occurrences of all the six global sea level peaks, recognized independently Table 3. Geological events of the Cauvery Basin as inferred from the exposed area. through foraminifer (RAJU & RAVINDRAN, 1990;RAJU et al. 1993) and geochemical data (RAMKUMAR et al. 2005b;2010b;, influence of climate controlled eustatic sea level changes, over the depositional pattern of the basin is affirmed. The element Y shows a peculiar polynomial peak across Aptian-Albian boundary (Fig. 3), subdued nature during most of the successive period until latter part of middle Albian and gradual increase then onward, a significant peak during Coniacian and finally a gradual decrease. In magnitude and scale, it mimics Zr (Fig. 3). As the element Y undergoes little or no diagenetic alterations DAS 1997;PINTO et al. 2004;MONTERO-SERRANO et al. 2010), presence of its short and significantly prominent peaks exactly coinciding faulting events (Fig. 1) and associated change in sedimentation pattern ( Table  2) indicates influx of Y immediately after major tectonic movements and resultant change in nature, quantum and composition of detrital influx into the basin. Sedimentation pattern and nature of sediments of the periods between Barremian-Coniacian and Santonian-Danian were different and are reflected in the patterns of Y and Zr during these two time spans. The differences between these elements in terms of temporal resolution may be a consequence of their differential response  to prevalent depositional environmental conditions as enforced/introduced by the major tectonic event. DUBICKA et al. (2014) also observed significant changes in environmental conditions due to Subhercynian tectonic movements in Ukrine during Coniacian-Santonian. Enrichment of these elements up to Coniacian and their subdued nature after Coniacian could be attributed to the changes brought in by major tectonic activity occurred during Santonian, across which significant changes in proximity of sediment source and nature and quantum of detrital influx were witnessed (SUNDARAM & RAO, 1986).
The abundance of Zr in clastic rocks was interpreted to be the result of detrital influx as well as sediment recycling (SPALLETTI et al. 2008). Occurrences of generally higher levels of Zr all through the Barremian-Danian with the exception of latest Campanian-middle Maastrichtian (Kallankurichchi Formation) and many episodes of positive excursions over this general trend suggest sediment starved nature of the basin and significant recycling of older sedimentary rocks. Ti and Zr are generally assumed to represent detrital inputs into a sedimentary basin and their variations should be related with changes in weathering conditions in the hinterland or changes of provenance (BELLANCA et al. 2002). Zr and Ti are considered to be effective in discriminating volcanoclastic sediments and also sediments of different diagenetic and tectonic histories (ANDREOZZI et al. 1997). Zirconium is mostly concentrated in zircons, which accumulate during sedimentation while less resistant phases are preferentially destroyed (ALVAREZ & ROSER, 2007). Peak enrichments of Zr during middle Cenomanian (Gypsiferous clay member), latest Cenomanian (Odium member), middle Campanian (Varakuppai member), middle-late Maastrichtian (Ottakoil Formation), early Danian (Anandavadi member) are observed and interpreted as the durations of influx and cessation of terrigenous materials which in turn might have been controlled by variations in source area weathering and/or a change from more humid to more arid conditions or tectonic movements (MUNNECKE & WESTPHAL, 2004). SANDULLI & RASPINI (2004) interpreted the elemental cycles as the precession and obliquity periodicities, the bundles and superbundles into short and long eccentricity cycles and similar inference could be made to the rocks under study.
The source area consists of granitic gneisses in low lying plains and massive hills of charnockite. These rocks consist of very coarse grained plagioclase, smaller grains of quartz, hypersthene, and amphibole as major minerals, magnetite, garnet, and biotite as minor minerals and zircon, rutile and apatite as accessory phases (SHARMA & RAJAMANI, 2001). Cutting across the granitic gneiss, pegmatite veins composed of large to very large feldspar crystals (at places ranging upto many tens of centimeters) occur frequently. The nature and extent of source rock weathering, physical sorting during transport and environmental conditions during deposition at the depocenters exert significant control over sediment geochemistry (SHARMA & RAJAMANI, 2001). The samples under study show that the period from Cenomanian-Coniacian have very high PIA values with a peak value during middle Turonian meaning that the plagioclase was almost totally destroyed by source area weathering during Cenomanian-Coniacian and during other periods, there was no such wholesome alteration. This observation, when compared with the conditions of chemical weathering at lower latitudes listed by BOUCOT & GREY (2001), and with paleogeographic location of the Cauvery Basin in the lower latitudes during Barremian-Maastrichtian, limited extent of the provenance and the configurations of the depositional basin and provenance, support the inference of weaker chemical weathering. SINGH & RAJAMANI (2001) studied the floodplain sediments of the modern (present day) Kaveri River and observed striking similarity of trace elemental and REE patterns between the rocks of the source area and the modern floodplain sediments. SHARMA & RAJAMANI (2000) reported weaker chemical weathering, exposure of fresh unaltered rocks in the provenance and interpreted these phenomena as the result of continued tectonic movements, due to which, only limited weathering profiles are exposed at the provenance. Taking clue from this, occurrences of unaltered basement rock clasts in rocks deposited during Barremian, Cenomanian, Aptian-Albian, Coniacian-Santonian, are interpreted as Discrimination of tectonic dynamism, quiescence and third order relative sea level cycles of the Cauvery Basin the durations of tectonic activity in this basin. These durations are also accompanied by significant positive excursions of Si, Ti, Zr and Y. This inference necessitates checking the consistency and dynamism of provenance and tectonic setting of these rocks.
The geochemical characteristics of clastic rocks have been used to decipher the provenance (TAYLOR & MCLENNAN 1985;PINTO et al. 2004). The SiO 2 /Al 2 O 3 ratio is sensitive to sediment recycling and the weathering process and can be used as an indicator of sediment maturity (ROSER & KORSCH, 1986). The average SiO 2 /Al 2 O 3 ratios in unaltered igneous rocks range from 3.0 (basic) to ~5.0 (acidic), while values >5.0-6.0 in sediments are an indication of progressive maturity (RO-SER et al. 1996). Examination of the rocks under study in the light of these precepts and by plotting the data in established discrimination diagrams of textural maturity, and tectonic setting have revealed the following.
The plots of two distinct clusters in the bivariate diagrams of oxide percentages (Fig. 4), most of the samples in the texturally immature fields (Fig. 5) namely, (litharenite, wacke, arkose, subarkose etc), all the samples below the average shale discriminant line, existence of two-cluster nature (Fig. 6), all the samples below the feldspar join together with selective samples of Dalmiapuram, Karai, Garudamangalam and Sillakkudi formations above the feldspar join ( Fig. 7) are all supportive of the inferences of limited extent of provenance, proximity to provenance, sediment starved nature of the sedimentary basin, prevalence of less significant chemical weathering, and predomination of siliciclastic-carbonate alternate cycles under the influences of relative sea level fluctuations.
The Indian subcontinent was located at the southern latitudes during the deposition of the Ottakoil and Kallamedu formations (RAI et al. 2012). The studies of LAL et al. (2009), KALE (2011), CHATTERJEE et al. (2013, have shown that the Indian subcontinent was on a flight at various rates and directions since its breakup from Africa-Antartica and was above the Reunion hotspot (MORGAN 1981;SHETH & CHANDRASEKHARAM 1997;CHATTERJEE et al. 2013) or the Vishnu Fracture (SHETH 1999) during the late Cretaceous. The present observations of plot of Barremian-Santonian samples in the active continental margin field, Campanian-Danian samples in the passive continental margin field and plot of few samples of Ottakoil and Kallamedu formations (Late Maastrichtian) in the island arc field (Fig. 8) are all supportive of changing palaeogeographic positions and tectonic dynamism of the Indian plate. The change of depositional pattern across Santonian as indicated by lithofacies and geochemical characteristics are also supported by the change of tectonic setting across Santonian (from active to passive continental margin), suggestive of the sensitivity of geochemical parameters to climate-sea level fluctuations, tectonic movements, rates of sediment influx and chemical weathering.
The recognition of island arc setting in the sedimentary records of the Kallamedu Formation is important from the point of Cretaceous-Tertiary transitional environmental conditions in this part of the country. Though previous studies have either presumed or suggested the influence of Deccan volcanism and the presence of vitrified volcanic ash deposits in this formation, due to the inherent lithological characteristics (thin lamina of fine grained and also diagenetically altered sediments amidst coarse, recycled sediments of varying bed thicknesses which in turn were cut across by calcrete and silcrete veins), and scattered and weathered nature of the exposures, usually thwarted characterizing these deposits so far. This is the first time, the affinity of argillaceous siltstone beds of the Kallamedu Formation are unequivocally affiliated with volcanogenic sediment source. ANDRE-OZZI et al. (1997) commented that distinctive beds, particularly volcaniclastic layers which may be useful for stratigraphic and environmental reconstruction, may escape field identification because their recognition generally depends on a marked lithological contrast with the surrounding sediments. Because of several factors such as fine grain size, intense diagenetic modifications, and selective weathering may hinder their identification. This statement stands true to the case of Kallamedu Formation.

Conclusions
The Barremian-Danian strata of the Cauvery Basin record all the six third order sea level cycles within which many high-frequency cycles could be recognized. These are reflected in the lithofacies and enrichment-depletion patterns of sensitive geochemical proxies.
The northward flight of the Indian subcontinent, in which the Cauvery Basin is located has experienced active and passive nature of the tectonic setting and passed through active volcanic plume, all of which are explicitly shown by the geochemical characteristics of the rocks contained in the Cauvery Basin.
The depositional system was under the predominant influence of climate-sea level fluctuations despite the recurrent major tectonic movements of fault blocks. Few of the tectonic fault movements have coincided with sequence boundaries (Barremian, Aptian-Albian, Coniacian-Santonian, Maastrichtian-Danian) and may have contributed to exacerbation of sea level cycles, particularly during the deposition of the Olaipadi, Varakuppai and Sadurbagam members. Thus, the present study supports the influence of tectonics, to the development of third order cycles of depositional system.
The predominance of mechanical weathering, prevalence of insignificant chemical weathering of the source rocks as indicated by textural immaturity and the occurrences of high-frequency cycles in the Barremian-Coniacian deposits that have experienced syndepositional tectonic events and the prevalence of relatively stable environmental conditions during the period of tectonic quiescence (Campanian-Danian) are all suggestive of dominant role played by climaterelative sea level fluctuations.
While the recurrent sediment recycling events suggest reduced rates of subsidence (BUCHBINDER et al. 2000), the predominance of textural immaturity and mechanical erosion suggest dynamic nature of tectonism (SHARMA & RAJAMANI, 2000) suggesting the existences of balance between eustatic sea level fluctuations by tectonic events. thanked for her invitation to MR to conduct collaborative research. Dr. ZSOLT BERNER, Head of Laboratories, Institute of Mineralogy, is thanked for scientific support and lively discussions. графским варијацијама, затим су приказани на успостављеним дијаграмима разврставања, узимајући у обзир услове површинског распадања што је све заједно потврдило главне геолошке догађаје.
Б. Р. Lithoclastic conglomerates of the Sivaganga Formation containing angular, cobble-bounder sized basement clasts. Note the random orientation and fresh nature of the clasts and the unsorted calcareous matrix with fossil fragments. Fig. 3.
Large (>2 m dia) boulders found embedded in the Olaipadi member. The boulders are of basement rocks (dark grey colored boulder at the bottom right of the photograph) and typical coral reef limestones (light yellowish pink colored boulder at the bottom centre of the photograph) and show angular nature. Angular nature of the clasts suggests little or no significant transportation. Fresh nature of these clasts suggests mechanical erosion, rapid transport, immediate burial and faster rate of deposition. These are embedded in parallel bedded Bouma sequences. The bedding planes of individual Bouma sequences follow the periphery of these large clasts and suggest syndepositional tectonic activity and erosion of basement as well as former marine regions. Location of the photograph: Quarry section located near Tirupattur. Fig. 4.
Field photograph showing large (>10 m dia) angular limestone boulder embedded in the Bouma sequences. Note that the bedding planes of the Bouma sequences follow the boundary surface of the clast signifying syndepositional tectonic event that might have eroded the coral reef located at fault margin en masse and dumped it at the adjacently located deeper regions of the basin wherein typical Bouma sequences were being deposited under the influence of turbidity currents. Location of the photograph: Quarry section located near Tirupattur. Fig. 5.
Close-up view of the coralalgal reef facies limestone boulder found embedded in the Bouma sequences. It is to be noted that these constitute typical reef-core and are not at all found anywhere in the basin, signifying, their development only in the former offshore regions of the paleosea, complete denudation during the syndepositional tectonic movements. Fig. 6.
Erosional and angular unconformity surface contact between the Odiyam sandyclay member (Early Turonian) of the Karai Formation and the Varakuppai member (Santonian) of the Sillakkudi Formation (Santonian) exposed at northwest of Varakuppai Village. The intervening Garudamangalam Formation is entirely either eroded and or missing. The major faulting across Coniacian-Santonian had brought down the previously positive areas under the influence of marine forces and the event was accompanied by intense erosion of continental and former offshore regions alike. Fig. 7.
The major faulting event was associated with the development of major fluvial channels that debouched at the fault margin coastlines of paleosea. The field photograph showing the development of climbing ripples consisting of large angular-subangular basement clasts and lithoclasts of older sedimentary rocks and unsorted granule-very coarse sand matrix. Location of the Photograph: Northwest of Varakuppai Village. Fig. 8.
Close-up view of the previous photograph showing the occurrences of recycled pebble-gravel sized clasts with angular and sub-rounded nature. Many a times, they show reverse grading, suggestive of increase in energy conditions, perhaps associated with syndepositional seismicity (aftershocks?). Fig. 9.
Field photograph showing the erosional offlap contact between Odiyam sandyclay member of the Karai Formation and the Sadurbagam member of the Sillakkudi Formation. The Sadurbagam member was deposited under middle shelf conditions and its occurrence over the Karai Formation signifies, differential depositional topography created by the faulting event and return of sea level fluctuation controlled depositional pattern after major faulting event and fluvial deposition. Fig. 10. Field photograph showing the erosional contact between Varanavasi member of the Sillakkudi Formation and Kallar member of the Kallankurichchi Formation. In addition, the beds on both the sides show parallel bedding, signifying simple sea level fall and rise across this boundary. Location of the photograph: Kallar river section near Tancem quarry I. Fig. 11. Field photograph showing conformable offlap between the Srinivasapuram member of the Kallankurichchi Formation and the Kallamedu Formation.
Though conformable, the depositional topography might have been variable due to the development of shallow ephemeral river channels that cut through paleosurface and over flown frequently. Location of the photograph: Quarry section located southeast of Kallankurichchi Village.