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Petrographic variations in compound flows of Deccan Traps and their significance
Abstract
The paper presents results of quantitative mineralogical studies of compound flows in Kasara-Kalsubai and Trimbak sections in Western Maharashtra. The flow units range in composition from tholeiite to picrite/ankaramite (olivine and augite phenocrysts vary from 1% to 24%) within a flow of overall tholeiitic composition. In view of extreme compositional variation, necessity of collecting representative samples based on petrographic study is emphasised as random sampling for geochemical studies is prone to project totally erroneous picture. -from Author
... 589) 'compound pahoehoe flows are developed on possibly a unique scale in the western part of the Deccan Traps'. This classification was further elaborated and applied across the province by Deshmukh (1988), who divided the Deccan lavas into three broad classes: (1) compound (pahoehoe), (2) simple and (3) áat ypes. An additional variety of 'mixed type' (Raja Rao et al. 1999) is also found in various reports of the Geological Survey of India. ...
... Very often small (10-100 m wide; generally less than 5 m thick) pahoehoe lobes are stacked one above the other and appear to be firmly welded into each other within the flow (Fig. 7d, e). This has led to them being categorized as the 'compound pahoehoe flows' in the literature of the DVP (Phadke and Sukhtankar 1971;Deshmukh 1988;Walker Fig. 6. Typical internal structures within áālobes in basaltic lava (modified after Walker 1971; Kale et al. 2020). ...
... Although tagged as 'pahoehoe' (= smooth surface, sensu MacDonald 1953; Walker 1971), it is characterized by a rough, jagged surface akin to the áāmorphology. Most of the lava flows occupying large areas with this morphology were wrongly tagged (Deshmukh 1988;GSI 2001) as simple/áaf ows earlier (Duraiswami et al. 2008;Chatterjee and Dash 2017). ...
We review and compare morphologies from continental flood basalts, using examples from the Deccan Volcanic Province to compile their internal configurations and mutual associations. The growth of the basaltic lava flow can be achieved by a single extrusion or by multiple pulses of endogenous emplacement that enable the lava to efficiently spread over large areas and thicken. We show that the morphology of a lobe manifests the response of the molten lava to several parameters (including volumetric rate of emplacement, substrate topography, viscosity, vapour loss, etc) that govern the dynamics and cooling history of basaltic lava. The lateral transition from one morphology to another is a testimony to the interactive response of the lava dynamics and rheology to variation in the local systems in which they were emplaced. The morphologies do not evolve as rigid partitioned categories from ‘áā and pāhoehoe lava types’ but as parametric progression of interactive variations in the spreading and cooling lava.
A hierarchical recognition of lobes, flows and flow fields and detailing of lobe morphology combined with the stacking patterns provides the volcanological framework for stratigraphic mapping of flood basalts. Such systematic documentation will lead to robust models of their eruptive histories.
... Rocks from basaltic magma are varied with different petrographic, physical and geochemical features whose determination lead to their characterization and to a better understanding of their condition of formation [1,2,[5][6][7]. They occur as aa, pillow, columnar or pahoehoe lava flow, or form dyke and sill which are easy to recognize in the field [2,[7][8][9]. Some of these rocks are mineralized (e.g., host interesting PGE concentration: or can host gemstones as xenocrysts and in xenoliths sourced from other rocks by the ascending magma) [10][11][12][13]. ...
... The aphyric basanites suggests rapid crystallization of melts lacking large suspended crystals and slightly porphyritic basanites a different stage of crystallization: when phenocrysts, grew in a magmatic chamber before rapid cooling at the surface produced a fine grained groundmass [1,2,7,9]. The more porphyritic basanites may signify some crystal fractionation and accumulation, as interpreted by Deshmukh [8]. ...
... Xenocrystic quartz with thin contact metamorphism zones suggest it came from post sedimentary materials from the surrounding sandstones. Olivine and clinopyroxene macrocrysts and microcrysts, in a very fine-grained ground mass in the picro-basalts may suggest three stages of crystallization: macrocrysts (slow cooling in a magmatic chamber); microcrysts (shallow depth cooling) and groundmass (rapid cooling at the surface) [8]. ...
Geologic prospecting, petrographic and geochemical analyses of mafic volcanic exposures in the west and southern part of the Mamfe Basin (SW Cameroon) distinguishes: basanites, picro-basalts, alkali basalts and tholeiitic basalts. They are relatively LREE-enriched, undersaturated, saturated or oversaturated due to presence or absence of normative nepheline, hypersthene or quartz. Basanites mainly form pillow-like lavas, and are aphyric or porphyritic. They have significant concentration of Ni (up to 387 ppm) and Ba (up to 436 ppm). These alkaline rocks cooled from less evolved mantle source magma. Picro-basaltic fragments exclusively found in the western part of the basin are Ni (up to 259 ppm) Ba (up to 2090 ppm)-enriched porphyritic, alkaline or subalkaline rocks. They also cooled from less evolved mantle source magma. Basalts form volcanoclasts, flow and dykes. They are aphyric or porphyritic, alkaline, transitional or subalkaline. Some of these rocks are Al-enriched. They crystallized from variably evolved mantle source magma within the Oceanic Island Basalt and Continental Rift Basalt tectonic settings.
... The basaltic lava flows in the DVP display three internal layers, namely the crust, core and base (Kezsthelyi et al. 1999) from top to bottom, respectively. Based on their internal structure (relative proportions of the upper crust, core and base, distribution of vesicles, etc.) and geometry, Walker (1971) and Deshmukh (1988) classified the Deccan basaltic flows into (i) compound with multiple units of pāhoehoe lobes, (ii) simple and (iii) áā types. ...
... Early loss of vapour phase results in enhanced viscosity of the lava that inhibits long distance spreading, leading to a pile up close to the vent. When such lobes are emplaced in rapid succession, they may be annealed together into a 'compound' flow (sensu Deshmukh 1988). The sheet flows have a much larger aerial spread and may display internal structures comparable to sheet/slabby/rubbly pāhoehoe along their length of exposures. ...
... The chemical stratigraphy established in the western parts of the DVP in the late 1980s (Table 8.2) led to the emergence of a central shield volcanic model for this province. This appeared to be consistent with the distribution of the lavas based on the Hawaiian volcanological classification (Deshmukh 1988). Subsequent workers (e.g. ...
The earliest description of the Deccan Volcanic Province (DVP) characterized by the step-like profile of the hill-slopes may be traced to Sykes (1833; cf., Pascoe in Manual of the geology of India and Burma. Geological Survey of India, Kolkata, pp 483–1343, 1956) who coined the name derived from (Sanskrit word) “Dakshin” meaning south and (Swedish word) “Trappa” meaning stairway).
... Based on their geometry and internal structure (relative proportions of the upper crust, core and base, distribution of vesicles, etc), the flows in the Deccan were classified into (i) compound (with multiple units of pahoehoe lobes), (ii) simple and (iii) áa types. The distribution map of simple and compound flows compiled by Deshmukh (1988) became the cornerstone of the shield volcano model of the DVP in collaboration with the chemostratigraphic classification. Subsequent workers on the volcanological aspects of the flows, including the compilations by Kale (2020). ...
... Self et al., 1998;Keszthelyi et al., 1999;Katterhorn and Schaefer, 2008;Glaze and Bolaoga, 2013;Cashman et al., 2013) allows a wider spread of the lava far from its eruptive edifice. Such flows (traceable continuously across long distances) were mapped as 'simple' flows (sensu -Deshmukh, 1988;GSI, 2001). However, they are unquestionably the result of multiple emplacements of lava enabling their larger aerial spread. ...
... Assumption of a singular eruptive edifice provided justification and the framework for the chemostratigraphic classification and correlation across the DVP. Using the distribution of the (simple & compound) flow-types compiled by Deshmukh (1988), this eruptive head was postulated to be north of Nasik (Watts and Cox, 1989;Jay et al., 2009;Richards et al., 2015). Absences of identifiable unambiguous eruptive centers as well as lack of exposures that display a feeder relationship between the dykes and flows were arguments against the erstwhile fissure-fed eruption model. ...
A review of the existing knowledge on the Deccan
Volcanic Province of India shows that it has a significant
geographic bias towards the western parts, while the rest
of the province is not as well constrained. Emerging data
on its structure, geochronology and volcanology in the
last decade suggests that many existing concepts and
models of this large Continental Flood Basalt Province
are open to revisions or replacement.
The explicit relation between the Deccan volcanism
and the Reunion hotspot makes it a unique laboratory
for studying magmatic evolution over active hotspots,
its upward trajectory through a thick continental crust
and the mode and mechanics of eruption and spread of
large volumes of lava on continental settings. The
temporal relation of the Deccan volcanism with the
terminal Cretaceous biotic upheaval has direct bearings
on understanding environmental crisis that result from
such eruptive events. The impact of this basaltic substrate
on the anthropogenic activity of more than 100 million
people living on it needs no explanation. A multifaceted
and interdisciplinary study with an aim of closing the
gaps in its knowledge will facilitate a well-constrained
understanding of the characters and robust models of
this province in the years to come.
... Based on their geometry and internal structure (relative proportions of the upper crust, core and base, distribution of vesicles, etc), the flows in the Deccan were classified into (i) compound (with multiple units of pahoehoe lobes), (ii) simple and (iii) áa types. The distribution map of simple and compound flows compiled by Deshmukh (1988) became the cornerstone of the shield volcano model of the DVP in collaboration with the chemostratigraphic classification. Subsequent workers on the volcanological aspects of the flows, including the compilations by Kale (2020). ...
... Self et al., 1998;Keszthelyi et al., 1999;Katterhorn and Schaefer, 2008;Glaze and Bolaoga, 2013;Cashman et al., 2013) allows a wider spread of the lava far from its eruptive edifice. Such flows (traceable continuously across long distances) were mapped as 'simple' flows (sensu -Deshmukh, 1988;GSI, 2001). However, they are unquestionably the result of multiple emplacements of lava enabling their larger aerial spread. ...
... Assumption of a singular eruptive edifice provided justification and the framework for the chemostratigraphic classification and correlation across the DVP. Using the distribution of the (simple & compound) flow-types compiled by Deshmukh (1988), this eruptive head was postulated to be north of Nasik (Watts and Cox, 1989;Jay et al., 2009;Richards et al., 2015). Absences of identifiable unambiguous eruptive centers as well as lack of exposures that display a feeder relationship between the dykes and flows were arguments against the erstwhile fissure-fed eruption model. ...
A review of the existing knowledge on the Deccan Volcanic Province of India shows that it has a significant geographic bias towards the western parts, while the rest of the province is not as well constrained. Emerging data on its structure, geochronology and volcanology in the last decade suggests that many existing concepts and models of this large Continental Flood Basalt Province are open to revisions or replacement. The explicit relation between the Deccan volcanism and the Reunion hotspot makes it a unique laboratory for studying magmatic evolution over active hotspots, its upward trajectory through a thick continental crust and the mode and mechanics of eruption and spread of large volumes of lava on continental settings. The temporal relation of the Deccan volcanism with the terminal Cretaceous biotic upheaval has direct bearings on understanding environmental crisis that result from such eruptive events. The impact of this basaltic substrate on the anthropogenic activity of more than 100 million people living on it needs no explanation. A multifaceted and interdisciplinary study with an aim of closing the gaps in its knowledge will facilitate a well-constrained understanding of the characters and robust models of this province in the years to come.
... Figure 2 is the updated version of the commonly used discriminant chemical parameters. Compositionally, the major element oxides (barring the Mg-number) do not provide any clear demarcation between successive units, and the trace elements are commonly transitional across the unit boundaries (Bodas et al., 1988;Deshmukh, 1988;Khadri et al., 1988Khadri et al., , 1999aChandrasekharam et al., 1999;Krishnamurthy, 2008). Only the 87 Sr/ 86 Sr ratios display sharp breaks and may be useful for identifying some of the boundaries, according to Mitchell and Widdow son (1991). ...
... Deccan lavas are largely modeled on the lines of Hawaiian lavas following the initial comparisons by Walker (1971). They were cate gorized as (i) compound (with multiple units of pāhoehoe type), (ii) simple or (iii) a'ā types (Deshmukh, 1988;Godbole et al., 1996). The chemostratigraphic classification of the DVP also uses this classification of lava flow types as a secondary parameter. ...
... Such transition of pāhoehoe to a'ā types within a single lava flow field recorded elsewhere (Duraiswami et al., , 2014Sen, 2017) further underscores the limitations of this classification in stratigraphic correlations. The "simple flows" (sensu Deshmukh, 1988;Geological Survey of India, 2001) can be demonstrated to have been emplaced through multiple pulses of emplacement and endogenous transfer across their length and breadth, with inflated (and disrupted) crusts as well as flow-top breccias (Kale et al., 2014). Many of them display typical pāhoehoe characters within their constituent lobes. ...
The Deccan Volcanic Province (DVP) is significant for its eruption close to Cretaceous–Paleogene (K-Pg) boundary. Chemostratigraphy
established in its western parts is the foundation of postulated long distance correlations across the province and consequential models of its eruptive history. A critical review of diagnostic parameters used to characterize stratigraphic units shows them to be probabilistic
rather than deterministic and therefore, they are ambiguous. We compile the previously overlooked mapping into district-wise
altitude-controlled logs across the province.
A reappraisal of the chronological and paleomagnetic data for the DVP shows that volcanism was not concurrent across the province and questions the validity of previous correlations. This analysis also shows that at least three separate eruptive phases occurred in disparate parts of the province, spread over ~7 million years, of which only one preceded the K-Pg boundary. We resurrect an eruptive model involving multiple eruptive centers and endorse a zonal stratigraphy
for the DVP. This approach provides a better context for correlations than the prevailing stratigraphy that clubs the entire province into a single entity.
... The recognition of the subhorizontal sheeted geometry of the lava flows in the DVP has been noted even in the earliest descriptions of the Deccan Traps, named after the steplike topographic profiles that develop on them. To a large extent, the volcanological description of the Deccan flows (flow fields) are modelled on the lines of Hawaiian lava flows following the initial comparisons by Walker (1971), modified by Deshmukh (1988). They are essentially classified as (1) compound pāhoehoe flows, comprising multiple lobes with chilled margins that are fused together; (2) simple flows 'representing a single volcanic episode' with chilled, vesicular top and basal margins of variable thicknesses and having a compact crystalline core sandwiched between vesicular layers, but without a'ā characters; or (3) a'ā flows with clinkery or blocky (brecciated) tops (Godbole et al. 1996: p.126). ...
... The different lava morphologies do not suggest primary differences in the lava constitution but are a manifestation of variations resulting from diversity in their emplacement, vapour loss and cooling processes. Deshmukh (1988) was the first to compile a province-wide map of the distribution of the flow types (see ), based on the classification of the flows into 'simple' and 'compound' types. This figure was used in subsequent works to extend the correlations of the chemostratigraphic units across the province and postulate a monocentric shield-type volcanic model for the DVP. ...
... It is interesting that the distribution of mixed flows corresponds with the incidence of dyke swarms in the Western and Central subprovinces. Inset depicts the compilation by Deshmukh (1988) of the distribution of simple and compound flows along with the postulated primary edifice of Deccan volcanism (modelled by Hawkesworth 1985, Subbarao andMitchell and Widdowson 1991;Jay and Widdowson 2008 amongst others) and the projected directions of the dispersal of the lavas, including the possible linkage with the Razole Province postulated by Baksi et al. 1994;Self et al. 2008b;Jay et al. 2009;Richards et al. 2015) V. S. Kale Richards et al. 2015). The positions of the GPB horizons included in this classification to define Formation boundaries are given with the names of the GPB horizons (after Bodas et al. 1988. ...
The Indian Peninsula hosts Cretaceous continental flood basalts(CFB) that manifest its passage over the Kerguelen and Reunion hotspots in succession. The former yielded the Early Cretaceous Rajmahal-Bengal-Sylhet Province (113-118 Ma) in the eastern parts of the Indian Plate. The ensuing passage over the Reunion yielded one of the largest CFB provinces, namely the Deccan Volcanic Province (~68-61 Ma), linked to end-Cretaceous mass extinction event. This compilation of the available knowledge on these two provinces enumerates some of the more evident gaps that require focus in future studies.
... 8 Fig. 2.1a: Map of the Deccan Traps showing distribution of compound and simple lavas (after Deshmukh, 1988) and major tectonic zones. Also note the locations of the Kachchh outlier and Saurashtra plateau in relation to the main Deccan plateau. ...
... Walker (1969, 1971) identied that there are fundamental differences between the form and type of Deccan lava morphologies and classied them as 'simple' and 'compound' based on the divisibility of the ows into different individual units. Subsequently, Deshmukh, (1988) and other workers from the Geological Survey of India identied that the compound ows senu lato are exposed around a triangular region (Pune-Dhule-Aurangabad) and the simple ows senu lato are predominant in the peripheral regions ( Fig. 2.1). Despite coining the terms 'simple' and 'compound' for describing lava ow types in the Deccan Traps, Walker (1971) was of the opinion that these terms had a limited usage especially in old dissected terrains. ...
... Each lava flow can further be divided into sub-units. In general, the Deccan basalts can be grouped into two categories, 'simple' or 'compound' depending on the viscosity of the primary lava (Deshmukh, 1988;Kale and Kulkarni, 1992). These basalts are also classified as pahoehoe and aa flows, the nomenclature adopted from volcanological studies in the Hawaiian region, where studies of active lava effusion are well documented. ...
... A distinction between simple and compound flows is provided by Deshmukh, 1988. The simple flows equate to classic flood basalts formed by quite effusive eruption of very large quantities of low viscosity lava from open fissures. ...
The Participatory Groundwater Management (PGWM) programme was launched by Arghyam Trust in January 2011 and the first phase of this programme ends in December 2013. PGWM programme includes three broad sets of activities: Training, Action Research and Advocacy. ACWADAM has selected two villages under Action Research in PGWM. Randullabad village, located in the Koregaontaluka of Satara district of Maharashtra is one of the Action Research sites. BAIF Development Research Foundation, Pune has implemented watershed development programme in
Randullabad through Village Watershed Committee between 2010 and 2012 with the funding from IGWP –NABARD. ACWADAM’s association with the village began in 2011 when Randullabad was selected as an Action Research site under Participatory Groundwater Management programme. Since then, ACWADAM is closely working with the community and BAIF in effective implementation of watershed
development programme in the village. ACWADAM has established a monitoring network in Randullabad and is collecting hydrogeological, agricultural and socio-economic data for the last three years. This report includes data collected by
ACWADAM during this period. It also includes analysis of this data along with some recommendations for the improved groundwater management in the village. This document describes in detail the process of Participatory Groundwater Management and discusses certain critical findings and experiences in
Randullabad. This document will benefit people who are sensitive about groundwater issues and are interested in developing alternative water management practices.
... Each lava flow can further be divided into sub-units. In general, the Deccan basalts can be grouped into two categories, 'simple' or 'compound' depending on the viscosity of the primary lava (Deshmukh, 1988;Kale and Kulkarni, 1992). These basalts are also classified as pahoehoe and aa flows, the nomenclature adopted from volcanological studies in the Hawaiian region, where studies of active lava effusion are well documented. ...
... A distinction between simple and compound flows is provided by Deshmukh, 1988. The simple flows equate to classic flood basalts formed by quite effusive eruption of very large quantities of low viscosity lava from open fissures. ...
ACWADAM has conducted a rapid hydrogeological study to provide inputs to WOTR's implementation strategy for watershed development and climate change adaptation programme in Akole and Sangamner clusters of Ahmednagar district. The main objective of this eight month study was to map the geology and
prepare detail hydrogeological map for 29 villages. Initially three clusters were identified for the study namely; Akole, Pathar and Gramodaya. However, a detail study was conducted in Akole and Pathar clusters only. The main objectives of the study were as below. Conduct broad geological mapping of the watershed ?Identify the natural groundwater recharge and discharge areas. Develop a groundwater management plan as a part of climate change adaptation strategy for
the three clusters
... Each lava flow can further be divided into sub-units. In general, the Deccan basalts can be grouped into two categories, 'simple' or 'compound' depending on the viscosity of the primary lava (Deshmukh, 1988;Kale and Kulkarni, 1992). These basalts are also classified as pahoehoe and aa flows, the nomenclature adopted from volcanological studies in the Hawaiian region, where studies of active lava effusion are well documented. ...
... A distinction between simple and compound flows is provided by Deshmukh, 1988. The simple flows equate to classic flood basalts formed by quite effusive eruption of very large quantities of low viscosity lava from open fissures. ...
Groundwater is the world’s largest, accessible source of freshwater. It is also
the primary source of drinking water to nearly half of the world's population
and, as the dominant source of water to irrigated land, which is critical to
global food security. South Asia is the largest user of groundwater with 230-
250 km2 / year, which is a fourth of the total global groundwater resource
(Shah, 2008).
... This seems to contradict the inference of higher post-KPB eruptive rates in the Wai subgroup; and suggests that there was no cognisable variance in the eruptive rates in the western subprovince. The Kalsubai subgroup is constituted of lobate lava flows with a braided architecture (earlier mapped as 'compound flows' : Deshmukh, 1988), which do not disperse far from their eruptive edifices, unlike the sheet flows with tabular architecture in the Wai subgroup (Kale et al., 2021). The same volume of lava will create thicker stacks with braided architecture, while it will be spread relatively thinly over a wider area in case of tabular stacking patterns. ...
... The monocentric shield volcano eruptive model (analogous to Hawaiian volcanics) that was the foundation of the long-distance province-wide correlations with overstepping chemostratigraphic formations across the DVP (Cox and Hawkesworth, 1985;Hooper, 1990;Jay and Widdowson, 2008;Sprain et al., 2019) is open to review as a consequence. This model relied on the spatial distribution of 'simple and compound flows' mapped by Deshmukh (1988) and the chemical affinities of lava flows exposed at a distance from known dykes swarms (Sheth et al., 2009;Hooper et al., 2010;Vanderkluysen et al., 2011). The primary argument against the earlier (Auden, 1949) fissure-fed eruptive model (analogous to the Iceland volcanics) was a marked absence of feeder dykes across much of the Western DVP. ...
Rapidly expanding geochronological, paleomagnetic and volcanological data of the Deccan Volcanic Province (DVP) has given new insights to the expansive knowledge on it that had been built up through the preceding decades. Precursory Late Cretaceous (80 – 68 Ma) magmatic activity across the Indian subcontinent preceded the main event of volcanism. The main Deccan event involved nearly continuous outpourings of ~1.5 million km3 of flood basalts in a span of less than 2 m.y. on either side of the Cretaceous-Paleocene Boundary (KPB), corresponding to 3 magnetic chrons. This was followed by basaltic and silicic flows and alkaline magmatism that continued up to ~61 Ma.
Several earlier postulated long-distance correlations of lava sequences based on chemical parameters are rendered invalid by the precision geochronology, leading to doubts regarding earlier models of volumetric eruptive rates. We suggest that pending better flow-field maps and correlations across the province, stacking rates based on thickness between chronological sampling points, combined with volcanological parameters provide a more robust and reproducible estimates of the eruptive rates. The stacking rates in different parts of the province were largely in the magnitude range of 103 m/m.y. and are comparable to those observed in other continental flood basalt provinces.
... We use this fact to discuss what the presence or absence of flow-lobe tumuli in a CFBP can tell us about the emplacement rate of pāhoehoe flows in CFBPs and how they can be used to qualitatively assess the relative position of a flow from its source. We also aim to disprove the statement that the presence of compound flows is indicative of proximity to source (Deshmukh 1988;Viereck et al. 1988;Lesher et al. 1999;El Hachimi et al. 2011), and suggest that flow-lobe tumuli can be used to indicate that a flow is medial or distal to source. ...
... It has been suggested that compound flows are indicative of proximity to source and sheet lobes indicative of distal locations (Deshmukh 1988;Viereck et al. 1988;Lesher et al. 1999;El Hachimi et al. 2011). However, we argue that this is incorrect: the thickness of inflated flows is determined by the length of time that lava can continuously flow through a lobe and inflate it, not how close it is to the vent. ...
Physical volcanological features are presented for a 710-m-thick section, of the Naude’s Nek Pass, within the lower part of the Lesotho remnant of the Karoo Large Igneous Province. The section consists of inflated pāhoehoe lava with thin, impersistent sedimentary interbeds towards the base. There are seven discreet packages of compound and hummocky pāhoehoe lobes containing flow-lobe tumuli, making up approximately 50% of the section. Approximately 45% of the sequence consists of 14 sheet lobes, between 10 and 52-m-thick. The majority of the sheet lobes are in two packages indicating prolonged periods of lava supply capable of producing thick sheet lobes. The other sheet lobes are as individual lobes or pairs, within compound flows, suggesting brief increases in lava supply rate. We suggest, contrary to current belief, that there is no evidence that compound flows are proximal to source and sheet lobes (simple flows) are distal to source and we propose that the presence of flow-lobe tumuli in compound flows could be an indicator that a flow is distal to source. We use detailed, previously published, studies of the Thakurvadi Formation (Deccan Traps) as an example. We show that the length of a lobe and therefore the sections that are ‘medial or distal to source’ are specific to each individual lobe and are dependent on the lava supply of each eruptive event, and as such flow lobe tumuli can be used as an indicator of relative distance from source.
... Sub-vertical to vertical fracture present in the flow. Deshmukh (1988) has reported the distribution of simple and compound flows in DVP (Fig. 1), where simple flows are commonly observed throughout the province whereas the majority of compound flows cover the central part of the province. The uppermost flows in the KBH7 core are simple flows, generally consistent with the regional- scale map of Deshmukh (1988). ...
... Deshmukh (1988) has reported the distribution of simple and compound flows in DVP (Fig. 1), where simple flows are commonly observed throughout the province whereas the majority of compound flows cover the central part of the province. The uppermost flows in the KBH7 core are simple flows, generally consistent with the regional- scale map of Deshmukh (1988). However, in addition to the simple flows, six compound flows, each with multiple flow units, have been identified mostly in the lower parts of the basalt core. ...
A 1251 m thick succession of Deccan lava flows has been recovered by scientific drilling in the Koyna region, western part of the Deccan Volcanic Province (DVP). Forty-six lava flows, starting with the first flow overlying the granitic basement in the region, have been identified through mesoscopic studies of cores obtained from a 1500 m deep borehole KBH7 in Panchgani village of Patan sub-division. Mesoscopic observations supported by petrographic studies bring out the characteristics of the basaltic pile. The salient findings are as follows. The thickness of Deccan trap in the Panchgani area is 1251.20 m, comprising a succession of 40 simple lava flows and 6 compound lava flows. The contact with the underlying granitic basement occurs over a short span of 90 cm. Infra-trappean sediments are absent. Overall, ∼74% of the basaltic pile is constituted of massive basalt and ∼24% vesicular/amygdaloidal basalt. Red bole horizons are observed in 7 flows. Nine giant plagioclase basalt (GPB) flows are identified in the single vertical section. The long basalt core may serve as a model Deccan trap section for correlation with the flows exposed at the surface in the Koyna and surrounding region and support detailed investigations to constrain the duration of Deccan volcanism.
... Koyna-Warna area is a part of Deccan Volcanic Province (DVP), which occupies a vast area (~5 lakh sq km) of western and central India. The DVP is unique for its large volume and thickness (~3000m thick) of volcanic pile erupted in a number of spells during a short period (< 5 million years) c.a. 65 million years ago (Deshmukh, 1988;Jay and Widdowson, 2008). Deccan flood basalt is closely similar to that of other two major continental flood basalts in the world, i.e. ...
... It is reported that a total of 48 flows are seen in DVP (West, 1999). According to present understanding, the basaltic flows in the Koyna-Warna region are essentially simple type of flows (Walker, 1999), though Deshmukh (1988) has indicated the presence of compound flows in nearby areas. Beane et al. (1986) has classified Deccan basalt of Western Ghats into three Subgroups and ten Formations. ...
Vertical deep boreholes of depth up to 1522.50m have been drilled in Koyna-Warna area of Maharashtra State within the Deccan Volcanic Province to study the most outstanding example of Reservoir Triggered Seismicity (RTS). The drilling of 9 bore-holes in the area has provided a window to earth scientists to peep into geological details available below Deccan Trap.
The 932.50m thick pile of Deccan basalt, consisting of 30 flows at Rasati, near Koyna, which has been physically seen through cores, present a marvellous geological repository for observations. The megascopic characteristics of various flows and variation in composition have been presented in this paper. The microscopic and geochemical characteristics have been kept out of this communication, as the relevant studies are not completed to draw any conclusion. This study records the presence of granite wash (≈1m thick) over basement and below basalt representing Late Archaean to Cretaceous period hiatus. The basement rocks, presumably of Late Archaean age have been described mega-scopically. A fair picture of sub-surface pre-Deccan topography is shown with the help of borehole data, which confirm the nearly flat topography of pre-Deccan surface especially in this part of the area occupied by 30 flows of Deccan basalt. Correlation of 30 flows with the established stratigraphy has also been attempted for subsurface existence of Ambenali (Upper) and Poladpur Formations of Wai Subgroup in Koyna-Warna area.
... Internal layering of the lava flows (namely Lower Colonnade Zone: LCZ, Entablature Zone: EZ, Upper Colonnade Zone: UCZ, Lower Vesicular Zone: LVZ and Upper Vesicular Zone: UVZ) and associated characters have been identified following the physical-volcanological criteria suggested by Nichols (1936), Walker (1971Walker ( , 1999, De (1972), Deshmukh (1988), Self et al. (1998), Keszthelyi et al. (1999), Lyle (2000), Jerram and Widdowson (2005), Hetényi et al. (2012), Bernardi et al. (2015) and Kale et al. (2022). The results have been shown in Tables 1a and 1b. Figure 2 (a-i) depicts some representative field photographs pertaining to those lava flows, associated sediments and dyke-sill intrusives. ...
Field studies around Pulivendla (14°33′36″N: 78°19′48″E) belonging to the Tadpatri Formation of Proterozoic Cuddapah Basin document three distinct lava flows (based on internal layering), associated sediments (shale and sandstone) and intrusive dyke-sill system. The presence of previously undocumented internal layering namely Lower Vesicular Zone (LVZ), Lower Colonnade Zone (LCZ), Entablature Zone (EZ), Upper Colonnade Zone (UCZ) and Upper Vesicular Zone (UVZ) helps to delineate three lava flows in the study area. The associated sedimentary beds either correspond to lava cessation-period or dynamic lava-sediment interaction due to lava-cascading. The present study in Tadpatri Formation reveals volcano-sedimentological features analogous to that of Deccan Traps. It is postulated that magmatism within Tadpatri Formation might have been largely controlled by Proterozoic syn-rift plume activity (needs further corroboration by high precision major/trace/isotopic analyses).
... Beane et al. 1986;Bondre et al. 2004) and of ~ 1 km elsewhere such as the Satpura Range in the northern part of the province, though in Saurashtra and Kachchh in the northwest, maximum preserved thicknesses are a few hundred metres (Sheth et al. 2022). Both compound flows and sheet lobes are found in abundance (Walker 1971;Deshmukh 1988;Bondre et al. 2004;Sheth 2018;Kale Vivek et al. 2022). The small-scale compound pāhoehoe flows (Fig. 6a, b) are usually pervasively altered, contain basal pipe vesicles, and are frequently hummocky, i.e. they contain tumuli (e.g. ...
The Deccan Traps continental flood basalt province, ~ 65 million years in age and covering ~ 500,000 km2 of western and central India today, contains some 1200 rock-cut caves. The largest and finest are the Ajanta Caves (second century B.C. to seventh century A.D.), famous for their Buddhist religious sculptures and murals, and the Ellora Caves (fifth to eleventh centuries A.D.), equally famous for their Hindu, Buddhist and Jain religious sculptures. Both sites are protected monuments of the Archaeological Survey of India and UNESCO World Heritage Sites, and extensive studies of their architectural and artistic heritage exist. However, no detailed geological-volcanological account of these monuments exists in the Deccan Traps literature, except for brief mentions of their well-developed compound pāhoehoe lava flows. This paper documents the well-exposed stacking geometry of these lava flows, compound at various size scales, and their internal structures. The latter include a three-tier division into upper crust, core and lower crust, basal pipe vesicles, upper crustal vesicular banding, ropy surfaces, and lobes and tumuli with tensional inflation clefts which sometimes produced lava squeeze-ups and were commonly filled by younger lava. The lava flows are thus hummocky pāhoehoe, like many modern basaltic lava flows of Kilauea. They may be distal parts of the same lava flows or flow fields which are represented by sheet lobes in proximal (near-vent) areas. The Ajanta and Ellora Caves, world-renowned historical, cultural, religious and artistic monuments and ancient rock-engineering marvels, are also monuments for flood basalt geology and volcanology and ancient volcanic geoheritage.
... In this area, dug wells tapping the shallow phreatic aquifers (sandy zone in thin alluvial formation / weathered zone of basalt) and semi confined to confined aquifers (fractures and vesicular zone) at moderate to deeper depth are common. Numerous geological, mineralogical, geomorphological, structural, tectonic, geochemistry and hydrological studies were carried out in Deccan Trap province since last few decades (Versey and Singh, 1982;Athavale , 1983;Subbarao, 1988Subbarao, , 1994Subbarao, , 1999Deshmukh, 1988;Deshmukh and Nair, 1996;Nair and Bhusari, 2001;Chandrasekharam , 2003, Narayanpethkar , 2008Kulkarni and Deolankar, 2008;Limaye, 2010;Rai , 2011). Rangarajan and Muralidharan, 2019) Aquifer mapping in an inhomogeneous anisotropic medium has always been a challenging task to attempt. ...
... In this area, dug wells tapping the shallow phreatic aquifers (sandy zone in thin alluvial formation / weathered zone of basalt) and semi confined to confined aquifers (fractures and vesicular zone) at moderate to deeper depth are common. Numerous geological, mineralogical, geomorphological, structural, tectonic, geochemistry and hydrological studies were carried out in Deccan Trap province since last few decades (Versey and Singh, 1982;Athavale , 1983;Subbarao, 1988Subbarao, , 1994Subbarao, , 1999Deshmukh, 1988;Deshmukh and Nair, 1996;Nair and Bhusari, 2001;Chandrasekharam , 2003, Narayanpethkar , 2008Kulkarni and Deolankar, 2008;Limaye, 2010;Rai , 2011). Rangarajan and Muralidharan, 2019) Aquifer mapping in an inhomogeneous anisotropic medium has always been a challenging task to attempt. ...
Two-Dimensional (2D) Electrical Resistivity Tomography (ERT) and geophysical logging and injected tritium tracer studies with hydrogeological tests were carried out at selected location in an area of 5 km2 near the coastal region of Tarapur, Thane district, Maharashtra. The area is in basaltic terrain, overlain by thin cap of alluvium formation and receives an annual rainfall of about 2000 mm. An integrated investigation method was adopted to delineate the subsurface lithological variations, understand the existing aquifer system up to 25 m depth, evaluate aquifer properties, recharge potential and also to monitor the groundwater flow characteristics. The investigation results showed a variable thickness of weathered zone of 1-3 m, existence of two basalt flows, low vertical natural recharge, high transmissivity, high hydraulic conductivity and high groundwater flow rates. The results also depicted that a combination of hydrogeological tests along with resistivity and tracer investigation is an effective tool in mapping and characterizing the shallow potential groundwater aquifer zone in Deccan traps. The integrated study carried out in the coastal area provided detailed subsurface information useful for planning specific water conservation strategies for sustainable groundwater supply. Keywords: Deccan Traps, ERT, Tritium Tracer, Recharge, Groundwater Flow
... In Deccan volcanic province compound flows are exposed around an elliptical region (Nashik-Igatpuri) and simple flows are dominant in peripheral region (Deshmukh, 1988) (Fig. No. 2). The study area is situated in the eastern part of the province in which is a 'simple' or 'aa' flow dominated area. ...
The Bhuleshwari river basin covers an area about 380 Sq. Km. from Bhatkuli and Achalpur Taluka, Amravati district, Maharashtra. It flows over varied geological formation from Deccan trap to Alluvium with groundwater quality varying from fresh water to saline water. The area has been studied to evaluate the impact of geomorphology on groundwater occurrence and its impact on hydrogeochemical evolution of groundwater. Number of field traverses and observation in the bank sections of the river and dug wells has been done in the given basin. The nature and lateral and vertical extent of aquifers are controlled by lithology, stratigraphy and structure of rock formations. Lithological characteristics of rocks are reflected in their storage and yield properties. The present work deals with the regional as well as local geological set of the area and its Stratigraphic position. It also deals with the lithological characteristics of the ‘basalt flows’ and structural features of the area. The detailed geology of the Bhuleshwari river basin has been discussed and presented in chapter two. Based on number of field traverses, in the geological map eight lavaflows has been identified in northern region and alluvium in southern region can be divided into younger and older alluvium. The Deccan trap is separated by alluvium with fault, boulder alluvium is seen to occur in this zone. The geological map of Bhuleshwari river basin modified from geological survey of India map, GSI (2001) is presented. Geologically the study area consists of 420 m thick Alluvium. Only the top 40 m is accessible for direct observation in the bank sections of the river and dug wells.
... These share characteristics with so-called hummocky phh flow fields of Hon et al. (1994), also called lobate flows by Kale et al. (2020a). Areas of compound flows (Figure 3c) in the Deccan were first identified by Deshmukh (1988) and later by a number of studies across the whole Deccan province (Bondre et al. 2000Duraiswami et al. 2001;Patel et al. 2020;Kale et al. 2021). These observations confirmed that the common structures and characteristics of the lavas support that they were emplaced by the process of inflation, as they contain several distinctive features of inflated phh ). ...
... These share characteristics with so-called hummocky phh flow fields of Hon et al. (1994), also called lobate flows by Kale et al. (2020a). Areas of compound flows (Figure 3c) in the Deccan were first identified by Deshmukh (1988) and later by a number of studies across the whole Deccan province (Bondre et al. 2000Duraiswami et al. 2001;Patel et al. 2020;Kale et al. 2021). These observations confirmed that the common structures and characteristics of the lavas support that they were emplaced by the process of inflation, as they contain several distinctive features of inflated phh ). ...
... Ahmad and Shrivastava (2004) attempted iron-titanium oxide geothermometry for the Mandla- (McHone, 1996;Sheth, 2000). In the Deccan basalts, extensive studies on the morphology and emplacement have demarcated two major types of flows, which are (i) compound pahoehoe flows (see Deshmukh, 1988) (similar to those in Hawaii and the Columbia River Basalt) and (ii) simple flows occurring in the younger sheet-like formations capped by highly vesicular weathered and flow top breccias (Bondre et al., 2004). According to the current eruptive model (Cox & Hawkesworth, 1985;Jay et al., 2009) Cumulate gabbro Dark-coloured, coarse grained with moderate specific gravity Essentially composed of coarser subhedral plagioclase, clinopyroxene and opaque mineral; the coarser grain size corresponds to cumulus crystals, relatively finergrained plagioclase and clinopyroxene also occur as intercumulus crystals. ...
Field investigations and lava flow mapping around Khandwa (21°49′ N:76°21′ E), Central India (within the eastern Deccan volcanic province) record three distinct lava flows which are in general, characterized by several structural zones, for example, Lower Vesicular Zone, Lower Colonnade Zone, Entablature Zone (EZ), Upper Colonnade Zone (UCZ), and Upper Vesicular Zone (UVZ). Different lava flows (often with chilled zones) in the field have been marked by discontinuous thin intertrappean beds. The occasional presence of chilled dyke and feeder dyke (both associated with Flow II) has also been noticed. The entire lava succession rests over coarse‐grained (cumulate) gabbroic (apparent) basement. Deduced clinopyroxene ordering clearly indicates that 100% initial ordering had been achieved for Flow II chilled zone, Flow II UCZ, Flow III UCZ, Flow III EZ, and cumulate gabbro. On the contrary, Flow II UCZ (97.35% initial ordering), feeder dyke (98.76% initial ordering), chilled dyke (99.82% initial ordering), and Flow I chilled zone (99.07% initial ordering) show initial clinopyroxene disordering (<100% ordering), which were later subjected to a gradual process to achieve ordering. Second‐order regression analyses clearly indicate that the progressive clinopyroxene ordering‐process is controlled by several differentiation parameters namely An% of coexisting plagioclase, lower thermometric values, and FeOt/MgO. In addition, roles of AlVI, Ti⁴⁺, and Fe³ were also suggested to influence the clinopyroxene ordering‐style. Based on Ti/6ox versus Al/6ox relation of clinopyroxene, it was deduced that cooling rate appreciably controls the clinopyroxene ordering‐behaviour. We contemplate that variation in clinopyroxene ordering‐pattern in basaltic rocks of Khandwa represents interplay of differentiation parameters and cooling rate of the ambient magma.
... These share characteristics with so-called hummocky phh flow fields of Hon et al. (1994), also called lobate flows by Kale et al. (2020a). Areas of compound flows (Figure 3c) in the Deccan were first identified by Deshmukh (1988) and later by a number of studies across the whole Deccan province (Bondre et al. 2000Duraiswami et al. 2001;Patel et al. 2020;Kale et al. 2021). These observations confirmed that the common structures and characteristics of the lavas support that they were emplaced by the process of inflation, as they contain several distinctive features of inflated phh ). ...
Large igneous provinces (LIPs) represent some of the greatest volcanic events in Earth history with significant impacts on ecosystems, including mass extinctions. However, some fundamental questions related to the eruption rate, eruption style, and vent locations for LIP lava flows remain unanswered. In this review, we use the Cretaceous–Paleogene Deccan Traps as an archetype to address these questions because they are one of the best preserved large continental flood basalt provinces. We describe the volcanological features of the Deccan flows and the potential temporal and regional variations as well as the spatial characteristics of potential feeder dikes. Along with estimates of mean long-term eruption rates for individual Deccan lavas from paleomagnetism and Hg proxy records of ∼50–250 km3/year (erupting for tens to hundreds of years), the Deccan volcanic characteristics suggest a unified conceptual model for eruption of voluminous (>1,000 km3) LIP lavas with large spatial extent (>40,000 km2). We conclude by highlighting a few key open questions and challenges that can help improve our understanding of how the Deccan flows, as well as LIP flows in general, erupted and the mechanisms by which the lavas may have flowed over distances up to 1,000 km.
... Bondre et al. 2004;Jay et al. 2009), though in Saurashtra and Kachchh in the northwest, maximum preserved thicknesses are a few hundred metres (Sheth et al. 2013). Both compound and simple flows are found in abundance (Walker, 1971;Deshmukh, 1988;Bondre et al. 2004;Sheth, 2018;Kale et al. 2022). The small-scale compound pāhoehoe flows are usually pervasively altered, contain basal pipe vesicles and are frequently hummocky, i.e. they contain tumuli (Neill et al. 2015). ...
The primary features (morphologies, structures, textures) of volcanic lava flows are determined by parameters such as composition, temperature, crystallinity, viscosity, flow velocity, strain rate and cooling rate. However, lava flows are open systems, and their primary features are strongly influenced by their emplacement environment. Among subaerial lava flows, those that solidify in a wet environment with rainfall develop very different internal structures (e.g. jointing patterns) and textures from those in a dry environment. Thus, the outcrop structures and textures of ancient lava flows, such as those forming continental flood basalt sequences thousands of metres thick, provide clues to their cooling histories and the palaeoclimates. Here we provide field, petrographic and geochemical data on large tholeiitic lava flows (sheet lobes) and associated dykes of the Saurashtra region in the northwestern Deccan Traps continental flood basalt province (India). The sheet lobes are dominantly pāhoehoe and rubbly pāhoehoe, and occasionally ‘a‘ā, with colonnade and entablature tiers. We show that the jointing patterns in the entablatures (irregular, chevron, rosette and skeleton jointing), and the textures of the sheet lobes and even some dykes (abundant glass, and quench crystals of plagioclase and Fe–Ti oxides) reflect convective heat removal, owing to widespread interaction with meteoric waters (rainfall) during solidification. The observations thus provide evidence for a wet climate in western India 65.5 million years ago.
... Basalts at the southern and southeastern limit of the DTVP commonly lie directly upon the Archean-Proterozoic granitic basement, although patchy, fossiliferous, Upper Cretaceous-lower Paleogene lacustrine sediments occasionally intervene between the basalts (i.e., intertrappeans) or between them and basement (i.e., infratrappeans). The source vent areas that fed the DTVP have not yet been unequivocally identified, but they are likely to have existed on its western margin, originally near or beyond the current Western Ghats escarpment where the thickest successions are recorded (Deshmukh, 1988;Widdowson and Cox, 1996;Kale et al., 2020). Further to the east these successions progressively thin, with fewer flow fields having extended to these greater distances. ...
The first Cretaceous mammals described from India were recovered from the Naskal locality, on the southeastern edge of the Deccan Traps Volcanic Province (DTVP), where it is preserved between two basalt flows. Because the DTVP eruptions spanned the Cretaceous-Paleogene boundary (KPB), it is often unknown whether trap-associated fossil sites are latest Cretaceous (Maastrichtian) or early Paleocene in age. The Naskal locality accounts for nearly half of published mammal records from DTVP-associated sediments as well as a host of other vertebrate microfossils. Its age takes on singular importance in the context of mammalian evolution in India and the effects of the end-Cretaceous mass extinction and subsequent evolutionary radiation of placentals. Here we describe two new mammal species, Indoclemensia naskalensis gen. et sp. nov. and I. magnus sp. nov., from Naskal and present evidence from ⁴⁰Ar/³⁹Ar geochronology, magnetostratigraphy, and chemostratigraphy of the over- and underlying basalt flows to refine the age of the Naskal locality and nearby Rangapur locality. In conjunction with palynostratigraphy and vertebrate biostratigraphy, these sites can be confidently restricted to a <100 kyr interval spanning the KPB. The most probable ⁴⁰Ar/³⁹Ar age is latest Cretaceous (66.136–66.056 Ma), but an earliest Paleogene age cannot be ruled out. We explore the implications of this age assignment for the Deccan chemostratigraphy and Deccan volcanism, Cretaceous-Paleogene (K/Pg) mass extinction, Indian mammalian faunal evolution, and the timing of the origin of placental mammals.
... Basalts at the southern and southeastern limit of the DTVP commonly lie directly upon the Archean-Proterozoic granitic basement, although patchy, fossiliferous, Upper Cretaceous-lower Paleogene lacustrine sediments occasionally intervene between the basalts (i.e., intertrappeans) or between them and basement (i.e., infratrappeans). The source vent areas that fed the DTVP have not yet been unequivocally identified, but they are likely to have existed on its western margin, originally near or beyond the current Western Ghats escarpment where the thickest successions are recorded (Deshmukh, 1988;Widdowson and Cox, 1996;Kale et al., 2020). Further to the east these successions progressively thin, with fewer flow fields having extended to these greater distances. ...
The first Cretaceous mammals described from India were recovered from the Naskal locality, located near the village of Naskal in the state of Telangana. The Naskal locality is located on the eastern edge of the Deccan Traps Volcanic Province (DTVP), where it is preserved between two basalt flows. Naskal and similarly preserved sites are “intertrappean” in position and are distinguished from “infratrappean” sedimentary exposures, which are positionally below the locally lowest basalt flow. Historically, this field-based designation has been used as a proxy for relative age assignments, with intertrappean sites generally considered to be of similar age to each other, but collectively younger than infratrappean (Lameta Formation) sites. However, the DTVP flow stratigraphy is complex, so this age proxy can be incomplete and misleading. Moreover, because the DTVP eruptions spanned the Cretaceous-Paleogene boundary (KPB), it is often unknown whether intertrappean sites, including Naskal, are Cretaceous or Paleogene in age.
Naskal accounts for nearly half of published mammal records from DVTP-associated sediments, as well as a host of other microfossils. The age of the Naskal locality takes on singular importance in the context of mammalian evolution in India and the effects of the end-Cretaceous mass extinction and subsequent evolutionary radiation. Here we present evidence from Ar/Ar geochronology, magnetostratigraphy, and chemostratigraphy of the over- and underlying basalt flows to narrow the permissible age of the sediments at the Naskal locality. In conjunction with palynostratigraphy and vertebrate biostratigraphy, this site can be confidently restricted to a <100 ka interval spanning the KPB. The most probable Ar/Ar age is latest Cretaceous, but an earliest Paleogene age cannot be ruled out. We explore the implications of this age assignment, and additionally describe two new mammal species from the same genus from Naskal.
... The relationship of typical lobe thicknesses among the various geochemical formations provides important insights into the changing style of eruption of typical Deccan units as the main lava pile grew during its ∼ 1 Ma lifetime (Sprain et al., 2019;Schoene et al., 2019). Our work also makes it possible to test and quantify the suggestions of Deshmukh (1988), Walker (1971), Walker (1999) that smaller "compound" lava lobes dominate in the northern areas of the main Deccan province and that thicker "simple" flows occur more commonly to the south and east ( Figure 1C). This observation was interpreted as being indicative of a lava morphology change due to changing distance from source. ...
Constraining the eruption rates of flood basalt lava flows remains a significant challenge despite decades of work. One potential observable proxy for eruption rates is flood basalt lava-flow lobe thicknesses, a topic that we tackle here quantitatively. In this study, we provide the first global compilation of pāhoehoe lava-lobe thicknesses from various continental flood basalt provinces (∼ 3,800 measurements) to compare characteristic thicknesses within and between provinces. We refer to thin lobes (∼ ≤5 m), characteristic of “compound” lavas, as hummocky pāhoehoe lava flows or flow-fields. Conversely, we term thicker lobes, characteristic of “simple” flows, as coming from sheet-lobe-dominated flows. Data from the Deccan Traps and Columbia River flood-basalt provinces are archetypal since they have the most consistent datasets as well as established chemo- and litho-stratigraphies. Examining Deccan lobe thicknesses, we find that previously suggested (and disputed) distinct temporal and regional distributions of hummocky pāhoehoe and sheet-lobe-dominated flow fields are not strongly supported by the data and that each geochemically defined formation displays both lobe types in varying amounts. Thin flow-lobes do not appear to indicate proximity to source. The modal lobe thickness of Deccan formations with abundant “thin” lava-lobes is 8 m, while the mode for sheet-lobe-dominated formations is only 17 m. Sheet-lobes up to 75–80 m are rare in the Deccan and Columbia River Provinces, and ones >100 m are exceptional globally. For other flood basalt provinces, modal thickness plots show a prevalence toward similar lobe thicknesses to Deccan, with many provinces having some or most lobes in the 5–8 m modal range. However, median values are generally thicker, in the 8–12 m range, suggesting that sheet-lobes dominate. By contrast, lobes from non-flood basalt flow-fields (e.g., Hawai’i, Snake River Plain) show distinctly thinner modes, sub-5 m. Our results provide a quantitative basis to ascertain variations in gross lava morphology and, perhaps, this will in future be related to emplacement dynamics of different flood basalt provinces, or parts thereof. We can also systematically distinguish outlier lobes (or regions) from typical lobes in a province, e.g., North American Central Atlantic Magmatic Province lava-lobes are anomalously thick and are closely related to feeder-intrusions, thus enabling a better understanding of conditions required to produce large-volume, thick, flood basalt lava-lobes and flows.
... The Late Cretaceous to Paleocene (~65 Ma) Deccan province currently occupies 500,000 km 2 of western and central India, and has been extensively studied in terms of lava stratigraphy and geochemistry (e.g., Krishnamurthy 2020a, b;Kale et al. 2020, and references therein). The lava flow types include voluminous "compound" pāhoehoe flows as well as "simple" sheet flows of pāhoehoe and rubbly pāhoehoe morphologies, with some 'a'a flows (e.g., Walker 1971;Deshmukh 1988;Bondre et al. 2004;Duraiswami et al. 2008;Brown et al. 2011). The abundant boles of the Deccan Traps have been extensively studied and variably interpreted (references herein). ...
Continental flood basalt (CFB) provinces such as the Deccan Traps show numerous inter-flow horizons called boles, most commonly red or brown. These have been variably interpreted as altered glassy bases of basalt flows, paleosols developed on exposed flow tops, altered volcanic ash beds, or local inter-flow sediments. We believe that each of these mechanisms may apply, singly or in combination, to specific red boles, and propose an additional mechanism, namely the weathering of flow-top and flow-bottom breccias. The breccias are inherently highly prone to weathering, and evidence for the mechanism is a close observed correspondence between breccia zones and red boles. The mechanism explains the absence of red boles in the compound pāhoehoe flows which characteristically lack breccias, and their abundance in rubbly pāhoehoe and ‘a’a lava flows. The latter observation has been misinterpreted as indicating significant eruptive hiatuses and a low eruption frequency. Importantly, even all breccia-derived boles do not have the same significance: those derived from flow-top breccias are paleosols, formed by subaerial weathering during eruptive breaks. Those derived from flow-bottom breccias, thus not in contact with the atmosphere, were formed due to groundwater ingress along flow contacts and fractures. These boles have developed slowly over long time periods. Significant development of all bole types must also have occurred in post-volcanism time and is arguably ongoing even today in the exposed and unexposed parts of CFB sequences. Recognizing multiple and complex origins of superficially similar-looking red boles is of critical importance in CFB volcanology and flow stratigraphy, and a warning sign to straightforward application of mineral chemical, mineral magnetic, geochemical, and similar data on boles to interpreting paleoweathering, paleoclimates, and paleoenvironments.
... The basaltic lava Cows from the Deccan Volcanic Province (DVP) were traditionally classiBed into (i) compound p ahoehoe Cows, (ii) simple Cows, and (iii) a' a Cows (Deshmukh 1988;GSI 2001). Bondre et al. (2004) concluded that most of the basaltic lava Cows in the DVP belong to either the compound p ahoehoe type or the simple type. ...
The crust is a vesicular layer that caps the compact core of sheet lava flows. We describe for the first time, a crust composed of multiple layers (each distinguished by a chilled glassy rind) from the Diveghat Formation in the western Deccan Volcanic Province. The multiple layers of crust developed over a single compact core of a single sheet lava flow, are shown to have been sequentially deformed in multiple phases., This is interpreted to have resulted from the endogenous emplacement of lava in successive pulses (rather than as a continuous stream) during the extrusion of the sheet lava flow. This model has several implications on the mechanism of emplacement of sheet flows in continental flood basalt provinces.
Key words:
Deccan Traps, Pulsed emplacement, Sheet flow
... Based on these characteristics, simple and compound lava flows are generally distinguished [16,25]. Compound flows are abundant in the northwestern and central parts of the MDP (Figure 1) [26] within the estimated distribution of the Kalsubai subgroup [20]. ...
The morphology, chemical, and mineralogical composition of subsurface filamentous fabrics (SFF) from the Deccan Volcanic Province (DVP) were investigated to determine the origin of these spectacular aggregates. SFF occur in a wide variety of morphologies ranging from pseudo-stalactites to irregular fabrics and are classified as SFFIr (irregular) or SFFMa (matted). The SFF samples exhibit a thread-like (or filament-like) center from which mineral precipitation starts to form the final macroscopic morphologies. Detailed investigations revealed organic material (fungal chitin) in the innermost filamentous core, which may have acted as an initial nucleus for the mineralization processes. The morphometric characteristics of certain filamentous fabrics are very similar to those of microbial filaments and the fabrics formed from them but are clearly distinct from similar types of non-biological precipitates (fibrous minerals, speleothems, and “chemical gardens”). These features indicate that the filamentous cores might be products of microbial communities that were active in the basaltic cavities. The SFF cross-sections display similar concentric layers of the mineral succession and reach thicknesses of several centimeters with spectacular lengths up to 100 cm and constant diameters. The typical mineralization sequence points to temporal variation in the chemical composition of the mineralizing fluids from Fe(Mg)-rich (Fe-oxides/-hydroxides, Fe-rich sheet silicates such as celadonite and di-/tri-smectite) to Ca-dominated (Ca-rich zeolites) and finally pure SiO2 (opal-CT, chalcedony, and macro-crystalline quartz). Assuming biological activity at least during the early mineralization processes, circumneutral pH conditions and maximum temperatures of 100–120 °C were supposed. The formation of filamentous cores including Fe-bearing phyllosilicates probably occurred near the surface after cooling of the lava, where the elements necessary for mineral formation (i.e., Si, Mg, Al, Fe) were released during alteration of the volcanic host rocks by percolating fluids.
... The Mahabaleshwar and Ambenali formations are exposed along the WGE and on the plateau sectors, while flows belonging to the Poladpur Formation (of this classification) are encountered at lower elevations (Fig. 8a). The basaltic flows in the study region are essentially the simple (a'a-) type flows (as described by Walker 1971Walker , 1999Deshmukh 1988). The flows in the study area consist of amygdaloidal and vesicular basalts underlain by compact basalts, in some cases separated by thin layers of flow-top breccias or oxidized, ferruginous powdery horizons described as 'bole' beds, which are characteristic of simple flows (Bondre et al. 2004). ...
Koyna, located in the Deccan Volcanic Province in western India, is the most significant site of reservoir triggered seismicity (RTS) globally. The largest RTS event of M 6.3 occurred
here on December 10, 1967. RTS at Koyna has continued. This includes 22 M ≥ 5.0 and thousands
of smaller events over the past 50 years. The annual loading and unloading cycles of the Koyna
Reservoir and the nearby Warna Reservoir influence RTS. Koyna provides an excellent natural laboratory to comprehend the mechanism of RTS because earthquakes here occur in a small area,
mostly at depths of 2–7 km, which are accessible for monitoring. A deep borehole laboratory is
therefore planned to study earthquakes in the near-field to understand their genesis, especially in
an RTS environment. Initially, several geophysical investigations were carried out to characterize
the seismic zone, including 5000 line kilometres of airborne gravity gradiometry and magnetic surveys, high-quality magnetotelluric data from 100 stations, airborne LiDAR surveys over 1064 km2,
drilling of 8 boreholes of approximately 1500 m depth and geophysical logging. To improve the
earthquake locations a unique network of borehole seismometers was installed in six of these boreholes. These results, along with a pilot borehole drilling plan, are presented here.
Squeeze-ups are common features of basaltic lava flow-fields on Earth. Squeeze-ups, rootless autointrusions of lava, drive intraflow resurfacing of active flow-fields, and the term is also used for linear or bulbous extrusions (syn. “breakouts”, “outflows”) from cracks in the solid crust, or from tensional clefts on tumuli. Despite the abundance of squeeze-ups in the active or Recent flow-fields of Hawaii, Etna or Iceland, and in the prehistoric continental flood basalt (CFB) provinces, there has been no dedicated study of them for about a century. Here we present a well-illustrated study of squeeze-ups in subaerial basaltic lavas, with a focus on the Deccan Traps CFB province of India, and show that squeeze-ups have a great range of sizes, shapes, orientations, and host flow-field morphologies including pāhoehoe, slabby pāhoehoe, rubbly pāhoehoe, slab-crusted lavas, and ‘a'ā. Squeeze-ups, as the name suggests, originate from overpressurisation of lava flow interiors, caused by mechanisms such as an increased lava flux, progressive downward solidification of the upper crust, crystallisation leading to volatile exsolution (second boiling), viscous fingering, and constricted or blocked lava tubes. The overpressurised lava may create a hydrofracture in the crustal roof in the manner of a dyke, or open an incompletely sealed contact between adjacent flow-units in a compound flow. Similar-looking features formed by passive tapping of interior lava by fractures forming in the cooling, contracting and deforming crust can be termed “lava crack-seals”. We offer a formal discussion of the theoretical and outcrop similarities and differences between dykes and squeeze-ups, features usually easy to distinguish but not always so. We also discuss the distinctions between feeder dykes and pseudodykes, and between squeeze-ups and lava fingers, features often liable to mutual confusion in outcrop. Finally, we review the existing definitions of squeeze-ups, and provide a new formal definition that includes their surface and subsurface realms, the product, and the process: “Squeeze-ups are rootless autointrusions that cause endogenic growth and intraflow resurfacing in lava flow-fields, or rootless extrusions produced by such resurfacing, involving brittle deformation of their host rock.” It is certain that, with future high-resolution remote sensing imagery, squeeze-ups will be recognised on the surfaces of the terrestrial planets other than Earth, given their ubiquity and essential role in the physical development of basaltic lava flow-fields on Earth.
The variation in petrographical characters of stratigraphic sequence gives valuable information on petrogenesis along with their crystallization history. The petrographic characters show a considerable range of variation both in texture and proportion of mineral constituents. The lava flows not only show variation with one another but also within the same flow. Each flow type shows a fair degree of similarity with minor difference present in them, indicating the variation in composition of the lava flow with respect to their crystallization. In this chapter, we have observed the 11 lava flow in the area.
In central India, fluoride contamination in deeper basaltic aquifer is geogenic. This study demonstrates the source of fluorine enrichment in aquifer matrix and its release mechanism into groundwater. Magmatic-hydrothermal residual melt, i.e., albitic–calcic-amphibole–apatite-rich intrusive rock is the main source of fluorine enrichment. The association of this rock with interflow carbonate-clay assemblage played a significant role for fluoride contamination. Fluorine-enriched residual melt interacted with interflow carbonate-clay association, and this interaction metasomatized the carbonates and enhanced fluorine concentration in sediments. Bulk fluorine concentration of 988 ppm is measured in the soil developed over the association of intrusive rock and carbonate-clay assemblage. X-ray diffraction and electron-probe micro analysis confirmed the presence of fluorine-bearing and/or containing minerals, i.e., fluorite, fluorapatite, and palygorskite. The presence of bicarbonate and Na+ (from albitic feldspar) in alkaline water enhanced desorption of fluoride from clays, and dissociation from fluorapatite and fluorite from carbonate-clay assemblage, which released fluoride from aquifer matrix to groundwater. Clay horizon acts as an impervious cap on the deeper aquifer and increases the residence time of groundwater. In such favorable physico-chemical condition, fluoride released from aquifer matrix to groundwater and gradually increasing the degree of fluoride contamination.
The scope of the study revolved around three basic questions. The First being estimation of the quantities of groundwater extracted in the city of Pune, say on an annual basis, while the second question was more specific in terms of the layout of Pune’s aquifers and their characteristics. The 2019 report focused on these two questions, while this report also brings the third, most important component, into focus, mainly, the basis for the planning, management, and governance of groundwater in Pune city. The report also includes short narratives of certain decisions and actions culminating from the earlier version of the report and suggests certain key aspects of the way forward.
This report is a culmination of efforts made by ACWADAM, in collaboration with UNICEF and Sevavardhini towards deriving a process for drinking water safety and security for villages in overexploited watersheds identified by the GSDA. It aims to strengthen local governance institutions with regards to the process and the elements therein. The primary objective of the Drops of Hope programme is drinking water safety and security, hence aquifers tapped by the drinking water source are given priority in estimation of a groundwater balance. Changes in aquifer storage, groundwater recharge, and groundwater discharge – mainly in the form of pumping and base flow are the major components of this groundwater balance.
The Drops of Hope programme intends to build the capacities of village institutions like the Gram Panchayat and Village Water Sanitation Health and Nutrition Committee (VWSC) to arrive at drinking water safety and security plans based on an understanding of the water resources in the area. As a part of the process, various stakeholders were sensitised about the processes listed in this document through various forms of engagements. Training programs were conducted for the VWSC and for community resource persons (CRPs) of the village.
This report consolidates the first set of observations and inferences based on a field visit by ACWADAM to Velu gram panchayat under the field facilitation for Paani foundation. ACWADAM conducted a rapid hydrogeological appraisal to understand the impact of implementation carried out during the Paani Foundation Water Cup competition in Velu
village in the context of groundwater scenario. Out of 116 villages, Velu from Koregaon Taluka, Satara District, Maharashtra participated in the ‘Satyamev Jayate Water Cup Competition- 2016’. These villages competed to create maximum water storage and make village water-sufficient. Velu village had won the competition by creating 281.69 crore liter of water storage, to become the most water sufficient village amongst other participating villages. The competition leads to participatory learning, planning and implementation of watershed work in respective villages. This watershed development programme had classical ‘ridge to valley’ approach. The report discusses the observations during field work and outlines possible ways for forward engagement.
Drinking water is a fundamental need of an individual. Drinking water requirement is the top priority within all water requirements. This is especially relevant to the water scarcity context in different parts of India. Specific programmes are designed by central and state agencies to ensure drinking water availability to all the desired stakeholders. These programs include National Rural Drinking Water Programme, Chief Minister’s Drinking Water Programme, and the more recent Pradhan Mantri Jal Jeevan Abhiyan translated into the Jal Jeevan Mission. The focus of these programmes and missions is to ensure year-round availability of drinking water to all the rural households. Although the
programme outline integrates elements like source sustainability, water supply infrastructure and the setting up of institutions for management, less attention is paid to ensure the sustainability of the 'resource' tapped by each drinking water source. The resource in this discussion is 'aquifer' and the 'source' is the drinking water dug well or bore well. The resources themselves are a function of the larger water system that includes nearly all the components of the water cycle. Hence, the source, through resource characteristics becomes subject to changes in both the system and the resource
Drinking water is a fundamental need of an individual. Drinking water requirement is the top priority within all water requirements. This is especially relevant to the water scarcity context in different parts of India. Specific programmes are designed by central and state agencies to ensure drinking water availability to all the desired stakeholders. These programs include National Rural Drinking Water Programme, Chief Minister’s Drinking Water Programme, and the more recent Pradhan Mantri Jal Jeevan Abhiyan translated into the Jal Jeevan Mission. The focus of these programmes and missions
is to ensure year-round availability of drinking water to all the rural households. Although the programme outline integrates elements like source sustainability, water supply infrastructure and the setting up of institutions for management, less attention is paid to ensure the sustainability of the 'resource' tapped by each drinking water source. The resource in this discussion is 'aquifer' and the 'source' is the drinking water dug well or bore well. The resources themselves are a function of the larger water system that includes nearly all the components of the water cycle. Hence, the source, through resource characteristics becomes subject to changes in both the system and the resource.
ACWADAM, AFARM and AOL are working together in 14 villages from Maan taluka of Satara district. This project is supported by Cummins India. The duration of the project is 15 months starting from Feb 2018.
Project objectives
1. To study the hydrogeology of fourteen villages to build an understanding of local aquifer systems.
2.To set up monitoring network and collect water level data to understand the changes in
the aquifer.
3. To delineate the aquifer systems in the 14 villages.
4. Identify potential recharge areas for the aquifers with the geology.
5.To provide inputs on the basis of the hydrogeological study for the implementation of
watershed activities with major focus on groundwater recharge.
6.To sensitise community/ KRPs on the issues of groundwater management.
We analyse two representative rubbly pāhoehoe lavas (F3 and F5) from drill cores at Tural-Rajwadi, southwest of Koyna, in the southern Deccan Traps. Low vesicle deformation (0.1 to 0.4) indicates that both lavas ultimately cooled under a low-stress regime. The crystal size distributions (CSDs) of most samples from F5 (especially those from within the core) are not linear but instead show kinks. These kinks are attributed to a rise in plagioclase nucleation due to degassing following the brecciation of the crust. Since it is difficult to constrain cooling time for ancient lava flows, we used the products of nucleation rates (Jt, 1.64 × 10–8 to 1.45 × 10–5 μm−3) and growth rates (Gt, 2.1 to 156 μm) with time. When compared with natural analogues as well as experimental results for basalt crystallisation, these values suggest a much faster lava cooling rate (~ 1 to 7℃/hr) than a conductive cooling model (≤ 0.1 ℃/hr). The CSDs for F3 fan with depth suggesting that the lava flow might represent local accumulation (ponding?) in a transitional lava flow field. CSDs for F5 show little variation with depth, with the exception of kinks for samples from the lower crust and core. The relatively higher number density of plagioclase microcrysts in our rubbly pāhoehoe (F5) and their CSD patterns are similar to those measured for transitional lavas from Hawaii. The vesicle data and CSDs indicate that brittle deformation was the primary mode of transition within these lavas. Identifying occurrence of thick ponded lavas within vertical stacks of rubbly pāhoehoe flows in the upper stratigraphic levels of the Deccan Traps are critically important as they demonstrate complex cooling styles, crystallisation histories, and emplacement dynamics. Transitional lavas such as rubbly pāhoehoe are important components of large CFB provinces such as the Deccan Traps and constitute nearly 46 to 85% of all lava types. Modelling of continental flood basalt provinces should therefore account for these diversities within lavas, and any oversimplified version using end-member morphotypes is unrealistic and untenable.
We analyse two representative rubbly pāhoehoe lavas (F3 and F5) from drill cores at Tural-Rajwadi, southwest of Koyna, in the southern Deccan Traps. Low vesicle deformation (0.1 to 0.4) indicates that both lavas ultimately cooled under a low-stress regime. The crystal size distributions (CSDs) of most samples from F5 (especially those from within the core) are not linear but instead show kinks. These kinks are attributed to a rise in plagioclase nucleation due to degassing following the brecciation of the crust. Since it is difficult to constrain cooling time for ancient lava flows, we used the products of nucleation rates (Jt, 1.64 × 10–8 to 1.45 × 10–5 μm−3) and growth rates (Gt, 2.1 to 156 μm) with time. When compared with natural analogues as well as experimental results for basalt crystallisation, these values suggest a much faster lava cooling rate (~ 1 to 7℃/hr) than a conductive cooling model (≤ 0.1 ℃/hr). The CSDs for F3 fan with depth suggesting that the lava flow might represent local accumulation (ponding?) in a transitional lava flow field. CSDs for F5 show little variation with depth, with the exception of kinks for samples from the lower crust and core. The relatively higher number density of plagioclase microcrysts in our rubbly pāhoehoe (F5) and their CSD patterns are similar to those measured for transitional lavas from Hawaii. The vesicle data and CSDs indicate that brittle deformation was the primary mode of transition within these lavas. Identifying occurrence of thick ponded lavas within vertical stacks of rubbly pāhoehoe flows in the upper stratigraphic levels of the Deccan Traps are critically important as they demonstrate complex cooling styles, crystallisation histories, and emplacement dynamics. Transitional lavas such as rubbly pāhoehoe are important components of large CFB provinces such as the Deccan Traps and constitute nearly 46 to 85% of all lava types. Modelling of continental flood basalt provinces should therefore account for these diversities within lavas, and any oversimplified version using end-member morphotypes is unrealistic and untenable.
‘Ghod River Basin management study’ was a joint collaboration between CII (Special Projects Department) and ACWADAM, supported through ITC’s grant to CII. In many ways, this is the first systematic compilation effort of groundwater-related information at the scale of a river basin in India.
Detailed field and petrographic studies of basaltic lava flows along the Amarkantak-Shahdol-Umaria traverse were carried out to describe the three significant basaltic flows of Amarkantak, Shahdol, and Umaria areas of the Eastern Deccan Volcanic Province (EDVP). The field observations suggest that pahoehoe lava flows in Amarknatak. These lava flows show profuse development of vesicles, joints, and cracks which are filled by secondary minerals like quartz, agate, calcite, and zeolites. However, Shahdol and Umaria are slightly coarse-grained than Amarkantak flows. These three flows have undergone considerably variable degrees of weathering and leaching/alteration. The structural changes and differences in nature in terms of jointing, weathering characteristics, secondary minerals, break-in slope etc. might help to decipher the approximate position of the contact of flows. The basaltic flows under thin section study are mainly composed of fine-grained plagioclase, augite, magnetite, volcanic glass, and rare olivine minerals. Zeolite, calcite, and occasional secondary quartz occur as secondary minerals. The nature of lava flows point towards slow rate of effusion. The field and petrographic evidence suggest textural variations as well as the variation of magma and their distinct mode of volcanism from Amarkantak to Umaria. Introduction :
My own notes have been made during a period of sixteen years’ service by the road-side, when marching; or in tracts less frequented, while on sporting excursions, when the hammer, compass, and clinometer accompanied the gun and spear; for I deemed it possible, even for those who run, to snatch a glimpse from nature's book.” – Captain Newbold, FRS
The Deccan Volcanic Province (DVP), covering presently an area of 0.5 million km2, and estimated to be 2-3 times larger during the Upper Cretaceous-Paleocene, is one of the largest continental flood basalt provinces of the world. Its formation has been linked to the foundering of the Gondwanaland and Greater India's northward drift, passing over the Reunion plume and eruption of over a million km3 of lava that apparently led to a mass extinction of global proportions. The DVP has thus been a major domain of scientific interest and study the world over. It had received attention since the 1830s, first from the army and civil service men of the British Raj and subsequently from the officers of the Geological Survey of India (GSI) founded in 1851, and academicians from a number of Indian Universities and research Institutions, often in collaboration with geologists from countries such as the UK, USA, Russia, France, Japan, Italy and others. Thus, studies of the DVP conducted for over 170 years, and especially in the last five decades, have provided a very large database that has led to a better understanding of the genesis and evolution of the this province and similar flood basalt provinces of the world.
The DVP is thickest in the Western Ghats, forming many individual 400 m to 1650 m thick sections over some 700 km. The structural evolution of the lava sequence envisages a pre–uplift, thick (c. 2-3 km), lensoid pile of dense basalt that gradually sank into the crust by the end of the eruptive phase, followed by an uplift of the western margin of the Deccan due to both denudational-isostasy reasons and the associated geomorphological and structural evolution of the lava pile from Tertiary uplift and coastal flexure formation (the Panvel structure). Such an evolution has led to stresses that get accommodated along fractures in the pre-Deccan basement at varying depths and apparently provide the loci for seismicity observed over the province. The DVP is predominantly composed of quartz- and hypersthene-normative tholeiitic basalts in the plateau regions (Western Ghats and adjoining central and eastern parts, Malwa and Mandla). However, along the ENE-WSW-trending Narmada-Tapi rift zones, the N-S to NNW-SSE-trending Western coastal tract, the Cambay rift zone, and the Saurashtra and Kutch regions, the DVP shows considerable diversity in terms of structures, dyke swarms and dyke clusters, and intrusive and extrusive centres with diverse rock types. These include: primary picrite basalts and their differentiates (e.g., Botad, Dhandhuka, Wadhwan Jn., Pavagadh), granophyre-rhyolite intrusive ring-complexes and mixed basalt-rhyolite associations (e.g., Alech, Barda, Osham, Chogat-Chamardi, Mumbai Island, and others), carbonatite-nephelinite associations (Amba Dongar-Kawant), gabbro-anorthosite-nepheline syenite-syenite ring/layered complexes(e.g., Mt. Girnar, Mundwara, Phenai Mata), mantle-derived spinel peridotite-hosting melanephelinites and basanites (e.g. Dhrubya, Vethon and others in Kutch), besides scores of alkaline and lamprophyre dykes. Some of these complexes are associated with high gravity anomalies indicating dense plutonic bodies at depths.
Flow morphological studies of the DVP have led to the recognition of two main types of flows, namely ‘a'a (typically forming simple, sheet flows) and pâhoehoe (typically forming compound, pāhoehoe lobate flows) with transitions between them that result in mixed types. The ‘a'a types are largely single units found in the peripheral parts where thicknesses of the flow sequence range from a few meters to a few tens of meters. The compound pâhoehoe flows contain many units or lobes and are largely found in the thicker sections of Western Ghats, and also in the central parts of the province. The flow sequences of the Western Ghats (c. 400 m to 1650 m thick and spread over an area of 400 km x 100 km along the N-S tract from north of Nasik to Belgaum) have been mapped and correlated using flow morphology, petrology and selected trace elements (Sr, Ba, Zr, Y and Ti) and Sr- isotopes. Such a combination of geochemical characters, constrained further by altitude and magnetic polarity (chrons 30N-29R-29N) have led to the delineation of the flow sequences from north to south into a Deccan Basalt Group, comprising three Subgroups from the base to the top, namely the Kalsubai, Lonavala and Wai Subgroups, with twelve (12) formations in total, each formation containing many flows. Giant plagioclase basalts (GPBs) and bole beds of diverse origin (intertrappean sediments, weathered basalt or tuffs with baking effects) have been found in many flow sequences of the DVP, especially in the Western Ghats and contiguous plateau regions, and these interflow units help in subregional-scale mapping and also provide insights into magma chamber processes and eruptive breaks in the volcanic cycles.
Field and geochemical studies of some twenty-three (23) flow sequences (10 from Western Ghats, five from central India and eight from eastern India) by several groups have enabled correlation of some formations of the Western Ghats such as the Ambenali (crustally uncontaminated) and Poladpur (contaminated) over long distances (c. 400-700 km) to Toranmal, Mhow, Chikaldara, Jabalpur and other sections. However, these formations occur at different stratigraphic elevations at these places and also differ in some isotopic characters (e.g. 206Pb/204Pb). Such features have cast doubts on long distance travel of flows from a single source and led to suggestions of multiple source areas (vents and dykes) as also inferred from the two zones of compositional diversity mentioned above.
Based on detailed field, petrological and geochemical characters including isotopic data and Ar-Ar ages, dyke swarms and clusters in the Narmada-Tapi and western coastal tracts have been shown to belong to two groups: (1) The randomly oriented group between Pune and Nasik as possible feeders to the lava flow sequences of the Western Ghats and (2) Some of the dykes from the east-west-oriented Narmada-Tapi swarm, attributed to active N-S extension during the flood basalt episode, and showing chemical affinities to the lower and middle formations (Jawhar, Igatpuri, Neral, Thakurwadi, Bhimashankar, Khandala). A wide variety of petrographic types of basalts have been observed in the DVP attesting to the diverse crystallisation and differentiation of the different magma types during transport and in magma chambers. Based on petrographic and mineralogical data from a number of thick sections, it has been inferred that minerals such as olivine (Fo90–Fo20), clinopyroxenes (diopsidic augite, augite, subcalcic augite and pigeonite), plagioclase (An84-An30) and opaque oxides including spinels show considerable variations depending upon the tholeiitic or alkaline character of the host magma and its degree of evolution. Secondary minerals, especially zeolites such as heulandite and stilbite, are found in all the ten formations of the Western Ghats whereas merlionite and analcite are only found in the Khandala Formation. Other ten species are of variable abundance are found in the ten formations of the Western Ghats and other areas. Zeolite zonation in DVP suggested earlier has not been substantiated by recent studies, instead multigeneration of secondary minerals in cavities is attributed to late hydrothermal activity from Paleocene to early Miocene.
Groundwater extraction has increased manifold globally, especially after the 19th century. Agriculture accounts for over three-quarters of the total groundwater extracted every year in the world. A large part of this extraction takes place in Asia alone. India became the country with the largest extraction of groundwater in the world – more than a quarter of the global groundwater extraction takes place in India – in the 1980s. India’s groundwater extraction, since the push for the green revolution in the 1960s and 70s, has been on an exponentially increasing trajectory. Groundwater is used in all sectors across India, with agriculture dominating the share of groundwater extraction. The large-scale dependencies on groundwater for domestic water supplies is also becoming obvious. The increasing dependency of the growing urban sector on groundwater resources, both as stand-alone water supplies and as supplements to formal surface water supplies, is hardly a part of India’s urban water planning. Current estimates in India’s towns and cities show that not only is half the urban population dependent upon groundwater but also that half of the total water supply in urban India is groundwater-based. Natural recharge areas in cities are lost to built-up infrastructure on large scales and even as infiltration
decreases, aquifer material is excavated (for foundations) leading to a reduction in the shallow groundwater stocks (shallow aquifers are the most productive groundwater resources in hard rock regions of India) Moreover, contaminants of various types leach into urban aquifers.
The growth of groundwater usage in urban India has also depended upon the growth of India’s towns and cities through a four-stage process involving the nucleus of a township, then its growth, followed by rapid expansion and finally two such expanded cities or metros literally fusing together into a large urban agglomeration. Groundwater is sourced from aquifers – geological formations underneath the ground that store and transmit water under different conditions – that exhibit great diversity in India. An aquifer typology clearly shows that of the nearly 6000 urban centres in India, nearly half are present over the alluvial aquifer system of north-central India, dominated by the plains of Ganga, Brahmaputra and Indus rivers. However, the most urbanised aquifer setting is that of the Himalayan mountain system while the least urbanised is the aquifer setting of the Deccan Volcanic Province of western and central India, a province that underlies large parts of Maharashtra and the entire region of Pune city and its neighbourhoods.
The fundamental exercise of mapping basalt aquifers in the Pune city area was conducted by ACWADAM during the course of a slightly prolonged first phase that involved a review of earlier work on groundwater in the city. Building on the first phase, ACWADAM conducted a more conventional, detailed hydrogeological investigation in Pune city, during the second phase, which has just concluded. This report presents results from both phases, but draws heavily upon the collection of primary and secondary data, apart from sharing this data during sensitisation and awareness workshops on groundwater and rainwater harvesting conducted by Mission Groundwater and CEE, both ACWADAM’s partners on this project.
The Late Cretaceous/Palaeogene Deccan Traps, spread over half a million square kilometres in west-central parts of the Indian Peninsula, comprises predominantly basalts and subordinate felsic rocks (rhyolite, trachyte, tinguaites and spilites). The use of Deccan basalts and trachyte in the range of Indian architectonic heritage, from antiquity to current times, is quite fascinating. The abundance and ease of workability of Deccan Trap rocks render them the most preferred building material in all the architectonic heritage structures that document various cultural and ethnic habitations in the west central India. The Buddhist, Hindu and Jain temples of Ajanta, Ellora and Elephanta are the oldest in-situ basalt cave temples, dating back to second century. A contemporary iconic architectonic heritage 'The Gateway of India' personifies a majestic edifice built in buff coloured trachyte. In the present times, the
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