Geomorphology 175–176 (2012) 163–175 Contents lists available at SciVerse ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph Holocene environmental changes of the Godavari Delta, east coast of India, inferred from sediment core analyses and AMS 14C dating Kakani Nageswara Rao a,⁎, Yoshiki Saito b, K.Ch.V. Nagakumar a, G. Demudu a, N. Basavaiah c, A.S. Rajawat d, Fuyuki Tokanai e, Kazuhiro Kato e, Rei Nakashima b a Department of Geo-Engineering, Andhra University, Visakhapatnam 530 003, India Geological Survey of Japan, AIST, Central 7, Higashi 1-1-1, Tsukuba, 305–8567, Japan Indian Institute of Geomagnetism, Mumbai 410218, India d Geosciences Division, Space Applications Centre, Ahmedabad 380015, India e Department of Physics, Yamagata University, Yamagata, 990–8560, Japan b c a r t i c l e i n f o Article history: Received 23 January 2012 Received in revised form 10 May 2012 Accepted 7 July 2012 Available online 16 July 2012 Keywords: Asia Delta Strandplain Human impact Holocene Godavari a b s t r a c t The Godavari delta in India is a major wave dominated delta of a tropical monsoon-fed river with one of the largest sediment deliveries in the world. While several earlier studies revealed the nature of landforms and progradation style of the delta plain during the Holocene, the present study attempts to reconstruct the depositional environment of the Godavari delta through the analysis of core sediment and accelerator mass spectrometry (AMS) 14C dating from three locations. The sediment core obtained from a 27.06 m deep borehole at Vilasavilli (VV) supported by 13 14C dates revealed the complete succession of the Holocene deposits unconformably overlying Pleistocene sediments. Textural analysis indicates the lower upward-fining and upper upward-coarsening units in the Holocene succession. Total organic carbon (TOC)/total nitrogen (TN) ratios of > 20; high content of TOC around 1.5–2.5%; and black to very dark colored sediment throughout the muddy part of the Holocene succession indicated a predominance of terrigenous material. The VV core and two other cores (DRP and SDG) with 14 14C dates indicated the thickness of the Holocene sediments in the Godavari delta plain is in the order of ~ 20–50 m, unconformably resting on a seaward sloping Pleistocene basement. Sediment facies and sediment accumulation of the three cores show the evolution of the Godavari delta. A transgressive phase is recognized as an upward-fining succession in the VV core, 8.4–8.0 cal ky BP, followed by a low accumulation period, 8.0–6.3 cal ky BP including the Holocene maximum transgression in the Godavari delta. After 6.3 cal ky BP, areas of high accumulation rates have changed laterally between the central part (VV site) and southwestern part (DRP and SDG sites), may be controlled by the location of river-mouths. Further analysis coupled with 11 more 14C dates compiled from earlier works indicated that the strandplain of the Godavari delta prograded seaward in three stages, and that the rate of progradation accelerated during the past ~ 3 ky, particularly in the last millennium. However, pronounced shoreline erosion led to a net negative growth of the delta during the recent decades due to sediment retention by upstream dams. Although this study provided insights into the sedimentation patterns and rate of seaward progradation of the Godavari delta, further studies on three-dimensional volume analysis of the deltaic sediments are necessary to estimate the overall rates of past sediment discharge and the Holocene growth of the Godavari delta. © 2012 Elsevier B.V. All rights reserved. 1. Introduction River deltas are the repositories of sediment records containing signatures of paleo-geographic and paleo-environmental conditions and changes in coastal zones. Extensive studies using sediment cores undertaken recently on a number of deltas all over the world enables reconstruction of their Holocene history, climatic and sea-level ⁎ Corresponding author. Tel.: +91 9441019341. E-mail address: nrkakani@yahoo.com (K. Nageswara Rao). 0169-555X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2012.07.007 changes, and human impacts (e.g., Ganges-Brahmaputra: Goodbred and Kuehl, 2000, Indus: Clift et al., 2008, Mekong: Ta et al., 2005; Tamura et al., 2009, Mississippi: Gonzalez and Tornqvist, 2009, Po: Amorosi et al., 2008, Red: Tanabe et al., 2006, Rhine-Meuse: Hijma and Cohen, 2011, Yangtze: Hori et al., 2002a, and Yellow: Saito et al., 2000). However, such systematic studies from Indian deltas are lacking at present leaving a major gap in understanding the monsoon-driven tropical climate through the Holocene. The east coast of India is predominantly a depositional coast with many rivers building their deltas into the Bay of Bengal. Notable among 164 K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 them are the deltas of the Mahanadi, Godavari, Krishna, and Cauvery rivers respectively from north to south along the coast (Fig. 1). These are predominantly wave-dominated deltas. The Godavari River, which is ranked 49th in the world in terms of drainage basin area, is particularly important being ranked as high as 9th in terms of sediment discharge (Milliman and Syvitski, 1992); it forms a large delta characterized by a complex of cuspate beach ridges (Nageswara Rao et al., 2005). The Godavari and Krishna rivers, which are the second and third largest river systems in India after the Ganga (Ganges), have built their deltas adjacent to each other almost coalescing into one large delta complex in the central part of the east coast of India (Figs. 1 and 2). The subaerial part of these twin deltas appears as a contiguous plain covering about 12,700 km 2. However these two deltas are often studied separately by confining their lateral extents up to the lateral-most abandoned distributaries found on both sides of the present river courses (e.g., Sambasiva Rao and Vaidyanadhan, 1979; Rengamannar and Pradhan, 1991; Nageswara Rao et al., 2003 on Godavari delta, and Babu, 1975; Nageswara Rao and Vaidyanadhan, 1978; Nageswara Rao, 1985a on Krishna delta). Thus, out of the total 12,700 km 2 area of the Holocene Krishna–Godavari twin delta complex (K–G deltas), the Godavari delta component is approximately 5200 km2 and that of the Krishna is about 4800 km2. The remaining 2700 km 2 area is the inter-delta plain between the two deltas on either side of it (Nageswara Rao, 1985b). Initial geomorphological studies, based on interpretation of aerial photographs, revealed traces of several abandoned distributaries on both sides of the present river courses, and series of beach ridges up to 30–35 km inland in the Krishna delta (e.g., Babu, 1975; Nageswara Rao and Vaidyanadhan, 1978), the Godavari delta (e.g., Sambasiva Rao and Vaidyanadhan, 1979), Mahanadi delta (e.g., Sambasiva Rao et al., 1978), and the Cauvery delta (Meijerink, 1971). Considering the possible location of the mouths of the abandoned distributaries with respect to the orientation of different sets of beach ridges, a number of attempts were made to reconstruct the Holocene evolution of these deltas (Nageswara Rao and Sadakata, 1993). Based on landform mapping and about ten accelerator mass spectrometry (AMS) 14C dates, Nageswara Rao et al. (2003, 2005) brought out a detailed account of the morphology and evolution of the Godavari delta. The plain of the delta has been divided into two major units: the upper (landward) fluvial plain and the lower (seaward) strandplain (Nageswara Rao et al., 2003). The former is a gently rolling, river-built plain sloping towards the coast characterized by landforms such as abandoned river courses and natural levees, while the lower strandplain Fig. 1. Location of major river deltas along the east coast of India. K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 165 Fig. 2. Satellite image of the Godavari and Krishna delta region, showing the three borehole locations. The bathymetry contours traced from the hydrographic charts are overlaid on the image (yellow colored lines with numbers representing depths in meters). The drainage basins of both the Godavari and Krishna rivers are shown in the inset with their combined delta area enclosed in a red colored rectangle. (The satellite image is a mosaic of four separate scenes of Landsat 1 MSS false colour composites pertaining to Paths/Rows: 152/ 48; 152/49; 153/48 and 153/49, respectively, dated January 8, 1977; June 1, 1977; February 14, 1977 and February 26, 1973.) exhibits features such as beach ridges, mudflats, mangrove swamps, lagoons, and spits reflecting the marine influence (Figs. 2 and 3). The presence of several abandoned river courses adjacent to the active distributaries indicates that the distributaries switched their courses several times in the deltaic reaches and decanted into the sea at various locations. The number of sandy beach ridges identified in the strandplain represents the former shoreline positions, which were stranded inland as the delta shoreline prograded seaward. The innermost beach ridge that lies up to 35 km inland from the present shoreline (Fig. 3) was dated to be around 6 cal ky BP, from where the Godavari delta was surmised to have prograded in three stages during the past 6 ky with an accelerated rate, especially during the last 3 ky, probably due to deforestation for agriculture in the drainage basin that led to increased sediment supply into the sea (Nageswara Rao et al., 2003, 2005). The existing literature on the Godavari delta is thus essentially based on mapping of landforms as well as AMS 14C dating of fossil shells recovered from highly disturbed discrete samples collected through auger drilling into shallow subsurface sediments. However, lack of detailed studies based on the analysis of continuous core sediments in the Godavari delta, or for that matter any of the east coast deltas of India, left a gap in understanding the Holocene sediment record and environmental history of deltas that reflect tropical monsoon setting. The present study therefore is an attempt to understand the growth of the Godavari delta during the Holocene based on recovery and analysis of 27-m deep undisturbed core sediment and two other deeper cores. These cores consist of not only Holocene deltaic sediments, but also Pleistocene basal sediments in their lower parts. This paper is the first report showing the whole succession of Holocene deltaic sediments, and the rate of seaward progradation of the Godavari delta, supported by a good number of AMS 14C dates and sedimentological analysis. 2. Study area The Godavari River originates at Nasik on the eastern slopes of the Western Ghats (close to the west coast of India) and flows toward the southeast across varied geological formations of the Indian peninsula over a length of about 1465 km before it decants into the Bay of Bengal. Joined by a number of tributaries, the river drains an area of about 3.1 × 10 5 km 2. The Deccan Traps occupy about 48% of its area in the upper reaches; Archean granites, phyllites, quartzites, amphibolites and gneisses occupy about 39% in its middle reaches, and the Precambrian and Gondwana sedimentaries constitute about 11% of its area followed by the Quaternary formations accounting for about 2% (Ahmed et al., 2009). A semiarid climate prevails over the basin with an average temperature of 22 °C in January and 35 °C in April. The average annual rainfall in the river basin is about 1100 mm (Selvam, 2003). The Godavari River comes out of the khondalites 166 K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 Fig. 3. Progradation stages for the Godavari delta and borehole locations (modified from Nageswara Rao et al., 2003, 2005). Location of the Godavari drainage basin and its delta in India is shown in the inset. and charnockites of the Eastern Ghats on to the coastal plain near Rajahmundry, from where it built a large delta along with its neighbouring Krishna River into a pericratonic basin known as the Krishna–Godavari (KG) basin (Prabhakar and Zutshi, 1993; Manmohan et al., 2003), located in the central part of the eastern passive continental margin of India (Rao, 2001; Gupta, 2006), which was formed due to the downwarping of the eastern part of the Indian shield subsequent to the break-up of the Gondwanaland (Murthy et al., 1995). The Godavari delta appears as a monotonous plain with a gentle seaward slope from about 12 m above the present sea level near its apex at Rajahmundry over a length of about 75 km. The river splits into two major distributary channels, the Gautami and the Vasishta at about 7 km downstream of its apex (Figs. 2 and 3). Accordingly, the subaerial part of the delta has two lobes — the Gautami lobe constituting the northeastern part of the delta built by the Gautami and its branch, the Nilarevu; and the Vasishta lobe constituting the southwestern part of the delta built by the Vasishta and its branch, the Vainateyam (Fig. 3). The delta front coast is about 170 km long punctuated by four distributary mouths. Being a monsoon-driven river system, the Godavari experiences a highly variable water discharge regime with 98% of its annual discharge occurring in the six-month monsoon period between June and November. The average annual water discharge through the Godavari River was 86 km 3 during the 41-year period between 1968 and 2008 with a maximum discharge of 177 km 3 recorded in 1990 and a minimum of 35 km 3 in 1974 (Nageswara Rao et al., 2010a). The river exhibits similar seasonal variations in its suspended sediment discharge with almost 98% of its load delivered into the sea during a four-month period between July and October. In absolute terms, the Godavari River carried an annual sediment discharge of about 113 million tons during the 37-year period between 1970 and 2006 with a highest annual discharge of 332 million tons in 1990 and as low as 24 million tons in 1997 (Nageswara Rao et al., 2010a). The Godavari River decants into a wave-dominated and microtidal coastal environment with a spring tide range of 1.3 m and a neap tide range of 0.5 m. Wave directions and energy levels are seasonally variable in the region. Waves move toward the northeast during the southwest summer monsoon and pre-monsoon, while a general southwestward movement prevails during the northeast winter monsoon. Significant wave heights in the region, obtained from Geosat altimeter data for a one-year period from November 1986 to October 1987 (Sastry et al., 1991) and simulation model studies (Nageswara Rao et al., 2008), are about 2 m during the southwest monsoon, and about 1 m during the rest of the year. Under the influence of seasonally reversible monsoons, bi-directional surface circulation patterns prevail over the Bay of Bengal, with the surface currents moving northeastward at speeds of about 5 knots during the southwest summer monsoon, and relatively weaker southwestward currents during the northeast winter monsoon off the Godavari delta region (LaFond and LaFond, 1968). High-energy wave conditions occasionally prevail in the Bay during storms of exceptional intensity (e.g., cyclones), when wave heights reach much beyond their normal range (Subba Rao, 1964). The Godavari delta coast is also affected by 3 to 4 m high storm surges that reach several kilometres inland. The K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 tsunami on 26 December 2004 rose to about 2.5 m high and reached about 1 km inland in some parts close to the Vasishta distributary mouth in the region (Nageswara Rao et al., 2007). 3. Materials and methods One borehole was drilled at Vilasavilli (VV) Village to recover undisturbed core in a 5.8-cm inner diameter PVC tube inserted into a steel pipe. The site is located at about 12.8 km inland from the present shoreline on one of the beach ridges in the strandplain of the Godavari delta (Figs. 2 and 3, Table 1). The steel pipe was hammered using a 75 kg weight to push the pipe into the subsurface sediment. The sediment core, recovered by pulling the pipe up at 1-m intervals was sealed on both sides and brought to the laboratory for analysis. The total depth of penetration was 27.06 m below the ground level. The core recovery was poor up to 12.25 m except in the initial 2.50 m as the predominantly loose fine to medium sand was hard to penetrate as well as to recover because the material was dropped as the core was being pulled up. However, the washed out sample was collected at approximately 0.5-m intervals. From 12.25 up to the refusal at 27.06 m, the core recovery was almost 60–70%. The operation was terminated at 27.06 m where hard pebbly gravel material was encountered. In addition to this core, sediment samples were also collected from two more locations further seaward in the strandplain, where some local farmers were drilling the boreholes for groundwater — one at Daritippa (DRP) Village and the other at Saddugadapa (SDG) Village (Figs. 2, 3, Table 1). Sediment samples were collected approximately at every half metre interval during drilling operations at these two locations. The total depth of the borehole was 54 m at DRP site and 110 m at SDG site below the ground level. The sediment samples collected into the polythene bags were then carried to the laboratory. The VV core was vertically split into two halves in the laboratory. The core section was described and photographed. Fossil shells and plant materials were carefully collected into polythene bags. Then, one-half of the core has been sub-sampled at 5-cm intervals for further analysis, while the other half is archived. Similarly, the discrete sediment samples collected at ~ 50-cm intervals from the DRP and SDG sites were described and fossils shells were separated. Sediment samples from the VV core were analyzed for estimating sediment grain size and the weight ratio of total organic carbon to total nitrogen (TOC/TN). Grain size analysis was done for 61 samples Table 1 Location details of the boreholes in the Godavari delta. amsl: Above the present mean sea level. Drilling depth (m) Location name code Longitude (E) Latitude (N) Elevation (m, amsl) Vedangi VD +4.5 12.0 Panangipalli PP +4.0 14.5 Velangi VL +4.5 7.0 Uppalaguptam UG +2.5 14.0 Vilasavilli VV +3.0 27.1 Daritippa DRP +3.3 54.0 Pippallavari Thota Pattigondi PT 16°33′ 55.65″ 16°44′ 53.87″ 16°52′ 04.51″ 16°33′ 12.20″ 16°34′ 46.80″ 16°24′ 11.20″ 16°24′ 34.32″ 16°44′ 31.93″ 16°23′ 24.26″ 16°20′ 41.20″ +1.5 14.0 +1.2 13.0 +2.3 11.5 +1.5 110.0 PD Sankaraguptam SG Saddugadapa SDG 81°42′ 57.49″ 82°01′ 14.55″ 82°06′ 38.03″ 82°05′ 51.10″ 82°03′ 23.59″ 81°30′ 06.70″ 81°37′ 35.89″ 82°14′ 36.12″ 81°51′ 44.25″ 81°40′ 28.90″ 167 taken at 20-cm interval from the muddy sediment part of the core from 12.25 to 27.06 m depths. The sand content (>63 μm) was separated by sieving, whereas the silt and clay were separated using CILAS 1063 laser-granulometer. The relative percentages of the sand, silt and clay contents were computed. Total carbon (TC) and TN were measured for 31 sediment samples picked up at every 40-cm interval, using an elemental analyzer (make: Elementar Vario EL, Germany). The measurements were made twice and the average of the two was taken. Total inorganic carbon (TIC) was measured from another 20–30 mg of the material from the respective samples first by flushing it through the TIC reactor, digesting with 5% hydrochloric acid and then estimating TIC using the same elemental analyzer. TOC was computed by subtracting TIC from TC for each of the 31 samples from the VV core. Accelerator mass spectrometry (AMS) 14C dating was conducted by Beta Analytic Inc. for 10 shell and three plant samples from the VV core, and by Yamagata University for seven shell samples from the DRP core and seven shell samples from SDG core (Tokanai et al., 2011). In addition, the delta growth stages surmised by Nageswara Rao et al. (2003, 2005) based on geomorphic mapping and 14C dates of fossil shells from different auger drill holes from the Godavari delta have been used in this study to infer the rate of delta progradation especially in the central part of the delta. The 14C ages were calibrated according to CALIB v. 6.0 (Stuiver et al., 2011). For shell samples, the marine carbon component was assumed 100% and the ΔR factor was taken at 22 ± 37 years as an average of four data near the study area (Dutta et al., 2001). The obtained 14C dates are shown in Table 2. 4. Results Sedimentary facies, geochemical characteristics and 14C ages of the VV core (Figs. 4 and 5) together with the 14C dated DRP and SDG cores (Fig. 6) are described and used as the basis for reconstruction of the Holocene sedimentary evolution of the Godavari delta. 4.1. VV core 4.1.1. Sediment facies and 14C ages The 27.06-m long VV core is divided into two units: Holocene sediment (V2: 0–26.90 m) and Pleistocene basement (V1: 26.90–27.06 m) marked by an erosional boundary. V2 unit is composed of seven subunits from V2a to V2g in ascending order (Figs. 4 and 5). Each sedimentary unit is characterized by a combination of its lithology, color, sedimentary structures, textures, contact character, lithological succession, fossil components, grain size (shown as sand, silt and clay contents), and 14C dates. The characteristics of the sedimentary units are described below. 4.1.1.1. Unit V1 (late Pleistocene sediment) 26.90–27.06 m. The lowermost part of the VV core consists of semi-consolidated dark greenish gray silt with thin fine to very fine sand layers and molluscan shells (Fig. 5H). 14C age of shells from 27.03 m depth shows 44,973–43,008 cal BP, indicating the late Pleistocene period. This Pleistocene basement is unconformably overlain by the Holocene sediments (Unit V2) with an erosional and irregular boundary at 26.83–26.90 m (Fig. 5H). 4.1.1.2. Unit V2 (Holocene sediment): 0–26.90 m. Holocene sediments comprising the Unit V2 are further divided into seven subunits: V2a to V2g in ascending order. Subunit V2a (24.90–26.90 m): This subunit shows an upwardfining succession consisting of black to very dark gray clayey silt intercalated by thin sand layers and sand partings (Fig. 5G, H). A number of marine molluscan shells are found in this layer. The lower parts from 26.90 to 26.75 m and at ~ 26.38 m contain angular to subangular pebbles. Subangular to subrounded gravels with a maximum size of 65 × 58 × 30 mm are found from 25.95 to 26.05 m (Fig. 5G), with 168 Table 2 Results of the 14 C dating of shells and plant material from the borehole sediments in the Godavari delta. Sample name Panangipalli Velangi PP1 VL1 VL2 UG3 UG5 UG7 PT4 PT10 PD7 SG7 SG11 Uppalaguptam Pippallavari Thota Pattigondi Sankaraguptam Vilasavilli Daritippa Saddugadapa Core name VV DRP SDG Sample depth (m) 11.5 4.0–4.5 5.0–5.5 3.5–4.0 5.5–6.5 6.5–7.5 3.0–3.5 6.0–6.5 9.5–10.5 3.5–4.0 6.5–7.0 5.6 13.95 Elevation (m, amsl) −7.5 0.0 to −0.5 to −1.0 to −3.0 to −4.0 to −1.5 to −4.5 to −8.3 to −1.2 to −4.2 to −2.6 −10.95 +0.5 −1.0 −1.5 −4.0 −5.0 −2.0 −5.0 −9.3 −1.7 −4.7 Materials Conventional 14 C age years BP δ13C (permil) Cal BP (1 sigma) Probability Cal BP (2 sigma) Probability Lab code Reference Shell Shell Shell Shell Shell Shell Shell Shell Shell Shell Shell 6010 ± 40 4620 ± 40 5110 ± 41 2300 ± 30 2430 ± 40 2380 ± 40 1390 ± 40 1460 ± 40 1460 ± 40 1190 ± 40 1240 ± 50 −2.0 0.3 −0.4 −0.4 −0.8 −1.8 0.6 −2.4 −0.6 −1.2 6451–6338 4875–4771 5542–5394 1935–1838 2106–1982 2042–1916 968-863 1033–932 1033–932 748–665 815–691 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 6505–6289 4948–4682 5560–5320 1986–1795 2162–1908 2106–1868 1022–791 1099–896 1099–896 813–639 886–665 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 Beta–147667 Beta-186562 Beta-186561 Beta-144181 Beta-167286 Beta-144180 Beta-155919 Beta-146143 Beta-156335 Beta-165826 Beta-165827 Nageswara Rao Nageswara Rao Nageswara Rao Nageswara Rao Nageswara Rao Nageswara Rao Nageswara Rao Nageswara Rao Nageswara Rao Nageswara Rao Nageswara Rao Shell Plant material 2890 ± 40 2980 ± 40 1.4 −25.6 2715–2580 3218–3136 1.000 0.643 2736–2481 3268–3059 1.000 0.905 Beta-292942 Beta-291036 This study This study Stage II Stage II 0.198 0.125 0.034 1.000 3052–3021 3323–3289 3016–3005 3378–3206 0.034 0.049 0.012 0.977 Beta-291037 This study Stage II 3183–3166 3489–3304 6211–5991 0.023 1.000 0.979 Beta-301745 Beta-291039 This study This study Stage II Stage II 6265–6247 0.021 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 0.984 0.016 1.000 1.000 1.000 1.000 Beta-307148 Beta-301746 Beta-304576 Beta-304577 Beta-301747 Beta-301748 Beta-304579 Beta-291042 Beta-285522 This This This This This This This This This study study study study study study study study study Stage Stage Stage Stage Stage Stage Stage Stage Stage II II II II II II II II II 1.000 1.000 1.000 1.000 1.000 1.000 1.000 Beta-285523 Beta-285524 Beta-285525 Beta-285526 Beta-285527 Beta-285528 YU-85 YU-86 YU-88 YU-89 YU-90 YU-92 YU-94 This This This This This This This This This This This This This study study study study study study study study study study study study study Stage Stage Stage Stage Stage Stage Stage Stage Stage Stage Stage Stage Stage II II II II II II III III III III III III III 16.22 −13.22 Charred material 3070 ± 40 −24.0 3133–3102 3096–3078 3238–3231 3353–3255 20.56 22.14 −17.56 −19.14 Shell Charred material 3530 ± 30 5320 ± 40 −2.0 −29.1 3433–3351 6082–6009 1.000 0.532 6159–6103 6182–6171 6329–6246 6370–6278 8049–7944 8332–8222 8344–8235 8463–8366 8177–8056 44503–43488 5453–5253 0.384 0.084 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 4424–4291 4389–4254 7638–7556 6451–6338 1.000 1.000 1.000 1.000 6376–6205 6428–6235 8127–7922 8365–8174 8372–8179 8525–8335 8250–8005 44973–43008 5550–5108 5102–5078 4499–4231 4427–4159 7675–7502 6505–6289 418–327 4851–4782 8258–8156 4850–4777 7331–7246 44837–44268 46049–45361 1.000 1.000 1.000 1.000 1.000 1.000 1.000 451–296 4907–4691 8311–8099 4900–4685 7394–7215 45208–43990 46435–45038 22.58 23.83 25.07 25.79 25.83 26.00 26.78 27.03 24.4 −19.58 −20.83 −22.07 −22.79 −22.83 −23.00 −23.78 −24.03 −21.1 Shell Shell Shell Shell Shell Shell Shell Shell Shell 5890 ± 30 5930 ± 40 7570 ± 40 7830 ± 40 7840 ± 40 7980 ± 40 7690 ± 40 40500 ± 610 5010 ± 80 −1.9 0.4 −0.8 0.2 −2.0 −1.3 −1.1 −2.4 −0.2 26.5 30.0 32.0 35.0 42.6 48.8 12.2 28.35 32.6 37.5 41.1 50.3 103.0 −23.2 −26.7 −28.7 −31.7 −39.3 −45.5 −10.7 −26.85 −31.1 −36.0 −39.6 −48.8 −101.5 Shell Shell Shell Shell Shell Shell Shell Shell Shell Shell Shell Shell Shell 4280 ± 40 4240 ± 40 7140 ± 40 6010 ± 40 >43500 >43500 755 ± 25 4615 ± 30 7750 ± 30 4610 ± 30 6785 ± 30 41170 ± 340 42960 ± 400 0.4 −0.4 −0.9 0.1 −2.9 −1.5 −2.08 ± 0.41 0.74 ± 0.75 −0.87 ± 0.36 −4.26 ± 0.50 0.10 ± 0.64 −6.76 ± 0.29 −1.64 ± 0.37 Delta progradation stage et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. (2010b) (2005) (2005) (2003) (2003) (2003) (2003) (2003) (2003) (2003) (2003) Stage Stage Stage Stage Stage Stage Stage Stage Stage Stage Stage I I I II II II II II II III III K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 Location name K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 169 Fig. 4. Borehole logs of the VV core and the result of grain-size composition, TOC (content of total organic carbon), the TOC/TN (total nitrogen) ratio, and the depth-age curve. Core location is shown in Figs. 2 and 3. oyster shells attached to them. Five 14C dates from this subunit ranged from 8.0 to 8.4 cal ky BP. The average accumulation rates are about 1.89 mm y −1 between 25.07 and 25.83 m and 16.6 mm y −1 between 25.07 and 26.78 m. Subunit V2b (20.85–24.90 m): This subunit is characterized by very dark gray laminated silty clay with 2–4 mm thick light yellowish brown to light brownish gray layers (Fig. 5E, F). Marine molluscan shells and shell fragments, and calcareous concretions are found. Banded feature is well developed around 20.85–21.30 m and 24.20–24.50 m. Three 14C dates from the middle part, which is sandwiched by the banded parts, ranged from 6.0 to 6.3 cal ky BP. The average accumulation rates are about 0.58 mm y −1 between 20.56 and 22.14 m; 7.39 mm y −1 between 22.14 and 23.84 m; and 0.73 mm y −1 between 23.84 and 25.07 m. Subunit V2c (12.25–20.85 m): This subunit is characterized by an upward-coarsening and thickening succession consisting of very dark gray silty clay to alternations of very dark gray to black coarse silt and silty clay (Fig. 5A, D). Silt layers show thickening upward from a few mm to ~ 10 cm, and are micaceous and laminated. Plant fragments, marine shells and shell fragments and calcareous concretions can be recognized. Three 14C dates obtained from this interval are within 3.1 to 3.4 cal ky BP. The average accumulation rates are about 28.4 mm y −1 between 13.95 and 20.56 m. Subunit V2d (8.0–12.25 m): Based on washed samples recovered from this interval using a valved sampler (locally known as ‘sand-valve’), sediment facies estimated in this subunit is an upward-coarsening succession from silt to fine sand. Marine molluscan shells are found through this interval. Silty parts also contain rich mica and plant fragments. Subunit V2e (5.0–8.0 m): Based on washed samples recovered using a valved sampler, sediment facies in this subunit is estimated to be gray medium to coarse sands with pebbly gravels and marine shells such as Placuna placenta (Linnaeus). One 14C date from this interval shows 2.6 cal ky BP. The average accumulation rate of subunits V2d and V2e is about 15 mm y − 1 between 5.6 and 13.95 m. Subunit V2f (1.0–5.0 m): Based on the recovered cores from 1.0 to 2.5 m depth and washed samples from 2.5 to 5.0 m depth, the sediment facies in this subunit is found to be dark brown medium sands, intercalated with very dark brown medium sand bands and fine sand with heavy minerals. Plant fragments and iron-stained concretions are also found. Subunit V2g (0–1.0 m): This interval consists of dark reddish brown mottled medium sands. 4.1.2. TOC and TOC/TN ratio Thirty-one samples from the muddy sediment part (12.25–27.06 m) of the VV core have been analyzed for TOC and TN contents. The results indicated that the TOC ranged between 0.6% and 2.4%. Particularly high TOC values (~2%) are recognized from 19 to 25 m depth. The TOC/TN ratio of the samples is widely ranged from 17 to 46 with most of the 170 K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 samples showing a ratio of more than 20 almost throughout the entire section (Fig. 4), which indicates that the main source of organic materials is from terrestrial plants (Lamb et al., 2006). 5. Discussion 4.1.3. Interpretation of the VV core The 14C age of 44973–43008 cal BP of the shell found at 27.03 m depth in Unit V1 (26.90–27.06 m) indicates that an erosional surface at 26.90 m is a bounding surface and an unconformity between the Pleistocene basement (Unit V1) and Holocene sediments (Unit V2). As the Holocene marine sediments overlying the erosional surface show an upward-fining succession with basal gravels (Subunit V2a), the erosional surface is interpreted as a wave ravinement surface (Allen and Posamentier, 1993) formed during a rise of sea level after the last glacial maximum. The Holocene sediment (Unit V2) is divided into two parts: an upward-fining succession in the lower part (Subunit V2a) and an overlying upward-coarsening succession (Subunits V2b through to V2g). The age-depth plot (Fig. 4) shows that the sediment accumulation rate was high during ~8.4–8.0 cal ky BP (Subunit V2a), 6.3–6.0 cal ky BP (middle part of Subunit V2b), and 3.4–2.6 cal ky BP (Subunits V2c through to V2e), and relatively low during 8.0–6.3 cal ky BP and 6.0–3.4 cal ky BP (lower and upper parts of Subunit V2b, respectively). While the upward-fining succession (in Subunit V2a) is interpreted as transgressive sediments, the maximum flooding surface (MFS) might correspond to the lower part of Subunit V2b with a low accumulation rate. The study on the Godavari delta based on the analysis of a sediment core showing the sedimentary structures and somewhat fine resolution dating has brought out three significant inferences. For the first time, the thickness of Holocene sediments in the delta could be estimated. The 14C age, 44973–43008 cal BP, of the shell sample recovered from 27.03 m depth below the ground level besides the occurrence of hard pebbly gravel material from 26.90 m in the VV core suggested that the Holocene sediments are approximately 27 m thick at this location which is about 12.78 km inland from the present shoreline. Considering that the VV core site is at 3.0 m above the mean sea level, the depth of the base of the Holocene sediments at this location is ~ 24 m below the present sea level. Further seaward the thickness of the Holocene sediments increased as can be inferred from the DRP and SDG sites. These are around 35.0–42.6 m at the DRP site, which is at an elevation of about 3.3 m above the mean sea level, at about 6 km inland from the shoreline, and around 41.1–50.3 m at the SDG site (+ 1.5 m in elevation), which is about 1.5 km inland from the present shoreline. The depth of the basement of the Holocene marine sediments increased seaward as a consequence of the nature of the paleo-topography during the lowstand of sea level of the last glacial maximum and the formation of a ravinement surface due to subsequent marine transgression. 4.2. DRP core 5.2. Sediment facies of Holocene deltaic sediments From the DRP core, although it was not possible to infer the sediment facies from the disturbed sediment recovered from the washed out material, the overall sediment column reconstructed from the discrete samples collected at ~0.5 m intervals showed the predominant clay content below the upper 10 m layer of fine to medium sand mixed with minor quantities of clay (Fig. 6). Shell assemblages indicate marine environments at 24.4 m (Costanuculana sp., Semelangulus sp.), 26.5 m (Costanuculana sp., Arcidae gen. et sp. indet., Anisocorbula sp., Glycydonta marica (Linnaeus), Veneridae gen. et sp. indet.), 30.0 m (Costanuculana sp., Gadila sp., Arcidae gen. et sp. indet., Cadella sp., corals, sea urchin), 32.0 m (Veneridae gen. et sp. indet., Scapharca sp.), 35.0 m (Paradentalium sp., Arcidae gen. et sp. indet., Tellinidae gen. et sp. indet., Cardiidae gen. et sp. indet.), and 36.5 m (Paradentalium sp.), brackish-water and marine environments at 42.6 m (Cadella sp., Ostreidae gen. et sp. indet.), and brackish-water environment at 48.8 m depth (Ostreidae gen. et sp. indet.). As 14C ages of brackish-water shells from 42.6 m and 48.8 m show >43,500 yBP (Table 2) and those of marine shells from 24.4 to 35.0 m indicated the Holocene age, the boundary between the Holocene and pre-Holocene (Pleistocene) is conjectured to be within the depth interval from 35.0 to 42.6 m. The second major inference that can be drawn from this study is the predominance of muddy sediment in the Holocene deposits of the Godavari delta strandplain. The fact that out of the 27 m thick Holocene sediment at the VV core, about 15 m column below the upper 10–11 m sandy layer is essentially composed of silt and clay. The situation in the DRP and SDG core sites is also more or less similar as the silt and clay predominate the Holocene deposits there too. The muddy interval of the VV core is divided into three parts: subunits V2c, V2b and V2a, and is characterized by black to very dark gray color, high TOC (1.5–2.5%), high TOC/TN (> ~ 20), and very high accumulation rates of ~28 mm y−1 in Subunit V2c; ~7 mm y −1 in the middle part of Subunit V2b; and ~17 mm y−1 in Subunit V2a. These characteristics indicate strong influence of terrigenous sediment supply to coastal and shelfal areas offshore during the Holocene, which is supported by the fact that more than 67% of the sediment load through the Godavari River is silt and clay (Biksham and Subramanian, 1988). A coarsening-upward succession from muddy sediments (Subunits V2b–V2c) to sandy sediments (subunits V2d through to V2g) constitutes a prograding deltaic succession in the strandplain of the Godavari delta. Delta front/shoreface is characterized by sand-dominated sediment facies in wave-dominated or wave-influenced deltas in general, followed by the transition zone to muddy prodeltas downward (Bhattacharya, 2011). Muddy deltaic sediments of the VV core is clearly divided into two parts by sediment facies and accumulation rates. The Subunit V2c consists of alternations of clay and laminated silt with a high accumulation rate of ~28 mm y−1, which is more than that of the overlying sandy facies at ~15 mm y−1. These high accumulation rates imply the progradation of a delta front slope while the low accumulation rates correspond to that of a bottomset, as is the case in the other Holocene delta systems (e.g., Kuehl et al., 1986; Michels et al., 1998; Hori et al., 2002b). Therefore, Subunit V2b is regarded as a bottomset, and the subunits V2c through to V2e as a delta front slope. The delta front slope consists of the upper sandy units V2d–V2e and the lower muddy unit V2c. As both the muddy subunits V2b and V2c are regarded as “pro-delta” (following Bhattacharya, 2011), then the boundaries between the delta front and pro-delta; and the delta front and bottomset (morphology: clinoform) should be considered different 4.3. SDG core The SDG core sediment, which was sampled at ~ 0.5 m intervals in a highly disturbed condition also showed predominant clay material throughout the upper 47 m column right from the surface with occasional sand layers in between (Fig. 6). Shell assemblages indicate marine environments at 12.2 m (Placuna placenta (Linnaeus)), 28.4 m (Trisidos sp., Placamen sp., Dentalium sp., Gadila sp., Costanuculana sp., Nassarius sp.), 32.6 m (Gadila sp., Turbonilla sp.), 37.5 m (Gadila sp., Paphia undulata (Born)) and 41.1 m (Paradentalium sp., Dentalium sp., Saccella sp., Costanuculana sp.), whereas brackish-water environment is indicated at 60.9 m (Cerithidea cingulata (Gmelin)). As 14C ages of shells at 50.3 m and 103 m show more than 40000 cal BP (Table 2), and those of marine shells from 12.2–41.1 m indicate the Holocene period, the boundary between the Holocene and Pleistocene is surmised to be within the depth interval from 41.1 to 50.3 m. 5.1. Basal topography of Holocene sediments K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 171 Fig. 5. Photos of sedimentary facies of the VV core. Depth range of each core section is in meters. PB: pebbles; BS: basement. Scale bar is 5-cm long for photos A to G. A: Subunit V2c (12.31–12.56 m), B: ditto (16.60–16.85 m), C: ditto (17.70–17.95 m), D: ditto (18.25–18.50 m), very dark gray silty clay to alternations of very dark gray to black coarse silt and silty clay. Silt layers show thickening upward from a few mm to ~10 cm (from D to A), and are micaceous and laminated. E: Subunit V2b (21.00–21.25 m), very dark gray laminated silty clay with 2–4 mm thick light brownish gray layers, F: Subunit V2b (22.90–23.15 m), dark gray laminated silty clay with 2–4 mm thick light yellowish brown gray layers, G: Subunit V2a (25.79–26.04 m), black to very dark gray clayey silt intercalated by thin sand layers and sand partings. Subangular to subrounded gravels (PB) with a maximum size of 65 × 58 × 30 mm are found, which is attached by oyster shells with 14C age of 8335–8525 cal BP, H: Unit V1 to Subunit V2a (26.73–27.03 m), 26.90 m. semi-consolidated dark greenish gray silt with thin fine to very fine sand layers in the lower part (Unit V1) and overlying black to very dark gray clayey silt intercalated by thin sand layers and sand partings (Subunit V2a), bounded by an erosional and irregular boundary at 26.83–26.90 m. as suggested by Hori and Saito (2007a). Therefore, the lower part of the delta front slope which is characterized by alternating silt and clay layers, besides indicating high accumulation rates (the middle part of V2b) should be considered as muddy delta front facies, not pro-delta facies. 5.3. Holocene evolution of the Godavari delta From sediment facies, 14C dating and geochemical analysis of the VV core and other two cores (DRP and SDG), the Holocene evolution of the Godavari delta is surmised. A transgressive phase of the Godavari delta region in the early Holocene is recognized as an upward-fining and upward-deepening succession in the VV core, 8.4–8.0 cal ky BP, resulted from the early Holocene sea-level rise from 9.0 cal ky BP to 8.0 cal ky BP (e.g., Hori and Saito, 2007b; Tamura et al., 2009; Hijma and Cohen, 2011). This rapid marine inundation of the delta region was followed by a low accumulation period in the VV core (0.58 mm y − 1 in the lower part of subunit V2b), 8.0–6.3 cal ky BP, including the Holocene maximum transgression in the Godavari delta. This is supported by relatively low TOC/TN ratios in the VV core indicating more of marine influence, or less of fluvial contributions in this period. High sediment accumulation is found in the VV core, during 6.3–6.0 cal ky BP (7.4 mm y − 1 in the middle part of subunit V2b) and during 3.4–2.6 cal ky BP (19.0 mm y − 1, covering subunits V2c to V2e). While a low accumulation rate of 0.73 mm y − 1 prevailed during 6.0–3.4 cal ky BP in the central part of the delta (VV site), about 10-m accumulation occurred at DRP site, 6.4–4.3 cal ky BP, and SDG site, 7.3–4.8 cal ky BP, in the western part indicating lateral shift in the depocentre in the delta. 5.4. Strandplains, delta progradation and human impact Based on mapping of abandoned distributaries and beach ridges, coupled with 14C ages of shell samples collected from several boreholes drilled using spiral auger in addition to a few more dates available from the published literature, Nageswara Rao et al. (2003, 2005) surmised that the landward limit of the strandplain in the Godavari delta is represented by the innermost beach ridge, which is located up to 30–35 km inland from the shoreline and that the delta has prograded seaward from there in three major stages (Figs. 3 and 7). Nageswara Rao et al. (2003, 2005) further inferred that the delta progradation accelerated during Stages II and III. The strandplain prograded for about 3–8 km seaward in Stage I (6.0 to 3.6 cal ky BP), and about 21 km in Stage II (3.6 to 1.0 cal ky BP), whereas 0–14 km in Stage III during the last millennium (Nageswara Rao et al., 2003). A number of studies made elsewhere documented rapid progradation of deltas from the increased sediment supply during the historical times under anthropogenic impacts. For example, the Po delta in Italy advanced by 30 km as a cuspate projection into the Adriatic Sea particularly since the 16th century when deforestation and agriculture activities were intensified in its catchment (Ciabatti, 1967; Cencini, 1998). The growth of the two prominent cuspate deltas of the Arno and Ambrone rivers on the west coast of Italy began during the Roman period and that the rate of delta progradation could be correlated with historically recorded changes in deforestation and farming activities in the river catchments (Pranzini, 2001). A similar type of progradation was also reported for the Tiber delta on the central west coast of Italy (Bellotti et al., 1994). The Ebro delta in Spain also showed a progradation rate of 30 m y−1 between 13th and 15th centuries AD and its cuspate extension began in the 15th century as a result of intense deforestation in the drainage 172 K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 Fig. 6. Borehole logs of the DRP and SDG cores. Core locations in the Godavari delta are shown in Figs. 2 and 3. basin (Guillen and Palanques, 1997). The sudden increase in sediment accumulation over the past 600–1000 years in the Mekong delta, which is evident from a thick upper part of the sedimentary succession, composed of floodplain and natural levee sediments was conjectured to reflect an increase in the sediment yield in the upper and middle reaches of the river catchment (Tamura et al., 2009), similar to that revealed in the sedimentation records of many other Asian deltas (Saito et al., 2001; Yi et al., 2003; Li et al., 2006; Tanabe et al., 2006; Wang et al., 2011). In a recent study, based on a borehole data in the Godavari delta at Panangipalli (PP), Nageswara Rao et al. (2010b) arrived at similar inference on the accelerated growth of the delta during the past 2 ky. The PP site is located on the northern side of the Gautami distributary close to the innermost beach ridge (Fig. 3). The borehole drilled using a spiral auger up to a depth of 14 m below the ground level revealed an upper 9 m thick fluvial deposit with predominant sand-silt content and a lower 5-m thick predominant silt-clay content with molluscan shells of intertidal habitat representing a lagoonal environment (Nageswara Rao et al., 2010b). Further, based on the 14C dating of an Anadara shell from 11.5 m depth in the borehole which indicated an age of 6505–6289 cal BP (recalibrated from Nageswara Rao et al., 2010b) and the abundant presence of Early Historic pottery from 3.5 to 9.0 m depth in the borehole (see PP bore log in Fig. 8), Nageswara Rao et al. (2010b) inferred that the site could be an Early Historic human habitation and that the sedimentation rate was greater during the past ~2.0 ky perhaps due to deforestation and agriculture activities in the river catchment. Taking the three-stage growth model envisaged by Nageswara Rao et al. (2003, 2005) and trying to fit the present data from the VV core into that model, we made an attempt here to estimate the variations in the seaward advance of the Godavari delta during the past 6 ky. We calculated the area of the strandplain within each of its three growth stages. Considering the duration of the respective stages, the rate of seaward progradation of the delta has been estimated (Figs. 7 and 9). The area of Stage I, accreted during the 2400 years from 6.0 to 3.6 cal ky BP, was about 677 km2 at a rate of 0.28 km2 y−1. This was followed by an increase in an area of about 1455 km 2 during the 2600-year long Fig. 7. Simplified progradational stages of the Godavari delta and calculated areas of each stage. K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 173 Fig. 8. Borehole logs showing the major sediment layers and the stratigraphic positions of the 14C dates (compiled from Nageswara Rao et al., 2005, 2010b). Borehole locations are shown in Fig. 3. stage II between 3.6 cal ky BP and 1.0 cal ky BP at a rate of 0.56 km2 y −1. The delta growth rate had further increased to about 1.01 km2 y −1, since the area built was about 1012 km2 in Stage III during the past 1.0 ky. On the millennial scale during the past 6 ky, therefore, the rate of seaward progradation of the Godavari delta increased from 0.28 km 2 y−1 during the initial 2400 years to double that rate at 0.56 km2 y−1 during the next 2600 years and further increased to 1.01 km2 y−1 during the past 1000 years. This could be due to extensive deforestation and consequent soil erosion in the catchment which led to increased sediment discharge into the delta (Nageswara Rao et al., 2005). The VV core site is in Stage II of the cuspate strandplain (Figs. 2, 3 and 7). The sediment accumulation at the site was high approximately during 3.4 to 2.6 cal ky BP at an average rate of ~19 mm y−1 in subunits V2c through to V2e (Fig. 4), indicating a rapid progradation of the delta front slope and consequent rapid shoreline migration seaward, which is also indicated by a series of cuspate beach ridges in the strandplain. Taking into consideration the 14C ages from the UG site in the cuspate strandplain (recalibrated from Nageswara Rao et al., 2003), and based on the orientation of the beach ridges, the progradation of the strandplain between the VV and UG core sites over a horizontal distance of about 4 km is assumed as shown in stippled pattern in Fig. 7. Considering the 14C ages of the sediment that represent the delta front successions in the upper parts of both the VV and UG cores (the latter is recalibrated from Nageswara Rao et al., 2003), the approximate age of the shoreline at the VV core site is 2608 cal BP, and that of the UG site is 1890 cal BP (average of the ages, at the 2-sigma range, of the uppermost dated samples from both the cores shown in Table 2). Therefore, the duration of the delta growth between the two locations is ~718 years during which the area accreted was about 260 km2 (stippled area in Fig. 7) at a rate of about 0.36 km2 y−1. Considering that the rate of seaward progradation of the strandplain accelerated from 0.28 km2 y−1 during Stage I (6.0–3.6 cal ky BP), to 0.56 km2 y−1 during Stage II (3.6–1.0 cal ky BP), the rate of 0.36 km2 y−1 between the VV and UG core sites suggests that the strandplain progradation might have progressively accelerated within Stage II from its initial to later parts and subsequently into Stage III (1.01 km2 y−1 during the past 1.0 ky). However, on the decadal scale the rate of delta growth has remarkably changed. Based on an analysis of multi-date maps and satellite images, Nageswara Rao et al. (2010a) estimated that a net area of 10.5 km 2 was accreted in the Godavari delta between 1930 and 1965 from where the shoreline erosion became dominant over deposition during the recent decades. As a result, the Godavari delta lost an area of about 20.1 km 2 during 1965 and 1990 and another 17.5 km 2 during the next 18 years between 1990 and 2008 (Nageswara Rao et al., 2010a). From these data, we also computed the rate of change in the Godavari delta on the decadal scale. During the 35-year period between 1930 and 1965 the rate of delta growth was 0.3 km 2 y − 1. But during the subsequent 25 years between 1965 and 1990 the net loss of area by predominant erosion was at a rate of 0.80 km 2 y − 1, which increased to 0.97 km 2 y − 1 during the next Fig. 9. Progradation rates of the Godavari delta on millennial and decadal scales. Decadal trends in the sediment discharges of the Godavari River into the sea during 1970– 2006 (upper right corner) after Nageswara Rao et al. (2010a). 174 K. Nageswara Rao et al. / Geomorphology 175–176 (2012) 163–175 18-year period between 1990 and 2008. The loss of land along the Godavari delta front coast is correlated to the three-fold reduction in the sediment delivery into the sea (Fig. 9) during a 37-year period between 1970 and 2006 (Nageswara Rao et al., 2010a). The study revealed that human activities are mainly responsible for the accelerated growth of the Godavari delta on the millennial scale, and for the increased erosion and negative delta growth on the decadal scale. While large scale deforestation for agriculture in the river catchment was considered responsible for the accelerated progradation of the Godavari delta during the past two to three millennia (Nageswara Rao et al., 2003, 2005), sediment retention at the many dams in the river catchment built during the past four decades led to large scale coastal erosion and loss of land in the delta (Nageswara Rao et al., 2010a). Similar changes of delta growth or sediment discharge for the last 1–3 ky has been reported from large rivers and deltas in East and Southeast Asia (Wang et al., 2011). Total sediment discharges of five large rivers (Mekong, Pearl, Red, Yangtze and Yellow) was ~ 600 Mt y − 1 in their pristine condition before 2 cal ky BP; which had increased more than three-fold to ~2200 Mt y−1 around 1950–1960; but suddenly decreased during the last 50 years to below their pristine levels (Wang et al., 2011). Negative growth of deltas due to sediment deprival by dam construction has been reported from a number of river deltas all over the world. For instance, the case studies along the Ebro, Mississippi and Rhone deltas (Day et al., 1995); Nile delta (Stanley and Warne, 1998), Volga delta (White et al., 2002), Yellow River delta (Chu et al., 2006), and Yangtze delta (Yang et al., 2011) revealed that pronounced coastal erosion leading to the negative growth of the deltas was due to the impact of dam construction which affected the sediment influx. The current situation of the Godavari delta is a complete reversal from what it experienced in its pristine conditions. Apparently, the Godavari delta has entered into an irreversible destructive phase. 6. Conclusion The study involving analysis of subsurface sediments from a 27.06 m long core and two more deeper cores coupled with a considerable number of AMS 14C dates has revealed that the thickness of the Holocene sediments in the Godavari delta plain is in the order of ~ 20–50 m resting on a seaward sloping Pleistocene basement unconformably with an erosional surface, which might be interpreted as a ravinement surface. The predominantly muddy sediment appears to be mainly terrigenous as inferred from its characteristics such as its black to very dark color; high TOC values of 1.5–2.5% and high TOC/TN ratios of > 20. The rate seaward progradation of the delta plain appears to have increased during the past ca. three millennia and further accelerated during the last millennium. The present study provided an initial insight into the delta sedimentation pattern. However, further studies on three-dimensional volume analysis of the deltaic sediments and more detailed delta evolution model are necessary to estimate the overall rates of past sediment discharge and the Holocene growth of the Godavari delta to resolve the possible recycling of sediment derived from coastal erosion within the delta system in addition to fresh inputs through the river. Acknowledgements The work is a part of the PRACRITI project funded by the Department of Space, Government of India. We are grateful to Dr. J.S. Parihar, Deputy Director, EPSA, Dr. Sushma Panigrahi, PRACRITI Project Director, and Dr. Ajai, Group Director, MPSG, Space Applications Centre, Ahmedabad, India, for their constant encouragement and support. Our thanks are also due to Prof. Noboru Sadakata and Prof. Sumiko Kubo for their support. This work was also partly supported by the Fukutake Science and Culture Foundation, the Tokyo Geographical Society, and the Sumitomo Foundation, Japan. 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