- Email: [email protected]
Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in Cretaceous–Paleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60–81
Cretaceous Research xxx (2016) 1e3
Contents lists available at ScienceDirect
Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes
Discussion
Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60e81 Sanjay K. Mukhopadhyay a, Sucharita Pal b, J.P. Shrivastava b, * a b
Formerly Geological Survey of India, Natural Energy Resources, Salt Lake, Kolkata 700091, India Department of Geology, University of Delhi, Delhi 110007, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 October 2016 Accepted in revised form 14 December 2016 Available online xxx
The paper published by Sial et al. (2016) contains geochemical information which does not fit into the scheme of the existing planktonic foraminiferal succession across the K/Pg boundary in the Um Sohryngkew River section, Meghalaya India, worked out by either Mukhopadhyay (2008) or Pandey (1981, 1990). The K/Pg boundary reported by Sial et al. (2016) is not compatible with any of these two. In this perspective some of the controversies are highlighted. © 2016 Elsevier Ltd. All rights reserved.
The above paper presents an informative account of the K/Pg sections from some well studied locations of the world along with additional geochemical input. The prerequisite of additional studies on a well established K/Pg boundary segment is the correct identification of the K/Pg boundary, but the geologic information on the biostratigraphically well constrained K/Pg interval of the Um Sohryngkew River section, Meghalaya India provided by Sial et al. (2016) is difficult to accept because they have faltered on the correct identification of the boundary segment. The boundary section exposed on the west bank of the Um Sohryngkew River represents the only of its kind in Indian subcontinent and one of the few occurrences in the tropic-subtropic belt outside the Mediterranean and Atlantic Coast. A more careful approach would have added valuable geochemical information to this K/Pg boundary segment. 1. The authors cited Mukhopadhyay (2008) to state that the Um Sohryngkew River Section, Meghalaya contains the K/Pg boundary in a biostratigraphically continuous section, but contrary to his finding, the authors considered that the K/Pg boundary occurs at the Mahadeo/Langpar contact (Table 3, lines 570e579, Sial et al., 2016) without providing micropaleontological or biostratigraphic evidence. Mukhopadhyay (2012a, Fig. 2A; 2012b, Fig, 2I) showed that the Mahadeo/Langpar
* Corresponding author. E-mail address: [email protected] (J.P. Shrivastava).
contact is soil covered on the west bank section of the Um Sohryngkew River, in which section the planktonic foraminifera based K/Pg boundary is developed. Based on the occurrences of Globotruncana sp. towards the top of the Mahadeo Formation and at the lower part of the overlying Langpar Formation, the concealed contact between the formations was assigned late Maastrichtian, and the planktonic foraminiferal biostratigraphy carried out by Mukhopadhyay (2008) indicated that the K/Pg boundary between the Plummerita hantkeninoides Zone (¼CF1 Zone) and the Guembelitria cretacea Zone (¼ P0 Zone) occurs within the Langpar Formation at about 28 m above the exposed base of the Langpar Formation. Therefore, the coinciding of the Mahadeo/Langpar contact with the K/Pg boundary as claimed by the authors is untenable until substantiated with biostratigraphic and planktonic foraminiferal evidence. 2. Along the Um Sohryngkew River, the thick bedded arenaceous Mahadeo Formation develops escarpments and the thin bedded argillocalcareous Langpar Formation occupies adjoining lower ground of the valley wall. This geomorphic difference is well represented around the MahadeoeLangpar contact; moreover, along the river bank, the Langpar is covered with thicker undergrowth than that of the Mahadeo. But the field photograph by the authors (Fig. 5a, Sial et al., 2016) shows continuity of bare exposures of bedded litho-unit ‘across the Mahadeo/Langpar contact’. Such exposures of the K/Pg transition section on the bank of the Um Sohryngkew River is very interesting since we
http://dx.doi.org/10.1016/j.cretres.2016.12.006 0195-6671/© 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mukhopadhyay, S.K., et al., Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60e81, Cretaceous Research (2016), http://dx.doi.org/10.1016/j.cretres.2016.12.006
2
S.K. Mukhopadhyay et al. / Cretaceous Research xxx (2016) 1e3
present below a field photograph (Fig. 1) of the only K/Pg transition section on the west bank at about 250 m downstream from the Therriaghat gorge and this has nothing in common with the photograph presented by the authors. Therefore, more details of this exposure (exact location, and lithological succession and illustration of fossil assemblages across the boundary) may help appreciate the claimed K/Pg boundary at the Mahadeo/Langpar contact. 3. Sial et al. (2016) followed Bhandari et al. (1987) to consider that the Ir anomaly marks the K/Pg boundary. Mukhopadhyay (2008, 2009, 2012a, 2012b) on the other hand recognized an anomaly of platinum group of elements (PGE) at two stratigraphic levels towards the upper Maastrichtian part of the Langpar Formation, and both of them occur below the biostratigraphically delineated K/Pg boundary. Of the two, the lower Ir anomaly of Bhandari et al. (1987) was recognized within the biozone CF4 and this was considered coeval with the first phase of the Deccan volcanic eruption, whereas, the upper anomaly was found within the biozone CF2 when the second and the most vigorous Deccan volcanic eruption occurred (65.4e65.2 Ma, Barrera, 1994; Courtillot et al., 1996; Hoffman et al., 2000; Keller, 2001; Shrivastava and Ahmad, 2005; Shrivastava et al., 2015). This younger anomaly level is marked by the high concentration of microspherule (Mukhopadhyay, 2012b). It seems that the segment dealt with by Sial et al. (2016) perhaps belongs to the biozone CF4 (if proved biostratigraphically) or may be older than CF4. 4. The authors placed their samples KT-1 to KT-7 below the K/Pg boundary clay layer and the samples from KT-8 to KT25 within the Danian Langpar Formation. Consequently, the samples KT-1 to KT-7 belong to the Mahadeo Formation. A field photograph of the K/Pg boundary clay layer at the MahadeoeLangpar contact and planktonic foraminifera from the layer may be very vital document in support of their boundary. Moreover, in Table 3 the sample KT-8 has been included in the Maastrichtian; this makes the location of this sample unclear with reference to the clay layer, and the correct location of this sample is not shown or stated in the paper.
5. In the studied section, the authors have shown 3 spikes of Hg/ TOC which were correlated with Deccan Phase 2 (Fig. 10, Sial et al., 2016). However, the lithosection shows neither the corresponding samples, nor their planktonic foraminifera; this makes it difficult to endorse the correlation. In view of the possibility of geochemical enrichment by secondary processes in the studied sediments which experienced prolonged erosion and weathering, the authors did not discuss the precautionary measures taken to avoid geochemical contamination. 6. The geochemical work presented by the authors is based on 25 samples covering a 2.5 m segment across the MaastrichtianeDanian boundary. Since the samples have not been calibrated in terms of standard biozones of the boundary segment, it is difficult to accept that the geochemical inference was actually reflecting the events of the K/Pg transition. The geochemical studies of the K/Pg boundary segment by the authors do not corroborate the geochemical results of Shrivastava et al. (2013) and Pal et al. (2015a, 2015b, 2015c), who carried out a series of systematic geochemical studies on well calibrated samples in terms of planktonic foraminiferal biozones by Mukhopadhyay (2008, 2012a). 7. The clay mineral studies (Shrivastava et al., 2013) across the K/Pg boundary in the Um-Sohryngkew river section revealed almost analogous clay mineralogical attributes, REE patterns and TOC contents as those of some well-known K/Pg boundary sections of the world; moreover, a significant shift in the redox condition has been recorded in the sediments corresponding to Biozones CF4 to Pla. An overall absence of these results in the geochemical studies of Sial et al. (2016) suggests that they might have dealt with a segment other than the K/Pg transition. 8. During the organic geochemical investigation across the K/Pg boundary of the Um-Sohryngkew river section, Pal et al. (2015a, 2015b) observed well defined spikes of n-alkanes (C14e22), nfatty acids (C14e18) and concentration of high molecular PAH compounds. Their other study (Pal et al., 2015c) indicated a significant increase in the kaolinite content and layer-interlayer charges in the illites occurring in the yellowish brown clay layer, which are almost at par with the clays of some well-established K/Pg boundary sections of the Mediterranean region. These vital results of the boundary section are also not reflected in Sial et al. (2016). 9. Regarding the report of a continuous planktonic foraminiferal biozones from CF2 to P1a (2) across the MahadeoeLangpar contact (Fig. 10, Sial et al., 2016), a mention may be made on which basis such continuity has been shown because in the Um Sohryngkew River section, Pandey's (1981, 1990) biostratigraphic analysis indicated an unconformity at the CretaceouseTertiary boundary, and Mukhopadhyay's (2008) recovery of the zonal indices of the successive biozones across the boundary are from a part of the Langpar Formation as stated in points 1 and 2. With respect to above, the authors (Sial et al., 2016) should address the points (1e9) to justify that they dealt with a right section. This is necessary because there cannot be two K/Pg boundary sections in the Um Sohryngkew river section unless repeated by structural disturbance.
Fig. 1. Looking southwest through the west bank of the Um Sohryngkew River; the Langpar beds dip towards south showing the tentatively marked K/Pg boundary at about 250 m south (downstream) of the Therriaghat gorge; the section is paleontologically and biostratigraphically continuous across the boundary; in the background, the upper Maastrichtian calcareous shale containing earthy limestone bands is conformably overlain by the lower Danian shaly marl; thick undergrowth covers the exposures; pool of waters of the Um Sohryngkew River in the foreground.
Acknowledgements Sincere thanks are due to Prof. Robert P. Speijer, KU Leuven, Belgium for reviewing the manuscript and suggesting improvements. We also acknowledge Dr. Eduardo Koutsoukos, University of Heidelberg, Germany for editorial handling.
Please cite this article in press as: Mukhopadhyay, S.K., et al., Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60e81, Cretaceous Research (2016), http://dx.doi.org/10.1016/j.cretres.2016.12.006
S.K. Mukhopadhyay et al. / Cretaceous Research xxx (2016) 1e3
SKM as Convener and JPS as a Member acknowledge the IGCPProjectGrant-507 to carry out the field work. SP acknowledges CSIR, New Delhi for financial support [Project Grant No. 24 (0315)/ 11/EMR-II]. References Barrera, E., 1994. Global environmental changes preceding the Cretaceous-Tertiary boundary: early-upper Maastrichtian transition. Geology 22, 877e880. Bhandari, M., Shukla, P.M., Pandey, J., 1987. Iridium enrichment at CretaceousTertiary boundary in Meghalaya. Current Science 56, 1003e1005. Courtillot, V., Jaeger, J.J., Yang, Z., Feraud, G., Hofmann, C., 1996. The influence of continental flood basalts on mass extinctions: where do we stand? In: Ryder, G., Fastovsky, D., Gartner, S. (Eds.), The Cretaceous-Tertiary Event and Other Catastrophes in Earth History. Geological Society of America Special Paper 307, 513e525. Hoffman, C., Feraud, G., Courtillot, V., 2000. 40Ar/39Ar dating of mineral separates and whole rock from the western Ghat lava pile: further constraints on duration and age of Deccan Traps. Earth and Planetary Science Letters 180, 13e27. Keller, G., 2001. The end-Cretaceous mass extinction in the marine realm: year 2000 assessment. Planetary Space Science 49, 817e830. Mukhopadhyay, S.K., 2008. Planktonic foraminiferal succession in late Cretaceous to early Palaeocene strata in Meghalaya, India. Lethaia 41, 71e84. Mukhopadhyay, S.K., 2009. Convener's report for 2008 on the progress of work in the IGCP Project 507, on ‘Palaeoclimate in Asia during the Cretaceous: their variations, causes, and biotic and environmental responses’. IGCP India Newsletter 29, 11e13. Mukhopadhyay, S.K., 2012a. Guembelitria (Foraminifera) in the Upper CretaceousLower Paleocene succession of the Langpar Formation, India, and its paleoenvironmental implication. Geological Society of India 79, 627e651. Mukhopadhyay, S.K., 2012b. Morphogroups and small sized tests in Pseudotextularia elegans (Rzehak) from the Late Maastrichtian succession of Meghalaya, India as
3
indicators of biotic response to paleoenvironmental stress. Journal of Asian Earth Sciences 48, 111e124. Pal, S., Shrivastava, J.P., Mukhopadhyay, S.K., 2015a. Polycyclic Aromatic Hydrocarbon compound excursions and K/Pg transition in the late Cretaceous-early Paleogene succession of the Um-Sohryngkew River section, Meghalaya. Current Science 109, 1140e1150. Pal, S., Shrivastava, J.P., Mukhopadhyay, S.K., 2015b. Physils and organic matter-base palaeoenvironmental records of the K/Pg boundary transition from the late Cretaceous-early Palaeogene succession of the Um Sohryngkew river section of Meghalaya, India. Chemie der Erde Geochemistry 75, 445e463. Pal, S., Shrivastava, J.P., Mukhopadhyay, S.K., 2015c. Mineral chemistry of clays associated with the late Cretaceous-early Palaeogene succession of the Um Sohryngkew river section of Meghalaya: palaeoenvironmental inferences and K/Pg transition. Journal of Geological Society of India 86, 631e647. Pandey, J., 1981. Cretaceous foraminifera of Um Sohryngkew River section, Meghalaya. Journal of Palaeontological Society of India 25, 53e74. Pandey, J., 1990. Cretaceous/Tertiary boundary, iridium anomaly and foraminifer break in the Um Sohryngkew River section. Current Science 59, 570e575. Shrivastava, J.P., Ahmad, M., 2005. A review of research on Late Cretaceous volcanicsedimentary sequences of the Mandla Lobe: implications for Deccan volcanism and the Cretaceous/Palaeogene boundary. Cretaceous Research 26, 145e156. Shrivastava, J.P., Mukhopadhyay, S.K., Pal, S., 2013. Chemico-mineralogical attributes of clays from the late Cretaceouse-early Palaeogene succession of the UmSohryngkew River section of Meghalaya, India: palaeoenvironmental inferences and the K/Pg boundary. Cretaceous Research 45, 247e257. Shrivastava, J.P., Duncan, R.A., Kashyap, M., 2015. Post-K/PB younger 40Ar-39Ar ages of the Mandla lavas: implications for the duration of the Deccan volcanism. Lithos 224e225, 214e224. Sial, A.N., Chen, J., Lacerda, L.D., Frei, R., Tewari, V.C., Pandit, M.K., Gaucher, C., Ferreira, V.P., Cirilli, S., Peralta, S., Korte, C., Barbosa, J.A., Pereira, N.S., 2016. Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: links to volcanism and palaeoenvironmental impacts. Cretaceous Research 66, 60e81.
Please cite this article in press as: Mukhopadhyay, S.K., et al., Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60e81, Cretaceous Research (2016), http://dx.doi.org/10.1016/j.cretres.2016.12.006
Contents lists available at ScienceDirect
Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes
Discussion
Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60e81 Sanjay K. Mukhopadhyay a, Sucharita Pal b, J.P. Shrivastava b, * a b
Formerly Geological Survey of India, Natural Energy Resources, Salt Lake, Kolkata 700091, India Department of Geology, University of Delhi, Delhi 110007, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 October 2016 Accepted in revised form 14 December 2016 Available online xxx
The paper published by Sial et al. (2016) contains geochemical information which does not fit into the scheme of the existing planktonic foraminiferal succession across the K/Pg boundary in the Um Sohryngkew River section, Meghalaya India, worked out by either Mukhopadhyay (2008) or Pandey (1981, 1990). The K/Pg boundary reported by Sial et al. (2016) is not compatible with any of these two. In this perspective some of the controversies are highlighted. © 2016 Elsevier Ltd. All rights reserved.
The above paper presents an informative account of the K/Pg sections from some well studied locations of the world along with additional geochemical input. The prerequisite of additional studies on a well established K/Pg boundary segment is the correct identification of the K/Pg boundary, but the geologic information on the biostratigraphically well constrained K/Pg interval of the Um Sohryngkew River section, Meghalaya India provided by Sial et al. (2016) is difficult to accept because they have faltered on the correct identification of the boundary segment. The boundary section exposed on the west bank of the Um Sohryngkew River represents the only of its kind in Indian subcontinent and one of the few occurrences in the tropic-subtropic belt outside the Mediterranean and Atlantic Coast. A more careful approach would have added valuable geochemical information to this K/Pg boundary segment. 1. The authors cited Mukhopadhyay (2008) to state that the Um Sohryngkew River Section, Meghalaya contains the K/Pg boundary in a biostratigraphically continuous section, but contrary to his finding, the authors considered that the K/Pg boundary occurs at the Mahadeo/Langpar contact (Table 3, lines 570e579, Sial et al., 2016) without providing micropaleontological or biostratigraphic evidence. Mukhopadhyay (2012a, Fig. 2A; 2012b, Fig, 2I) showed that the Mahadeo/Langpar
* Corresponding author. E-mail address: [email protected] (J.P. Shrivastava).
contact is soil covered on the west bank section of the Um Sohryngkew River, in which section the planktonic foraminifera based K/Pg boundary is developed. Based on the occurrences of Globotruncana sp. towards the top of the Mahadeo Formation and at the lower part of the overlying Langpar Formation, the concealed contact between the formations was assigned late Maastrichtian, and the planktonic foraminiferal biostratigraphy carried out by Mukhopadhyay (2008) indicated that the K/Pg boundary between the Plummerita hantkeninoides Zone (¼CF1 Zone) and the Guembelitria cretacea Zone (¼ P0 Zone) occurs within the Langpar Formation at about 28 m above the exposed base of the Langpar Formation. Therefore, the coinciding of the Mahadeo/Langpar contact with the K/Pg boundary as claimed by the authors is untenable until substantiated with biostratigraphic and planktonic foraminiferal evidence. 2. Along the Um Sohryngkew River, the thick bedded arenaceous Mahadeo Formation develops escarpments and the thin bedded argillocalcareous Langpar Formation occupies adjoining lower ground of the valley wall. This geomorphic difference is well represented around the MahadeoeLangpar contact; moreover, along the river bank, the Langpar is covered with thicker undergrowth than that of the Mahadeo. But the field photograph by the authors (Fig. 5a, Sial et al., 2016) shows continuity of bare exposures of bedded litho-unit ‘across the Mahadeo/Langpar contact’. Such exposures of the K/Pg transition section on the bank of the Um Sohryngkew River is very interesting since we
http://dx.doi.org/10.1016/j.cretres.2016.12.006 0195-6671/© 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mukhopadhyay, S.K., et al., Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60e81, Cretaceous Research (2016), http://dx.doi.org/10.1016/j.cretres.2016.12.006
2
S.K. Mukhopadhyay et al. / Cretaceous Research xxx (2016) 1e3
present below a field photograph (Fig. 1) of the only K/Pg transition section on the west bank at about 250 m downstream from the Therriaghat gorge and this has nothing in common with the photograph presented by the authors. Therefore, more details of this exposure (exact location, and lithological succession and illustration of fossil assemblages across the boundary) may help appreciate the claimed K/Pg boundary at the Mahadeo/Langpar contact. 3. Sial et al. (2016) followed Bhandari et al. (1987) to consider that the Ir anomaly marks the K/Pg boundary. Mukhopadhyay (2008, 2009, 2012a, 2012b) on the other hand recognized an anomaly of platinum group of elements (PGE) at two stratigraphic levels towards the upper Maastrichtian part of the Langpar Formation, and both of them occur below the biostratigraphically delineated K/Pg boundary. Of the two, the lower Ir anomaly of Bhandari et al. (1987) was recognized within the biozone CF4 and this was considered coeval with the first phase of the Deccan volcanic eruption, whereas, the upper anomaly was found within the biozone CF2 when the second and the most vigorous Deccan volcanic eruption occurred (65.4e65.2 Ma, Barrera, 1994; Courtillot et al., 1996; Hoffman et al., 2000; Keller, 2001; Shrivastava and Ahmad, 2005; Shrivastava et al., 2015). This younger anomaly level is marked by the high concentration of microspherule (Mukhopadhyay, 2012b). It seems that the segment dealt with by Sial et al. (2016) perhaps belongs to the biozone CF4 (if proved biostratigraphically) or may be older than CF4. 4. The authors placed their samples KT-1 to KT-7 below the K/Pg boundary clay layer and the samples from KT-8 to KT25 within the Danian Langpar Formation. Consequently, the samples KT-1 to KT-7 belong to the Mahadeo Formation. A field photograph of the K/Pg boundary clay layer at the MahadeoeLangpar contact and planktonic foraminifera from the layer may be very vital document in support of their boundary. Moreover, in Table 3 the sample KT-8 has been included in the Maastrichtian; this makes the location of this sample unclear with reference to the clay layer, and the correct location of this sample is not shown or stated in the paper.
5. In the studied section, the authors have shown 3 spikes of Hg/ TOC which were correlated with Deccan Phase 2 (Fig. 10, Sial et al., 2016). However, the lithosection shows neither the corresponding samples, nor their planktonic foraminifera; this makes it difficult to endorse the correlation. In view of the possibility of geochemical enrichment by secondary processes in the studied sediments which experienced prolonged erosion and weathering, the authors did not discuss the precautionary measures taken to avoid geochemical contamination. 6. The geochemical work presented by the authors is based on 25 samples covering a 2.5 m segment across the MaastrichtianeDanian boundary. Since the samples have not been calibrated in terms of standard biozones of the boundary segment, it is difficult to accept that the geochemical inference was actually reflecting the events of the K/Pg transition. The geochemical studies of the K/Pg boundary segment by the authors do not corroborate the geochemical results of Shrivastava et al. (2013) and Pal et al. (2015a, 2015b, 2015c), who carried out a series of systematic geochemical studies on well calibrated samples in terms of planktonic foraminiferal biozones by Mukhopadhyay (2008, 2012a). 7. The clay mineral studies (Shrivastava et al., 2013) across the K/Pg boundary in the Um-Sohryngkew river section revealed almost analogous clay mineralogical attributes, REE patterns and TOC contents as those of some well-known K/Pg boundary sections of the world; moreover, a significant shift in the redox condition has been recorded in the sediments corresponding to Biozones CF4 to Pla. An overall absence of these results in the geochemical studies of Sial et al. (2016) suggests that they might have dealt with a segment other than the K/Pg transition. 8. During the organic geochemical investigation across the K/Pg boundary of the Um-Sohryngkew river section, Pal et al. (2015a, 2015b) observed well defined spikes of n-alkanes (C14e22), nfatty acids (C14e18) and concentration of high molecular PAH compounds. Their other study (Pal et al., 2015c) indicated a significant increase in the kaolinite content and layer-interlayer charges in the illites occurring in the yellowish brown clay layer, which are almost at par with the clays of some well-established K/Pg boundary sections of the Mediterranean region. These vital results of the boundary section are also not reflected in Sial et al. (2016). 9. Regarding the report of a continuous planktonic foraminiferal biozones from CF2 to P1a (2) across the MahadeoeLangpar contact (Fig. 10, Sial et al., 2016), a mention may be made on which basis such continuity has been shown because in the Um Sohryngkew River section, Pandey's (1981, 1990) biostratigraphic analysis indicated an unconformity at the CretaceouseTertiary boundary, and Mukhopadhyay's (2008) recovery of the zonal indices of the successive biozones across the boundary are from a part of the Langpar Formation as stated in points 1 and 2. With respect to above, the authors (Sial et al., 2016) should address the points (1e9) to justify that they dealt with a right section. This is necessary because there cannot be two K/Pg boundary sections in the Um Sohryngkew river section unless repeated by structural disturbance.
Fig. 1. Looking southwest through the west bank of the Um Sohryngkew River; the Langpar beds dip towards south showing the tentatively marked K/Pg boundary at about 250 m south (downstream) of the Therriaghat gorge; the section is paleontologically and biostratigraphically continuous across the boundary; in the background, the upper Maastrichtian calcareous shale containing earthy limestone bands is conformably overlain by the lower Danian shaly marl; thick undergrowth covers the exposures; pool of waters of the Um Sohryngkew River in the foreground.
Acknowledgements Sincere thanks are due to Prof. Robert P. Speijer, KU Leuven, Belgium for reviewing the manuscript and suggesting improvements. We also acknowledge Dr. Eduardo Koutsoukos, University of Heidelberg, Germany for editorial handling.
Please cite this article in press as: Mukhopadhyay, S.K., et al., Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60e81, Cretaceous Research (2016), http://dx.doi.org/10.1016/j.cretres.2016.12.006
S.K. Mukhopadhyay et al. / Cretaceous Research xxx (2016) 1e3
SKM as Convener and JPS as a Member acknowledge the IGCPProjectGrant-507 to carry out the field work. SP acknowledges CSIR, New Delhi for financial support [Project Grant No. 24 (0315)/ 11/EMR-II]. References Barrera, E., 1994. Global environmental changes preceding the Cretaceous-Tertiary boundary: early-upper Maastrichtian transition. Geology 22, 877e880. Bhandari, M., Shukla, P.M., Pandey, J., 1987. Iridium enrichment at CretaceousTertiary boundary in Meghalaya. Current Science 56, 1003e1005. Courtillot, V., Jaeger, J.J., Yang, Z., Feraud, G., Hofmann, C., 1996. The influence of continental flood basalts on mass extinctions: where do we stand? In: Ryder, G., Fastovsky, D., Gartner, S. (Eds.), The Cretaceous-Tertiary Event and Other Catastrophes in Earth History. Geological Society of America Special Paper 307, 513e525. Hoffman, C., Feraud, G., Courtillot, V., 2000. 40Ar/39Ar dating of mineral separates and whole rock from the western Ghat lava pile: further constraints on duration and age of Deccan Traps. Earth and Planetary Science Letters 180, 13e27. Keller, G., 2001. The end-Cretaceous mass extinction in the marine realm: year 2000 assessment. Planetary Space Science 49, 817e830. Mukhopadhyay, S.K., 2008. Planktonic foraminiferal succession in late Cretaceous to early Palaeocene strata in Meghalaya, India. Lethaia 41, 71e84. Mukhopadhyay, S.K., 2009. Convener's report for 2008 on the progress of work in the IGCP Project 507, on ‘Palaeoclimate in Asia during the Cretaceous: their variations, causes, and biotic and environmental responses’. IGCP India Newsletter 29, 11e13. Mukhopadhyay, S.K., 2012a. Guembelitria (Foraminifera) in the Upper CretaceousLower Paleocene succession of the Langpar Formation, India, and its paleoenvironmental implication. Geological Society of India 79, 627e651. Mukhopadhyay, S.K., 2012b. Morphogroups and small sized tests in Pseudotextularia elegans (Rzehak) from the Late Maastrichtian succession of Meghalaya, India as
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indicators of biotic response to paleoenvironmental stress. Journal of Asian Earth Sciences 48, 111e124. Pal, S., Shrivastava, J.P., Mukhopadhyay, S.K., 2015a. Polycyclic Aromatic Hydrocarbon compound excursions and K/Pg transition in the late Cretaceous-early Paleogene succession of the Um-Sohryngkew River section, Meghalaya. Current Science 109, 1140e1150. Pal, S., Shrivastava, J.P., Mukhopadhyay, S.K., 2015b. Physils and organic matter-base palaeoenvironmental records of the K/Pg boundary transition from the late Cretaceous-early Palaeogene succession of the Um Sohryngkew river section of Meghalaya, India. Chemie der Erde Geochemistry 75, 445e463. Pal, S., Shrivastava, J.P., Mukhopadhyay, S.K., 2015c. Mineral chemistry of clays associated with the late Cretaceous-early Palaeogene succession of the Um Sohryngkew river section of Meghalaya: palaeoenvironmental inferences and K/Pg transition. Journal of Geological Society of India 86, 631e647. Pandey, J., 1981. Cretaceous foraminifera of Um Sohryngkew River section, Meghalaya. Journal of Palaeontological Society of India 25, 53e74. Pandey, J., 1990. Cretaceous/Tertiary boundary, iridium anomaly and foraminifer break in the Um Sohryngkew River section. Current Science 59, 570e575. Shrivastava, J.P., Ahmad, M., 2005. A review of research on Late Cretaceous volcanicsedimentary sequences of the Mandla Lobe: implications for Deccan volcanism and the Cretaceous/Palaeogene boundary. Cretaceous Research 26, 145e156. Shrivastava, J.P., Mukhopadhyay, S.K., Pal, S., 2013. Chemico-mineralogical attributes of clays from the late Cretaceouse-early Palaeogene succession of the UmSohryngkew River section of Meghalaya, India: palaeoenvironmental inferences and the K/Pg boundary. Cretaceous Research 45, 247e257. Shrivastava, J.P., Duncan, R.A., Kashyap, M., 2015. Post-K/PB younger 40Ar-39Ar ages of the Mandla lavas: implications for the duration of the Deccan volcanism. Lithos 224e225, 214e224. Sial, A.N., Chen, J., Lacerda, L.D., Frei, R., Tewari, V.C., Pandit, M.K., Gaucher, C., Ferreira, V.P., Cirilli, S., Peralta, S., Korte, C., Barbosa, J.A., Pereira, N.S., 2016. Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: links to volcanism and palaeoenvironmental impacts. Cretaceous Research 66, 60e81.
Please cite this article in press as: Mukhopadhyay, S.K., et al., Comments on the paper published by Sial et al (2016), Mercury enrichments and Hg isotopes in CretaceousePaleogene boundary successions: Links to volcanism and palaeoenvironmental impacts. Cretaceous Research, v. 66, pp. 60e81, Cretaceous Research (2016), http://dx.doi.org/10.1016/j.cretres.2016.12.006