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Ostracodes as indicators of brackish water environments in the Catskill Magnafacies (Devonian) of New York State: reply
Palaeogeography, Palaeoclimatology, Palaeoecology 171 (2001) 81±83
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Ostracodes as indicators of brackish water environments in the Catskill Magnafacies (Devonian) of New York State: reply Larry W. Knox* Department of Earth Sciences, Tennessee Technological University, Cookeville, TN 38505, USA Received 22 September 2000; received in revised form 20 March 2001; accepted for publication 27 March 2001 Keywords: Paleoenvironments; Brackish; Fluvial; Ostracoda; Catskill magnafacies; Devonian; New York State
1. Introduction The purpose of Knox and Gordon (1999) was to document as brackish water facies a stratigraphically restricted (4.5 m) interval within the Catskill Magnafacies based on sedimentological, paleontological and mineralogical evidence from a single locality near East Windom, New York State. Although the Catskill (nonmarine) Magnafacies has been generally interpreted as ¯uvial in origin, some strata contain features that suggest marine in¯uence on low-relief areas of the ¯oodplain (Halperin and Bridge, 1988). Recognition of these marginal marine deposits will allow a more precise determination of the position of the paleoshoreline within these ¯uvially dominated environments. Understanding how shoreline deposits vary is crucial for correlation between ¯uvial and marine areas and establishing the relative control of tectonism, climate change or eustatic sea-level variation within the basin (Bridge and Willis, 1994). Knox and Gordon did not suggest that all deposits at East Windom belong to this brackish water facies. Friedman and Lundin, in their discussion, focus on exposures some 8 m below Knox and Gordon's studied interval. At this lower exposure they note the presence of sandstone bodies with channel-form geometry and associated interbedded siltstones and * Fax: 11-931-372-3363. E-mail address: [email protected] (L.W. Knox).
mudstones, which they interpret to represent pointbar, overbank and swamp environments of a ¯oodplain. Previously Johnson and Friedman (1969) noted the great similarity of the sedimentary structures of the East Windom channels with Wadden Sea tidal channels. They reported that the East Windom channels, however, lack both coquinoid, basal lag concentrates and strata of marine origin that are associated with Wadden tidal channels. Largely on this basis they interpreted the East Windom channels to be of ¯uvial origin. The presence of brackish water facies some 4.5 m above the channel might weaken their interpretation, but in the absence of more de®nitive evidence for a tidal origin, such as tidal bundles within the sandstone crossbeds, I concur with their interpretation of a ¯uvial environment for the lower part of the section. 2. Features of the 4.5 m brackish interval Friedman and Lundin, in their discussion, argue that the 4.5 m exposure studied by Knox and Gordon represents deposition in a ¯oodplain environment. The evidence they cite for this interpretation is the presence there of root stigmaria and subaerial calcretes. The 4.5 m exposure is not associated with large, channelized sandstone bodies, and I presume that Friedman and Lundin's interpretation of the stratigraphically higher exposure is also based on similarity
0031-0182/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0031-018 2(01)00264-4
82
L.W. Knox / Palaeogeography, Palaeoclimatology, Palaeoecology 171 (2001) 81±83
of bedding and color of mudstones/siltstones there with strata representing overbank/swamp environments in the lower, channeled exposure. Knox and Gordon discussed the signi®cance of the following sedimentary features within the 4.5 m exposure of calcareous mudstones, silty mudstones, siltstone and thin calcareous sandstones: (1) the mineral amesite; (2) intense manganese-oxide staining; (3) mudcracks, and wave and interference ripple marks; (4) desiccation cracks; (5) algal laminations; (6) lingulid brachiopods; (7) cosmine-bearing ®sh fragments; (8) vertical meniscate burrows; (9) the trace fossil Spirophyton; (10) the conchostracan Eustheria; (11) impressions of small bivalves; and (12) the ostracodes Leperditia? sp. and Welleria sp. Most of these features are absent from immediately adjacent, presumed freshwater, ¯oodplain deposits. Calcretes are absent within this interval, although they occur just above and below. The distribution of this collective set of sedimentary features within the interval and their absence from adjacent, presumed freshwater, ¯oodplain deposits, suggests deposition in a brackish water environment near the paleoshoreline. I agree with Friedman and Lundin's discussion statement that the sediments of the 4.5 m interval do not come from ªthe same environment of deposition nor from the same stratigraphic level as those of Friedman and Lundin (1998); Lundin and Friedman (1998).º 3. Ostracodes from the brackish interval Knox and Gordon reported numerous specimens of only two ostracode species, Leperditia? sp. and Welleria sp., from a 6 cm thick calcareous mudstone located nearly in the middle of the 4.5 m interval. They did not invoke the concept of taxonomic uniformitarianism, in its strict sense, in order to interpret paleoecological relationships for these long extinct ostracode taxa. They did, however, use the ancient version of that approach by making interpretations based on the range of environmental conditions that have been reported elsewhere for closely related species and genera of ostracodes that range in age from Ordovician through the Devonian. No leperditicopid ostracode (except for Sollenella? Friedman and Lundin, 1998) nor any species of the palaeocopid
Welleria has ever been reported from freshwater paleoenvironments (Berdan, 1984; Knox and Gordon, 1999; Siveter, 1984; Vannier et al., 2001). Conversely, during early- to mid- Paleozoic time geographically widespread (North America, Europe and China) leperditicopids occurred commonly in marginal marine habitats subject to salinity variation as well as in shallow marine environments (Becker, 1971; Berdan, 1969, 1984, and references therein; Milhau et al., 1997; Vannier et al., 2001, and references therein; Walker and Laporte, 1970; Warshauer and Smosna, 1977; Williams and Siveter, 1996). Most of these authors report monospeci®c or low-diversity, high-abundance ostracode faunas interpreted to represent stressed environments, such as brackish lagoons, shallow shoreline embayments or tidal ¯ats. Furthermore, I am unaware of any other palaeocopid ostracode reputed to be of freshwater origin, except for two species based on molds reported by Zabert (1985) from the Permian of Paraguay. In my opinion, the taxonomic assignment of Zabert's Permian species to the Palaecopida is very questionable. The population structures (low diversity and great abundance) of Leperditia? and Welleria sp. are identical to those reported for the most closely related ostracode taxa from restricted environments through their geologic range. By reference to this form of ancient taxonomic uniformitarianism, I maintain that the rocks from which Leperditia? and Welleria sp. were found are more likely to have been deposited in near-shore brackish water environments than in freshwater alluvial plain sediments. The interpretation presented by Friedman and Lundin requires that three species of ostracodes belonging to two families of the Order Leperditicopida (Sollenella? sp. and Leperditia? sp.) and to the Order Palaeocopida (Welleria sp.) adapted to freshwater environments at about the same time in the Devonian. Because there are numerous reports of ostracodes closely related to these three species (at the generic level) from Paleozoic brackish (and marine) environments, I consider their interpretation of a freshwater origin, at least for the 4.5 m interval, to be unlikely. 4. Summary I conclude that the sedimentological evidence presented by Friedman and Lundin for the 4.5 m
L.W. Knox / Palaeogeography, Palaeoclimatology, Palaeoecology 171 (2001) 81±83
interval is not suf®cient to demonstrate alluvial deposition. Rather the body of evidence reported by Knox and Gordon indicates the likelihood that rocks of this restricted interval were deposited in estuarine environments, or were the result of a short transgressive-regressive cycle that intercalated brackish sediments into a low-relief alluvial plain. Nevertheless, I welcome the discussion by Friedman and Lundin on this problem. It may stimulate others to study additional features (palaeopedology, geochemistry, isotopic signatures, etc.) in these rocks in order to gain insights into their depositional character. References Becker, G., 1971. Paleoecology of Middle Devonian ostracods from the Eifel Region, Germany, p. 801±816. In: Oertli, H.J. (Ed.), PaleÂoeÂcologie des Ostracodes. Bull. Centre Rech. Pau-SNPA. 5 (Suppl.), 1±953. Berdan, J., 1969. Possible paleoecologic signi®cance of leperditiid ostracodes. Geol. Soc. Am. Spec. Pap. 121, 337. Berdan, J., 1984. Leperditicopid ostracodes from Ordovician rocks of Kentucky and nearby states and characteristic features of the Order Leperditicopida. U.S. Geol. Surv. Prof. Pap. 1066, 1±40. Bridge, J.S., Willis, B.J., 1994. Marine transgressions and regressions recorded in Middle Devonian shore-zone deposits of the Catskill clastic wedge. Geol. Soc. Am. Bull. 106, 1140±1458. Friedman, G.M., Lundin, R.F., 1998. Freshwater ostracodes from upper Middle Devonian ¯uvial facies, Catskill Mountains, New York. J. Paleontol. 72, 485±490. Halperin, A., Bridge., J.S., 1988. Marine to non-marine transitional deposits in the Frasnian Catskill clastic wedge, south-central New York. In: The nineteenth Annual Appalachian Petroleum Geology Symposium; Geology of the Appalachian Basin Devonian clastics. W. Va. Geol. Econ. Surv. Rep. C-42, 29. Johnson, K.G., Friedman, G.M., 1969. The Tully clastic corre-
83
latives (Upper Devonian) of New York State: A model for recognition of alluvial, dune (?), tidal, nearshore (bar and lagoon), and offshore sedimentary environments in a tectonic delta complex. J. Sed. Petrol. 39, 451±485. Knox, L.W., Gordon, E.A., 1999. Ostracodes as indicators of brackish water environments in the Catskill Magnafacies (Devonian) of New York State. Palaeogeogr., Palaeoclimatol., Palaeoecol. 148, 9±22. Lundin, R.F., Friedman, G.M., 1998. Sollenella? SP.: Additional isochilinid ostracode specimens from a freshwater backswamp ¯uvial facies (Upper Middle Devonian), Catskill Mountains, New York. Northeastern Geol. Environ. Sci. 20, 242±243. Milhau, B., Hongfei, H., Xiantao, W., 1997. PreÂsence de Leperditiidae (Ostracoda) dans le DeÂvonien terminal d'Etaoucun (Guangxi Chine du Sud). Geobios, MeÂmoire SpeÂcial 20, 387± 395. Siveter, D.J., 1984. Habitats and modes of life of Silurian ostracodes. In: Bassett, M.G., Lawson, J.D. (Eds.), Autecology of Silurian Organisms. Palaeontol. Soc. Lond. Spec. Pap. Palaeontol., 32, pp. 71±85. Vannier, J., Wang, S.Q., Coen, M., 2001. Leperditicopid arthropods (Ordovician±Late Devonian): functional morphology and ecological range. J. Paleontol. 75, 75±95. Walker, K.R., Laporte, L.F., 1970. Congruent fossil communities from Ordovician and Devonian carbonates of New York. J. Paleontol. 44, 928±944. Warshauer, S. M., Smosna, R., 1977. Paleoecologic controls on the ostracode communities in the Tonoloway Limestone (Silurian; Pridoli) of the central Appalachians, p. 475±485. In: LoÈf¯er, H., Danielopol (Eds.), Aspects of Ecology and Zoogeography of Recent and Fossil Ostracoda, p. 1±521. Junk, The Hague. Williams, M., Siveter, D.J., 1996. Lithofacies-in¯uenced ostracod associations in the middle Ordovician Bromide Formation Oklahoma, USA. J. Micropaleontol. 15, 69±81. Zabert, L.L., 1985. Ostracodos de agua dulce Permico Superior de Colonia Independencia (Depto Guaira), Paraguay. Ameghiniana. 22, 121±131.
www.elsevier.nl/locate/palaeo
Ostracodes as indicators of brackish water environments in the Catskill Magnafacies (Devonian) of New York State: reply Larry W. Knox* Department of Earth Sciences, Tennessee Technological University, Cookeville, TN 38505, USA Received 22 September 2000; received in revised form 20 March 2001; accepted for publication 27 March 2001 Keywords: Paleoenvironments; Brackish; Fluvial; Ostracoda; Catskill magnafacies; Devonian; New York State
1. Introduction The purpose of Knox and Gordon (1999) was to document as brackish water facies a stratigraphically restricted (4.5 m) interval within the Catskill Magnafacies based on sedimentological, paleontological and mineralogical evidence from a single locality near East Windom, New York State. Although the Catskill (nonmarine) Magnafacies has been generally interpreted as ¯uvial in origin, some strata contain features that suggest marine in¯uence on low-relief areas of the ¯oodplain (Halperin and Bridge, 1988). Recognition of these marginal marine deposits will allow a more precise determination of the position of the paleoshoreline within these ¯uvially dominated environments. Understanding how shoreline deposits vary is crucial for correlation between ¯uvial and marine areas and establishing the relative control of tectonism, climate change or eustatic sea-level variation within the basin (Bridge and Willis, 1994). Knox and Gordon did not suggest that all deposits at East Windom belong to this brackish water facies. Friedman and Lundin, in their discussion, focus on exposures some 8 m below Knox and Gordon's studied interval. At this lower exposure they note the presence of sandstone bodies with channel-form geometry and associated interbedded siltstones and * Fax: 11-931-372-3363. E-mail address: [email protected] (L.W. Knox).
mudstones, which they interpret to represent pointbar, overbank and swamp environments of a ¯oodplain. Previously Johnson and Friedman (1969) noted the great similarity of the sedimentary structures of the East Windom channels with Wadden Sea tidal channels. They reported that the East Windom channels, however, lack both coquinoid, basal lag concentrates and strata of marine origin that are associated with Wadden tidal channels. Largely on this basis they interpreted the East Windom channels to be of ¯uvial origin. The presence of brackish water facies some 4.5 m above the channel might weaken their interpretation, but in the absence of more de®nitive evidence for a tidal origin, such as tidal bundles within the sandstone crossbeds, I concur with their interpretation of a ¯uvial environment for the lower part of the section. 2. Features of the 4.5 m brackish interval Friedman and Lundin, in their discussion, argue that the 4.5 m exposure studied by Knox and Gordon represents deposition in a ¯oodplain environment. The evidence they cite for this interpretation is the presence there of root stigmaria and subaerial calcretes. The 4.5 m exposure is not associated with large, channelized sandstone bodies, and I presume that Friedman and Lundin's interpretation of the stratigraphically higher exposure is also based on similarity
0031-0182/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0031-018 2(01)00264-4
82
L.W. Knox / Palaeogeography, Palaeoclimatology, Palaeoecology 171 (2001) 81±83
of bedding and color of mudstones/siltstones there with strata representing overbank/swamp environments in the lower, channeled exposure. Knox and Gordon discussed the signi®cance of the following sedimentary features within the 4.5 m exposure of calcareous mudstones, silty mudstones, siltstone and thin calcareous sandstones: (1) the mineral amesite; (2) intense manganese-oxide staining; (3) mudcracks, and wave and interference ripple marks; (4) desiccation cracks; (5) algal laminations; (6) lingulid brachiopods; (7) cosmine-bearing ®sh fragments; (8) vertical meniscate burrows; (9) the trace fossil Spirophyton; (10) the conchostracan Eustheria; (11) impressions of small bivalves; and (12) the ostracodes Leperditia? sp. and Welleria sp. Most of these features are absent from immediately adjacent, presumed freshwater, ¯oodplain deposits. Calcretes are absent within this interval, although they occur just above and below. The distribution of this collective set of sedimentary features within the interval and their absence from adjacent, presumed freshwater, ¯oodplain deposits, suggests deposition in a brackish water environment near the paleoshoreline. I agree with Friedman and Lundin's discussion statement that the sediments of the 4.5 m interval do not come from ªthe same environment of deposition nor from the same stratigraphic level as those of Friedman and Lundin (1998); Lundin and Friedman (1998).º 3. Ostracodes from the brackish interval Knox and Gordon reported numerous specimens of only two ostracode species, Leperditia? sp. and Welleria sp., from a 6 cm thick calcareous mudstone located nearly in the middle of the 4.5 m interval. They did not invoke the concept of taxonomic uniformitarianism, in its strict sense, in order to interpret paleoecological relationships for these long extinct ostracode taxa. They did, however, use the ancient version of that approach by making interpretations based on the range of environmental conditions that have been reported elsewhere for closely related species and genera of ostracodes that range in age from Ordovician through the Devonian. No leperditicopid ostracode (except for Sollenella? Friedman and Lundin, 1998) nor any species of the palaeocopid
Welleria has ever been reported from freshwater paleoenvironments (Berdan, 1984; Knox and Gordon, 1999; Siveter, 1984; Vannier et al., 2001). Conversely, during early- to mid- Paleozoic time geographically widespread (North America, Europe and China) leperditicopids occurred commonly in marginal marine habitats subject to salinity variation as well as in shallow marine environments (Becker, 1971; Berdan, 1969, 1984, and references therein; Milhau et al., 1997; Vannier et al., 2001, and references therein; Walker and Laporte, 1970; Warshauer and Smosna, 1977; Williams and Siveter, 1996). Most of these authors report monospeci®c or low-diversity, high-abundance ostracode faunas interpreted to represent stressed environments, such as brackish lagoons, shallow shoreline embayments or tidal ¯ats. Furthermore, I am unaware of any other palaeocopid ostracode reputed to be of freshwater origin, except for two species based on molds reported by Zabert (1985) from the Permian of Paraguay. In my opinion, the taxonomic assignment of Zabert's Permian species to the Palaecopida is very questionable. The population structures (low diversity and great abundance) of Leperditia? and Welleria sp. are identical to those reported for the most closely related ostracode taxa from restricted environments through their geologic range. By reference to this form of ancient taxonomic uniformitarianism, I maintain that the rocks from which Leperditia? and Welleria sp. were found are more likely to have been deposited in near-shore brackish water environments than in freshwater alluvial plain sediments. The interpretation presented by Friedman and Lundin requires that three species of ostracodes belonging to two families of the Order Leperditicopida (Sollenella? sp. and Leperditia? sp.) and to the Order Palaeocopida (Welleria sp.) adapted to freshwater environments at about the same time in the Devonian. Because there are numerous reports of ostracodes closely related to these three species (at the generic level) from Paleozoic brackish (and marine) environments, I consider their interpretation of a freshwater origin, at least for the 4.5 m interval, to be unlikely. 4. Summary I conclude that the sedimentological evidence presented by Friedman and Lundin for the 4.5 m
L.W. Knox / Palaeogeography, Palaeoclimatology, Palaeoecology 171 (2001) 81±83
interval is not suf®cient to demonstrate alluvial deposition. Rather the body of evidence reported by Knox and Gordon indicates the likelihood that rocks of this restricted interval were deposited in estuarine environments, or were the result of a short transgressive-regressive cycle that intercalated brackish sediments into a low-relief alluvial plain. Nevertheless, I welcome the discussion by Friedman and Lundin on this problem. It may stimulate others to study additional features (palaeopedology, geochemistry, isotopic signatures, etc.) in these rocks in order to gain insights into their depositional character. References Becker, G., 1971. Paleoecology of Middle Devonian ostracods from the Eifel Region, Germany, p. 801±816. In: Oertli, H.J. (Ed.), PaleÂoeÂcologie des Ostracodes. Bull. Centre Rech. Pau-SNPA. 5 (Suppl.), 1±953. Berdan, J., 1969. Possible paleoecologic signi®cance of leperditiid ostracodes. Geol. Soc. Am. Spec. Pap. 121, 337. Berdan, J., 1984. Leperditicopid ostracodes from Ordovician rocks of Kentucky and nearby states and characteristic features of the Order Leperditicopida. U.S. Geol. Surv. Prof. Pap. 1066, 1±40. Bridge, J.S., Willis, B.J., 1994. Marine transgressions and regressions recorded in Middle Devonian shore-zone deposits of the Catskill clastic wedge. Geol. Soc. Am. Bull. 106, 1140±1458. Friedman, G.M., Lundin, R.F., 1998. Freshwater ostracodes from upper Middle Devonian ¯uvial facies, Catskill Mountains, New York. J. Paleontol. 72, 485±490. Halperin, A., Bridge., J.S., 1988. Marine to non-marine transitional deposits in the Frasnian Catskill clastic wedge, south-central New York. In: The nineteenth Annual Appalachian Petroleum Geology Symposium; Geology of the Appalachian Basin Devonian clastics. W. Va. Geol. Econ. Surv. Rep. C-42, 29. Johnson, K.G., Friedman, G.M., 1969. The Tully clastic corre-
83
latives (Upper Devonian) of New York State: A model for recognition of alluvial, dune (?), tidal, nearshore (bar and lagoon), and offshore sedimentary environments in a tectonic delta complex. J. Sed. Petrol. 39, 451±485. Knox, L.W., Gordon, E.A., 1999. Ostracodes as indicators of brackish water environments in the Catskill Magnafacies (Devonian) of New York State. Palaeogeogr., Palaeoclimatol., Palaeoecol. 148, 9±22. Lundin, R.F., Friedman, G.M., 1998. Sollenella? SP.: Additional isochilinid ostracode specimens from a freshwater backswamp ¯uvial facies (Upper Middle Devonian), Catskill Mountains, New York. Northeastern Geol. Environ. Sci. 20, 242±243. Milhau, B., Hongfei, H., Xiantao, W., 1997. PreÂsence de Leperditiidae (Ostracoda) dans le DeÂvonien terminal d'Etaoucun (Guangxi Chine du Sud). Geobios, MeÂmoire SpeÂcial 20, 387± 395. Siveter, D.J., 1984. Habitats and modes of life of Silurian ostracodes. In: Bassett, M.G., Lawson, J.D. (Eds.), Autecology of Silurian Organisms. Palaeontol. Soc. Lond. Spec. Pap. Palaeontol., 32, pp. 71±85. Vannier, J., Wang, S.Q., Coen, M., 2001. Leperditicopid arthropods (Ordovician±Late Devonian): functional morphology and ecological range. J. Paleontol. 75, 75±95. Walker, K.R., Laporte, L.F., 1970. Congruent fossil communities from Ordovician and Devonian carbonates of New York. J. Paleontol. 44, 928±944. Warshauer, S. M., Smosna, R., 1977. Paleoecologic controls on the ostracode communities in the Tonoloway Limestone (Silurian; Pridoli) of the central Appalachians, p. 475±485. In: LoÈf¯er, H., Danielopol (Eds.), Aspects of Ecology and Zoogeography of Recent and Fossil Ostracoda, p. 1±521. Junk, The Hague. Williams, M., Siveter, D.J., 1996. Lithofacies-in¯uenced ostracod associations in the middle Ordovician Bromide Formation Oklahoma, USA. J. Micropaleontol. 15, 69±81. Zabert, L.L., 1985. Ostracodos de agua dulce Permico Superior de Colonia Independencia (Depto Guaira), Paraguay. Ameghiniana. 22, 121±131.