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Sedimentology of the thacher limestone (lower devonian helderberg group), New York state-discussion
Sedimentary Geology, 86 (1993) 325-327
325
Elsevier Science Publishers B.V., Amsterdam
Discussion
Sedimentology of the Thacher Limestone (Lower Devonian Helderberg Group), New York State-discussion Gerald M. F r i e d m a n Department of Geology, Brooklyn College and Graduate School of the City University of New York, Brooklyn, NY 11210, and Northeastern Science Foundation, Inc. affiliated with Brooklyn College (CUNY), Rensselaer Center for Applied Geology, P.O. Box 746, Troy, N.Y. 12181-0746, USA Received September 2, 1992; revised version accepted December 8, 1992
Kradyna (1991) discussed the sedimentology of the Thacher Member of the Lower Devonian Manlius Formation (Lower Devonian Helderberg Group) of New York and developed a model for sediment accumulation. His paper is a modification of his previous paper (Kradyna, 1988), which he, however, did not reference, and in which he correlated the Thacher Member between Cherry Valley and Catskill, New York. I served as a reviewer of both his papers and requested him for his 1991 paper to compare his 1988 and 1991 section of Cherry Valley with that of Gurney and Friedman (1986) who modelled transgressive-regressive cycles and published on this subject before him. Kradyna omitted all reference to this previous work, including his own, and lost the opportunity to compare and contrast different interpretations. Since publication of his 1988 paper Kradyna inserted the section at Thacher Park, and in my review of his manuscript I asked that he compare his Thacher Park section with that which I had previously published (Friedman et al., 1989; Friedman, 1990). This suggestion was not accepted, hence, to supplement Kradyna's (1991) paper, I have inserted the columnar section at Thacher Park (Fig. 1; Friedman et al., 1989; Friedman, 1990) in this discussion using the concepts of parasequences and parasequence sets which Kradyna did not employ (Van Wagoner,
1985; Van Wagoner et al., 1988). The ThacherPark section exposes an excellent case history of sequence stratigraphy. Lower Devonian limestones of the Helderberg Group reveal three parasequences which may be recognized among
Coeymans
20
PS 15 EXPLANATION
PS
Skeletalgmst.
10 '~
Reef
R
Micrite
i
Stromatolites
H
Dolostone, solution collapse
m
-,.-~,.,
Parasequence - Ps
Fig. 1. Columnar section showing parasequences of Lower Devonian limestones at Thacher Park, New York. (Friedman, 1990, fig. 3, p. 16.)
0037-0738/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
326
the exposed formations (Rondout, Manlius, and Coeymans formations) (Fig. 1). Parasequences are the building blocks of vertical sequences. A parasequence is defined as a relatively conformable succession of genetically related beds bounded by surfaces (called parasequence surfaces) of erosion, nondeposition, or their correlative conformities (Van Wagoner, 1985). Each sequence is initiated by a eustatic fall in sea level rapid enough to overcome subsidence (Van Wagoner, 1985) or by epeirogenic upward motion. A parasequence surface commonly is an unconformity surface. Two of the three parasequences are constituted as follows: a skeletal grainstone is overlain by patch reefs and these, in turn, are overlain by interreef grainstone [interval between the upper PS (parasequence surface) and the scale mark for 20 m on Fig. 1]. An underlying parasequence consists of skeletal grainstone that grades up into stromatolites (algal-laminated mudstone). A third parasequence (between the Rondout and the lowermost PS) reflects a lowenergy setting. Each of these three parasequences consists of strata that were formed when a depositional slope prograded seaward. The surfaces bounding the parasequences (labeled PS in Fig. 1) are inferred to have resulted from rapid submergence. These three repeating parasequences, as shown in Fig. 1, form a parasequence set. In more detail the parasequences reveal that: the top of the section is composed of skeletal grainstone (locally skeletal packstone) in which fossils, especially brachiopods, corals and crinoids, are evident; the pentamerid Gypidula coemanensis is prevalent. This facies is part of the Coeymans Formation. Its lower contact is sharp and obvious in the field. Below this contact follows the Manlius Formation which underlies most of this escarpment. A stromatoporoid reef with locally intercalated skeletal grainstone represents the top of this formation. The stromatoporoids show their distinctive globular concentric structures resembling cabbage heads. Previous authors (Rickard, 1962; Fisher, 1987) have termed this reef facies a biostrome, presumably because its geometry in outcrop is sheet-like rather than mound-shaped. In my experience with reefs I
G.M. F R I E D M A N
have observed that most large reefs are flat on top and bottom, especially on the scale of this exposure. Other geologists share this experience, thus Shaver and Sunderman (1989) note "virtually all large reefs seen on outcrop have eroded, flattened tops, whereas smaller reefs that were not naturally aborted and what were unaffected by erosion as seen on outcrop have convex-upward rounded tops." Close examination of the reef facies reveals a fine-grained matrix between the frameworkbuilding stromatoporoids. This matrix resembles micrite, a lithified former lime mud; hence this facies may be misinterpreted as representing a low-energy setting. However, in analogous modern reefs cement forms millimeters to centimeters beneath the living part which in thin section is finely crystalline (cryptocrystalline) and semiopaque. Hence the matrix in such reefrock looks just like low-energy micrite (Friedman, 1985). Therefore the observation of a fine-grained matrix between the framework builders does not deter, in fact confirms, the interpretation that this part of the section formed as a high-energy reef facies, and not in a low-energy setting. The stromatoporoids are massive which in the ecologic zonation of Devonian reefs represents the shallowest-water zone of a subtidal setting. Below the reef facies occurs a stromatolitic (finely laminated) facies which is recessed back creating a near cave-like morphologic feature. By analogy with modern environments the stromatolitic facies represents a low-energy intertidal or supratidal setting. The sharp contact between the intertidal or supratidal low-energy stromatolitic facies and overlying subtidal high-energy reef facies represents a parasequence surface. Downward from the stromatolites a stromatoporoid reef facies once again recurs, separated by bedded skeletal grainstone from the stromatolites; in fact the reef facies is present twice. Hence, downward the setting changes from intertidal or supratidal to subtidal shallow water. Below this double reef section the change is again to interpreted intertidal or supratidal stromatolites. Hence, once again a parasequence surface separates the subtidal high-energy reef facies from the underlying intertidal to supratidal stromatolites.
DISCUSSION
Below this lower stromatolite facies the lithology and facies are that of a low-energy thin-bedded micrite with local skeletal grainstone occurring as finely interbedded couplets, scour-and-fill structures, local cross-bedding, and some beds containing abundant spiriferid brachiopods, tentaculitids, ostracodes, and bryozoans. Near the base of the Manlius Formation occur several thicker beds, up to about 20 cm in thickness. Near the base of the section is the Rondout Formation. Its exact contact with the overlying Manlius Formation is subject to debate. In the columnar section of Fig. 1, the Rondout Formation is identified where solution-collapse features are prominent and the lithology changes to dolomitic, especially dolomitic stromatolites, with sporadic intercalated calcitic laminae and shale laminae, an interpreted supratidal facies. Clasts of solution-collapse breccia are prominent together with gypsum-filled veins. The angular clasts of the collapse breccia resulted from collapse and brecciation of overlying carbonate strata when evaporites underlying them were dissolved. It represents a karst setting. For additional data, see Friedman (1991) and Friedman et al., (1992, especially pp. 179-180). References Fisher, D.W., 1987. Lower Devonian limestones, Helderberg Escarpment, New York. Geological Society of America Centennial Field Guide, Northeastern Section, pp. 119122. Friedman, G.M., 1985. The problem of submarine cement in classifying reefrock: an experience in frustration. In: N. Schneiderman and P.M. Harris (Editors), Carbonate Cements. Soc. Econ. Paleontol. Mineral., Spec. Publ., 36: 117-112. Friedman, G.M., 1990. Vertical parasequences of Lower-Devonian Limestones, Heiderberg Escarpment. The Indian
327 Ladder Trail at the John Boyd Thacher State Park, near Albany, N.Y. Northeast. Geol., 12: 14-18. Friedman, G.M., 1991. The founders of American geology. A visit to their tombs, labs, and their favorite exposures: the Devonian limestones of the Capital District; a study of the sequence stratigraphy of their limestones. In: J.R. Ebert (Editor), Field Trip Guidebook. New York State Geological Association, 63rd Annual Meeting, pp. 55-70. Friedman, G.M., Grasso, T.X., Rodgers, J., Belt, E.S., Johnson, M.E. and Naylor, R.S., 1989. IGC Field trip T169: Boston to Buffalo, in the footsteps of Amos Eaton and Edward Hitchcock. In: W.M. Jordan (Editor), 28th Int. Geological Congress, 99 pp. Friedman, G.M., Sanders, J.E. and Kopaska-Merkel, D.C., 1992. Principles of Sedimentary Deposits: Stratigraphy and Sedimentology. MacMillian, New York, N.Y., 717 pp. Gurney, G.G. and Friedman, G.M., 1986. Transgressive-regressive cycles in vertical sequences: an example from Devonian carbonates in Cherry Valley, New York. Northeast. Geol., 8: 201-217. Kradyna, J.W., 1988. Reevaluation of the punctuated aggradational cycle (PAC) hypothesis; Thacher Member, Manlius Formation (Lower Devonian, Helderberg Group), New York State. Northeast. Geol., 9: 12-31. Kradyna, J.W., 1991. Sedimentoiogy of the Thacher Limestone (Lower Devonian Helderberg Group), New York State. Sediment. Geol., 73: 273-297. Rickard, L.V., 1962. Lake Cayugan (Upper Silurian) Helderbergian (Lower Devonian) stratigraphy on New York. New York State Museum Bull. 386, 157 pp. Shaver, R.H. and Sunderman, J.A., 1989. Silurian seascapes: water depth, clinothems, reef geometry, and other motifs - - a critical review of the Silurian reef model. Geol. Soc. Am., 101: 939-951. Van Wagoner, J.C., 1985. Reservoir facies distribution as controlled by sea-level change. Soc. Econ. Paleontol. Mineral., Abstr., Annu. Midyear Mtg., II: 91. Van Wagoner, J.C., Posamentier, H.W., Mitchum, R.M., Jr., Vail, P.R., Sarg, J.F., Loutit, T.S. and Hardenbol, J., 1988. An overview of the fundamentals of sequence stratigraphy and key definitions. In: C.K. Wilgus, B.S. Hastings, C.G.St.C. Kendall, H.W. Posamentier, C.A. Ross and J.C. Van Wagoner (Editors), Sea-level Changes: an Integrated Approach. Soc. Econ. Paleontol. Mineral., Spec. Publ., 42: pp. 39-45.
325
Elsevier Science Publishers B.V., Amsterdam
Discussion
Sedimentology of the Thacher Limestone (Lower Devonian Helderberg Group), New York State-discussion Gerald M. F r i e d m a n Department of Geology, Brooklyn College and Graduate School of the City University of New York, Brooklyn, NY 11210, and Northeastern Science Foundation, Inc. affiliated with Brooklyn College (CUNY), Rensselaer Center for Applied Geology, P.O. Box 746, Troy, N.Y. 12181-0746, USA Received September 2, 1992; revised version accepted December 8, 1992
Kradyna (1991) discussed the sedimentology of the Thacher Member of the Lower Devonian Manlius Formation (Lower Devonian Helderberg Group) of New York and developed a model for sediment accumulation. His paper is a modification of his previous paper (Kradyna, 1988), which he, however, did not reference, and in which he correlated the Thacher Member between Cherry Valley and Catskill, New York. I served as a reviewer of both his papers and requested him for his 1991 paper to compare his 1988 and 1991 section of Cherry Valley with that of Gurney and Friedman (1986) who modelled transgressive-regressive cycles and published on this subject before him. Kradyna omitted all reference to this previous work, including his own, and lost the opportunity to compare and contrast different interpretations. Since publication of his 1988 paper Kradyna inserted the section at Thacher Park, and in my review of his manuscript I asked that he compare his Thacher Park section with that which I had previously published (Friedman et al., 1989; Friedman, 1990). This suggestion was not accepted, hence, to supplement Kradyna's (1991) paper, I have inserted the columnar section at Thacher Park (Fig. 1; Friedman et al., 1989; Friedman, 1990) in this discussion using the concepts of parasequences and parasequence sets which Kradyna did not employ (Van Wagoner,
1985; Van Wagoner et al., 1988). The ThacherPark section exposes an excellent case history of sequence stratigraphy. Lower Devonian limestones of the Helderberg Group reveal three parasequences which may be recognized among
Coeymans
20
PS 15 EXPLANATION
PS
Skeletalgmst.
10 '~
Reef
R
Micrite
i
Stromatolites
H
Dolostone, solution collapse
m
-,.-~,.,
Parasequence - Ps
Fig. 1. Columnar section showing parasequences of Lower Devonian limestones at Thacher Park, New York. (Friedman, 1990, fig. 3, p. 16.)
0037-0738/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
326
the exposed formations (Rondout, Manlius, and Coeymans formations) (Fig. 1). Parasequences are the building blocks of vertical sequences. A parasequence is defined as a relatively conformable succession of genetically related beds bounded by surfaces (called parasequence surfaces) of erosion, nondeposition, or their correlative conformities (Van Wagoner, 1985). Each sequence is initiated by a eustatic fall in sea level rapid enough to overcome subsidence (Van Wagoner, 1985) or by epeirogenic upward motion. A parasequence surface commonly is an unconformity surface. Two of the three parasequences are constituted as follows: a skeletal grainstone is overlain by patch reefs and these, in turn, are overlain by interreef grainstone [interval between the upper PS (parasequence surface) and the scale mark for 20 m on Fig. 1]. An underlying parasequence consists of skeletal grainstone that grades up into stromatolites (algal-laminated mudstone). A third parasequence (between the Rondout and the lowermost PS) reflects a lowenergy setting. Each of these three parasequences consists of strata that were formed when a depositional slope prograded seaward. The surfaces bounding the parasequences (labeled PS in Fig. 1) are inferred to have resulted from rapid submergence. These three repeating parasequences, as shown in Fig. 1, form a parasequence set. In more detail the parasequences reveal that: the top of the section is composed of skeletal grainstone (locally skeletal packstone) in which fossils, especially brachiopods, corals and crinoids, are evident; the pentamerid Gypidula coemanensis is prevalent. This facies is part of the Coeymans Formation. Its lower contact is sharp and obvious in the field. Below this contact follows the Manlius Formation which underlies most of this escarpment. A stromatoporoid reef with locally intercalated skeletal grainstone represents the top of this formation. The stromatoporoids show their distinctive globular concentric structures resembling cabbage heads. Previous authors (Rickard, 1962; Fisher, 1987) have termed this reef facies a biostrome, presumably because its geometry in outcrop is sheet-like rather than mound-shaped. In my experience with reefs I
G.M. F R I E D M A N
have observed that most large reefs are flat on top and bottom, especially on the scale of this exposure. Other geologists share this experience, thus Shaver and Sunderman (1989) note "virtually all large reefs seen on outcrop have eroded, flattened tops, whereas smaller reefs that were not naturally aborted and what were unaffected by erosion as seen on outcrop have convex-upward rounded tops." Close examination of the reef facies reveals a fine-grained matrix between the frameworkbuilding stromatoporoids. This matrix resembles micrite, a lithified former lime mud; hence this facies may be misinterpreted as representing a low-energy setting. However, in analogous modern reefs cement forms millimeters to centimeters beneath the living part which in thin section is finely crystalline (cryptocrystalline) and semiopaque. Hence the matrix in such reefrock looks just like low-energy micrite (Friedman, 1985). Therefore the observation of a fine-grained matrix between the framework builders does not deter, in fact confirms, the interpretation that this part of the section formed as a high-energy reef facies, and not in a low-energy setting. The stromatoporoids are massive which in the ecologic zonation of Devonian reefs represents the shallowest-water zone of a subtidal setting. Below the reef facies occurs a stromatolitic (finely laminated) facies which is recessed back creating a near cave-like morphologic feature. By analogy with modern environments the stromatolitic facies represents a low-energy intertidal or supratidal setting. The sharp contact between the intertidal or supratidal low-energy stromatolitic facies and overlying subtidal high-energy reef facies represents a parasequence surface. Downward from the stromatolites a stromatoporoid reef facies once again recurs, separated by bedded skeletal grainstone from the stromatolites; in fact the reef facies is present twice. Hence, downward the setting changes from intertidal or supratidal to subtidal shallow water. Below this double reef section the change is again to interpreted intertidal or supratidal stromatolites. Hence, once again a parasequence surface separates the subtidal high-energy reef facies from the underlying intertidal to supratidal stromatolites.
DISCUSSION
Below this lower stromatolite facies the lithology and facies are that of a low-energy thin-bedded micrite with local skeletal grainstone occurring as finely interbedded couplets, scour-and-fill structures, local cross-bedding, and some beds containing abundant spiriferid brachiopods, tentaculitids, ostracodes, and bryozoans. Near the base of the Manlius Formation occur several thicker beds, up to about 20 cm in thickness. Near the base of the section is the Rondout Formation. Its exact contact with the overlying Manlius Formation is subject to debate. In the columnar section of Fig. 1, the Rondout Formation is identified where solution-collapse features are prominent and the lithology changes to dolomitic, especially dolomitic stromatolites, with sporadic intercalated calcitic laminae and shale laminae, an interpreted supratidal facies. Clasts of solution-collapse breccia are prominent together with gypsum-filled veins. The angular clasts of the collapse breccia resulted from collapse and brecciation of overlying carbonate strata when evaporites underlying them were dissolved. It represents a karst setting. For additional data, see Friedman (1991) and Friedman et al., (1992, especially pp. 179-180). References Fisher, D.W., 1987. Lower Devonian limestones, Helderberg Escarpment, New York. Geological Society of America Centennial Field Guide, Northeastern Section, pp. 119122. Friedman, G.M., 1985. The problem of submarine cement in classifying reefrock: an experience in frustration. In: N. Schneiderman and P.M. Harris (Editors), Carbonate Cements. Soc. Econ. Paleontol. Mineral., Spec. Publ., 36: 117-112. Friedman, G.M., 1990. Vertical parasequences of Lower-Devonian Limestones, Heiderberg Escarpment. The Indian
327 Ladder Trail at the John Boyd Thacher State Park, near Albany, N.Y. Northeast. Geol., 12: 14-18. Friedman, G.M., 1991. The founders of American geology. A visit to their tombs, labs, and their favorite exposures: the Devonian limestones of the Capital District; a study of the sequence stratigraphy of their limestones. In: J.R. Ebert (Editor), Field Trip Guidebook. New York State Geological Association, 63rd Annual Meeting, pp. 55-70. Friedman, G.M., Grasso, T.X., Rodgers, J., Belt, E.S., Johnson, M.E. and Naylor, R.S., 1989. IGC Field trip T169: Boston to Buffalo, in the footsteps of Amos Eaton and Edward Hitchcock. In: W.M. Jordan (Editor), 28th Int. Geological Congress, 99 pp. Friedman, G.M., Sanders, J.E. and Kopaska-Merkel, D.C., 1992. Principles of Sedimentary Deposits: Stratigraphy and Sedimentology. MacMillian, New York, N.Y., 717 pp. Gurney, G.G. and Friedman, G.M., 1986. Transgressive-regressive cycles in vertical sequences: an example from Devonian carbonates in Cherry Valley, New York. Northeast. Geol., 8: 201-217. Kradyna, J.W., 1988. Reevaluation of the punctuated aggradational cycle (PAC) hypothesis; Thacher Member, Manlius Formation (Lower Devonian, Helderberg Group), New York State. Northeast. Geol., 9: 12-31. Kradyna, J.W., 1991. Sedimentoiogy of the Thacher Limestone (Lower Devonian Helderberg Group), New York State. Sediment. Geol., 73: 273-297. Rickard, L.V., 1962. Lake Cayugan (Upper Silurian) Helderbergian (Lower Devonian) stratigraphy on New York. New York State Museum Bull. 386, 157 pp. Shaver, R.H. and Sunderman, J.A., 1989. Silurian seascapes: water depth, clinothems, reef geometry, and other motifs - - a critical review of the Silurian reef model. Geol. Soc. Am., 101: 939-951. Van Wagoner, J.C., 1985. Reservoir facies distribution as controlled by sea-level change. Soc. Econ. Paleontol. Mineral., Abstr., Annu. Midyear Mtg., II: 91. Van Wagoner, J.C., Posamentier, H.W., Mitchum, R.M., Jr., Vail, P.R., Sarg, J.F., Loutit, T.S. and Hardenbol, J., 1988. An overview of the fundamentals of sequence stratigraphy and key definitions. In: C.K. Wilgus, B.S. Hastings, C.G.St.C. Kendall, H.W. Posamentier, C.A. Ross and J.C. Van Wagoner (Editors), Sea-level Changes: an Integrated Approach. Soc. Econ. Paleontol. Mineral., Spec. Publ., 42: pp. 39-45.