JOURNAL OF SEDIMENTARY RESEARCH,VOL. 69, NO. 3, MAY, 1999, P. 772–783 Copyright  1999, SEPM (Society for Sedimentary Geology) 1073-130X/99/069-772/$03.00 CONTROL OF TERRESTRIAL STABILIZATION ON LATE DEVONIAN PALUSTRINE CARBONATE DEPOSITION: CATSKILL MAGNAFACIES, NEW YORK, U.S.A. STAN P. DUNAGAN* AND STEVEN G. DRIESE Department of Geological Sciences, The University of Tennessee–Knoxville, Knoxville, Tennessee 37996-1410, U.S.A. e-mail: dunagans@apsu01.apsu.edu ABSTRACT: Upper Devonian (Frasnian) terrestrial strata of south-cen- tral New York contain palustrine and lacustrine carbonate deposited within the well-developed Catskill clastic wedge succession. These non- marine limestone beds (8–50 cm thick) were repeatedly subaerially ex- posed and subjected to pedogenic processes. Palustrine features include subaerial exposure surfaces with soil crusts, pseudo-microkarst and microkarst, brecciation, desiccation cracks, horizontal, planar, and cir- cumgranular cracks, and rhizoliths. Lacustrine carbonate sedimenta- tion was derived primarily from biogenically induced precipitation and from degradation of calcified charophyte stems and ostracodes. These deposits accumulated in relatively shallow water depths, probably  10 m. The results of stable isotope analyses ( 13 C  -4.0 to -4.7‰ PDB;  18 O from -6.8 to -8.7‰ PDB) reveal covariance between  13 C and  18 O values. The high degree of covariance (r  0.75) suggests that these Late Devonian carbonate lakes were hydrologically closed; high rates of surface-water productivity resulted in the heavier  13 C values. Late Devonian carbonate lakes developed as a result of landscape stabilization by the developing rhizosphere. In addition, plants of small to moderate stature functioned as clastic filters, trapped terrigenous clastic sediment along lake margins, and thereby permitted carbonate sedimentation to occur in a system otherwise dominated by terrigenous clastics. These Upper Devonian lacustrine deposits contain the oldest recognized occurrence of ‘‘palustrine’’ facies. The temporal distribu- tion of palustrine carbonate deposits therefore appears limited to post- Silurian strata. INTRODUCTION Palustrine carbonate and terrigenous clastic deposits that display evi- dence of pedogenic modification are commonly associated with shallow lacustrine and marginal marine settings (Platt and Wright 1992), particu- larly where dominated by low-energy margins with low gradients (Platt and Wright 1991). Under these conditions, fluctuations in lake level and sea level subject extensive areas of the carbonate substrate to episodic sub- aerial exposure and pedogenic modification. Palustrine carbonates are rec- ognized by the diagnostic set of characteristics superimposed on the sedi- mentary fabric resulting from the pedogenic processes. Typical palustrine features include mottling, fenestrae, desiccation and pedogenic cracks, brec- ciation, nodularization and/or grainification, rhizoliths, coated grains, pseu- do-microkarst, and Microcodium (Freytet 1973; Freytet and Plaziat 1982; Platt and Wright 1992; Alonso Zarza et al. 1992; Wright and Platt 1995). Palustrine carbonate facies have been described extensively from the Mesozoic and Cenozoic terrestrial deposits of Europe and the U.S.A. (see review in Platt and Wright 1992, and examples in Gierlowski-Kordesch and Kelts 1994). Our knowledge of Paleozoic palustrine carbonate deposits, however, is restricted to examples from the Permian and Pennsylvanian of Spain (Valero Garce ´s 1994a, 1994b), France (Toutin-Morin 1994), Ger- many (Scha ¨fer and Sneh 1983; Stapf 1989), and the U.S.A. (Weedman 1994; Valero Garce ´s and Gierlowski-Kordesch 1994; Valero Garce ´s et al. 1997; Dunagan, unpublished data). * Present address: Department of Geology and Geography, Austin Peay State University, P.O. Box 4418, Clarksville, Tennessee 37044, U.S.A. Well-developed palustrine features are present in Upper Devonian (Fras- nian) terrestrial carbonate and terrigenous clastic deposits from the Catskill Magnafacies, New York. Facies associations and characteristics indicate a lacustrine depositional setting for these palustrine deposits. We interpret that these Upper Devonian palustrine carbonate and clastic facies represent the oldest known recognized occurrence of palustrine facies. It is the pur- pose of this paper to: (1) describe the palustrine and lacustrine carbonate facies, (2) interpret palustrine and lacustrine paleoenvironments and the dynamics of carbonate sedimentation, (3) discuss implications for Late De- vonian paleoclimate and paleohydrology, and (4) compare the Catskill pal- ustrine features with those developed in younger lacustrine and marginal marine systems, and discuss the temporal distribution of Phanerozoic pal- ustrine carbonate deposits. This study provides new insights into the lacustrine and palustrine car- bonate depositional environments present within the Catskill paleoecosys- tem. The Catskill palustrine carbonates record major changes that occurred within terrestrial ecosystems associated with the Ordovician to Devonian development of the rhizosphere, as well as the resulting sedimentary impact of vascular land plants along paleolake margins. The presence of a rhizo- sphere and of vascular land plants significantly changed the nature of ter- restrial sedimentary environments, thereby allowing a post-Devonian pro- liferation of both palustrine and lacustrine carbonate depositional systems, primarily as a result of landscape stabilization. PREVIOUS INVESTIGATIONS AND GEOLOGIC SETTING The Catskill Magnafacies was deposited in the Acadian foreland basin on the western flank of the Appalachian orogen (Faill 1985). In New York, the Catskill is characterized by a generally westward-thinning, coarsening- upward, regressive succession dominated by siliciclastic deposits (Gordon and Bridge 1987). These terrigenous clastic deposits were interpreted as representing overbank floodplain (crevasse splay, levee, and floodbasin), soil, and fluvial channel environments deposited across a low-gradient al- luvial plain that graded westward into sluggish tidal rivers and estuaries (Bridge and Gordon 1985a, 1985b; Demicco et al. 1987). Although typi- cally sandstones represent deposits of laterally migrating and aggrading single-channel rivers (Bridge and Gordon 1985a), estuarine and tidal sand- stone, siltstone, and mudstone–claystone paleosol units dominate in the study area (Fig. 1). Nonmarine carbonate deposits from the Catskill clastic wedge have been discussed only rarely in the literature despite intense interest in this sedimentary succession for over 150 years. Probable non- marine calcareous beds were first reported by Johnson and Friedman (1969). The first general sedimentologic and stratigraphic descriptions were by Demicco et al. (1987), who examined a single carbonate bed and sug- gested a freshwater-marsh to shallow-lake setting for the bed. We examined Catskill Magnafacies exposures containing nonmarine car- bonate intervals in south-central New York state (Fig. 1). Demicco et al. (1987) and Bridge and Willis (1994) reported that these exposures are in the lower part of the Oneonta Formation (Fig. 2). Three stratigraphic sec- tions were measured and described in detail (Fig. 3). Because of the limited nature of the outcrop exposures, lateral control was poor, although in the Davenport Quarry locality, a single carbonate bed is exposed continuously for over 110 m.