Control of terrestrial stabilization on Late Devonian palustrine carbonatedeposition: Catskill Magnafacies, New York, USA

Upper Devonian (Frasnian) terrestrial strata of south-central New York cont ain palustrine and lacustrine carbonate deposited within the well-developed Catskill elastic wedge succession. These non marine limestone beds (8-50 c m thick) were repeatedly subaerially exposed and subjected to pedogenic pro cesses. Palustrine features include subaerial exposure surfaces with soil c rusts, pseudo-microkarst and microkarst, brecciation, desiccation cracks, h orizontal, planar, and circumgranular cracks, and rhizoliths. Lacustrine ca rbonate sedimentation was derived primarily from biogenically induced preci pitation 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 (delta(13)C = -4.0 to -4.7% PD B; delta(18)O from -6.8 to -8.7% PDB) reveal covariance between delta(13)C and delta(18)O values. The high degree of covariance (r = 0.75) suggests th at these Late Devonian carbonate lakes were hydrologically closed; high rat es of surface-water productivity resulted in the heavier delta(13)C values. Late Devonian carbonate lakes developed as a result of landscape stabilizat ion by the developing rhizosphere. In addition, plants of small to moderate stature functioned as elastic filters, trapped terrigenous elastic sedimen t along lake margins, and thereby permitted carbonate sedimentation to occu r in a system otherwise dominated by terrigenous clastics. These Upper Devo nian lacustrine deposits contain the oldest recognized occurrence of "palus trine" facies, The temporal distribution of palustrine carbonate deposits t herefore appears Limited to post-Silurian strata.