Diagenetic apatite character and in situ ion microprobe U–Pb age, Keeseville Formation, Potsdam Group, New York State

Abstract

An occurrence of diagenetic fluorapatite cement is documented within the Cambro-Ordovician Keeseville Formation, Potsdam Group, near Chateaugay in New York State. The fluorapatite cement occurs as stratiform layers within ephemeral fluvial quartz arenites, which have been reworked by aeolian processes prior to burial. The paragenetic sequence includes the following: compaction of dust-rimmed grains → quartz cementation → minor kaolinite → fluorapatite cementation followed by secondary dissolution porosity and telogenetic hematite cementation. Mesogenetic illitization of kaolinite may have taken place prior to or following fluorapatite cementation. The fluorapatite occurs as elongated bladed crystals that characteristically contain ladder-like, inclusion-rich cores running parallel to crystal length, surrounded by clearer rims, and larger blocky crystals towards the middle of interstices. In situ SHRIMP analyses of blocky fluorapatite crystals yield a U–Pb age of 486 ± 29 Ma, indicating that the cement formed during mesogenetic burial processes and (or) during fluid flow driven by Taconic orogenic events. There is no obvious source of phosphorous for the fluorapatite cement within the Potsdam Group, but phosphorous-rich lithologies are known from the adjacent basement of the Adirondack Dome. Phosphorous-rich fluids may have been derived from these basement lithologies. The occurrence of the rare fluorapatite cement in the Keeseville Formation adjacent to the Chateaugay Lake Fault raises the possibility that alkaline phosphatic fluids were focused within the fault and migrated laterally away from the fault into the host Keeseville Formation to form stratiform fluorapatite cement in the sandstone.

Early Paleozoic rifting and reactivation of a passive-margin rift: Insights from detrital zircon provenance signatures of the Potsdam Group, Ottawa graben

“…Landing et al also contend that we have made numerous biostratigraphic errors in correlation. However, our framework uses age constraints from all available documented and newly published fossil ages from the Ottawa graben Potsdam succession (Walcott, 1891;Flower, 1964;Fisher, 1968;Greggs and Bond, 1972;Brand and Rust, 1977;Salad Hersi et al, 2002;Dix et al, 2004;Landing et al, 2009;Lowe et al, 2017), augmented with age constraints from available paleomagnetic (Seguin et al, 1981) and new radiometric ages (Gall et al, 2017). Precise depositional ages are lacking from most of the Ottawa graben Potsdam succession due to an absence of volcanic ash beds and fossils, leaving much of the stratigraphic age interpretation to be based on the relative ages of units, the nature of stratigraphic contacts, the thicknesses and thickness variability of stratal units, the distribution of depositional lithofacies, detrital composition, and sediment provenance, bracketed where possible by sparse age-diagnostic fossils.…”

“…Although lithologically similar to the Theresa, the Galway is an older unit confined to the Appalachian Basin. Paleontology, paleomagnetic data, and U-Pb geochronology (e.g., Fisher, 1968;Greggs and Bond, 1972;Brand and Rust, 1977;Seguin et al, 1981;Salad Hersi et al, 2002;Dix et al, 2004;Landing et al, 2009;Gall et al, 2017;Lowe et al, 2017) suggest that coeval strata in the Ottawa graben were deposited in mainly ter-restrial to marginal marine environments and thereby represent a depositional continuum from hinterland terrestrial sedimentation (the Ottawa graben) to marine shelf carbonate and clastic sedimentation during the Late Cambrian (northern Appalachian Basin; e.g., Lowe et al, 2017).…”

Geochemical Characteristics of Dolomitic Phosphorite Containing Rare Earth Elements and Its Weathered Ore

“…If rare earth elements are adsorbed on clays or other minerals, they (REE) can generally be leached out by inorganic salts [33][34][35]. In this experiment, a 5 g composite sample was leached with NH 4 Cl and NaCl for 2 h in 100 mL inorganic salts with different concentrations and the results are shown in Figure 6.…”

“…The leaching rate of rare earth increases slowly with increasing concentration of inorganic salts until at 2.6%, which indicates a low amount of adsorbed REE. Taking into account experimental errors, its content is likely to be between 2% and 3% [33][34][35][36].…”

Groundwater silcrete linked to brine migration in a continental rift: An alternative to the near-surface model of silcrete

“…These field relationships, described in detail below, suggest a role of faults as conduits for silicifying fluids. Notably also, fluid migration along faults leading to the diagenetic precipitation of apatite, calcite, sulphides, hematite, and monazite in Potsdam strata have been documented in nearby parts of the St. Lawrence Rift along the northern margin of the Adirondacks (Selleck, 2005;Allaz et al, 2013;Gall et al, 2017). To test this hypothesis, the paragenesis of silica cements and thermometry and petrography of their fluid inclusions are documented to constrain the potential sources and migration pathways of the silica-bearing fluids for this silcrete.…”