GLACIAL GEOLOGY OF THE ALBANY 15-MINUTE QUADRANGLE, EASTERN NEW YORK STATE

The Albany 15-minute Quadrangle (Quad) lies in the mid Hudson Lowlands of NYS. It was covered by glacial ice at least twice during the Late Wisconsinan glaciation. The glacier retreated north of the Quad during the Erie Interstade and then readvanced to Kingston. NY. Only the last advance-retreat cycle is recorded in the Quad.

Proglacial Lake Albany flooded the Hudson Lowlands as the ice retreated. Lake deposits are more than 91 m thick in preglacial channels and thin to absent over bedrock highs. Several ice margins were built in the lake; they record still-stands during ice retreat. They include the Schenectady-Niskayuna, Meadowdale-Kinderhook, McKownville-Rensselaer, and Guilderland-Hampton margins. A large delta was built at Schenectady when the ice retreated to the Schenectady-Niskayuna ice margin. Prodelta sand prograded across the northern third of the Quad.

Ice-contact subaqueous fans and deltas were deposited at the mouths of meltwater tunnels and outwash streams flowed into the lake from the uplands. Sandy to clayey silt and turbidites were deposited in front of the ice and by meltwater from adjacent valleys. Stages of Lake Albany included Hampton and Rennselaer at 107 and 102 m, and 102 m (Albany I), and 96 m (Albany II), with a brief 108 m level in-between. The 108 m level was caused by a catastrophic flood from the Mohawk Lowlands. The flood caused the level to drop 6 m to Albany II. Quaker Springs’ levels include 82 and 76 m, followed by the 67 to 49 m levels of the Coveville stage. The Fort Ann stages cut terraces from 43 to 12 m. The lower water levels did not last long because catastrophic floods repeatedly eroded the lake outlet. In addition, glacial-isostatic uplift decanted the lowlands southwards. The rebounded water planes of the Albany I and II stages are greater than 0.7 m/km north of Ravena. Quaker Spring’s gradient is 0.4 m/km and Coveville’s gradient is 0.3 m/km.

As the lake levels dropped, northwest and southwest winds scoured the exposed lake sand and built an extensive dune field. The dune-building episode lasted from Lake Albany II to the post-glacial, early Pine Pollen Zone. The modern Hudson occupies the Fort Ann flood channel. The channel at Castleton was scoured to 10 m below sea level. The Holocene Hudson River has built a tidal delta between Castleton and Catskill, NY.