Sedimentology and petrography of a lower cambrian transgressive sequence: Altona formation (Potsdam group) in Northeastern New York

Abstract

The Altona Formation, the oldest unit in Potsdam Group, is a heterolithic shallow marine deposit recording fair weather and storm deposition in a marginal marine setting associated with the onlap of the Laurentian Craton in the latest early Cambrian (Olenellus Zone) to middle middle Cambrian (Bathyuriscus-Elrathina Zone). Six lithofacies are recognized within the Altona Formation including non-marine sheet flood, nearshore bay/estuary, and upper and middle shoreface. These lithofacies occur in the stratigraphy in response to relative sea level change and sediment supply. Onlap of Precambrian Grenville basement represents initial transgressive systems tract deposition which was succeeded by highstand deposition, and with it, diminished terrigenous input and the onset of carbonate deposition. Renewed input of terrigenous sand in the upper third of the Altona resulted in shoreline progradation followed by a second cycle of transgressive and highstand systems tract deposition. The overlying Ausable Formation marks the transition to falling sea level and onset of non-marine deposition. Analysis of gamma ray log data confirms that terrigenous sediment input varied through the stratigraphy, which is interpreted as a response to rising sea level trapping sediment on the coastal plain. Predominantly compositionally immature sandstone, the Altona also contains arenaceous dolostone, dolostone and silty shale. Modal analysis of the sandstones indicates an arkosic composition for the sandstones, with an accessory mineral suite including apatite, ilmenite, rutile, and zircon. This accessory suite, along with detrital zircon ages, indicates an Adirondack massif source rock.