Improved Constraints on Sedimentary Environments of Palygorskite Deposits of the Hawthorne Formation, Southern Georgia, from a Detailed Study of a Core

Abstract

AbstractThe sedimentology and mineralogy of a 2.5 m core from a palygorskite deposit of the Miocene Hawthorne Formation, southern Georgia is described. The lithology involves laminated clay-rich sediment composed of ∼90% clay and 10% sand, with six clay-pebble layers present. Sand to pebble-size clasts of phosphate material are common throughout the core. The sand laminations are probably flood-related and the clay-pebble layers are storm deposits, with the pebbles being derived locally from subaerial environments. Phosphate clasts are reworked bone material.The sands are quartz-rich and are subarkosic in composition with average quartz counts of 86.50% and average total feldspar counts of 11.50%. Heavy minerals observed include orthopyroxene, clinopyroxene, amphibole, zircon, rutile, garnet, tourmaline, kyanite, muscovite, biotite, spinels and opaques. Palygorskite fibers dominate the clay-size fraction of the samples and comprise ∼80–90% of sample material with smectite comprising the remainder. Hydroxylapatite comprises ∼3% of sediment volume and occurs as individual euhedral hexagonal crystals and as clusters of crystals.Investigation of this core suggests that the palygorskite deposit represents a dynamic system with regular flooding and storm deposition being common. Mineral composition of sands may be useful for stratigraphic correlation of palygorskite deposits in the Apalachicola Embayment. This study supports the general environmental interpretations of previous workers for the palygorskite deposits of southern Georgia, but provides greater detail.