Depositional Environment and Mineralization of Late Mississippian Surprise Canyon Formation, a Carbonate-Clastic Estuarine Deposit, Grand Canyon, Arizona: ABSTRACT

Abstract

During Late Mississippian and Early Pennsylvanian time, a change in relative sea level caused marine invasion of ancient stream valleys cut into the top of the Redwall Limestone. These deposits are now exposed as isolated lens-shaped patches up to 120 m thick and 370 m wide in the walls of the western Grand Canyon. The basal unit of the valley fill consists of a fining-upward sequence from chert-pebble conglomerate to ripple-laminated and flat-bedded sandstone and siltstone, suggesting a transition from fluvial domination to tidal domination. The middle unit is a yellow-brown, cliff-forming skeletal limestone with a diverse marine fauna. This limestone unit has a large, distinct channel outline and commonly exhibits trough cross-strata having bimodal current directions. The dominant flow direction is upstream, suggesting a flood-tidal channel that filled with skeletal debris. Skeletal grainstone beds are commonly paired with a dark purple-brown sandy limestone, interpreted to be the ebb-tidal channel. Diagenetic patterns within the grainstone show good reserve possibilities within the flood-tidal channel. Above the limestone are mud-cracked and bimodally ripple-laminated sandstone and siltstone with interbedded algal, ostracodal limestone that suggest restricted intertidal conditions. Within the conglomerates and limestones are opaque hematitic clasts and two types of quartz grains thatmore » suggest early ferruginization and early silicification of evaporites on the newly exposed Redwall platform.« less