Vertical Grain-Size Progressions as an Aid in Depositional Environment Interpretation of Queen City Formation (Eocene), East Texas: ABSTRACT

Abstract

Vertical grain-size progressions of sand deposits in the Queen City Formation (Eocene) of east Texas, were studied to find textural patterns capable of distinguishing depositional environments. Results from this study indicate that certain groups of environments are easily distinguished from other groups. Lower point bar, fluvial distributary channel, and distributary-mouth bar deposits are more readily differentiated from distal bar, lower shoreface, and upper point bar deposits by their coarser mean grain size and mode, higher sand content, and more prevalent saltation mode and smaller suspension component. The lower point bar may have the coarsest mean grain size and mode. Lower shoreface deposits may be distinguished from upper point bar and distal bar sands by having a higher sand content and a consistent 3.5 phi suspension mode. Flood-tidal deltaic sands are characterized by their consistent mean grain size, mode, sorting, and predominance of the saltation mode throughout a thick single sequence. Tidal-flat sands resemble certain fluvial and fluvial-deltaic sands. The overlap in grain size traits among many of the environments is attributed to the well-sorted and fine-grained nature of the source for the Queen City sand, similarities in transport mechanisms among environments and, to a lesser degree, diagenetic changes in themore » original grain size distributions.« less