Iron-Stained Quartz as Record of Recent Reworking of Older Sediment by Natural and Anthropogenic Processes, Rio Grande Delta, Texas

摘要: The iron-coated quartz grain record in the Rio Grande deltaic plain southern Texas, determined from petrologic study of surface and core samples, does not show distribution pattern typically observed other deltas. ironstained patterns this delta are highly irregular both time space, do display low proportions ( 20%) stained grains underlying Pleistocene alluvial strata. Intermediate (> 10%) to large (>20%) amounts partially plus fully coated particles measured most surficial samples 10 sampled depositional environments Holocene sections. This is a result (1) pre-dam fluvial transport older, iron-stained material basin areas cover its Gulf Mexico margin, (2) erosion recent reworking landward sediment terrains now submerged on inner mid-shelf, (3) possible situ formation lower valley proper, (4) intensified post-depositional upper sections by human activity during past century. We suggest that anthropogenic has replaced natural processes, especially transport, as primary means mixing older onto younger plain. delta's present interpreted 'palimpsest' comprising admixtures reworked modern relict material, particularly where formerly buried continues be artificially exposed modified. anticipate proportion will remain high at replace dominant process.