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A 5.4-m sequence of peat and marl overlying a basal clay in a northern Belize wetland was studied to assess salinity changes over the past 7000 yr. The distribution of ostracods, gastropods, and foraminifers revealed initially freshwater conditions in a terrestrial wetland, changing to at least mesohaline conditions by about 5600 yr B.P. The mesohaline conditions corresponded to the formation of an open-water lagoon (and precipitation of a lacustrine marl) that was contemporaneous with rapidly rising sea level in the area. A mangrove peat filled the lagoon by 4800 yr B.P. probably as a result of increasingly shallow waters as sea level rise slowed and marl precipitation continued. A new lagoon began to form sometime after 3400 yr B.P. Freshwater ostracods and gastropods found in the marl of this lagoon suggest that it formed under near-limnetic conditions. Freshwater input likely resulted from massive deforestation by the Maya that began by 4400 yr B.P. Subsidence of the mangrove peat likely permitted the formation of a lagoon. A peat has filled the lagoon since at least 500 yr B.P.

Lake Theo (Briscoe County, Texas) is a well stratified archaeological site with Paleoindian (Folsom, Plainview) and Archaic occupations. It is located immediately east of the Southern High Plains (Llano Estacado). Preliminary field and laboratory investigations of site stratigraphy, soils, and microbiology were initiated in order to reconstruct late Quaternary paleoenvironments and date the Paleoindian occupations. The site contains a series of ten late Quaternary fluvial, and possible aeolian, deposits; and five soils (ranging from weakly to moderately well developed) formed therein. Radiocarbon ages of 9950 ± 110 years B.P. (SMU-866) and 9420 ± 85 years B.P. (SMU-856) were determined on humates from the bottom and top (respectively) of a thick, slowly aggrading, buried A horizon. The lower date is associated with a Plainview occupation and immediately overlies a Folsom occupation. Comparison of dates and associated stratigraphic and pedologic data with other sediments and soils in the section indicates that during the past 12,000 years, most sedimentation was relatively rapid and sporadic with intervening periods of soil formation of varying lengths. Citrate soluble phosphorous analysis of the soils did not show notable evidence of intense human occupation at any time. Invertebrates recovered indicate a progressive, local extirpation of terrestrial gastropods since Folsom times. The progression is a result of decreased effective precipitation. The most marked stage of extirpation occurred during deposition of Unit 7 (9000 to 8000 B.P.).

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