Absolute pollen deposition in a Connecticut lake over a 4000-year interval has been estimated from pollen frequencies in a core of late-glacial sediment dated by radiocarbon techniques. The rate of total sediment accumulation as measured after burial was statistically constant at 0.036 centimeter per year, but the rate of deposition of pollen grains onto the sediment increased from 600 to 900 grains 14,000 years ago to 9000 per square centimeter per year 10,000 years ago. A major increase in the deposition of tree pollen occurred about 11,500 years ago, at the beginning of the spruce pollen zone. Presentation of data in conventional (percentage) form masks the magnitude of this change and distorts many of the changes in accumulation rates for individual types of pollen; moreover it magnifies statistical variation in the herb zone where all pollen is scarce.

The following list of dates, measured since the publication of Yale IV, includes a few repetitions of published dates, noted as such by the addition of bis to their number. One of these (Y-140 bis) was a new preparation of CO2 from a sample previously measured as acetylene; the others are rechecks of repurified CO2, repeated because instrumental difficulties plagued our laboratory throughout the year beginning in September 1958 and might have affected some dates published in Yale IV. No important differences were found, however. Several measurements of geochemical interest, on lake water and other lacustrine materials for which C13 analyses have been reported (Oana and Deevey, 1960), are not included here but will form the subject of a separate paper.

One of the series of "Yale natural radiocarbon measurements, II" [ Science 122, 954 (1955)], by Richard S. Preston, Elaine Person, and E. S. Deevey, was incorrectly reported through a technical error. The date for sample Y-293A (South Haven, Mich.: peat) was 10,790 ± 200 yr, not 9500 ± 250 yr as reported on page 958.

Research Article| November 01, 1956 SEDIMENTS OF LAKE PATZCUARO, MICHOACAN, MEXICO G. E HUTCHINSON; G. E HUTCHINSON OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY, NEW HAVEN, CONNECTICUT; ACADEMY OF NATURAL SCIENCES, PHILADELPHIA, PENNSYLVANIA; OSBORN ZOOLOGICAL LABORATORY, YALF UNIVERSITY, NEW HAVEN, CONNECTICUT Search for other works by this author on: GSW Google Scholar RUTH PATRICK; RUTH PATRICK OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY, NEW HAVEN, CONNECTICUT; ACADEMY OF NATURAL SCIENCES, PHILADELPHIA, PENNSYLVANIA; OSBORN ZOOLOGICAL LABORATORY, YALF UNIVERSITY, NEW HAVEN, CONNECTICUT Search for other works by this author on: GSW Google Scholar EDWARD S DEEVEY EDWARD S DEEVEY OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY, NEW HAVEN, CONNECTICUT; ACADEMY OF NATURAL SCIENCES, PHILADELPHIA, PENNSYLVANIA; OSBORN ZOOLOGICAL LABORATORY, YALF UNIVERSITY, NEW HAVEN, CONNECTICUT Search for other works by this author on: GSW Google Scholar Author and Article Information G. E HUTCHINSON OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY, NEW HAVEN, CONNECTICUT; ACADEMY OF NATURAL SCIENCES, PHILADELPHIA, PENNSYLVANIA; OSBORN ZOOLOGICAL LABORATORY, YALF UNIVERSITY, NEW HAVEN, CONNECTICUT RUTH PATRICK OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY, NEW HAVEN, CONNECTICUT; ACADEMY OF NATURAL SCIENCES, PHILADELPHIA, PENNSYLVANIA; OSBORN ZOOLOGICAL LABORATORY, YALF UNIVERSITY, NEW HAVEN, CONNECTICUT EDWARD S DEEVEY OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY, NEW HAVEN, CONNECTICUT; ACADEMY OF NATURAL SCIENCES, PHILADELPHIA, PENNSYLVANIA; OSBORN ZOOLOGICAL LABORATORY, YALF UNIVERSITY, NEW HAVEN, CONNECTICUT Publisher: Geological Society of America Received: 23 Aug 1955 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1956, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1956) 67 (11): 1491–1504. https://doi.org/10.1130/0016-7606(1956)67[1491:SOLPMM]2.0.CO;2 Article history Received: 23 Aug 1955 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation G. E HUTCHINSON, RUTH PATRICK, EDWARD S DEEVEY; SEDIMENTS OF LAKE PATZCUARO, MICHOACAN, MEXICO. GSA Bulletin 1956;; 67 (11): 1491–1504. doi: https://doi.org/10.1130/0016-7606(1956)67[1491:SOLPMM]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The recent sedimentary history of Lake Patzcuaro was investigated by pollen analysis in 1944, and a dry climatic phase, probably hundreds or thousands of years ago, seemed to be indicated by maximal abundance of nonarboreal (grass, chenopod, and composite) pollen. The work of Sears on Lake Texcoco, 250 km east, prompted a reinvestigation of the Patzcuaro pollen sequence and a study of the chemistry and the diatom flora of the sediment cores. On the basis of Sears' Index of Humidity (the ratio of Quercus +Alnus+ Abies pollen to the total arboreal pollen, which is minimal in the driest intervals when Pinus is most abundant), there is clear evidence of a dry phase within the zone of abundant nonarboreal pollen, but the latter now seems to have no direct climatic significance. Instead, since the nonarboreal pollen, particularly its chenopod (+ amaranth?) component, is most abundant during moist phases just preceding and just following the newly defined dry phase, the fluctuations of nonarboreal pollen seem to reflect agricultural practice and, ultimately, demographic history.The sequence as now interpreted correlates remarkably well with that from the Valley of Mexico, and, using the archaeologic dates that Sears established there, there are: zone D, pre-Archaic (before 1500 B.C.), dry; zone C, early and middle Archaic (1500–500 B.C.), moist; zone B, late Archaic-Teotihuacan (500 B.C.–A.D. 900), climate fluctuating, but with at least one markedly dry episode; zone A, Nahua (A.D. 900–1521), moist. The few archaeologic data and the folklore from the Patzcuaro region tend to confirm this interpretation. There are some differences between the Patzcuaro and the Texcoco pollen sequences, notably in the less well marked character of the last (moist) phase in Patzcuaro.Of particular interest is the evidence of relatively intense aridity shown in the cores at the inferred late Archaic or Teotihuacan level: a minimum of Sears' Index corresponds to a strong increase in the calcium content of the sediments, and to a zone having only shallow-water benthic and littoral diatoms, above and below which the normal planktonic diatom flora is recorded. The two independent evidences for increased evaporation or reduced rainfall suggest that the dry phase was due to climatic causes and not to culture or volcanism. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

op. cit., for zinc amalgam confirm this conclusion. For iron, on the other hand, the anodic surface becomes larger, the higher the value of current density externally applied for anodic polarization, and, hence, A is usually less than unity. 22 D. Leussing and I. Kolthoff, J. Am. Chem. Soc., 75, 2476 (1953).

: Tabulated assay data for modern wood and shell corrected to 100% carbon indicated that modern wood gives a consistent series of C14 values; however, modern marine shell provided some contradictions. The data of 10 analyses agreed in 2 cases with published evidence that the marine-shell C14 content is 10% higher than modern wood; 5 cases agreed very closely with modern wood. In 1 case, the mollusk flesh showed the same specific activity as the shells. Possible methods of depositing calcium carbonate by mollusks are suggested to explain these differences. The stratigraphy is included of the moa deposit at Pyramid Valley in the South Island of New Zealand. Features include the use of radiocarbon dates to confirm interhemisphere correlation of late- Pleistocene climate sequences and the age of the moas. The tabulated ages of calcareous samples were calculated on the assumption that the shell and wood C14 contents are identical and that the modern shell contains 10% more C14 than modern wood. The age of the moa (670 yr) is presumed to be correctly given by the age of the organic fraction of its crop contents. The date suggests that Dinornis as well as Euryapteryx (large and small species) were contemporary with man and were exterminated by him.The peat-age confirmation (suggested to be sub- Boreal on pollen-sequence basis) is considered the most important stratigraphic result of the study.