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Quantitative Paleolimnology and Fossil Conchostracans

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Quantitative Paleolimnology and Fossil Conchostracans Analysis of Ellsworth Mountains and The gabbroic rocks are exposed in the northeastern part of the Ruppert Coast (including Mount Giles, Ruppert Coast Geologic Data Cape Burks, and parts of the Mount Gray area). Some of the outcrops display a distinct layering trend- BERNHARD SPORLI ing from ENE to NNE. Andesite flows predominate and in the metavolcanic suite; a few rhyolites and agglo- merates are also present. Structural trends in the de- CAMPBELL CRADDOCK formed flows average northwest. Both of the mafic groups are intruded by a com- Department of Geology and Geophysics plex suite of granitic rocks. In the western part of the University of Wisconsin (Madison) area, quartz monzonites are most common, and in the eastern part (in the vicinity of Mount Gray), quartz During the past year, laboratory study of rocks syenites predominate. The rocks contain much par- obtained in the Ellsworth Mountains has continued, tially assimilated material. Peculiar spherical mafic and work was initiated on material collected on the inclusions, probably similar to the proto-orbicules de- Ruppert Coast of Marie Byrd Land in the 1966-1967 scribed by Leveson (1966), are present at Landry season (Sporli and Craddock, 1967). In June 1967, Peak. Various felsic and mafic dikes cut the intrusive these activities were transferred from the University granitic rocks. Some of these dikes are offset by small of Minnesota to the University of Wisconsin. faults. Information gathered during four seasons in the The compilation of a general geologic map of the Ellsworth Mountains has been extracted from field Ruppert Coast and of several detailed sketch maps notes and is being plotted on maps. Structural and constructed from trimetrogon and hand-held-camera sedimentological measurements were registered on photographs has been completed. data cards and are being plotted on hemispheric dia- grams with the help of a computer program. The re- References suits of this study are incomplete, but they suggest a complex geometry for the large anticlinorium of the Leveson, D. J. 1966. Orbicular rocks; a review. Geological Ellsworth Mountains and the presence of interference Society of America. Bulletin, 77: 409. Sporli, B. and C. Craddock. 1967. Geology of the Ruppert folds in parts of the chain. Coast. Antarctic Journal of the U.S., H (4): 94. Petrographic study has centered on the mafic in- trusive and extrusive rocks exposed in the Heritage Range and the southern tip of the Sentinel Range. Modal analysis is nearly complete, but the exact classi- Quantitative Paleolimnology and fication of the rocks is difficult because of their ex- treme alteration. Continued petrographic study of the Fossil Conchostracans sedimentary rocks has shown that subgraywackes and quartzose sandstones are as abundant in the Crash- PAUL TASCH site Quartzite as true graywackes. Department of Geology Dr. Adolf Seilacher (University of Tubingen) Wichita State University kindly appraised several specimens containing trace fossils from beds equivalent to the lower part of the Some aspects of the paleolimnology of the fossil- Crashsite Quartzite in the northwestern Heritage conchostracan Leaia zone (Ohio Range) have been Range. An Ordovician age is indicated by traces deciphered. Others are still being studied. Fifteen closely related to Cruziana furcifera dOrb. leaiid (ribbed) and two lioestheriid (unribbed) The geologic map of the Heritage Range is under generations intermittently inhabited Permian ponds compilation. With the availability of the new topo- or pools on a coastal floodplain during intervals of graphic bases (1:250,000 Reconnaissance Series, 137± years (Tasch, 1967). sheets "Union Glacier" and "Liberty Hills") the con- Conchostracan occupancy during less than 1/2 struction of reliable cross sections has become feasible. centuries corresponded to a slightly fluctuating phos- A major part of the year has been devoted to the phate paleosalinity of 30-31 parts per mille (ppt). study of the Ruppert Coast materials. Chemical an- Where they disappear from the section, paleosalinity alyses and age determinations are still in progress, attained 33 ppt. Cessation of clam shrimp occupancy but petrographic work, including about 80 modal is attributed to this initial increase of salinity (Tasch analyses, has been completed. The rock collection has and Gafford, 1968). been divided into four groups—metagabbros, meta- Lower in the formation, beds of equivalent lithology volcanics, granitic intrusives, and dikes. had paleosalinities of 29-31 ppt. These findings per- September-October 1968 179 mit a new kind of index for a sedimentary formation correlations between specific fossil conchostracan —the paleosalinity signature. Thus, for the Mount zones in Antarctica and similar zones on other South- Glossopteris Formation, it was found to be 29 to 33 ern Hemisphere continents have been indicated for ppt. (With a built-in correction factor, in this inst- both the Permian and the Jurassic. These correlations ance, negative, i.e.,-4.0 ppt, the salinity would be re- must now be further documented by additional col- duced to 25-29 ppt, as compared with 35 ppt for lections and studies. normal seawater.) Among incidental findings for which results have Partitions of samples into freshwater or marine, been finalized are the detection of a mineral not based on trace elements, tend to confirm phosphate previously reported from Antarctica and a new trace paleosalinity determinations. The latter determina- fossil. X-ray diffraction analysis of the mineral which tions, as this study suggests, may help to resolve occurred in salt efflorescences of the Ohio Range anomalous results for the same sample between dif- showed it to be magnesium sulphate hexahydrite ferent geochemical partitions (i.e., boron alone or (Tasch and Angino, 1968). Other salt efflorescences boron vs. vanadium or gallium). Accordingly, a included pure gypsum and gypsum admixed with hex- sample that plots as both marine and fresh may be ahydrite in the Ohio Range and with calcite in the shown to be brackish by parts-per-mule determina- Sentinel Range. A new trace fossil (Cochlichnus tions. antarcticus) in the Mount Glossopteris Formation of These paleontological/geochemical studies mark the Ohio Range was represented by a vermiform the advent of a new field of investigation: quantita- excavation in an in situ floodplain siltstone that was tive paleolimnology. (In geochemical studies of trace about 30 m above the base of Mercer Ridge. It has elements, the brackish-water component among sam- been described and figured (Tasch, 1968). SAMPLE 021 p6 2 021.18 Geochemical analysis of trace elements in selected argil- 11 V 0212 6 lites (Mount Glossopteris Formation, Mercer Ridge, 021.3 Ohio Ridge). Details are in Tasch and Gafford (1968). Fossil Leaia zone (station 0) includes beds 0-21.13 021.4- -- (oldest) through 0-21.2 (youngest). Stations I and II O2I STA. A N are time equivalents of station 0 (bed 21.8, lower 0.3 feet) and are 20 and 65 feet north of station 0 respec- 02 8UP 0 2- tively. Beds 0-18 (oldest) and 0-20 (youngest) are <- > - closer to the base of the ridge and far below the Leaia 021,8 LOW 0.3-,e zone. Sample 0-17, morainal debris far to the south- 021.10 west, is of same lithology as the other samples. Above 02112- ?ko_ bed 0-21.2, fossils disappear from the section where 021.13 paleosalinity changes from 31 parts per mile (ppt) to 020 33 ppt. Accompanying trace-element changes are most marked for V and K. (Ni-Nickel, Ga-Gallium, Pb-Lead, 019- - - - B-Boron, Cu-Copper, and Cr-Chromium are shown in 018 parts per million (ppm), and K-Potassium, in percent). 017 O 25 50 75 100 200 300 400 500 TRACE-ELEMENTS(PPM) (Prepared by E. L. Gafford) References pies, if one exists, is not defined. Quite by chance, i.e., both methods—a way to detect this Elliot, David H. and Paul Tasch. 1967. Lioestheriid con- by employing chostracans—a new Jurassic locality and Gondwana component may have been found as described above.) correlations. Journal of Paleontology, 41: 1561-1563. Equivalents of the fossil clam shrimps (lioestheriids) Tasch, Paul. 1967. Antarctica leaiid zone: seasonal events. from the interbeds of the Kirkpatrick Basalts (Queen Asociación Geológica Argentina. Restmenes, p. 16-17; Alexandra Range) occur in the presumed Jurassic ditto, Asociación Geologica Argentina. Special Publica- tion. In press. volcanic sequence of Victoria Land and in association Tasch, Paul. 1968. A Permian trace fossil from the antarctic with the Lebombo volcanics of Mozambique (Elliot Ohio Range. Kansas Academy of Science. Transactions, and Tasch, 1967b). They occur in the Jurassic of 71(1): 33-37. India as well. Tasch, Paul and Edward L. Gafford. 1968. Paleosalinity An additional locality on the Mauger Nunatak, of Permain nonmarine deposits in Antarctica. Science, 160: 1221-1222. found by David Elliot this past season, demonstrates Tasch, Paul and Ernest E. Angino. 1968. Sulfate and car- that such clam-shrimp beds are more widely distrib- bonate salt efflorescences from the antarctic interior. In uted than had been thought. In terms of drift theory, preparation. 180 ANTARCTIC JOURNAL.
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