Beck Spring Dolomite Research Articles

New microbial fossils from ∼1.3 billion‐year‐old rocks of Eastern California

New types of microbial fossils and new occurrences of fossils previously reported only from the Beck Spring Dolomite of the Pahrump Group are now recognized from each of the three formations of the Pahrump Group (Crystal Spring Formation, Beck Spring Dolomite, and Kingston Peak Formation) approximately 1.3 X 10° years old. Comprising perhaps eight or nine distinctive forms, these fossils are characteristically preserved as faint ghostlike structures whose low‐contrast outlines are clearly revealed only when illuminated by a xenon lamp and recorded on high‐contrast film. They represent a distinctive, previously overlooked or neglected type of preservation that has significantly extended the known distribution of microbial fossils in the Pahrump. They include the oldest occurrence known to us of filaments designatable as Girvanella and apparently the first from rocks of pre‐Phanerozoic age. Similar fossils were also found, using the same techniques, in the Chuar Group of the Grand Canyon and in the Uluntui ...

Possible Algal Microfossils from the Late Pre-Cambrian of California

SEVERAL organically preserved microbiotas in cherts of Pre-Cambrian age have been described during the past few years1–10, some with structures such as cell walls and intracellular organelles intact8,9. Pyrite and/or haematite replacement of possible Pre-Cambrian microorganisms, with loss of structural detail, has also been reported10,11. Crystals of pyrite 5–10 microns in diameter and closely spaced along organic filaments “resembling a string of beads” are known from the Gunflint Iron Formation of Ontario, Canada10. “Chains of cells”, which our preliminary examination suggests are haematite crystals, were reported from the Belt “series” of Montana11. We here describe similar crystalline chains interpreted as biological in origin from the late Pre-Cambrian Beck Spring Dolomite of southern California.

PROTEROZOIC EUCARYOTES FROM EASTERN CALIFORNIA

Both procaryotic and eucaryotic nannofossils occur in chert from the upper Beck Spring Dolomite (Pahrump Group) in northeastern San Bernardino County, California. These fossils include the oldest reasonably certain records to date of chlorophycean and chrysophycean algae, and hence of the eucaryotic or mitosing cell. Associated with these are cyanophycean procaryotes of still more ancient affinities. Indirect radiometric evidence implies an age of 1.2 to 1.4 aeons (1.2 to 1.4 x 10(9) years) for the enclosing rocks. Associated stromatolites are consistent with such an age assignment.

Petrology and Depositional Environments of the Beck Spring Dolomite (Precambrian), Kingston Range, California

ABSTRACT The Beck Spring Dolomite (upper Precambrian), Kingston Range, California, is divided into three informal members: lower laminated--150 to 200 m thick, composed of alternating laminae of pelletal and mosaic dolomite; middle oolitic--100 to 150 m thick, composed of mosaic dolomite with oolite, pisolite, and grapestone; and upper cherty--100 to 150 m thick, similar to the middle oolitic member except that it includes stromatolites and has been partially silicified and dedolomitized. Textural evidence suggests that the lower laminated member was deposited in a supratidal environment, and the middle and upper members in shallow, agitated waters of a subtidal environment. The characteristics of the Beck Spring Dolomite are similar to those of sediments now being deposited in parts of the Ba ama Banks.

Stratigraphy and Petrology of Beck Spring Dolomite (Precambrian), Kingston Range, San Bernardino County, California: ABSTRACT

The Beck Spring Dolomite (Pahrump Group, upper Precambrian) has an average thickness of 1,300 feet in the type area, Kingston Range, San Bernardino County, California, where it is divided into three unnamed members. The lower member, 500-700 feet thick, is composed of alternating laminae of finely crystalline and medium-crystalline dolomite mosaic. Allochem ghosts are scarce but include intraclasts and pellets. The laminae are primary features modified by replacement and recrystallization. The middle member, a replaced oolite calcarenite, is 300-400 feet thick, composed of finely to medium-crystalline dolomite mosaic with abundant ghosts of oolites, pisolites, and pellet-lump intraclasts. Selective replacement by quartz is fairly common, as well as re-dolomitization in so e places. The upper member, 400-500 feet thick, resembles the middle member, but is partly laminated, has been extensively replaced by chert, and is brecciated and recemented. Allochem ghosts are similar to those found in the middle member. Although contacts are gradational, the three members can be traced throughout the type area. End_of_Article - Last_Page 467------------