Norwick, Stephen
http://hdl.handle.net/10211.1/374
2024-03-28T13:44:54Z(Abstract) Healdsburgite - a New Tektite and Associated Tektite Strewnfield in North Central California
http://hdl.handle.net/10211.1/1574
(Abstract) Healdsburgite - a New Tektite and Associated Tektite Strewnfield in North Central California
Erickson, Rolfe; Norwick, Stephen; Byrd, Caitlin; Deino, Alan
A Distinctive Glass Clast Population In numerous locations in Sonoma and Solano Counties in north central California, over an area of ~ 200 km2, distinctive ~ 1-5 cm dominantly ovoid glass clasts are found as part of the pebble population in young sediments. They are composed of black massive aphyric nonvesicular glass whose surfaces are totally covered with a texture of adjoining small deep pits and grooves. The pits are hemispherical, 1-10 mm across, and join at sharp edges composed of straight segments. The grooves, where present, are the width and depth of the pits and may be up to several cm long and vermicular. Some clasts have internal layering resembling flow textures. These glass objects were brought to our attention by a local resident, Ms. Diane Moore, about 20 years ago. Four of these glass clasts from widely separated locations in the exposure area have been dated by the laser incremental-heating Ar39/Ar40 method at the Berkeley Geochronology Center, with an age of ~ 2.81 Ma (upper Pliocene). The four samples have mutually overlapping ages at one sigma. Chemical analyses of the 10 major and 50 minor elements, of four widely separated clasts, were obtained at commercial laboratories. The clasts are all rhyolites and cluster tightly on the TAS diagram of Le Maitre et al (2002). All available data show that all these pitted and grooved clasts are part of a single population. II. The Clasts are Tektites We believe these distinctive glass clasts to be tektites for the following reasons: 1. Pits are always present and wholly cover the clast surface. Perhaps half the clasts also have distinctive irregular vermicular grooves superimposed on the pitted surface. This surface pattern is like those on other long-recognized ‘classic’ tektites, like indochinites. The clasts look like tektites; compare McCall (2001, Figure 2.30) for example. 2. The clasts show no significant weathering. Once cleaned of adhering sediment, they are solid and vitreous. There are also no cases of partial development of the distinctive surface texture, as might be expected if it were a consequence of in situ weathering. 3. The clasts do not have a detrital origin; they are not obsidian pebbles. The pit and groove pattern, which is uniformly well developed on clasts throughout the distribution area, is fragile and could not have survived much transport. 4. The clasts are not volcanic in origin (i.e., ‘apache tears’). The pit and groove pattern contrasts with the relatively smooth surface of apache tears, and the clasts bear no resemblance to lapilli. Their distinctive appearance and uniform age and chemistry suggests that these objects are tektites in a strewnfield, only a small part of which has been identified to date. No related impact site has been identified, but clast composition suggests a continental target. We suggest these clasts, heretofore informally called Healdsburg glass, be recognized as tektites and called healdsburgites, in the manner of other tektites. A public domain PDF format copy of this poster will be available for download in the digital archive in the Sonoma State University library.
2012-01-01T00:00:00Z(Poster) Healdsburgite - a New Tektite and Associated Tektite Strewnfield in North Central California
http://hdl.handle.net/10211.1/1643
(Poster) Healdsburgite - a New Tektite and Associated Tektite Strewnfield in North Central California
Erickson, Rolfe; Norwick, Stephen; Byrd, Caitlin; Deino, Alan
2012-01-01T00:00:00ZLessons from a Mixed Deterministic Stochastic Model of Periglacial Gnamma Development.
http://hdl.handle.net/10211.1/1426
Lessons from a Mixed Deterministic Stochastic Model of Periglacial Gnamma Development.
Norwick, Stephen
A theory of periglacial gnamma development in Chile, Minnesota, and
Portugal claims that the maximum depth of gnammas (h) divided by the
maximum depth of water which can be held by the gnammas (u) can be used
to identify numerous periods of gnamma initiation on the rock surfaces.
Surprisingly, h and u are positively correlated in the real data but must be
negatively correlated in the theory. A deterministic computer model shows
that if the rate of deepening of the gnamma is more rapid than in the
spillway connected to the gnamma, h and u must be positively correlated as
in the data. The simulations also show that it is more likely that all the
gnammas on a surface develop at about the same time, a few centuries after
the surface is exposed, and after that, few if any new gnammas are formed.
The models also explain why the frequency distributions of h/u are
asymmetric and skewed toward the small size gnammas. In the simulations,
and on the outcrop, h/u approaches a steady state after thousands of years
that is a function of the average rate of weathering of rock, not the initiation
of new sets of gnammas.
2012-04-19T00:00:00ZGravity, Levity, Sin, Physics and a Little Astronomy: How the Idea of Gravity Expressed the Attitudes of the Greeks, Romans, Medieval, and Modern European Cultures toward nature
http://hdl.handle.net/10211.1/853
Gravity, Levity, Sin, Physics and a Little Astronomy: How the Idea of Gravity Expressed the Attitudes of the Greeks, Romans, Medieval, and Modern European Cultures toward nature
Norwick, Stephen
This is a history of the theory of gravity from Aristotle to Newton. It is the thesis
of this essay that the history of the feelings about gravity contains a message about
the changes in attitudes toward nature that occurred in European cultures in the last
3000 years. Hellenic and Hellenistic people revered gods who were associated with
nature, and their attitudes toward gravitation expressed this positive feeling. The
transition to Christianity was associated with the development of very negative
feelings about nature that is clearly demonstrated by the moral character of the
medieval theory of gravitation. The revolutions, that we call "Copernican" and
"Newtonian" were, for the theory of gravity, a single rather slow evolution, and
represented a great improvement in the value that European society placed on
nature.
2011-05-27T00:00:00Z