Sunday, February 27, 2011

What a Geologist Sees - Part 34 - Urban Beaches

The photo above, from near the Portside Towers in Jersey City, NJ is not intended to represent the entirety of "urban beaches", but rather to consider what makes up a particular sand and where does all that stuff come from?

The darkness of the sand suggests a significant heavy mineral percentage, however it is likely that as the tide was receding, the last waves moved the lighter quartz downslope, exposing a thin veneer of heavy minerals. Under the microscope, heavy minerals are not the dominant mineral-type. As in most sands, quartz is the dominant mineral.

To get a wider perspective of the location, the large building in the left foreground is the Goldman Sachs building. In the right background is a portion of downtown Manhattan, with the Hudson River between the two. To the left of the beach is a narrow spit of land adjacent to a portion of an abandoned, historic canal.

In an effort to prevent erosion of the narrow spit, a wide variety of materials have been piled in the upper beach area, as well as miscellaneous old tires as well as other items of human flotsam and jetsam.

The remainder of the photos are to illustrate different perspectives on the beach materials that contribute to the sand chemistry with the never-ending wave action.

Under the microscope a brief examination of the sand - without concern to relative percentages - the constituents of the sampled beach sands include: 1) Angular quartz; 2) Well-rounded quartz; 3) Brick; 4) Glass; 5) Coal fragments; 6) Greenish Fe-Mg minerals; 7) Garnet; 8) Rutile; 9) Magnetite; 10) Ilmenite; 11) Slag,...

Among the particles, there are some odd, spherical grains that seem slightly magnetic, a quick guess might be magnetite, slag, or (least likely) Fe-Ni micro-meteorites. There will be some more examinations of the sand and the spheres in particular.

The Results of Accretionary Wedge #31 are Posted...

Here and Here at The Geology P.A.G.E.

Here is my humble contribution.

Enjoy.

Thursday, February 24, 2011

All Owls are Equal, But Some are More Equal Than Others

You may well remember the controversy of the 1980s and 1990s over the apparently-declining numbers of Northern Spotted Owls in the Pacific Northwest. The Spotted Owl (Strix occidentalis) population of the Western United States is actually made up of three, closely-related subspecies, the Northern Spotted Owl (Strix occidentalis caurina), the California Spotted Owl (Strix occidentalis occidentalis) and the Mexican Spotted Owl (Strix occidentalis lucida).

This source provides some information about the range and habitats of the Spotted Owls, as well as the recently-recognized competition from its close relative, the larger Barred Owl (Strix varia).

From the Answers.com link (with slight paraphrasing):

...The nearly contiguous range of the Northern Spotted Owl extends from SW British Columbia south through western Washington and Oregon through the north-central coast of California.

The range of the California Spotted Owl overlaps the range of the Northern Spotted Owl in the southern Cascade Mountain Range, and extends south through the western Sierra Nevada to Tulare County, CA. Discrete populations of the California Spotted Owl also occur in mountainous areas of coastal and southern California from Monterey County to northern Baja California.

In the United States the Mexican Spotted Owl occurs in geographically separated populations in mountain ranges and canyons of Utah, Colorado, Arizona, New Mexico, and extreme western Texas. In Mexico it ranges from Sonora, Chihuahua, Nuevo León, and eastern Coahuila through the Sierra Madre Occidental and Sierra Madre Oriental as far south as Michoacán...


For the original citations and more information, please see the Answers.com entry.

Within the realm of nature, it is not unusual for there to be more than one reason for something happening. Habitat-loss due to logging and other events, e.g., the Mount St. Helens eruptions and windstorms, has been cited as a significant cause of population declines. More recently, the apparent entry of the larger Barred Owl into the ranges of the California and Northern Spotted Owls has resulted in population declines due to the Barred Owls being: 1) More aggressive in territorial defense; 2) Having a broader (more adaptable) diet and; 3) Occurring in more varied habitats. As the Barred Owls are closely-related (having had a common ancestor in the recent past), there is some hybridization in the overlapping areas, blurring the distinction between the Barred Owl and the Spotted Owl.

So, there appears to be a combination of human influences and natural influences in the changes facing the Spotted Owls. Unfortunately (from the title-linked article), some people in the Federal Government are of the opinion that these changes need to be "stopped" by intervening and killing at least some of the Barred Owls in the range of the Northern Spotted Owls. Rather than letting "nature take its course."

As both species occupy the same niche in their habitat overlaps - thus there are niche overlaps and habitat overlaps - under entirely-natural conditions, the Barred Owl would eventually dominate the Spotted Owls, forcing the Spotted Owls to: 1) Migrate to find other habitats with less competition; 2) Engage in Resource Partitioning (finding other food sources in the same habitat) or; 3) Become extinct. It is not "fair", but it is "nature's way."

These Secondary/Tertiary Carnivores serve to keep predated species population numbers under control and though part of this issue may be due to human intervention, humans "playing favorites" among the predators may lead to "unintended consequences". It might be better for the humans to resist their temptation to "make things more fair" and just sit back, watch, and learn from this event, as it unfolds.

Playing in the Snow

While we were visiting our daughter and her family in Jersey City, NJ - for Christmas - we were gifted with the 6th heaviest snowfall in NYC history. The Jersey City-area received about 23 inches itself.

So after 2 - 3 days of playing with my grandson and faced with the beginnings of "cabin fever" (including issues with the wireless internet), I ventured out with my cameras.

The "dryness" of the snow and the almost-constant wind during and after the snowfall resulted in "sedimentary structures" and eolian, dune-like features (2nd photo) in the snow drifts.





The shifting wind directions and wind speeds interplayed with trees and artifical structures to produce a number of interesting scour and dune features analagous to what one might see at the leading edge of a dune field, prior to obstructions being totally covered by the advancing, fine-grained sand.




In all of the photos, except the second one, the wind erosion has revealed the (layered) stratification of the snow. As in the case of bedding planes in layered sediments and sedimentary rocks, the revealed layers suggest a brief cessation of deposition during the snowfall (perhaps due to increased wind gusts), when there was a slight consolidation (freezing) of the exposed snow surface, which was then followed by another round of snow deposition.


If this snow had fallen at a slightly-higher temperature and without the wind interaction, these "sedimentary structures" would not have been formed, nor preserved. Other deposition and erosion analogies could be applied in this setting, comparing the contrasting the effects of water and wind in shaping short-term and long-term landforms, both large and small.

Monday, February 21, 2011

An Interesting Geology-Related Book [Original Post Date 11/02/08]

While browsing a used book store a little over 2 years ago, I picked up an interesting book, "Volcano Cowboys", by Dick Thompson.

It is about the quantum leaps made in understanding volcanoes, especially the explosive composite volcanoes, between the time of the Mount St. Helens eruption (1980) and the Mount Pinatubo eruption (1991). Having skimmed through it and then reading through most of the first chapter, I have already learned several new things, including learning about the Osceola Mudflow.

As composite volcanoes are the tallest of the volcanoes, it is not unusual for them to have glacier-capped peaks. When an eruption suddenly melts tons of ice and snow and it mixes with the previously-erupted ash and broken rock, it can be a recipe for disaster, producing what we call lahar flows (volcanic mudflows). A lahar killed an estimated 23,000 to 25,000 people in Armero, Colombia, in the middle 1980s. An "average" lahar may have a consistency of wet concrete and carry with it boulders the size of cars and downed trees.

Mapping by USGS geologists revealed that the Osceola Mudflow was produced by a partial collapse of a portion of Mt. Rainier, about 5700 years ago. It traveled a reported 60 miles from Mt. Rainier to Puget Sound. The worst part is that today, five towns have been built on the volcanic sediments of the Osceola Mudflow. If it happened once, it is likely to happen again.

There could well have been a few human inhabitants of the Puget Sound area at that time.

Just something to consider if you ever get a job offer from the Seattle/Tacoma area.

A Brief Explanation for Any Visitors...

For those posts with [Original Post Date .......], that means the post was copied from another blog of mine, a more eclectic one that includes political rants and other stuff. This blog is just supposed to be about science. I may transfer (actually copy) a few more posts from the old blog, as time permits.

Natural Gas in North Carolina,...Perhaps [Original Post Date 05/21/09]

According to this geology.com article, technologies now being practiced in areas producing shale gas might be utilized in two Triassic "Newark Basins" on the North Carolina Piedmont, the Dan River Basin and the Deep River Basin. (I tried to copy and post the NC map shown in the linked article, but it didn't work. I also tried to find a suitable diagram of a graben basin, with no luck.)

Basically, the Newark Basins are a series of elongate graben basins that form during periods of crustal extension. When the brittle crust is stretched and broken, some sections of the crust will subside along normal (gravity) faults. These basins are related to the Triassic and Jurassic Periods when Pangea was being stretched in "preparation" of splitting to begin the growth of the Atlantic Ocean basin. Before the basins were connected and deep-enough for ocean water ingress, they existed as inland basins with lakes and swamps. Without through-flowing river systems, organic material preserved in the shales and silts of these swamps could generate natural gas and oil under certain conditions (there is already some oil (and maybe gas) production from Newark Basins in other states).

Offshore Oil Rigs and Coral Reefs Co-existing [Original Post Date 06/03/08]

Here is an article addressing some of the concerns about offshore drilling in the Gulf of Mexico.

Offshore oil platforms have operated for decades at the Flower Garden Reef. Here is more on this reef, off the Texas/Louisiana coast. The benefits of rigs to certain organisms are described here. Basically, rigs create new vertical habitats for organisms that must attach to some sort of structure. Once these attaching organisms are established, other organisms are attracted to the area. From the following link:

..."Natural structure and hard bottom are rare in the Gulf of Mexico where the bottom is pretty much a vast featureless plain of mud and sand. Where structure does occur, natural or otherwise, it is like an oasis in a desert. Virtual gardens of sessile (permanently attached) invertebrates like barnacles, corals, sponges, clams, anemones, bryozoans and hydroids quickly attach to every available surface and in every nook and cranny. "...

When the well (or wells) "plays out", removing the rig structure would damage the established reef organisms and disrupt the system. So a program was established to leave the structures in place (below a certain depth) and use the rig housing as additional structure for reef growth.

Rigs-to-Reefs program. From this website:

..."Since 1990, cooperating oil and gas companies have donated more than 64 obsolete petroleum platforms and contributed one half of the savings realized by reefing their rigs to the Artificial Reef Fund. These dedicated funds allow the Program to be relatively self-sufficient and finance research, administration, maintenance, liability coverage and construction of new artificial reefs."...

It is possible that the corals and other organisms in this area (SE of Galveston) are simply hardier, due to the natural oil seeps in the bottom of the Gulf. Whether or not reef organisms, in other areas, would "welcome" oil rigs might be debateable, but the record looks good. Imagine the disruptive scenario when a well plays out after decades and an emotion-driven demand is made for a total removal of the structure, even that portion well-below the wave base. Or imagine the damage done if the oil companies are not allowed a tax write-off for the abandoned rig.

These benefits are brought about by the free-market system and the sensible give-and-take regarding governments and their regulations. None of this is to suggest that these endeavors are risk-free (that world doesn't exist), but risks can be managed and minimized.

Our oil companies do listen to public concerns, but sometimes it takes years to find a solution to address the public concerns. Government-owned firms of China, Cuba, or Venezuela may not find Public Relations to be a priority.

Saturday, February 19, 2011

Another Follow-Up, on the Subject of Gold...

on a previous post (January 19, 2001) I copied a post from my other blog, on the presence of gold in a local stream. Just a small amount, judging by the tiny grains I have seen so far, but it is gold, nonetheless. The small, unnamed creek is a small tributary of the Chattahoochee River and the place I usually pan is about 1/4 mile from the river.

Now that I have had some time to think about it and revisit the place several times, there are two likely sources for the gold. It should be noted that this area is within a geologic feature called the Brevard Fault Zone (or Brevard Zone of Cataclasis), which has been (at various times) interpreted as a thrust fault, a normal fault, or as a large strike-slip fault. The rock types around here are mylonites, phylonites, muscovite button schists, sheared gneisses, quartzites, garnet muscovite schists, graphite schists,...things that wouldn't normally suggest the presence of gold.

The only thing I have seen along this particular creek (I need to explore more of the creek) that might be a likely source of gold is; 1) A siliceous, brecciated zone, with eroded, angular cavities in the rock suggesting past (sulfide?) mineralization; or 2) Eroded, old Chattahoochee River gravels and sands.

What remains is for me to "pan my way up" the creek to the point where the gold stops, i.e., I am upstream of the source. There are several branches of this creek, which cris-crosses several local roads, but there are enough wooded areas where I can collect sand samples, to take home for refinement panning. I use a screen atop a small bucket to sieve out the gravel and larger sand, leaving fine- to medium-grained sand within the bucket (which is obviously easier to carry).

I hope to get at least some of the searching over with before snake season begins.

Just a Quick Follow-up on the Previous Post...

I referenced having found a grain of platinum while panning gold in north Georgia, 30+ years ago, in the "greater" Dahlonega area.

To explain a little further and to give some insight as to how I determined that the grain was most likely platinum, I did a few tests on it (it was l - 1.5 mm in diameter, large enough to study). From the way it "behaved" in the gold pan, I determined that it had a slightly-higher specific gravity than gold (check). It was maleable (check), it was light gray to whitish gray (check) and it was lightly magnetic - see below (check). Worked for me.

Though I don't remember where, I seem to remember that some element that commonly is in a natural alloy with platinum is magnetic. This Wikipedia entry is interesting, though it doesn't mention the magnetism property. Perhaps a tiny bit of nickel and/or cobalt? As one would expect platinum from mafic rocks, nickel would also likely be present in at least trace quantities.

Being a coin-collector at the time, I took the flattened grain and stapled it into a cellophane-center cardboard holder, which has been misplaced during one of the times that we moved. I am not convinced that it is gone forever. There are still a few boxes unopened from the last couple of times that we moved. Such as it is when we get older.

Friday, February 18, 2011

Accretionary Wedge #31 - Geo-Epiphanies

This is not exactly a "new" epiphany, but one that has gradually become a greater interest. Sand. In particular, Heavy Mineral Sands. And the more diversity there is in the composition, the better.

I guess the epiphany is that - though I consider myself to be a field Geologist - it would be so easy to get "lost" in the endeavor of peering through a binocular microscope for hours on end. I actually did this with point-counting of petrographic thin sections, when I was an undergrad. In my youthful vigor, I decided it was necessary to count 500 points per thin section, for about 18 or so thin sections (for my undergrad "thesis"). That "cured" me of a desire for microscope work for a few years. My Master's Thesis was field mapping-oriented, so there were only 4 or 5 thin sections, with only a minimum of point-counting.

Anyway, the junior college at which I teach part-time is gradually building a sand collection. Students and faculty (and our friends) have been repeatedly asked to bring a ziplock bag of sand from a vacation spot. Some sand samples which have been collected (by my friends and relatives) include from Jamaica, Grand Cayman, and the Giza Pyramids.


Being a native of north Georgia, gold panning has long been a hobby of mine, but the heavy mineral concentrates in each pan have usually been discarded after any gold (or platinum in one case) has been picked out and saved. That includes heavy mineral concentrates from places I may never again have time to visit, such as the South Fork of the American River, near Coloma and Placerville, California or Aguirre Springs, Doña Ana County, New Mexico (above photo). Nowadays, I have a bit more respect for heavy minerals. Here is a brief blogpost (primarily for non-geologists, including my students). Though, as the intense study of heavy minerals is a bit esoteric, finding texts and articles (on how to distinguish monazite from zircon, for example) is a bit difficult.

After looking for new and interesting lab assignments for my lab classes, I began to spend more time looking through a binocular microscope at sands in general and heavy mineral sands in particular. Here is an example of an online sand exercise. As for studying local north Georgia heavy mineral sand samples, it becomes easier to keep the students' attention, if you tell them that there might be gold in their particular sample. I also tell them that small diamonds have been found in several Georgia heavy-mineral concentrates.


The above-linked online exercise led me to seek, not only creek and river sand samples, but beach sand samples, too. In contrast to the beach sands of the Georgia barrier islands - which are usually 99%+ quartz, the sands of the New York City-area are a fascinating mix. The "urban beach" photo above is from near the Portside Towers in Jersey City, NJ (near where my daughter and her family live). Between the chunks of old bricks, concrete, coal fragments, and other materials dumped for erosion control, you can see the distinctive dark color to the sand that hints at an interesting mix of heavy minerals.

Though I haven't studied these sands in detail, the literature suggests they are largely magnetite and garnet. One of my goals is to visit Montauk Point on Long Island and Sandy Hook, NJ to collect some sand samples from those two areas. And I would also like to revisit the area near Auraria, Georgia where I found a grain of platinum (along with the gold) in my pan, so many years ago.

Yeah, with a good supply of heavy-mineral samples, I could stand to be "chained" to a microscope for a little while. So, "Here's sand in your eye."

Sunday, February 13, 2011

Milankovitch Cycles and Carbonate Deposition...

Are described in this post over at Rapid Uplift, with important links to other posts, including - at Open Mind - Glacial Cycles, Part 1 and Glacial Cycles, Part 2.

Just a brief bit from Rapid Uplift:

"...Milankovitch cycles are orbital cycles which result in periodic fluctuations in the amount of solar energy received by the earth. Three types of cyclical changes in the earth's movement around the sun, eccentricity, obliquity and precession are said to determine climatic cycles on earth."...

A bit more:

"...One explanation has been that Milankovitch cycles causes growth and decay of ice sheets. This periodic locking in and release of sea water by ice sheets causes fluctuations in sea level resulting in changing water depths and cyclical deposition of sediment. A great many carbonate sequences have been explained as being deposited under the influence of sea level changes caused by such orbital forcing. The image below is one of the most famous examples of Milankovitch forced cycles.. the Triassic dolomite platform which makes up the famous dolomite mountains in Italy."

Stated in a different way, whenever you seen the alternations of sedimentary layers, in relatively thin layers, it is telling you that there were fluctuations of some sort. Milankovitch cycles (as described in the linked posts above); tectonic fluctuations of sea level and/or the local sea bottom; or fluctuations in sediment supply, which may reflect climate and/or tectonic fluctuations in the sediment source-area (on a nearby land mass).

Thicker layers represent more long-term fluctuations of the same types, as long as the alternating layers each remain within a given range of lithologies.

New Madrid Earthquake Bicentennial Begins

Here linked are several YouTube videos related to the 1811 - 1812 earthquakes in the New Madrid Fault Zone. As this area of the Mid-Continent was not settled during that time, the cities that have grown since then are not used to earthquakes, as are California cities. In other words, they are so not ready for any significant earthquakes.

This first video is from Mitch Withers:



The second video is from Walter Mooney:



I plan to add more...

Thursday, February 10, 2011

Geo-Epiphanies?

Accretionary Wedge #31 is now open and accepting entries with a February 18 deadline.

The subject is "What geological concept or idea did you hear about that you had no notion of before (and likely surprised you in some way)?".

The hosting Geoblog for this round is The Geology P.A.G.E. (Presenting Alternatives in Geoscience Education).