Sunday, July 1, 2007
Rocky Point (Oak Harbor) floating Metasediments
Anomalous Rocks on Whidbey Island
WI is mostly covered with young glacial layers- mainly till and stream wash deposited in the last 50,000 years. Occasionally, there are outcrops of older rocks, such as at the Deception Pass area, just near the bridge, and surrounding the hiway 20. These rocks are named Metasediments (sediments which have been metamorphosed- squeezed at depth), and they are from the Mesozoic Era and older which outcrop regularly to the north and on the San Juan Islands. This means that they are older than 65 m.y. (Cretaceous and older), compared to the rest of the island- which is no more than ¼ million years of age.
A small outcrop of these older rocks occurs anomalously at Rocky Point- which is a section of west beach, on the Naval Reservation, in Section 21 T33N R1E (anomalously in the sense that they are surrounded by very young glacial Pre-Stone with age less than one million years)- see the above photos. The stone has been shoved up and laterally by shearing in the earth- the metasediments are being carried between two faults running about 120 degrees from north (almost SE-NW). This means that they are dragged by shear similar to that which caused them to be metamorphosed in the first place. The important questions to be asked here are as follows:
1. How and Why are the rocks being forced to the surface, when the only obvious movement anywhere nearby was that at the Deception Pass, where the continental hard rocks have been shoved almost due west, referenced to the Pacific plate rocks? Incidentally, this large faulting with several thrusts has created the San Juan Islands (in layers stacked on top of each other-but out of regular sequence), and the fault surface can be seen just outside of DP Park on the east side (where a E-W vertical wall or scarp occurs).
2. How can these heavy rocks (relative to the light weight till) be floating at the surface of the earth; if anything, they should at least sink in the soft sediments surrounding them?
3. How can we be sure that the metasediments are not connected with similar stone at their base? We can see that they protrude into the air, and are obviously disconnected on the north and south sides- but there is one side unseen and not open to inspection- the bottom. Why could not the metasediments curve upward from a near horizontal position deep in the earth and gradually bend and protrude vertically?
Analysis from the Photos
First, if these layers are being dragged along a 120 degree fault plane or shear surface on the south side (and the LIDAR map shows this clearly as a fault), then they cannot be connected to the original basement there. This means that the beds, if they are curving upward to a vertical expression, cannot curve upward from the south- since this is the discontinuous side. The fault plane on the north side would tell the same story, but this fault is not shown on the LIDAR map. This fault is only seen in the cliffs at the northern contact with the glacial deposits, and this is the weakest part of the analysis.
Second, the outcrop has a visible fracture running about NW-SE in one of the photos. This is seen as a large break in the rock with vegetation, a cavity, fractures, and seepage. This has remained damp over the 10 years I have visited it. The entire outcrop, which is about ½ km from north to south, has vertical bedding consistently oriented toward the 120 degree direction (which is the orientation of the LIDAR fault). It seems reasonable that the fault is left lateral, which results in the outcrop jutting into the sea on the north side, since all faulting measured by me for the north side of the island are left-lateral (2 cases). There are no other vertical beds anywhere on the island- even at Deception Pass. The NW fracture is the type occurring now on the island, and this indicates that the outcrops occurred first.
Thirdly, Rocky point is some 8 km or more from similar rock at Deception Pass, and not likely to be connected in the basement. There are the Silver Creek and Mariner’s Cove faults which I have inspected, which intervene in that distance. There is nothing nearby which indicates a connection- Rocky Point is anomalous! We still haven’t proved that Rocky point metasediments are not connected in the basement (subsurface) with others of its type, on the north side. But I hope to show the larger picture for Whidbey Island- to indicate that small events may sometimes be rationalized by looking at what happens regularly nearby.
CONCLUSIONS;1. The Rocky Point outcrop is anomalous, in that it is not connected with anything near at the surface- it is Mesozoic or older, contains metamorphosed sediments (metasediments), it is oriented in a direction of bedding pointing 120 degree from north, and it is faulted at least on the south side by a similarly-oriented fault as seen by LIDAR mapping.
2. The RP outcrop is surrounded on the ground surface by young, soft Till and non-indurated or non-strongly cemented sediments- it is anomalous in terms of strength, position, and orientation (except for the parallel faulting on the south side).
3. RP is a true point, meaning that it is resistant to storm erosion and juts into the Sound. It is increasingly covered by storm wash, as noticed for the ten years I have observed it (the sea is rising near 1 mm/year as measured by an independent geologist, near Admiralty Head).
4. RP is fractured in its mid-section by a NW-SE, or thereabouts, opening- which has an obvious accompanying seepage. This rock is the highest of those remaining- indicating that it is being shoved upward from below (which would be a reason why the metasediments are floating). If this is correct, then it is connected with the basement in some way- but not necessarily with the original neighboring metasediments.
5. Since the entire outcrop aligns in the common direction (120 degrees from north of ½ km aligned rock) it is likely that it is a separate block broken off from the original bedrock and carried along the active shearing zone. It must be sitting on top of other basement- with a low probability that it is connected with its original neighboring rock.
6. The orientation of 120 degrees from north, when extrapolated to the east side of the island is coincident with the location of Eerkes spring (which creates road breakage and can be found by looking for patches and a low place in the pavement on Torpedo Road, just NE of the Naval Commissary). IF these are connected in the subsurface, this indicates that the Rocky Point fault is of great significance. The orientation would connect with an obvious large and active fault at Utsalady Point on Camano Island, which can be seen on LIDAR decisively.