Fossil Point, Tuxedni Bay

Fossil Point, Tuxedni Bay

by | Jun 21, 2022

Fossil Point is a prominent landmark in Lake Clark National Park and Preserve on the southern shore of Tuxedni Bay, at the north end of Tuxedni Channel and west of Chisik Island, about 56 miles (90 km) southwest of Kenai and 54 miles (87 km) northwest of Homer, Alaska. The local name was first published in 1912 by U.S. Coast and Geodetic Survey. Lake Clark National Park and Preserve was first proclaimed a national monument by President Jimmy Carter using the Antiquities Act on December 1, 1978, and then was established as a national park and preserve in 1980 by the Alaska National Interest Lands Conservation Act. The park and preserve extend from Cook Inlet in the east across the Chigmit and Neacola Mountains to the upper reaches of the Mulchatna River watershed in the west. The park protects the coastline of Cook Inlet, alpine tundra, glaciers, glacial lakes, major salmon-bearing rivers, and the volcanoes Mount Redoubt and Mount Iliamna, both over 10,000 feet (3,050 m), that flank Tuxedni Bay and vent steam from snow-capped summit craters. Tuxedni Bay is about 4 miles (7 km) wide at its mouth and narrows rapidly as it extends inland 12 miles (20 km) to the braided delta of the Tuxedni River. Chisik and Duck islands are located at the mouth of Tuxedni Bay. The geology of Tuxedni Bay was first described by Karl Eduard von Eichwald based on samples collected in 1871 by the Russian mining engineer Peter P. Doroschin and sent to the Russian capital at Saint Petersburg. Eichwald was from present-day Latvia and of German ancestry but spent much of his later career in Saint Petersburg as a preeminent geologist. The Tuxedni Bay region has about 26,600 feet (8,100 m) of Early, Middle, and Late Jurassic age rocks, formed about 201 to 145 million years ago, in what may be one of the thickest and most nearly complete sequences of bedded Jurassic rocks in the United States. The rocks exposed at Fossil Point are part of the Tuxedni Group, layers of marine sedimentary rocks 4,970 to 9,715 feet (1,515-3,000 m) thick that were deposited in a deep ocean trench during the Middle and Late Jurassic age. They now consist of greywacke sandstone, conglomerate, siltstone, and shale with extremely prolific fossil invertebrate marine fauna.

The glacial history of the Tuxedni Bay area is not well known due to a general lack of glacial deposits. Late Pleistocene and Holocene glacial moraines have been mapped near the present terminus of Tuxedni Glacier. A small remnant moraine attributed to the Naptowne Glaciation is located on the north shore of the bay, and some Naptowne-age deposits are mapped in drainages entering Tuxedni Bay from the south, but more recent alluvial and colluvial deposits obscure most evidence of glaciation. The end of the most recent stage of the Naptowne Glaciation is dated in other parts of the Cook Inlet basin to about 11,000 years ago. The presence of glacial ice may have restricted prehistorical human passage through upper Tuxedni Bay. Sockeye and chum salmon are present in the Tuxedni River at the head of Tuxedni Bay, and a significant run of sockeye enters Crescent River, bound for Crescent Lake. Pacific razor clams are also abundant on sandy Cook Inlet beaches. These resources have attracted human settlement since the area was deglaciated. Magnetic Island is a small island on the north side of Tuxedni Bay surrounded by mudflats that are submerged during high tides. The island is named for the compass deviations observed during a geological survey in 1951 and probably caused by the presence of magnetite. The island is important for providing evidence of prehistoric human habitation from about 4,100 to 3,500 years ago. The archaeological site consists of a series of depressions that were excavated in 2012 and revealed fire-cracked stones and hearths, and stone tools associated with the Arctic small tool tradition. The period around 3,500 years ago had heightened volcanic activity throughout the Chigmit Mountains and southwest along the Alaska Peninsula. The burial of the Magnetic Island site by volcanic ash may represent an example of what terminated the spread of Arctic small tool tradition people into the Cook Inlet basin. Following the Alaska Purchase in 1867, Tuxedni Bay attracted miners and fishers, a clam cannery from 1919 to 1980 at Snug Harbor on Chisik Island, and commercial and subsistence salmon fisheries that are ongoing. The shores of the bay now include multiple private and Alaska Native inholdings.

Fossil Point is important because it contains one of the most productive marine invertebrate fossil sites known in Alaska. Fossil Point has long been known to Cook Inlet fishers and despite a prohibition on collecting, private fossil collectors have put specimens on display in many local homes and businesses. The most common megafossils found at Fossil Point belong to the Middle Jurrasic bivalves of the genus Retroceramus, Pleuromya, Pholadomya, and Pinna, and the cephalopods Belemnites and Ammonites. Eichwald identified four new species of the genus Inoceramidae now named Retroceramus, although present-day paleontologists debate whether all four species are valid, or merely represent ecological variants belonging to one or two species. Pleuromya was a burrowing bivalve in soft sediment and only its long siphon tubes reached up to the sediment-water interface. Pleuromya fossils are commonly found in a life position with the posterior end directed upward. Pholadomya is a genus of saltwater clams with one species still present in the Caribbean. Pinna is a genus of bivalve molluscs, commonly called pen shells that can reach a length of about 31 to 35 inches (80–90 cm) and are geographically widely distributed. They are characterized by thin, elongated, wedge-shaped, and almost triangular shells with long, toothless edges. These bivalves most commonly lie point-first on the sea bottom in which they live, anchored by a net of byssus threads. Belemnites is a genus of an extinct group of cephalopods that were fast-moving nektonic carnivores in the Early Jurassic period. Ammonites are also an extinct cephalopod that are related to living octopus, squid, and cuttlefish, even though they more closely resemble the living nautilus species. The last species of ammonites either vanished in the Cretaceous–Paleogene extinction event or shortly after, during the Paleocene. Read more here and here. Explore more of Fossil Point and Tuxedni Bay here:

About the background graphic

This ‘warming stripe’ graphic is a visual representation of the change in global temperature from 1850 (top) to 2021 (bottom). Each stripe represents the average global temperature for one year. The average temperature from 1971-2000 is set as the boundary between blue and red. The color scale goes from -0.7°C to +0.7°C. The data are from the UK Met Office HadCRUT4.6 dataset. 

Credit: Professor Ed Hawkins (University of Reading). Click here for more information about the #warmingstripes.

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