Using the standard Jurassic zonal scheme, this work attempts to determine the ages of the four members of the Snowshoe Formation that crop out in the Izee area. As a corollary, regional correlations are possible. The stratigraphic relationship between the Snowshoe Formation, the subjacent Hyde Formation and the superjacent Trowbridge Formation is also investigated. Over one thousand fossils were collected from five stratigraphic sections and eight localities. The sections were measured using tape and compass techniques and the relative stratigraphic ranges of the fossils calculated using a computer program written specifically for this project. The ammonite fauna, dominated by the families Hildoceratidae, Stephanoceratidae and Sonniniidae, is systematically described. The Snowshoe Formation was deposited in marine waters of neritic depths during late Toarcian to early Callovian time, with the Bathonian apparently unrepresented. The lower member correlates in part with the Weberg and Warm Springs Members of the Snowshoe Formation in the Suplee area whereas the middle and Silvies members correlate in part with the Basey Member. Most of the Snowshoe Formation has, or probably has, correlatives within the North American continent. The lower contact of the Snowshoe Formation in the Izee area is gradational and the basal deposits non-diachronous whereas the upper contact is either diachronous or represents an unconformity.

No description available.

No description available.

Several recent morphological studies have addressed the interrelationships of Osteoglossomorpha, a group that sometimes is considered the sister group of all other living teleostean fishes. Many characters used in these studies were found to be poorly defined, to be coded incorrectly or illogically, or to display more variation than was described. The goal of this study is to address these concerns and contribute generally to knowledge of the morphology and systematic relationships of osteoglossomorphs. Analysis of 72 characters scored for 20 genera resulted in 2 most parsimonious cladograms. The only difference in the topologies of these cladograms is in the position of †Lycoptera (recovered as either the sister group of all other osteoglossomorphs sampled or of †Eohiodon + Hiodon). †Ostariostoma is recovered as the sister group of all non-hiodontiform osteoglossomorphs. Mormyrids are sister group of notopterids + osteoglossids (including Pantodon). Mormyrids and notopterids usually are considered more closely related to each other than to any other group; characters not included here support this relationship and future consideration of these characters must be made. † Palaeonotopterus is interpreted as sister-group of all mormyrids sampled; however, only 22% of characters could be scored for it and its resemblance to notopterids are undeniable. General problems of character definition are discussed in my review of characters used in previous analyses.

The revised age models for the upper Oligocene to middle Miocene interval of the Marion Plateau have been used to identify eleven sequence boundaries and sequences sets at the Marion Plateau; MSA1.2 (23.1 Ma), MSA1.4 (22.1 Ma), MSA2.1 (21.2 Ma), MSB1.1 (18.4 Ma), MSB1.2 (17.3 Ma), MSB2.1 (16.5 Ma), MSB2.2 (15.6 Ma), MSB2.3 (14.8 Ma), MSB3.1 (13.6 Ma), MSB3.2 (12.9 Ma), and MSB3.3 (11.8 Ma). The complementary Miocene oxygen isotope events Mi1, Mi1a, Mi1aa, Mi2, Mi2b, Mi3a, Mi3, Mi4, Mi5a, Mi5, and Mi6 are recognized in the Marion Plateau sequences. In addition correlation to sequences on the New Jersey margin, the Gulf of Papua, Great Australian Bight, and McMurdo Sound Antarctica indicate that these sequences are controlled by glacio-eustasy, primarily the increase of ice volume on Antarctica. Changes in the preservation, assemblage structure and diversity of calcareous nannofossils as well as %planktic foraminifera, %neritics coincide with transgressive phases and sequence boundaries. The principles of `highstand shedding' are illustrated at the Marion Plateau by enhanced preservation of calcareous nannofossil, deposition of glauconite, unconformities and condensed intervals associated with early to middle Miocene sequence boundaries. Variations in surface water nutrient and temperature conditions at the Marion Plateau throughout the Miocene coincide with climatic events of the early Miocene (23 – 17 Ma), the Middle Miocene Climatic Optimum (17.6 – 15.4 Ma), and Middle Miocene Climatic Transition (14.8 – 13.8 Ma), and the stepwise growth of ice sheets on Antarctica. Calcareous nannofossil communities show evidence for precessional and eccentricity orbital forcing during the Middle Miocene Climatic Optimum, as well as a significantly cooler surface water mass at the Marion Plateau coinciding with the onset of the Middle Miocene Climatic Transition and Mi3a (14.8 Ma) glacial event. Changes in surface water fertility and temperature during the Middle Miocene Climatic Optimum agree with other studies that posit growth of significant ice volume on Antarctica starting as early as ∼17.35 Ma. Further evidence for significant cooling at the Mi3a (14.8 Ma) glacial event agrees with studies suggesting a step-wise cooling for the formation of a semi- permanent Antarctic ice sheet and thermohaline circulation, starting first at 14.8 Ma (Mi3a) and intensifying at 13.9 Ma (Mi3).

The Lower Mystic Lake (Medford/Arlington, MA) is a 24 m deep, ectogenically meromictic, low elevation (1 m a.s.l.), coastal lake directly connected to Boston Harbor by the Mystic River. About 1,000 years ago, steadily rising sea level in the Boston area finally reached a point at which occasional marine water delivery events via the river channel could actually reach the lake basin. Since then, such events have continued with enough frequency to maintain the meromictic condition. Meromixis has allowed the Lower Mystic Lake to accumulate an exquisitely laminated, annually resolvable (i.e. varved) archive of sedimentation in the lake over the last 1,000 years. A varve chronology was developed from this record. Multiple lines of robust evidence verify and validate the accuracy of the chronology. A series of anomalous, graded beds was found in the stratigraphy, and they show excellent coordination with known historic hurricanes that have affected the Boston area. The graded beds appear to be the result of intense, hurricane-strength rains which cause erosive overland flow that entrains sediment which is carried into the lake where it is deposited as a graded bed. This is enhanced by hurricane-strength winds which disturb vegetation, and uproot trees to expose fresh, loose sediment. By analogy, similar graded beds in the prehistoric portion of the stratigraphy probably represent similar hurricane events. This record of hurricane activity was compared to a record of sand layers in nearby Belle Isle Marsh (Boston Harbor) which are presumably the result of storm surge overwash events. Such sand layers in low resolution coastal archives are the main form of proxy evidence that paleotempestology studies have used to piece together longer term records of hurricane activity. Even when using multiple techniques, chronologic control in such archives is difficult, and linking sand layers to any particular storm is only tentative at best. Importantly, the Belle Isle Marsh record shows an apparent 600-year quiescent period. However, this is not due to a lack of hurricanes or storms, but to an unknown geomorphic change which affected the marsh, and it therefore serves as a cautionary note for the use of such archives.

2 volumes available.

No description available.

No description available.

No description available.