Geology, Stratigraphic

Tugidak Island, the northenunost of the Trinity Islands off the S W coast of
Kodiak Island is the stratotype of the Tugidak Formation. The continuous section ofthe
Tugidak Formation crops out in the sea cliffs along the northern and southwestern parts
of the island and is the most complete section in the Trinity Islands. The exposed section
of the Tugidak Formation is composed of 1395 m of glacial marine diamictite containing
abundant molluscan fossils. Seismic profiles and well data indicate a regionally
extensive deposition of the Tugidak Formation across the Kodiak Shelf. Paleomagnetic
sampling and diatom analysis in this work has further refined the age of the Tugidak
Formation as early-middle Pleistocene. By attempting a reconstruction of the tectonic
evolution and through faunal identification, inferences are made about the
paleobiogeography, paleoclimate and timing of sedimentary depositional cycles, around
Tugidak Island.

Analysis of2D seismic reflection profiles, magnetic anomaly data and four well
logs reveals that the continental shelf of the Beaufort Sea is in many ways, a direct
geological extension ofthe prolific oil and gas province ofthe North Slope of Alaska.
Stratigraphy is divided into four sequences. The organic rich shales are
characterized as potential source rocks and the carbonates and marine to non marine
sandstones are interpreted to be the reservoir rocks.
Structural interpretation has revealed the presence of five structures capable of
trapping hydrocarbons. These structures were identified as the Barrow arch, Camden
anticline, Dinkum graben, shale diapirs and normal faults.
The combination of these structures and stratigraphy offer petroleum exploration
companies a promising target for large accumulations of hydrocarbons.

The Arcadia Formation is a mixed carbonate-siliciclastic rock unit that existed as
a shallow carbonate ramp to platform environment during the Late Oligocene to Early
Miocene Epoch. It can be divided into two distinct, informal sections based on
lithological properties: the upper Arcadia Formation and lower Arcadia Formation. The
sections are part of a major, third-order sequence that can be further divided into four
higher-frequency, lower magnitude sequences: ARS1, ARS2, ARS3, and ARS4. The
sequence boundary separating ARS2 and ARS3 represents a drastic change in the
depositional regime from a high-energy, inner ramp/platform to a lower-energy, deep
outer ramp environment. ARS3 represents the period of maximum flooding and
constitutes a major portion of the regressive system tract (RST) of the third order depositional sequence. In certain sections, the Arcadia Formation is heavily bioturbated
including ichnotaxa from the glossifungites, cruziana, and scolithos inchofacies.
Thalassinoides sp. burrows of the glossifungites ichnofacies were found to be commonly
associated with firmground substrates and breaks in sedimentation. The lithofacies
associations were grouped into paleodepositional environments that ranged from
restricted marine to deep outer ramp with lithology ranging from grainstone to
wackestone to mudstone with variable amounts of siliciclastic and phosphatic
constituents. Each sequence boundary extends regionally south from Broward County to
southern Miami-Dade County utilizing gamma-ray geophysical signatures unique to each
sequence.

The oèolitic limestone that makes up the bedrock of Miami-Dade and parts of Broward County, Florida, is a relatively well studied formation, with poorly studied fossil content. No published systematic record of Pleistocene fossils in the Miami Limestone is available. Besides the basic knowledge of taxonomy and biodiversity of the mollusks, comparison with extant assemblages can yield important information about the biodiversity changes in southern Florida during the past ~130,000 years. Preliminary surveys of several localities, both previously described and new, within the Dade County yielded a record of diverse mollusks from over 28 families, 34 genera and 40 species. The preliminary findings of molluscan fossils have led to a new, unstudied and unpublished fossil locality with the second discovery of a possible Strombus costatus in the Miami Limestone. Miami Limestone fossils are being compared to recent South Florida mollusks indicating patterns of local diversification and extinction related to the minor changes in sea level and disappearance of certain habitats such as the rocky shore substrates that Cittarium pica once thrived on.