Coastal mountains in the northeastern Gulf of Alaska expose continuous, along-strike sections over many tens of kilometers through the 5-km-thick infill (Yakataga Formation) of a glacially influenced active margin basin. The basin has been thrust and uplifted as a result of continuing compression between the underlying Pacific and North American plates. The Yakataga Formation is the best exposed and most complete late Cenozoic record of cool temperate and glacially influenced marine sedimentation in the world. Glacial marine sedimentation began during the late Miocene and is recorded in lowermost Yakataga strata exposed at Yakataga Reef by the abrupt arrival in a deep basin of turbidites and chaotically bedded debris flows. Debris flows, as much as 19 m thick are composed largely of glacial debris brought down to sea level by tidewater glaciers. A depositional setting characterized by a narrow shelf terminating in a steep slope and deep water, and subject to frequent downslope mass flow events is indicated. Overlying Yakataga strata exposed at Icy Bay are characterized by interbedded turbidites, diamictites, and shallow marine sandstones; these facies probably record progradation of a continental slope by mass flow processes in response to high rates of sediment supply from glaciers draining rapidly uplifting (1 to 10 m/yr) and eroding coastal mountains, and earthquake activity. Seismic and outcrop data show that the slope experienced multiple episodes of syndepositional compressional folding, resulting in a pronounced structural influence on sedimentation style. Uppermost Yakataga strata exposed on Middleton Island are dominated by thick “rain-out” diamictites resulting from iceberg transport of coarser debris and the deposition of muds from suspended sediment plumes in an outer shelf setting. Graded gravel facies record the infilling of submarine channels similar to the valleys that traverse the modern Gulf of Alaska shelf; coquinas indicate episodic sediment starvation. Boulder pavements record repeated surge-like ice advances to the outer continental shelf. By this time (late Pliocene to Pleistocene) a low-relief subsiding shelf was established in the Gulf of Alaska on which a high-resolution record of sea-level change, tectonism, and glaciation was preserved; deposition rates may have been as high as 10 m/ky. The single most important influence on sedimentation in the late Miocene to Pleistocene Gulf of Alaska, especially in allowing the preservation of a thick active margin basin fill in a compressional tectonic setting, has been, and continues to be, the abundant production of meltwater from temperate tidewater glaciers and associated sediment from rapidly uplifting (10 m/ky) coastal mountains.

Abstract The Long Beach Unit comprises part of the giant Wilmington Oil Field, Los Angeles Basin. Total original oil in place for the Long Beach Unit has been estimated at 3.8 billion barrels of oil, of which 645 million barrels have been produced to date. Petroleum reservoirs occur within seven zones called the Tar, Ranger, Upper Terminal, Lower Terminal, Union Pacific, Ford, and 237 (top to bottom). The Ranger zone, which is the largest reservoir, is >1000 ft (305 m) thick in the Long Beach Unit. Six cores through the Ranger, totalling about 5000 ft (1524 m), have been examined to evaluate depositional environments, reservoir quality, and geologic controls on reservoir properties. Foraminiferal analyses indicate the Ranger zone comprises the Puente and Pico Formations of late Miocene to early Pliocene age. Water depths at the time of deposition ranged from lower middle to upper middle bathyal (1640-6560 ft; 500-2000 m) with a slight deepening-upward trend. Sedimentary features indicate the Ranger sediments were deposited by a variety of mass-gravity flow processes in a submarine fan setting. The three major lithologies are massive sand, graded sand, and shale. These are arranged into three facies, Thin-Bedded Sand, Thick-Bedded Sand, and Shale. Owing to the tremendous size of the M 10 -Pliocene submarine fan system in the Wilmington Field area relative to the size of the Long Beach Unit study area, it is not currently possible to interpret depositional subenvironments. The sands are first cycle arkoses to feldspathic litharenites, subjected to limited chemical weathering in the source terrain as well as limited transport to the depositional site, and derived mainly from plutonic rocks to the north and/or east. Ranger zone sands exhibit good reservoir porosities and permeabilities. Permeability appears to vary with facies, suggesting a lithologic control on reservoir quality. The Spontaneous Potential, Gamma Ray, and Compensated Neutron log are all sensitive to lithologic variability. The Compensated Neutron log can resolve beds down to 2 ft (0.6 m) thick. All three logs are useful for distinguishing thin-bedded and thick-bedded sands, and for estimating shaliness.