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The AAPG/Datapages Combined Publications Database
The complex Quaternary history of the northeast Gulf of Alaska has resulted in a variety of sedimentary deposits ranging from glacially derived marine silt and clay to coarse glacial ice-contact moraines and tills. Four major sedimentary units crop out on the continental
shelf. These units, defined on the basis of seismic reflection and sedimentologic data, are (1) Holocene glacial-marine sediments, (2) Holocene end morainal deposits, (3) Holocene (neoglacial) and Pleistocene glacial sediments, and (4) Pleistocene and older lithified sedimentary rocks. Each of these four units is divisible into facies on the basis of depositional environment. Each of the units was derived either totally or in part as a result of glaciation, hence each unit is a chronofacies or lithofacies of the overall glacial and glacial-marine depositional picture of the northeast Gulf of Alaska during the Quaternary.
The Holocene glacial-marine sedimentary unit contains sediment originally glacially eroded and transported that was (and is) deposited in the marine environment through glacial-fluvial, eolian, or ice-transported mechanisms. Facies in this unit vary from unimodal clayey silt to bimodal pebbly silt and clay with large percentages of ice-rafted components. The end moraine unit, which contains deposits representing the farthest penetration onto the shelf of fiord-filling piedmont and valley glaciers, contains facies ranging from massive boulder and cobble accumulations to fine-grained silt and clay that accumulated in basins within the lobes of the moraine. The Holocene (neoglacial) and Pleistocene sedimentary unit is the most variable of the four units as it contains sediment ranging fr m multi-modal ablation and lodgment tills, to recessional glacial-lacustrine and outwash facies, to marine pebbly mud. Post-depositional winnowing has further modified the textural and compositional nature of this unit.
The lithified sedimentary rock unit, typified by submarine outcrops of the Yakataga Formation, contains components of each of the three other units. The lithified unit, however, represents glacial and glacial marine events predating Holocene time. Stratigraphic and paleontological evidence suggests that the depositional environments producing the facies present in the Quaternary sedimentary units have changed little since middle Miocene time, and the influence of glaciation has been the primary controlling factor in the shaping of upper Tertiary and Quaternary depositional sequences.
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