commonly develop a vertical profile related to chemical and biological activity 

 (Nelson, 1962). The result is a thin layer of oxidized, semi-fluid sediment lying 

 over a thin layer of darker sediments where microbiological activity is at a peak. 

 Rapid burial of this profile could lead to its preservation and may be represented In 

 the cores from Penobscot Bay by the black layers and laminae. 



In the entrance to the bay, little marine sedimentation has taken place relative 

 to the northern areas. Most of the fines, which may have been present orginally, 

 have been removed from the shallower areas by wave action and currents and depos- 

 ited in the deep basins and depressions or carried away from the area. The many 

 vertical changes in the cores reflect frequent short period changes in energy condi- 

 tions over the past . 



To aid in the Interpretation of the present sedimentary regime of the surveyed 

 area, the percentages of sand (including pebbles), silt, and clay found In the top 

 2 inches of the cores and In the grab samples were plotted to show the relationship 

 of sediment type with distance from the northern part of the bay (Fig. 16) and to 

 show any dependence of the median diameters of the sediments upon depth of water 

 (Fig. 17). The surface sediment graphs show an Increase in the percentage of sand 

 to the south, but they show little relationship between grain size and water depth 

 except for a slight trend toward finer sediments with depth in the approaches to the 

 bay. Apparently toward the south, the increasing energy conditions, wave agitation 

 and currents, ore more important in the most recent bay sedimentation than proximity 

 to the Penobscot River. The sedimentary data seem to indicate that the major geo- 

 logic process in Penobscot Bay is the reworking of previously deposited sediments. 

 This is characteristic of many estuaries. The amount of sediment In suspension In 

 bay waters often exceeds that in the river or in the open sea adjacent to the bay. 



At many of the grab sample stations, the surface sediments consisted of two 

 layers: a thin upper layer of olive-gray sediments over olive-black sediments. The 

 upper layer was liquid and seemed to contain more silt and fine sand than the sedi- 

 ments below. (These features were observed in the field and are not shown in the 

 laboratory analysis.) There are two areas where the surface sediments consisted 

 of two layers. One extends roughly from the middle of the central segment of the 

 bay to the entrance off Rockland, and the other consists of a few locations in the 

 approaches to the bay. To the north of the major area of two sediments, the surface 

 sediments are olive black, but in the approaches to the bay where the two layers 

 were not found, the sediment color was olive gray. This distribution did not show 

 any obvious dependence on depth — only distance from the bay head was significant. 



A possible explanation for these features of the surface and near surface sedi- 

 ments is that the finer fraction is being winnowed from previously deposited sediments 

 in a zone extending from the central sector of the bay through the approaches. The 



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