Author: F.M. Anderson
From the original introduction: Geological and paleontological work on the Cretaceous deposits in California and Oregon was begun as early as 1854, but in great measure the foundations upon which all subsequent work has been based were laid by J.D. Whitney, W.H. Brewer, and W.M. Gabb in the period from 1860 to 1884. This work was followed by that of G.F. Becker and C.A. White, and from 1891 to 1905 by the more important work of J.S. Diller and T.W. Stanton, from whose results all later work has proceeded. The knowledge of the stratigraphic succession and the faunas of the Cretaceous in California and Oregon developed by these later workers was a great advance from the generalized results of the earlier explorers. But it soon became evident, however, that other demands upon their time had left this work unfinished, far from the stage to which their interest and energy would have led them to attain. As concerns the early Cretaceous deposits, their stratigraphic limitations, relationships, and distribution, further advance was hardly possible prior to 1907 and the three succeeding years. During these years some notable advance in Cretaceous paleontology was made by Pavlow (1907), Diller (1908), Smith (1909, p. 347-349), Knowlton (1910), and others. The work of these men led the way to a solution of a primary problem—namely, a proper discrimination of the Lower Cretaceous from the late Jurassic sequence in these western States. A brief review of this subject was given by the writer (1933, p. 1237-1265), with a summary account of the more recent work done on the west border of the Sacramento Valley in California in tracing the boundary between these great sedimentary series. It was pointed out that, in many areas of contact between the Knoxville (Upper Jurassic) and the Shasta (Lower Cretaceous) series, evidences of unconformity are abundant, clearly showing that an interval of disturbance and of erosion had intervened, which seems to have extended along the Pacific Coast from California to Alaska, and far beyond. Prior to the last decade, a knowledge of the stratigraphic subdivisions in the Shasta series in California and Oregon and of their respective faunas was quite imperfect, and conceptions of these matters were much confused owing to the lack of criteria by which satisfactory distinctions could be made. During these years a number of notable contributions were made to the paleontology and faunal succession of the Lower Cretaceous in other parts of the world by Spath (1924), Whitehouse (1926), Steinmann (1929), Burckhardt (1930), and others. These works have made it possible to attain a more satisfactory interpretation of the faunas found in the Lower Cretaceous deposits of the West Coast. These works have also led to a desire to obtain more definite information as to the stratigraphical and faunal successions in the richly fossiliferous strata of the Knoxville and Shasta series in California and Oregon, and a persistent effort has been made in recent years to do this. As a result large collections of invertebrate fossils have been gathered from the lower units of the Shasta series and from the upper units of the Knoxville in California and Oregon, and it is now possible to fix more definitely the line of demarcation between them, even in areas in which stratigraphical unconformity is not evident. However, it is not believed that either class of evidence is complete, or that mapping will always be easy. Two major stratigraphical groups have been recognized in the Shasta series in California, both of which were foreshadowed in the work of Diller and Stanton, although these writers did not go so far as to distinguish them clearly. These are the Paskenta group below and the Horsetown group above, bearing evidence of a disconformity between them, as will be shown in the following pages. In its general faunal aspects the Shasta series presents two distinct or not closely related faunal assemblages corresponding to the major stratigraphic groups, both of which are distinct from that of the Knoxville series. The study of these assemblages reveals cogent evidence as to important diastrophic changes of wide geographical extent supporting the deductions derived from the stratigraphical relationships in the field. In the Paskenta group there are many forms of Mollusca, including Aucellas and cephalopods, the nearest analogues of which are found in contemporary deposits in Russia, as noted by Pavlow and earlier writers. In fact suggestions have been made by Stanton and others as to routes of migration, or of exchange, between Russia and western America. The boreal character of Aucella has suggested routes of exchange by way of the Arctic seas, notwithstanding the fact that species of this genus have been found in lower latitudes (Mexico and India).
Published: 11/30/1938
ISBN Number: 9780813720166
Pages: 349
Product Category: EBooks