New Brunswick is divided into five tectonostratigraphic zones based upon Cambrian-Ordovician and to a lesser extent Upper Precambrian lithofacies. Sub-zones are distinguished by the characteristics of overlying pre-Carboniferous strata, and tectonic styles.
The paleogeography and tectonic evolution of these zones can be related to the development of two oceanic basins, which transgressed onto the adjacent disrupted continental crust. Opening of the northern oceanic basin began during the Cambrian and closing was completed during late Ordovician time. The southern basin was initiated during the late Precambrian or Cambrian, and closed during the Silurian to early Devonian.
The description of tectonostratigraphic zones in this report is based upon a synthesis of detailed stratigraphie and structural studies carried out in New Brunswick during the past 10 years. Most of these surveys were conducted under the auspicies of the Geological Survey of Canada and Mineral Resources Branch, New Brunswick Department of Natural Resources with financial assistance of the Canada Department of Regional Economic Expansion. The present synthesis constitutes a progress report (Canadian Contribution No. 4) of a continuing investigation conducted in co-operation with the Canadian IGCP (International Geological Correlation Program) Caledonide Orogen Project.
Five major tectonostratigraphic zones (Fig. 1) were delineated in the present study based upon contrasting lithostratigraphic faciès of Cambrian-Ordovician and to a lesser extent, Upper Precambrian strata. Subdivisions of these zones are mainly based upon characteristics of overlying Silurian and Lower Devonian rocks, and structural style. As this study is confined to the pre-Carboniferous tectonic evolution, the Carboniferous strata are designated as cover rocks. Previous structural-stratigraphie subdivisions, based upon the characteristics of the dominant exposed rock units in various belts, were mainly designed to assist in the delineation of mineral zones (Potter et al., 1969) or major structural complexes (Rodgers, 1970). A previous tectonostratigraphic zonation based upon correlation with Newfoundland (Williams et al., 1972) did not adequately represent the geology of New Brunswick. Similarly, previous tectonic interpretations by Bird and Dewey (1970) and McKerrow and Ziegler (1971), required revision, but some aspects of models proposed by Poole (1976) and Rast era/., (1976a) are consistent with the tectonostratigraphic zonation outlined in this report.
Facies models for extensive eolian sand deposits must be based on the characteristics of modern ergs ("sand seas"). Peripheral areas of ergs, where supply of sand is sparse, are characterized by barchansand longitudinal dunes: neither of these seems very likely to be preserved in the geological record. The central parts of ergs, where accumulated sand thickness reaches several hundred metres, are composed of complex pyramidal dunes (draas) with superimposed complex transverse dune types. Almost nothing is known by direct observation of the cross-bedding formed in such dunes, but it is possible that it is not as variable as the complex external morphology might suggest. Identification of ancient sandstone formations as eolian is based mainly upon one major criterion: the very large scale and relatively high angle of the cross-bedding. In many cases minor indicators, such as eolian ripples (orientated at large angles to the trend of the major foresets), avalanch scours, animal tracks, soft-sand faults, raindrop impressions, etc., are also present. Negative evidence is equally important: the only known alternative model, that of a submarine tidal sand-wave field, is not known to produce large scale, high angle cross-bedding: it probably produces medium-scale cross-bedding resulting mainly from migration of megaripples or sand waves of relatively small scale, superimposed on the large scale features. The cross-bedding probably shows at least some bipolar orientation of cross-bed directions, a feature absent from all classic ancient eolian sandstones. Furthermore, in the tidal sand wave model, sand deposits are associated with muddy sediments bearing a marine fauna, and this is not the case in the classic ancient eolian sandstones of the western U.S.A. and elsewhere.
The unconsolidated sediments off eastern Canada contain interstitial methane up to 22,000 ppm. The presence of methane is associated with anoxic conditions found in fine sediments deposited in small basins. The foraminiferal assemblages and Carbon-14 dating of the gaseous deposits indicate rapid rates of sedimentation.