Document generated on 10/01/2021 4:07 a.m. Géographie physique et Quaternaire Marine Regression and Palaeoenvironments During the Holocene in the Richardson River Basin, District of Mackenzie, N.W.T. Régression marine et paléoenvironnements au cours de l’Holocène dans le bassin de la rivière Richardson, District de Mackenzie, T.-N.-O. Daniel E. Kerr Volume 38, Number 2, 1984 Article abstract A detailed stratigraphie analysis was carried out on a river-bank section of late URI: https://id.erudit.org/iderudit/032551ar Quaternary marine sediments in the Richardson River Basin, N.W.T. The DOI: https://doi.org/10.7202/032551ar sedimentary sequence represents a gradual shallowing of the sea in an estuarine environment, from a relatively shallow marine faciès to an intertidal See table of contents environment. The withdrawal of the sea from the Richardson River Basin began prior to 10,300 years BP. Isostatic uplift caused the gradual regression of the sea to its present-day level. The marine sediments yielded 26 ostracode and Publisher(s) 14 foraminifer species. Faunal evidence is indicative of brackish-water marginal marine conditions resulting from the dilution of nearshore marine Les Presses de l'Université de Montréal waters by freshwater discharge from the many streams and rivers draining the basin of the Richardson River. ISSN 0705-7199 (print) 1492-143X (digital) Explore this journal Cite this note Kerr, D. E. (1984). Marine Regression and Palaeoenvironments During the Holocene in the Richardson River Basin, District of Mackenzie, N.W.T. Géographie physique et Quaternaire, 38(2), 185–192. https://doi.org/10.7202/032551ar Tous droits réservés © Les Presses de l'Université de Montréal, 1984 This document is protected by copyright law. Use of the services of Érudit (including reproduction) is subject to its terms and conditions, which can be viewed online. https://apropos.erudit.org/en/users/policy-on-use/ This article is disseminated and preserved by Érudit. Érudit is a non-profit inter-university consortium of the Université de Montréal, Université Laval, and the Université du Québec à Montréal. Its mission is to promote and disseminate research. https://www.erudit.org/en/ Géographie physique et Quaternaire, 1984, vol. XXXVIII, n° 2, p. 185-192, 5 fig., 1 tabl. Notes MARINE REGRESSION AND PALAEOENVIRONMENTS DURING THE HOLOCENE IN THE RICHARDSON RIVER BASIN, DISTRICT OF MACKENZIE, N.W.T. Daniel E. KERR, Department of Geology, University of Ottawa, Ottawa, Ontario K1N 6N5. ABSTRACT A detailed stratigraphie analysis was carried out on a RÉSUMÉ Régression marine et paléoenvironnements au cours de river-bank section of late Quaternary marine sediments in the Rich­ l'Holocène dans le bassin de la rivière Richardson, District de Mac­ ardson River Basin, N.W.T. The sedimentary sequence represents kenzie, T.-N.-O. Nous avons effectué une étude détaillée d'une coupe a gradual shallowing of the sea in an estuarine environment, from a stratigraphique de dépôts marins dans le bassin de la rivière Ri­ relatively shallow marine faciès to an intertidal environment. The chardson, T.-N.-O. La séquence sédimentaire étudiée représente withdrawal of the sea from the Richardson River Basin began prior une régression marine dans un milieu estuarien. Elle débute par un to 10,300 years BP. Isostatic uplift caused the gradual regression of faciès marin mis en place en eau peu profonde et évolue vers un the sea to its present-day level. The marine sediments yielded 26 faciès intertidal. Le retrait de la mer dans ce bassin a commencé ostracode and 14 foraminifer species. Faunal evidence is indicative avant 10 300 ans BP. Le relèvement isostatique terrestre est of brackish-water marginal marine conditions resulting from the dilution responsable de la régression marine graduelle jusqu'à son niveau of nearshore marine waters by freshwater discharge from the many actuel. Les sédiments marins contiennent 26 espèces d'ostracodes streams and rivers draining the basin of the Richardson River. et 14 espèces de foraminifères; cette microfaune témoigne de con­ ditions marines marginales d'eaux saumâtres résultant de la dilution de l'eau marine littorale par un apport d'eau douce des rivières drainant le bassin de la rivière Richardson. INTRODUCTION elucidate the Quaternary history of this region. Evidence for a postglacial marine transgression was first discovered by The purpose of this study is to investigate the stratigraphy, Craig who postulated a marine limit at an altitude of approx­ sedimentology and fauna of late Quaternary marine sediments imately 100 m a.s.l. in the Richardson River Basin. This limit in the Richardson River Basin, District of Mackenzie, N.W.T. decreases in altitude towards the north and north-west due (Fig. 1). Palaeoenvironmental conditions are also established to the relatively less important isostatic rebound towards the by comparing the marine faunal assemblages to published north-west (BLAKE, 1970). data on late Quaternary marine assemblages, notably those of the Champlain Sea. However, such a comparison must be In the northern part of the Coppermine River Valley (Fig. 1), done with caution as regional differences undoubtedly affected the maximum marine limit has been determined to be 170 m the fauna between the two areas. a.s.l. (ST-ONGE and BRUNEAU, 1982), based on evidence of deltas and raised beaches. METHODOLOGY The recent study carried out by MERCIER (1983, 1984a, 1984b) in the Richardson River Basin indicates that the marine About 25-100 g of sediment from each unit were washed limit, based on the extent of reworked glacial drift surfaces, through a 4.0 0 mesh wire sieve and examined for microfossils. lies at approximately 170 m a.s.l. Ostracodes and foraminifer tests were handpicked from the sediment with the help of a binocular microscope and were identified by use of published references. The present material STRATIGRAPHY was collected from the study site (Fig. 1 ) by the author (KERR, AND DEPOSITIONAL ENVIRONMENTS 1984). These deposits are stratigraphically poorly known and their spatial distribution remains uncertain. The study of a river-bank exposure at approximately 25 m a.s.l. (Fig. 1) indicates that a variety of marine environments once existed in the Richardson River Basin. For the purpose PREVIOUS WORK of field research, the stratigraphie sequence has been sub­ A regional study of the north-central District of Mackenzie, divided into seven lithological units illustrated schematically N.W.T. by CRAIG (1960) was the first major endeavor to in Figure 2. These units were sampled for granulometric anal- 186 DE. KERR FIGURE 1. Palaeogeographic map showing marine limit and sue- Carte paléogéographique du bassin de la rivière Richardson, illustrant cessive stages of marine regression in the Richardson River Basin. Ia limite marine et les différentes étapes du retrait de la mer. ysis and examined for their micro and macrofossil contents. Unit 3 to 10-15 cm near the middle and top of the unit. However, A synthesis of the characteristics and structures of each unit this trend in increasing thickness is not a continuous one, as is also presented in Figure 2. The following is a brief discussion thicker layers are interbedded with thinner ones (Fig. 3). Layers of the environmental conditions interpreted from this exposure. from both subunits have gradational upper and lower contacts, and appear to lack any type of internal sedimentary structures. Unit 1 is interpreted as being a relatively shallow water Occurring in both subunits are deformational features which marine faciès, which enabled silt to settle out of suspension have been attributed to biogenic activity at the time of dep­ in a tranquil environment. The differentiation of this unit into osition. These bioturbation features, primarily in the form of Subunits 1a, 1b and 1c is based on slight differences in grain burrows, are restricted to certain layers and are neither wide­ size and fossil content. Nevertheless, the subunits remain spread nor particularly common. genetically related, showing a general sedimentological continuity. The rhythmic deposition of Unit 3 is believed to be the Unit 2 is marked by an increase in dispersed organic detritus result of variations in sedimentation due to seasonal discharge including rare fossil terrestrial arthropods. Mottling is also a cycles. However, it remains to be determined whether the common phenomenon throughout this unit. The increase in cycles of discharge and sedimentation occur in response to sand content may suggest a growing continental influence, annual climatic cycles or to short-term weather changes within probably related to a prograding shoreline as a result of the the annual cycle. Deposits similar to these found in Québec lowering of sea level, hence indicating an increase in the (HILLAIRE-MARCEL, 1979), are characteristic of shallow, fluvial contribution to these sediments. isolated marginal marine basins in which they complete the marine sequence. Unit 3 is comprised of rhythmites which are made up of alternating layers of sand (Subunit 3a) and sandy silt The basal part of Unit 4 is composed of rhythmites, similar (Subunit 3b). This difference in granulometry is responsible to those in Unit 3. However, the differentiation of the individual for a change in color between the alternating layers (Fig. 3). alternating layers is less apparent because of their similarity Although these layers retain their thickness laterally, they vary in grain size. These rhythmites grade up vertically into lenticular, in thickness vertically from a few millimetres at the base of undulatory, followed by flaser bedding, as seen in Figure 4. MARINE REGRESSION AND PALEOENVIRONMENTS 187 FIGURE 2. Generalized stratigraphie section showing characteristic Coupe stratigraphique généralisée résumant les caractéristiques features and environmental relationships. des unités et de leur milieu de dépôt. 188 D.E. KERR • - 4 FIGURE 3. Rhythmites of Unit 3 (Subunit 3a = light gray, Subunit 3b FIGURE 5. Iron oxide aureoles, Unit 4 (scale = 25 cm).