The Geology of Newfoundland Broadly Records The Evolution of Gondwana

The geology of Newfoundland broadly records the evolution of Gondwana, Laurentia,
and associated terranes as they were tectonically accreted during orogenesis related to the
Early Palaeozoic closing of the Iapetus and Rheic oceans (O'Brien et al., 1983; Murphy and
Nance, 1996). The peri-Gondwanan terranes Ganderia and Avalonia are represented by the
Gander and Avalon zones in central and eastern Newfoundland, respectively. The Avalon
Zone of Eastern Newfoundland (Fig 1B) formed as a volcanic arc complex outboard of the
Gondwana during the Neoproterozoic. The Avalon Zone consists of three geologic regions
(western, central, and eastern; Myrow, 1995; Nance et al., 2002). The Eastern region of the
Avalon zone, cropping out mainly on the Avalon Peninsula, is considered the most inboard
zone relative to the Gondwanan margin (O'Brien, 1988). The eastern Avalon zone consists of
bimodal plutonic-volcanic rocks of the Harbour Main Group (631 – 606 Ma) overlain by
volcaniclastic submarine fan-slope strata of the Conception Group (ca. 584 Ma to 565 Ma:
Bowring et al., 2003; Ichaso, 2007; Matthews, 2020), passing upward into shallow marine to
alluvial deposits of the St. John's and Signal Hill groups (Myrow, 1995; King, 1990). The
Harbour Main Group is exposed along the eastern shore of Conception Bay. The Conception
Group crops out east of the Topsail Fault and underlies much of the eastern Avalon Peninsula
(Fig. 1B). King (1990) considers the base of the Conception Group as a conformable contact
above the Harbour Main Group; whereas (Sparkes et al., 2021) show that the Harbour Main-
conception groups contact is at least locally unconformable. According to King (1990), the
Conception Group is conformably overlain by a shallowing-upward succession of dark-grey,
marine shale, and sandstone of the St. John's Group, which occurs in the eastern part of the
map area. A thick deltaic and alluvial-plain succession, the Signal Hill Group conformably
overlies the St. John's Group and is presumed to be the latest Precambrian to possibly Early
Paleozoic (King, 1990).
Late Neoproterozoic volcaniclastic and sedimentary successions of the Conception
Group exposed along the eastern and southern margin of the Avalon Peninsula. The Mistaken
Point Formation is about 400 m thick throughout the Avalon Peninsula, defined as the
uppermost part of a thick succession of the volcaniclastic submarine fan strata of the
Conception Group. A tuff bed of the upper Mistaken Point Formation has yielded a
radiometric U-Pb zircon date of 565 ± 3 Ma (Benus, 1988), which was chosen by Williams
and King (1979) to define the top of the Conception Group. As the uppermost part of
Conception Group and transition to the St. John's group, this formation records the conditions
of arc-adjacent volcaniclastic sedimentation at or below the transformation of the basin to
prodelta pull-apart basin sedimentation. The MPF is subdivided into two members: the lower
Middle Cove Member, defined by medium-bedded, fossiliferous sandstone, volcanic ash, and
chert; and the upper Hibbs Cove member, defined by medium-to-thick beds of red-green
siltstone interbedded with fine-grained sandstone with parallel laminations. The thickness of
this upper member increases from the southern to the northern Avalon Peninsula. The
boundary between these two members is sharp and conformable with a change from highly
silicified strata to more argillaceous rocks.
This project aims to reconstruct sedimentary processes, tectonostratigraphic evolution, and
paleoenvironments of the Mistaken Point Formation using a combination of representative
facies and architectural analysis, detailed stratigraphy, paleoflow, and provenance. These data
of 20-25 outcrops and 5-6 key sections will be integrated to evaluate the existing
interpretations of sedimentation under the theoretical framework of the ongoing regional
paleoenvironment and tectonic evolution of the Avalon Zone. Specifically, to test existing
models of Mistaken Point basin evolution and to understand if paleoenvironmental changes
were driven by basin type and configuration. Developing a better understanding of the
sedimentary processes, environments of deposition, and basin configuration(s) is expected to
help address the correlation to the sedimentary environments and provide context for ongoing
palaeoecological studies in the Mistaken Point Formation. This study will also document the
evidence of deep-water depositional processes through facies and architectural analysis. In
addition, the architectural elements of the submarine setting, e.g., channels, lobes, etc., will
help develop a comprehensive understanding depositional history.
The specific objectives of this research are the following:
 To classify facies associations and interpret their depositional environments and

conditions.
 To investigate the stratal architecture of facies associations to define a hierarchy
of stratal bounding surfaces and to interpret macroform evolution of submarine
lobes, fans, channel, etc.
 To reconstruct stratigraphic correlations to place facies association and
macroforms in stratigraphic context.
 To constrain current direction of sediment gravity flows and bottom currents in
the basin by measuring paleoflow.
 To identify the sediment provenance and constrain sediment routing from
hinterlands to the basin by using representative detrital zircon geochronology.
The MPF is subdivided into two members: the lower Middle Cove Member, defined by
medium-bedded, fossiliferous sandstone, volcanic ash, and chert; and the upper Hibbs Cove
member, defined by medium-to-thick beds of red-green siltstone interbedded with fine-
grained sandstone with parallel laminations. The thickness of this upper member increases
from the southern to the northern Avalon Peninsula. The boundary between these two
members is sharp and conformable with a change from highly silicified strata to more
argillaceous rocks. To bring out more details about depositional environment and processes,
four stratigraphic sections of the MPF in the St. John's area were measured. Seven facies
were recognized, including: massive sandstone (F1); graded sandstone (F2); graded cross-
laminated sandstone (F3); siltstone (F4); volcanic ash/ tuff (F5); matrix-supported
conglomerate (F6); and red-purple mudstone (F7). Preliminary stratigraphic evidence
suggests MPF strata in the study area were deposited by concentrated density flows to low-
energy turbidity currents. In the lower part of the succession, F1, F2, F6 dominate, whereas in
the upper part, F3, F4, F7 dominate, suggesting an overall upward reduction in grain size and
flow energy. The abundance of volcanic ash layers (F5) throughout suggests proximity to an
island arc, and deposition by hemipelagic fall out of volcanic ash from discrete eruptions. The
absence of wave-generated structures, erosional features, and debris flow deposits suggest
that deposition occurred in a deep-water setting, on generally flat submarine fan, lacking
prominent distributary channels. Ongoing investigations of the facies, paleoflow, and
provenance will be used to better constrain the details and conditions of basin
reconfiguration, and provide environmental context for Ediacaran fossils, or the lack thereof.

The Geology of Newfoundland Broadly Records The Evolution of Gondwana

Uploaded by

Copyright:

Available Formats

The Geology of Newfoundland Broadly Records The Evolution of Gondwana

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

The Geology of Newfoundland Broadly Records The Evolution of Gondwana

Uploaded by

Copyright:

Available Formats

The geology of Newfoundland broadly records the evolution of Gondwana, Laurentia,

The specific objectives of this research are the following:

 To classify facies associations and interpret their depositional environments and

You might also like