{{short description|Geologic formation In Canada}} {{Infobox rockunit | name = Drook Formation | image = | caption = | type = Formation | age = Ediacaran {{Geological range|579.88|574}}<ref name="Fitzgerald">{{cite journal |last1=Fitzgerald |first1=Danielle M. |last2=Narbonne |first2=Guy M. |last3=Pufahl |first3=Peir K. |last4=Dalrymple |first4=Robert W. |title=The Mall Bay Formation (Ediacaran) and the protracted onset of the Gaskiers glaciation in Newfoundland, Canada |journal=Precambrian Research |date=June 2024 |volume=405 |article-number=107369 |doi=10.1016/j.precamres.2024.107369|doi-access=free |hdl=1974/32568 |hdl-access=free }}</ref> | period = Ediacaran | prilithology = Siliceous Siltstone<ref name="GotAPN">{{cite web|url = https://www.gov.nl.ca/iet/files/88-01.pdf |title=GEOLOGY OF THE AVALON PENINSULA, NEWFOUNDLAND}}</ref> | otherlithology = Sandstone, Tuff<ref name="GotAPN"/> | namedfor = Drook | namedby = S.B. Misra | year_ts = 1971<ref name="Misra1971">{{cite journal |last1=Misra |first1=S. B. |title=Stratigraphy and Depositional History of Late Precambrian Coelenterate-Bearing Rocks, Southeastern Newfoundland |journal=Geological Society of America Bulletin |date=1971 |volume=82 |issue=4 |pages=979 |doi=10.1130/0016-7606(1971)82[979:SADHOL]2.0.CO;2}}</ref> | region = Newfoundland and Labrador | country = Canada | coordinates = | unitof = Conception Group<ref name=liu>{{Cite journal|url=https://www.academia.edu/download/41916560/Horizontal_surface_traces_from_the_Ferme20160202-3945-1jxueem.pdf|title=Horizontal Surface Traces from the Fermeuse Formation, Ferryland (Newfoundland, Canada), and their Place within the Late Ediacaran Ichnological Revolution|author1=A.G. Liu|author2=D. McIlroy|journal=Geological Association of Canada - Special Paper|issue=9|date=September 2014}}{{dead link|date=July 2022|bot=medic}}{{cbignore|bot=medic}}</ref> | subunits = Clam Cove, Peter's River, Biscay, Cape English, Torbay, Bauline Line and Broad Cove River Members<ref name="GotAPN"/> | underlies = * Briscal Formation<ref name="GotAPN"/> * Mistaken Point Formation<ref name="GotAPN"/> | overlies = Gaskiers Formation<ref name=liu/><ref name="GotAPN"/> | thickness = 770 m (2,526 ft) | extent = | area = | map = Drook Formation map.svg | map_caption = }}
The '''Drook Formation''' is a geologic formation in Newfoundland and Labrador. It preserves fossils dating back to the Ediacaran period which have been dated to {{Ma|575.8|error=0.5}}, making them the oldest macroscopic complex fossils in Newfoundland until the discovery of fossils in the pre-Gaskiers glaciation Rocky Harbour Formation.
== Geology == The Drook Formation is predominately composed of well-bedded banded green cherts, silicified siltstones, and argillites. A majority of the chert beds contain the silicified siltstones, and range in thickness from a fraction of an inch to {{cvt|2|in|0}}. The base of the formation is not exposed, as such its full thickness is unknown.<ref name="Misra1971"/> It can be found outcropping in the Conception Bay area and the Avalon Peninsula.<ref name="Ichaso2007">{{cite journal |last1=Ichaso |first1=Aitor A |last2=Dalrymple |first2=Robert W |last3=Narbonne |first3=Guy M |title=Paleoenvironmental and basin analysis of the late Neoproterozoic (Ediacaran) upper Conception and St. John's groups, west Conception Bay, Newfoundland |journal=Canadian Journal of Earth Sciences |date=1 January 2007 |volume=44 |issue=1 |pages=25–41 |doi=10.1139/e06-098}}</ref>
== Paleoenvironment == The depositional environment of the formation was first considered to be that of a shallow-marine environment inferred from the high silica content of the rocks, the abundance of calcareous nodules, as well as large ripple marks covering exposed surfaces.<ref name="Misra1971"/>
A later study done in 2003 would suggest that the Drook Formation was deposited on a deep basin-floor, due to the thick bedding and coarser grains found within it, and the evidence of both south-westerly and north-easterly paleocurrents.<ref name="Wood2003">{{cite journal |last1=Wood |first1=Donald A |last2=Dalrymple |first2=Robert W |last3=Narbonne |first3=Guy M |last4=Gehling |first4=James G |last5=Clapham |first5=Matthew E |title=Paleoenvironmental analysis of the late Neoproterozoic Mistaken Point and Trepassey formations, southeastern Newfoundland |journal=Canadian Journal of Earth Sciences |date=1 October 2003 |volume=40 |issue=10 |pages=1375–1391 |doi=10.1139/e03-048}}</ref><ref name="Narbonne2005">{{cite journal |last1=Narbonne |first1=Guy M. |title=THE EDIACARA BIOTA: Neoproterozoic Origin of Animals and Their Ecosystems |journal=Annual Review of Earth and Planetary Sciences |date=31 May 2005 |volume=33 |issue=1 |pages=421–442 |doi=10.1146/annurev.earth.33.092203.122519}}</ref> This was further supported with the study of the Drook Formation in the Conception Bay area confirming that sediments were likely deposited in a deep distal-fan to basin-plain environment, again inferred from the thickness of the various layers, and the discovery of medium-association bedded turbidites.<ref name="Ichaso2007"/>
== Dating == Both the base and top of the Drook formation has been dated using U–Pb dating and various zircon crystal samples. Samples collected from the top of the underlying Gaskiers Formation, and thus the base of the Drook Formation, recovered a date of {{val|579.88|0|ul=Ma}}, whilst samples collected from the top of the formation recovered a date of {{val|575|0|ul=Ma}}.<ref name="Fitzgerald"/><ref name="Bowring2003">{{cite journal |last1=Bowring |first1=S. |last2=Myrow |first2=P. |last3=Landing |first3=E. |last4=Ramezani |first4=J. |last5=Grotzinger |first5=J. |title=Geochronological constraints on terminal Neoproterozoic events and the rise of Metazoan |journal=Astrobiology |date=April 2003 |pages=113–114 |bibcode=2003EAEJA....13219B}}</ref>
== Paleobiota == The Drook Formation is home to a small collection of fossils only found on its outcrops within the Avalon Peninsula,<ref name="Ichaso2007"/> which are predominately frondose in nature, such as the tall ''Trepassia'' and the classic ''Charnia''. Specimens of poorly preserved organisms in the form of Ivesheadiomorphs are also present, including the ''Blackbrookia'' form.<ref name="TEFotAP">{{cite web |last1=Liu |first1=A. |last2=Conliffe |first2=J. |title=The Ediacaran Fossils of the Avalon Peninsula |url=https://www.gov.nl.ca/iet/files/mines-geoscience-publications-openfiles-gac-seg-mac-ft-guides-of-nfld-3320-ft-2015.pdf |website=www.gov.nl.ca}}</ref> The formation also notably contains an abundance of the cone-like fossil ''Thectardis'', numbering up to 140 known specimens, and constituting up to 58% of the known fossil community, with the formation also serving as the type locality for the holotype fossil.<ref name="Clapham2004">{{cite journal |last1=Clapham |first1=Matthew E. |last2=Narbonne |first2=Guy M. |last3=Gehling |first3=James G. |last4=Greentree |first4=Carolyn |last5=Anderson |first5=Michael M. |title=Thectardis avalonensis: A new Ediacaran fossil from the Mistaken Point biota, Newfoundland |journal=Journal of Paleontology |date=November 2004 |volume=78 |issue=6 |pages=1031–1036 |doi=10.1666/0022-3360(2004)078<1031:TAANEF>2.0.CO;2}}</ref>
There can also be found an assemblage entirely composed of juvenile fronds, including juvenile stages of ''Charnia'' and ''Trepassia'', and is the first fossil assemblage to be dominated by juvenile frondose forms in the Ediacaran, providing rare insights into the ontogeny and ecology of the rangeomorphs.<ref name="Liu2012">{{cite journal |last1=Liu |first1=Alexander G. |last2=McIlroy |first2=Duncan |last3=Matthews |first3=Jack J. |last4=Brasier |first4=Martin D. |title=A new assemblage of juvenile Ediacaran fronds from the Drook Formation, Newfoundland |journal=Journal of the Geological Society |date=July 2012 |volume=169 |issue=4 |pages=395–403 |doi=10.1144/0016-76492011-094}}</ref>
The fossils from this formation for a number of decades were considered to be the oldest examples of complex Ediacaran fossils in Newfoundland,<ref name="Narbonne2003">{{cite journal |last1=Narbonne |first1=Guy M. |last2=Gehling |first2=James G. |title=Life after snowball: The oldest complex Ediacaran fossils |journal=Geology |date=2003 |volume=31 |issue=1 |pages=27 |doi=10.1130/0091-7613(2003)031<0027:LASTOC>2.0.CO;2}}</ref><ref name="Wood2003"/><ref name="Narbonne2005"/><ref name="Ichaso2007"/><ref name="Bamforth2008">{{cite journal |last1=Bamforth |first1=Emily L. |last2=Narbonne |first2=Guy M. |last3=Anderson |first3=Michael M. |title=Growth and Ecology of a Multi-branched Ediacaran Rangeomorph from the Mistaken Point Assemblage, Newfoundland |journal=Journal of Paleontology |date=July 2008 |volume=82 |issue=4 |pages=763–777 |doi=10.1666/07-112.1}}</ref> although this would change in 2020 with the discovery of ''Palaeopascichnus'' and tentative ''Orbisiana'' fossils the Rocky Harbour Formation, which has been dated to {{Ma|579}}, making them 3 million years older than the Drook fossils.<ref name="Liu2021">{{cite journal |last1=Liu |first1=Alexander G. |last2=Tindal |first2=Benjamin H. |title=Ediacaran macrofossils prior to the ~580 Ma Gaskiers glaciation in Newfoundland, Canada |journal=Lethaia |date=April 2021 |volume=54 |issue=2 |pages=260–270 |doi=10.1111/let.12401}}</ref>
{{Paleobiota-key-compact}}
=== Petalonamae ===
{| class="wikitable" style="width:100%;" |- !Genus !Species !Notes !Images |- |''Charnia''<ref name="TEFotAP"/><ref name="Liu2012"/> | *''C. masoni'' |Sessile frondose organism. |center|100px |- |''Charniodiscus''<ref name="TEFotAP"/><ref name="Liu2012"/> | *''Charniodiscus'' sp. |Sessile frondose organism. |center|100px |- |''Trepassia''<ref name="Narbonne2009">{{cite journal |last1=Narbonne |first1=Guy M. |last2=Laflamme |first2=Marc |last3=Greentree |first3=Carolyn |last4=Trusler |first4=Peter |title=Reconstructing a lost world: Ediacaran rangeomorphs from Spaniard's Bay, Newfoundland |journal=Journal of Paleontology |date=July 2009 |volume=83 |issue=4 |pages=503–523 |doi=10.1666/08-072R1.1}}</ref><ref name="TEFotAP"/> | *''T. wardae'' |Sessile frondose organism. Previously reported under the genus ''Charnia'' as ''Charnia wardi''.<ref name="Narbonne2003"/> |center|100px |- |''Vinlandia''<ref name="Brasier2012">{{cite journal |last1=Brasier |first1=Martin D. |last2=Antcliffe |first2=Jonathan B. |last3=Liu |first3=Alexander G. |title=The architecture of Ediacaran Fronds |journal=Palaeontology |date=September 2012 |volume=55 |issue=5 |pages=1105–1124 |doi=10.1111/j.1475-4983.2012.01164.x}}</ref><ref name="TEFotAP"/> | *''V. antecedens'' |Sessile frondose organism. Previously reported under the genus ''Charnia'' as ''Charnia antecedens''.<ref name="Laflamme2007">{{cite journal |last1=Laflamme |first1=M. |last2=Narbonne |first2=G. M. |last3=Greentree |first3=C. |last4=Anderson |first4=M. M. |title=Morphology and taphonomy of an Ediacaran frond: Charnia from the Avalon Peninsula of Newfoundland |journal=Geological Society, London, Special Publications |date=January 2007 |volume=286 |issue=1 |pages=237–257 |doi=10.1144/SP286.17}}</ref> |center|100px |- |}
=== ''incertae sedis'' ===
{| class="wikitable" style="width:100%;" |- !Genus !Species !Notes !Images |- |''Aspidella''<ref name="Liu2012"/> | *''A. terranovica'' |Enigmatic discoidal fossil. |center|100px |- |''Thectardis''<ref name="Clapham2004"/> | *''T. avalonensis'' |Sessile cone-like organism, they are the most abundant fossil in the Drook Formation. |center|100px |- |}
=== Ivesheadiomorph ===
{| class="wikitable" style="width:100%;" |- !Genus !Species !Notes !Images |- |style="background:#FEF6E4;"|''Ivesheadia''<ref name="TEFotAP"/><ref name="Liu">{{cite journal |last1=Liu |first1=Alexander G. |last2=Mcilroy |first2=Duncan |last3=Antcliffe |first3=Jonathan B. |last4=Brasier |first4=Martin D. |title=Effaced preservation in the Ediacara biota and its implications for the early macrofossil record |journal=Palaeontology |date=May 2011 |volume=54 |issue=3 |pages=607–630 |doi=10.1111/j.1475-4983.2010.01024.x}}</ref> |style="background:#FEF6E4;"| *''Ivesheadia'' sp. |style="background:#FEF6E4;"|Poorly preserved organism. |style="background:#FEF6E4;"| |- |style="background:#FEF6E4;"|''Blackbrookia''<ref name="TEFotAP"/> |style="background:#FEF6E4;"| *''Blackbrookia'' sp. |style="background:#FEF6E4;"|Poorly preserved organism. |style="background:#FEF6E4;"| |- |}
=== Undescribed ===
{| class="wikitable" style="width:100%;" |- !Genus !Species !Notes !Images |- |Filaments<ref name="Liu2012"/> | *''???'' |Filamentous fossils numbering up to 139 in total, ranging in lengths of {{cvt|6-130|mm|0}}, affinities remain unknown. | |- |}
==See also== {{Portal|Earth sciences|Canada|Paleontology|}} * List of fossiliferous stratigraphic units in Newfoundland and Labrador
==References== {{Reflist}} * {{cite web|title= Fossilworks: Gateway to the Paleobiology Database|author= ((Various Contributors to the Paleobiology Database))|url= https://www.fossilworks.org|access-date= 17 December 2021}}
Category:Ediacaran Newfoundland and Labrador Category:Geologic formations of Newfoundland and Labrador Category:Siltstone formations of Canada Category:Sandstone formations of Canada Category:Tuff formations of Canada Category:Lagerstätten