#squantum — Public Fediverse posts
Live and recent posts from across the Fediverse tagged #squantum, aggregated by home.social.
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A bizarre #sedimentary feature
Some layers in the #Neoproterozoic #Squantum Member of the #Roxbury #Conglomerate have been rolled up like a pie crust, into a tube. If this were a #tillite, as it once was thought to be, then it could have been caused by the drag of a #Gaskiers #glacier over the till. These rocks are mostly interpreted as deposited by submarine debris flows these days, in which case they could’ve been deformed during a slump and flow. Site of a field trip for #UMassBoston.
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A small #outcrop of the #Squantum Member of the #Roxbury #Conglomerate
These #rocks are in the #BostonBay Group, which is currently dated to #Neoproterozoic. The Squantum Member was interpreted as a #tillite, possibly associated with the #Gaskiers #glaciation, although there a scant signs like scratched pebbles or faceted cobbles. It is currently commonly interpreted as a #debrite (debris flow). Details in captions.
#geology #glacier #turbidite #Quincy #Boston #Massachusetts #NewEngland -
Anomalous pebble in layered #sedimentary #rock
An angular pebble is conformably surrounded by argillaceous and sandy layers in this #photograph of the #Neoproterozoic #Squantum Member of the #Roxbury Conglomerate. The wide range of clast sizes led to an interpretation as a #glacial #tillite thru the 1970s, but the Squantum Member is now mostly interpreted as a #debrisFlow (#debrite or #turbidite). My #photo.
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Deformed bedding in meta#sedimentary #rocks
The horizontal bedding of the #Squantum Member of the #Roxbury Conglomerate (#Neoproterozoic, #Boston Bay Group) has been disturbed locally.
In the #glacial #tillite interpretation of the Squantum (favored through at least the 1970s), the distortion might be caused by glaciotectonic drag at the ice base. The current interpretation as a #debrite or #turbidite would probably attribute the deformations to synsedimentary slumping. My #photo. #fieldTrip
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The #glacier went that-a-way
The #striations on this face of the #Ediacaran (ca. 560 Ma) #Squantum Member of the #Roxbury #Conglomerate were probably left by the #Pleistocene #Laurentide ice sheet, which retreated ca. 12 ka. The striations have the right orientation, from northwest to southeast.
The Squantum Member was once interpreted as a (#glacial) #tillite. The most common contemporary model is a peri-#Gondwana #debrite (#turbidite).
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Interbedded argillaceous & tuffaceous #sediments
These photos are of #Cambridge #Argillite, exposed above the #Squantum Member of the #Roxbury Conglomerate (#Neoproterozoic). Prior to the 1970s or so, the Squantum Member was interpreted as #glacial sediments; it's now broadly interpreted as debris flows, with the Cambridge being distal turbidites overlying it. I lead a field trip here for #UMassBoston. See captions.
#outcrop #fieldTrip #photo #rocks #tuff #Fufjilm #Venus 65mm #macro #Quincy