Chris White · @Ceedave
151 followers · 278 posts · Server sciencemastodon.com
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
#outcrop #squantum #roxbury #conglomerate #rocks #bostonbay #Neoproterozoic #tillite #gaskiers #glaciation #debrite #geology #Glacier #turbidite #quincy #boston #massachusetts #newengland
Chris White · @Ceedave
140 followers · 259 posts · Server sciencemastodon.com
View about eastward over #Quincy Bay, #Squantum on the left, just south of #Boston, #Massachusetts USA
#NewEngland #Fujifilm my #photo #landscape
18/2 @ 5.6 1/950 s ISO 200 X-H1
#quincy #squantum #boston #massachusetts #newengland #fujifilm #photo #landscape
Chris White · @Ceedave
128 followers · 241 posts · Server sciencemastodon.com
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.
#sedimentary #rock #photograph #Neoproterozoic #squantum #roxbury #glacial #tillite #debrisflow #debrite #turbidite #photo #boston #fieldtrip #umassboston
Chris White · @Ceedave
127 followers · 237 posts · Server sciencemastodon.com
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
#rocks #squantum #roxbury #Neoproterozoic #boston #glacial #tillite #debrite #turbidite #photo #fieldtrip
Chris White · @Ceedave
126 followers · 235 posts · Server sciencemastodon.com
Rapid changes in #clast size in #sedimentary #rocks
The #Neoproterozoic #Squantum Member of the #Roxbury Conglomerate (#Boston Bay Group) transitions from sandstone, to almost-clast-supported conglomerate, to laminated argillite…in about 25 cm. Fifty years ago, it was interpreted as a #glacial deposit and called the Squantum #Tillite, presumably associated with the #Gaskiers Glaciation. Paucity of evidence (e.g., few scratches or faceted clasts) suggests a debris flow. My #photo.
#clast #sedimentary #rocks #Neoproterozoic #squantum #roxbury #boston #glacial #tillite #gaskiers #photo
Chris White · @Ceedave
124 followers · 231 posts · Server sciencemastodon.com
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).
#Glacier #striations #ediacaran #squantum #roxbury #conglomerate #Pleistocene #laurentide #glacial #tillite #gondwana #debrite #turbidite #photo #boston #geology #newengland #fieldtrip
Chris White · @Ceedave
124 followers · 228 posts · Server sciencemastodon.com
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
#sediments #cambridge #argillite #squantum #roxbury #Neoproterozoic #glacial #umassboston #outcrop #fieldtrip #photo #rocks #tuff #fufjilm #venus #macro #quincy
Chris White · @Ceedave
124 followers · 228 posts · Server sciencemastodon.comInterbedded 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 15mm #macro #Quincy
#sediments #cambridge #argillite #squantum #roxbury #Neoproterozoic #glacial #umassboston #outcrop #fieldtrip #photo #rocks #tuff #fufjilm #venus #macro #quincy
Chris White · @Ceedave
124 followers · 228 posts · Server sciencemastodon.comInterbedded 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 15mm #macro #Quincy
#sediments #cambridge #argillite #squantum #roxbury #Neoproterozoic #glacial #umassboston #outcrop #fieldtrip #photo #rocks #tuff #fufjilm #venus #macro #quincy