Intrusions or fossils?

[RCD]

Heys guys. Another one. Wondering if the intrusions on this one are fossils. Of the intrusions looked rather bone-like, so I wanted to post up and get some opinions. Area is SF East Bay area, CA, creek bed which drains a diverse range from Miocene to Jurassic and in between. Thanks in advance. RCD

[Plantguy]

Great pics! I dont think you are looking at intrusives. I can see why you might think that from the irregular shapes/positions. 

These look more like sedimentary features to me. Perhaps some mudstone rip-up clasts or concretionary masses maybe calcareous in sandstone matrix/beds. Used to have turbidite deposits out there in central/northern calif...little underwater landslides/debris running down channels from the coastline...tearing up previously deposited layers. You might occasionally find some fossils in the various layers that may give you a clue as to the actual age. I can recall finding some bivalve/pieces in some of the layers. 

 

Regards, Chris 

 

 

[RCD]

1 hour ago, Plantguy said:

Great pics! I dont think you are looking at intrusives. I can see why you might think that from the irregular shapes/positions. 

These look more like sedimentary features to me. Perhaps some mudstone rip-up clasts or concretionary masses maybe calcareous in sandstone matrix/beds. Used to have turbidite deposits out there in central/northern calif...little underwater landslides/debris running down channels from the coastline...tearing up previously deposited layers. You might occasionally find some fossils in the various layers that may give you a clue as to the actual age. I can recall finding some bivalve/pieces in some of the layers. 

 

Regards, Chris 

 

 

Thanks Chris. The area borders on Tdu (Eocene/Domingene form.) and Kbs (Early Cretaceous). I think you're right, as there were quite a few similar morphology rocks I found in the area. Yep, found several really nice bivalves (nearly palm sized), lots of spirally brachiopod fossils, and some nice apparently rugose coral fossils. Thanks again for your very educational reply. 

[RCD]

24 minutes ago, RCD said:

Thanks Chris. The area borders on Tdu (Eocene/Domingene form.) and Kbs (Early Cretaceous). I think you're right, as there were quite a few similar morphology rocks I found in the area. Yep, found several really nice bivalves (nearly palm sized), lots of spirally brachiopod fossils, and some nice apparently rugose coral fossils. Thanks again for your very educational reply. 

Correction: "spirally" gastropod fossils (not brachiopod)