How can i date the age of rocks?

[Jurassicz1]

So how can i date the age of fossil rocks found on beaches? And can i locate what formation it came from? 

[Fossildude19]

The reality is you can't reliably date rocks on beaches. 

They could be from off shore formations, or could have been brought as ship's ballast. They could have come from nearby countries.

They could be glacial erratics.  They could be from the cliffs near the shore.

 

Unless you find some index fossils that can lead to identifying the age of the matrix, I think you would be hard pressed to be able to pinpoint the origin of rocks found on a beach.  

[Bob Saunders]

my club, rocks="older than dirt". Fossils, as written above and, usually within 150 millions years or so  time periods depending on the type and locations. 

[erose]

Yep, plum near impossible..... but always an exception... As mentioned the right fossil could do the trick, or a least narrow things down considerably. But the fossil needs to be a recognizable index fossil. Basically a distinct genus or species that is known from a very specific time frame.  

[Macrophyseter]

At best you probably can only estimate what deposit beach fossils originated from, but as others said above, even that may at times be difficult to plain impossible.

 

But if you are able to trace it back to a deposit and are able to successfully identify an associated index fossil, you can look up a geologic time scale that calibrates the approximate datings of various index fossils. The one I personally use is The Geologic Time Scale 2012 (Gradstien et al., 2012) and its updated 2016 edition (Ogg et al., 2016), although both require purchase as far as I know. Additional stratigraphic literature might help correlate local index fossils not mentioned in such books with ones that are.

[DPS Ammonite]

Everyone above gives good ideas on how to date a rock. My suggestion is to get a geology map and learn about the features of each formation including their age. You often can match a rock to the formation of origin by looking at features other than fossils such as composition, color and bedding.

 

Do you have a particular beach that you need geological information on? 

[Jurassicz1]

6 hours ago, DPS Ammonite said:

Everyone above gives good ideas on how to date a rock. My suggestion is to get a geology map and learn about the features of each formation including their age. You often can match a rock to the formation of origin by looking at features other than fossils such as composition, color and bedding.

 

Do you have a particular beach that you need geological information on? 

All the beaches have same stuff i Think its from denmark. I live in sweden so its pretty close i mostly find flint. If im not wrong its around 60-95 mil years ago flint was formed?

[Ludwigia]

@Jurassicz There are people who specialize in glacial erratics which can be found on and near the beaches of the North and Baltic Seas and some of them have published books and scientific papers on the subject. They are able to recognize, name and determine the origin of a large portion of these rocks. I'm sure that doing a google search will hit the target, but maybe @Johannes can give you some more concrete suggestions.

[Johannes]

In general: if you did not have the scientific technical equipment, you have only learning, experience and knowledge to give an answer to this question. So, you need to know a lot about the rocks common in your area (and, in terms of fossil-bearing rocks, the associated index-fossils and their stratigraphic and palaeogeographic distribution)*. This is extremle challenging if you are situated in the northern european glacial erratics, because they are covering faunas and floras from the Ediacarian up to the Pleistocene.

 

For your special situation: You need to know the directions from where the glaciers in the different stages of the last scandinavien glaciations have moved from. And then a good knowledge about the rocks there. (And there are quite a lot rocktypes, and a lot non known until today because they are covered by glacial debris or were eliminated(eroded) by the ancient glaciers completly).

 

For your special question about Flint: first (and mentioned some times before), I did not really believe in a relevant amount of danish glacial erratics in your area due to not existing pleistocene glacier movement from W to E in your region. Sometimes you have material (e.g. flints from the danish or british paleocene (reworked in eocene deposits)) brought by ships as ballast from the late medival up to the late 18th century, like observed on Gotland.

 

Flint occurs mostly in Upper Cretaceous (Campanian) Sediments in Sweden, as far as I know. Some of the areas of swedish cretaceous flints you can see here, but there are a lot more. Additionally, there are some rarer flints in swedish Middle Ordovician strata, too.

 

 

*because people with knowledge (and a primitive microscope) are sometimes still cheaper than advanced machines in our times, micropalaeontologists have still positions in drilling companies.

[Mark Kmiecik]

I have found the best way to date a beach rock is to put one in your pocket and then take to dinner and a movie. 

Sorry, I just couldn't resist this one!

[Johannes]

4 hours ago, Mark Kmiecik said:

I have found the best way to date a beach rock is to put one in your pocket and then take to dinner and a movie. 

Sorry, I just couldn't resist this one!

Unfortunately the others will be jealous and will bite you in your face, next time you hit them with your hammer...