I have to write a brief geological history of a region starting with the oldest events with schist being the oldest it says i should not speculate but concentrate on the evidence
have what i wrote on the right lines if not can you give me some pointers
The schist would have probably originally been deposited first as a layer of mudstone, which through metamorphism formed into the layer of schist. An unknown layer of rock above the schist would have been present for the gabbro to then intrude into it (it could have formed by rapid cooling on the surface). Then through erosion/ weathering, the layers of rock above the schist would have eventually exposed the upper part of gabbro intrusion, finally more than one layer of sandstone would have been deposited and lithified (by being compacted and cemented) to form sandstone. I would assume the sandstone wasn’t present when the intrutsion took place because it hasn’t gone through the phase of metamorphism
Your explanation is on the right track, but here are a few pointers to improve it:
1. Provide more evidence: Instead of speculating about how the schist was deposited, try searching for evidence of its formation. Look for scientific studies, geological surveys, or research papers that discuss the origin of schist in the region you are studying. This will help you provide a more accurate and evidence-based explanation.
2. Be more specific about the gabbro intrusion: Instead of assuming that the gabbro formed by rapid cooling on the surface, try to find supporting evidence for this hypothesis. Look for geological features such as cross-cutting relationships or mineralogical studies that can shed light on the formation of the gabbro intrusion. If you cannot find specific evidence, you can mention that the exact process of gabbro intrusion is currently unknown or under debate in the scientific community.
3. Consider the timing and sequence of events: When discussing the layers of rock above the schist and their exposure, try to provide a more specific timeline and sequence of events. For example, you could mention how erosion and weathering gradually removed the overlying layers, exposing the gabbro intrusion over time. Use terms like "gradually," "over millions of years," or "through geological processes" to indicate the passage of time.
4. Support your assumptions with evidence: When assuming that the sandstone wasn't present during the intrusion, provide evidence or reasoning to support this claim. Are there any mineralogical changes or geological features that suggest the absence of sandstone during the intrusion? If not, you can state that the relationship between the gabbro intrusion and the sandstone is still unclear or requires further investigation.
Remember, the key is to focus on the evidence available and avoid speculation. By conducting thorough research and citing credible sources, you can provide a more accurate and evidence-based geological history of the region.